Home

DAQ basics

1. 25 6 Generating a Pulse Train 25 7 Generating a Continuous Pulse Train 25 7 TIO ASIC DAQ STC Am9513 25 7 8253 54 25 9 Generating a Finite Pulse Train 25 9 TIO ASIC DAQ STC Am9513 25 10 DAQ STC 25 11 8253 54 25 11 Counting Operations When All Your Counters Are Used 25 12 Knowing the Accuracy of Your Counters 25 13 8253 54 25 14 Stopping Counter Generations 25 14 DAQ STC Am9513
2. 27 3 Connecting Counters to Measure Frequency and Period 27 3 TIO ASIC DAQ STC Am9513 27 3 Measuring the Frequency and Period of High Frequency Signals 27 4 TIO ASIC DAQ STC 27 4 Am9513 27 4 TIO ASIC DAQ STC Am9513 27 5 8253 54 27 6 Contents National Instruments Corporation xiii LabVIEW Data Acquisition Basics Manual Measuring the Period and Frequency of Low Frequency Signals 27 7 TIO ASIC DAQ STC 27 7 Am9513 27 7 TIO ASIC DAQ STC Am9513 27 8 8253 54 27 8 Chapter 28
3. 20 4 Figure 22 1 Measuring a Single Module with the Acquire and Average VI 22 7 Figure 22 2 Measuring Temperature Sensors Using the Acquire and Average VI 22 8 Contents LabVIEW Data Acquisition Basics Manual xvi www ni com Figure 22 3 Continuously Acquiring Data Using Intermediate VIs 22 9 Figure 22 4 Measuring Temperature Using Information from the DAQ Channel Wizard 22 12 Figure 22 5 Measuring Temperature Using the Convert RTD Reading VI 22 13 Figure 22 6 Half Bridge Strain Gauge 22 14 Figure 22 7 Measuring Pressure Using Information from the DAQ Channel Wizard 22 15 Figure 22 8 Inputting Digital Signals through an SCXI Chassis Using Easy Digital VIs 22 17 Figure 22 9 Outputting Digital Signals through an SCXI Chassis Using Easy Digital VIs 22 19 Figure 24 1 Counter Gating Modes 24 4 Figure 24 2 Wiring a 7404 Ch
4. 6 3 Figure 6 2 Using the Intermediate VIs for a Basic Non Buffered Application 6 4 Figure 7 1 How Buffers Work 7 2 Figure 7 2 Simple Buffered Analog Input Example 7 5 Figure 7 3 Writing to a Spreadsheet File after Acquisition 7 6 Figure 7 4 How a Circular Buffer Works 7 7 Figure 7 5 Basic Circular Buffered Analog Input Using the Intermediate VIs 7 10 Figure 8 1 Diagram of a Digital Trigger 8 2 Figure 8 2 Digital Triggering with Your DAQ Device 8 3 Figure 8 3 Diagram of an Analog Trigger 8 5 Figure 8 4 Analog Triggering with Your DAQ Device 8 6 Figure 8 5 Timeline of Conditional Retrieval 8 9 Figure 8 6 The AI Read VI Conditional Retrieval Cluster 8 10 Figure 9 1 Channel and Scan Intervals Using the Channel Clock 9 1 Figure 9 2 Round Robin Scanning Using the Channel Clock 9 2 Figure 9 3 Examp
5. 5 15 Important Terms You Should Know 5 18 Chapter 6 One Stop Single Point Acquisition Single Channel Single Point Analog Input 6 1 Multiple Channel Single Point Analog Input 6 2 Using Analog Input Output Control Loops 6 5 Using Software Timed Analog I O Control Loops 6 5 Using Hardware Timed Analog I O Control Loops 6 6 Improving Control Loop Performance 6 7 Contents National Instruments Corporation vii LabVIEW Data Acquisition Basics Manual Chapter 7 Buffering Your Way through Waveform Acquisition Can You Wait for Your Data 7 1 Acquiring a Single Waveform 7 2 Acquiring Multiple Waveforms 7 3 Simple Buffered Analog Input Examples 7 4 Simple Buffered Analog Input with Graphing
6. 3 5 Advanced VIs 3 5 VI Parameter Conventions 3 5 Default and Current Value Conventions 3 6 Common DAQ VI Parameters 3 7 Error Handling 3 8 Contents LabVIEW Data Acquisition Basics Manual vi www ni com Channel Port and Counter Addressing 3 8 Channel Name Addressing 3 9 Channel Number Addressing 3 10 Limit Settings 3 11 Data Organization for Analog Applications 3 14 Chapter 4 Where You Should Go Next Questions You Should Answer 4 3 PART II Catching the Wave with Analog Input
7. 3 15 Figure 3 11 Extracting a Single Channel from a Column Major 2D Array 3 15 Figure 3 12 Analog Output Buffer 2D Array 3 16 Figure 5 1 Types of Analog Signals 5 2 Figure 5 2 Grounded Signal Sources 5 3 Figure 5 3 Floating Signal Sources 5 3 Figure 5 4 The Effects of Resolution on ADC Precision 5 4 Figure 5 5 The Effects of Range on ADC Precision 5 5 Figure 5 6 The Effects of Limit Settings on ADC Precision 5 6 Figure 5 7 8 Channel Differential Measurement System 5 10 Figure 5 8 Common Mode Voltage 5 11 Figure 5 9 16 Channel RSE Measurement System 5 12 Figure 5 10 16 Channel NRSE Measurement System 5 13 Contents National Instruments Corporation xv LabVIEW Data Acquisition Basics Manual Figure 6 1 Acquiring a Voltage from Multiple Channels with the AI Sample Channels VI
8. 7 4 Simple Buffered Analog Input with Multiple Starts 7 5 Simple Buffered Analog Input with a Write to Spreadsheet File 7 6 Triggered Analog Input 7 6 Do You Need to Access Your Data during Acquisition 7 6 Continuously Acquiring Data from Multiple Channels 7 8 Asynchronous Continuous Acquisition Using DAQ Occurrences 7 9 Circular Buffered Analog Input Examples 7 10 Basic Circular Buffered Analog Input 7 10 Other Circular Buffered Analog Input Examples 7 11 Simultaneous Buffered Waveform Acquisition and Waveform Generation 7 11 Chapter 8 Controlling Your Acquisition with Triggers Hardware Triggering 8 1 Digital Triggering 8 2 Digital Triggering Examples 8 4 Digital Triggering Examples 8 5 Analog Triggering Exam
9. 16 3 Immediate I O Using the Advanced Digital VIs 16 3 6533 Family 16 3 8255 Family 16 3 E Series Family 16 4 Chapter 17 Handshaked Digital I O Handshaking Lines 17 2 6533 Family 17 2 8255 Family 17 2 Digital Data on Multiple Ports 17 2 6533 Family 17 2 8255 Family 17 3 Types of Handshaking 17 4 Nonbuffered Handshaking 17 5 653
10. 25 14 8253 54 25 15 Chapter 26 Measuring Pulse Width Measuring a Pulse Width 26 1 Determining Pulse Width 26 2 TIO ASIC DAQ STC 26 2 Am9513 26 4 8253 54 26 4 Controlling Your Pulse Width Measurement 26 5 TIO ASIC DAQ STC or Am9513 26 5 Buffered Pulse and Period Measurement 26 6 Increasing Your Measurable Width Range 26 7 Chapter 27 Measuring Frequency and Period Knowing How and When to Measure Frequency and Period 27 1 TIO ASIC DAQ STC Am9513 27 2 8253 54
11. NI 4060 With no scan clock the channel clock is used to switch between each channel at an equal interval The same delay exists among all channel samples as well as between the last channel of a scan and the first channel in the next scan For boards with scan and channel clocks round robin scanning occurs when you disable the scan clock by setting the scan rate to 0 and using the interchannel delay of the AI Config VI to control your acquisition rate LabVIEW is scan clock oriented In other words when you select a scan rate LabVIEW automatically selects the channel clock rate for you LabVIEW selects the fastest channel clock rate that allows adequate settling time for the ADC LabVIEW adds an extra 10 s to the interchannel delay to compensate for any unaccounted factors However LabVIEW does not consider this additional delay for purposes of warnings If you have specified a scan rate that is adequate for acquisition but too fast for LabVIEW to apply the 10 s delay it configures the acquisition but does not return a warning channel interval 0 1 2 3 0 1 2 3 0 1 2 3 Chapter 9 Letting an Outside Source Control Your Acquisition Rate National Instruments Corporation 9 3 LabVIEW Data Acquisition Basics Manual You can set your channel clock rate with the interchannel delay input of the AI Config VI which calls the Advanced AI Clock Config VI to actually configure the channel clock The simplest method to
12. 4 8 mV device range 2resolution 10 216 15 mV device range 2resolution 20 216 3 mV Chapter 5 Things You Should Know about Analog Input LabVIEW Data Acquisition Basics Manual 5 8 www ni com For more information about the device range and limit settings for your device refer to the tables in Appendix B Hardware Capabilities in the LabVIEW Function and VI Reference Manual or select Help Online Reference These tables contain information about gain settings for each device Also refer to the Limit Settings section of Chapter 3 Basic LabVIEW Data Acquisition Concepts for more information about gain Now that you know which kind of ADC to use and what settings to use for your signal you can connect your signals to be measured On most DAQ devices there are three different ways to configure your device to read the signals differential referenced single ended RSE and nonreferenced single ended NRSE Table 5 1 Measurement Precision for Various Device Ranges and Limit Settings 12 Bit A D Converter Device Voltage Range Limit Settings Precision1 0 to 10 V 0 to 10 V 0 to 5 V 0 to 2 5 V 0 to 1 25 V 0 to 1 V 0 to 0 1 V 0 to 20 mV 2 44 mV 1 22 mV 610 V 305 V 244 V 24 4 V 4 88 V 5 to 5 V 5 to 5 V 2 5 to 2 5 V 1 25 to 1 25 V 0 625 to 0 625 V 0 5 to 0 5 V
13. DAC Digital to analog converter An electronic device often an integrated circuit that converts a digital number into a corresponding analog voltage or current DAQ Channel Wizard Utility that guides you through naming and configuring your DAQ analog and digital channels DAQ Solution Wizard Utility that guides you through specifying your DAQ application from which it provides a custom DAQ solution DAQ STC Data Acquisition System Timing Controller data acquisition Process of acquiring data typically from A D or digital input plug in boards data flow Programming system consisting of executable nodes in which nodes execute only when they have received all required input data and produce output automatically when they have executed LabVIEW is a dataflow system default input The default value of a front panel control default load area One of three parts of the SCXI EEPROM The default load area is where LabVIEW automatically looks to load calibration constants the first time you access an SCXI module When the module is shipped this area contains a copy of the factory calibration constants The other EEPROM areas are the factory area and the user area Glossary National Instruments Corporation G 5 LabVIEW Data Acquisition Basics Manual default setting A default parameter value recorded in the driver In many cases the default input of a control is a certain value often 0 that means use the current default
14. Chapter 5 Things You Should Know about Analog Input Defining Your Signal 5 1 What Is Your Signal Referenced To 5 2 Grounded Signal Sources 5 2 Floating Signal Sources 5 3 Choosing Your Measurement System 5 4 Resolution 5 4 Device Range 5 5 Signal Limit Settings 5 6 Considerations for Selecting Analog Input Settings 5 7 Differential Measurement System 5 9 Referenced Single Ended Measurement System 5 12 Nonreferenced Single Ended Measurement System 5 13 Channel Addressing with the AMUX 64T 5 14 The AMUX 64T Scanning Order
15. Internal or External Internal Read Chapter 13 Letting an Outside Source Control Your Update Rate External Read Chapter 18 Timed Digital I O Timed Chapter 4 Where You Should Go Next National Instruments Corporation 4 3 LabVIEW Data Acquisition Basics Manual Questions You Should Answer 1 Measuring Device DAQ Device or SCXI Module Are you working in a noisy environment If you are you may have SCXI modules connected to your DAQ device or the parallel port of your computer SCXI modules can filter and isolate noise from signals They also can amplify low signals SCXI modules expand the number of channels to acquire or generate data DAQ devices are primarily used alone when extra signal conditioning is not necessary If you are using a DAQ device read question 2 If you are using SCXI go to Part V SCXI Getting Your Signals in Great Condition 2 Analog or Digital Signal Analysis Does your signal have two discrete values that are TTL signals If so you have a digital signal Otherwise you have an analog signal The type of information you would need to know from an analog signal is the level discrete value shape and frequency content 3 Analog or Digital Signal Acquisition or Generation If you want to measure and analyze signals from a source outside the computer you want to acquire signals If you want to send signals to an outside instrument to control its operation you want to ge
16. National Instruments Corporation 3 1 LabVIEW Data Acquisition Basics Manual 3 Basic LabVIEW Data Acquisition Concepts This chapter explains how data acquisition works with LabVIEW Before you start building your data acquisition DAQ application you should know some of the following basic LabVIEW DAQ concepts Where to find common DAQ examples Where to find the DAQ VIs in LabVIEW How the DAQ VIs are organized VI parameter conventions Default and current value conventions Common DAQ VI parameters How DAQ VIs handle errors Channel port and counter addressing Limit settings Data organization for analog applications Refer to the LabVIEW User Manual or the G Programming Reference Manual for information about basic LabVIEW programming concepts Location of Common DAQ Examples The DAQ examples address many common applications involving data acquisition in LabVIEW You can find these examples in labview examples daq NI DAQ 5 x 6 x There are two ways to locate DAQ examples One way is to run the DAQ Solution Wizard The other way is to run the Search Examples Online Help available in LabVIEW version 5 0 and higher You can launch either tool directly from the LabVIEW launch screen Chapter 3 Basic LabVIEW Data Acquisition Concepts LabVIEW Data Acquisition Basics Manual 3 2 www ni com The following list briefly describes the VI libraries designated by
17. SCXI terminal blocks have two different kinds of sensors an Integrated Circuit IC sensor or a thermistor For terminal blocks that have IC sensors such as the SCXI 1300 and the SCXI 1320 you can multiply the voltage read from the IC sensor by 100 to get the ambient temperature in degrees Centigrade at the terminal block For terminal blocks that have thermistors such as the SCXI 1303 SCXI 1322 SCXI 1327 and SCXI 1328 use the Thermistor Conversion VI found in the Functions Data Acquisition Signal Conditioning palette to convert the raw voltage data into units of temperature You cannot sample other SCXI channels from the same module while you are sampling the mtemp sensor However if you are in parallel mode you can sample the dtemp sensor along with other channels on the same module at the same time because you are not performing any multiplexing on the SCXI module You also can sample the cjtemp sensor along with other channels on the SCXI 1101 SCXI 1102 SCXI 1112 SCXI 1125 and SCXI 1127 For the SCXI 1102 cjtemp must be the first channel in the channel list The SCXI 1112 and SCXI 1125 can sample cjtemp channels in any order in the channel list For greater accuracy take several readings from the temperature sensor and average those readings to yield one value If you do not want to average several readings take a single reading using the Easy Analog Input VI AI Sample Channel Modules Channel SCXI 1100 1 SCXI 1
18. The CTR Control VI is an Advanced VI that is used to check if the GATE pulse has completed The Counter Read VI returns the count value from counter which is used to determine the frequency and pulse width Finally the Counter Stop VI stops the counter operation Figure 27 5 Frequency Measurement Example Using Intermediate VIs Chapter 27 Measuring Frequency and Period LabVIEW Data Acquisition Basics Manual 27 6 www ni com 8253 54 The Measure Frequency gt 1 kHz 8253 VI located in labview examples daq counter 8253 llb initiates the counter to count the number of rising edges of a TTL signal at the CLK of counter during a known pulse at the GATE of counter The known pulse is created by counter 0 and its width is determined by gate width The maximum width of the pulse is 32 ms if your DAQ device has a 2 MHz internal timebase and 65 ms if your DAQ device has a 1 MHz internal timebase This maximum pulse is why this example only reads frequencies higher than 1 kHz A frequency of 1 kHz generates 32 cycles during the 32 ms pulse As this cycle count decreases as with lower frequencies the frequency measurement becomes less accurate Frequency is the output for this example and period is determined by taking the inverse of the frequency You must externally wire the signal to be measured to the CLK of counter and the OUT of counter 0 must be wired through a 7404 inverter chip to the GATE of counter Notice the ICTR Control G
19. 28 6 to 28 7 events 28 4 finite pulse train generation 25 10 to 25 11 Index National Instruments Corporation I 3 LabVIEW Data Acquisition Basics Manual frequency and period measurement connecting counters 27 3 to 27 4 high frequency signals 27 4 to 27 5 how and when to measure 27 2 to 27 3 low frequency signals 27 7 to 27 8 internal timebases with maximum pulse width measurements table 26 8 single square pulse generation 25 5 to 25 6 square pulse generation 25 3 stopping counter generations 25 14 to 25 15 amplification increasing signal to noise ratio figure 19 4 methods for minimizing noise note 19 4 amplifier offset reading 22 5 to 22 6 AMUX 64T devices addressing with MIO boards A 1 analog input channel range table 5 14 channel addressing 5 14 to 5 18 scanning order for DAQ devices 5 15 to 5 18 four AMUX 64Ts table 5 17 one or two AMUX 64Ts table 5 16 specifying number for AMUX 64T device table 5 18 analog input See also buffered waveform acquisition AMUX 64T external multiplexer device 5 14 to 5 18 analog input output control loops 6 5 to 6 8 channel clock control 9 3 to 9 5 9 7 circular buffered analog input examples 7 10 to 7 11 continuous acquisition from multiple channels 7 8 to 7 9 defining signals 5 1 to 5 2 digital triggering 8 2 to 8 5 external control of acquisition rate 9 1 to 9 3 hardware triggering 8 1 to 8 8 measurement systems 5 4 to 5 6 multipl
20. 5 00 2 50 0 2 50 5 00 7 50 10 00 Chapter 5 Things You Should Know about Analog Input LabVIEW Data Acquisition Basics Manual 5 6 www ni com Signal Limit Settings Limit settings are the maximum and minimum values of the signal you are measuring A more precise limit setting allows the ADC to use more digital divisions to represent the signal Figure 5 6 shows an example of this theory Using a 3 bit ADC and a device range setting of 0 00 to 10 00 V Figure 5 6 shows the effects of a limit setting between 0 and 5 V and 0 and 10 V With a limit setting of 0 to 10 V the ADC uses only four of the eight divisions in the conversion But using a limit setting of 0 to 5 V the ADC now has access to all eight digital divisions This makes the digital representation of the signal more accurate Figure 5 6 The Effects of Limit Settings on ADC Precision Limit Settings 0 to 10 V Limit Settings 0 to 5 V 10 00 8 75 7 5 6 25 5 00 3 75 2 50 1 25 0 00 111 110 101 100 011 010 001 000 V 10 00 8 75 7 5 6 25 5 00 3 75 2 50 1 25 0 00 V 000 001 010 011 100 101 110 111 Limit Settings 0 to 5 V Chapter 5 Things You Should Know about Analog Input National Instruments Corporation 5 7 LabVIEW Data Acquisition Basics Manual Considerations for Selecting Analog Input Settings The resolution and device range of a DAQ device determine the smallest detectabl
21. 50 to 50 mV 10 to 10 mV 2 44 mV 1 22 mV 610 V 305 V 244 V 24 4 V 4 88 V 10 to 10 V 10 to 10 V 5 to 5 V 2 5 to 2 5 V 1 25 to 1 25 V 1 to 1 V 0 1 to 0 1 V 20 to 20 mV 4 88 mV 2 44 mV 1 22 mV 610 V 488 V 48 8 V 9 76 V 1 The value of 1 Least Significant Bit LSB of the 12 bit ADC In other words the voltage increment corresponding to a change of 1 count in the ADC 12 bit count Chapter 5 Things You Should Know about Analog Input National Instruments Corporation 5 9 LabVIEW Data Acquisition Basics Manual Differential Measurement System In a differential measurement system you do not need to connect either input to a fixed reference such as earth or a building ground DAQ devices with instrumentation amplifiers can be configured as differential measurement systems Figure 5 7 depicts the 8 channel differential measurement system used in the MIO series devices Analog multiplexers increase the number of measurement channels while still using a single instrumentation amplifier For this device the pin labeled AIGND the analog input ground is the measurement system ground Chapter 5 Things You Should Know about Analog Input LabVIEW Data Acquisition Basics Manual 5 10 www ni com Figure 5 7 8 Channel Differential Measurement System CH0 CH2 CH1 CH7 CH0 CH2 CH1 CH7 MUX MUX Vm Instrumentation Amplifier
22. Acquiring Multiple Waveforms You can acquire more than one waveform at a time with another of the Easy Analog Input VIs AI Acquire Waveforms This VI also has a minimal set of inputs but it allows inputs of more than one channel to read and returns data from all channels read The channel input for this VI is a string where you can enter a list of channels Refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts for more information on channel specification in LabVIEW LabVIEW outputs a two dimensional 2D array in the waveforms output for this VI where each channel has a different column and the samples are in each row Chapter 3 contains more information on how data is organized for analog applications You can set the high limit and low limit inputs for all the channels to the same value Chapter 3 contains more information on gain specifications Like the other Easy VIs you cannot use any advanced programming features with the AI Acquire Waveforms VI The built in error checking of this VI alerts you to any errors that occur in the program You also can acquire multiple waveforms using the Intermediate VIs The Intermediate VIs give you more control over your data acquisition processes such as the capability to read any part of the buffer An example is the Acquire N Scans VI located in labview examples daq anlogin anlogin llb With these Intermediate Analog Input VIs you must wire a taskID to identify the DAQ operation and the s
23. Counting Signal Highs and Lows Connecting Counters to Count Events and Time 28 1 Am9513 28 2 Counting Events 28 3 TIO ASIC DAQ STC 28 3 Am9513 28 4 8253 54 28 5 Counting Elapsed Time 28 5 TIO ASIC DAQ STC 28 5 Am9513 28 6 8253 54 28 7 Chapter 29 Dividing Frequencies TIO ASIC DAQ STC Am9513 29 2 8253 54 29 3
24. Figure 2 4 Accessing the Device Configuration Dialog Box in NI DAQ 2 5 Figure 2 5 Device Configuration Dialog Box and I O Connector Display in NI DAQ 2 6 Figure 2 6 Accessing the NI DAQ SCXI Configuration Dialog Box 2 8 Figure 2 7 SCXI Configuration Dialog Box in NI DAQ 2 9 Figure 3 1 Analog Input VI Palette Organization 3 4 Figure 3 2 LabVIEW Help Window Conventions 3 6 Figure 3 3 LabVIEW Error In Input and Error Out Output Error Clusters 3 8 Figure 3 4 Channel String Controls 3 9 Figure 3 5 Channel String Array Controls 3 11 Figure 3 6 Limit Settings Case 1 3 12 Figure 3 7 Limit Settings Case 2 3 13 Figure 3 8 Example of a Basic 2D Array 3 14 Figure 3 9 2D Array in Row Major Order 3 14 Figure 3 10 2D Array in Column Major Order
25. Figure 3 5 shows several ways you can address onboard channels 0 1 and 2 The top three examples apply to VIs whose channel parameters are string arrays The bottom two examples apply to VIs whose channel parameters are scalar strings Chapter 3 Basic LabVIEW Data Acquisition Concepts National Instruments Corporation 3 11 LabVIEW Data Acquisition Basics Manual Figure 3 5 Channel String Array Controls Note Refer to Appendix B Hardware Capabilities in the LabVIEW Function and VI Reference Manual or select Help Online Reference for the number of channels your device can acquire data from at one time Limit Settings Limit settings are the maximum and minimum values of the analog signal s you are measuring or generating The pair of limit setting values can be unique for each analog input or output channel For analog input applications the limit setting values must be within the range for the device Refer to Chapter 5 Things You Should Know about Analog Input for information about the range for your device Each pair of limit setting values forms a cluster Analog output limits have a third member the reference source For simplicity LabVIEW refers to limit settings as a pair of values LabVIEW uses an array of these clusters to assign limits to the channels in your channel string array If you use the DAQ Channel Wizard to configure your analog input channels the physical unit you specified for a particular channel name
26. How to Use This Book Chapter 2 Installing and Configuring Your Data Acquisition Hardware Installing and Configuring Your National Instruments Device 2 4 Installing and Configuring Your DAQ Device Using NI DAQ 5 x 6 x 2 4 Configuring Your DAQ Device Using NI DAQ 4 8 x on the Macintosh 2 4 Installing and Configuring Your SCXI Chassis 2 6 Hardware Configuration 2 6 NI DAQ 5 x 6 x Software Configuration 2 8 NI DAQ 4 8 x for Macintosh Software Configuration 2 8 Configuring Your Channels in NI DAQ 5 x 6 x 2 11 Chapter 3 Basic LabVIEW Data Acquisition Concepts Location of Common DAQ Examples 3 1 Locating the Data Acquisition VIs in LabVIEW 3 3 DAQ VI Organization 3 3 Easy VIs 3 4 Intermediate VIs 3 5 Utility VIs
27. Part V SCXI Getting Your Signals in Great Condition Things You Should Know about SCXI Hardware and Software Setup for Your SCXI System Special Programming Considerations for SCXI Common SCXI Applications SCXI Calibration Increasing Signal Measurement Precision Part VI Counting Your Way to High Precision Timing Things You Should Know about Counters Generating a Square Pulse or Pulse Trains Measuring Pulse Width Measuring Frequency and Period Counting Signal Highs and Lows Dividing Frequencies Part VII Debugging Your Data Acquisition Application Debugging Techniques Chapter 1 How to Use This Book National Instruments Corporation 1 3 LabVIEW Data Acquisition Basics Manual If you already have started a LabVIEW DAQ application please refer to Chapter 2 Installing and Configuring Your Data Acquisition Hardware to check your configuration Refer to Part VII Debugging Your Data Acquisition Application for information on common errors The following flowchart shows the steps to follow before running your application 1 Install and Configure Your Hardware When you install LabVIEW the program prompts you to have the data acquisition DAQ drivers installed This manual guides you through setting up NI DAQ software with your DAQ device and SCXI hardware You should read any unique installation instructions for your platform in Chapter 2 Installing and Configuring Your Data Acquisition Hardware
28. TC The valid output of the example VI indicates whether the counter measured the pulse without overflowing reaching TC However valid does not tell you whether a whole pulse was measured when measuring a pulse within a pulse train For a complete description of this example refer to the information found in Windows Show VI Info 8253 54 Open the block diagram of the Measure Short Pulse Width 8253 VI located in labview examples daq counter 8253 llb This VI counts the number of cycles of the internal timebase of Counter 0 to measure a high pulse width You can measure a single pulse or a pulse within a train of multiple pulses However the pulse must occur after the Chapter 26 Measuring Pulse Width National Instruments Corporation 26 5 LabVIEW Data Acquisition Basics Manual counter starts This means it may be difficult to measure a pulse within a fast pulse train because the counter uses high level gating To measure a low pulse width insert a 7404 inverter chip between your pulse source and the GATE input of counter 0 On the Measure Short Pulse Width 8253 VI block diagram the first call to ICTR Control VI sets up counting mode 4 which tells the counter to count down while the gate input is high The Get Timebase 8253 VI is used to get the timebase of your DAQ device A DAQ device with an 8253 54 counter has an internal timebase of either 1 MHz or 2 MHz depending on the device Inside the While Loop ICTR Con
29. buffer configurations and so forth A port cannot belong to more than one group digital trigger A TTL signal that you can use to start or stop a buffered data acquisition operation such as buffered analog input or buffered analog output DIO devices Refers to all devices capable of performing immediate and or latched digital input output unless otherwise noted DIP Dual Inline Package dithering The addition of Gaussian noise to an analog input signal By applying dithering and then averaging the input data you can effectively increase the resolution by another one half bit Glossary LabVIEW Data Acquisition Basics Manual G 6 www ni com DLL Dynamic Link Library DMA Direct Memory Access A method by which you can transfer data to computer memory from a device or memory on the bus or from computer memory to a device while the processor does something else DMA is the fastest method of transferring data to or from computer memory down counter Performing frequency division on an internal signal driver Software that controls a specific hardware device such as a DAQ device E E Series MIO device Boards such as the PCI MIO 16E 1 and the AT MIO 16E 2 that use the MITE chip on PCI boards for bus mastering the DAQ PnP chip for Plug and Play configuration the DAQ STC chip for instrumentation class counting and timing and the NI PGIA for high accuracy analog input measurements EEPROM Electrically erasable
30. counting elapsed time Am9513 28 6 TIO ASIC and DAQ STC 28 5 to 28 6 counting events 28 3 to 28 5 digital input application 22 17 digital output application 22 19 finite pulse train generation 25 9 to 25 10 grouping two or more ports A 2 immediate digital I O 16 2 to 16 3 limitations 6 3 measuring frequency and period high frequency signals 27 4 to 27 5 low frequency signals 27 7 multiple channel single point analog input 6 3 multiple immediate updates 11 2 multiple waveform acquisition 7 3 overview 3 4 single square pulse generation 25 6 single channel single point analog input 6 1 single immediate updates 11 1 to 11 2 single waveform acquisition 7 2 to 7 3 strain gauge application 22 15 waveform generation 12 1 to 12 2 edges of signals 24 2 EEPROM for storing calibration constants 23 1 to 23 2 default load area 23 2 factory area 23 2 user area 23 2 elapsed time counting See events or elapsed time counting Error Handler VIs 30 2 error handling debugging VIs 30 2 to 30 3 error in and error out error clusters 3 8 Event or Time Counter Config VI counting events Am9513 28 4 DAQ STC 28 3 counting time Am9513 28 7 DAQ STC 28 6 measuring frequency and period 27 5 events or elapsed time counting 28 1 to 28 7 adjacent counters for counter chips table 28 2 connecting counters 28 1 to 28 3 Am9513 28 2 to 28 3 cascading counters figures 28 2 to 28 3 external connections figures 28 1
31. elapsed time 28 5 to 28 7 8253 54 28 6 to 28 7 Am9513 28 6 to 28 7 TIO ASIC and DAQ STC 28 5 to 28 6 Index LabVIEW Data Acquisition Basics Manual I 12 www ni com events 28 3 to 28 5 8253 54 28 5 Am9513 28 4 TIO ASIC and DAQ STC 28 3 to 28 4 execution highlighting 30 3 external control acquisition rate 9 1 to 9 7 channel and scan intervals using channel clock figure 9 1 channel clock control 9 3 to 9 5 choosing between triggering and external clock control 4 4 description 9 1 to 9 3 multi point acquisition with internal or external clock 4 5 round robin scanning figure 9 2 scan clock control 9 5 to 9 7 simultaneous control of scan and channel clocks 9 7 update clock 13 1 to 13 2 Generate N Updates ExtUpdateClk VI 13 1 to 13 2 input pins table 13 2 supplying test clock from DAQ device 13 2 external conversions 9 4 EXTUPDATE signal table 13 2 F Finite Pulse Train 8253 VI 25 12 finite pulse train generation 25 9 to 25 12 8253 54 25 11 to 25 12 DAQ STC 25 11 physical connections figure 25 10 TIO ASIC DAQ STC and Am9513 25 10 to 25 11 Finite Pulse Train Adv DAQ STC VI 25 11 Finite Pulse Train Easy 9513 VI 25 10 Finite Pulse Train Easy DAQ STC VI 25 10 Finite Pulse Train Int 9513 VI 25 10 Finite Pulse Train Int DAQ STC VI 25 10 finite timed digital I O 18 1 to 18 2 with triggering 18 2 without triggering 18 1 to 18 2 floating signal sources 5 3 FOUT pi
32. handshaking pulses the software spends less time reading or writing data leaving more time for other operations Port x 1 ACK External Device last port in portList Port x n Port x 2 ACK ACK OBF OBF OBF Chapter 17 Handshaked Digital I O National Instruments Corporation 17 5 LabVIEW Data Acquisition Basics Manual Note On an AT DIO 32F device with nonbuffered handshaking you can group 1 2 or 4 ports together For buffered handshaking on the AT DIO 32F you can group only 2 or 4 ports together You can use only Intermediate or Advanced Digital I O VIs for digital handshaking in LabVIEW The Intermediate I O VIs work for most nonbuffered and buffered digital handshaking applications However for some DAQ devices you might need a combination of Intermediate and Advanced I O VIs Nonbuffered Handshaking Nonbuffered handshaking occurs when your program transfers one digital value after receiving a digital pulse on the handshaking lines LabVIEW does not store these digital values in computer memory You should use nonbuffered handshaking when you expect only a few digital handshaking pulses For multiple pulsed or high speed applications you should use buffered handshaking 6533 Family The example Dig Word Handshake In 653x VI shows how to read nonbuffered data using handshaking The example Dig Word Handshake Out 653x VI shows how to write nonbuffered data using handshaking These exam
33. the signal level is treated as being relative to the physical units specified for the channel For example if you configure a channel called temperature to have a physical unit of Deg C the value you specify for the trigger signal level is relative to Deg C If you are not using channel names the signal level is treated as volts In Figure 8 3 the analog trigger is set to start the data acquisition on the rising slope of the signal when the signal reaches 3 2 Figure 8 3 Diagram of an Analog Trigger Level and Slope of Signal Initiates Data Capture 3 2 0 Chapter 8 Controlling Your Acquisition with Triggers LabVIEW Data Acquisition Basics Manual 8 6 www ni com Figure 8 4 illustrates analog triggering for post triggered data acquisition using a timeline You configure your DAQ hardware in LabVIEW to begin taking data when the incoming signal is on the rising slope and when the amplitude reaches 3 2 Your DAQ device begins capturing data when the specified analog trigger conditions are met Figure 8 4 Analog Triggering with Your DAQ Device Analog Trigger Signal Analog Data DAQ Device waits until analog trigger conditions are met Then DAQ Device External Device DAQ Device External Device Chapter 8 Controlling Your Acquisition with Triggers National Instruments Corporation 8 7 LabVIEW Data Acquisition Basics Manual Analog Triggering Examples A common example of analog triggering in
34. 1 By writing to or reading from a port you can simultaneously set or retrieve the states of multiple digital lines Refer to Appendix B Hardware Capabilities of the LabVIEW Function and VI Reference Manual or your hardware user manual Or refer to the LabVIEW Online Reference by selecting Help Online Reference for port information on your device Figure 15 1 Digital Ports and Lines Data latches and drivers Data latches and drivers Device or Module Output Port Input Port Output Lines Input Lines Chapter 15 Things You Should Know about Digital I O LabVIEW Data Acquisition Basics Manual 15 2 www ni com Types of Digital Acquisition Generation There are several types of digital acquisition generation nonlatched or immediate latched or handshaked and timed or pattern With immediate digital I O your system updates the digital lines immediately via software calls With handshaked digital I O a device or module accepts or transfers data after a digital pulse has been received With pattern I O data or patterns are written or read at fixed rate The 6533 family of boards can perform pattern I O Handshaked digital I O can be either nonbuffered or buffered Not all devices and modules support handshaked digital I O Refer to the hardware tables in Appendix B Hardware Capabilities or to the LabVIEW Online Reference by selecting Help Online Reference to see if your device or module supports it
35. 1 transducers common transducers table 19 1 to 19 2 excitation 19 5 linearization 19 6 signal conditioning for common types of transducers signals figure 19 3 Transpose 2D Array option note 3 15 transposing arrays 3 15 7 5 triggered data acquisition 8 1 to 8 11 analog hardware triggering description 8 5 to 8 6 examples 8 7 to 8 8 deciding which digital trigger setting to use A 3 digital hardware triggering description 8 2 to 8 3 examples 8 4 to 8 6 hardware triggering 8 1 to 8 8 overview 8 1 software triggering conditional retrieval examples 8 11 description 8 8 to 8 11 triggering vs external clock control 4 4 triggering defined 8 1 triggers defined 8 1 two dimensional 2D arrays 3 14 to 3 16 analog output buffers 3 15 to 3 16 column major order 3 14 to 3 15 extracting single channel 3 15 illustration 3 14 row major order 3 14 two point calibration 23 6 to 23 7 U unipolar range 3 13 5 7 update clock controlling externally 13 1 to 13 2 Generate N Updates ExtUpdateClk VI 13 1 to 13 2 input pins table 13 2 overview 13 1 supplying test clock from DAQ device 13 2 Utility VIs 3 5 V VIs See also Advanced VIs Easy VIs Intermediate VIs channel port and counter addressing 3 8 to 3 11 common DAQ VI parameters 3 7 data organization for analog applications 3 14 to 3 16 debugging 30 1 to 30 4 default and current value conventions 3 6 error handling 3 8 finding VIs i
36. 1 to 21 2 digital and relay modules 20 6 SCXI 1200 Windows 20 6 My Single Scan Processing VI 6 4 Index LabVIEW Data Acquisition Basics Manual I 16 www ni com N National Instruments Web support B 1 to B 2 NI DAQ software channel configuration in NI DAQ 5 x 6 x 2 11 configuring for SCXI modules NI DAQ 4 8 x for Macintosh 2 8 to 2 10 NI DAQ 5 x 6 x for Windows 2 9 driver files Macintosh versions 2 3 versions of NI DAQ drivers note 2 1 Windows versions 2 3 installing NI DAQ 4 8 x on Macintosh 2 4 to 2 6 NI DAQ 5 x or 6 x 2 4 relationship between LabVIEW NI DAQ and DAQ hardware figure 2 3 NIDAQ32 DLL file 2 3 non buffered handshaking 17 5 nonlatched digital I O Advanced Digital VIs 16 3 to 16 4 channel names 16 1 to 16 2 choosing between non latched or latched digital I O 4 5 defined 15 2 Easy Digital VIs 16 2 to 16 3 overview 16 1 non referenced signal sources 5 2 nonreferenced single ended NRSE measurement system 5 13 to 5 14 16 channel NRSE system figure 5 13 when to use 5 14 Nyquist frequency 5 2 Nyquist Theorem 5 2 O OBF Output Buffer Full line 17 2 one point calibration 23 5 to 23 6 online problem solving and diagnostic resources B 1 OUT output pin 24 2 OUT2 signal table 13 2 Output Buffer Full OBF line 17 2 P parallel mode SCXI analog input modules 20 6 to 20 7 channel addressing 21 1 to 21 2 digital modules 20 7 SCXI 1200 Windows 20 7 pa
37. 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 Chapter 5 Things You Should Know about Analog Input National Instruments Corporation 5 17 LabVIEW Data Acquisition Basics Manual Complete the following steps to determine which AMUX 64T channels LabVIEW scans and the scanning order 1 Locate the channel for each DAQ device channel in your channel list in the DAQ Device Channel column in Tables 5 3 or 5 4 Start with the first device channel and continue through the list in your specified channel order 2 Read from left to right along the table row where you located the channel number to find the AMUX 64T scanning order To read a single AMUX 64T channel use channel specifier AMy x This specifier returns data from channel x of the AMUX 64T with ID y To read more than one AMUX 64T channel use channel specifier OBx y This specifier returns data from the AMUX 64T channels that correspond to device channel x through device channel y Table 5 4 Scanning Order for Each DAQ Device Input Channel with Four AMUX 64T Multiplexers DAQ Device Channel AMUX 64T Channels Device 1 Device 2
38. 27 4 External Connections for Period Measurement Measuring the Frequency and Period of High Frequency Signals How you measure the frequency and period of high frequency signals depends on the counter chip on your DAQ device If you are unsure of which chip your DAQ device has refer to your hardware documentation TIO ASIC DAQ STC The Measure Frequency Easy DAQ STC VI located in labview examples daq counter DAQ STC llb uses the Easy VI Measure Frequency which can be found in Functions Data Acquisition Counter This VI initiates the counter to count the number of rising edges of a TTL signal at the SOURCE of counter during a known pulse at the GATE of counter The width of that known pulse is determined by gate width Frequency is the output for this example and period is calculated by taking the inverse of the frequency Remember you must externally wire your signal to be measured to the SOURCE of counter and the OUT of counter 1 must be wired to the GATE of counter For a complete description of this example refer to the information found in Windows Show VI Info Am9513 The Measure Frequency Easy 9513 VI located in labview examples daq counter Am9513 llb uses the Easy VI Measure Frequency which can be found in Functions Data Acquisition Counter This VI initiates the counter to count the number of rising edges of a TTL signal at the SOURCE of counter during a known pulse at the GATE of counter The width of that
39. 5 VI Examples 22 6 Measuring Temperature with RTDs 22 10 Measuring Pressure with Strain Gauges 22 13 Analog Output Application Example 22 17 Digital Input Application Example 22 17 Digital Output Application Example 22 19 Multi Chassis Applications 22 20 Chapter 23 SCXI Calibration Increasing Signal Measurement Precision EEPROM Your System s Holding Tank for Calibration Constants 23 1 Calibrating SCXI Modules 23 3 SCXI Calibration Methods for Signal Acquisition 23 4 One Point Calibration 23 5 Two Point Calibration 23 6 Calibrating SCXI Modules for Signal Generation 23 7 PART VI Counting Your Way
40. 54 Generating a finite pulse train with the 8253 54 chip uses all three counters Figure 25 11 shows how to externally connect your counters Because counter 0 is internally connected to a clock source counter 0 is used to generate the timebase used by counter 1 and counter 2 counter 1 generates a single low pulse used to gate counter 2 Because counter 2 Chapter 25 Generating a Square Pulse or Pulse Trains LabVIEW Data Acquisition Basics Manual 25 12 www ni com must be gated with a high pulse the output of counter 1 is passed through a 7404 inverter chip prior to being connected to the GATE of counter 2 counter 2 is set up to generate a pulse train at its OUT pin Figure 25 11 External Connections Diagram from the Front Panel of Finite Pulse Train 8253 VI The example Finite Pulse Train 8253 VI located in labview examples daq counter 8253 llb shows how to generate a finite pulse train This example uses a sequence structure to divide the basic tasks involved In frame 0 of the sequence all of the counters are reset Notice counter 1 is reset so its output state starts high In frame 1 of the sequence the counters are set up for different counting modes counter 0 is set up to generate a timebase using the ICTR Timebase Generator VI counter 1 is set up to output a single low pulse using the ICTR Control VI counter 2 is set up to output a pulse train using the ICTR Timebase Generator VI In frame 2 of the sequence a dela
41. 7 Scan 8 Scan 5 Scan 5 Scan 6 Scan 6 Scan 7 Scan 7 Scan 8 Scan 8 Chapter 8 Controlling Your Acquisition with Triggers LabVIEW Data Acquisition Basics Manual 8 10 www ni com The conditional retrieval cluster of the AI Read VI specifies the analog signal conditions of retrieval as shown in Figure 8 6 Figure 8 6 The AI Read VI Conditional Retrieval Cluster Tip The actual data acquisition is started by running your VI The conditional retrieval just controls how data already being acquired is returned When acquiring data with conditional retrieval you typically store the data in a memory buffer similar to hardware triggering applications After you start running the VI the data is placed in the buffer Once the retrieval conditions have been met the AI Read VI searches the buffer for the desired information As with hardware analog triggering you specify the analog channel of the triggering signal by specifying its channel index an index number corresponding to the relative order of a single channel in a channel list You also specify the slope rising or falling and the level of the trigger signal Note The channel index might not be equal to the channel value You can use the Channel to Index VI to get the channel index for a channel You can find this VI in Data Acquisition Calibration and Configuration The AI Read VI begins searching for the retrieval conditions in the buffer at the read s
42. 8250 or compatible UART you can use only up to 19 200 baud SCXI 1000 SCXI MAINFRAME Unconditioned Signals from Transducers Analog and Digital Bus Backplane Conditioned Signals to DAQ Device or Parallel Port Chapter 20 Hardware and Software Setup for Your SCXI System National Instruments Corporation 20 5 LabVIEW Data Acquisition Basics Manual SCXI Operating Modes The SCXI operating mode determines the way that DAQ devices access signals There are two basic operating modes for SCXI modules multiplexed and parallel You designate the mode in the operating mode input in the configuration utility or Measurement amp Automation Explorer Also you may have to set up jumpers on the module for the correct operating mode Check your SCXI module user manual for more information Note National Instruments recommends that you use the multiplexed mode for most purposes Multiplexed Mode for Analog Input Modules When an analog input module operates in multiplexed mode all of its input channels are multiplexed to one module output When you cable a DAQ device to a multiplexed analog input module the DAQ device has access to that module s multiplexed output as well as all other modules in the chassis through the SCXIbus The analog input VIs route the multiplexed analog signals on the SCXIbus for you transparently So if you operate all modules in the chassis in multiplexed mode you need to cable only one of the modu
43. Cont Acq to Spreadsheet File VI 7 11 Cont Acq amp Chart Async Occurrence VI 7 9 Cont Acquire amp Chart immediate VI 6 4 Cont Change Detection Input VI 18 3 Cont Handshake Input VI 17 8 Cont Handshake Output VI 17 8 Cont Pattern Input VI 18 3 Cont Pattern Output VI 18 3 Cont Pulse Train 8253 VI 25 9 29 3 Cont Pulse Train Easy 9513 VI 25 8 Cont Pulse Train Easy DAQ STC VI 25 8 Cont Pulse Train Int 9513 VI 25 8 Cont Pulse Train Int DAQ STC VI 25 8 continuous acquisition from multiple channels 7 8 to 7 9 Continuous Generation example VI 12 3 Index National Instruments Corporation I 7 LabVIEW Data Acquisition Basics Manual Continuous Pulse Generator Config VI continuous pulse train generation 25 8 finite pulse train generation 25 10 to 25 11 continuous pulse train generation 25 7 to 25 9 8253 54 25 9 TIO ASIC DAQ STC and Am9513 25 7 to 25 8 continuous timed digital I O 18 2 to 18 3 Continuous Transducer VI 22 6 control loops See analog input output control loops Convert RTD Reading VI 22 12 Convert Strain Gauge Reading VI 22 15 to 22 16 Convert Thermocouple Reading VI 22 8 Count Events 8253 VI 28 5 Count Events or Time Easy VI events 28 3 time Am9513 28 6 TIO ASIC and DAQ STC 28 5 to 28 6 Count Events Easy 9513 VI 28 4 Count Events Easy DAQ STC VI 28 3 Count Events Int 9513 VI 28 4 Count Events Int DAQ STC VI 28 3 Count Time 8253 VI 28 6 to 28 7 Count Time Ea
44. Corporation 26 3 LabVIEW Data Acquisition Basics Manual The type of measurement menu choices for this VI are shown in Figure 26 3 Figure 26 3 Menu Choices for Type of Measurement for the Measure Pulse Width or Period DAQ STC VI Use the first two menu choices when you want to measure the width of a single pulse In these cases the GATE of the counter must start out in the opposite phase of the pulse you want to measure For example if you choose measure high pulse width of a single pulse the GATE must start out low when you run the VI If you attempt to measure a single high pulse and the GATE is already high such as in the middle of a pulse train when you run the VI an error will occur Use the last two menu choices when you want to measure the width of a single pulse within a train of multiple pulses In these cases it is the previous GATE transition that arms the counter to measure the next pulse For example if you choose measure one high pulse width of multiple pulses the first high to low GATE transition from one pulse would arm the counter to measure the very next pulse The timebase you choose determines how long a pulse you can measure with the 24 bit counter For example the 100 kHz timebase allows you to measure a pulse up to 224 10 s 167 seconds long The 20 MHz timebase allows you to measure a pulse up to 838 ms long For a complete description of this example refer to the information found in Windows Sho
45. DAQ operations on channels in multiple SCXI chassis at the same time For example the first element of your channels array could be ob0 sc1 md1 0 31 and the second element of the channels array could be ob1 sc2 md1 0 31 Then LabVIEW would scan 32 channels on module 1 of SCXI chassis 1 using onboard channel 0 then the 32 channels on module 1 in SCXI chassis 2 using onboard channel 1 Remember that the scan rate you specify is how many scans per second LabVIEW performs For each scan LabVIEW reads every channel in the channels array You can practice reading channels from different chassis by using the channel strings explained above in the Easy VIs National Instruments Corporation 23 1 LabVIEW Data Acquisition Basics Manual 23 SCXI Calibration Increasing Signal Measurement Precision Your SCXI module ships to you factory calibrated for the specified accuracy You need to recalibrate the module only if the precision of your signal measurement is not acceptable because of shifts in environmental conditions Note This chapter does not apply to the SCXI 1200 For calibration on the SCXI 1200 you should use the 1200 Calibrate VI which you can find in Functions Data Acquisition Calibration and Configuration If you are using an SCXI 1200 in a remote SCXI configuration National Instruments recommends that you connect directly to your parallel port to perform calibration because it works much faster EEPROM Your System s
46. Device 3 Device 4 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 Chapter 5 Things You Should Know about Analog Input LabVIEW Data Acquisition Basics Manual 5 18 www ni com When the channel list contains a single AMUX 64T channel you also must specify the number of the AMUX 64T device as shown in the following table Refer to AMUX 64T channels only when a single AMUX 64T channel comprises the entire list Otherwise you refer to them indirectly through the device channels
47. Holding Tank for Calibration Constants When you calibrate your SCXI module in LabVIEW the calibration constants can be stored in electronically erasable programmable read only memory EEPROM The EEPROM stores calibration constant information in your module s memory There are three parts to the EEPROM the factory area the default load area and the user area Note Only the SCXI 1102 SCXI 1102B SCXI 1102C SCXI 1104 SCXI 1104C SCXI 1112 SCXI 1122 SCXI 1124 SCXI 1125 SCXI 1141 SCXI 1142 and SCXI 1143 have EEPROMs All other SCXI modules do not store calibration constants Note The SCXI 1125 does not have a user area in its EEPROM Chapter 23 SCXI Calibration Increasing Signal Measurement Precision LabVIEW Data Acquisition Basics Manual 23 2 www ni com The factory area has a set of factory calibration constants already stored in it when you receive your SCXI module You cannot write into the factory area but you can read from it so you can always access and use these factory constants if they are appropriate for your application The default load area is where LabVIEW automatically looks to load calibration constants the first time you access the module When the module is shipped the default load area contains a copy of the factory calibration constants Note You can overwrite the constants stored in the default load area of EEPROM with a new set of constants using the SCXI Cal Constants VI To learn m
48. INCLUDING THE RISK OF BODILY INJURY AND DEATH SHOULD NOT BE RELIANT SOLELY UPON ONE FORM OF ELECTRONIC SYSTEM DUE TO THE RISK OF SYSTEM FAILURE TO AVOID DAMAGE INJURY OR DEATH THE USER OR APPLICATION DESIGNER MUST TAKE REASONABLY PRUDENT STEPS TO PROTECT AGAINST SYSTEM FAILURES INCLUDING BUT NOT LIMITED TO BACK UP OR SHUT DOWN MECHANISMS BECAUSE EACH END USER SYSTEM IS CUSTOMIZED AND DIFFERS FROM NATIONAL INSTRUMENTS TESTING PLATFORMS AND BECAUSE A USER OR APPLICATION DESIGNER MAY USE NATIONAL INSTRUMENTS PRODUCTS IN COMBINATION WITH OTHER PRODUCTS IN A MANNER NOT EVALUATED OR CONTEMPLATED BY NATIONAL INSTRUMENTS THE USER OR APPLICATION DESIGNER IS ULTIMATELY RESPONSIBLE FOR VERIFYING AND VALIDATING THE SUITABILITY OF NATIONAL INSTRUMENTS PRODUCTS WHENEVER NATIONAL INSTRUMENTS PRODUCTS ARE INCORPORATED IN A SYSTEM OR APPLICATION INCLUDING WITHOUT LIMITATION THE APPROPRIATE DESIGN PROCESS AND SAFETY LEVEL OF SUCH SYSTEM OR APPLICATION National Instruments Corporation v LabVIEW Data Acquisition Basics Manual Contents About This Manual Conventions Used in This Manual xix LabVIEW Data Types xxi Related Documentation xxii PART I Before You Get Started Chapter 1
49. Input Applications for Measuring Temperature and Pressure Two common transducers for measuring temperature are thermocouples and RTDs A common transducer for measuring pressure is strain gauges Read the following sections on special measuring considerations needed for each transducer If you use the DAQ Channel Wizard to configure your analog input channels you can simplify the programming needed to measure your channels This section describes methods of measuring data using named channels configured in the DAQ Channel Wizard and using the conventional method Note For more information about using the DAQ Channel Wizard to configure your channels refer to the Configuring Your Channels in NI DAQ 5 x 6 x section of Chapter 2 Installing and Configuring Your Data Acquisition Hardware For more information about using channel names refer to the Channel Name Addressing section of Chapter 3 Basic LabVIEW Data Acquisition Concepts Measuring Temperature with Thermocouples If you want to measure the temperature of the environment you can use the temperature sensors in the terminal blocks But if you want to measure the temperature of an object away from the SCXI chassis you must use a transducer such as a thermocouple A thermocouple is a junction of two dissimilar metals that gives varying voltages based on the temperature However when using thermocouples you need to compensate for the thermocouple voltages produced at the screw termi
50. Only the following three subVIs were needed to create the examples in this section DIO Port Config VI DIO Port Read VI and DIO Port Write VI 6533 Family The examples Read from 1 Dig Port 653x VI and Write to 1 Dig Port 653x VI show how to use the Advanced Digital I O VIs to read from or write to one digital 8 bit port The examples Read from 2 Dig Ports 653x VI and Write to 2 Dig Ports 653x VI show how to use the Advanced Digital I O VIs to read from or write to two separate 8 bit ports The examples Read from Digital Port 653x VI and Write to Digital Port 653x VI show how to use the Advanced Digital I O VIs to read from or write to one digital port where the port width can be 8 16 24 or 32 bits These examples are located in labview examples daq digital 653x llb 8255 Family The examples Read from 1 Dig Port 8255 VI and Write to 1 Dig Port 8255 VI show how to use the Advanced Digital I O VIs to read from or write to one digital 8 bit port The examples Read from 2 Dig Ports 8255 VI and Write to 2 Dig Ports 8255 VI show how to use the Advanced Digital I O VIs to read from or write to two separate 8 bit ports The examples Read from Digital Port 8255 VI and Write to Digital Port 8255 VI show how to use the Advanced Digital I O VIs to read from or write to one digital port where the port width can be 8 16 24 or 32 bits These examples are located in labview examples daq digital 8255 llb Chapter 16 Immediate Digital I
51. PART VII Debugging Your Data Acquisition Application Chapter 30 Debugging Techniques Hardware Connection Errors 30 1 Software Configuration Errors 30 1 VI Construction Errors 30 2 Error Handling 30 2 Single Stepping through a VI 30 3 Execution Highlighting 30 3 Using the Probe Tool 30 4 Setting Breakpoints and Showing Advanced DAQ VIs 30 4 Appendix A LabVIEW Data Acquisition Common Questions Contents LabVIEW Data Acquisition Basics Manual xiv www ni com Appendix B Technical Support Resources Glossary Index Figures Figure 2 1 Installing and Configuring DAQ Devices 2 2 Figure 2 2 How NI DAQ Relates to Your System and DAQ Devices 2 3 Figure 2 3 NI DAQ Device List Display 2 5
52. SCXI 1140 SCXI 1140 SCXI 1140 SCXI 1140 SCXI 1001 MAINFRAME SCXI SCXI Signal Conditioning Modules Conditioned Signals PC Plug In DAQ Device SCXI 1140 SCXI 1140 SCXI 1140 SCXI 1140 SCXI 1001 MAINFRAME SCXI SCXI Signal Conditioning and DAQ Modules Front End Signal Conditioning for Plug In DAQ Devices Parallel Port Link SCXI 1200 12 Bit Data Acquisition and Control Module External Data Acquisition and Control System SCXI 1140 Chapter 20 Hardware and Software Setup for Your SCXI System National Instruments Corporation 20 3 LabVIEW Data Acquisition Basics Manual Figure 20 2 Components of an SCXI System Refer to the SCXI tables in Appendix B Hardware Capabilities of the LabVIEW Function and VI Reference Manual for tables containing specifications for all the SCXI modules or refer to the LabVIEW Online Reference by selecting Help Online Reference This appendix also includes a list of all the SCXI modules and the compatible terminal blocks Note For information on how to set up each module and transducer consult your hardware user manuals and the Getting Started with SCXI manual How do you transfer data from the SCXI chassis to the DAQ device or parallel or serial port Figure 20 3 shows a diagram of an SCXI chassis When you use SCXI as a front end signal conditioning system the analog and digital bus backplane also known as the SCXIbus transfers analog and or digita
53. TO RECOVER DAMAGES CAUSED BY FAULT OR NEGLIGENCE ON THE PART OF NATIONAL INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER NATIONAL INSTRUMENTS WILL NOT BE LIABLE FOR DAMAGES RESULTING FROM LOSS OF DATA PROFITS USE OF PRODUCTS OR INCIDENTAL OR CONSEQUENTIAL DAMAGES EVEN IF ADVISED OF THE POSSIBILITY THEREOF This limitation of the liability of National Instruments will apply regardless of the form of action whether in contract or tort including negligence Any action against National Instruments must be brought within one year after the cause of action accrues National Instruments shall not be liable for any delay in performance due to causes beyond its reasonable control The warranty provided herein does not cover damages defects malfunctions or service failures caused by owner s failure to follow the National Instruments installation operation or maintenance instructions owner s modification of the product owner s abuse misuse or negligent acts and power failure or surges fire flood accident actions of third parties or other events outside reasonable control Copyright Under the copyright laws this publication may not be reproduced or transmitted in any form electronic or mechanical including photocopying recording storing in an information retrieval system or translating in whole or in part without the prior written consent of National Instruments Corporation Trademarks DAQ STC DAQCa
54. You can restart a counter for the same operation it just completed you can reconfigure it to do something else or you can call a specific VI to stop it All of these methods allow you to use counters for different operations without resetting the entire device DAQ STC Am9513 Figure 25 13 shows how to stop a counter using the Intermediate VI Counter Stop Notice that the Wait ms VI is called before Counter Stop The Wait ms VI allows you to wire a time delay so that the previous counter operation has time to complete before the Counter Stop VI is called The Wait ms and Counter Stop VIs are located in Functions Data Acquisition Counter Intermediate Counter Figure 25 13 Using the Generate Delayed Pulse and Stopping the Counting Operation To stop a generated pulse train you can use another Generate Pulse Train VI with the number of pulses input set to 1 shown in Figure 25 14 This example expects that a pulse train is already being generated The call to Generate Pulse Train VI stops the counter and the call to Generate Delayed Pulse VI sets the counter up for a different operation Chapter 25 Generating a Square Pulse or Pulse Trains National Instruments Corporation 25 15 LabVIEW Data Acquisition Basics Manual Figure 25 14 Stopping a Generated Pulse Train 8253 54 Calling ICTR Control VI with a control code of 7 reset can stop a counter on the 8253 54 chip National Instruments Corporation 26 1 L
55. and your computer from large voltage spikes and makes sure the measurements from the DAQ device are not affected by differences in ground potentials K Kwords 1 024 words of memory Glossary National Instruments Corporation G 9 LabVIEW Data Acquisition Basics Manual L Lab 1200 devices Boards such as the Lab PC 1200 and the DAQCard 1200 which use the 8253 type counter timer chip LabVIEW Laboratory Virtual Instrument Engineering Workbench latched digital I O A type of digital acquisition generation where a device or module accepts or transfers data after a digital pulse has been received Also called handshaked digital I O Legacy MIO device Boards such as the AT MIO 16 which typically are configured with jumpers and switches and are not Plug and Play compatible They also use the 9513 type counter timer chip limit settings The maximum and minimum voltages of the analog signals you are measuring or generating linearization A type of signal conditioning in which LabVIEW linearizes the voltage levels from transducers so the voltages can be scaled to measure physical phenomena LSB Least Significant Bit M MB Megabytes of memory 1 MB is equal to 1 024 KB memory buffer See buffer Measurement amp Automation Explorer The standard National Instruments hardware configuration and diagnostic environment for Windows multibuffered I O Input operation for which you allocate more than one memory b
56. background while LabVIEW retrieves the acquired data Figure 7 4 How a Circular Buffer Works A circular buffer differs from a simple buffer only in how LabVIEW places the data into it and retrieves data from it A circular buffer is filled with data just as a simple buffer However when it gets to the end of the buffer it returns to the beginning and fills up the same buffer again This means data can read continuously into computer memory but only a defined amount of memory can be used Your VI must retrieve data in blocks from one location in the buffer while the data enters the circular buffer at a different Incoming Data from the Board to the PC AI Start vi End of Data Current Read Mark End of Data Data transferred from PC buffer to LabVIEW AI Read vi Current Read Mark End of Data End of Data Current Read Mark Chapter 7 Buffering Your Way through Waveform Acquisition LabVIEW Data Acquisition Basics Manual 7 8 www ni com location so that unread data is not overwritten by newer data Because of the buffer maintenance you can use only the Intermediate or Advanced VIs with this type of data acquisition While a circular buffer works well in many applications there are two possible problems that can occur with this type of acquisition Your VI could try to retrieve data from the buffer faster than data is placed into it or your VI might not retrieve data from the buffer fast enough before LabVIEW overwrite
57. between successive rising edges of your TTL signal by counting the number of internal timebase cycles that occur during the period The period is the count divided by the timebase The frequency is determined by taking the inverse of the period The valid output indicates if the period was measured without overflow Overflow occurs when the counter reaches its highest value or terminal count TC You must choose timebase such that it does not reach TC With a timebase of 1 MHz the Am9513 can measure a period up to 65 ms With a timebase of 100 Hz you can measure a period up to 655 seconds Chapter 27 Measuring Frequency and Period LabVIEW Data Acquisition Basics Manual 27 8 www ni com TIO ASIC DAQ STC Am9513 If you need more control over when period measurement begins and ends use the Intermediate VIs instead of the Easy VIs Figure 27 6 shows how to measure period and frequency Figure 27 6 Measuring Period Using Intermediate Counter VIs The Intermediate VIs used in Figure 27 6 include Pulse Width or Period Meas Config Counter Start Counter Read and Counter Stop The Pulse Width or Period Meas Config VI configures the counter for period measurement The Counter Start VI begins the counting operation The Counter Read VI returns the count value from the counter which is used to determine the period and frequency The Counter Stop VI stops the counter operation 8253 54 The 8253 54 chip does not support period measuremen
58. but the device does not return any data to LabVIEW unless the data meets your retrieval conditions LabVIEW scans the input data and performs a comparison with the conditions but does not store the data until it meets your specifications Figure 8 5 shows a timeline of events that typically occur when you perform conditional retrieval The read search position pointer traverses the buffer until it finds the scan location where the data has met the retrieval conditions Offset indicates the scan location from which the VI begins reading data relative to the read search position A negative offset indicates that you need pretrigger data data prior to the retrieval conditions If offset is greater than 0 you need posttrigger data data after retrieval conditions Chapter 8 Controlling Your Acquisition with Triggers National Instruments Corporation 8 9 LabVIEW Data Acquisition Basics Manual Figure 8 5 Timeline of Conditional Retrieval Signal Checked for Trigger Conditions Rest of Data When trigger conditions are met at Scan 4 When Offset 0 When Offset lt 0 When Offset gt 0 Scan 2 Scan 3 Scan Scan 1 Scan 4 read search position External DAQ Device Device Scan 2 Scan 3 Scan Scan 1 Scan 4 Offset read search position Start reading data Scan 2 Scan 3 Scan Scan 1 Scan 4 Offset Start reading data read search position Start reading data Scan 5 Scan 6 Scan
59. channel It queries for information about the physical quantity being measured the sensor or actuator being used and the associated DAQ hardware As you configure channels in the DAQ Channel Wizard you give each channel configuration a unique name that is used when addressing your channels in LabVIEW The channel configurations you define are saved in a file that instructs the NI DAQ driver how to scale and process each DAQ channel by its name You can simplify the programming required to measure your signal by using the DAQ Channel Wizard to configure your channels Refer to the online help for specific instructions on how to install and configure your DAQ device If you are using Windows with NI DAQ 6 5 or higher refer to the help file for Measurement amp Automation Explorer by selecting Help Help Topics DAQ Help If you are using an earlier version of NI DAQ for Windows you can find the help file in Start Programs LabVIEW NI DAQ Configuration Utility Help If you are using a Macintosh you can find the help file in the Help menu of the NI DAQ Configuration Utility Refer to the Channel Name Addressing section of Chapter 3 Basic LabVIEW Data Acquisition Concepts for information about how to use your named channels in LabVIEW Now that you have successfully installed and configured your DAQ hardware for LabVIEW read Chapter 3 Basic LabVIEW Data Acquisition Concepts for more information about data acquisition with LabVIEW
60. channel string syntax to access channels on the SCXI 1200 module Use 0 for channel 0 1 for channel 1 and so on The SCXI 1200 module is identified by its logical device number Note When you connect any type of SCXI module to a DAQ device certain analog input and digital lines on the DAQ device are reserved for SCXI control On MIO Series devices lines 0 1 and 2 are unavailable for general purpose digital I O On MIO E Series devices lines 0 1 2 and 4 are unavailable for general purpose digital I O For more channel information refer to the LabVIEW Online Reference by selecting Help Online Reference For the fastest performance in parallel mode on digital modules use the appropriate onboard port numbers instead of the SCXI channel string syntax in the digital VIs Channel List Element Channel Specified obz scx mdy a Channel a on the module in slot y of the chassis with ID x is multiplexed into onboard channel z obz scx mdy a b Channels a through b inclusive on the module in slot y of the chassis with ID x are multiplexed into onboard channel z obz scx mdy a b c Channels a b and c nonconsecutive on the module in slot y of the chassis with ID x are multiplexed into onboard channel z Only on certain SCXI modules such as the SCXI 1125 Chapter 21 Special Programming Considerations for SCXI National Instruments Corporation 21 3 LabVIEW Data Acquisition Basics Manual SCXI Gains SCXI modules provide
61. counters which you might need for other reasons You also can use the Pulse Train VIs to create an external test clock These VIs are located in examples daq counter DAQ STC llb examples daq counter NI TIO llb examples daq counter Am9513 llb and examples daq counter 8253 llb Table 13 1 External Update Clock Input Pins Device External Update Clock Input Pin All E Series Devices with analog output Any PFI pin Default PFI5 UPDATE Non E Series MIO type devices OUT2 Lab PC 1200 devices AT AO 6 10 EXTUPDATE National Instruments Corporation 14 1 LabVIEW Data Acquisition Basics Manual 14 Simultaneous Buffered Waveform Acquisition and Generation This chapter describes how to perform buffered waveform acquisition and generation simultaneously on the same DAQ device Using E Series MIO Boards E series devices such as the PCI MIO 16E 1 have separate counters dedicated to analog input and analog output timing For this reason they are the best choice for simultaneous input output Software Triggered Open the Simul AI AO Buffered E Series MIO VI located in labview examples daq anlog_io anlog_io llb and examine its block diagram This example VI uses Intermediate DAQ VIs It uses the same VIs you used for analog input in Chapter 7 Buffering Your Way through Waveform Acquisition AI Config AI Start AI Read and AI Clear for waveform acquisition This example VI also uses the same VIs you us
62. data from the buffer of a size equal to either 1 000 scans or the size of the scan backlog whichever one is larger The VI does this by using the Max amp Min function to determine the larger of the two values You do not have to use the Max amp Min function in this way for the application to work but this function helps control the size of the scan backlog which is how many samples that are left over in the buffer This VI continuously reads and displays the data from channel 0 until an error occurs or until you click the Stop button Figure 7 5 Basic Circular Buffered Analog Input Using the Intermediate VIs Chapter 7 Buffering Your Way through Waveform Acquisition National Instruments Corporation 7 11 LabVIEW Data Acquisition Basics Manual Other Circular Buffered Analog Input Examples There are many other circular buffered analog input VIs that are included with your LabVIEW application The following list describes some of these VIs You can find the first two VIs in labview examples daq anlogin anlogin llb and the rest of the example VIs in labview examples daq anlogin strmdisk llb For information on how these examples work and how to modify them open Windows Show VI Info or open the Help window by selecting Help Show Help Cont Acq amp Chart buffered VI Demonstrates circular buffered analog input similarly to the previous example but this VI includes other front panel inputs Cont Acq amp Graph
63. delay of 10 ms which affects the maximum possible scan rate Scanning multiple SCXI 1122 channels many times can quickly wear out the relay To avoid this acquire data from the SCXI 1122 module one channel at a time For further information on reading SCXI 1122 channels refer to the SCXI 1122 User Manual or to the SCXI 1122 Voltage example VI in labview examples daq scxi scxi_ai llb Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 10 www ni com If you are measuring temperature with the SCXI 1120 and SCXI 1121 modules refer to the SCXI 1120 1121 Thermocouple example VI located in labview examples daq scxi scxi_ai llb This VI is similar to the VI used to measure temperature on the SCXI 1100 Both VIs average and linearize temperature data using the Intermediate analog input VIs The main differences between the VIs are that the SCXI 1120 1121 VI does not measure the amplifier offset and the input limits for the module and the temperature sensor are different from the input limits for the SCXI 1100 The SCXI 1120 and SCXI 1121 modules do not have the internal switch used to programmatically ground the amplifiers as in the SCXI 1100 for the amplifier offset measurement To determine the amplifier offset you must manually wire the amplifier terminals to ground and use a separate VI to read the offset voltage You also can manually calibrate the SCXI 1120 and SCXI 1121 to remove any amplifier offset on a chann
64. frequency division for signal dividers and down counters by software as previously described you can trigger using the GATE signal You can trigger while the GATE signal is high low or on the rising or falling edge For more information refer to the Down Counter or Divide Config VI description in Chapter 27 Intermediate Counter VIs of the LabVIEW Function and VI Reference Manual or the LabVIEW Online Reference available by selecting Help Online Reference 8253 54 To divide a frequency with the 8253 54 counter chip use the example Cont Pulse Train 8253 VI located in labview examples daq 8253 llb This example is explained in Chapter 25 Generating a Square Pulse or Pulse Trains in the Generating a Pulse Train section For a complete description of this example refer to the information found in Windows Show VI Info National Instruments Corporation VII 1 LabVIEW Data Acquisition Basics Manual Part VII Debugging Your Data Acquisition Application This part of the manual contains an explanation of ways you can debug your data acquisition application to make sure your application is accurate and runs smoothly Part VII Debugging Your Data Acquisition Application contains Chapter 30 Debugging Techniques which describes some tips to help determine why your VI is not working National Instruments Corporation 30 1 LabVIEW Data Acquisition Basics Manual 30 Debugging Techniques Is your VI not working as you e
65. in Figure 29 2 outputs a high pulse lasting one cycle of the source signal once the counter reaches its TC For more information on the different types of signal outputs refer to the Down Counter or Divide Config VI description in Chapter 27 Intermediate Counter VIs of the LabVIEW Function and VI Reference Manual or the LabVIEW Online Reference available by selecting Help Online Reference The previous block diagram counts the rising edges of the SOURCE signal the default value of the source edge input To locate the inputs and outputs on this VI use the Help window Open this window by choosing Help Show Help The Counter Start VI tells the counter to start counting the SOURCE signal edges The counter stops the frequency division only when you click the STOP button The Counter Stop VI stops the counter immediately and clears the count register It is a good idea to always check your errors at the end of an operation to see if the operation was successful You can alter the Down Counter or Divide Config VI to create a down counter To do this change the timebase value from 0 0 external SOURCE to a frequency available on your counter With the Am9513 chip you can choose timebases of 1 MHz 100 kHz 10 kHz 1 kHz and 100 Hz With the DAQ STC chip you can choose timebases of 20 MHz and 100 kHz Chapter 29 Dividing Frequencies National Instruments Corporation 29 3 LabVIEW Data Acquisition Basics Manual Instead of triggering
66. in parallel mode you can specify an SCXI channel either by specifying the corresponding onboard channels or by using the SCXI channel syntax described in this section If you operate the modules in multiplexed mode you must use the SCXI channel syntax An SCXI channel number has four parts the onboard channel optional the chassis ID the module number and the module channel In the following table of examples x is any chassis ID y is any module number a is any module channel and b is any module channel greater than a z is the onboard channel from which the conditioned data is Chapter 21 Special Programming Considerations for SCXI LabVIEW Data Acquisition Basics Manual 21 2 www ni com retrieved If you operate in multiplexed mode analog input channel 0 reads the data from the first cabled chassis If you use VXI SC submodules LabVIEW ignores the onboard channel because VXI DAQ provides a special channel for retrieving data from submodules The channel input for DAQ VIs is either a string with the Easy I O VIs or an array of strings Each string value can list the channels for only one module With the array structure for channel values you can list the channels for several modules Therefore for one scanning operation you can scan several modules You can scan an arbitrary number of channels for each module but the channels of each module must be scanned in consecutive ascending order Note You do not need the SCXI
67. is applied to the limit settings For example if you configured a channel in the DAQ Channel Wizard to have physical units of Deg C the limit settings are treated as limits in degrees Celsius LabVIEW configures your hardware to make the measurement in terms of your channel name configuration Unless you need to overwrite your channel name configuration do not wire this input Allow LabVIEW to set it up for you Chapter 3 Basic LabVIEW Data Acquisition Concepts LabVIEW Data Acquisition Basics Manual 3 12 www ni com Note For NI DAQ 6 5 and higher the DAQ Channel Wizard is part of Measurement amp Automation Explorer Data Neighborhood If you are not using the DAQ Channel Wizard the default unit applied to the limit settings is usually volts although the unit applied to the limit settings may be volts current resistance or frequency depending on the capability and configuration of your device The default range of the device set in the configuration utility or by LabVIEW according to the channel name configuration in the DAQ Channel Wizard is used whenever you leave the limit settings terminal unwired or you enter 0 for your upper and lower limits As explained previously in the Channel Port and Counter Addressing section LabVIEW uses an array of strings to specify which channels belong to a group Also remember LabVIEW lists one channel to as many as all of the device s channels in a single array element in the channel
68. latest digital input or immediately write a new digital output value you should use non latched immediate digital I O When a DAQ device accepts or transfers data after a digital pulse has been received it is called latched handshaked digital I O With latched digital I O you can store the values you want to transfer in a buffer Only one value will be transferred after each handshaked pulse If you want to read or write digital data patterns at a fixed rate using a clock source you should use timed digital I O If you want to use non latched immediate digital I O refer to Chapter 16 Immediate Digital I O If you need to perform latched handshaked digital I O refer to Chapter 17 Handshaked Digital I O If you want to perform timed digital I O refer to Chapter 18 Timed Digital I O 10 Counters Counting or Generating Digital Pulses If you want to generate digital pulses from a counter at a certain rate read Chapter 25 Generating a Square Pulse or Pulse Trains If you want to measure the width of a digital pulse refer to Chapter 26 Measuring Pulse Width If you want to measure the frequency or period of a digital signal refer to Chapter 27 Measuring Frequency and Period If you just want to count how many times a digital signal rises or falls refer to Chapter 28 Counting Signal Highs and Lows To learn how to slow the frequency of a digital signal refer to Chapter 29 Dividing Frequencies National Instruments C
69. measuring strain gauge data there are some parameters on the Convert Strain Gauge Reading VI you should know Vsg the strain gauge value is the only parameter wired in Figure 22 7 The other parameters for this VI have default values but those values may not be correct for your strain gauge You should check the following parameters Rg The resistance of the strain gauge before strain is applied You usually can ignore the lead resistance Bridge Configuration Vex The excitation voltage Vinit The voltage across the strain gauge before strain is applied always measure at the beginning of the VI Rl The lead resistance Rl For strain gauges unless the leads are several feet For more information on any of the parameters for this VI refer to Chapter 30 Signal Conditioning VIs in the LabVIEW Function and VI Reference Manual or refer to the LabVIEW Online Reference by selecting Help Online Reference Chapter 22 Common SCXI Applications National Instruments Corporation 22 17 LabVIEW Data Acquisition Basics Manual Analog Output Application Example You can output isolated analog signals using the SCXI 1124 analog output module If you use the DAQ Channel Wizard to configure your analog output channels generating signals using the SCXI 1124 is no different from the techniques in Part III Making Waves with Analog Output The remainder of this section describes how to generate signa
70. of a known internal timebase The Counter Start VI begins the measurement The Counter Read VI determines if the measurement is complete and Chapter 26 Measuring Pulse Width LabVIEW Data Acquisition Basics Manual 26 6 www ni com displays the count value After the While Loop is stopped the Counter Stop VI stops the counter operation Finally the General Error Handler VI notifies you of any errors Figure 26 5 Measuring Pulse Width with Intermediate VIs Buffered Pulse and Period Measurement With the TIO ASIC and DAQ STC chips LabVIEW provides a buffer for counter operations You typically would use buffered counter operations when you have a gate signal to trigger a counter several times For an example open the block diagram of the Meas Buffered Pulse Period DAQ STC VI located in labview examples daq counter DAQ STC llb Also refer to the examples located in labview examples daq counter NI TIO llb With the Meas Buffered Pulse Period DAQ STC VI you can perform four types of buffered measurements Buffered period measurement Measures a number of periods in a pulse train Buffered semi period measurement Measures a number of high and low pulses in a pulse train Buffered pulse width measurement Measures a number of high or low pulses in a pulse train Buffered counting Each rising edge loads the current count into a finite buffer Chapter 26 Measuring Pulse Width National Instru
71. of how digital triggering works for post triggered data acquisition In this example an external device sends a trigger or TTL signal to your DAQ device As soon as your DAQ device receives the signal and your trigger conditions are met your device begins acquiring data TTL Signal Connect to STARTTRIG EXTTRIG or DTRIG Pins Falling Edge of Signal Data Capture Initiated Chapter 8 Controlling Your Acquisition with Triggers National Instruments Corporation 8 3 LabVIEW Data Acquisition Basics Manual With NI 406x hardware start trigger pulses can be generated externally or internally The following start trigger pulse sources apply Software start trigger External trigger Figure 8 2 Digital Triggering with Your DAQ Device External DAQ Digital Trigger Signal Analog Data DAQ Device waits until digital trigger conditions are met Then Device Device DAQ Device External Device Chapter 8 Controlling Your Acquisition with Triggers LabVIEW Data Acquisition Basics Manual 8 4 www ni com Digital Triggering Examples An example of digital triggering is the Acquire N Scans Digital Trig VI found in labview examples daq anlogin anlogin llb Open this VI and examine its block diagram This VI uses the Intermediate VIs to perform a buffered acquisition where LabVIEW stores data in a memory buffer during acquisition After the acquisition completes the VI retrieves all the data from th
72. or current value to your SCXI analog output module LabVIEW uses the calibration constants loaded for the given module channel and output range to scale the voltage or current value to the appropriate binary value to write to the output channel By default calibration constants for the SCXI 1124 are loaded into the memory from the EEPROM default load area Recalibrate your SCXI analog output module by following these steps 1 Use the AO Single Update VI to output a binary value If you are calibrating a voltage output range enter 0 in the binary array input of the VI If you are calibrating current range enter 255 into the binary array input of the VI 2 Measure the output voltage or current at the output channel with a voltmeter or ammeter This is your first volt binary measurement Binary 1 0 and Volt Amp Hz 1 is the voltage or current you measured at the output Chapter 23 SCXI Calibration Increasing Signal Measurement Precision LabVIEW Data Acquisition Basics Manual 23 8 www ni com 3 Use the AO Single Update VI to output a binary value of 4 095 4 Measure the output voltage or current at the output channel This is your second volt binary measurement Binary 2 should be 4095 and Volt Amp 2 is the voltage or current you measured at the output 5 Use SCXI Cal Constants VI with the first voltage binary measurement from step 2 as the Volt Amp Hz 1 and Binary 1 inputs and the second measurement from step 4 as the
73. port These subVIs are located in Functions Data Acquisition Digital I O Use the Easy Digital VIs for most digital testing purposes All of the Easy Digital VIs have error reporting The following sections identify the examples you can access for further information 6533 Family The examples Read from 1 Dig Line 653x VI and Write to 1 Dig Line 653x VI show how to use the Easy Digital I O VIs to read from or write to one digital line These examples are located in labview examples daq digital 653x llb You could write similar examples to read from or write to a single port 8255 Family The examples Read from 1 Dig Line 8255 VI and Write to 1 Dig Line 8255 VI show how to use the Easy Digital I O VIs to read from or write to one digital line These examples are located in labview examples daq digital 8255 llb You could write similar examples to read from or write to a single port Chapter 16 Immediate Digital I O National Instruments Corporation 16 3 LabVIEW Data Acquisition Basics Manual E Series Family The examples Read 1 Pt from Dig Line E VI and Write 1 Pt to Dig Line E VI show how to use the Easy Digital I O VIs to read from or write to one digital line These examples are located in labview examples daq digital E series llb You could write similar examples to read from or write to a single port Immediate I O Using the Advanced Digital VIs The Advanced Digital I O subVIs give you more programming flexibility
74. select an interchannel delay is to gradually increase the delay or clock period until the data appears consistent with data from the previous delay setting Refer to your hardware manuals for the required settling time for your channel clock You also can find the interchannel delay by running the low level AI Clock Config VI for the channel clock with no frequency specified Externally Controlling Your Channel Clock There are times when you might need to control the channel clock externally The channel clock rate is the same rate at which analog conversions occur For instance suppose you need to know the strain value at an input every time an infrared sensor sends a pulse Most DAQ devices have an EXTCONV pin or a PFI pin on the I O connector for providing your own channel clock For NI 406x Series devices use the EXTRIG input pin This external signal must be a TTL level signal The asterisk on the signal name indicates that the actual conversion occurs on the falling edge of the signal as shown in Figure 9 3 For devices with PFI lines and for the NI 406x Series devices you can select either the rising edge or falling edge using LabVIEW With devices that have a RTSI connector you can get your channel clock from other National Instruments DAQ devices Figure 9 3 Example of a TTL Signal TTL Signal rising edge falling edge Chapter 9 Letting an Outside Source Control Your Acquisition Rate LabVIEW Data Acquisition Basics
75. setting For example the default input for a parameter may be do not change current setting and the default setting may be no AMUX 64T boards If you do change the value of such a parameter the new value becomes the new setting You can set default settings for some parameters in the configuration utility device A DAQ device inside your computer or attached directly to your computer through a parallel port Plug in boards PC cards and devices such as the DAQPad 1200 which connects to your computer s parallel port are all examples of DAQ devices SCXI modules are distinct from devices with the exception of the SCXI 1200 which is a hybrid device number The slot number or device ID number assigned to the device when you configured it DIFF Differential A differential input is an analog input consisting of two terminals both of which are isolated from computer ground and whose difference you measure differential measurement system A way you can configure your device to read signals in which you do not need to connect either input to a fixed reference such as earth or a building ground digital input group A collection of digital input ports You can associate each group with its own clock rates handshaking modes buffer configurations and so on A port cannot belong to more than one group digital output group A collection of digital output ports You can associate each group with its own clock rates handshaking modes
76. shows a large duty cycle of 0 9 where phase 1 is very short and the phase 2 duration is longer Figure 25 1 Pulse Duty Cycles Note A high duty cycle denotes a long pulse phase relative to the delay phase How you generate a square pulse varies depending upon which counter chip your DAQ hardware has If you are unsure which chip your device uses refer to your hardware documentation counter starts phase 1 phase 2 Duty Cycle 0 5 Duty Cycle 0 1 Duty Cycle 0 9 Chapter 25 Generating a Square Pulse or Pulse Trains National Instruments Corporation 25 3 LabVIEW Data Acquisition Basics Manual TIO ASIC DAQ STC and Am9513 When generating a pulse or pulse train with the TIO ASIC DAQ STC or Am9513 chip you can define the polarity of the signal as positive or negative Figure 25 2 shows these pulse polarities Notice that for a signal with a positive polarity the initial state is low while a signal with negative polarity has a positive initial state Figure 25 2 Positive and Negative Pulse Polarity Each counter generated pulse consists of two phases If the counter is configured to output a signal with positive polarity and toggled output as shown in the following diagram the period of time from when the counter starts counting to the first rising edge is called phase 1 The time between the rising and the following falling edge is called phase 2 If you configure the counter to generate a continuous pulse tr
77. single analog output call to update all the output channels The following sections describe the two different types of analog I O control loop techniques software timed and hardware timed analog I O Using Software Timed Analog I O Control Loops With software timed analog control loops the analog acquisition rate and subsequent control loop rate are controlled by a software timer such as the Wait Until Next ms Multiple timer The acquisition is performed during each loop iteration when the AI Single Scan VI is called and the control loop is executed once for each time interval Your loop timing can be interrupted by any user interaction which means your acquisition rate is not as consistent as that which can be achieved through hardware timed control loops Generally if you do not need a precise acquisition rate for your control loop software timing is appropriate Besides user interaction a large number or large sized front panel indicators like charts and graphs affect control loop rates Refreshing the monitor screen interrupts the system clock which controls loop rates Therefore you should keep the number of charts and graphs to a minimum when you are using software timed control loops An example of software timed control loops is the Analog IO Control Loop immed VI located in labview examples daq anlog_io anlog_io llb Open this example VI to see how it performs software timed analog I O using the AI Read One Scan and AO Wr
78. such as the NEC AI 16E 4 AIGND The analog input ground pin on a DAQ device Glossary LabVIEW Data Acquisition Basics Manual G 2 www ni com amplification A type of signal conditioning that improves accuracy in the resulting digitized signal and reduces noise Am9513 based devices Devices with an Am9513 counter timer chip These devices include the NB MIO 16 NB MIO 16X NB A2000 NB TIO 10 and NB DMA2800 on the Macintosh and the AT MIO 16 AT MIO 16F 5 AT MIO 16X AT MIO 16D and AT MIO 64F 5 and PC TIO 10 in Windows AMUX devices See analog multiplexer analog input group A collection of analog input channels You can associate each group with its own clock rates trigger and buffer configurations and so on A channel cannot belong to more than one group Because each device has one ADC only one group can be active at any given time That is once a control VI starts a timed acquisition with group n subsequent control and read calls must also refer to group n You use the task ID to refer to the group analog multiplexer Devices that increase the number of measurement channels while still using a single instrumentation amplifier Also called AMUX devices analog output group A collection of analog output channels You can associate each group with its own clock rates buffer configurations and so on A channel cannot belong to more than one group analog trigger A trigger that occurs at a user selected level and
79. the llb file extension and directories located in the daq directory accessories Folder containing VIs that work with specific accessories anlog_io Folder containing VIs for analog I O control loops and simultaneous analog input and output anlogin Folder containing VIs that perform analog input and VIs that write or stream acquired data to disk anlogout Folder containing VIs that generate single values or multiple values waveforms to output through analog channels counter Folder containing VIs that perform various counter timer operations digital Folder containing VIs that perform immediate digital I O and digital handshaking multidev Folder containing VIs that perform synchronized analog input with multiple devices scxi Folder containing VIs for use with specific SCXI modules solution Folder containing a variety of ready to run application VIs run_me llb Library containing VIs that perform basic operations concerning analog I O digital I O and counters Each chapter in this manual teaches the basic concepts behind several of the DAQ examples For a brief description of any example open the example VI and select Windows Show VI Info for a text description of the example You also can choose Help Show Help to open the Help window Chapter 3 Basic LabVIEW Data Acquisition Concepts National Instruments Corporation 3 3 LabVIEW Data Acquisition Basics Manual Locating the Data Acquisition VI
80. to 5 8 Index LabVIEW Data Acquisition Basics Manual I 10 www ni com description 5 5 effect on ADC precision figure 5 5 measurement precision for various ranges and limit settings table 5 8 setting range and polarity 3 13 diagnostic resources online B 1 differential measurement system 5 9 to 5 11 8 channel differential system figure 5 10 common mode voltage figure 5 11 when to use 5 11 Dig Buf Hand Iterative 653x VI 17 7 Dig Buf Hand Iterative 8255 VI 17 7 Dig Buf Handshake In 8255 VI 17 6 Dig Buf Handshake Out 8255 VI 17 6 Dig Word Handshake In 653x VI 17 5 Dig Word Handshake In 8255 VI 17 5 Dig Word Handshake Out 653x VI 14 3 to 14 4 Dig Word Handshake Out 8255 VI 17 5 digital and relay SCXI modules 20 6 digital I O buffered handshaking 17 6 to 17 8 circular buffered examples 17 7 to 17 8 simple buffered examples 17 6 chip familes 15 2 to 15 3 6533 family 15 3 8255 family 15 3 E Series family 15 3 choosing between non latched or latched digital I O 4 5 digital vs counter interfacing 4 4 handshaking latched digital I O 17 1 to 17 8 buffered handshaking 17 6 to 17 8 digital data on multiple ports 17 2 to 17 4 handshaking lines 17 2 nonbuffered handshaking 17 5 types of handshaking 17 4 to 17 5 immediate non latched digital I O 16 1 to 16 4 non buffered handshaking 17 5 overview 15 1 SCXI application examples digital input 22 17 to 22 18 digital output 22 19
81. to High Precision Timing Chapter 24 Things You Should Know about Counters Knowing the Parts of Your Counter 24 2 Knowing Your Counter Chip 24 4 TIO ASIC 24 5 DAQ STC 24 5 Am9513 24 5 8253 54 24 5 Chapter 25 Generating a Square Pulse or Pulse Trains Generating a Square Pulse 25 1 TIO ASIC DAQ STC and Am9513 25 3 8253 54 25 4 Contents LabVIEW Data Acquisition Basics Manual xii www ni com Generating a Single Square Pulse 25 4 TIO ASIC DAQ STC Am9513 25 5 8253 54
82. understanding how data acquisition works with LabVIEW Chapter 4 Where You Should Go Next directs you to the chapter or chapters in the manual best suited to answer questions about your data acquisition application National Instruments Corporation 1 1 LabVIEW Data Acquisition Basics Manual 1 How to Use This Book This chapter explains how this manual is organized The following outline shows you what information you can find in this manual Part I Before You Get Started How to Use This Book Installing and Configuring Your Data Acquisition Hardware Basic LabVIEW Data Acquisition Concepts Where You Should Go Next Part II Catching the Wave with Analog Input Things You Should Know about Analog Input One Stop Single Point Acquisition Buffering Your Way through Waveform Acquisition Controlling Your Acquisition with Triggers Letting an Outside Source Control Your Acquisition Rate Part III Making Waves with Analog Output Things You Should Know about Analog Output One Stop Single Point Generation Buffering Your Way through Waveform Generation Letting an Outside Source Control Your Update Rate Simultaneous Buffered Waveform Acquisition and Generation Part IV Getting Square with Digital I O Things You Should Know about Digital I O Immediate Digital I O Handshaked Digital I O Timed Digital I O Chapter 1 How to Use This Book LabVIEW Data Acquisition Basics Manual 1 2 www ni com
83. you can specify the number of pulses frequency duty cycle and pulse polarity of your pulse train The Wait ms VI is used as a delay before the counters are reset The Intermediate VI Counter Stop is called twice to stop the counters You also can create a finite pulse train using Intermediate VIs Open the block diagram of the Finite Pulse Train Int DAQ STC VI located in labview examples daq counter DAQ STC llb You also can use the example Finite Pulse Train Int 9513 VI located in labview examples daq counter Am9513 llb These examples show how to use the Intermediate VIs Continuous Pulse Generator Config and Delayed Pulse Generator Config Here you use counter to generate a continuous pulse train with level gating while using counter 1 to generate a minimum delayed pulse to gate the counter long enough to generate the desired number of pulses The Continuous Pulse Generator Config VI configures counter to generate a continuous pulse train Then the Delayed Pulse Generator Config VI configures counter 1 to generate a single delayed pulse The first Counter Start VI in the flow begins the continuous pulse generation and the next Chapter 25 Generating a Square Pulse or Pulse Trains National Instruments Corporation 25 11 LabVIEW Data Acquisition Basics Manual Counter Start VI generates a pulse after a specified time The gate mode must be specified as level gating on the Continuous Pulse Generator Config VI in order for the
84. your SCXI module every time the VI is called you should use the Intermediate analog input VIs as well as the Strain Gauge Conversion VI as shown in Figure 22 7 The Convert Strain Gauge Reading VI located in Functions Data Acquisition Signal Conditioning converts the voltage read by the strain gauge to units of strain Using the DAQ Channel Wizard to configure your channels simplifies the programming required to measure your signal as shown in Figure 22 7 LabVIEW configures the hardware with the appropriate input limits and gain measures the strain gauge and scales the measurement for you Enter the name of your configured channel in the channels input You do not need to wire the device or input limits input The acquired data is in the physical units you specified in the DAQ Channel Wizard Figure 22 7 Measuring Pressure Using Information from the DAQ Channel Wizard Figure 22 7 continually acquires data until an error occurs or you stop the VI from executing In order to perform continuous acquisition you need to set up a buffer In this example the buffer is 10 times the number of points acquired for each channel After your device averages the voltage data from Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 16 www ni com the AI Read VI it converts the voltage values to strain values After completing the acquisition remember to always clear the acquisition by using the AI Clear VI When
85. your volt binary measurements are 0 V 0 and 5 V 2045 Your input names may vary depending on your application setup Chapter 23 SCXI Calibration Increasing Signal Measurement Precision National Instruments Corporation 23 7 LabVIEW Data Acquisition Basics Manual 9 If you are using SCXI 1102 or SCXI 1122 inputs you can save the constants in the module user area in EEPROM Store constants in the user area as you are calibrating and use the SCXI Cal Constants VI again at the end of your calibration sequence to copy the calibration table in the user area to the default load area in EEPROM Remember constants stored in the default load area can be overwritten If you want to use a set of constants later keep a copy of the constants stored in the user area in EEPROM Note If you are storing calibration constants in the SCXI 1102 or SCXI 1122 EEPROM your binary offset and gain adjust factors must not exceed the ranges given in the respective module user manuals For other analog input modules you must store the constants in the memory Unfortunately calibration constants stored in the memory are lost at the end of a program session You can solve this problem by creating a file and saving the calibration constants to this file You can load them again in subsequent application runs by passing them into the SCXI Cal Constants or the Scale Constant Tuner VIs Calibrating SCXI Modules for Signal Generation When you output a voltage
86. 0 Boards 14 4 Contents National Instruments Corporation ix LabVIEW Data Acquisition Basics Manual PART IV Getting Square with Digital I O Chapter 15 Things You Should Know about Digital I O Types of Digital Acquisition Generation 15 2 Knowing Your Digital I O Chip 15 2 6533 Family 15 3 8255 Family 15 3 E Series Family 15 3 Chapter 16 Immediate Digital I O Using Channel Names 16 1 Immediate I O Using the Easy Digital VIs 16 2 6533 Family 16 2 8255 Family 16 2 E Series Family
87. 01 to 0 01 1000 1 0 ob0 sc1 md1 0 7 0 001 to 0 001 2000 5 1 0 sc1 md1 0 7 0 001 to 0 001 2000 1 0 1 ob0 sc1 md1 0 3 ob0 sc1 md1 4 15 0 1 to 0 1 0 01 to 0 01 100 100 1 10 0 1 ob0 sc1 md1 0 15 ob0 sc1 md1 16 31 0 01 to 0 01 1 0 to 1 0 10 10 100 2 1 0 1 2 ob0 sc1 md1 0 3 ob0 sc1 md1 4 15 ob0 sc1 md2 0 7 1 0 to 1 0 0 1 to 0 1 0 01 to 0 01 10 10 1000 1 10 1 1 Applies if the MIO AI device supports a gain of 5 some MIO AI devices do not 2 This case forces a smaller gain at the SCXI module than at the MIO AI device because the input limits for the next channel range on the module require a small SCXI gain This type of gain distribution is not recommended because it defeats the purpose of providing amplification for small signals at the SCXI module The small input signals are only amplified by a factor of 10 before they are sent over the ribbon cable where they are very susceptible to noise To use the optimum gain distribution for each set of input signals do not mix very small input signals with larger input signals on the same SCXI 1100 module unless you are sampling them at different times Chapter 21 Special Programming Considerations for SCXI National Instruments Corporation 21 5 LabVIEW Data Acquisition Basics Manual SCXI Settling Time The filter and gain settings of your SCXI modules affect the settling time of the SCXI amplifiers
88. 120 SCXI 1120D 15 use referenced single ended mode SCXI 1121 4 SCXI 1122 1 Chapter 22 Common SCXI Applications National Instruments Corporation 22 5 LabVIEW Data Acquisition Basics Manual For more information look at the SCXI Thermocouple example VIs found in the appropriate module DLL in labview examples daq scxi These VIs use the cjtemp or mtemp string to read the temperature sensor and use the reading for thermocouple cold junction compensation Amplifier Offset The SCXI 1100 SCXI 1101 SCXI 1112 SCXI 1122 SCXI 1125 SCXI 1141 SCXI 1142 and SCXI 1143 have a special calibration feature that enables LabVIEW to ground the module amplifier inputs so that you can read the amplifier offset For the other SCXI analog input modules you must physically wire your terminals to ground The measured amplifier offset is for the entire signal path including the SCXI module and the DAQ device To read the grounded amplifier on the SCXI 1100 SCXI 1101 or SCXI 1122 use the standard SCXI string syntax in the channels array with calgnd substituted for the channel number as shown in the following table For example you can run the Getting Started Analog Input VI found in labview examples daq run_me llb with the channel string ob0 sc1 md1 calgnd to read the grounded amplifier of the module in slot 1 of SCXI chassis 1 The voltage reading should be very close to 0 V The AI Start VI grounds the amplifier before starting the
89. 2 Learn Basic Data Acquisition Concepts Chapter 3 Basic LabVIEW Data Acquisition Concepts shows you the location of DAQ example VIs DAQ VI organization VI parameter conventions default and current value conventions common VI parameter definitions error handling channel port and counter addressing limit settings and data organization for analog applications Install and Configure Your Hardware Learn Basic Data Acquisition Concepts Go to Your Specific Application Section Review LabVIEW Example Applications Learn How to Debug Your Application Chapter 1 How to Use This Book LabVIEW Data Acquisition Basics Manual 1 4 www ni com 3 Go to Your Specific Application Section Chapter 4 Where You Should Go Next shows you where to find information in this manual for your application 4 Review LabVIEW Example Applications The remaining chapters teach you basic concepts in analog input and output digital I O counters and SCXI Each application section first lists example VIs then describes the basic concepts needed to understand these example VIs Whenever possible you should have the VI open as you refer to these examples 5 Learn How to Debug Your Application Chapter 30 Debugging Techniques describes the different ways you can debug your application This chapter helps you troubleshoot for common programming errors National Instruments Corporation 2 1 LabVIEW Data Acquisition Basics Manual 2
90. 253 54 The Count Events 8253 VI located in labview examples daq counter 8253 llb uses the Intermediate VI ICTR Control found in Functions Data Acquisition Counter Intermediate Counter This VI initiates the counter to count the number of rising edges of a TTL signal at the CLK of counter Looking at the block diagram the first call to ICTR Control loads the count register and sets up counter to count down The second call to ICTR Control reads the count register Inside the first While Loop the count is read until it changes While the count register has previously been loaded the new value is not active until the first edge is counted on the CLK pin Once the first edge comes in the second While Loop takes over and continually reads the count until you click the STOP button or an error occurs You must externally wire your signal to be counted to the CLK of counter For a complete description of this example refer to the information found in Windows Show VI Info Counting Elapsed Time How you count elapsed time depends upon which counter chip is on your DAQ device If you are unsure of which chip your DAQ device has refer to your hardware documentation TIO ASIC DAQ STC The Count Time Easy DAQ STC VI located in labview examples daq counter DAQ STC llb uses the Easy VI Count Events or Time which can be found in Functions Data Acquisition Counter This VI initiates the counter to count the number of rising edges o
91. 3 SCXI Calibration Increasing Signal Measurement Precision National Instruments Corporation 23 5 LabVIEW Data Acquisition Basics Manual One Point Calibration Use one point calibration when you need to adjust only the binary offset in your module If you need to adjust both the binary offset and the gain error of your module refer to the Two Point Calibration section later in this chapter Note If you are using an AT MIO 16F 5 AT MIO 64F 5 AT MIO 16X device or an E Series device you should calibrate your DAQ device first using either the MIO Calibrate VI or E Series Calibrate VI Complete the following steps to perform a one point calibration calculation in LabVIEW 1 Make sure you set the SCXI gain to the gain you want to use in your application If your modules have gain jumpers or DIP switches they must be set appropriately Refer to your SCXI module user manual for jumper or switch setting information If your modules have software programmable gain use the input limits parameter in the AI Config VI to set gain 2 Program the module for a single channel operation by using the AI Config VI with the channel that you are calibrating as the channels parameter in the VI 3 Ground your SCXI input channel to determine the binary zero offset You should ground inputs because offset can vary at different voltage levels due to gain error If you are using an SCXI 1100 or SCXI 1122 you can ground your input channels withou
92. 3 2 one point calibration 23 5 to 23 6 overview 23 3 signal acquisition 23 4 to 23 7 signal generation 23 7 to 23 8 two point calibration 23 6 to 23 7 SCXI modules See also signal conditioning components chassis figure 20 4 illustration 20 3 overview 20 2 to 20 3 hardware configurations illustration 20 2 overview 20 1 procedure 2 6 to 2 7 installation and configuration 20 8 sampling rate limits for Remote SCXI note 20 4 software configuration Macintosh systems 2 8 to 2 10 Windows environment 2 8 when to use 4 3 SCXI operating modes 20 5 to 20 7 multiplexed mode analog input modules 20 5 to 20 6 analog output modules 20 6 channel addressing 21 1 to 21 2 digital and relay modules 20 6 SCXI 1200 Windows 20 6 Index National Instruments Corporation I 19 LabVIEW Data Acquisition Basics Manual parallel mode analog input modules 20 6 to 20 7 channel addressing 21 1 to 21 2 digital modules 20 7 SCXI 1200 Windows 20 7 SCXI programming considerations 21 1 to 21 5 channel addressing 21 1 to 21 2 gains 21 3 to 21 5 SCXI 1100 channel arrays input limits array and gains table 21 4 settling time 21 5 SCXI Temperature Monitor VI 22 9 SCXI thermocouple example VIs 22 5 SCXI 100 thermocouple VI 22 6 SCXI 1100 Voltage example 22 6 SCXI 1120 1121 Thermocouple example VI 22 10 SCXI 116x Digital Output VI 22 20 SCXI 1162 1162HV Digital Input VI 22 18 SCXI 1200 module multiplexed mode
93. 3 Family 17 5 8255 Family 17 5 Buffered Handshaking 17 6 Simple Buffered Handshaking 17 6 6533 Family 17 6 8255 Family 17 6 Iterative Buffered Handshaking 17 7 Contents LabVIEW Data Acquisition Basics Manual x www ni com 6533 Family 17 7 8255 Family 17 7 Circular Buffered Handshaking 17 7 Chapter 18 Timed Digital I O Finite Timed Digital I O 18 1 Finite Timed I O without Triggering 18 1 Finite Timed
94. 4 Figure 27 5 Frequency Measurement Example Using Intermediate VIs 27 5 Figure 27 6 Measuring Period Using Intermediate Counter VIs 27 8 Figure 28 1 External Connections for Counting Events 28 1 Figure 28 2 External Connections for Counting Elapsed Time 28 1 Figure 28 3 External Connections to Cascade Counters for Counting Events 28 2 Figure 28 4 External Connections to Cascade Counters for Counting Elapsed Time 28 3 Figure 29 1 Wiring Your Counters for Frequency Division 29 1 Figure 29 2 Programming a Single Divider for Frequency Division 29 2 Figure 30 1 Error Checking Using the General Error Handler VI 30 2 Figure 30 2 Error Checking Using the Simple Error Handler VI 30 3 Tables Table 5 1 Measurement Precision for Various Device Ranges and Limit Settings 12 Bit A D Converter 5 8 Table 5 2 Analog Input Channel Range 5 14 Table 5 3 Scanning Order for Each DAQ Device Input Channel with One or Two AMUX 64Ts
95. 5 16 Table 5 4 Scanning Order for Each DAQ Device Input Channel with Four AMUX 64T Multiplexers 5 17 Table 9 1 External Scan Clock Input Pins 9 6 Table 13 1 External Update Clock Input Pins 13 2 Table 19 1 Phenomena and Transducers 19 1 Table 21 1 SCXI 1100 Channel Arrays Input Limits Arrays and Gains 21 4 Table 26 1 Internal Counter Timebases and Their Corresponding Maximum Pulse Width Period or Time Measurements 26 8 Table 28 1 Adjacent Counters for Counter Chips 28 2 National Instruments Corporation xix LabVIEW Data Acquisition Basics Manual About This Manual The LabVIEW Data Acquisition Basics Manual includes the information you need to get started with data acquisition and LabVIEW You should have a basic knowledge of LabVIEW before you try to read this manual If you have never worked with LabVIEW please read through the LabVIEW QuickStart Guide or the LabVIEW Online Tutorial before you begin This manual shows you how to configure your software teaches you basic concepts needed to accomplish your task and refers you to common example VIs in LabVIEW If you have used Lab
96. 6 2 single ended measurement system nonreferenced 5 13 to 5 14 referenced 5 12 single immediate updates 11 1 Index LabVIEW Data Acquisition Basics Manual I 20 www ni com single point analog output choosing between single point or multiple point generation 4 4 overview 10 1 single stepping through VIs 30 3 single waveform acquisition 7 2 to 7 3 software configuration errors debugging 30 1 to 30 2 software related resources B 2 software timed analog input output control loops 6 5 to 6 6 software timing 10 1 software triggering conditional retrieval examples 8 11 description 8 8 to 8 11 timeline of conditional retrieval figure 8 9 SOURCE input for counters 24 2 spreadsheet files Cont Acq to Spreadsheet File VI 7 11 simple buffered analog input example 7 6 square pulse generation 25 1 to 25 7 8253 54 25 4 duty cycle figure 25 2 overview 25 1 to 25 2 single square pulse generation 25 4 to 25 7 8253 54 25 6 to 25 7 TIO ASIC DAQ STC and Am9513 25 5 to 25 6 terminology related to 25 1 TIO ASIC DAQ STC and Am9513 25 3 square wave frequency measuring figure 27 2 Start amp Stop Trig VI 18 2 STB Strobe Input line 17 2 Strain Gauge Conversion VI 22 15 strain gauges for measuring pressure example 22 13 to 22 16 Strobe Input STB line 17 2 T technical support resources B 1 to B 2 temperature measurement applications SCXI amplifier offset 22 5 to 22 6 sensors for cold ju
97. 6D NB MIO 16X or EXTTRIG or DTRIG for any other device that has that pin If you are using an E series device you can select which PFI pin to connect to If you do not specify the PFI pin it uses the defaults as the PFI pin names suggest for example PFI0 TRIG1 The only analog input devices on which you cannot do a digital trigger are the LPM devices DAQCard 700 DAQCard 500 and the 516 devices Refer to the AI Trigger Config description in Chapter 18 Advanced Analog Input VIs in the LabVIEW Function and VI Reference Manual or the LabVIEW Online Reference available by selecting Help Online Reference for more information on the use of digital triggers on your DAQ device Note The NB MIO 16 has an EXTTRIG pin but cannot support start and stop triggering When are the data acquisition devices initialized All data acquisition devices are initialized automatically when the first DAQ VI is loaded in on a diagram when you start LabVIEW You also can initialize a particular device by calling the Device Reset VI National Instruments Corporation B 1 LabVIEW Data Acquisition Basics Manual B Technical Support Resources This appendix describes the comprehensive resources available to you in the Technical Support section of the National Instruments Web site and provides technical support telephone numbers for you to use if you have trouble connecting to our Web site or if you do not have internet access NI Web Support To pr
98. AIGND Chapter 5 Things You Should Know about Analog Input National Instruments Corporation 5 11 LabVIEW Data Acquisition Basics Manual In general a differential measurement system is preferable because it rejects not only ground loop induced errors but also the noise picked up in the environment to a certain degree Use differential measurement systems when all input signals meet the following criteria Low level signals for example less than 1 V Long or non shielded cabling wiring traveling through a noisy environment Any of the input signals require a separate ground reference point or return signal An ideal differential measurement system reads only the potential difference between its two terminals the positive and negative inputs Any voltage present at the instrumentation amplifier inputs with respect to the amplifier ground is called a common mode voltage An ideal differential measurement system completely rejects does not measure common mode voltage as shown in Figure 5 8 Figure 5 8 Common Mode Voltage While a differential measurement system is often the best choice a single ended configuration uses twice as many measurement channels A single ended measurement system is acceptable when the magnitude of the induced errors is smaller than the required accuracy of the data Vs Vcm Instrumentation Amplifier Measured Voltage Grounded Signa
99. AQ Channel Wizard channel name addressing 3 9 limit settings 3 11 SCXI programming considerations note 21 1 DAQ devices vs SCXI devices 4 3 DAQ examples location of example files 3 2 locations 3 1 to 3 2 DAQ hardware See hardware installation and configuration DAQ Occurrence Config VI 7 9 DAQ Solution Wizard 3 1 DAQ VIs See VIs DAQ STC counter buffered pulse and period measurement 26 6 continuous pulse train generation 25 7 to 25 8 Index National Instruments Corporation I 9 LabVIEW Data Acquisition Basics Manual controlling pulse width measurement 26 5 to 26 6 counting operations with no counters available 25 12 to 25 13 description 24 5 determining pulse width 26 2 to 26 3 dividing frequencies 29 2 to 29 3 events or elapsed time counting events 28 3 to 28 4 time 28 5 to 28 6 finite pulse train generation using Advanced VIs 25 11 using Easy and Intermediate VIs 25 10 to 25 11 frequency and period measurement connecting counters 27 3 to 27 4 high frequency signals 27 4 to 27 5 how and when to measure 27 2 to 27 3 low frequency signals 27 7 to 27 8 internal timebases with maximum pulse width measurements table 26 8 single square pulse generation 25 5 to 25 6 square pulse generation 25 3 stopping counter generations 25 14 to 25 15 data acquisition See also analog input VIs analog input output control loops 6 5 to 6 8 basic LabVIEW data acquisition concepts 3 1 to 3 16 data o
100. Advanced VIs in a While Loop you should stop the loop if the status in the error out cluster reads TRUE If you wire the error cluster to the General Error Handler VI or the Simple Error Handler VI the VI interprets the error information and describes the error to you Figures 30 1 and 30 2 show how to wire a typical DAQ VI to an error handler Figure 30 1 Error Checking Using the General Error Handler VI Chapter 30 Debugging Techniques National Instruments Corporation 30 3 LabVIEW Data Acquisition Basics Manual Figure 30 2 Error Checking Using the Simple Error Handler VI The following figure shows an example of the dialog box the Error Handler VIs display if an error occurs Refer to the LabVIEW Function and VI Reference Manual or the LabVIEW Online Reference available by selecting Help Online Reference for more information on the error handler VIs Single Stepping through a VI Single stepping through a VI allows you to execute one node at a time in the block diagram A node can be subVIs functions structures formula nodes and attribute nodes Refer to Chapter 2 Creating VIs in the LabVIEW User Manual and Chapter 4 Executing and Debugging VIs and SubVIs in the G Programming Reference Manual for more information about single stepping Execution Highlighting Execution highlighting the light bulb button on the block diagram shows you how data passes from one node to another in your program When you activate e
101. Analog Output Modules 20 6 Multiplexed Mode for Digital and Relay Modules 20 6 Parallel Mode for Analog Input Modules 20 6 Parallel Mode for the SCXI 1200 Windows 20 7 Parallel Mode for Digital Modules 20 7 SCXI Software Installation and Configuration 20 8 Chapter 21 Special Programming Considerations for SCXI SCXI Channel Addressing 21 1 SCXI Gains 21 3 SCXI Settling Time 21 5 Contents National Instruments Corporation xi LabVIEW Data Acquisition Basics Manual Chapter 22 Common SCXI Applications Analog Input Applications for Measuring Temperature and Pressure 22 2 Measuring Temperature with Thermocouples 22 2 Temperature Sensors for Cold Junction Compensation 22 3 Amplifier Offset 22
102. Australia 03 9879 5166 Austria 0662 45 79 90 0 Belgium 02 757 00 20 Brazil 011 284 5011 Canada Calgary 403 274 9391 Canada Ontario 905 785 0085 Canada Qu bec 514 694 8521 China 0755 3904939 Denmark 45 76 26 00 Finland 09 725 725 11 France 01 48 14 24 24 Germany 089 741 31 30 Greece 30 1 42 96 427 Hong Kong 2645 3186 India 91805275406 Israel 03 6120092 Italy 02 413091 Japan 03 5472 2970 Korea 02 596 7456 Mexico D F 5 280 7625 Mexico Monterrey 8 357 7695 Netherlands 0348 433466 Norway 32 27 73 00 Poland 48 22 528 94 06 Portugal 351 1 726 9011 Singapore 2265886 Spain 91 640 0085 Sweden 08 587 895 00 Switzerland 056 200 51 51 Taiwan 02 2377 1200 United Kingdom 01635 523545 National Instruments Corporation G 1 LabVIEW Data Acquisition Basics Manual Glossary Prefix Meaning Value k kilo 103 M mega 106 m milli 10 3 micro 10 6 n nano 10 9 Numbers Symbols 1D One dimensional 2D Two dimensional A A Amperes AC Alternating current A D Analog to digital ADC Analog to digital converter An electronic device often an integrated circuit that converts an analog voltage to a digital number ADC resolution The resolution of the ADC which is measured in bits An ADC with 16 bits has a higher resolution and thus a higher degree of accuracy than a 12 bit ADC AI Analog input AI device An analog input device that has AI in its name
103. C llb You also can use the example Cont Pulse Train Int 9513 VI located in labview examples daq counter Am9513 llb These examples show how to generate a simple pulse train using Intermediate VIs With these VIs you can specify the frequency duty cycle and pulse polarity of your pulse train If the duty cycle is set to 0 0 or 1 0 the closest achievable duty cycle is used to generate a train of positive or negative pulses The Continuous Pulse Generator Config VI configures the counter for the operation and the Counter Start VI controls the initiation of the pulse train For example you may want to generate a continuous pulse train as the result of meeting certain conditions If you use the Easy VI the pulse train starts immediately With the Intermediate VIs you can configure the counter at the beginning of your application then wait to call Counter Start after the conditions are met This approach will improve performance When you click the STOP button the While Loop stops and Counter Stop is called to stop the pulse train You must stop the counter if you want to use it for other purposes For more information on stopping counters refer to the Stopping Counter Generations section at the end of this chapter counter your device your device gate source out Chapter 25 Generating a Square Pulse or Pulse Trains National Instruments Corporation 25 9 LabVIEW Data Acquisition Basics Manual 8253 54 Figure 25 8 show
104. CXI example 22 17 calibrating SCXI modules for signal generation 23 7 to 23 8 AO Start VI circular buffered output 12 4 external control of update clock 13 1 simultaneous buffered waveform acquisition and generation 14 1 waveform generation 12 2 to 12 3 AO Trigger and Gate Config VI 14 2 AO Update Channel VI 11 1 AO Update Channels VI 11 1 AO Wait VI 12 3 AO Waveform Gen VI 12 1 Index National Instruments Corporation I 5 LabVIEW Data Acquisition Basics Manual AO Write One Update VI analog I O control loops 6 5 to 6 6 multiple immediate updates 11 2 single immediate updates 11 1 AO Write VI circular buffered output 12 4 simultaneous buffered waveform acquisition and generation 14 1 waveform generation 12 2 Array amp Cluster option 3 15 arrays transposing 3 15 7 5 two dimensional 2D arrays 3 14 to 3 16 B bipolar range 3 13 5 7 breakpoints setting 30 4 Buff Handshake Input VI 17 6 Buff Handshake Output VI 17 6 buffered handshaking 17 6 to 17 8 circular buffered examples 17 7 to 17 8 iterative buffered examples 17 7 simple buffered examples 17 6 Buffered Pattern Input VI 18 1 Buffered Pattern Input Trig VI 18 2 Buffered Pattern Output VI 18 1 Buffered Pattern Output Trig VI 18 2 buffered pulse and period measurement 26 6 to 26 7 buffered waveform acquisition 7 1 to 7 11 circular buffered analog input 7 6 to 7 11 asynchronous continuous acquisition using DAQ occurrences 7 9
105. DAQ hardware has If you are not sure which chip your device uses refer to your hardware manual You can use the Easy I O VI Generate Pulse Train or a stream of Intermediate VIs to generate a finite pulse train With either technique you must use two counters as shown in Figure 25 9 Refer to Chapter 28 Counting Signal Highs and Lows for more information on how to determine counter 1 and how to use the adjacent counter VI The Chapter 25 Generating a Square Pulse or Pulse Trains LabVIEW Data Acquisition Basics Manual 25 10 www ni com maximum number of pulses in the pulse train is 216 1 for Am9513 devices and 224 1 for DAQ STC devices Figure 25 9 shows the physical connections to produce a finite pulse train on the OUT pin of a counter counter generates the finite pulse train with high level gating counter 1 provides counter with a long enough gate pulse to output the number of desired pulses You must externally connect the OUT pin of the counter 1 to the GATE pin of counter You also can gate counter 1 Figure 25 9 Physical Connections for Generating a Finite Pulse Train TIO ASIC DAQ STC Am9513 These examples show how to use the Easy counter VI Generate Pulse Train to generate a finite pulse train Refer to the Finite Pulse Train Easy DAQ STC VI located in labview examples daq counter DAQ STC llb or the example Finite Pulse Train Easy 9513 VI located in labview examples daq counter Am9513 llb With these VIs
106. DC value You can use the single point analog output VIs to produce this type of output With single point analog output any time you want to change the value on an analog output channel you must call one of the VIs that produces a single update a single value change Therefore you can change the output value only as fast as LabVIEW calls the VIs This technique is called software timing You should use software timing if you do not need high speed generation or the most accurate timing Refer to Chapter 11 One Stop Single Point Generation for more information on single point output Buffered Analog Output Sometimes in performing analog output the rate that your updates occur is just as important as the signal level This is called waveform generation or buffered analog output For example you might want your DAQ device to act as a function generator You can do this by storing one cycle of sine wave data in an array and programming the DAQ device to generate the values continuously in the array one point at a time at a specified rate This is known as single buffered waveform generation But what if you want to generate a continually changing waveform For example you might have a large file stored on disk that contains data you want to output Because LabVIEW cannot store the entire waveform in a single buffer you must continually load new data into the buffer during the generation This Chapter 10 Things You Should Know about Analog
107. DIO 24 devices 6507 6508 DIO 96 devices Lab 1200 Series devices E Series family devices MIO 16DE 10 6025E devices Note Only E Series boards with more than eight digital lines those that have an additional 8255 chip onboard support handshaking These boards also are part of the 8255 family Chapter 17 Handshaked Digital I O LabVIEW Data Acquisition Basics Manual 17 2 www ni com Note You cannot use handshaking with channel names that were configured in the DAQ Channel Wizard Handshaking Lines 6533 Family The names and functions of handshaking signals vary The DIO 32 devices have two main handshaking lines the REQ request line and the ACK acknowledge line REQ is an input indicating the external device is ready ACK is an output indicating the DIO 32 device is ready Burst mode on a 6533 device also uses a third handshaking signal PCLK peripheral clock 8255 Family For 8255 based DAQ devices that perform handshaking there are four handshaking signals Strobe Input STB Input Buffer Full IBF Output Buffer Full OBF Acknowledge Input ACK You use the STB and IBF signals for digital input operations and the OBF and ACK signals for digital output operations When the STB line is low LabVIEW loads data into the DAQ device After the data has been loaded IBF is high which tells the external device that the data has been read For digital out
108. Data Acquisition Basics Manual LabVIEW Data Acquisition Basics Manual January 2000 Edition Part Number 320997E 01 Worldwide Technical Support and Product Information www ni com National Instruments Corporate Headquarters 11500 North Mopac Expressway Austin Texas 78759 3504 USA Tel 512 794 0100 Worldwide Offices Australia 03 9879 5166 Austria 0662 45 79 90 0 Belgium 02 757 00 20 Brazil 011 284 5011 Canada Calgary 403 274 9391 Canada Ontario 905 785 0085 Canada Qu bec 514 694 8521 China 0755 3904939 Denmark 45 76 26 00 Finland 09 725 725 11 France 01 48 14 24 24 Germany 089 741 31 30 Greece 30 1 42 96 427 Hong Kong 2645 3186 India 91805275406 Israel 03 6120092 Italy 02 413091 Japan 03 5472 2970 Korea 02 596 7456 Mexico D F 5 280 7625 Mexico Monterrey 8 357 7695 Netherlands 0348 433466 Norway 32 27 73 00 Poland 48 22 528 94 06 Portugal 351 1 726 9011 Singapore 2265886 Spain 91 640 0085 Sweden 08 587 895 00 Switzerland 056 200 51 51 Taiwan 02 2377 1200 United Kingdom 01635 523545 For further support information see the Technical Support Resources appendix To comment on the documentation send e mail to techpubs ni com Copyright 1995 2000 National Instruments Corporation All rights reserved Important Information Warranty The media on which you receive National Instruments software are warranted not to fail to execute programming instructions due to defects in materials and work
109. Explorer by selecting Help Help Topics DAQ Help If you are using an earlier version of NI DAQ for Windows you can find the help file in Start Programs LabVIEW NI DAQ Configuration Utility Help If you are using a Macintosh you can find the help file in the Help menu of the NI DAQ Configuration Utility Configuring Your DAQ Device Using NI DAQ 4 8 x on the Macintosh After you check and record your jumper settings turn off your computer and insert your National Instruments devices Turn your computer back on You can find NI DAQ in your Control Panels folder The NI DAQ icon looks like the one shown to the left Double click on this icon to launch NI DAQ When you launch the program NI DAQ displays a list of all of the devices in your computer Each device has a list of attributes as shown in Figure 2 3 The number specified in the device line is the logical device number that NI DAQ assigned to the device Use this device number in LabVIEW to select the device for any operation Chapter 2 Installing and Configuring Your Data Acquisition Hardware National Instruments Corporation 2 5 LabVIEW Data Acquisition Basics Manual Figure 2 3 NI DAQ Device List Display Now show the Device Configuration dialog box by selecting Device Configuration from the menu as shown in Figure 2 4 Figure 2 4 Accessing the Device Configuration Dialog Box in NI DAQ Figure 2 5 shows the NI DAQ Device Configuration dialog box You can edit the
110. For specific information about the Digital I O VIs refer to Chapter 14 Introduction to the LabVIEW Data Acquisition VIs in the LabVIEW Function and VI Reference Manual or refer to the LabVIEW Online Reference by selecting Help Online Reference Knowing Your Digital I O Chip The digital I O chips in most National Instruments DAQ devices belong to one of three families 6533 E Series or 8255 The 6533 family includes 6533 boards such as the PXI 6533 and PCI DIO 32HS The E Series board family typically has one 8 bit digital I O port as a part of the DAQ STC The 8255 family includes low cost Lab 1200 devices and 650x type boards DIO 24 and DIO 96 which use the 8255 DIO chip Note Some E Series boards have more than eight digital lines These boards typically have an additional 8255 chip This means that with regards to digital I O they belong to both the E Series and 8255 families Chapter 15 Things You Should Know about Digital I O National Instruments Corporation 15 3 LabVIEW Data Acquisition Basics Manual 6533 Family The 6533 family of digital devices uses the National Instruments DAQ DIO ASIC a 32 bit general purpose digital I O interface specifically designed for high performance The 6533 devices can perform single point I O pattern I O and high speed data transfer using a wide range of handshaked protocols These devices also are equipped with sophisticated trigger circuitry to start or stop
111. I O with Triggering 18 2 Continuous Timed Digital I O 18 2 PART V SCXI Getting Your Signals in Great Condition Chapter 19 Things You Should Know about SCXI What Is Signal Conditioning 19 1 Amplification 19 4 Isolation 19 5 Filtering 19 5 Transducer Excitation 19 5 Linearization 19 6 Chapter 20 Hardware and Software Setup for Your SCXI System SCXI Operating Modes 20 5 Multiplexed Mode for Analog Input Modules 20 5 Multiplexed Mode for the SCXI 1200 Windows 20 6 Multiplexed Mode for
112. I Sample Channels VI The Easy Analog Input VIs have several benefits You need only one icon in your block diagram to perform the task Easy VIs require only a few basic inputs and they have built in error checking However these VIs have limited programming flexibility Because Easy VIs have only a few inputs you cannot implement some of the more detailed features of DAQ devices such as triggering or interval scanning In addition these VIs always reconfigure at start up which can slow down processing time When you need more speed and efficiency use the Intermediate VIs which configure an acquisition only once and then continually acquire data without re configuring The Intermediate VIs also offer more error handling control more hardware functionality and more efficiency in developing your application than the Easy VIs You typically use the Intermediate VIs to perform buffered acquisitions Refer to Chapter 7 Buffering Your Way through Waveform Acquisition for more information about buffered acquisitions The Intermediate Analog Input VI AI Single Scan VI does multiple channel single point acquisitions The AI Single Scan VI returns one scan of data You also can use this VI to read only one point if you specify one channel Use this VI only in conjunction with the AI Config VI Figure 6 2 shows a simplified block diagram for non buffered applications LabVIEW calls the AI Config VI which configures the channels selects the
113. IO 32F has three pins for each direction If you use the Write To Digital Port VI you will output on the OUT pins If you use the Read From Digital Port VI you will input from the IN pins I want to be able to write up to four lines on the digital port on my jumpered MIO non E Series device while also reading in four lines of digital data on the remaining free digital lines How do I do this Use the DIO Port Config VI twice once to configure four lines for output and once more to configure four lines for input Now call the DIO Port Write VI or the DIO Port Read VI for the appropriate lines Avoid calling the Easy I O VIs for digital I O as they reconfigure the port direction each time the VI is called Appendix A LabVIEW Data Acquisition Common Questions National Instruments Corporation A 3 LabVIEW Data Acquisition Basics Manual I want to use a TTL digital trigger pulse to start data acquisition on my DAQ device I noticed there are two types of triggers Digital Trigger A and Digital Trigger A amp B Which digital trigger setting should I use and where should I connect the signal You should use Digital Trigger A which stands for first trigger to start a data acquisition Digital Trigger B which stands for second trigger should be used only if you are doing both a start and a stop trigger for your data acquisition Connect your trigger signal to either STARTTRIG pin 38 if you are using an AT MIO 16 AT MIO 1
114. Installing and Configuring Your Data Acquisition Hardware This chapter explains how to set up your system to use data acquisition with LabVIEW and your data acquisition hardware The chapter contains hardware installation and configuration and software configuration instructions and some general information and techniques Note The LabVIEW installer prompts you to have the NI DAQ driver software installed All National Instruments data acquisition DAQ devices are packaged with NI DAQ driver software The version of NI DAQ packaged with your DAQ device might be newer than the version installed by LabVIEW You can determine the NI DAQ version in LabVIEW by running the Get DAQ Device Information VI located in Functions Data Acquisition Calibration and Configuration After installing LabVIEW and the NI DAQ driver follow the steps in Figure 2 1 to install your hardware and complete the software configuration LabVIEW uses the software configuration information to recognize your hardware and to set default DAQ parameters Chapter 2 Installing and Configuring Your Data Acquisition Hardware LabVIEW Data Acquisition Basics Manual 2 2 www ni com Figure 2 1 Installing and Configuring DAQ Devices NI DAQ driver software provides LabVIEW with a high level interface to DAQ devices and signal conditioning hardware Install Plug in Devices Use Measurement amp Automation Explorer or Your Configuration Utility to Configure Devices Instal
115. LabVIEW Data Acquisition Basics Manual Figure 7 2 Simple Buffered Analog Input Example If you want to display the data on the same graph look again at the Acquire N Scans example VI found in labview examples daq anlogin anlogin llb This example shows a simple buffered input application that uses graphing For a 2D array to be displayed on a waveform graph each row of data must represent a single plot This is because waveform graphs are in row major order Because the channel data is in each column you must transpose the 2D array You can do this by popping up on the front panel of the graph and choosing Transpose Array Simple Buffered Analog Input with Multiple Starts In some cases you might not want to acquire contiguous data such as in an oscilloscope application In this case you would want to take only a specified number of samples as a snapshot of what the input looks like periodically For an example using the Intermediate VIs open the Acquire N Multi Start VI found in labview examples daq anlogin anlogin llb This example is similar to the Acquire N Scans example except the acquisition only occurs each time the start button on the front panel is pressed This example is similar to the standard simple buffered analog input VI but now both the AI Start and AI Read VIs are in a While Loop which means the program takes a number of samples every time the While Loop iterates Note The AI Read VI returns 1 000 samples ta
116. LabVIEW is the Acquire N Scans Analog Hardware Trig VI located in labview examples daq anlogin anlogin llb This VI uses the Intermediate VIs to perform buffered acquisition where data is stored in a memory buffer during acquisition After the acquisition completes the VI retrieves all the data from the memory buffer and displays it For more information on buffered acquisition read Chapter 7 Buffering Your Way through Waveform Acquisition You must tell your device the conditions on which to start acquiring data In LabVIEW you can acquire data both before and after an analog trigger signal If the pretrigger scans is greater than 0 your device acquires data before the triggering conditions It then subtracts the pretrigger scans value from the number of scans to acquire value to determine the number of scans to collect after the triggering conditions are met If pretrigger scans is 0 then the number of scans to acquire is acquired after the triggering conditions are met Complete the following steps before you start acquiring data 1 Specify in the trigger slope input whether to trigger the acquisition on the rising or falling edge of the analog trigger signal 2 Enter the trigger channel to use for connecting the analog triggering signal 3 Specify the trigger level on the triggering signal needed to begin acquisition After you specify the channel of the triggering signal LabVIEW waits until the slope and trigger lev
117. Manual 9 4 www ni com Open the Acquire N Scans ExtChanClk VI located in labview examples daq anlogin anlogin llb This example demonstrates how to set up your acquisition for an externally controlled channel clock The VI includes the AI Clock Config VI and the clock source was connected to the I O connector You can enable external conversions by calling the advanced level AI Clock Config VI Remember that the AI Clock Config VI which is called by the AI Config VI normally sets internal channel delay automatically or manually with the interchannel delay control However calling the AI Clock Config VI after the AI Config VI resets the channel clock so that it comes from an external source for external conversion Also notice that the scan clock is set to 0 to disable it allowing the channel clock to control the acquisition rate Note The 5102 devices do not support external channel clock pulses because there is no channel clock on the device On most devices external conversions occur on the falling edge of the EXTCONV line Consult your hardware reference manual for timing diagrams On devices with PFI lines such as E Series devices you can set the Clock Source Code input of AI Clock Config VI to the PFI pin with either falling or rising edge or use the default PFI2 Convert pin where the conversions occur on the falling edge Note The AT MIO 16 AT MIO 16D NB MIO 16 and NB MIO 16X cannot support both an external channel clo
118. NRSE measurement system All measurements are made with respect to a common reference but the voltage at this reference can vary with respect to the measurement system ground NRSE Nonreferenced single ended O onboard channels Channels provided by the plug in data acquisition device OUT pin A counter output pin where the counter can generate various TTL pulse waveforms output limits The upper and lower voltage or current outputs for an analog output channel The output limits determine the polarity and voltage reference settings for a device Glossary National Instruments Corporation G 11 LabVIEW Data Acquisition Basics Manual P parallel mode A type of SCXI operating mode in which the module sends each of its input channels directly to a separate analog input channel of the device to the module pattern generation A type of handshaked latched digital I O in which internal counters generate the handshaked signal which in turn initiates a digital transfer Because counters output digital pulses at a constant rate this means you can generate and retrieve patterns at a constant rate because the handshaked signal is produced at a constant rate PCI Peripheral Component Interconnect An industry standard high speed databus PGIA Programmable Gain Instrumentation Amplifier Plug and Play devices Devices that do not require DIP switches or jumpers to configure resources on the devices Also called switchle
119. O LabVIEW Data Acquisition Basics Manual 16 4 www ni com E Series Family The examples Read from 1 Dig Port E VI and Write to 1 Dig Port E VI show how to use the Advanced Digital I O VIs to read from or write to one digital 8 bit port These examples are located in labview examples daq digital E series llb National Instruments Corporation 17 1 LabVIEW Data Acquisition Basics Manual 17 Handshaked Digital I O If you want to pass a digital pattern after receiving a digital pulse you should use latched handshaked digital I O Handshaking allows you to synchronize digital data transfer between your DAQ device and instrument For example you might want to acquire an image from a scanner The process involves the following steps 1 The scanner sends a pulse to your DAQ device after the image has been scanned and it is ready to transfer the data 2 Your DAQ device reads an 8 16 or 32 bit digital pattern 3 Your DAQ device then sends a pulse to the scanner to let it know the digital pattern has been read 4 The scanner sends out another pulse when it is ready to send another digital pattern 5 After your DAQ device receives this digital pulse it reads the data 6 This process repeats until all the data is transferred Many DAQ devices support digital handshaking including the following 6533 family devices 6533 DIO 32HS devices DIO 32F 8255 family devices 6503
120. Output LabVIEW Data Acquisition Basics Manual 10 2 www ni com process requires the use of circular buffered analog output in LabVIEW To learn more about single or circular buffering read Chapter 12 Buffering Your Way through Waveform Generation National Instruments Corporation 11 1 LabVIEW Data Acquisition Basics Manual 11 One Stop Single Point Generation This chapter shows you which VIs to use in LabVIEW to perform single point updates Single Immediate Updates The simplest way to program single point updates in LabVIEW is by using the Easy Analog Output VI AO Update Channels This VI writes values to one or more output channels on the output DAQ device Notice that an array of values is passed as an input to the VI The first element in the array corresponds to the first entry in the channel string and the second array element corresponds to the second channel entry If you use channel names configured in the DAQ Channel Wizard in your channel string values is relative to the physical units you specify in the DAQ Channel Wizard Otherwise values is relative to volts For more information on channel string syntax refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts Remember that Easy VIs already have built in error handling For an example of writing values for multiple channels open the block diagram of the Generate 1 Point on 1 Channel VI located in labview examples daq anlogout anlogout llb This VI g
121. TL signal Frequency division results in a pulse or pulse train from a counter for every N cycles of an internal or external source Counters can only decrease divide down the frequency of the source signal The resulting frequency is equal to the input frequency divided by N timebase divisor N must be an integer number greater than 1 Performing frequency division on an internal signal is called a down counter Frequency division on an external signal is called a signal divider Figure 29 1 shows typical wiring for frequency division Figure 29 1 Wiring Your Counters for Frequency Division counter your device your device your device gate source out counter your device gate source out Frequency Division for a Signal Divider Frequency Division for a Down Counter Chapter 29 Dividing Frequencies LabVIEW Data Acquisition Basics Manual 29 2 www ni com TIO ASIC DAQ STC Am9513 Figure 29 2 shows an example of a signal divider It uses the Intermediate counter VIs Down Counter or Divide Config Counter Start and Counter Stop Figure 29 2 Programming a Single Divider for Frequency Division The Down Counter or Divide Config VI configures the specified counter to divide the SOURCE signal by the timebase divisor value and output a signal when the counter reaches its terminal count TC Using Down Counter or Divide Config VI you can configure the type of output to be pulse or toggled The block diagram
122. The Utility VIs found in many of the LabVIEW DAQ palettes are also intermediate level VIs and thus have more hardware functionality and efficiency in developing your application than the Easy VIs Advanced VIs The Advanced VIs are the lowest level interface to the DAQ driver Very few applications require the use of the Advanced VIs Use the Advanced VIs when the Easy or Intermediate VIs do not have the inputs necessary to control an unusual DAQ function Advanced VIs return the greatest amount of status information from the DAQ driver VI Parameter Conventions In each LabVIEW DAQ VI front panel or Help window the appearance of the control and indicator labels denote the importance of that parameter Control and indicator names shown in bold are required and must be wired to a node on the block diagram for your application to run Parameter names that appear in plain text are optional and are not necessary for your program to run You rarely need to use the parameters with labels in square brackets Keep in mind that these conventions apply only to the information in the Help window and on the front panel Both this manual and the LabVIEW Function and VI Reference Manual list all parameter names in bold to distinguish them from other elements of the text Default input values appear in parentheses to the right of the parameter names Chapter 3 Basic LabVIEW Data Acquisition Concepts LabVIEW Data Acquisition Basics Manual 3 6 www n
123. VIEW Data Acquisition Basics Manual Measuring the Period and Frequency of Low Frequency Signals How you measure the period and frequency of low frequency signals depends on which counter chip is on your DAQ device If you are uncertain which chip your DAQ device has refer to your hardware documentation TIO ASIC DAQ STC The Measure Period Easy DAQ STC VI located in labview examples daq counter DAQ STC llb uses the Easy VI Measure Pulse Width or Period which is located in Functions Data Acquisition Counter You connect your signal of unknown period to the GATE of counter The counter measures the period between successive rising edges of your TTL signal by counting the number of internal timebase cycles that occur during the period The period is the count divided by the timebase The frequency is determined by taking the inverse of the period You must choose timebase such that the counter does not reach its highest value or terminal count TC Refer to Table 26 1 Internal Counter Timebases and Their Corresponding Maximum Pulse Width Period or Time Measurements for maximum measurable periods for TIO ASIC and DAQ STC devices Am9513 The example Measure Period Easy 9513 VI located in labview examples daq counter Am9513 llb uses the Easy VI Measure Pulse Width or Period located in Functions Data Acquisition Counter You connect your signal of unknown period to the GATE of counter The counter measures the period
124. VIEW for data acquisition before you can use this book as a troubleshooting guide This manual supplements the LabVIEW User Manual and assumes that you are familiar with that material You also should be familiar with the operation of LabVIEW your computer your computer s operating system and your data acquisition DAQ device Conventions Used in This Manual The following conventions are used in this manual Square brackets enclose optional items for example response The symbol leads you through nested menu items and dialog box options to a final action The sequence File Page Setup Options directs you to pull down the File menu select the Page Setup item and select Options from the last dialog box This icon denotes a tip which alerts you to advisory information This icon denotes a note which alerts you to important information bold Bold text denotes items that you must select or click on in the software such as menu items and dialog box options Bold text also denotes parameter names About This Manual LabVIEW Data Acquisition Basics Manual xx www ni com italic Italic text denotes variables emphasis a cross reference or an introduction to a key concept This font also denotes text that is a placeholder for a word or value that you must supply monospace Text in this font denotes text or characters that you should enter from the keyboard sections of code programming examples and synta
125. Volt Amp Hz 2 and Binary 2 inputs of the VI You can save the constants on the module in the user area in EEPROM Use the user area as you are calibrating and use the SCXI Cal Constants VI again at the end of your calibration sequence to copy the calibration table in the user area to the default load area in EEPROM Remember constants stored in the default load area can be overwritten If you want to use a set of constants later keep a copy of the constants stored in the user area in EEPROM Repeat the procedure above for each channel and range you want to calibrate Subsequent analog outputs will use your new constants to scale voltage or current to the correct binary value For more information on the SCXI Cal Constants VI refer to Chapter 29 Calibration and Configuration VIs in the LabVIEW Function and VI Reference Manual or refer to the LabVIEW Online Reference by selecting Help Online Reference National Instruments Corporation VI 1 LabVIEW Data Acquisition Basics Manual Part VI Counting Your Way to High Precision Timing This part of the manual describes the different ways you can use counters with your data acquisition application including generating a pulse or pulses measuring pulse width frequency and period counting events and time and dividing frequencies for precision timing Part VI Counting Your Way to High Precision Timing contains the following chapters Chapter 24 Things You Should Know a
126. Windows 20 6 parallel mode Windows 20 7 settling time SCXI 21 5 Show Help option 3 2 Show VI Info option 3 2 signal conditioning amplification 19 4 common transducers table 19 1 to 19 2 common types of signal conditioning 19 2 conditioning for common types of transducers signals figure 19 3 defined 19 2 filtering 19 5 isolation 19 5 linearization 19 6 transducer excitation 19 5 signal divider 29 1 signal edges 24 2 signal voltage range See limit settings signals See also analog input signals choosing between analog and digital signals 4 3 simple buffered analog input examples displaying waveforms on graphs 7 4 to 7 5 sampling with multiple starts 7 5 to 7 6 multiple waveform acquisition 7 3 to 7 4 overview 7 1 single waveform acquisition 7 2 to 7 3 waiting to analyze data 7 1 to 7 2 Simple Error Handler VI analog output SCXI example 22 17 debugging VIs 30 2 to 30 3 multiple channel single point analog input 6 4 single immediate updates 11 1 Simul AI AO Buffered E series MIO VI 14 2 Simul AI AO Buffered Lab 1200 VI 14 4 Simul AI AO Buffered legacy MIO VI 14 3 Simul AI AO Buffered Trigger E series MIO VI 14 2 Simul AI AO Buffered Trigger Lab 1200 VI 14 4 simultaneous buffered waveform acquisition and generation See buffered waveform acquisition single channel single point analog input choosing between single point and multi point acquisition 4 4 description 6 1 to
127. You specify this channel list as an array of DAQ device channel numbers indicating the order in which LabVIEW scans the DAQ device channels When scanning multiple channels list only the device channels not the AMUX 64T channels Use the AMy x syntax in your channel list only when you sample a single AMUX 64T channel LabVIEW then scans four eight or 16 channels for every device channel for one two or four AMUX 64T devices respectively However the AMUX 64T has a fixed scanning order Table 5 3 shows the order in which LabVIEW scans the AMUX 64T channels for every DAQ device input channel when you use one or two AMUX 64T devices Table 5 4 shows the order in which LabVIEW scans the AMUX 64T channels for every DAQ device input channel when you use four AMUX 64T devices You must enter the device channels in your scan list if you want to scan more than one AMUX 64T channel Table 5 3 Scanning Order for Each DAQ Device Input Channel with One or Two AMUX 64Ts DAQ Device Channel AMUX 64T Channels One Device Two Devices Device 1 Device 1 Device 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
128. a Acquisition Basics Manual I 14 www ni com immediate updates multiple 11 2 single 11 1 Index Array function 3 15 initialization of data acquisition devices A 3 Input Buffer Full IBF line 17 2 input range and input setting selection 5 7 to 5 8 installation and configuration channel configuration in NI DAQ 5 x or 6 x 2 11 DAQ devices installing and configuring figure 2 2 using NI DAQ 4 8 x on Macintosh 2 4 to 2 6 using NI DAQ 5 x or 6 x 2 4 debugging software configuration errors 30 1 to 30 2 relationship between LabVIEW NI DAQ and DAQ hardware figure 2 3 SCXI chassis hardware configuration 2 6 to 2 7 software configuration 2 8 to 2 10 NI DAQ 4 8 x for Macintosh 2 8 to 2 10 NI DAQ 5 x or 6 x 2 9 Intermediate VIs See also VIs advantages 6 4 asynchronous continuous acquisition using DAQ occurrences 7 9 circular buffered output 12 3 to 12 4 continuous acquisition from multiple channels 7 8 to 7 9 continuous pulse train generation 25 8 controlling pulse width measurement 26 5 to 26 6 counting elapsed time 8253 54 28 6 to 28 7 Am9513 28 6 to 28 7 TIO ASIC or DAQ STC 28 6 counting events 8253 54 28 5 Am9513 28 4 TIO ASIC and DAQ STC 28 3 digital handshaking 17 5 dividing frequencies 29 2 to 29 3 finite pulse train generation 25 9 to 25 11 measuring frequency and period high frequency signals 27 5 low frequency signals 27 8 multiple channel single point analog input 6 3 to 6 4 m
129. a DAQ device in your computer to control your SCXI chassis connect the mounting bracket of the SCXI 134x where x is a number cable assembly to the back of one of the modules and screw it into the chassis frame Connect the other end of the cable to the DAQ device in your computer In multiplexed mode you need to connect only one module to the DAQ device In most cases it does not matter which module you cable The following are three special cases where you must cable a specific module to the device If you use SCXI 1140 modules with other types of modules cable one of the SCXI 1140 modules to the DAQ device If you want to use the simultaneous sample and hold cable either the SCXI 1530 or SCXI 1531 module to the DAQ device If you use analog input modules and other types of modules cable one of the analog input modules to the DAQ device 7 Turn on your chassis power Refer to the Getting Started with SCXI manual for more information about related topics such as multichassis cabling Chapter 2 Installing and Configuring Your Data Acquisition Hardware LabVIEW Data Acquisition Basics Manual 2 8 www ni com NI DAQ 5 x 6 x Software Configuration Refer to the online help for specific instructions on how to install and configure your DAQ device If you are using Windows with NI DAQ 6 5 or higher refer to the help file for Measurement amp Automation Explorer by selecting Help Help Topics DAQ Help If you are
130. abVIEW Data Acquisition Basics Manual 26 Measuring Pulse Width This chapter describes how you can use a counter to measure pulse width There are several reasons you may need to determine pulse width For example to determine the duration of an event set your application to measure the width of a pulse that occurs during that event Another example is determining the interval between two events In this case you measure the pulse width between the two events An example of when you might use this type of application is determining the time interval between two boxes on a conveyor belt or the time it takes one box to be processed through an operation The event is an edge every time a box goes by a point which prompts a digital signal to change in value Measuring a Pulse Width You can measure an unknown pulse width by counting the number of pulses of a faster known frequency that occur during the pulse to be measured Connect the pulse you want to measure to the GATE input pin and a signal of known frequency to the SOURCE CLK input pin as shown in Figure 26 1 The pulse of unknown width Tpw gates the counter configured to count a timebase clock of known period Ts The pulse width equals the timebase period times the count or Tpw Ts count The SOURCE CLK input can be an external or internal signal Figure 26 1 Counting Input Signals to Determine Pulse Width GATE SOURCE OUT Count Register Ts Tpw frequen
131. acquisition and the AI Clear VI removes the grounds from the amplifier after the acquisition completes The SCXI 1112 SCXI 1125 SCXI 1141 SCXI 1142 and SCXI 1143 have separate amplifiers for each channel so you must specify the channel number when you ground the amplifier To specify the channel number attach the channel number to the end of the string calgnd For example calgnd2 grounds the amplifier inputs for channel 2 and reads the offset Channel List Element Channel Specified ob0 scx mdy calgnd SCXI 1100 and SCXI 1122 only The grounded amplifier of the module in slot y of the chassis with ID x ob0 scx mdy calgndz Where z is the appropriate SCXI channel needing shunting for the SCXI 1112 SCXI 1125 SCXI 1141 SCXI 1142 or SCXI 1143 Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 6 www ni com You also can specify a range of channels The string calgnd0 7 grounds the amplifier inputs for channels 0 through 7 and reads the offset for each amplifier Use the Scaling Constant Tuner VI from Functions Data Acquisition Signal Conditioning to modify the scaling constants so LabVIEW automatically compensates for the amplifier offset when scaling binary data to voltage The SCXI 1100 Voltage example found in labview examples daq scxi scxi_ai llb shows you a way to use the Scaling Constant Tuner VI VI Examples If you use the DAQ Channel Wizard to configure your channels you can
132. ain the counter repeats this process many times as shown on the bottom line of Figure 25 3 Figure 25 3 Pulses Created with Positive Polarity and Toggled Output Positive Polarity Negative Polarity counter starts phase 1 phase 2 phase 1 phase 2 phase 1 phase 2 Single Pulse Pulse Train Chapter 25 Generating a Square Pulse or Pulse Trains LabVIEW Data Acquisition Basics Manual 25 4 www ni com 8253 54 When generating a pulse with the 8253 54 chip the hardware limits you to a negative polarity pulse as shown in Figure 25 2 The period of time from when the counter starts counting to the falling edge is called phase 1 The time between the falling and following rising edge is called phase 2 Figure 25 4 shows these phases for a single negative polarity pulse To create a positive polarity pulse you can connect your negative polarity pulse to an external 7404 inverter chip Figure 25 4 Phases of a Single Negative Polarity Pulse When generating a pulse train with the 8253 54 chip the hardware limits you to positive polarity pulses Furthermore the value loaded in the count register is divided equally to create phase 1 and phase 2 This means you will always get a 0 5 duty cycle if the count register is loaded with an even number If you load the count register with an odd number phase 1 will be longer than phase 2 by one cycle of the counter CLK signal Now that you know the terms involving generating a single squ
133. al 9 6 www ni com The appropriate pin to input your external scan clock can be found in Table 9 1 Note Some devices do not have internal scan clocks and therefore do not support external scan clocks These devices include but are not limited to the following NB MIO 16 PC LPM 16 PC LPM 16PnP PC 516 DAQCard 500 DAQCard 516 DAQCard 700 NI 4060 Lab NB Lab SE and Lab LC After connecting your external scan clock to the correct pin set up the external scan clock in software The example Acquire N Scans ExtScanClk VI located in labview examples daq anlogin anlogin llb shows how to do this Two Advanced VIs AI Clock Config and AI Control are used in place of the Intermediate AI Start VI This allows access to the clock source input This is necessary because it allows access to the clock source string which is used to identify the PFI pin to be used for the scan clock for E Series boards The clock source also includes the clock source code on the front panel which is set to I O connector The 0 0 wired to the Clock Config VI disables the internal clock The NB MIO 16X cannot support external scan clocks as the other devices can The device layout does not allow you to directly provide an external scan clock Instead you can offer a timebase to the internal counter counter 5 that generates the scan clock Do this by sending a timebase into the SOURCE5 pin and calling the Advanced VI AI Clock Config In addition wire the alte
134. al Instruments Corporation 3 15 LabVIEW Data Acquisition Basics Manual Figure 3 10 2D Array in Column Major Order To graph a column major order 2D array you must configure the waveform chart or graph to treat the data as transposed by turning on this option in the graph pop up menu Note This option is dimmed until you wire the 2D array to a graph To convert the data to row major order select Functions Array amp Cluster Transpose 2D Array To extract a single channel from a column major 2D array use the Index Array function from Functions Array amp Cluster Add a dimension so that you have two black rectangles in the lower left corner The top rectangle selects the row and the bottom rectangle selects the column Pop up on the row rectangle and select Disable Indexing Now when you select a column or channel by wiring your selection to the bottom rectangle the Index Array function produces the entire column of data as a 1D array as shown in Figure 3 11 Figure 3 11 Extracting a Single Channel from a Column Major 2D Array Analog output buffers that contain data for more than one channel are also column major 2D arrays To create such an array first make the data from each output channel a 1D array Then select the Build Array function from Functions Array amp Cluster Add as many input terminals rows to the Build Array terminal as you have channels of data Wire each 1D array to the Build Array terminal to combine th
135. al retrieval example 8 11 conditional retrieval input cluster 8 10 controlling startup times note 7 5 to 7 6 forcing time limit for 9 4 9 7 multiple waveform acquisition 7 3 one point calibration 23 5 SCXI temperature measurement 22 8 simple buffered analog input with multiple starts 7 5 to 7 6 simultaneous buffered waveform acquisition and generation 14 1 software triggering 8 10 AI Sample Channel VI 6 1 to 6 2 AI Sample Channels VI 6 2 AI Single Scan VI basic non buffered application 6 3 hardware timed analog I O control loops 6 6 to 6 7 improving control loop performance 6 7 to 6 8 multiple channel single point analog input 6 3 to 6 4 one point calibration 23 5 software timed analog I O control loops 6 5 AI Start VI amplifier offset 22 5 hardware timed analog I O control loops 6 6 to 6 7 multiple waveform acquisition 7 3 one point calibration 23 5 scan clock control 9 6 SCXI temperature measurement 22 8 simple buffered analog input with multiple starts 7 5 simultaneous buffered waveform acquisition and generation hardware triggered 14 2 software triggered 14 1 Am9513 counter continuous pulse train generation 25 7 to 25 8 controlling pulse width measurement 26 5 to 26 6 counting operations with no counters available 25 12 to 25 13 description 24 5 determining pulse width 26 4 dividing frequencies 29 2 to 29 3 events or elapsed time counting connecting counters 28 2 to 28 3 elapsed time
136. alculate the period for you Connecting Counters to Measure Frequency and Period Figure 27 3 shows typical external connections for measuring frequency In the figure your device provides the signal with the frequency to be measured to the SOURCE CLK of counter It optionally can control the GATE of counter 1 The OUT of counter 1 supplies a known pulse to the GATE of counter Finally counter counts the number of cycles of the unknown pulse during the known GATE pulse Figure 27 3 External Connections for Frequency Measurement TIO ASIC DAQ STC Am9513 Figure 27 4 shows typical external connections for measuring period In the figure your device provides the signal with the period to be measured to the GATE of counter A timebase of known frequency is supplied to the SOURCE This usually is an internal timebase but it can be externally supplied The counting range of your counter must not be exceeded during the period measurement The range of the Am9513 is 65 335 the range of the DAQ STC is 16 777 216 and the range of the TIO ASIC is 232 1 If the counting range is exceeded select a slower internal timebase period measurement 1 frequency measurement frequency measurement 1 period measurement Chapter 27 Measuring Frequency and Period LabVIEW Data Acquisition Basics Manual 27 4 www ni com Figure
137. all amounts of data relative to memory constraints single ended inputs Analog inputs that you measure with respect to a common ground software trigger A programmed event that triggers an event such as data acquisition Glossary LabVIEW Data Acquisition Basics Manual G 14 www ni com software triggering A method of triggering in which you to simulate an analog trigger using software Also called conditional retrieval SOURCE input pin An counter input pin where the counter counts the signal transitions STC System Timing Controller strain gauge A thin conductor which is attached to a material that detects stress or vibrations in that material subVI VI used in the block diagram of another VI comparable to a subroutine switchless device Devices that do not require DIP switches or jumpers to configure resources on the devices Also called Plug and Play devices syntax The set of rules to which statements must conform in a particular programming language T task A timed I O operation using a particular group See task ID task ID A number generated by LabVIEW which identifies to the NI DAQ drive the task at hand The following table gives the function code definitions Function Code I O Operation 1 analog input 2 analog output 3 digital port I O 4 digital group I O 5 counter timer I O TC Terminal count The highest value of a counter Glossary National Instruments Corp
138. and multiplexers Always enter your jumpered filter settings and your jumpered gain settings if applicable in the Measurement amp Automation Explorer or the configuration utility LabVIEW uses the gain and filter settings to determine a safe interchannel delay that allows the SCXI amplifiers and multiplexers to settle between channel switching before sampling the next channel LabVIEW calculates the delay for you If you set a scan rate that is too fast to allow for the default interchannel delay LabVIEW shrinks the interchannel delay and returns a warning from the AI Start or AI Control VIs Refer to your hardware manuals for SCXI settling times You can open the advanced level AI Clock Config VI to retrieve the channel clock selection Set the which clock control to channel clock 1 and set the clock frequency to 1 00 no change Now run the VI The actual clock rate specification cluster is on the right side of the panel Note When using NI 406x devices with SCXI you cannot use the external triggering feature of the NI 406x device National Instruments Corporation 22 1 LabVIEW Data Acquisition Basics Manual 22 Common SCXI Applications Now that you have your SCXI system set up and you are aware of the special SCXI programming considerations you should learn about some common SCXI applications This section covers example VIs for analog input analog output and digital modules For analog input you will learn how to mea
139. ant a pulse to be generated the counter can immediately begin without having to configure the counter In this situation using Intermediate VIs improves performance You must stop the counter if you want to use it for other purposes For more information on stopping counters refer to the Stopping Counter Generations section at the end of this chapter 8253 54 The example Delayed Pulse 8253 VI located in labview examples daq counter 8253 llb shows how to generate a negative polarity pulse Due to the nature of the 8253 54 chip three counters are used to generate this pulse Because only counter 0 is internally connected to a clock source it is used to generate the timebase counter 1 is used to create the pulse delay that gates counter 2 counter 2 is used to generate the pulse which occurs on the OUT pin Using multiple counters requires external wiring which is shown in Figure 25 6 as well as being described on the front panel of the VI Figure 25 6 External Connections Diagram from the Front Panel of Delayed Pulse 8253 VI The block diagram uses a sequence structure to divide the basic tasks involved In frame 0 of the sequence all of the counters are reset Notice that counters 1 and 2 are reset so their output states start out high Chapter 25 Generating a Square Pulse or Pulse Trains National Instruments Corporation 25 7 LabVIEW Data Acquisition Basics Manual In frame 1 of the sequence the counters are set up for
140. ardware triggers digital and analog In the following two sections you will learn about the necessary conditions to start an acquisition with a digital or an analog signal Chapter 8 Controlling Your Acquisition with Triggers LabVIEW Data Acquisition Basics Manual 8 2 www ni com Digital Triggering A digital trigger is usually a transistor transistor logic TTL signal having two discrete levels a high and a low level When moving from high to low or low to high a digital edge is created There are two types of edges rising and falling You can set your analog acquisition to start as a result of the rising or falling edge of your digital trigger signal In Figure 8 1 the acquisition begins after the falling edge of the digital trigger signal Usually digital trigger signals are connected to STARTTRIG EXTTRIG DTRIG EXT TRIG IN or PFI pins on your DAQ device If you want to know which pin your device has check your hardware manual or refer to the AI Trigger Config VI description in Chapter 18 Advanced Analog Input VIs of the LabVIEW Function and VI Reference Manual You also can refer to the LabVIEW Online Reference available by selecting Help Online Reference The STARTTRIG and EXTTRIG pins which have and asterisk after their names regard a falling edge signal as a trigger Make sure you account for this when specifying your triggering conditions Figure 8 1 Diagram of a Digital Trigger Figure 8 2 shows a timeline
141. are pulse or a pulse train you can learn about the LabVIEW VIs and the physical connections needed to implement your application Generating a Single Square Pulse You can use a single pulse to trigger analog acquisition or to gate another counter operation You also can use a single pulse to stimulate a device or circuit for which you need to acquire and test the response counter starts phase 1 phase 2 Chapter 25 Generating a Square Pulse or Pulse Trains National Instruments Corporation 25 5 LabVIEW Data Acquisition Basics Manual TIO ASIC DAQ STC Am9513 Figure 25 5 shows two ways to connect your counter to generate a square pulse In the Basic Connection the edges of the internal SOURCE signal are counted to generate the output signal the GATE is not used software start and the pulse signal on the OUT pin gets connected to your device The Optional Connections use an external SOURCE from your device and is gated by your device You can use either or both of these options Figure 25 5 Physical Connections for Generating a Square Pulse Two examples of using the Easy level Generate Delayed Pulse VI are the Delayed Pulse Easy DAQ STC VI located in labview examples daq counter DAQ STC llb and the example Delayed Pulse Easy 9513 VI located in labview examples daq counter Am9513 llb Open these VIs and study their block diagrams The Generate Delayed Pulse VI found in Functions Data Acquisition Counter te
142. asure the temperature of an object after applying heat to it An electrical thermometer sends a step voltage to your DAQ device after the heating completes If you have no way to begin measuring data immediately after your device receives the step voltage then you must acquire more points some before the step voltage and some after it so you can capture the data you need This solution is an inefficient use of computer memory and disk space because you must allocate and use more than is necessary Sometimes the data you need may be closer to the front of the buffer and other times it may be closer to the end of the buffer You can start an acquisition based on the condition or state of an analog or digital signal using a technique called triggering Generally a trigger is any event that starts data capture There are two basic types of triggering hardware and software triggering In LabVIEW you can use software triggering to start acquisitions or use it with an external device to perform hardware triggering Hardware Triggering Hardware triggering lets you set the start time of an acquisition and gather data at a known position in time relative to a trigger signal External devices produce hardware trigger signals In LabVIEW you specify the triggering conditions that must be reached before acquisition begins When the conditions are met the acquisition begins You also can analyze the data before the trigger There are two types of h
143. ault input for a parameter may be do not change the current setting and the current setting may be no AMUX 64T boards If you change the value of such a parameter the new value becomes the current setting Chapter 3 Basic LabVIEW Data Acquisition Concepts National Instruments Corporation 3 7 LabVIEW Data Acquisition Basics Manual Common DAQ VI Parameters The device input on analog I O digital I O and counter VIs specifies the number the DAQ configuration software assigned to your DAQ device Your software assigns a unique number to each DAQ device The device parameter usually appears as an input to the configuration VIs Another common configuration VI output task ID assigns your specific I O operation and device a unique number that identifies it throughout your program flow The task ID also can contain group information about the channels and gain used in your operation Some DAQ VIs perform either the device configuration or the I O operation while other DAQ VIs perform both configuration and the operation The VIs that handle both functions have an iteration input When your VI has the iteration set to 0 LabVIEW configures the DAQ device and then performs the specific I O operation For iteration values greater than 0 LabVIEW uses the existing configuration to perform the I O operation You can improve the performance of your application by not configuring the DAQ device every time an I O operation occurs Typically you s
144. aying the error number and description and the VI stops running As with single point analog output you can use the Analog Output Utility VI AO Waveform Gen VI for most of your programming needs This VI has several inputs and outputs that the Easy I O VI does not have You have the option of having the data array generated once several times or continuously through the generation count input Figure 12 1 shows an example block diagram of how to program this VI Chapter 12 Buffering Your Way through Waveform Generation LabVIEW Data Acquisition Basics Manual 12 2 www ni com Figure 12 1 Waveform Generation Using the AO Waveform Gen VI In this example LabVIEW generates the data in the array two times before stopping The Generate N Updates example VI located in labview examples daq anlogout anlogout llb uses the AO Waveform Gen VI Placing this VI in a loop and wiring the iteration terminal of the loop to the iteration input on the VI optimizes the execution of this VI When iteration is 0 LabVIEW configures the analog output channels appropriately If the iteration is greater than 0 LabVIEW uses the existing configuration which improves performance With the AO Waveform Gen VI you also can specify the limit settings input for each analog output channel For more information on limit settings refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts If you want even more control over your analog output application use t
145. bout Counters shows you how to add high precision timing to your DAQ system by using counters and explains basic counter concepts Chapter 25 Generating a Square Pulse or Pulse Trains describes the ways you can generate a square pulse or multiple pulses called pulse trains using the counters available on your DAQ device with the Easy Intermediate and Advanced Counter VIs in LabVIEW Chapter 26 Measuring Pulse Width describes how you can use a counter to measure pulse width Chapter 27 Measuring Frequency and Period describes the various ways you can measure frequencies and periods using the counters on your DAQ device Chapter 28 Counting Signal Highs and Lows teaches you how to use counters to count external events or elapsed time Chapter 29 Dividing Frequencies shows you how to divide the available device frequencies to get the frequency you need for your data acquisition application National Instruments Corporation 24 1 LabVIEW Data Acquisition Basics Manual 24 Things You Should Know about Counters Counters add counting or high precision timing to your DAQ system Counters respond to and output TTL signals square pulse signals that are 0 V low or 5 V high in value The following diagram shows a TTL signal Although counters count only the signal transitions edges of a TTL source signal you can use this counting capability in many ways You can generate square TTL p
146. buffer then data is coming into the buffer faster than your VI can read all of the previous buffer data and LabVIEW returns an error code 10846 overWriteError If you increase the size of the buffer so that it takes longer to fill up your VI has more time to read data from it If you slow down the scan rate you reduce the speed at which the buffer fills up which also gives your program more time to retrieve data You also can increase the number of scans to read at a time This retrieves more data out of the buffer each time and effectively reduces the number of times to Chapter 7 Buffering Your Way through Waveform Acquisition National Instruments Corporation 7 9 LabVIEW Data Acquisition Basics Manual access the buffer before it becomes full Check the output scan backlog to see how many data values remain in the circular buffer after the read Because this uses Intermediate VIs you also can control parameters such as triggering coupling and additional hardware Asynchronous Continuous Acquisition Using DAQ Occurrences The main advantage of acquiring data as described in the previous section is that you are free to manipulate your data between calls to the AI Read VI One limitation however is that the acquisition is synchronous This means that once you call the AI Read VI you cannot perform any other tasks until the AI Read VI returns your acquired data If your DAQ device is still busy collecting data you will have to s
147. buffer is 10 times the number of points acquired for each channel For each acquisition your device averages the temperature data After completing the acquisition always clear the acquisition by using the AI Clear VI If you are not using the DAQ Channel Wizard you must use the RTD Conversion VI in addition to specifying additional input parameters as shown in Figure 22 5 The Convert RTD Reading VI in Functions Data Acquisition Signal Conditioning converts the voltage read from the RTD to a temperature representation Note Use the RTD conversion function in LabVIEW only for platinum RTDs If you do not have a platinum RTD the voltage temperature relation is different so the LabVIEW conversion function cannot be used Chapter 22 Common SCXI Applications National Instruments Corporation 22 13 LabVIEW Data Acquisition Basics Manual Figure 22 5 Measuring Temperature Using the Convert RTD Reading VI The VI in Figure 22 5 continually acquires data until an error occurs or you stop the VI from executing For continuous hardware timed acquisition you need to set up a buffer In this example the buffer is 10 times the number of points acquired for each channel After your device averages the voltage data from the AI Read VI it converts the voltage values to temperature After completing the acquisition remember to always clear the acquisition by using the AI Clear VI Measuring Pressure with Strain Gauges Strain gauges giv
148. buffered VI Is similar to the Cont Acq amp Chart buffered VI except this VI displays data in a waveform graph Cont Acq to File binary VI Acquires data through circular buffered analog input and stores it in a specified file as binary data This process is more commonly called streaming to disk Cont Acq to File scaled VI Is similar to the previous binary VI with the exception that this VI writes the acquired data to a file as scaled voltage readings rather than binary values Cont Acq to Spreadsheet File VI Continuously reads data that LabVIEW acquires in the circular buffer and stores this data to a specified file in spreadsheet format You can view the data stored in a spreadsheet file by this VI in any spreadsheet application Simultaneous Buffered Waveform Acquisition and Waveform Generation You might discover that along with your analog input acquisition you also want to output analog data If so refer to Chapter 14 Simultaneous Buffered Waveform Acquisition and Generation for more information National Instruments Corporation 8 1 LabVIEW Data Acquisition Basics Manual 8 Controlling Your Acquisition with Triggers The single point and waveform acquisitions described in the previous chapters start at random times relative to the data However there are times when you need to be able to set your analog acquisition to start at a certain time An example of this would be if you wanted to me
149. can clock The clock controlling the time interval between scans On boards with interval scanning support for example the AT MIO 16F 5 this clock gates the channel clock on and off On boards with simultaneous sampling for example the EISA A2000 this clock clocks the track and hold circuitry scan rate The number of times or scans per second that LabVIEW acquires data from channels For example at a scan rate of 10 Hz LabVIEW samples each channel in a group 10 times per second scan width The number of channels in the channel list or number of ports in the port list you use to configure an analog or digital input group SCXI Signal Conditioning eXtensions for Instrumentation The National Instruments product line for conditioning low level signals within an external chassis near sensors so only high level signals in a noisy environment are sent to data acquisition boards settling time The amount of time required for a voltage to reach its final value within specified limits signal conditioning The manipulation of signals to prepare them for digitizing signal divider Performing frequency division on an external signal simple buffered I O Input output operation that uses a single memory buffer big enough for all of your data LabVIEW transfers data into or out of this buffer at the specified rate beginning at the start of the buffer and stopping at the end of the buffer You use simple buffered I O when you acquire sm
150. chart for display on the front panel The Wait Until Next ms Multiple metronome function controls the loop timing After you enter a scan rate the application converts the value into milliseconds and passes the converted value to the Wait Until Next ms Multiple function The loop then executes at the rate of scanning The loop ends when you press the stop button or an when error occurs After the loop finishes the Simple Error Handler VI displays any errors that occurred The previous examples use software timed acquisition With this type of acquisition the CPU system clock controls the rate at which you acquire data Your system clock can be interrupted by user interaction so if you do not need a precise acquisition rate use software timed analog input Chapter 6 One Stop Single Point Acquisition National Instruments Corporation 6 5 LabVIEW Data Acquisition Basics Manual Using Analog Input Output Control Loops When you want to output analog data after receiving some analog input data use analog input output I O control loops With control loops this process is repeated over and over again The single point analog input and output VIs support several analog I O control loops at once because you can acquire analog inputs from several different channels in one scan and write all the analog output values with one update You perform a single analog input call process the analog output values for each channel and then perform a
151. ck and a digital trigger signal at the same time You must choose one or the other Because LabVIEW determines the length of time before the AI Read VI times out based on the interchannel delay and scan clock rate you may need to force a time limit for the AI Read VI as illustrated in the Acquire N Scans ExtChanClk VI described previously Note On the Lab PC and 1200 devices the first clock pulse on the EXTCONV pin configures the acquisition but does not cause a conversion However all subsequent pulses cause conversions Chapter 9 Letting an Outside Source Control Your Acquisition Rate National Instruments Corporation 9 5 LabVIEW Data Acquisition Basics Manual Figure 9 4 shows an example of using an external scan clock to perform a buffered acquisition Figure 9 4 Block Diagram of a VI Acquiring Data with an External Scan Clock Externally Controlling Your Scan Clock External scan clock control might be more useful than external channel clock control if you are sampling multiple channels but might not be as obvious to find because it does not have the input on the I O connector labeled ExtScanClock the way the EXTCONV pin does Note Some MIO devices have an output on the I O connector labeled SCANCLK which is used for external multiplexing and is not the analog input scan clock This cannot be used as an input Chapter 9 Letting an Outside Source Control Your Acquisition Rate LabVIEW Data Acquisition Basics Manu
152. configured in two ways a front end signal conditioning system for plug in DAQ devices or an external data acquisition and control system Furthermore when SCXI is configured as an external data acquisition and control system it can be connected to the computer s parallel port using an SCXI 1200 or the computer s serial port using either an SCXI 2000 remote chassis or an SCXI 2400 remote communications module in an SCXI 100x chassis For Macintosh computers SCXI hardware can be used only as a front end signal conditioning system for plug in DAQ devices Figure 20 1 demonstrates these configurations Chapter 20 Hardware and Software Setup for Your SCXI System LabVIEW Data Acquisition Basics Manual 20 2 www ni com Figure 20 1 SCXI System Figure 20 2 shows the components of an SCXI system An SCXI system consists of an SCXI chassis that houses signal conditioning modules terminal blocks that plug directly into the front of the modules and a cable assembly that connects the SCXI system to a plug in DAQ device or the parallel or serial port of a computer If you are using SCXI as an external DAQ system where there are no plug in DAQ devices you can use the SCXI 1200 module which is a multifunction analog digital and timing I O counters module The SCXI 1200 can control several SCXI signal conditioning modules installed in the same chassis The functionality of the SCXI 1200 module is similar to the plug in 1200 series devices
153. continuous acquisition from multiple channels 7 8 to 7 9 determining adequate buffer capacity A 2 examples 7 10 to 7 11 how circular buffers work 7 7 to 7 8 overview 7 6 to 7 7 simple buffered analog input displaying waveforms on graphs example 7 4 to 7 5 how buffers work 7 2 multiple waveform acquisition 7 3 to 7 4 overview 7 1 sampling with multiple starts example 7 5 to 7 6 single waveform acquisition 7 2 to 7 3 waiting to analyze data 7 1 to 7 2 simultaneous acquisition and generation 14 1 to 14 4 E series MIO boards 14 1 to 14 2 Lab 1200 boards 14 4 legacy MIO boards 14 3 buffered waveform generation buffered analog output 12 1 to 12 3 examples 12 4 to 12 5 choosing between single point or multiple point generation 4 4 circular buffered output 12 3 to 12 4 eliminating errors 12 4 overview 10 1 to 10 2 Burst Mode Input VI 17 6 Burst Mode Output VI 17 6 C calibration See SCXI calibration cascading counters defined 28 2 external connections figures 28 2 to 28 3 Change Detection Input VI 18 2 Index LabVIEW Data Acquisition Basics Manual I 6 www ni com channel addressing 3 8 to 3 11 AMUX 64T devices 5 14 to 5 18 analog input channel range table 5 14 scanning order 5 15 to 5 18 channel name addressing 3 9 channel number addressing 3 10 to 3 11 SCXI modules 21 1 to 21 2 channel clock 9 3 to 9 5 channel and scan intervals using channel clock figure 9 1 consideratio
154. counter to wait for the gate signal from counter 1 The gate mode for the Delayed Pulse Generator Config VI can be set to a single or multiple edges In other words you could produce one finite pulse train or multiple pulse trains The GATE signal for counter 1 can be from an external device or from another counter on your DAQ device DAQ STC With the DAQ STC chip you can internally route the OUT of one counter to the GATE of the next higher order counter as shown in Figure 25 10 You optionally can GATE counter 1 While you use two counters you do not need to externally wire between the OUT of counter 1 and the GATE of counter Figure 25 10 External Connections Diagram from the Front Panel of Finite Pulse Train Adv DAQ STC VI The example Finite Pulse Train Adv DAQ STC VI located in labview examples daq counter DAQ STC llb takes advantage of internal wiring This example uses the Advanced counter VIs The top row of counter VIs sets up counter to output a pulse train Notice that the gate source input to the CTR Mode Config VI is set to output of next lower order counter This sets the internal wiring such that counter will be gated by counter 1 The bottom row of counter VIs sets up counter 1 to output a single pulse The width of the pulse is calculated so it gates counter just long enough to output the chosen number of pulses For a complete description of this example refer to the information found in Windows Show VI Info 8253
155. counting methods 4 5 counting events or elapsed time 28 1 to 28 7 connecting counters 28 1 to 28 3 elapsed time 28 5 to 28 7 events 28 3 to 28 5 counting operations with no counters available 25 12 to 25 13 digital vs counter interfacing 4 4 dividing frequencies 29 1 to 29 3 frequency and period measurement 27 1 to 27 8 connecting counters for measuring 27 3 to 27 4 high frequency signals 27 4 to 27 6 how and when to measure 27 1 to 27 2 low frequency signals 27 7 to 27 8 gating modes figure 24 4 pulse train generation 25 7 to 25 12 continuous pulse train 25 7 to 25 9 finite pulse train 25 9 to 25 12 pulse width measurement 26 1 to 26 8 controlling pulse width measurement 26 5 to 26 6 determining pulse width 26 2 to 26 5 increasing measurable width range 26 7 to 26 8 square pulse generation 25 1 to 25 7 8253 54 25 4 single square pulse generation 25 4 to 25 7 TIO ASIC DAQ STC and Am9513 25 3 stopping counter generations 25 14 to 25 15 timebase uncertainty 25 13 CTR Buffer Config VI 26 7 CTR Buffer Read VI 26 7 CTR Control VI buffered pulse and period measurement 26 7 enabling and disabling FOUT signal 25 12 measuring frequency and period 27 5 CTR Group Config VI 26 7 CTR Mode Config VI buffered pulse and period measurement 26 7 finite pulse train generation 25 11 current setting for VIs 3 6 current value conventions for VIs 3 6 D daisy chaining SCXI chassis 22 20 to 22 21 D
156. cquired Do you want to acquire a predetermined or indefinite number of data points If you want to analyze your data as it is being measured and the number of data points does not matter read the Do You Need to Access Your Data during Acquisition section in this chapter If you acquire a predetermined number of data points and you want to analyze the data after it has been acquired refer to the Can You Wait for Your Data section in this chapter Also throughout the chapter are some basic examples of some common DAQ applications that use these two methods Can You Wait for Your Data One way to acquire multiple data points for one or more channels is to use the non buffered methods described in the previous chapter in a repetitive manner For example you could compare this method to a trip to the grocery store You need to get 20 items from the store but because you can t carry all 20 items at once you decide you must make 20 separate trips to the store Grocery shopping in this manner would be very inefficient and time consuming The same applies for when you are acquiring a single data point from one or more channels over and over Also with this method of acquisition you do not have accurate control over the time between each sample or channel Going back to the example of grocery shopping it would be much more efficient to use a shopping bag to hold all 20 food items at once so that you have to make only one trip In the sa
157. ctions for determining pulse width figure 26 2 Pulse Width or Period Meas Config VI 27 8 pulsed counter signal generation 25 1 Q questions about using DAQ devices 4 3 to 4 5 LabVIEW data acquisition questions A 1 to A 3 R range See device range Read 1 Pt from from Dig Line E VI 16 3 Read from 1 Dig Port 653x VI 16 3 Read from 1 Dig Port 8255 VI 16 3 Read from 1 Dig Port E VI 16 4 Read from 1Dig Line 653x VI 16 2 Read from 1Dig Line 8255x VI 16 2 Read from 2 Dig Port 653x VI 16 3 Read from 2 Dig Port 8255 VI 16 3 Read from Digital Port VI 22 17 Read from Digital Port 653x VI 16 3 Read from Digital Port 8255 VI 16 3 referenced signal sources 5 2 referenced single ended RSE measurement system 5 12 relay SCXI modules 20 6 Remote SCXI sampling rate limits note 20 4 REQ Request line 17 2 Resistance Temperature Detectors RTDs 22 10 to 22 13 resolution of ADC 5 4 round robin scanning figure 9 2 row major order 3 14 RSE referenced single ended measurement system 5 12 RTD Conversion VI 22 12 RTDs for measuring temperature 22 10 to 22 13 S SC 2042 RTD device 22 11 Scale Constant Tuner VIs 23 7 Scaling Constant Tuner VI 22 6 22 8 scan clock 9 5 to 9 7 block diagram of VI acquiring data figure 9 5 channel and scan intervals using channel clock figure 9 1 Index LabVIEW Data Acquisition Basics Manual I 18 www ni com devices without scan clocks note 9 6
158. cy source Chapter 26 Measuring Pulse Width LabVIEW Data Acquisition Basics Manual 26 2 www ni com An internal signal is based upon the type of counter chip on your DAQ device With TIO ASIC devices you can choose internal timebases of 20 MHz 100 kHz and a device specific maximum timebase With DAQ STC devices you have a choice between internal timebases of 20 MHz and 100 kHz With Am9513 devices you can choose internal timebases of 1 MHz 100 kHz 10 kHz 1 kHz and 100 Hz With 8253 54 devices the internal timebase is either 2 MHz or 1 MHz depending on which device you have Figure 26 2 shows how to physically connect the counter on your device to measure pulse width Figure 26 2 Physical Connections for Determining Pulse Width Determining Pulse Width How you determine a pulse width depends upon which counter chip is on your DAQ device If you are uncertain of which counter chip your DAQ device has refer to your hardware documentation TIO ASIC DAQ STC Refer to the block diagram of the Measure Pulse Easy DAQ STC VI located in labview examples daq counter DAQ STC llb which uses the Easy VI Measure Pulse Width or Period The Measure Pulse Width or Period VI counts the number of cycles of the specified timebase depending on your choice from the type of measurement menu located on the front panel of the VI counter your device gate source out Chapter 26 Measuring Pulse Width National Instruments
159. d Analog Input For information on starting your acquisition with triggers refer to Chapter 8 Controlling Your Acquisition with Triggers Do You Need to Access Your Data during Acquisition You can apply the simple buffering techniques in many DAQ applications but there are some applications where these techniques are not appropriate If you need to acquire more data than your computer memory can hold or if you want to acquire data over long periods of time you should not use these simple buffered techniques For these types of applications you should set up a circular buffer to store acquired data in memory Earlier in this chapter buffered input was compared to shopping for groceries You Chapter 7 Buffering Your Way through Waveform Acquisition National Instruments Corporation 7 7 LabVIEW Data Acquisition Basics Manual typically use a cart or bag your buffer to hold as many groceries your acquired data as possible so that you have to make only one trip to the store In this case imagine that you must prepare a meal and you are unable to go shopping yet periodically you need things from the store for your recipe If you send someone else to the store for you you can continue to prepare dinner while someone else retrieves the other items you need You can compare this scenario to circular buffered data acquisition shown in Figure 7 4 Using a circular buffer you can set up your device to continuously acquire data in the
160. d Know about Analog Input Hunting has been a part of survival from the beginning of time People used to hunt for the things they needed to survive like food and water Today engineers and scientists use data acquisition to hunt down the information they need to survive in the information age This chapter focuses on defining the tools you need to be a successful hunter in the world of data acquisition Defining Your Signal You and your friends plan a hunting trip for this weekend What do you plan to bring with you This question is really not valid because you must know first what you will be hunting before you pack your fishing pole or elephant rifle The same idea applies to scientists and engineers engaged in the quest for information You must know the defining characteristics of what you want to hunt be it a wild animal or an analog signal You cannot just say I will hunt voltages or even I will hunt analog voltages Voltages come in various forms This chapter gives you the terms tools and techniques designed to help show you the best way to catch your wave Analog signals can be grouped into three categories DC time domain and frequency domain You must ask yourself Is the information I seek primarily contained in the level the shape or the frequency content of my signal Figure 5 1 illustrates which signals correspond to certain types of signal information Chapter 5 Things You Should Kno
161. d handshaking and simple buffered handshaking is that with iterative handshaking data is read from the buffer before the buffer has been filled This allows you to see data as it is acquired as opposed to waiting until all the data has been handshaked into the buffer It also may free up processor time spent waiting for the buffer to fill 6533 Family The example Dig Buf Hand Iterative 653x VI shows how to read data as it is being handshaked into a buffer Select Windows Show VI Info for more information about using and testing this VI 8255 Family The example Dig Buf Hand Iterative 8255 VI shows how to read data as it is being handshaked into a buffer Another example Dig Buf Hand Occur 8255 VI also uses iterative reads This example which works only on the Windows platform also shows how to use DAQ Occurrences to search for specific bit patterns in a port These examples are located in labview examples daq digital 8255 llb Select Windows Show VI Info for any of these examples for more information about using and testing them Circular Buffered Handshaking A circular buffer differs from a simple buffer only in the way your program places the data into it and retrieves data from it A circular buffer fills with data the same as a simple buffer but when it reaches the end of the buffer LabVIEW returns to the beginning of the buffer and fills up the same buffer again Use simple buffered handshaking when you have a predetermined n
162. d module in each chassis to a DAQ device to communicate with any multiplexed modules in the chassis Multiplexed Mode for Digital and Relay Modules Multiplexed mode is referred to as serial mode in the digital and relay module hardware manuals When you operate your digital or relay module in multiplexed mode LabVIEW communicates the module channel states serially over the SCXIbus backplane Parallel Mode for Analog Input Modules When an analog input module operates in parallel mode the module sends each of its channels directly to a separate analog input channel of the DAQ device cabled to the module You cannot multiplex parallel outputs of a module on the SCXIbus You must cable a DAQ device directly to a module in parallel mode to access its input channels In this configuration the number of channels available on the DAQ device limits the total number of analog input channels In some cases however you can cable more than one DAQ device to separate modules in an SCXI chassis For example you can use two NB MIO 16X or AT MIO 16E 2 devices operating in parallel mode and cable each one to a separate SCXI 1120 module in the chassis For more information on how to configure the cabled device refer to the help file for Measurement amp Automation Explorer by Chapter 20 Hardware and Software Setup for Your SCXI System National Instruments Corporation 20 7 LabVIEW Data Acquisition Basics Manual selecting Help Help Topics DAQ H
163. default settings for parameters such as analog input polarity and range on a per device basis If you are using AMUX 64T or signal conditioning devices with your DAQ device select the appropriate device from the Accessories menu LabVIEW uses these settings when initializing the device instead of the default settings listed in the descriptions of the hardware configuration VIs Use these VIs to change any setting recorded Chapter 2 Installing and Configuring Your Data Acquisition Hardware LabVIEW Data Acquisition Basics Manual 2 6 www ni com by NI DAQ When you click the name of the device NI DAQ displays the I O connector for the device as shown in Figure 2 5 Figure 2 5 Device Configuration Dialog Box and I O Connector Display in NI DAQ Click the Help button to find additional information If at any time during configuration you need to view a list of the LabVIEW DAQ error codes and their meanings click the NI DAQ menu bar located to the right of the Help button and select Errors Note Some DAQ devices such as the Lab NB and NB MIO 16 devices require hardware jumper changes in addition to software configuration Consult your DAQ device hardware reference manual for more information Installing and Configuring Your SCXI Chassis The following section describes the procedures for installing and configuring your SCXI chassis Hardware Configuration Your SCXI hardware kit includes the Getting Started with SCXI manual whic
164. different counting modes counter 0 is set up to generate a timebase using the ICTR Timebase Generator subVI counter 1 is set up to toggle its output low to high when it reaches terminal count TC This toggled output is used to gate counter 2 counter 2 is set up to output a low pulse when its gate goes high In frame 2 of the sequence a delay occurs so the delayed pulse has time to complete before the example can be run again This is useful if the example is used as a subVI that is called repeatedly While this example works well for most pulses it has limitations when your pulse delay gets very short in the microsecond range or when the ratio of pulse delay to pulse width gets very large For a complete description of this example refer to the information found in Windows Show VI Info Generating a Pulse Train There are two types of pulse trains continuous and finite You can use a continuous pulse train as the SOURCE CLK of another counter or as the clock for analog acquisition or generation You can use a finite pulse train as the clock of an analog acquisition that acquires a predetermined number of points or to provide a finite clock to an external circuit Generating a Continuous Pulse Train How you generate a continuous pulse varies depending upon which counter chip your DAQ hardware has If you are not sure which chip your device uses refer to your hardware manual TIO ASIC DAQ STC Am9513 Figure 25 7 shows
165. different input limits for channels on the same module by splitting up your channel range over multiple elements of the channel array and using a different set of input limits for each element LabVIEW selects one module gain suitable for all of the input limits for that module then chooses different MIO AI gains to achieve the different input limits The last three examples in Table 21 1 illustrate this method The last example shows a channel list with two modules Chapter 21 Special Programming Considerations for SCXI LabVIEW Data Acquisition Basics Manual 21 4 www ni com You can open the AI Hardware Config VI to see the gain selection After running this VI the group channel settings cluster array at the right side of the panel shows the settings for each channel The gain indicator displays the total gain for the channel which is the product of the SCXI gain and the DAQ device gain and the actual limit settings The group channel settings cluster array also shows the input limits for each channel LabVIEW scales the input data as you specified unless you select binary data only Therefore the gains are transparent to the application You can specify the input signal limits and let LabVIEW do the rest Table 21 1 SCXI 1100 Channel Arrays Input Limits Arrays and Gains Array Index SCXI 1100 Channel List Array Input Limits Array LabVIEW Selected SCXI Gain LabVIEW Selected MIO AI Gain 0 ob0 sc1 md1 0 7 0
166. digital I O All DAQ devices and SCXI modules with digital components support this mode When your program calls a function subVI in nonlatched digital I O mode LabVIEW immediately writes or reads digital data If the digital direction is set to output LabVIEW updates the digital line or port output state If the digital direction is set to input LabVIEW returns the current digital line or port value For each function called LabVIEW inputs or outputs only one value on each digital line in this mode You can completely configure port and for some devices line direction in software and you can switch directions repeatedly in a program Application examples of nonlatched digital I O include controlling relays and monitoring alarm states You also can use multiple ports or groups of ports to perform digital I O functions If you want to group digital ports you must use Intermediate or Advanced I O VIs in LabVIEW Using Channel Names If you have configured channels using the DAQ Channel Wizard digital channel can consist of a digital channel name The channel name may refer to either a port or a line in a port You do not need to specify device line or port width because LabVIEW does not use these inputs if a channel name is specified in digital channel For more information about using the DAQ Channel Wizard to configure your channels refer to the Configuring Your Channels in NI DAQ 5 x 6 x section of Chapter 2 Installing and Con
167. e 5 5 resolution effects 5 4 adjacent counters for counter chips table 28 2 Adjacent Counters VI 27 5 Advanced VIs See also VIs Advanced Counter VIs note 26 7 analog output SCXI example 22 17 buffered pulse and period measurement 26 7 digital handshaking 17 5 external control of channel clock 9 4 finite pulse train generation 25 11 immediate digital I O 16 3 to 16 4 overview 3 5 AI Acquire Waveform VI 7 2 AI Acquire Waveforms VI multiple waveform acquisition 7 3 simple buffered analog input with graphing 7 4 to 7 5 AI Clear VI amplifier offset 22 5 multiple waveform acquisition 7 3 SCXI temperature measurement 22 8 simultaneous buffered waveform acquisition and generation 14 1 Index LabVIEW Data Acquisition Basics Manual I 2 www ni com AI Clock Config VI external control of channel clock 9 4 external conversions 9 4 retrieving channel clock setting 21 5 scan clock control 9 6 to 9 7 AI Config VI basic non buffered application 6 3 hardware timed analog I O control loops 6 6 to 6 7 interchannel delay 9 3 multiple channel single point analog input 6 4 multiple waveform acquisition 7 3 one point calibration 23 5 simultaneous buffered waveform acquisition and generation 14 1 AI Control VI 9 6 AI Hardware Config VI 21 4 AI Read One Scan VI 6 5 to 6 6 AI Read VI advantages and disadvantages of reading backlog A 1 asynchronous continuous acquisition using DAQ Occurrences 7 9 condition
168. e assembly combined with your SCXI module and its configuration settings Note If your SCXI module has independent gains on each channel the calibration constants for each channel are stored at each gain setting Chapter 23 SCXI Calibration Increasing Signal Measurement Precision LabVIEW Data Acquisition Basics Manual 23 4 www ni com SCXI Calibration Methods for Signal Acquisition There are two ways you can calibrate your SCXI module through one point calibration or two point calibration The following illustration explains why you may need to calibrate your SCXI module This illustration shows the difference between the ideal reading and the actual reading This difference is called Vos or the binary offset before the two readings intersect The difference in slope between the actual and ideal readings is called the gain error One point calibration removes the Vos binary offset by measuring a 0 V signal and comparing the actual reading to it Two point calibration removes the Vos binary offset and corrects gain error by first performing a one point calibration Then you measure a voltage at x volts and compare it to the actual reading The x must be as close as possible to the full scale range The following sections explain how to perform a one point and two point calibration Binary Reading Binary Offset Gain Error Vos Actual Voltage in Binary Representation Actual Reading Ideal Reading Chapter 2
169. e input limits range and polarity the VIs can infer the onboard gains when you do not use SCXI input range The difference between the maximum and minimum voltages an analog input channel can measure at a gain of 1 The input range is a scalar value not a pair of numbers By itself the input range does not uniquely determine the upper and lower voltage limits An input range of 10 V could mean an upper limit of 10 V and a lower of 0 V or an upper limit of 5 V and a lower limit of 5 V The combination of input range polarity and gain determines the input limits of an analog input channel For some boards jumpers set the input range and polarity while you can program them for other boards Most boards have programmable gains When you use SCXI modules you also need their gains to determine the input limits interrupt A signal indicating that the central processing unit should suspend its current task to service a designated activity interval scanning Scanning method where there is a longer interval between scans than there is between individual channels comprising a scan I O Input output The transfer of data to or from a computer system involving communications channels operator interface devices and or data acquisition and control interfaces ISA Industry Standard Architecture isolation A type of signal conditioning in which you isolate the transducer signals from the computer for safety purposes This protects you
170. e 12 3 Circular Buffered Waveform Generation Using Intermediate VIs The Function Generator VI located in labview examples daq anlogout anlogout llb is a more advanced example than the one shown in Figure 12 3 This VI changes the output waveform on the fly responding to changing signal types sine or square amplitude offset update rate and phase settings on the front panel Eliminating Errors from Your Circular Buffered Application If you get error number 10843 underFlowError while performing circular buffered output it means your program cannot write data fast enough to the buffer to output the data at the update rate To solve this problem decrease the speed of the update rate If adjusting the update rate does not fix this error in your application increase the buffer size Buffered Analog Output Examples Another example VI in this library you might find helpful is the Display and Output Acq d File scaled VI You can use this VI in conjunction with the Cont Acq to File scaled VI located in labview examples daq anlogin anolgin llb The Display and Output Acq d File scaled VI also is described in Chapter 7 Buffering Your Way through Waveform Acquisition After running the Cont Acq to File scaled VI and saving your acquired data to disk you can Chapter 12 Buffering Your Way through Waveform Generation National Instruments Corporation 12 5 LabVIEW Data Acquisition Basics Manual run the Display and O
171. e Period 25 13 Figure 25 13 Using the Generate Delayed Pulse and Stopping the Counting Operation 25 14 Figure 25 14 Stopping a Generated Pulse Train 25 15 Figure 26 1 Counting Input Signals to Determine Pulse Width 26 1 Figure 26 2 Physical Connections for Determining Pulse Width 26 2 Figure 26 3 Menu Choices for Type of Measurement for the Measure Pulse Width or Period DAQ STC VI 26 3 Figure 26 4 Menu Choices for Type of Measurement for the Measure Pulse Width or Period 9513 VI 26 4 Figure 26 5 Measuring Pulse Width with Intermediate VIs 26 6 Figure 27 1 Measuring Square Wave Frequency 27 2 Contents National Instruments Corporation xvii LabVIEW Data Acquisition Basics Manual Figure 27 2 Measuring a Square Wave Period 27 2 Figure 27 3 External Connections for Frequency Measurement 27 3 Figure 27 4 External Connections for Period Measurement 27
172. e SCXI Cal Constants VI and each of its parameters or refer to the LabVIEW Online Reference by selecting Help Online Reference For the SCXI 1112 and SCXI 1125 modules you can use the SCXI Calibrate VI for easy one point calibration SCXI 1125 or two point calibration SCXI 1112 without the separate function calls necessary with the SCXI Cal Constants VI One and two point calibration are described in the SCXI Calibration Methods for Signal Acquisition section later in this chapter You also can find the SCXI Calibrate VI in Functions Data Acquisition Calibration and Configuration By default calibration constants for the SCXI 1102 SCXI 1102B SCXI 1102C SCXI 1104 SCXI 1104C SCXI 1112 SCXI 1122 SCXI 1125 SCXI 1141 SCXI 1142 and SCXI 1143 are loaded from the module EEPROM The SCXI 1141 SCXI 1142 and SCXI 1143 have only gain adjust constants in the EEPROM They do not have the binary zero offset All other analog input modules do not have calibration constants by default and do not assume any binary offset and ideal gain settings This means you must use one of the procedures described in the SCXI Calibration Methods for Signal Acquisition section to store calibration constants for your module if it is not an SCXI 1102 SCXI 1112 SCXI 1122 SCXI 1125 SCXI 1141 SCXI 1142 or SCXI 1143 You can determine calibration constants based on your application setup which includes your type of DAQ device DAQ device settings and cabl
173. e change in the input signal You can calculate the smallest detectable change called the code width using the following formula For example a 12 bit DAQ device with a 0 to 10 V input range detects a 2 4 mV change while the same device with a 10 to 10 V input range detects only a change of 4 8 mV A high resolution A D converter provides a smaller code width given the device voltage ranges shown above The smaller your code width the more accurate your measurements will be There are times you must know whether your signals are unipolar or bipolar Unipolar signals are signals that range from 0 value to a positive value for example 0 to 5 V Bipolar signals are signals that range from a negative to a positive value for example 5 to 5 V To achieve a smaller code width if your signal is unipolar specify that the device range is unipolar as shown previously If your signal range is smaller than the device range set your limit settings to values that more accurately reflect your signal range Table 5 1 shows how the code width of the 12 bit DAQ devices varies with device ranges and limit settings because your limit settings automatically adjust the gain on your device code width device range 2resolution device range 2resolution 10 212 2 4 mV device range 2resolution 20 212
174. e data is stored in a circular buffer in memory in order to reuse finite computer memory resources Circular buffering for input works in the following manner while the buffer is being filled by data acquired from the board LabVIEW reads data out of the buffer for processing for example to save to disk or update screen graphics When the buffer is filled the operation resumes at the beginning of the buffer In this manner continuous data collection and processing can Chapter 18 Timed Digital I O National Instruments Corporation 18 3 LabVIEW Data Acquisition Basics Manual be sustained indefinitely assuming your application can retrieve and process data faster than the buffer is being filled A similar buffering technique is used when generating digital output data continuously The Cont Pattern Input VI Cont Change Detection Input VI and Cont Pattern Output VI show how to continuously acquire or generate digital data These examples are located in labview daq examples digital 653x llb National Instruments Corporation V 1 LabVIEW Data Acquisition Basics Manual Part V SCXI Getting Your Signals in Great Condition This part of the manual contains basic information about setting up and using SCXI modules with your data acquisition application special programming considerations common SCXI applications and calibration information Part V SCXI Getting Your Signals in Great Condition contains the following cha
175. e is multiplexed in the channel list For example if you have no AMUX 64T devices a channel list element of 0 specifies device channel 0 If you have an AMUX 64T device a channel list element of 0 specifies channels 0 through 3 on each AMUX 64T device Table 5 2 shows the number of channels available on a DAQ device with an external multiplexer Table 5 2 Analog Input Channel Range Number of AMUX 64Ts Channel Range Single Ended Channel Range Differential 0 0 through 15 0 through 7 1 AM1 0 through AM1 63 AM1 0 through AM1 31 2 AM1 0 through AM1 63 AM2 0 through AM2 63 AM1 0 through AM1 31 AM2 0 through AM2 31 4 AM1 0 through AM1 63 AM2 0 through AM2 63 AM3 0 through AM3 63 AM4 0 through AM4 63 AM1 0 through AM1 31 AM2 0 through AM2 31 AM3 0 through AM3 31 AM4 0 through AM4 31 Chapter 5 Things You Should Know about Analog Input National Instruments Corporation 5 15 LabVIEW Data Acquisition Basics Manual You specify the number of AMUX devices through the configuration utility or the AI Hardware Config VI Refer to the LabVIEW Function and VI Reference Manual or select Help Online Reference for more information about this VI The AMUX 64T Scanning Order This section explains how LabVIEW scans channels from the AMUX 64T You must know this scanning order so that you can determine which analog input channel LabVIEW scanned during a data acquisition operation The scanning counters on t
176. e memory buffer and displays it For more information on buffered acquisitions refer to Chapter 7 Buffering Your Way through Waveform Acquisition You must tell your device the conditions on which to start acquiring data For this example the choose trigger type Boolean should be set to START OR STOP TRIGGER Select START amp STOP TRIGGER only when you have two triggers start and stop In addition if you use a DAQ device with PFI lines for example E Series 5102 devices you can specify the trigger signal condition in the trigger channel control in the analog chan amp level cluster For more information on valid trigger channel names or two trigger applications refer to the AI Trigger Config VI description in Chapter 18 Advanced Analog Input VIs of the LabVIEW Function and VI Reference Manual or to the LabVIEW Online Reference available by selecting Help Online Reference You can acquire data both before and after a digital trigger signal If pretrigger scans is greater than 0 your device acquires data before the triggering conditions are met It then subtracts the pretrigger scans value from the number of scans to acquire value to determine the number of scans to collect after the triggering conditions are met If pretrigger scans is 0 you acquire the number of scans to acquire after the triggering conditions are met Before you start acquiring data you must specify in the trigger edge input whether the acquisition is t
177. e signal to a DAQ device without some type of isolation Another reason for isolation is to make sure the measurements from the DAQ device are not affected by differences in ground potentials When the DAQ device and the signal are not referenced to the same ground potential a ground loop may occur Ground loops can cause an inaccurate representation of the measured signal If the potential difference between the signal ground and the DAQ device ground is large damage can even occur to the measuring system Using isolated SCXI modules eliminates the ground loop and ensures that the signals are accurately measured Filtering Signal conditioning systems can filter unwanted signals or noise from the signal you are trying to measure You can use a noise filter on low rate or slowly changing signals such as temperature to eliminate higher frequency signals that can reduce the accuracy of the digitized signal A common use of a filter is to eliminate the noise from a 50 or 60 Hz AC power line A lowpass filter of 4 Hz which exists on several SCXI modules is suitable for removing the 50 or 60 Hz AC noise from signals sampled at low rates A lowpass filter eliminates all signal frequency components above the cutoff frequency The SCXI 1141 SCXI 1142 and SCXI 1143 modules have lowpass filters that have software selectable cutoff frequencies from 10 Hz to 25 kHz Transducer Excitation Signal conditioning systems can generate excitation for som
178. e transducers Strain gauges and RTDs require external voltage and currents respectively to excite their circuitry into measuring physical phenomena This type of excitation is similar to a radio that needs power to receive and decode audio signals Some plug in DAQ devices and SCXI modules including the SCXI 1121 and SCXI 1122 modules provide the necessary excitation for transducers Chapter 19 Things You Should Know about SCXI LabVIEW Data Acquisition Basics Manual 19 6 www ni com Linearization Many transducers such as thermocouples have a nonlinear response to changes in the physical phenomena being measured LabVIEW can linearize the voltage levels from transducers so the voltages can be scaled to the measured phenomena LabVIEW provides simple scaling functions to convert voltages from strain gauges RTDs thermocouples and thermistors For specific information about the VIs you can use with your SCXI module in LabVIEW refer to Chapter 29 Calibration and Configuration VIs in the LabVIEW Function and VI Reference Manual or refer to the LabVIEW Online Reference by selecting Help Online Reference National Instruments Corporation 20 1 LabVIEW Data Acquisition Basics Manual 20 Hardware and Software Setup for Your SCXI System SCXI hardware conditions signals close to the signal source and increases the number of analog and digital signals that a DAQ device can analyze With PC compatible computers SCXI can be
179. e varying voltages in response to stress or vibrations in materials Strain gauges are thin conductors attached to the material to be stressed Resistance changes in parts of the strain gauge to indicate deformation of the material Strain gauges require excitation generally voltage excitation and linearization of their voltage measurements Depending on the strain gauge configuration another requirement for using strain gauges with SCXI is a configuration of resistors As shown in Figure 22 6 the resistance from the strain gauges combined with the SCXI hardware form a diamond shaped configuration of resistors known Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 14 www ni com as a Wheatstone bridge When you apply a voltage to the bridge the differential voltage Vm varies as the resistor values in the bridge change The strain gauge usually supplies the resistors that change value with strain Figure 22 6 Half Bridge Strain Gauge Strain gauges come in full bridge half bridge and quarter bridge configurations For a full bridge strain gauge the four resistors of the Wheatstone bridge are physically located on the strain gauge itself For a half bridge strain gauge the strain gauge supplies two resistors for the Wheatstone bridge while the SCXI module supplies the other two resistors as shown above For a quarter bridge strain gauge the strain gauge supplies only one of the four resistors for a Whea
180. e waveform acquisition 7 3 to 7 4 multiple channel single point analog input 6 2 to 6 4 scan clock control 9 5 to 9 7 9 7 SCXI applications for measuring temperature example 22 2 to 22 13 selecting input settings 5 7 to 5 14 calculating code width 5 7 considerations for selecting 5 7 to 5 8 differential measurement system 5 9 to 5 11 measurement precision for various device ranges and limit settings table 5 8 nonreferenced single ended measurement system 5 13 to 5 14 referenced single ended measurement system 5 12 signals 4 3 5 1 to 5 6 simple buffered analog input examples 7 4 to 7 6 simultaneous scan and channel clock control 9 7 single waveform acquisition 7 2 to 7 3 single channel single point analog input 6 1 to 6 2 software triggering 8 8 to 8 11 terminology 5 18 triggering 8 5 to 8 8 Analog Input palette 6 1 analog input SCXI modules applications for measuring temperature example 22 2 to 22 13 multiplexed mode 20 5 to 20 6 parallel mode 20 6 to 20 7 Index LabVIEW Data Acquisition Basics Manual I 4 www ni com analog input signals choosing a measurement system 5 4 to 5 6 choosing between analog and digital signals 4 3 defining signals 5 1 to 5 2 device range 5 5 floating signal sources 5 3 grounded signal sources 5 2 to 5 3 referenced and non referenced 5 2 resolution of ADC 5 4 signal limit settings 5 6 types of analog signals figure 5 2 analog input output control loop
181. earch position another input of the AI Read VI The offset a value of the conditional retrieval input cluster is where you specify the scan locations from which the VI begins reading data relative to the read search position A negative offset indicates data prior to the retrieval condition pretrigger data and a positive offset indicates data after the retrieval condition posttrigger data The skip count input is where you specify the number of times the trigger conditions are met The hysteresis input is where you specify the range you will use to meet retrieval conditions Once the slope and level conditions on channel index have been found the read search position indicates the location where the retrieval conditions were met Chapter 8 Controlling Your Acquisition with Triggers National Instruments Corporation 8 11 LabVIEW Data Acquisition Basics Manual If you are using channel names configured in the DAQ Channel Wizard level and hysteresis are treated as being relative to the physical units specified for the channel If you are not using channel names these inputs are treated as volts For more information on the conditional retrieval input cluster refer to the AI Read VI description in Chapter 16 Intermediate Analog Input VIs in the LabVIEW Function and VI Reference Manual or the LabVIEW Online Reference available by selecting Help Online Reference Conditional Retrieval Examples The Acquire N Scans Analog Software Tr
182. ed The AI Single Scan VI scaled data output array is empty if the scan was not yet acquired Poll for your analog input by using a Wait ms or Wait Until Next ms Multiple function together with the AI Single Scan VI in a While Loop within your control loop diagram Set the wait time smaller than your control loop interval at least half as small If the scaled data output array is not empty exit the polling loop passing out the scaled data array and execute the rest of your control loop diagram This method does not return data as soon as the scan has been acquired as in the example described previously but provides ample time for other VIs and loops to execute This method is a good technique for balancing the CPU load between several loops and VIs running in parallel For more control examples refer to the VIs located in examples daq solution control llb National Instruments Corporation 7 1 LabVIEW Data Acquisition Basics Manual 7 Buffering Your Way through Waveform Acquisition If you want to take more than one reading on one or more channels there are two techniques you can use depending on what you want to do with the data after you acquire it This chapter reviews these different methods and explains how LabVIEW stores the acquired data with each method You can determine which method you should use by answering the following questions Do you want to analyze your data as it is being acquired or after it has been a
183. ed for analog output in Chapter 12 Buffering Your Way through Waveform Generation AO Config AO Write AO Start and AO Clear for waveform generation here By following the error cluster wire which enters each DAQ VI on the bottom left and exits on the bottom right you can see that because of data dependency the waveform generation starts before the waveform acquisition and each task is configured to run continuously This example VI is software triggered because it starts via software when you click the Run button Once you call the AO Start and AI Start VIs the While Loop executes Inside the While Loop the AI Read VI returns acquired data from the analog input buffer There is not a call to the AO Write VI inside the While Loop because it is not needed if the same data from the first AO Write VI Chapter 14 Simultaneous Buffered Waveform Acquisition and Generation LabVIEW Data Acquisition Basics Manual 14 2 www ni com is regenerated continuously To generate new data each time the While Loop iterates add an AO Write VI inside the While Loop The While Loop stops when an error occurs or you click the Stop button Your DAQ device resources are cleared by calling the AI Clear and AO Clear VIs after the loop stops For a complete description instructions and I O connections for this VI select Windows Show VI Info from the front panel of the VI Hardware Triggered Open the Simul AI AO Buffered Trigger E Series MIO VI loca
184. ed signal sources have voltage signals that are referenced to a system ground such as earth or a building ground Devices that plug into a building ground through wall outlets such as signal generators and power supplies are the most common examples of grounded signal sources as shown in Figure 5 2 Analog Signal Time Domain Frequency Domain DC ADC DAC slow ADC DAC fast ADC fast Analysis Level Shape Freq Content t t f 0 985 Chapter 5 Things You Should Know about Analog Input National Instruments Corporation 5 3 LabVIEW Data Acquisition Basics Manual Figure 5 2 Grounded Signal Sources Floating Signal Sources Floating signal sources contain a signal such as a voltage that is not connected to an absolute reference such as earth or a building ground Some common examples of floating signals are batteries battery powered sources thermocouples transformers isolation amplifiers and any instrument that explicitly floats its output signal Notice that in Figure 5 3 neither terminal of the floating source is connected to the electrical outlet ground Figure 5 3 Floating Signal Sources Now that you know how your signal is referenced read on to learn about the different systems available to acquire these signals Vs Ground _ Vs Ground _ Chapter 5 Things You Should Know about Analog Input LabVIEW Data Acquisition Basics Manual 5 4 www ni com Choosing You
185. el by channel basis Refer to the SCXI 1120 or SCXI 1121 user manuals for specific instructions If you are measuring thermocouples with the SCXI 1125 or the SCXI 1112 refer to the examples in the appropriate LLB for the module located in labview examples daq scxi These examples demonstrate how to scan the cold junction compensation channel cjtemp while scanning the thermocouple channels By scanning the cold junction sensor with the thermocouple channels these examples are better suited to take temperature measurements over longer periods of time by accounting for temperature changes at the thermocouple junction inside the terminal block The SCXI 1125 thermocouple example also demonstrates the ability to shunt the inputs and take an offset reading before collecting temperature data This allows you to compensate for any offset drift due to operation at elevated temperatures or for offset produced by the system along the signal path Measuring Temperature with RTDs Resistance temperature detectors RTDs are temperature sensing devices whose resistance increase with temperature They are known for their accuracy over a wide temperature range RTDs require current excitation to produce a measurable voltage RTDs are available in 2 wire 3 wire or 4 wire configuration The lead wires in the 4 wire configuration are resistance matched If you use a 2 wire or 3 wire RTD they are unmatched Resistance in the lead wires that connect your RTD to
186. el conditions are met before starting a buffered acquisition If you use channel names configured in the DAQ Channel Wizard trigger level is treated as being relative to the physical units specified for the channel in the DAQ Channel Wizard Otherwise trigger level is treated as volts Chapter 8 Controlling Your Acquisition with Triggers LabVIEW Data Acquisition Basics Manual 8 8 www ni com The Acquire N Scans Analog Hardware Trig VI example located in labview examples daq anlogin anlogin llb holds the data in a memory buffer until the device completes data acquisition The number of data points you want to acquire must be small enough to fit in memory This VI views and processes the information only after the acquisition If you need to view and process information during the acquisition use the Acquire amp Proc N Scans Trig VI located in labview examples daq anlogin anlogin llb If you expect multiple analog trigger signals that will start multiple acquisitions use the example Acquire N Multi Analog Hardware Trig VI located in labview examples daq anlogin anlogin llb Software Triggering With software triggering you can simulate an analog trigger using software This form of triggering is often used in situations where hardware triggers are not available Another name for software triggering signals specifically analog signals is conditional retrieval With conditional retrieval you set up your DAQ device to collect data
187. elp or the Installing and Configuring Your SCXI Chassis section in Chapter 2 Installing and Configuring Your Data Acquisition Hardware for the Macintosh By default when a module operates in parallel mode the module sends its channel 0 output to differential analog input channel 0 of the DAQ device the channel 1 output to analog input channel 1 of the DAQ device and so on When you use the analog input VIs specify the correct onboard channel for each parallel SCXI channel If you are using a range of SCXI channels LabVIEW assumes the onboard channel numbers match the SCXI channel numbers Refer to the SCXI Channel Addressing section in Chapter 21 Special Programming Considerations for SCXI for the proper SCXI channel syntax Parallel Mode for the SCXI 1200 Windows In parallel mode the SCXI 1200 reads only its own analog input channels The SCXI 1200 does not have access to the analog bus on the SCXI backplane in parallel mode You should use parallel mode if you are not using other SCXI analog input modules in the chassis with the SCXI 1200 Parallel Mode for Digital Modules When you operate a digital module in parallel mode the digital lines on your DAQ device directly drive the individual digital channels on your SCXI module You must cable a DAQ device directly to every module operated in parallel mode You may want to use parallel mode instead of multiplexed mode for faster updating or reading of the SCXI digital channel
188. en the VI and continue reading this section To reduce the noise on the slowly varying signals produced by thermocouples you can average the data and then linearize it For greater accuracy you can measure the amplifier offset which helps scale the data and lets you eliminate the offset error from your measurement The following block diagram shows how you can program the Acquire and Chapter 22 Common SCXI Applications National Instruments Corporation 22 7 LabVIEW Data Acquisition Basics Manual Average VI to measure the amplifier offset You can find this VI in vi lib daq zdaqutil llb This VI acquires 100 measurements from the amplifier offset designated in the offset channel input by calgnd and then averages the measurements When you determine the amplifier offset you must always use the same input limits and clock rates that you will be using in the acquisition The Acquire and Average VI can measure the amplifier offset of many modules at once but in Figure 22 1 it measures only one module Figure 22 1 Measuring a Single Module with the Acquire and Average VI After measuring the amplifier offset measure the temperature sensor for cold junction compensation Both the amplifier offset and cold junction measurements should be taken before any thermocouple measurements are taken Use the Acquire and Average VI to measure temperature sensors as shown in Figure 22 2 The main differences between the amplifier offset measuremen
189. enerates one value for one channel If you want more control over the limit settings for each channel you also can program a single point update using the Intermediate Analog Output VI AO Write One Update In this VI your program passes the error information to the Simple Error Handler VI The iteration input optimizes the execution of this VI if you place it in a loop With Intermediate VIs you gain more control over when you can check for errors Chapter 11 One Stop Single Point Generation LabVIEW Data Acquisition Basics Manual 11 2 www ni com Multiple Immediate Updates Open the Write N Updates example VI located in labview examples daq anlogout anlogout llb to see a VI that performs multiple updates Its block diagram resembles the one shown for the AO Write One Update VI described previously except that the While Loop executes the subVI repeatedly until either the error status or the stop Boolean is TRUE You can use the Easy Analog Output VI AO Write One Update in a loop but this is inefficient because the Easy I O VIs configure the device every time they execute The AO Write One Update VI configures the device only when the value of the iteration input is set to 0 The Write N Updates example VI illustrates an immediate software timed analog output VI application This means that software timing in a loop controls the update rate One good reason to use immediate software timed output is that your application calcula
190. er the device or input limits Instead enter a channel name in the channel input and the value returned is relative to the physical units you specified for that channel in the DAQ Channel Wizard If you specify the input limits they are treated as being relative to the physical units of the channel LabVIEW ignores the device input when channel names are used This principle applies throughout this manual The Acquire 1 Point from 1 Channel VI shows how to use the AI Sample Channel VI to acquire data This example is located in labview examples daq anlogin anlogin llb Open and examine its block diagram Chapter 6 One Stop Single Point Acquisition LabVIEW Data Acquisition Basics Manual 6 2 www ni com The Acquire 1 Point from 1 Channel VI initiates an A D conversion on the DAQ device and returns the scaled value as an output The high limit is the highest expected level of the signals you want to measure The low limit is the lowest expected level of the signals you want to measure If you want to acquire multiple points from a single channel refer to Chapter 7 Buffering Your Way through Waveform Acquisition Single channel acquisition makes acquiring one channel very basic but what do you do if you need to take more than one channel sample For example you may need to monitor the temperature of the fluid as well as the fluid level of the tank In this case two transducers must be monitored You can monitor both transducers using a mu
191. es and pulse trains GATE SOURCE CLK OUT Count Register Chapter 24 Things You Should Know about Counters National Instruments Corporation 24 3 LabVIEW Data Acquisition Basics Manual Use the OUT signal of a counter to generate various TTL pulse waveforms If you are incrementing the count register value you can configure the OUT signal to either toggle signal states or pulse when the count register reaches a certain value The highest value of a counter is called the terminal count TC If you are decrementing the count register TC value is 0 If you chose to have pulsed output the counter outputs a high pulse that is equal in time to one cycle of the counter SOURCE signal which can be either an internal or external signal If you chose a toggled output the state of the output signal changes from high to low or from low to high For more control over the length of high and low outputs use a toggled output Refer to Chapter 25 Generating a Square Pulse or Pulse Trains for more information You can achieve a greater counting range on most devices by concatenating multiple counters For more information on how to concatenate counters refer to Chapter 28 Counting Signal Highs and Lows Chapter 24 Things You Should Know about Counters LabVIEW Data Acquisition Basics Manual 24 4 www ni com Knowing Your Counter Chip Most National Instruments DAQ devices contain one of four different counter chips the TIO ASIC
192. ese arrays into a single row major 2D array Then use the Transpose 2D Array function to convert the array to a column major array Chapter 3 Basic LabVIEW Data Acquisition Concepts LabVIEW Data Acquisition Basics Manual 3 16 www ni com The finished array is ready for the AO Write VI as shown in Figure 3 12 Figure 3 12 Analog Output Buffer 2D Array National Instruments Corporation 4 1 LabVIEW Data Acquisition Basics Manual 4 Where You Should Go Next This chapter directs you to the chapter in this manual best suited to answer questions about your data acquisition application You answer a series of questions that help determine the purpose of your application At first the questions are general and then become more focused until you reach a reference to a specific section in the manual dealing with your type of application Note This manual is divided into parts You always should read the Things You Should Know About chapter at the beginning of each part specific to your application The Things You Should Know About chapters teach you about basic concepts dealing with your application Use the following flowchart as a guide as you answer the questions that follow it The questions should pinpoint the sections in the manual you should read for your particular application Chapter 4 Where You Should Go Next LabVIEW Data Acquisition Basics Manual 4 2 www ni com Type of Measuring Device Analyzing Analog or D
193. ess open the Generate N Updates ExtUpdateClk VI located in labview examples daq anlogout anlogout llb To use an external update clock you must set the clock source of the AO Start VI to I O connector When you connect your external clock you find that different DAQ devices use different pins for this input However if you select Show VI Info in the Windows menu of the example VI you find that all the I O connections are explained for you These input pins also are described in Table 13 1 Chapter 13 Letting an Outside Source Control Your Update Rate LabVIEW Data Acquisition Basics Manual 13 2 www ni com For waveform generation you must supply an array of waveform data The example Generate N Updates ExtUpdateClk VI described previously uses data created in the Compute Waveform VI When you run the example VI the data is output on channel 0 the DAC0OUT pin of your DAQ device Supplying an External Test Clock from Your DAQ Device To use an external update clock when you do not have an external clock available create an external test clock using outputs from a counter timer on your DAQ device and then wire the output to your external update clock source If your DAQ device has an FOUT or FREQ_OUT pin you can generate a 50 duty cycle TTL pulse train using the Generate Pulse Train on FOUT or FREQ_OUT VI located in labview examples daq counter DAQ STC llb The advantage of this VI is that it does not use one of the available
194. et Timebase 8253 and Wait ms VIs on the block diagram The first two ICTR Control VIs reset counter and counter 0 The next ICTR Control sets up counter to count down while its GATE input is high The Get Timebase 8253 VI returns the internal timebase period for counter 0 of device This value is multiplied by the gate width to yield the count to be loaded into the count register of counter 0 The next ICTR Control VI loads this count and sets up counter 0 to output a low pulse during which cycles of the signal to be measured are counted One advantage of this example is that it uses only two counters However this example has two notable limitations One limitation is that it cannot accurately measure low frequencies If you need to measure lower frequencies use the Measure Frequency lt 1 kHz 8253 VI located in labview examples daq counter 8253 llb This VI uses three counters The other limitation is that there is a software dependency which causes counter 0 to output a pulse slightly longer than the count it is given This is the nature of the 8253 chip and it can increase the readings of high frequencies To avoid this software delay use the Measure Frequency Dig Start gt 1 kHz 8253 located in labview examples daq counter 8253 llb For a complete description of each example refer to the information found in Windows Show VI Info Chapter 27 Measuring Frequency and Period National Instruments Corporation 27 7 Lab
195. et of channels used in the acquisition and to make sure the VIs execute in the correct order You can use the Intermediate VIs to configure triggering coupling acquisition timing retrieval and additional hardware and to control when each step of the data acquisition process occurs Use the AI Config VI to configure the different parameters of the acquisition such as the channels to be read and the size of the buffer to use Use the AI Start VI to specify parameters used in your program to start the acquisition such as the number of scans to acquire the rate at which your VI takes the data and the trigger settings In the AI Read VI you specify parameters to retrieve the data from the data acquisition buffer Your application then calls the AI Clear VI to deallocate all buffers and other resources used for the acquisition by invalidating the taskID If an error occurs in any of these Chapter 7 Buffering Your Way through Waveform Acquisition LabVIEW Data Acquisition Basics Manual 7 4 www ni com VIs your program passes the error through the remaining VIs to the Simple Error Handler VI which notifies you of the error For many DAQ devices the same ADC samples many channels instead of only one The maximum sampling rate per channel is The scan rate input in all the VIs described above is the same as the sampling rate per channel To determine your maximum scan rate divide the maximum sampling rate by the number of channels Refer t
196. evel VIs Easy VIs automatically alert you to errors with a dialog box that allows you to stop the execution of the VI or to ignore the error The Easy VIs usually are composed of Intermediate VIs which are in turn composed of Advanced VIs The Easy VIs provide a basic interface with only the most commonly used inputs and outputs For more complex applications use the intermediate or advanced level VIs to achieve more functionality and better performance Refer to the LabVIEW Function and VI Reference Manual or select Help Online Reference for specific VI information 1 Easy Analog Input VIs 2 Intermediate Analog Input VIs 3 Advanced Analog Input VIs 4 Analog Input Utility VIs 1 2 3 4 Chapter 3 Basic LabVIEW Data Acquisition Concepts National Instruments Corporation 3 5 LabVIEW Data Acquisition Basics Manual Intermediate VIs The Intermediate VIs have more hardware functionality and efficiency in developing your application than the Easy VIs The Intermediate VIs contain groups of Advanced VIs but they use fewer parameters and do not have some of the more advanced capabilities Intermediate VIs give you more control over error handling than the Easy VIs With each VI you can check for errors or pass the error cluster on to other VIs Note Most LabVIEW data acquisition examples shown in this manual are based on the Intermediate VIs You can find these example VIs in the examples folder Utility VIs
197. eves the data After the compensated voltage data from the AI Read VI is averaged the voltage values are converted to temperature and linearized by using the Convert Thermocouple Reading VI in Functions Data Acquisition Signal Conditioning After completing the acquisition remember to always clear the acquisition by using the AI Clear VI Chapter 22 Common SCXI Applications National Instruments Corporation 22 9 LabVIEW Data Acquisition Basics Manual Figure 22 3 Continuously Acquiring Data Using Intermediate VIs Another temperature acquisition example using the SCXI 1100 module is the SCXI Temperature Monitor VI located in labview examples daq scxi scxi_ai llb This VI continually acquires thermocouple readings and sets an alarm if the temperature readings go above a user defined limit You can use the SCXI 1100 examples with the SCXI 1122 module Both modules have the capability to programmatically measure the amplifier offsets and both modules need the cold junction compensation to linearize thermocouple measurements The main differences between the two modules include the type of temperature sensors available on their terminal blocks and the way module channels are multiplexed The SCXI 1100 uses a CMOS multiplexer which is capable of fast channel multiplexing whereas the SCXI 1122 uses an electromechanical relay to switch one of its 16 channels Because the SCXI 1122 uses a relay this module imposes a minimum interchannel
198. f a known internal timebase at the SOURCE of counter The Count Events or Time VI takes care of dividing the count by the timebase frequency to determine the elapsed time The counter continues timing until you click the STOP button You do not need to make any external connections The length of time that can be counted depends on the maximum count of the counter and the chosen timebase Refer to Table 26 1 Internal Counter Timebases and Their Corresponding Maximum Pulse Width Period or Time Measurements for maximum measurable time information Chapter 28 Counting Signal Highs and Lows LabVIEW Data Acquisition Basics Manual 28 6 www ni com If you need more control over when your elapsed timing begins and ends use the Intermediate VIs instead of the Easy VIs For an example open the Count Time Int DAQ STC VI located in labview examples daq counter DAQ STC llb This example uses the Intermediate VIs Event or Time Counter Config Counter Start Counter Read and Counter Stop The Event or Time Counter Config VI configures counter to count the number of rising edges of a known internal timebase The Counter Start VI begins the counting operation for counter The Counter Read VI returns the count until you click the STOP button or an error occurs The count value is divided by the timebase to determine the elapsed time Finally the Counter Stop VI stops the counter operation You do not need to make any external connections but you ca
199. figuring Your Data Acquisition Hardware For more information about using channel names refer to the Channel Name Addressing section of Chapter 3 Basic LabVIEW Data Acquisition Concepts As an alternative digital channel can consist of a port number The port number specifies the port of digital lines that you will use during your digital operation In this case you also must specify device line and Chapter 16 Immediate Digital I O LabVIEW Data Acquisition Basics Manual 16 2 www ni com port width where applicable to further define your digital operation The device input identifies the DAQ device you are using The line input is an individual port bit or line in the port specified by digital channel The port width input specifies the number of lines that are in the port you are using If you are using an SCXI module for nonlatched digital I O and you are not using channel names refer to the SCXI Channel Addressing section in Chapter 21 Special Programming Considerations for SCXI for instructions on how to specify port numbers The pattern or line state is the value s you want to read from or write to a device You can display pattern values in decimal default hexadecimal octal or binary form Immediate I O Using the Easy Digital VIs You can use the Easy Digital VIs for nonlatched digital I O There are four Easy I O subVIs you can use to immediately read data from or write data to a single digital line or to an entire
200. g generating a single point or multiple points Part III Making Waves with Analog Output contains the following chapters Chapter 10 Things You Should Know about Analog Output explains how to use LabVIEW to produce all of the different types of analog output signals Chapter 11 One Stop Single Point Generation shows you which VIs to use in LabVIEW to perform single point updates Chapter 12 Buffering Your Way through Waveform Generation shows you which VIs to use in LabVIEW to perform buffered analog updates Chapter 13 Letting an Outside Source Control Your Update Rate shows you which VIs to use in LabVIEW to control your update rate with an external source Chapter 14 Simultaneous Buffered Waveform Acquisition and Generation describes how to perform buffered waveform acquisition and generation simultaneously on the same DAQ device National Instruments Corporation 10 1 LabVIEW Data Acquisition Basics Manual 10 Things You Should Know about Analog Output Some measuring systems require that analog signals be generated by a DAQ device Each of these analog signals can be a steady or slowly changing signal or a continuously changing waveform This chapter describes how to use LabVIEW to produce all of these different types of signals Single Point Output When the signal level at the output is more important than the rate at which the output value changes you need to generate a steady
201. gnal Figure 5 4 The Effects of Resolution on ADC Precision 16 Bit Versus 3 Bit Resolution 5 kHz Sine Wave 0 50 100 150 200 Time s Amplitude volts 111 110 101 100 011 010 001 000 8 75 10 00 7 50 6 25 5 00 3 75 2 50 1 25 0 16 bit 3 bit Chapter 5 Things You Should Know about Analog Input National Instruments Corporation 5 5 LabVIEW Data Acquisition Basics Manual Device Range Range refers to the minimum and maximum analog signal levels that the ADC can digitize Many DAQ devices feature selectable ranges so you can match the ADC range to that of the signal to take best advantage of the available resolution For example in Figure 5 5 the 3 bit ADC as shown in the left chart has eight digital divisions in the range from 0 to 10 V If you select a range of 10 00 to 10 00 V as shown in the right chart the same ADC now separates a 20 V range into eight divisions The smallest detectable voltage increases from 1 25 to 2 50 V and you now have a much less accurate representation of the signal Figure 5 5 The Effects of Range on ADC Precision Range 0 to 10 V 0 50 100 150 200 Time s Amplitude volts 111 110 101 100 011 010 001 000 8 75 10 00 7 50 6 25 5 00 3 75 2 50 1 25 0 Range 10 to 10 V 0 50 100 150 200 Time s Amplitude volts 111 110 101 100 011 010 001 000 7 50 10 00
202. h contains detailed instructions for assembling your SCXI system module jumper settings cable assemblies and terminal blocks Chapter 2 Installing and Configuring Your Data Acquisition Hardware National Instruments Corporation 2 7 LabVIEW Data Acquisition Basics Manual The following are the basic steps you must complete to assemble your SCXI system 1 Check the jumpers on your modules Generally you will leave the jumpers in their default positions However the Getting Started with SCXI manual contains a section for each module type that lists cases where you might want to change the jumper settings 2 Turn off the chassis power Plug in your modules through the front of the chassis You can put the modules in any slot For simplicity start with slot 1 on the left side of the chassis and move right with each additional module Be sure to tightly screw the modules into the chassis frame 3 If you are using an SCXI 1180 feedthrough panel install the SCXI 1180 in the slot immediately to the right of the module that you will cable to the DAQ device Otherwise the cable connectors might not fit together conveniently 4 If you have more than one chassis select a unique jumpered address for each additional chassis by using the jumpers directly behind the front panel of the chassis 5 Plug the appropriate terminal blocks into the front of each module and screw them tightly into the chassis frame 6 If you are using
203. h hardware timed control loops your acquisition is not interrupted by user interaction Hardware timed analog input automatically places the data in your DAQ device FIFO buffer at an interval determined by the analog input scan rate You can synchronize your control loop diagram to this precise analog input scan rate by repeatedly calling the AI Single Scan VI to read the oldest data in the FIFO buffer The AI Single Scan VI returns as soon as the next scan has been acquired by the DAQ device If more than one scan is stored in the DAQ device FIFO buffer when the AI Single Scan VI is called then LabVIEW was not able to keep up with the acquisition rate You can detect this by monitoring the data remaining output of the AI Single Scan VI In other words you have missed at least one control loop interval This indicates that your software overhead is preventing you from keeping up with your hardware timed loop rate In the Analog IO Control Loop hw timed VI the loop too slow Boolean indicator is set to TRUE whenever this occurs In this block diagram the AI Config VI configures the device to acquire data on channels 0 and 1 The application does not use a buffer created in CPU memory but instead uses the DAQ device FIFO buffer input limits also known as limit settings affects the expected range of the input signals For more information about input limits limit settings refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts The AI Sta
204. he Intermediate DAQ VIs as shown in Figure 12 2 Figure 12 2 Waveform Generation Using Intermediate VIs With these VIs you can set up an alternate update clock source such as an external clock or a clock signal coming from another device or return the update rate The AO Config VI sets up the channels you specify for analog output The AO Write VI places the data in the buffer the AO Start VI Chapter 12 Buffering Your Way through Waveform Generation National Instruments Corporation 12 3 LabVIEW Data Acquisition Basics Manual begins the actual generation at the update rate and the AO Wait VI waits until the waveform generation completes Then the AO Clear VI clears the analog channels The Generate Continuous Sinewave VI located in labview examples daq anlogout anlogout llb is similar in structure to Figure 12 2 This example VI continually outputs a sine waveform through the channel you specify Changing the Waveform during Generation Circular Buffered Output When the waveform data is too large to fit in a memory buffer or is constantly changing use a circular buffer to output the data You also can use the Easy Analog Output VIs in a loop to create a circular buffered output but this sacrifices efficiency because Easy VIs configure allocate and deallocate a buffer every time they execute which causes time gaps between the data output Open the AO Continuous Gen VI to see one way to perform circular buffered a
205. he digital Easy Digital VI Write to Digital Port as shown in Figure 22 9 Figure 22 9 Outputting Digital Signals through an SCXI Chassis Using Easy Digital VIs If you configure channels using the DAQ Channel Wizard digital channel can consist of a digital channel name The channel name can refer to either a port or a line in a port You do not need to specify device line or port width as these inputs are not used by LabVIEW if a channel name is specified in digital channel As an alternative digital channel can be expressed in the scx mdy 0 format where you are trying to output from the digital output module on slot y of chassis x The last identifier is always port 0 because the whole module is considered one port In this case you also must specify device and port width The port width should be the number of lines on your SCXI module if you are operating in multiplexed mode The SCXI 1160 has 16 relays the SCXI 1161 has eight relays and the SCXI 1163 1163R have 32 relays You can not use the SCXI 1160 or SCXI 1161 in parallel mode For the SCXI 1163 1163R the port width in parallel mode should be the number of lines on your DAQ device or SCXI 1200 module The 6533 device can access all 32 lines of the SCXI 1163 1163R modules at once by using the SCXI 1348 cable assembly The DIO 24 and the DIO 96 devices can access only the first 24 lines of the SCXI 1163 1163R when configured in parallel mode For the fastest performance in paralle
206. he AMUX 64T and on the DAQ device perform automatic scanning of the AMUX 64T analog input channels When you perform a multiple channel scanned data acquisition with an AMUX 64T a counter on the DAQ device switches the DAQ device multiplexers When you connect a single AMUX 64T device to the DAQ device you must scan four AMUX 64T input channels for every DAQ device channel If you attach two AMUX 64T devices to the DAQ device LabVIEW scans eight AMUX 64T channels for every DAQ device input channel For example assume that channels 0 through 3 on AMUX 64T device 1 and channels 0 through 3 on AMUX 64T device 2 are multiplexed together into DAQ device channel 0 In this case LabVIEW scans the first four channels on AMUX 64T device 1 followed by the first four channels on AMUX 64T device 2 If you attach four AMUX 64T devices to the DAQ device LabVIEW scans 16 AMUX 64T channels for every DAQ device input channel For example channels 0 through 3 on AMUX 64T device 1 2 3 and 4 are multiplexed together into DAQ device channel 0 In this case LabVIEW scans the first four channels on device 1 followed by the first four channels on device 2 the first four channels on device 3 and then the first four channels on device 4 Chapter 5 Things You Should Know about Analog Input LabVIEW Data Acquisition Basics Manual 5 16 www ni com The order in which LabVIEW scans channels depends on the channel list you specify in the AI Group Config VI
207. he gating modes the TIO ASIC supports depends upon the application You can set the configuration parameters described above using the Advanced VI Counter Set Attribute DAQ STC You can configure the DAQ STC to count either low to high or high to low transitions of the SOURCE input The counter has a 24 bit count register with a counting range of 0 to 224 1 It can be configured to increment or decrement for each counted edge Furthermore you can use an external line to control whether the count register increments or decrements which is useful for encoder applications Of the gating modes shown in Figure 24 1 the gating modes the DAQ STC supports depends upon the application You can set the configuration parameters discussed above using the Advanced VI Counter Set Attribute Am9513 You can configure the Am9513 to count either low to high or high to low transitions of the SOURCE input The counter has a 16 bit count register with a counting range of 0 to 65 535 and can be configured to increment or decrement for each counted edge The Am9513 supports all of the gating modes shown in Figure 24 1 You can set the configuration parameters discussed above using the Advanced VI CTR Mode Config 8253 54 The 8253 54 chip counts low to high transitions of the CLK input The counter has a 16 bit count register with a counting range of 65 535 to 0 that decrements for each counted edge Of the gating modes shown in Figure 24 1 the 8253 54 s
208. he number of pulses of a known frequency fs during one period of the signal to be measured As shown in Figure 27 2 the signal of a known frequency is connected to the SOURCE and the signal to be measured is connected to the GATE The period is the count divided by the known frequency TG count fs Figure 27 2 Measuring a Square Wave Period You typically use period measurement for low frequency signals where the signal to be measured is significantly slower than the chosen internal timebase The internal timebases for the TIO ASIC are 20 MHz 100 kHz and a device specific maximum timebase The internal timebases for the DAQ STC are 20 MHz and 100 kHz The internal timebases for the Am9513 are 1 MHz 100 kHz 10 kHz 1 kHz and 100 Hz Whether you use period measurement or frequency measurement you always can obtain GATE SOURCE CLK OUT Count Register TG input of unknown frequency fs pulse of known width GATE SOURCE OUT Count Register TG input of known frequency fs Chapter 27 Measuring Frequency and Period National Instruments Corporation 27 3 LabVIEW Data Acquisition Basics Manual the other measurement by taking the inverse of the current one as shown in the following equations 8253 54 The 8253 54 chip does not support period measurement but you can use frequency measurement for a pulse train and take the inverse to get the period The frequency examples discussed in this chapter c
209. he update clock produces one update that sends one new sample to every analog output channel in the group update rate The number of output updates per second update width The number of channels in the channel list or number of ports in the port list you use to configure an analog or digital output group Glossary LabVIEW Data Acquisition Basics Manual G 16 www ni com user area One of three parts of the SCXI EEPROM The user area is where you store calibration constants that you calculate using the SCXI Cal Constants VI If you want LabVIEW to load your constants automatically you can put a copy of your constants in the default load area The other EEPROM areas are the factory area and the default load area V V Volts VDC Volts Direct Current VI Virtual Instrument A LabVIEW program so called because it models the appearance and function of a physical instrument Vref Voltage reference W waveform Multiple voltage readings taken at a specific sampling rate wire Data path between nodes write mark Points to the update at which a write operation begins Analogous to a file I O pointer the write mark moves every time you write data into an output buffer After the write is finished the write mark points to the next update to be written Because multiple buffers are possible you need both the buffer number and the update number to express the position of the write mark National Instruments Corporat
210. higher analog input gains than those available on most DAQ plug in devices Note Before reading this section you should have already read the Limit Settings section in Chapter 3 Basic LabVIEW Data Acquisition Concepts Enter the gain jumper settings in Measurement amp Automation Explorer or the NI DAQ Configuration utility for each channel on each module with jumpered gains LabVIEW stores these gain settings and uses them to scale the input data When you use the input limits control of the analog input VIs LabVIEW chooses onboard gains that complement the jumpered SCXI gains to achieve the given input limits as closely as possible For analog input modules with programmable gains LabVIEW uses the gain setting you enter in Measurement amp Automation Explorer or the NI DAQ Configuration utility for each module as the default gain for that module LabVIEW uses the default gain for the module whenever you leave the input limits terminal to the analog input VIs unwired or if you enter 0 for your upper and lower input limits When you use the input limits to specify non zero limits for a module with programmable gains LabVIEW chooses the most appropriate SCXI gain for the given limits LabVIEW selects the highest SCXI gain possible for the given limits and then selects additional DAQ device gains if necessary If your module has programmable gains and only one gain for all channels and you are using an MIO AI DAQ device you can specify
211. hould wire the iteration input to an iteration terminal in a loop as shown in the following illustration Wiring the iteration input this way means the device is configured only on the first I O operation Subsequent I O operations use the existing configuration Chapter 3 Basic LabVIEW Data Acquisition Concepts LabVIEW Data Acquisition Basics Manual 3 8 www ni com Error Handling Each Easy VI contains an error handling VI A dialog box appears immediately if an error occurs in an Easy VI Each Intermediate and Advanced VI contains an error in input cluster and an error out output cluster as shown in Figure 3 3 The clusters contain a Boolean that indicates whether an error occurred the code for the error and source or the name of the VI that returned the error If error in indicates an error the VI passes the error information to error out and does not execute any DAQ functions Figure 3 3 LabVIEW Error In Input and Error Out Output Error Clusters For more information about error handling refer to Part VII Debugging Your Data Acquisition Application in this manual Channel Port and Counter Addressing The Analog Input and Analog Output VIs have a channel list parameter where you can specify the channels from which the VIs read or to which they write The Digital Input and Output VIs have a similar parameter called digital channel list and the equivalent value is called counter list for the Counter VIs Note To simpl
212. how to connect your counter and device to generate a continuous pulse train The edges of the internal source signal are counted to generate the output signal You obtain the continuous pulse train for your external device from the counter OUT pin You optionally can gate the operation with a signal connected to the GATE input pin Instead of having an internal timebase as your SOURCE you can connect an external signal Chapter 25 Generating a Square Pulse or Pulse Trains LabVIEW Data Acquisition Basics Manual 25 8 www ni com Figure 25 7 Physical Connections for Generating a Continuous Pulse Train Two examples show how to use the Easy Counter VI Generate Pulse Train to specify the frequency duty cycle and pulse polarity of your pulse train Open the Cont Pulse Train Easy DAQ STC VI located in labview examples daq counter DAQ STC llb and study its block diagram You also can refer to the example Cont Pulse Train Easy 9513 VI located in labview examples daq counter Am9513 llb The number of pulses parameter defaults to 0 for continuous generation When you click the STOP button the While Loop stops and a second call to Generate Pulse Train with the number of pulses set to 1 stops the counter If you are generating a pulse train and want more control over when the counter starts use the Intermediate VIs For an example open the block diagram of the Cont Pulse Train Int DAQ STC VI located in labview examples daq counter DAQ ST
213. i com Figure 3 2 illustrates these Help window parameter conventions for the AI Read One Scan VI As the window text for this VI indicates you must wire the device if you are not using channel names channels error in and iteration input parameters and the scaled data and error out output parameters To pass error information from one VI to another connect the error out cluster of the current VI to the error in cluster of the next VI The coupling amp input config input limits output units and number of AMUX boards input parameters and the binary data output parameter are optional Figure 3 2 LabVIEW Help Window Conventions Default and Current Value Conventions To use the DAQ VIs you need to know the difference between a default input a default setting and a current setting A default input is the default value of a front panel control When you do not wire an input to a terminal of a VI the default input for the control associated with that terminal passes to the driver The Help window shows the default inputs inside parentheses beside the parameter names A default setting is a default parameter value recorded in the driver The current setting is the value of a control at any given moment The current setting of a control is the default setting until you change the value of the control In many cases a control input defaults to a certain value most often 0 which means you can use the current setting For example the def
214. iew examples daq counter 8253 llb uses the ICTR Control Int VI which can be found in Functions Data Acquisition Counter Intermediate Counter This VI initiates the counter to count the number of rising edges of a TTL timebase at the CLK of counter Counter 0 creates the timebase Looking at the block diagram the Timebase Generator 8253 VI sets up Counter 0 to generate a timebase by dividing down its internal timebase The first call to ICTR Control loads the count register and sets up counter to count down Inside the While Loop ICTR Control reads the count which is divided by the actual timebase frequency to determine the elapsed time The elapsed time increments until you click the STOP button or an error occurs The last two calls to ICTR Control reset Counter 0 and counter Remember that you must externally wire the OUT of Counter 0 to the CLK of counter You optionally can gate counter with a pulse to control when it starts and stops timing To do this wire your pulse to the GATE of counter For a complete description of this example refer to the information found in Windows Show VI Info National Instruments Corporation 29 1 LabVIEW Data Acquisition Basics Manual 29 Dividing Frequencies Dividing TTL frequencies is useful if you want to use an internal timebase and the frequency you need does not exist You can divide an existing internal frequency to get what you need You also can divide the frequency of an external T
215. ify the explanation of channel addressing concepts the channel list digital channel list and counter list parameters are all referred to as channel list in this section Any special exceptions for these parameters are noted Each channel you specify in the channel list becomes a member of a group For each group you can acquire or generate data on the channels listed in the group VIs scan during acquisition or update during generation the channels in the same order they are listed To erase a group pass an empty channel list and the group number to the VI or assign a new channel list to the group Changing groups can be done only at the Advanced VI level Chapter 3 Basic LabVIEW Data Acquisition Concepts National Instruments Corporation 3 9 LabVIEW Data Acquisition Basics Manual Refer to the LabVIEW Function and VI Reference Manual or select Help Online Reference for more information Channel Name Addressing If you use the DAQ Channel Wizard to configure your analog and digital channels you can address your channels by name in the channel list parameter in LabVIEW channel list can be an array of strings or as with the Easy VIs a scalar string control as shown in Figure 3 4 If you have a channel list array you can use one channel entry per array element specify the entire list in a single element or use any combination of these two If you enter multiple channel names in channel list all of the channels in the list mu
216. ig VI example located in labview examples daq anlogin anlogin llb uses the Intermediate VIs Open this VI and examine its block diagram The main difference between this software triggering example and hardware triggering is the use of the conditional retrieval input for the AI Read VI You set up the trigger channel trigger slope and trigger level the same way for both triggering methods The pretrigger scans value is negated and connected to the offset value in the conditional retrieval cluster of the AI Read VI When the trigger conditions are met the VI returns the requested number of scans National Instruments Corporation 9 1 LabVIEW Data Acquisition Basics Manual 9 Letting an Outside Source Control Your Acquisition Rate Typically a DAQ device uses internal counters to determine the rate to acquire data but sometimes you might need to capture your data at the rate of particular signals in your system For example you also can read temperature channels every time a pulse occurs which represents pressure rising above a certain level In this case internal counters are inefficient for your needs You must control your acquisition rate by some other external source You can compare a scan of your channels to taking a snapshot of the voltages on your analog input channels If you set your scan rate to 10 scans per second you are taking 10 snapshots each second of all the channels in your channel list In this case an inte
217. igital Signals Signal Acquisition or Generation Digital or Counter Interfacing Single Point or Multiple Point Generation Single Point or Multiple Point Acquisition Using an Internal or External Clock Triggering a Signal Immediate Handshaked or Timed Digital I O Plug in DAQ Device Only SCXI Analog Digital Digital Counter Handshaked Immediate Acquisition Generation Single Multiple Internal External Single Yes No Read about the DAQ Channel Wizard in Chapters 2 and 3 and Part V SCXI Getting Your Signals in Great Condition Read Chapter 24 Things You Should Know about Counters Read Chapter 17 Handshaked Digital I O Read Chapter 6 One Stop Single Point Acquisition Read Chapter 8 Controlling Your Acquisition with Triggers Read Chapter 7 BufferingYour Way Through Waveform Acquisition Read Chapter 9 Letting an Outside Source Control Your Acquisition Rate Read Chapter 11 One Stop Single Point Generation Multiple Read Chapter 12 Buffering Your Way through Waveform Generation Read Chapter 16 Immediate Digital I O Read Chapter 25 Generating a Square Pulse or Pulse Train Read Chapter 26 Measuring Pulse Width Read Chapter 27 Measuring Frequency and Period Read Chapter 28 Counting Signal Highs and Lows Read Chapter 29 Dividing Frequencies Both Read Chapter 14 Simultaneous Buffered Waveform Acquisition and Generation
218. igned specifically for RTD measurement and can be used as an alternative to SCXI modules Refer to the National Instruments catalog for more information You do not have to worry about cold junction compensation with RTDs as you do when measuring thermocouples To build an application in LabVIEW you can use the Easy I O analog input VIs If you are measuring multiple transducers on several different channels you will need to scan the necessary channels with little overhead Because the Easy I O VIs reconfigure your SCXI module every time your application performs an acquisition it is recommended that you use the Intermediate analog input VIs instead Using the DAQ Channel Wizard to configure your channels can simplify the programming needed to measure your signal as shown in Figure 22 4 LabVIEW configures the hardware with appropriate input limits and gain measures the RTD and scales the measurement for you Enter the name of your configured channel in the channels input parameter The acquired data is in the physical units you specify in the DAQ Channel Wizard Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 12 www ni com Figure 22 4 Measuring Temperature Using Information from the DAQ Channel Wizard The VI in Figure 22 4 continually acquires data until an error occurs or you stop the VI from executing To perform a continuous hardware timed acquisition you must set up a buffer In this example the
219. ine how long of a pulse width can be measured The internal timebase acts as the SOURCE When measuring the pulse width of a signal you count the number of source edges that occur during the pulse being measured The counted number of SOURCE edges cannot exceed the counting range of the counter Slower internal timebases allow you to measure longer pulse widths but faster timebases give you a more accurate pulse width measurement If you need a slower timebase than is available on your counter as shown in Table 26 1 set up an additional counter for pulse train generation and use the OUT of that counter as the SOURCE of the counter measuring pulse width Chapter 26 Measuring Pulse Width LabVIEW Data Acquisition Basics Manual 26 8 www ni com Table 26 1 Internal Counter Timebases and Their Corresponding Maximum Pulse Width Period or Time Measurements Counter Type Internal Timebases Maximum Measurement TIO ASIC Maximum depends on device 20 MHz 214 748 s 100 kHz 11 h 55 m 49 67 s DAQ STC 20 MHz 838 ms 100 kHz 167 s Am9513 1 MHz 65 ms 100 kHz 655 ms 10 kHz 6 5 s 1 kHz 65 s 100 Hz 655 s 8253 54 2 MHz 32 ms 1 MHz 65 ms You can obtain this timebase by calling the Counter Get Attribute VI A DAQ device with an 8253 54 counter has one of these internal timebases available on counter 0 but not both National Instruments Corporation 27 1 LabVIEW Data Acquisition Ba
220. ing counters when counting elapsed time Notice that the OUT of counter is connected to the SOURCE of counter 1 Figure 28 4 External Connections to Cascade Counters for Counting Elapsed Time Counting Events How you count events depends upon which counter chip is on your DAQ device If you are uncertain which counter your DAQ device has refer to your hardware documentation TIO ASIC DAQ STC The Count Events Easy DAQ STC VI located in labview examples daq counter DAQ STC llb uses the Easy VI Count Events or Time which can be found in Functions Data Acquisition Counter This VI initiates the counter to count the number of rising edges of a TTL signal at the SOURCE of counter The counter continues counting until you click the STOP button You must externally wire your signal to be counted to the SOURCE of counter For a description of this example refer to the information found in Windows Show VI Info If you need more control over when your event counting begins and ends use the Intermediate VIs instead of the Easy VIs For an example open the Count Events Int DAQ STC VI located in labview examples daq counter DAQ STC llb This example uses the Intermediate VIs Event or Time Counter Config Counter Start Counter Read and Counter Stop The Event or Time Counter Config VI configures counter to count the number of rising edges of a TTL signal at its SOURCE input pin The Counter Start VI begins the counting operation f
221. input limits the high limit and low limit inputs in the Easy VIs and generates a taskID The program passes the taskID and the error cluster to the AI Single Scan VI which returns the data in an array one point for each channel specified Chapter 6 One Stop Single Point Acquisition LabVIEW Data Acquisition Basics Manual 6 4 www ni com Figure 6 2 Using the Intermediate VIs for a Basic Non Buffered Application The Cont Acquire amp Chart immediate VI shows how you can program the AI Config and AI Single Scan VIs to perform a series of single scans by using software timing a While Loop and processing each scan Open this VI from labview examples daq anlogin anlogin llb and examine its block diagram The advantage to using the intermediate level VIs is that you do not have to configure the channels every time you want to acquire data as you do when using the Easy VIs To call the AI Config VI only once put it outside of the While Loop in your program The AI Config VI configures channels selects a high low limit and generates a taskID Then the AI Config VI passes the taskID and error cluster into the While Loop LabVIEW calls the AI Single Scan VI to retrieve a scan and passes the returned data to the My Single Scan Processing VI With this VI you can program whatever processing needs your application calls for such as looking for a limit to be exceeded The VI then passes the data through the Build Array function to a waveform
222. input pins table 9 6 MIO devices without scan clocks note 9 5 scan clock orientation of LabVIEW 9 2 simultaneous control of scan and channel clocks 9 7 scans channel clock rate parameter 5 18 defined 5 18 interval scanning 5 18 maximum scan rate calculating 7 4 number of samples parameter 5 18 number of scans to acquire parameter 5 18 round robin scanning figure 9 2 scan rate parameter 5 18 SCXI 1124 Update Channels VI 22 17 SCXI application examples 22 1 to 22 21 analog input application for measuring temperature 22 2 to 22 13 analog output application 22 17 DAQ example files 3 2 digital input application 22 17 to 22 18 digital output application 22 19 to 22 20 multi chassis applications 22 20 to 22 22 17 overview 22 1 pressure measurement with strain gauges 22 13 to 22 16 temperature measurement applications amplifier offset 22 5 to 22 6 sensors for cold junction compensation 22 3 to 22 5 using RTDs 22 10 to 22 13 using thermocouples 22 2 to 22 3 VI examples 22 6 to 22 10 SCXI Cal Constants VI calculation of calibration constants 23 3 calibrating SCXI modules for signal generation 23 8 loading saved calibration constants 23 7 23 8 one point calibration 23 6 overwriting default constants in EEPROM note 23 2 two point calibration 23 6 to 23 7 SCXI calibration 23 1 to 23 8 EEPROM for storing calibration constants 23 1 to 23 2 default load area 23 2 factory area 23 2 user area 2
223. ion I 1 LabVIEW Data Acquisition Basics Manual Index Numbers 2D arrays 3 14 to 3 16 8253 54 counter accuracy 25 14 continuous pulse train generation 25 9 description 24 5 to 24 6 determining pulse width 26 4 to 26 5 dividing frequencies 29 3 elapsed time counting 28 6 to 28 7 event counting 28 5 finite pulse train generation 25 11 to 25 12 frequency and period measurement high frequency signals 27 6 how and when to measure 27 3 low frequency signals 27 8 internal timebases with maximum pulse width measurements table 26 8 single square pulse generation 25 6 to 25 7 square pulse generation 25 4 stopping counter generations 25 15 A ACK Acknowledge Input line 17 2 Acquire amp Proc N Scans Trig example VI 8 5 8 8 Acquire amp Process N Scans VI 7 8 Acquire 1 Point from 1 Channel VI 6 1 to 6 2 Acquire and Average VI 22 6 to 22 7 Acquire N Scans Analog Hardware Trig example VI 8 7 to 8 8 Acquire N Scans Analog Software Trig example VI 8 11 Acquire N Scans Digital Trig example VI 8 4 to 8 5 Acquire N Scans example VI 7 3 7 5 Acquire N Scans ExtChanClk example VI 9 4 9 6 Acquire N Multi Analog Hardware Trig example VI 8 8 Acquire N Multi Digital Trig example VI 8 5 Acquire N Multi Start example VI 7 5 to 7 6 acquisition rate See external control ADC limit settings effects figure 5 6 measurement precision for various device ranges and limit settings table 5 8 range effects figur
224. ion input to optimize your digital operation When iteration is 0 default LabVIEW calls the DIO Port Config VI an Advanced VI to configure the port If iteration is greater than zero LabVIEW bypasses reconfiguration and remembers the last configuration which improves performance You can wire this input to an iteration terminal of a loop With the DIO 24 and DIO 96 devices every time you call the DIO Port Config VI the digital line values are reset to default values If you want to maintain the integrity of the digital values from one loop iteration to another do not set iteration to 0 except for the first iteration of the loop For an example on SCXI digital input refer to SCXI 1162 1162HV Digital Input VI located in labview examples daq scxi scxi_dig llb Even though this VI uses Advanced VIs it is functionally equivalent to the Easy I O Digital VI Read from Digital Port Note The DIO Port Config VI resets output lines on adjacent ports on the same 8255 chip for DIO 24 DIO 96 AT MIO 16D AT MIO 16DE and Lab and 1200 Series devices Note If you also are using SCXI analog input modules make sure your cabling DAQ device is cabled to one of them Chapter 22 Common SCXI Applications National Instruments Corporation 22 19 LabVIEW Data Acquisition Basics Manual Digital Output Application Example To output digital signals through an SCXI chassis you can use the SCXI 1160 SCXI 1161 SCXI 1163 and SCXI 1163R modules and t
225. ip to Invert a TTL Signal 24 6 Figure 25 1 Pulse Duty Cycles 25 2 Figure 25 2 Positive and Negative Pulse Polarity 25 3 Figure 25 3 Pulses Created with Positive Polarity and Toggled Output 25 3 Figure 25 4 Phases of a Single Negative Polarity Pulse 25 4 Figure 25 5 Physical Connections for Generating a Square Pulse 25 5 Figure 25 6 External Connections Diagram from the Front Panel of Delayed Pulse 8253 VI 25 6 Figure 25 7 Physical Connections for Generating a Continuous Pulse Train 25 8 Figure 25 8 External Connections Diagram from the Front Panel of Cont Pulse Train 8253 VI 25 9 Figure 25 9 Physical Connections for Generating a Finite Pulse Train 25 10 Figure 25 10 External Connections Diagram from the Front Panel of Finite Pulse Train Adv DAQ STC VI 25 11 Figure 25 11 External Connections Diagram from the Front Panel of Finite Pulse Train 8253 VI 25 12 Figure 25 12 Uncertainty of One Timebas
226. iple Point Generation Are you outputting a steady DC signal or are you generating a changing signal at a certain rate A constant or slowly changing signal output is called single point generation The output of a changing signal at a certain rate is called multiple point or waveform generation If you want to perform single point generation refer to Chapter 11 One Stop Single Point Generation If you want multiple point generation refer to Chapter 12 Buffering Your Way through Waveform Generation 7 Triggering a Signal or Using a Clock You can start an analog acquisition when a certain analog or digital value occurs by triggering the acquisition If you want to trigger an analog acquisition refer to Chapter 8 Controlling Your Acquisition with Triggers Chapter 4 Where You Should Go Next National Instruments Corporation 4 5 LabVIEW Data Acquisition Basics Manual 8 Multiple Point Acquisition with an Internal or External Clock Multiple point or waveform acquisition can be done at a rate set by an internal DAQ device clock or an external clock The external clock will be a TTL signal produced at a certain rate If you want to acquire a waveform at the rate of an external signal refer to Chapter 9 Letting an Outside Source Control Your Acquisition Rate If not read Chapter 7 Buffering Your Way through Waveform Acquisition 9 Immediate Handshaked or Timed Digital I O If you want your program to read the
227. isition and Generation National Instruments Corporation 14 3 LabVIEW Data Acquisition Basics Manual Using Legacy MIO Boards Legacy MIO devices such as the AT MIO 16 have a total of five counters of which two or more can be used for data acquisition and generation However certain counters are dedicated to certain tasks and you must be aware of this as you design your system Software Triggered Open the Simul AI AO Buffered legacy MIO VI located in labview examples daq anlog_io anlog_io llb and examine its block diagram Because legacy MIO type boards have only one clock available for signal acquisition scan timing and generation update timing the same clock is used for both The acquisition uses counter 2 by default The generation is set up to use the I O connector at the clock source input to the AO Start VI Because the I O connector scan clock input is the OUT2 pin which already has the acquisition timing signal on it no external clock wiring is required The result is that the waveform acquisition and generation start simultaneously and occur at the same rate using the same clock Your waveform generation occurs at the same rate as the scan rate you choose for waveform acquisition For a complete description instructions and I O connections for this VI select Windows Show VI Info from the front panel of the VI Hardware Triggered Open the Simul AI AO Buffered Trigger legacy MIO VI located in labview e
228. it idle until it finishes If you need the efficiency of not having to wait for the AI Read VI then asynchronous acquisition is for you You can acquire asynchronous continuous data from multiple channels using the same intermediate DAQ VIs by adding DAQ Occurrences To see an example open the block diagram of the Cont Acq amp Chart Async Occurrence VI located in labview examples daq anlogin anlogin llb Notice that it is very similar to the example described previously the Acquire amp Process N Scans VI The difference is that this example uses the DAQ Occurrence Config VI and the Wait on Occurrence function to control the reads The first DAQ Occurrence Config VI sets the DAQ Event In this example the DAQ Event is to set the occurrence every time a number of scans is acquired equal to the value of general value A where general value A is the number of scans to read at a time Inside the While Loop the Wait on Occurrence function sleeps in the background until the chosen DAQ Event takes place Notice that the timed out output from the Wait on Occurrence function is wired to the selection terminal of the Case structure that encloses the AI Read VI This means that AI Read is not called until the number of scans to read at a time have been acquired The result is that the While Loop is effectively put to sleep because you do not try to read the data until you know it has been acquired This frees up processor time to do other tasks while y
229. ital Signals through an SCXI Chassis Using Easy Digital VIs Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 18 www ni com If you configure channels using the DAQ Channel Wizard digital channel can consist of a digital channel name The channel name can refer to either a port or a line in a port You do not need to specify device line or port width as these inputs are not used by LabVIEW if a channel name is specified in digital channel As an alternative digital channel can be expressed in the scx mdy 0 format where you are trying to input from the digital input module on slot y of chassis x The last identifier is always port 0 because the whole module is considered one port In this example you also must specify device and port width The port width should be the number of lines in a port on your SCXI module if you are operating in multiplexed mode For the SCXI 1162 and SCXI 1162HV the port width is 32 lines If you are operating in parallel mode the port width should be the number of lines on your DAQ device The DIO 32F DIO 32HS 6533 device can access all 32 lines of the SCXI modules at once by using the SCXI 1348 cable assembly The DIO 24 and the DIO 96 devices can access only the first 24 lines of these modules when configured in parallel mode For the fastest performance in parallel mode you can use the appropriate onboard port numbers instead of the SCXI channel string syntax Use the iterat
230. ite One Update VIs The AI Read One Scan VI configures your DAQ device to acquire data from analog input channels 0 and 1 Once your program acquires a data point from channels 0 and 1 it performs calculations on the data and outputs the results through analog output channels 0 and 1 Because the Chapter 6 One Stop Single Point Acquisition LabVIEW Data Acquisition Basics Manual 6 6 www ni com iteration count is connected to the AI Read One Scan and AO Write One Update VIs the application configures the DAQ device for analog input and output only on the first iteration of the loop The loop rate as well as the acquisition rate is specified by loop rate The reason why the actual loop period is important is because user interaction affects the loop and acquisition rate For example pressing the mouse button interrupts the system clock which controls the loop rate If your analog acquisition rate for control loops does not need to be consistent then use software timed control loops For more control examples refer to the VIs located in examples daq solution control llb Using Hardware Timed Analog I O Control Loops For more precise timing of your control loops and more precise analog input scan rate use hardware timed control loops An example of hardware timed non buffered control loops is the Analog IO Control Loop hw timed VI located in labview examples daq anlog_io anlog_io llb Open and examine its block diagram Wit
231. ken at 5 000 samples per second every time the While Loop iterates However the duration of the iterations of the While Loop can vary greatly This means that with this VI you can control the rate at which samples are taken but you may not be able to designate exactly when your application starts acquiring Chapter 7 Buffering Your Way through Waveform Acquisition LabVIEW Data Acquisition Basics Manual 7 6 www ni com each set of data If this start up timing is important to your program read the Do You Need to Access Your Data during Acquisition section in this chapter to see how to control acquisition start up times Simple Buffered Analog Input with a Write to Spreadsheet File If you want to write the acquired data to a file there are many file formats in which you can store the data The spreadsheet file format is used most often because you can read it using most spreadsheet applications for later data graphing and analysis In LabVIEW you can use VIs to send data to a file in spreadsheet format or read back data from such a file You can locate these VIs in Functions File I O The VI used in this example is the Write to Spreadsheet File VI shown in Figure 7 3 In this exercise the Intermediate analog input VIs acquire an array of data graph the data using the actual sample period for the x axis timebase and create a spreadsheet file containing the data Figure 7 3 Writing to a Spreadsheet File after Acquisition Triggere
232. known pulse is determined by gate width Frequency is the output for this example and period is calculated by taking the inverse of the frequency The valid output lets you know if Chapter 27 Measuring Frequency and Period National Instruments Corporation 27 5 LabVIEW Data Acquisition Basics Manual the measurement completed without an overflow The number of counters to use input lets you choose one counter for 16 bit measurement or two counters for 32 bit measurement Remember that you must externally wire your signal to be measured to the SOURCE of counter and the OUT of counter 1 must be wired to the GATE of counter For a complete description of this example refer to the information found in Windows Show VI Info TIO ASIC DAQ STC Am9513 If you need more control over when your frequency measurement begins and ends use the Intermediate VIs instead of the Easy VIs Figure 27 5 shows one approach for this that uses the Event or Time Counter Config Adjacent Counters Delayed Pulse Generator Config Counter Start CTR Control Counter Read and Counter Stop VIs The Delayed Pulse Generator Config VI configures counter to count the number of pulses while its GATE is high The Adjacent Counters VI is used to determine the correct counter 1 The Delayed Pulse Generator Config VI then configures counter 1 to generate a single pulse for the GATE signal The Counter Start VI begins the counting operation for counter first then counter 1
233. l Source Common Mode Voltage Ground Potential Noise etc Chapter 5 Things You Should Know about Analog Input LabVIEW Data Acquisition Basics Manual 5 12 www ni com Referenced Single Ended Measurement System An RSE measurement system is used to measure a floating signal because it grounds the signal with respect to building ground Figure 5 9 depicts a 16 channel RSE measurement system You should use this measurement system only when you need a single ended system and your device does not work with NRSE measurement Figure 5 9 16 Channel RSE Measurement System CH0 CH2 CH1 CH15 MUX Vm Instrumentation Amplifier AIGND Chapter 5 Things You Should Know about Analog Input National Instruments Corporation 5 13 LabVIEW Data Acquisition Basics Manual Nonreferenced Single Ended Measurement System DAQ devices often use a variant of the RSE measurement technique known as the NRSE measurement system In an NRSE measurement system all measurements are made with respect to a common reference because all of the input signals are already grounded Figure 5 10 depicts an NRSE measurement system where AISENSE is the common reference for taking measurements and AIGND is the system ground All signals must share a common reference at AISENSE Figure 5 10 16 Channel NRSE Measurement System In general a differential measurement system is preferable because it rejects n
234. l and Configure SCXI Read Chapter 3 Basic Data Acquisition Concepts and Chapter 4 Where You Should Go Now Using SCXI Yes No Use Measurement amp Automation Explorer Data Neighborhood NI DAQ 6 5 or higher for Windows 9x NT to configure AI AO or DIO channels or Use the DAQ Channel Wizard NI DAQ 6 1 or lower Windows 9x NT or Macintosh to configure AI AO or DIO channels Chapter 2 Installing and Configuring Your Data Acquisition Hardware National Instruments Corporation 2 3 LabVIEW Data Acquisition Basics Manual Figure 2 2 shows the relationship between LabVIEW NI DAQ and DAQ hardware Figure 2 2 How NI DAQ Relates to Your System and DAQ Devices NI DAQ 4 8 x for Macintosh NI DAQ 4 8 x for the Macintosh device drivers are bundled in a single file that determines which drivers to load When you restart your computer this control panel driver called NI DAQ determines which devices are installed in the system and loads their corresponding drivers NI DAQ uses its control panel settings to determine what Signal Conditioning eXtensions for Instrumentation SCXI hardware is configured and what the default device settings are for devices in the computer If you use DMA NI DAQ also communicates with the NI DMA DSP for DMA services When you install LabVIEW the installer places both of these files on your hard drive NI DAQ 6 x for Macintosh The NI DAQ driver called NI DAQ is installed in the National Inst
235. l data to the DAQ device Some of the analog and digital lines on the DAQ device are reserved for SCXI chassis communication To find out which lines are reserved on your device refer to the tables in Appendix B Hardware Capabilities in the LabVIEW Function and VI Reference Manual or refer to the LabVIEW Online Reference by selecting Help Online Reference SCXI 1140 SCXI 1140 SCXI 1001 MAINFRAME SCXI Terminal Blocks Signal Conditioning and or DAQ Modules SCXI Chassis SCXI Cable Assembly or Parallel Port Cable Plug in DAQ Device Optional Personal Computer Chapter 20 Hardware and Software Setup for Your SCXI System LabVIEW Data Acquisition Basics Manual 20 4 www ni com Figure 20 3 SCXI Chassis When you use SCXI as an external DAQ system only some of the digital I O lines of the DAQ device are reserved for SCXI chassis communication when other modules are present The DAQ device digitizes any analog input data and transfers it back to the computer through the parallel or serial port Note When using remote SCXI be aware of the sampling rate limitations from the data being sent over the serial port To reduce delays in serial port communication National Instruments recommends that you use the fastest baud rate possible for your computer s serial port If you have a 16550 or compatible universal asynchronous receiver transceiver UART you can use baud rates up to 57 600 baud If you have an
236. l mode you can use the appropriate onboard port numbers instead of the SCXI channel string syntax Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 20 www ni com Use the iteration input to optimize your digital operation When iteration is 0 default LabVIEW calls the DIO Port Config VI an Advanced VI to configure the port If iteration is greater than zero LabVIEW bypasses reconfiguration and remembers the last configuration which improves performance You can wire this input to an iteration terminal of a loop Every time you call the DIO Port Config VI the digital line values are reset to default values If you want to maintain the integrity of the digital values from one loop iteration to another do not set iteration to 0 except for the first iteration of the loop For an example on SCXI digital output refer to the SCXI 116x Digital Output VI located in labview examples daq scxi scxi_dig llb Even though this VI uses Advanced VIs it is functionally equivalent to the Easy Digital VI Write to Digital Port Note If you also are using SCXI analog input modules make sure your cabling DAQ device is cabled to one of them Multi Chassis Applications Multiple SCXI 1000 SCXI 1000DC or SCXI 1001 chassis can be daisy chained using the SCXI 1350 or SCXI 1346 multichassis cable adapters and an MIO Series DAQ device other than the DAQPad MIO 16XE 50 Every module in each of the chassis must be in multip
237. l of the data is handshaked into the buffer before it is read into LabVIEW 6533 Family The examples Buff Handshake Input VI and Buff Handshake Output VI show how to read or write data respectively using buffered handshaking These examples are located in labview examples daq digital 653x llb Select Windows Show VI Info for any of these examples for more information about using and testing them The examples Burst Mode Input VI and Burst Mode Output VI demonstrate the use of the burst mode protocol for maximum device throughput These examples are located labview examples daq digital 653x llb Select Windows Show VI Info for any of these examples for more information about using and testing them 8255 Family The example Dig Buf Handshake In 8255 VI shows how to read buffered data using handshaking The example Dig Buf Handshake Out 8255 VI shows how to write buffered data using handshaking These examples are located in labview examples daq digital 8255 llb Select Windows Show VI Info for any of these examples for more information about using and testing them Chapter 17 Handshaked Digital I O National Instruments Corporation 17 7 LabVIEW Data Acquisition Basics Manual Iterative Buffered Handshaking Iterative buffered handshaking sets up a buffer the same way as simple buffered handshaking With iterative buffered handshaking one or more ports can be used to read or write data What differs between iterative buffere
238. le DAQ device non Remote SCXI each chassis multiplexes all of its analog input channels into a separate onboard analog input channel The first chassis in the chain uses onboard channel 0 the second chassis in the chain uses onboard channel 1 and so on To access channels in the second chassis you must select the correct onboard channel as well as the correct chassis ID The string ob1 sc2 md1 0 means channel 0 on the module in slot 1 of SCXI chassis 2 multiplexed into onboard channel 1 Remember to use the correct chassis ID number from the configuration utility and to put the jumpers from the power supply module in the correct position for each chassis When an MIO AI Series device is cabled by a ribbon cable or shielded cable to multiple chassis the number of reserved analog input channels depends on the number of chassis On MIO Series devices lines 0 1 and 2 are unavailable On MIO E Series devices lines 0 1 2 and 4 are unavailable For more channel information refer to the LabVIEW Online Reference by selecting Help Online Reference When you access digital SCXI modules you do not use onboard channels Therefore if you have multiple chassis you only have to choose the correct SCXI chassis ID and module slot When you use Remote SCXI to address analog input channels specify the device number of the SCXI 1200 that is located in the same chassis containing the analog input module from which you take samples You can perform
239. le Waveform You can acquire a waveform from a single channel by using the AI Acquire Waveform VI You can find this VI in Functions Data Acquisition Analog Input Because AI Acquire Waveform is an Easy Analog Input VI it has the minimal number of inputs needed to acquire a waveform from a single channel These minimal inputs are the device channel string number of samples from the channel and the sample rate You can programmatically set the gain by setting the high limit and the low limit Using only the minimal set of inputs makes programming the VI easier but the VI lacks more advanced capabilities such as triggering Built in error handling is another useful feature of the Easy VIs If an error occurs the program stops running and notifies you with a dialog box explaining the error writing and reading T N Chapter 7 Buffering Your Way through Waveform Acquisition National Instruments Corporation 7 3 LabVIEW Data Acquisition Basics Manual Note If you set up your channel in the DAQ Channel Wizard you do not need to enter the device or input limits Instead enter a channel name in the channel input and the value returned is relative to the physical units you specify for that channel in the DAQ Channel Wizard If you do specify input limits they also are treated as relative to the physical units of the channel LabVIEW ignores the device input when channel names are used This principle applies throughout this manual
240. le of a TTL Signal 9 3 Figure 9 4 Block Diagram of a VI Acquiring Data with an External Scan Clock 9 5 Figure 9 5 Controlling the Scan and Channel Clock Simultaneously 9 7 Figure 12 1 Waveform Generation Using the AO Waveform Gen VI 12 2 Figure 12 2 Waveform Generation Using Intermediate VIs 12 2 Figure 12 3 Circular Buffered Waveform Generation Using Intermediate VIs 12 4 Figure 15 1 Digital Ports and Lines 15 1 Figure 17 1 Connecting Signal Lines for Digital Input 17 3 Figure 17 2 Connecting Signal Lines for Digital Output 17 4 Figure 19 1 Common Types of Transducers Signals and Signal Conditioning 19 3 Figure 19 2 Amplifying Signals near the Source to Increase Signal to Noise Ratio SNR 19 4 Figure 20 1 SCXI System 20 2 Figure 20 2 Components of an SCXI System 20 3 Figure 20 3 SCXI Chassis
241. les directly to the DAQ device Note MIO AI devices and Lab PC and 1200 devices support multiple channel and multiple scan acquisitions in multiplexed mode The Lab NB and Lab LC LPM devices and DAQCard 700 support only single channel or single scan acquisitions in multiplexed mode When you connect a DAQ device to a multiplexed module the multiplexed output of the module and all other multiplexed modules in the chassis appears at analog input channel 0 of the DAQ device by default Chapter 20 Hardware and Software Setup for Your SCXI System LabVIEW Data Acquisition Basics Manual 20 6 www ni com Multiplexed Mode for the SCXI 1200 Windows In multiplexed mode the SCXI 1200 can access the analog signals on the SCXI bus The DAQ VIs can multiplex the channels of analog input modules and send them on the SCXIbus This means that if you configure the SCXI 1200 for multiplexed mode you can read the multiplexed output from other SCXI analog input modules in the chassis Note The SCXI 1200 reads analog input module channels configured only in multiplexed mode not in parallel mode Make sure that you change the jumper in the SCXI 1200 to the ground position to connect the SCXI 1200 and SCXIbus grounds together Refer to the SCXI 1200 User Manual for more details Multiplexed Mode for Analog Output Modules Because LabVIEW communicates with the multiplexed modules over the SCXIbus backplane you need to cable only one multiplexe
242. lexed mode Only one of the chassis will be connected directly to the DAQ device Also if you are using Remote SCXI with RS 485 you can daisy chain up to 31 chassis on a single RS 485 port Because you can configure only up to 16 devices on the NI DAQ Configuration Utility you can have only up to 16 SCXI 1200s in your system Note Lab Series devices LPM devices DAQCard 500 516 devices DAQCard 700 1200 Series other than SCXI 1200 and DIO 24 devices do not support multi chassis applications If you use the DAQ Channel Wizard to configure your analog input channels you simply address channels in multiple chassis by their channel names Channel names can be combined separated by commas to measure data from multiple modules in a daisy chain configuration at the same time For example if you have a named channel called temperature on one module in the daisy chain and pressure on another module in the same daisy chain your channels array could be temperature pressure You Chapter 22 Common SCXI Applications National Instruments Corporation 22 21 LabVIEW Data Acquisition Basics Manual must enter the chassis in a sequential order in the NI DAQ Configuration Utility assigning the first chassis in the chain an ID number of 1 the second chassis an ID number of 2 and so forth If you are not using the DAQ Channel Wizard there are special considerations for addressing the channels When you daisy chain multiple chassis to a sing
243. limit settings or input limits cluster array on the same VI Assignment of limits to channels works exactly as described above Refer to the LabVIEW Function and VI Reference Manual or select Help Online Reference for more information on how to assign limit settings to a particular analog channel using the Advanced VIs the Group Config VI and the Hardware Config VI In analog applications you not only specify the range of the signal you also must specify the range and the polarity of the device A unipolar range is a range containing either positive or negative values but never both A bipolar range is a range that has both positive and negative values When a device uses jumpers or DIP switches to select its range and polarity you must enter the correct jumper setting in the configuration utility In DAQ hardware manuals and in the configuration utility you may find reference to the concept of gain Gain is the amplification or attenuation of a signal Most National Instruments DAQ devices have programmable gains no jumpers but some SCXI modules require the use of jumpers or DIP switches Limit settings determine the gain for all DAQ devices used with LabVIEW However for some SCXI modules you must enter the gain in the configuration utility Chapter 3 Basic LabVIEW Data Acquisition Concepts LabVIEW Data Acquisition Basics Manual 3 14 www ni com Data Organization for Analog Applications If you acquire data from more than o
244. lls your device to generate a single delayed pulse This VI is self contained and checks for errors automatically With the Generate Delayed Pulse VI you must connect the pulse delay phase 1 and pulse width phase 2 controls to define the output pulse Sometimes the actual pulse delay and pulse width are not the same as you specified SOURCE GATE OUT Count Register Your Device SOURCE GATE OUT Count Register Your Device Your Device Basic Connection Optional Connections Chapter 25 Generating a Square Pulse or Pulse Trains LabVIEW Data Acquisition Basics Manual 25 6 www ni com To gain more control over when the counter begins generating a single square pulse use Intermediate VIs instead of the Easy VIs Open the Delayed Pulse Int DAQ STC VI located in labview examples daq counter DAQ STC llb and study its block diagram You also can use the example Delayed Pulse Int 9513 VI located in labview examples daq counter Am9513 llb These examples show how to generate a single pulse using Intermediate level VIs The Delayed Pulse Generator Config VI configures the counter and the Counter Start VI generates the TTL signal An example of this is generating a pulse after meeting certain conditions If you used the Easy Counter VI the VI configures and then immediately starts the pulse generation With the Intermediate VIs you can configure the counter long before the actual pulse generation begins As soon as you w
245. located nearest to the signal source as shown in Figure 19 2 Figure 19 2 Amplifying Signals near the Source to Increase Signal to Noise Ratio SNR Note You can minimize noise that lead wires pick up by using shielded cables or a twisted pair of cables and by minimizing wire length Also keeping signal wires away from AC power cables and monitors helps reduce 50 Hz or 60 Hz noise If you amplify the signal at the DAQ device the signal is measured and digitized with noise that may have entered the lead wires However if you amplify the signal close to the signal source with an SCXI module noise has a less destructive effect on the signal In other words the digitized representation is a better reflection of the original low level signal For more information consult Application Note 025 Field Wiring and Noise Considerations for Analog Signals You can access this note from the National Instruments web site www ni com ADC DAQ Device Instrumentaion Amplifier MUX Low Level Signal External Amplifier Lead Wires Noise Chapter 19 Things You Should Know about SCXI National Instruments Corporation 19 5 LabVIEW Data Acquisition Basics Manual Isolation Another common way to use SCXI is to isolate the transducer signals from the computer for safety purposes When the signal being monitored contains large voltage spikes that could damage the computer or harm the operator you should not directly connect th
246. ls with the SCXI 1124 when you do not use the DAQ Channel Wizard The SCXI 1124 can generate voltage and current signals Refer to the example analog output VI SCXI 1124 Update Channels VI located in labview examples daq scxi scxi_ao llb This VI uses the analog output Advanced VIs because the output mode whether you have voltage or current data must be accessible in order to change the value The program calls the AO Group Config VI to specify the device and output channels The AO Hardware Config VI specifies the output mode and the output range or limit settings for all the channels specified in the channels string This advanced level VI is the only place where you can specify a voltage or current output mode If you are going to output voltages only consider using the AO Config VI an Intermediate VI instead of the AO Group Config and AO Hardware Config VIs You can program individual output channels of the SCXI 1124 for different output ranges by using the arrays for channels output mode and limit settings The AO Single Update VI initiates the update of the SCXI 1124 output channels To help debug your VIs it is always helpful to display any errors in this case using the Simple Error Handler VI Digital Input Application Example To input digital signals through an SCXI chassis you can use the SCXI 1162 and SCXI 1162HV modules and the Easy Digital VI Read from Digital Port as shown in Figure 22 8 Figure 22 8 Inputting Dig
247. ltiple channel single point acquisition in LabVIEW Multiple Channel Single Point Analog Input With a multiple channel single point read or scan LabVIEW returns the value on several channels at once Use this type of operation when you have multiple transducers to monitor and you want to retrieve data from each transducer at the same time Your DAQ device executes a scan across each of the specified channels and returns the values when finished Refer to Appendix B Hardware Capabilities in the LabVIEW Function and VI Reference Manual for the number of channels your device can scan at one time You also can refer to the LabVIEW Online Reference available by selecting Help Online Reference The Easy I O VI AI Sample Channels acquires single values from multiple channels The AI Sample Channels VI performs a single A D conversion on the specified channels and returns the scaled values in a one dimensional 1D array The expected range for all the signals specified by high limit and low limit inputs applies to all the channels Figure 6 1 shows how to acquire a signal from multiple channels using this VI Note Remember to use commas to delimit individual channels in the channel string Use a colon to indicate an inclusive list of channels Chapter 6 One Stop Single Point Acquisition National Instruments Corporation 6 3 LabVIEW Data Acquisition Basics Manual Figure 6 1 Acquiring a Voltage from Multiple Channels with the A
248. lustration Two Point Calibration The following steps show you how to perform a two point calibration calculation in LabVIEW Use two point calibration when you need to correct both the binary offset and the gain error in your SCXI module Note If you are using an AT MIO 16F 5 AT MIO 64F 5 or AT MIO 16X device or an E Series device you should calibrate your DAQ device first using either the MIO Calibrate VI or E Series Calibrate VI To perform a two point calibration calculation in LabVIEW follow steps 1 through 5 in the previous section One Point Calibration then complete the following steps 6 Now apply a known stable non zero voltage to your input channel at the terminal block This input voltage should be close to the upper limit of your input voltage range for the given gain setting For example if your input voltage range is 5 to 5 V apply an input voltage that is as close to 5 V as possible but does not exceed 5 V 7 Take another binary reading or average of readings If your binary reading is the maximum binary reading for your DAQ device try a smaller input voltage This is your second volt binary measurement 8 Use the SCXI Cal Constants VI with the first volt binary measurement from step 4 as Volt Amp Hz 1 and Binary 1 inputs and the second measurement from step 7 as Volt Amp Hz 2 and Binary 2 inputs of the VI The following illustration shows how you should enter the values into these inputs in LabVIEW if
249. manship for a period of 90 days from date of shipment as evidenced by receipts or other documentation National Instruments will at its option repair or replace software media that do not execute programming instructions if National Instruments receives notice of such defects during the warranty period National Instruments does not warrant that the operation of the software shall be uninterrupted or error free A Return Material Authorization RMA number must be obtained from the factory and clearly marked on the outside of the package before any equipment will be accepted for warranty work National Instruments will pay the shipping costs of returning to the owner parts which are covered by warranty National Instruments believes that the information in this document is accurate The document has been carefully reviewed for technical accuracy In the event that technical or typographical errors exist National Instruments reserves the right to make changes to subsequent editions of this document without prior notice to holders of this edition The reader should consult National Instruments if errors are suspected In no event shall National Instruments be liable for any damages arising out of or related to this document or the information contained in it EXCEPT AS SPECIFIED HEREIN NATIONAL INSTRUMENTS MAKES NO WARRANTIES EXPRESS OR IMPLIED AND SPECIFICALLY DISCLAIMS ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE CUSTOMER S RIGHT
250. me sense Chapter 7 Buffering Your Way through Waveform Acquisition LabVIEW Data Acquisition Basics Manual 7 2 www ni com you can use a data buffer in computer memory as your shopping bag with which you acquire data With buffered I O LabVIEW transfers data taken at timed intervals from a DAQ device to a data buffer in memory Figure 7 1 illustrates how the data fills up the buffer only once however the overall size of the buffer is specified in your VI In this illustration think of N as the number of scans or updates the buffer can hold and T as the trigger occurrence whether the trigger is because of an external signal or the start of the execution of your VI Refer to Chapter 8 Controlling Your Acquisition with Triggers for more information about triggering your acquisition from another signal Figure 7 1 How Buffers Work In your VI you must specify the number of samples to be taken and the number of channels from which LabVIEW will take the samples From this information LabVIEW allocates a buffer in memory to hold a number of data points equal to the number of samples per channel multiplied by the number of channels As the data acquisition continues the buffer fills with the data However the data may not actually be accessible until LabVIEW acquires all the samples N Once the data acquisition is complete the data in the buffer can be analyzed stored to disk or displayed to the screen by your VI Acquiring a Sing
251. mebase determines the elapsed time Figure 28 2 External Connections for Counting Elapsed Time Chapter 28 Counting Signal Highs and Lows LabVIEW Data Acquisition Basics Manual 28 2 www ni com Am9513 With the Am9513 you can extend the counting range of a counter by connecting the OUT of one counter to the SOURCE of the next higher order counter counter 1 This is called cascading counters By cascading counters you can increase your counting range from a 16 bit counting range of 65 535 to a 32 bit counting range of 4 294 967 295 The Am9513 chip has a set of five counters where higher order counters can be cascaded The TIO 10 device has two Am9513 chips for a total of 10 counters Table 28 1 identifies adjacent counters on the Am9513 one and two chips This information is useful when cascading counters Figure 28 3 shows typical external connections for cascading counters when counting events Notice that the OUT of counter is connected to the SOURCE of counter 1 Figure 28 3 External Connections to Cascade Counters for Counting Events Table 28 1 Adjacent Counters for Counter Chips Next Lower Counter Counter Next Higher Counter 5 1 2 1 2 3 2 3 4 3 4 5 4 5 1 10 6 7 6 7 8 7 8 9 8 9 10 9 10 6 Chapter 28 Counting Signal Highs and Lows National Instruments Corporation 28 3 LabVIEW Data Acquisition Basics Manual Figure 28 4 shows typical external connections for cascad
252. ment amp Automation Explorer Appendix A LabVIEW Data Acquisition Common Questions LabVIEW Data Acquisition Basics Manual A 2 www ni com How can I tell when a continuous data acquisition operation does not have enough buffer capacity The scan backlog rises with time either steadily or in jumps or takes a long time to drop to normal after an interrupting activity like mouse movement If you can open another VI during the operation without receiving an overrun error you should have adequate buffer capacity I want to group two or more ports using my DIO32 DIO24 or DIO 96 device but I do not want to use handshaking I just want to read one group of ports just once How can I set it up in software Use Easy I O VIs Write to Digital Port or Read from Digital Port or Advanced Digital VIs DIO Port Config DIO Port Write or DIO Port Read and set multiple ports in the port list For Easy I O VIs you can specify up to four ports in the port list Whatever data you try to output to each port of your group will correspond to each element of the data array This also applies for input I want to use the OUT1 OUT2 OUT3 and IN1 IN2 IN3 pins on my DIO 32F device How do I address those pins using the Easy I O Digital VIs in LabVIEW These output and inputs pins are addressed together as port 4 OUT1 and IN1 are referred to as bit 0 OUT2 and IN2 are referred to as bit 1 and OUT3 and IN3 are referred to as bit 2 Only the NB D
253. ments Corporation 26 7 LabVIEW Data Acquisition Basics Manual This example uses a single buffer The block diagram uses the following Advanced VIs CTR Group Config CTR Buffer Config CTR Mode Config CTR Control and CTR Buffer Read CTR Group Config takes the counter and device and sets up a taskID CTR Buffer Config sets up a finite buffer whose size is determined by the value you enter in counts per buffer CTR Mode Config determines what type of counting operation to perform based on your choices for gate parameters and config mode CTR Control starts the counting operation but does not return until the counting has completed CTR Buffer Read reads the buffer of data and returns the values to buffered counts The buffered times are determined by dividing the counts by your chosen timebase For a complete description of this example refer to the information found in Windows Show VI Info Note Continuous buffered operations are supported by the new Advanced Counter VIs in NI DAQ 6 5 and higher Note If you are using NI DAQ 6 5 or higher National Instruments recommends you use the new Advanced Counter VIs such as Counter Group Config Counter Get Attribute Counter Set Attribute Counter Buffer Read and Counter Control For more information refer to the LabVIEW Online Reference by selecting Help Online Reference Increasing Your Measurable Width Range The maximum counting range of a counter and the chosen internal timebase determ
254. n 13 2 25 12 FREQ_OUT pin 13 2 25 12 frequency and period measurement 27 1 to 27 8 connecting counters for measuring 27 3 to 27 4 equation for obtaining measurements 27 3 high frequency signals 27 4 to 27 6 how and when to measure 27 1 to 27 2 low frequency signals 27 7 to 27 8 square wave frequency measurement figure 27 2 square wave period measurement figure 27 2 frequency division 29 1 to 29 3 8253 54 29 3 TIO ASIC DAQ STC and Am9513 29 2 to 29 3 wiring figure 29 1 Function Generator VI 12 4 Functions palette Array amp Cluster 3 15 DAQ 6 1 locating VIs 3 3 G gain defined 3 13 gains SCXI default gain 21 3 description 21 3 to 21 4 Index National Instruments Corporation I 13 LabVIEW Data Acquisition Basics Manual SCXI 1100 channel arrays input limits array and gains table 21 4 GATE input for counters 24 2 General Error Handler VI debugging VIs 30 2 pulse width measurement 26 6 Generate Continuous Sinewave VI 12 3 Generate Delayed Pulse VI single square pulse generation 25 5 stopping counter generations 25 14 Generate N Updates example VI 12 2 Generate N Updates ExtUpdateClk VI 13 1 to 13 2 Generate Pulse Train on FOUT VI 13 2 25 13 Generate Pulse Train on FREQ_OUT VI 13 2 25 13 Generate Pulse Train VI continuous pulse train generation 8253 54 25 9 TIO ASIC DAQ STC and Am9513 25 8 finite pulse train generation DAQ STC and Am9513 25 10 stopping coun
255. n unknown TTL signal frequency or use a single pulse to trigger an analog acquisition There are two basic types of counter signal generation toggled and pulsed When a counter reaches a certain value a counter configured for toggled output changes the state of the output signal while a counter configured for pulsed output outputs a single pulse The width of the pulse is equal to one cycle of the counter SOURCE signal The following is a list of terms you should know before outputting a pulse or pulse train using LabVIEW phase 1 refers to the first phase or delay to the pulse phase 2 refers to the second phase or the pulse itself period is the sum of phase 1 and phase 2 Frequency is the reciprocal of the period 1 period In LabVIEW you can adjust and control the times of phase 1 and phase 2 in your counting operation You do this by specifying a duty cycle The duty cycle equals phase 2 period where period phase 1 phase 2 Chapter 25 Generating a Square Pulse or Pulse Trains LabVIEW Data Acquisition Basics Manual 25 2 www ni com Examples of various duty cycles are shown in Figure 25 1 The first line shows a duty cycle of 0 5 where phase 1 and phase 2 are the same duration A signal with a 0 5 duty cycle acts as a SOURCE for counter operations The second line shows a duty cycle of 0 1 where phase 1 has increased and phase 2 has decreased The final line
256. n LabVIEW 3 3 to 3 4 limit settings 3 11 to 3 13 organization 3 3 to 3 4 parameter conventions 3 5 to 3 6 SCXI examples 22 6 to 22 10 Utility VIs 3 5 Index LabVIEW Data Acquisition Basics Manual I 22 www ni com W Wait ms VI 6 7 6 8 Wait ms VI finite pulse train generation 25 10 stopping counter generations 25 14 Wait on Occurrence function 7 9 Wait Until Next ms Multiple VI improving control loop performance 6 8 multiple channel single point analog input 6 4 software timed analog I O control loops 6 5 waveform acquisition See buffered waveform acquisition waveform generation See buffered waveform generation Web support from National Instruments B 1 to B 2 online problem solving and diagnostic resources B 1 software related resources B 2 Wheatstone bridge 22 14 Windows environment installation and configuration DAQ devices 2 4 SCXI software 2 8 NI DAQ driver 2 3 Worldwide technical support B 2 Write 1 Pt to Dig Line E VI 16 3 Write N Updates example VI 11 2 Write to 1 Dig Line 653x VI 16 2 Write to 1 Dig Line 8255 VI 16 2 Write to 1 Dig Port 653x VI 16 3 Write to 1 Dig Port 8255 VI 16 3 Write to 1 Dig Port E VI 16 4 Write to 2 Dig Port 653x VI 16 3 Write to 2 Dig Port 8255 VI 16 3 Write to Digital Port VI 22 19 Write to Digital Port 653x VI 16 3 Write to Digital Port 8255 VI 16 3 Write to Spreadsheet File VI 7 6
257. n optionally gate counter with a pulse to control when it starts and stops timing To do this wire your pulse to the GATE of counter and choose the appropriate gate mode from the front panel menu For a complete description of this example refer to the information found in Windows Show VI Info Am9513 The Count Time Easy 9513 VI located in labview examples daq counter Am9513 llb uses the Easy VI Count Events or Time which can be found in Functions Data Acquisition Counter This VI initiates the counter to count the number of rising edges of a known internal timebase at the SOURCE of counter The Count Events or Time VI takes care of dividing the count by the timebase frequency to determine the elapsed time The counter continues timing until you click the STOP button You do not need to make any external connections if the number of counters to use menu is set to one counter 16 bits If you set the number of counters to use menu to two counters 32 bits you must externally wire the OUT of counter to the SOURCE of counter 1 The length of time that can be counted depends on the maximum count of the counter s and the chosen timebase For example the 65 535 16 bit count of the Am9513 and a timebase of 1 MHz can count time for 65 ms Using the 100 Hz timebase and two counters 32 bits you can count time for over a year For a complete description of this example refer to the information found in Windows Show VI Info If you
258. nal because the junction with the screw terminals itself forms another thermocouple You can use the resulting voltage from the temperature sensor on the terminal block for cold junction compensation The cold junction compensation voltage is used when linearizing voltage readings from thermocouples into temperature values The SCXI modules used to measure temperature in this section are the SCXI 1100 SCXI 1101 SCXI 1102 SCXI 1112 SCXI 1120 SCXI 1120D SCXI 1121 SCXI 1122 SCXI 1125 SCXI 1127 SCXI 1141 SCXI 1142 and SCXI 1143 Most of the terminal blocks used with these modules have temperature sensors that can be used as cold junction compensation Chapter 22 Common SCXI Applications National Instruments Corporation 22 3 LabVIEW Data Acquisition Basics Manual In addition the SCXI 1100 SCXI 1112 SCXI 1122 SCXI 1125 SCXI 1141 SCXI 1142 and SCXI 1143 offer a way for you to ground the module amplifier inputs so you can read the amplifier offset You can subtract the amplifier offset value to determine the actual voltages Temperature Sensors for Cold Junction Compensation The temperature sensors in the terminal blocks for the analog input modules can be used for cold junction compensation If you are operating your SCXI modules in multiplexed mode leave the cold junction sensor jumper on the terminal block in the mtemp factory default position If you are using parallel mode you can use the dtemp jumper setting N
259. nalog Output 12 1 Changing the Waveform during Generation Circular Buffered Output 12 3 Eliminating Errors from Your Circular Buffered Application 12 4 Buffered Analog Output Examples 12 4 Chapter 13 Letting an Outside Source Control Your Update Rate Externally Controlling Your Update Clock 13 1 Supplying an External Test Clock from Your DAQ Device 13 2 Chapter 14 Simultaneous Buffered Waveform Acquisition and Generation Using E Series MIO Boards 14 1 Software Triggered 14 1 Hardware Triggered 14 2 Using Legacy MIO Boards 14 3 Software Triggered 14 3 Hardware Triggered 14 3 Using Lab 120
260. nalog output using the Intermediate VIs This VI is more efficient than the Easy Analog Output VIs in that it configures and allocates a buffer when its iteration input is 0 and deallocates the buffer when the clear generation input is TRUE With the AO Continuous Gen VI you can configure the size of the data buffer and the limit settings of each channel For more information on how to set limit settings refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts The Continuous Generation example VI located in labview examples daq anlogout anlogout llb uses the AO Continuous Gen VI In this example the data completely fills the buffer on the first iteration On subsequent iterations new data is written into one half of the buffer while the other half continues to output data To gain more control over your analog output application use the Intermediate VIs shown in Figure 12 3 With these VIs you can set up an alternate update clock source and you can monitor the update rate the VI actually uses The AO Config VI sets up the channels you specify for Chapter 12 Buffering Your Way through Waveform Generation LabVIEW Data Acquisition Basics Manual 12 4 www ni com analog output The AO Write VI places the data in a buffer The AO Start VI begins the actual generation at the update rate The AO Write VI in the While Loop writes new data to the buffer until you click the Stop button The AO Clear VI clears the analog channels Figur
261. nction compensation 22 3 to 22 5 using RTDs 22 10 to 22 13 using thermocouples 22 2 to 22 3 VI examples 22 6 to 22 10 terminal count TC 24 3 Thermistor Conversion VI 22 4 thermocouples measuring temperature example 22 2 to 22 3 SCXI Thermocouple example VIs 22 5 SCXI 1100 Thermocouple VI 22 6 SCXI 1120 1121 Thermocouple example VI 22 10 timebase period uncertainty 25 13 timed digital I O 18 1 to 18 3 continuous timed digital I O 18 2 to 18 3 finite timed digital I O 18 1 to 18 2 with triggering 18 2 without triggering 18 1 to 18 2 overview 18 1 pattern digital I O defined 15 2 TIO ASIC counter buffered pulse and period measurement 26 6 continuous pulse train generation 25 7 to 25 8 controlling pulse width measurement 26 5 to 26 6 counting operations with no counters available 25 12 to 25 13 description 24 5 Index National Instruments Corporation I 21 LabVIEW Data Acquisition Basics Manual determining pulse width 26 2 to 26 3 dividing frequencies 29 2 to 29 3 event counting 28 3 to 28 4 finite pulse train generation 25 10 to 25 11 frequency and period measurement connecting counters 27 3 to 27 4 high frequency signals 27 4 to 27 5 how and when to measure 27 2 to 27 3 low frequency signals 27 7 to 27 8 internal timebases with maximum pulse width measurements table 26 8 single square pulse generation 25 5 to 25 6 square pulse generation 25 3 toggled counter signal generation 25
262. ne channel multiple times the data is returned as a two dimensional 2D array If you were to create a 2D array and label the index selectors on a LabVIEW front panel the array might look like Figure 3 8 Figure 3 8 Example of a Basic 2D Array The two vertically arranged boxes on the left are the row and column index selectors for the array The top index selects a row and the bottom index selects a column You can organize data for a 2D array in one of two ways First you can organize the data by rows If the array contained data from analog input channels each row holds data from one channel Selecting a row selects a channel while selecting a column selects a scan of data This ordering method is often referred to as row major order When you create data in a nested For Loop the inner loop creates a row for each iteration of the outer loop If you were to label your index selectors for a row major 2D array the array might look like Figure 3 9 Figure 3 9 2D Array in Row Major Order You also can organize 2D array data by columns The Analog Input VIs organize their data in this way Each column holds data from one channel so selecting a column selects a channel Selecting a row selects a scan of data This ordering method is often called column major order If you were to label your index selectors for a column major 2D array the array might look like Figure 3 10 Chapter 3 Basic LabVIEW Data Acquisition Concepts Nation
263. need more control over when your elapsed timing begins and ends use the Intermediate VIs instead of the Easy VIs For an example open the Count Time Int 9513 VI located in labview examples daq counter Am9513 llb Chapter 28 Counting Signal Highs and Lows National Instruments Corporation 28 7 LabVIEW Data Acquisition Basics Manual This example uses the Intermediate VIs Event or Time Counter Config Counter Start Counter Read and Counter Stop The Event or Time Counter Config VI configures counter to count the number of rising edges of a known internal timebase The Counter Start VI begins the counting operation for counter The Counter Read VI returns the count until you click the STOP button or an error occurs The count value is divided by the timebase to determine the elapsed time Finally the Counter Stop VI stops the counter operation You optionally can gate counter with a pulse to control when it starts and stops timing To do this wire your pulse to the GATE of counter and choose the appropriate gate mode from the front panel menu Additionally you can cascade two counters by choosing two counters 32 bits in the number of counters to use menu This extends your elapsed time range You also must wire the OUT of counter to the SOURCE of counter 1 for this increased range For a complete description of this example refer to the information found in Windows Show VI Info 8253 54 The Count Time 8253 VI located in labv
264. nerate signals If you want to acquire analog signals go to question 5 If you want to generate analog signals refer to question 6 If you want to acquire and generate analog signals refer to the Using Analog Input Output Control Loops section of Chapter 6 One Stop Single Point Acquisition If you want to acquire or generate digital signals read the next question Chapter 4 Where You Should Go Next LabVIEW Data Acquisition Basics Manual 4 4 www ni com 4 Digital or Counter Interfacing Digital I O interfaces primarily with binary operations such as turning external equipment on or off or sense logic states such as the on off position of the switch Counters generate individual digital pulses or waves or count digital events like how many times a digital signal rises or falls in value If you are performing digital I O refer to question 9 If you need to use counters read question 10 5 Single Point or Multiple Point Acquisition Do you want to acquire a signal value s at one time or over a period of time at a certain rate If you measure a signal at a given instant of time you are performing single point acquisition If you measure signals over a period of time at a certain rate you are performing multiple point or waveform acquisition If you want single point acquisition refer to Chapter 6 One Stop Single Point Acquisition If you want multiple point acquisition read question 7 6 Single Point or Mult
265. nfo If you need more control over when your event counting begins and ends use the Intermediate VIs instead of the Easy VIs For an example open the Count Events Int 9513 VI located in labview examples daq counter Am9513 llb This example uses the Intermediate VIs Event or Time Counter Config Counter Start Counter Read and Counter Stop The Event or Time Counter Config VI configures counter to count the number of rising edges of a TTL signal at its SOURCE input pin The Counter Start VI begins the counting operation for counter The Counter Read VI returns the count until you click the STOP button or an error occurs Finally the Counter Stop VI stops the counter operation You must externally wire your signal to be counted to the SOURCE of counter You optionally can gate counter with a pulse to control when it starts and stops counting To do this wire your pulse to the GATE of counter and choose the appropriate gate mode from the front panel menu Additionally you can cascade two counters by choosing two counters 32 bits in the number of counters to use menu This extends your counting range to over 4 billion You also must wire the OUT of counter to the SOURCE of counter 1 for this increased counting range For a complete description of this example read the information found in Window Show VI Info Chapter 28 Counting Signal Highs and Lows National Instruments Corporation 28 5 LabVIEW Data Acquisition Basics Manual 8
266. ns for specific devices notes 9 4 controlling externally 9 3 to 9 5 rate parameter 5 18 setting channel clock rate 9 3 simultaneous control of scan and channel clocks 9 7 TTL signal example 9 3 channel configuration in NI DAQ 5 x or 6 x 2 11 Channel to Index VI note 8 10 circular buffered analog input asynchronous continuous acquisition using DAQ occurrences 7 9 continuous acquisition from multiple channels 7 8 to 7 9 examples basic circular buffered analog input 7 10 Cont Acq amp Chart buffered VI 7 11 Cont Acq amp Graph buffered VI 7 11 Cont Acq to File binary VI 7 11 Cont Acq to File scaled VI 7 11 Cont Acq to Spreadsheet File VI 7 11 how circular buffers work figure 7 7 to 7 8 overview 7 6 to 7 7 circular buffered analog output changing waveform during generation 12 3 to 12 4 eliminating errors 12 4 circular buffered digital I O examples 17 7 to 17 8 clocks See channel clock scan clock update clock code width calculating 5 7 cold junction compensation 22 3 to 22 5 column major order 3 14 to 3 15 common questions about LabVIEW data acquisition A 1 to A 3 common mode voltage defined 5 11 illustration 5 11 conditional retrieval 8 8 See also software triggering configuration See installation and configuration Cont Acq amp Chart buffered VI 7 11 Cont Acq amp Graph buffered VI 7 11 Cont Acq to File binary VI 7 11 Cont Acq to File scaled VI 7 11 12 4
267. o Appendix B Hardware Capabilities in the LabVIEW Function and VI Reference Manual for a list of the maximum sampling rates for each DAQ device You also can refer to the LabVIEW Online Reference by selecting Help Online Reference Note When using the NB A2100 or the NB A2150 boards specifying an odd buffer size or an odd number of samples when acquiring data with one channel results in 10089 badTotalCountError To avoid this error specify an even number of samples and discard the extra sample Simple Buffered Analog Input Examples This section contains several different examples of simple buffered analog input Simple Buffered Analog Input with Graphing Figure 7 2 shows how you can use the AI Acquire Waveforms VI to acquire two waveforms from channels 0 and 1 and then display the waveforms on separate graphs This type of VI is useful for comparing two or more waveforms or for analyzing how a signal looks before and after going through a system In this illustration 1 000 scans of channels 0 and 1 are taken at the rate of 5 000 scans per second The actual scan period output displays in the actual timebase on the X Axis of the graphs Remember that each column of the 2D array contains the information for each channel maximum sampling rate number of channels Chapter 7 Buffering Your Way through Waveform Acquisition National Instruments Corporation 7 5
268. o the SCXI Operating Modes section of Chapter 20 Hardware and Software Setup for Your SCXI System for instructions about module cabling Operating Mode The system defaults to the multiplexed operating mode which is recommended for almost all SCXI applications Refer to the SCXI Operating Modes section of Chapter 20 Hardware and Software Setup for Your SCXI System for information about the operating modes available for each SCXI module type If the module is an analog input module enter the gain and filter settings for each channel in the bottom section of the dialog box The system disables the Channel control for any modules that use only one gain and filter setting for the entire module Chapter 2 Installing and Configuring Your Data Acquisition Hardware National Instruments Corporation 2 11 LabVIEW Data Acquisition Basics Manual Configuring Your Channels in NI DAQ 5 x 6 x After you install and configure your hardware you can configure your channels LabVIEW DAQ software includes the DAQ Channel Wizard which you can use to configure the analog and digital channels on your DAQ device DAQ plug in boards standalone DAQ products or SCXI modules NI DAQ 6 5 or higher integrates the DAQ Channel Wizard into Measurement amp Automation Explorer In NI DAQ 5 x you can configure only analog input channels The DAQ Channel Wizard helps you define the physical quantities you are measuring or generating on each DAQ hardware
269. of the following methods Onboard clock on 6533 DIO 32HS devices User supplied clock Change detection mode input only where a pattern is acquired whenever there is a state transition on one of the data lines There are two general categories of timed digital I O With Finite Timed Digital I O a predetermined number of patterns are acquired or generated at a rate controlled by one of the timing sources discussed above With Continuous Timed Digital I O digital data is continuously acquired or generated until the user stops the process The rate can be controlled by one of the timing sources discussed above Finite Timed Digital I O In finite timed digital I O mode LabVIEW allocates a single buffer of computer memory large enough to hold all the patterns Optionally you can use triggering in this mode of digital I O Finite Timed I O without Triggering In this mode the start and or stop of the digital I O process is not controlled by an external trigger event Instead it initiates as soon as the VI is run The Buffered Pattern Input VI and Buffered Pattern Output VI show how to perform finite timed I O In these examples the 6533 onboard clock is programmed to the clock frequency value when the clock source Chapter 18 Timed Digital I O LabVIEW Data Acquisition Basics Manual 18 2 www ni com parameter on the VI front panel is set to internal A user supplied clock is used when the clock so
270. og Input VIs Channel List Parameter Channel Specified AMy x Channel x on AMUX 64T device y AM4 8 Channel 8 on AMUX 64T device 4 National Instruments Corporation 6 1 LabVIEW Data Acquisition Basics Manual 6 One Stop Single Point Acquisition This chapter shows how you can acquire one data point from a single channel and then one data point from each of several channels using LabVIEW Single Channel Single Point Analog Input A single channel single point analog input is an immediate non buffered operation In other words the software reads one value from an input channel and immediately returns the value to you This operation does not require any buffering or timing Use single channel single point analog input when you need one data point from one channel An example of this would be if you periodically needed to monitor the fluid level in a tank You can connect the transducer that produces a voltage representing the fluid level to a single channel on your DAQ device and initiate a single channel single point acquisition whenever you want to know the fluid level For most basic operations use the AI Sample Channel VI located in the Functions Data Acquisition Analog Input palette The Easy Analog Input VI AI Sample Channel measures the signal attached to the channel you specify on your DAQ device and returns the scaled value Note If you set up your channel in the DAQ Channel Wizard you do not need to ent
271. onsiderations for SCXI When you want LabVIEW to acquire data from SCXI analog input channels you use the analog input VIs in the same way that you acquire data from onboard channels You also read and write to your SCXI relays and digital channels using the digital VIs in the same way that you read and write to onboard digital channels You can write voltages to your SCXI analog output channels using the analog output VIs The following sections describe special programming considerations for SCXI in LabVIEW including channel addressing gains limit settings and settling time Note This chapter does not apply if you use the DAQ Channel Wizard to configure your channels In NI DAQ 6 5 or higher the DAQ Channel Wizard is part of Measurement amp Automation Explorer If you use the DAQ Channel Wizard you address SCXI channels the same way you address onboard channels by specifying the channel name s LabVIEW configures your hardware by selecting the best input limits and gain for the named channel based on the channel configuration For more information about using the DAQ Channel Wizard to configure your channels see the Configuring Your Channels in NI DAQ 5 x 6 x section of Chapter 2 Installing and Configuring Your Data Acquisition Hardware For more information about using channel names refer to the Channel Name Addressing section of Chapter 3 Basic LabVIEW Data Acquisition Concepts SCXI Channel Addressing If you operate a module
272. or counter The Counter Read VI returns the count until you click the STOP button or an error occurs Finally the Counter Stop VI stops the counter operation Remember that you must externally wire your signal to be counted to the SOURCE of counter You optionally can gate counter with a pulse to control when it starts and stops counting To do this Chapter 28 Counting Signal Highs and Lows LabVIEW Data Acquisition Basics Manual 28 4 www ni com wire your pulse to the GATE of counter and choose the appropriate gate mode from the front panel menu For a complete description of this example refer to the information found in Windows Show VI Info Am9513 The Count Events Easy 9513 VI located in labview examples daq counter Am9513 llb uses the Easy VI Count Events or Time which can be found in Functions Data Acquisition Counter This VI initiates the counter to count the number of rising edges of a TTL signal at the SOURCE of counter The counter continues counting until you click the STOP button You must externally wire your signal to be counted to the SOURCE of counter Additionally you can cascade two counters by choosing two counters 32 bits in the number of counters to use menu This extends your counting range to over 4 billion You also must wire the OUT of counter to the SOURCE of counter 1 for this increased counting range For a complete description of this example refer to the information found in Windows Show VI I
273. or each chassis and enter it in the Address field 4 Leave the Method set to Serial In this setting LabVIEW communicates with the chassis serially using a DIO port of the plug in DAQ device The Path automatically sets itself to the device number of the appropriate DAQ device when you enter the Cabled Device information in step 5b Chapter 2 Installing and Configuring Your Data Acquisition Hardware LabVIEW Data Acquisition Basics Manual 2 10 www ni com 5 Enter the configuration for each slot in the chassis The fields in the bottom two sections of the dialog box reflect the settings for the selected Module number Refer to your SCXI chassis hardware manual to determine how the slots in a chassis are numbered You must set the following fields for each SCXI module you install Module type Select the correct module type for the module installed in the current slot If the current slot does not have a module leave this field set to None and advance the Module number to the next slot Cabled Device If the module in the current slot is directly cabled to a DAQ device in your computer set this field to the device number of that DAQ device Leave the Cabled Device field set to None if the module in the current slot is not directly cabled to a DAQ device If you are operating your modules in multiplexed mode you need to cable only one module in each chassis to your DAQ device If you are not using multiplexed mode refer t
274. or instance if your channels are 0 1 and 2 you can specify a list of channels in a single element by separating the individual channels by commas for example 0 1 2 Or because 0 refers to the first channel in a consecutive channel range and 2 refers to the last channel you can specify the range by separating the first and last channels with a colon for example 0 2 Some Easy and Advanced Digital VIs and Intermediate Counter VIs need only one port or counter to be specified Refer to the LabVIEW Function and VI Reference Manual or select Help Online Reference for more information You also can select Help Show Help and put your cursor on the VI to view the VI Help window for the VI you intend to use LabVIEW recognizes three types of analog channels on a DAQ device onboard AMUX 64T and SCXI channels It recognizes two types of digital ports and counters onboard and SCXI This section describes addressing onboard channels ports and counters AMUX 64T addressing is described later in Chapter 5 Things You Should Know about Analog Input SCXI channel port and counter addressing is described in Chapter 19 Things You Should Know about SCXI Onboard channels refer to analog or digital I O channels provided by the plug in DAQ device If x is an onboard channel you can specify this by entering x or OBx as the channel list element Refer to the description of your device in your hardware user manual for restrictions on channel order
275. oration G 15 LabVIEW Data Acquisition Basics Manual timed digital I O A type of digital acquisition generation where LabVIEW updates the digital lines or port states at a fixed rate The timing is controlled either by a clock or by detection of a change in the pattern Timed digital I O can be either finite or continuous Also called pattern generation or pattern digital I O TIO ASIC Timing I O Application Specific Integrated Circuit Found on 660x devices toggled output A form of counter signal generation by which the output changes the state of the output signal from high to low or low to high when the counter reaches a certain value top level VI VI at the top of the VI hierarchy This term is used to distinguish the VI from its subVIs track and hold A circuit that tracks an analog voltage and holds the value on command transducer excitation A type of signal conditioning that uses external voltages and currents to excite the circuitry of a signal conditioning system into measuring physical phenomena trigger Any event that causes or starts some form of data capture TTL Transistor Transistor Logic U unipolar A signal range that is either always positive or negative but never both for example 0 to 10 V not 10 to 10 V update One or more analog or digital output samples Typically the number of output samples in an update is equal to the number of channels in the output group For example one pulse from t
276. ore about this VI refer to Chapter 29 Calibration and Configuration VIs in the LabVIEW Function and VI Reference Manual or refer to the LabVIEW Online Reference by selecting Help Online Reference The user area is an area for you to store your own calibration constants that you calculate using the SCXI Cal Constants VI You also can put a copy of your own constants in the default load area if you want LabVIEW to automatically load your constants for subsequent operations You can read and write to the user area Note Use the user area in EEPROM to store any calibration constants that you may need to use later This prevents you from accidentally overwriting your constants in the default load area because you will have two copies of your new constants You can revert to the factory constants by copying the factory area to the default load area without wiping out your new constants entirely Chapter 23 SCXI Calibration Increasing Signal Measurement Precision National Instruments Corporation 23 3 LabVIEW Data Acquisition Basics Manual Calibrating SCXI Modules The SCXI Cal Constants VI in LabVIEW automatically calculates the calibration constants for your module with the precision you need for your particular application You can find this VI in Functions Data Acquisition Calibration and Configuration Refer to Chapter 29 Calibration and Configuration VIs in the LabVIEW Function and VI Reference Manual for specifics on th
277. orporation II 1 LabVIEW Data Acquisition Basics Manual Part II Catching the Wave with Analog Input This part of the manual contains basic information about acquiring data with LabVIEW including acquiring a single point or multiple points triggering your acquisition and using outside sources to control acquisition rates Part II Catching the Wave with Analog Input contains the following chapters Chapter 5 Things You Should Know about Analog Input explains basic concepts on using analog input with LabVIEW Chapter 6 One Stop Single Point Acquisition shows you how to acquire one data point from a single channel and then one data point from each of several channels using LabVIEW and explains how software timing and or hardware timing affects the performance of analog I O Chapter 7 Buffering Your Way through Waveform Acquisition reviews the different methods of reading multiple channels and explains how LabVIEW stores the acquired data with each method Chapter 8 Controlling Your Acquisition with Triggers explains how to set your analog acquisition to occur at a certain time using either software or hardware triggering methods Chapter 9 Letting an Outside Source Control Your Acquisition Rate shows you how to control your data acquisition rate by some other external source in your system National Instruments Corporation 5 1 LabVIEW Data Acquisition Basics Manual 5 Things You Shoul
278. ot only ground loop induced errors but also the noise picked up in the environment to a certain degree On the other hand the single ended configuration allows for twice as many measurement channels and is acceptable when the magnitude of the induced errors is smaller than the required accuracy of the data CH0 CH1 CH2 CH15 MUX Vm Instrumentation Amplifier AISENSE AIGND Chapter 5 Things You Should Know about Analog Input LabVIEW Data Acquisition Basics Manual 5 14 www ni com You can use single ended measurement systems when all input signals meet the following criteria High level signals normally greater than 1 V Short or properly shielded cabling wiring traveling through a noise free environment normally less than 15 ft All signals can share a common reference signal at the source Use differential connections when your system violates any of the above criteria Channel Addressing with the AMUX 64T An AMUX 64T external multiplexer device expands the number of analog input signals a plug in DAQ device can measure You can address AMUX 64T channels when you attach one two or four AMUX 64T devices to a plug in DAQ device With this device you can multiplex four eight or 16 AMUX 64T channels into one device channel The scanning order of these AMUX 64T channels is fixed To specify a range of AMUX 64T channels enter the device channel into which the rang
279. ote The SCXI 1101 SCXI 1102 SCXI 1112 and SCXI 1127 use the cjtemp string only in multiplexed mode The SCXI 1125 also uses the cjtemp string when the temperature sensor is configured in mtemp mode To read the temperature sensor use the standard SCXI string syntax in the channels array with mtemp substituted for the channel number as shown in the following table Channel List Element Channel Specified ob0 scx mdy mtemp The temperature sensor configured in mtemp mode on the multiplexed module in slot y of the chassis with ID x ob0 scx mdy cjtemp The temperature sensor configured in cjtemp mode on the multiplexed SCXI 1102 module in slot y of the chassis with ID x or the temperature sensor configured in mtemp mode on the multiplexed SCXI 1125 module in slot y of the chassis with ID x ob0 scx mdy cjtempz The temperature sensor configured in cjtemp mode for the analog channel z on the multiplexed SCXI 1112 module in slot y of the chassis with ID x Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 4 www ni com If you want to read the cold junction temperature sensor in dtemp mode you can read the following onboard channels for these modules For example you can run the Getting Started Analog Input VI found in labview examples daq run_me llb with the channel string ob0 sc1 md1 mtemp to read the temperature sensor on the terminal block connected to the module in slot 1 of SCXI chassis 1
280. ou are waiting for the DAQ Event If the DAQ Occurrence times out the timed out output value would be TRUE and AI Read would never be called When your acquisition is complete DAQ Occurrence is called again to clear all occurrences Chapter 7 Buffering Your Way through Waveform Acquisition LabVIEW Data Acquisition Basics Manual 7 10 www ni com Circular Buffered Analog Input Examples The only differences between the simple buffered applications and circular buffered applications in the block diagram is the number of scans to acquire input of the AI Start VI is set to 0 and you must call the AI Read VI repeatedly to retrieve your data These changes can be applied to many of the examples in the previous section on simple buffered analog input However this section reviews the basic circular buffered analog input VI here and describes some other example VIs that are included with LabVIEW Basic Circular Buffered Analog Input Figure 7 5 shows an example VI that brings data from channel 0 at a rate of 1 000 samples s into a buffer that can hold 4 000 samples This type of example might be handy if you wanted to watch the data from a channel over a long period of time but you could not store all the data in memory at once The AI Config VI sets up the channel specification and buffer size then the AI Start VI initiates the background data acquisition and specifies the rate Inside the While Loop the AI Read VI repeatedly reads blocks of
281. output in the first frame of a sequence inside the loop and additional processing in subsequent frames of the sequence Keep in mind that this additional processing must be less than your control loop interval Otherwise you will not be able to keep up with your control loop rate Improving Control Loop Performance There are some performance issues you should take into account if you plan to have other VIs or loops execute in parallel with your hardware timed control loop When you call the AI Single Scan VI in a hardware timed control loop the VI waits until the next scan is acquired before returning which means that the CPU is waiting inside the NI DAQ driver until the scan is acquired Consequently if you try to run other LabVIEW VIs or while loops in the same block diagram in parallel with your hardware timed control loop they may run more slowly or intermittently You can reduce this problem by putting a software delay with the Wait ms VI at the end of your loop after you write your analog output values Your other LabVIEW VIs and loops can then execute during this time Another good technique is to poll for your analog input without waiting in the driver You can set the AI Single Scan VI time limit in sec to 0 Then the VI reads the DAQ Device FIFO buffer and returns immediately Chapter 6 One Stop Single Point Acquisition LabVIEW Data Acquisition Basics Manual 6 8 www ni com regardless of whether the next scan was acquir
282. ovide you with immediate answers and solutions 24 hours a day 365 days a year National Instruments maintains extensive online technical support resources They are available to you at no cost are updated daily and can be found in the Technical Support section of our Web site at www ni com support Online Problem Solving and Diagnostic Resources KnowledgeBase A searchable database containing thousands of frequently asked questions FAQs and their corresponding answers or solutions including special sections devoted to our newest products The database is updated daily in response to new customer experiences and feedback Troubleshooting Wizards Step by step guides lead you through common problems and answer questions about our entire product line Wizards include screen shots that illustrate the steps being described and provide detailed information ranging from simple getting started instructions to advanced topics Product Manuals A comprehensive searchable library of the latest editions of National Instruments hardware and software product manuals Hardware Reference Database A searchable database containing brief hardware descriptions mechanical drawings and helpful images of jumper settings and connector pinouts Application Notes A library with more than 100 short papers addressing specific topics such as creating and calling DLLs developing your own instrument driver software and porting a
283. ples 8 7 Software Triggering 8 8 Conditional Retrieval Examples 8 11 Chapter 9 Letting an Outside Source Control Your Acquisition Rate Externally Controlling Your Channel Clock 9 3 Externally Controlling Your Scan Clock 9 5 Externally Controlling the Scan and Channel Clocks 9 7 Contents LabVIEW Data Acquisition Basics Manual viii www ni com PART III Making Waves with Analog Output Chapter 10 Things You Should Know about Analog Output Single Point Output 10 1 Buffered Analog Output 10 1 Chapter 11 One Stop Single Point Generation Single Immediate Updates 11 1 Multiple Immediate Updates 11 2 Chapter 12 Buffering Your Way through Waveform Generation Buffered A
284. ples are located in labview examples daq digital 653x llb Select Windows Show VI Info for any of these examples for more information about using and testing them 8255 Family The example Dig Word Handshake In 8255 VI shows how to read nonbuffered data using handshaking The example Dig Word Handshake Out 8255 VI shows how to write nonbuffered data using handshaking These examples are located in labview examples daq digital 8255 llb Select Windows Show VI Info for any of these examples for more information about using and testing them Chapter 17 Handshaked Digital I O LabVIEW Data Acquisition Basics Manual 17 6 www ni com Buffered Handshaking With buffered handshaking you can store multiple points in computer memory You also can access data as it is being acquired through the read location and scan backlog terminals of the DIO Read subVI Use this technique if multiple pulses are expected on the handshaking lines Buffered handshaking comes in several forms simple iterative and circular You can use simple and iterative buffered handshaking on all DAQ devices that support handshaking You can perform circular buffered handshaking only on 6533 devices Simple Buffered Handshaking You can think of a simple buffer as a storage place in computer memory where buffer size equals the number of updates multiplied by the number of ports With simple buffered handshaking one or more ports can be used to read or write data Al
285. pplications between platforms and operating systems Appendix B Technical Support Resources LabVIEW Data Acquisition Basics Manual B 2 www ni com Software Related Resources Instrument Driver Network A library with hundreds of instrument drivers for control of standalone instruments via GPIB VXI or serial interfaces You also can submit a request for a particular instrument driver if it does not already appear in the library Example Programs Database A database with numerous non shipping example programs for National Instruments programming environments You can use them to complement the example programs that are already included with National Instruments products Software Library A library with updates and patches to application software links to the latest versions of driver software for National Instruments hardware products and utility routines Worldwide Support National Instruments has offices located around the globe Many branch offices maintain a Web site to provide information on local services You can access these Web sites from www ni com worldwide If you have trouble connecting to our Web site please contact your local National Instruments office or the source from which you purchased your National Instruments product s to obtain support For telephone support in the United States dial 512 795 8248 For telephone support outside the United States contact your local branch office
286. programmable read only memory Read only memory that you can erase with an electrical signal and reprogram EISA Extended Industry Standard Architecture event The condition or state of an analog or digital signal external trigger A voltage pulse from an external source that triggers an event such as A D conversion F factory area One of three parts of the SCXI EEPROM The factory area contains factory set calibration constants This area is read only The other EEPROM areas are the default load area and the user area FIFO A first in first out memory buffer In a FIFO the first data stored is the first data sent to the acceptor filtering A type of signal conditioning that allows you to filter unwanted signals from the signal you are trying to measure Glossary National Instruments Corporation G 7 LabVIEW Data Acquisition Basics Manual floating signal sources Signal sources with voltage signals that are not connected to an absolute reference or system ground Some common example of floating signal sources are batteries transformers or thermocouples Also called nonreferenced signal sources G gain The amplification or attenuation of a signal GATE input pin A counter input pin that controls when counting in your application occurs grounded measurement system See referenced single ended RSE measurement system grounded signal sources Signal sources with voltage signals that are referenced to a sys
287. pters Chapter 19 Things You Should Know about SCXI includes basic concepts on how to use SCXI modules with LabVIEW for data acquisition Chapter 20 Hardware and Software Setup for Your SCXI System explains how to set up your SCXI hardware to work with data acquisition in LabVIEW Chapter 21 Special Programming Considerations for SCXI describes special programming considerations for SCXI in LabVIEW including channel addressing gains limit settings and settling time Chapter 22 Common SCXI Applications covers example VIs for analog input analog output and digital SCXI modules Chapter 23 SCXI Calibration Increasing Signal Measurement Precision teaches you how to calibrate SCXI modules and shows you where LabVIEW stores your calibration constants National Instruments Corporation 19 1 LabVIEW Data Acquisition Basics Manual 19 Things You Should Know about SCXI SCXI is a highly expandable signal conditioning system The next few chapters describe the basic concepts of signal conditioning the setup procedure for SCXI hardware the hardware operating modes the procedure for software installation and configuration the special programming considerations for SCXI in LabVIEW and some common SCXI applications Note For a better understanding of signal conditioning concepts the chapters in Part V SCXI Getting Your Signals in Great Condition refer to SCXI However the concepts and
288. put OBF is low while LabVIEW sends the data to an external device After the external device receives the data it sends a low pulse back on the ACK line Refer to your hardware manual to determine which digital ports you can configure for handshaking signals Digital Data on Multiple Ports 6533 Family You can group multiple ports together so you can send more digital values out at a time For DIO 32 devices the ports in the group determine which handshaking lines are used If the group includes port 0 or 1 handshaking occurs on the group 1 handshaking lines Otherwise if the group consists only of a combination of ports 2 and 3 handshaking occurs on the group 2 Chapter 17 Handshaked Digital I O National Instruments Corporation 17 3 LabVIEW Data Acquisition Basics Manual handshaking lines In either case the LabVIEW group number does not affect which handshaking lines are used 8255 Family For 8255 devices the ports in the group and the order of the ports both affect which handshaking lines are used If you want to group ports 0 and 1 and you list the ports in the order of 0 1 you should use the handshaking lines associated with port 1 In other words always use the handshaking lines associated with the last port in the list So if the ports are listed 1 0 use the handshaking lines associated with port 0 For 8255 based devices that perform handshaking such as the DIO 24 or DIO 96 connect all the STB lines togethe
289. r Measurement System Now that you have defined your signal you must choose a measurement system You have an analog signal so you must convert the signal with an ADC measurement system which converts your signal into information the computer can understand Some of the issues you must resolve before choosing a measurement system are your ADC bit resolution device range and signal range Resolution The number of bits used to represent an analog signal determines the resolution of the ADC You can compare the resolution on a DAQ device to the marks on a ruler The more marks you have the more precise your measurements Similarly the higher the resolution the higher the number of divisions into which your system can break down the ADC range and therefore the smaller the detectable change A 3 bit ADC divides the range into 23 or 8 divisions A binary or digital code between 000 and 111 represents each division The ADC translates each measurement of the analog signal to one of the digital divisions Figure 5 4 shows a sine wave digital image as obtained by a 3 bit ADC Clearly the digital signal does not represent the original signal adequately because the converter has too few digital divisions to represent the varying voltages of the analog signal By increasing the resolution to 16 bits however the ADC s number of divisions increases from 8 to 65 536 216 The ADC now can obtain an extremely accurate representation of the analog si
290. r if you are grouping ports for digital input as shown in Figure 17 1 Connect only the IBF line of the last port in the port list to the other device No connection is needed for the IBF signals for the other ports in the port list Figure 17 1 Connecting Signal Lines for Digital Input Port x 1 STB IBF last port in portList Port x n STB IBF Port x 2 STB IBF External Device Chapter 17 Handshaked Digital I O LabVIEW Data Acquisition Basics Manual 17 4 www ni com If you group ports for digital output on an 8255 based device connect only the handshaking signals of the last port in the port list as shown in Figure 17 2 Figure 17 2 Connecting Signal Lines for Digital Output Types of Handshaking Digital handshaking can be either nonbuffered or buffered Nonbuffered handshaking is similar to nonlatched digital I O because LabVIEW updates the digital lines immediately after every digital or handshaked pulse Note For the 6533 devices LabVIEW returns immediately after storing data in its FIFO buffer With buffered handshaking LabVIEW stores digital values in memory to be transferred after every handshaked pulse Both nonbuffered and buffered handshaking transfer one digital value after each handshaked pulse Use nonbuffered handshaking for basic digital applications Use buffered handshaking when your application requires multiple handshaking pulses or high speeds By using a buffer with multiple
291. r the Generate Pulse Train on FOUT VI located in examples daq counter Am9513 llb These examples generate a pulse train on these outputs Knowing the Accuracy of Your Counters When you generate a waveform there can be an uncertainty of up to one timebase period between the start signal and the first counted edge of the timebase This is due to the uncertainty in the exact relation of the start signal which the software calls or the gate signal supplies to the first edge of the timebase as shown in Figure 25 12 Figure 25 12 Uncertainty of One Timebase Period phase 1 phase 2 uncertainty of 1 timebase period output timebase starting signal 1 timebase period Chapter 25 Generating a Square Pulse or Pulse Trains LabVIEW Data Acquisition Basics Manual 25 14 www ni com 8253 54 In addition to the previously described uncertainty the 8253 54 chip has an additional uncertainty when used in mode 0 Mode 0 generates a low pulse for a chosen number of clock cycles but a software delay is involved This delay is because with mode 0 the counter output is set low by a software write to the mode setting Afterward the count can be loaded and the counter starts counting down The time between setting the output to low and loading the count is included in the output pulse This time was found to be 20 s when tested on a 200 MHz Pentium computer Stopping Counter Generations You can stop a counting operation in several ways
292. rameters for VIs common DAQ VI parameters 3 7 conventions 3 5 to 3 6 pattern generation I O See timed digital I O Period Meas Config VI 26 5 period measurement See frequency and period measurement PFI5 UPDATE signal table 13 2 polling for analog input 6 7 to 6 8 ports digital ports and lines 15 1 grouping ports with handshaking 17 2 to 17 4 without handshaking A 2 port addressing 3 8 to 3 11 writing to digital port while reading digital data A 2 pressure measurement with strain gauges example 22 13 to 22 16 Probe tool 30 4 problem solving and diagnostic resources online B 1 pulse generation square See square pulse generation Index National Instruments Corporation I 17 LabVIEW Data Acquisition Basics Manual pulse train generation 25 7 to 25 12 8253 54 25 4 continuous pulse train 25 7 to 25 9 8253 54 25 9 TIO ASIC DAQ STC and Am9513 25 7 to 25 8 duty cycles figure 25 2 finite pulse train 25 9 to 25 12 8253 54 25 11 to 25 12 DAQ STC 25 11 physical connections figure 25 10 TIO ASIC DAQ STC and Am9513 25 10 to 25 11 TIO ASIC DAQ STC and Am9513 25 3 pulse width measurement 26 1 to 26 8 buffered pulse and period measurement 26 6 to 26 7 controlling pulse width measurement 26 5 to 26 6 counting input signals figure 26 1 determining pulse width 26 2 to 26 5 increasing measurable width range 26 7 to 26 8 measuring pulse width 26 1 to 26 2 overview 26 1 physical conne
293. rces referenced single ended RSE measurement system All measurements are made with respect to a common reference or a ground Also called a grounded measurement system RMS Root Mean Square row major order A way to organize the data in a 2D array by rows RSE Referenced Single Ended RTD Resistance Temperature Detector A temperature sensing device whose resistance increases with increases in temperature RTSI Real Time System Integration bus The National Instruments timing bus that interconnects data acquisition boards directly by means of connectors on top of the boards for precise synchronization of functions S s Seconds sample A single analog or digital input or output data point sample and hold A circuit that acquires and stores an analog voltage on a capacitor for a short period of time Glossary National Instruments Corporation G 13 LabVIEW Data Acquisition Basics Manual sample counter The clock that counts the output of the channel clock in other words the number of samples taken On boards with simultaneous sampling this counter counts the output of the scan clock and hence the number of scans scan One or more analog or digital input samples Typically the number of input samples in a scan is equal to the number of channels in the input group For example one pulse from the scan clock produces one scan that acquires one new sample from every analog input channel in the group s
294. rd DAQPad LabVIEW MITE National Instruments ni com NI DAQ NI PGIA PXI RTSI and SCXI are trademarks of National Instruments Corporation Product and company names mentioned herein are trademarks or trade names of their respective companies WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS 1 NATIONAL INSTRUMENTS PRODUCTS ARE NOT DESIGNED WITH COMPONENTS AND TESTING FOR A LEVEL OF RELIABILITY SUITABLE FOR USE IN OR IN CONNECTION WITH SURGICAL IMPLANTS OR AS CRITICAL COMPONENTS IN ANY LIFE SUPPORT SYSTEMS WHOSE FAILURE TO PERFORM CAN REASONABLY BE EXPECTED TO CAUSE SIGNIFICANT INJURY TO A HUMAN 2 IN ANY APPLICATION INCLUDING THE ABOVE RELIABILITY OF OPERATION OF THE SOFTWARE PRODUCTS CAN BE IMPAIRED BY ADVERSE FACTORS INCLUDING BUT NOT LIMITED TO FLUCTUATIONS IN ELECTRICAL POWER SUPPLY COMPUTER HARDWARE MALFUNCTIONS COMPUTER OPERATING SYSTEM SOFTWARE FITNESS FITNESS OF COMPILERS AND DEVELOPMENT SOFTWARE USED TO DEVELOP AN APPLICATION INSTALLATION ERRORS SOFTWARE AND HARDWARE COMPATIBILITY PROBLEMS MALFUNCTIONS OR FAILURES OF ELECTRONIC MONITORING OR CONTROL DEVICES TRANSIENT FAILURES OF ELECTRONIC SYSTEMS HARDWARE AND OR SOFTWARE UNANTICIPATED USES OR MISUSES OR ERRORS ON THE PART OF THE USER OR APPLICATIONS DESIGNER ADVERSE FACTORS SUCH AS THESE ARE HEREAFTER COLLECTIVELY TERMED SYSTEM FAILURES ANY APPLICATION WHERE A SYSTEM FAILURE WOULD CREATE A RISK OF HARM TO PROPERTY OR PERSONS
295. rdware component that controls timing for reading from or writing to groups cluster A set of ordered unindexed data elements of any data type including numeric Boolean string array or cluster The elements must be all controls or all indicators code width The smallest detectable change in an input voltage of a DAQ device column major order A way to organize the data in a 2D array by columns common mode voltage Any voltage present at the instrumentation amplifier inputs with respect to amplifier ground conditional retrieval A method of triggering in which you to simulate an analog trigger using software Also called software triggering configuration utility Refers to a utility that allows you to configure your hardware This utility is either Measurement amp Automation Explorer Windows or the NI DAQ Control Panel Macintosh Glossary LabVIEW Data Acquisition Basics Manual G 4 www ni com conversion device Device that transforms a signal from one form to another For example analog to digital converters ADCs for analog input digital to analog converters DACs for analog output digital input or output ports and counter timers are conversion devices counter timer group A collection of counter timer channels You can use this type of group for simultaneous operation of multiple counter timers coupling The manner in which a signal is connected from one location to another D D A Digital to analog
296. re with Digital I O contains the following chapters Chapter 15 Things You Should Know about Digital I O explains basic concepts of digital I O Chapter 16 Immediate Digital I O explains how to use digital lines to acquire and generate data immediately Chapter 17 Handshaked Digital I O shows you how you can synchronize digital data transfers between your DAQ devices and instruments Chapter 18 Timed Digital I O describes how you can synchronize digital data transfers at a fixed rate for either finite or continuous I O National Instruments Corporation 15 1 LabVIEW Data Acquisition Basics Manual 15 Things You Should Know about Digital I O Digital I O interfaces often are used to control processes generate patterns for testing and communicate with peripheral equipment such as heaters motors and lights Digital I O components on DAQ devices and SCXI modules consist of hardware parts that generate or accept binary on off signals As shown in Figure 15 1 all digital lines are grouped into ports on DAQ devices and banks on SCXI modules The number of digital lines per port or bank is specific to the particular device or module used but most ports or banks consist of four or eight lines Except for the 6533 DIO 32HS in immediate mode TIO 10 and E Series devices the lines within the same port or bank must all be of the same direction must either be all input or all output as shown in Figure 15
297. rganization for analog applications 3 14 to 3 16 limit settings 3 11 to 3 13 location of common DAQ examples 3 1 to 3 2 buffered See buffered waveform acquisition common questions about LabVIEW data acquisition A 1 to A 3 important terms 5 18 multiple channel single point 6 2 to 6 4 single channel single point 6 1 to 6 2 triggered See triggered data acquisition data acquisition hardware See hardware Data Acquisition palette 3 3 data organization for analog applications 3 14 to 3 16 column major order 3 14 to 3 15 row major order 3 14 two dimensional 2D arrays 3 14 to 3 16 data types for LabVIEW xxi debugging VIs 30 1 to 30 4 error handling 30 2 to 30 3 execution highlighting 30 3 hardware connection errors 30 1 setting breakpoints and showing advanced DAQ VIs 30 4 single stepping through VIs 30 3 software configuration errors 30 1 to 30 2 using Probe tool 30 4 VI construction errors 30 2 to 30 4 default input for VIs 3 6 default setting for VIs 3 6 Delayed Pulse 8253 VI 25 6 Delayed Pulse Generator Config VI finite pulse train generation 25 10 to 25 11 measuring frequency and period 27 5 single square pulse generation 25 6 Delayed Pulse Easy 9513 VI 25 5 Delayed Pulse Easy DAQ STC VI 25 5 Delayed Pulse Int 9513 VI 25 6 Delayed Pulse Int DAQ STC VI 25 6 delays for improving control loop performance 6 7 to 6 8 device range considerations for selecting analog input settings 5 7
298. riggered on the rising or falling edge of the digital trigger signal You also can specify a value for the time limit the maximum amount of time the VI waits for the trigger and requested data Chapter 8 Controlling Your Acquisition with Triggers National Instruments Corporation 8 5 LabVIEW Data Acquisition Basics Manual Digital Triggering Examples The Acquire N Scans Digital Trig VI example holds the data in a memory buffer until your device completes the acquisition The number of data points you need to acquire must be small enough to fit in memory This VI views and processes the information only after the acquisition To view and process information during the acquisition use the Acquire amp Proc N Scans Trig VI found in labview examples daq anlogin anlogin llb If you expect multiple digital trigger signals that start multiple acquisitions use the Acquire N Multi Digital Trig VI located in labview examples daq anlogin anlogin llb You connect analog trigger signals to the analog input channels the same channels where you connect analog data Your DAQ device monitors the analog trigger channel until trigger conditions are met You configure the DAQ device to wait for a certain condition of the analog input signal such as the signal level or slope either rising or falling Once the device identifies the trigger conditions it starts an acquisition Note If you are using channel names configured in the DAQ Channel Wizard
299. rnal clock within your device the scan clock sets the scan rate which controls the time interval between scans Also remember that most DAQ devices those that do not sample simultaneously proceed from one channel to the next or from one sample to the next depending on the channel clock rate Therefore the channel clock is the clock controlling the time interval between individual channel samples within a scan which means the channel clock proceeds at a faster rate than the scan clock The faster the channel clock rate the more closely in time your system samples the channels within each scan as shown in Figure 9 1 Note For devices with both a scan and channel clock lowering the scan rate does not change the channel clock rate Figure 9 1 Channel and Scan Intervals Using the Channel Clock channel interval 0 1 2 3 0 1 2 3 0 1 2 3 scan interval Chapter 9 Letting an Outside Source Control Your Acquisition Rate LabVIEW Data Acquisition Basics Manual 9 2 www ni com Some DAQ devices do not have scan clocks but rather use round robin scanning Figure 9 2 shows an example of round robin scanning Figure 9 2 Round Robin Scanning Using the Channel Clock The devices that always perform round robin scanning include but are not limited to the following NB MIO 16 PC LPM 16 PC LPM 16PnP PC 516 DAQCard 500 DAQCard 516 DAQCard 700 Lab NB Lab SE Lab LC
300. rnate clock rate specification into the AI Clock Config VI Table 9 1 External Scan Clock Input Pins Device External Scan Clock Input Pin All E Series Devices Any PFI Pin Default PF17 STARTSCAN Lab PC 1200 devices OUT B1 AT MIO 16 AT MIO 16F 5 AT MIO 16X AT MIO 16D AT MIO 64F 5 OUT2 Chapter 9 Letting an Outside Source Control Your Acquisition Rate National Instruments Corporation 9 7 LabVIEW Data Acquisition Basics Manual Remember that the which clock input of the AI Clock Config VI should be set to scan clock 1 Note You must divide the timebase by some number between 2 and 65 535 or you will get a bad input value error Because LabVIEW determines the length of time before AI Read times out based on the interchannel delay and scan clock rate you may need to force a time limit into AI Read In the example Acquire N Scans ExtScanClk VI the time limit is 5 seconds Externally Controlling the Scan and Channel Clocks You can control the scan and channel clocks simultaneously However make sure that you follow the proper timing Figure 9 5 demonstrates how you can set up your application to control both clocks Figure 9 5 Controlling the Scan and Channel Clock Simultaneously National Instruments Corporation III 1 LabVIEW Data Acquisition Basics Manual Part III Making Waves with Analog Output This part of the manual contains basic information about generating data with LabVIEW includin
301. rt VI begins the Chapter 6 One Stop Single Point Acquisition National Instruments Corporation 6 7 LabVIEW Data Acquisition Basics Manual analog acquisition at the loop rate scan rate parameter On the first iteration of the loop the AI Single Scan VI reads the newest data in the FIFO buffer Some data may have been acquired between the execution of the AI Start and the AI Single Scan VIs On the first iteration of the loop the application reads the latest data acquired between the AI Start and the AI Single Scan VIs On every subsequent iteration of the loop the application reads the oldest data in the FIFO buffer which is the next acquired point in the FIFO buffer If more than one value was stored in the DAQ device FIFO buffer when you read it your application was not able to keep up with the control loop acquisition and you have not responded with one control loop interval This eventually leads to an error condition which makes the loops complete After the application completes analog acquisition and generation the AI Clear VI clears the analog input task The block diagram of the Analog IO Control Loop hw timed VI also includes a waveform chart in the control loop This reduces your maximum loop rate You can speed up the maximum rate of the control loop by removing this graph indicator You easily can add other processing to your analog I O control loop by putting the analog input control loop calculations and analog
302. ruments folder in your Macintosh Extensions folder NI DAQ 5 x 6 x for Windows The NI DAQ driver nidaq32 dll is installed in your Windows system or system32 directory For information regarding hardware support for LabVIEW refer to Appendix B Hardware Capabilities in the LabVIEW Function and VI Reference Manual or select Help Online Reference LabVIEW VIs NI DAQ Drivers Data Acquisition Devices Chapter 2 Installing and Configuring Your Data Acquisition Hardware LabVIEW Data Acquisition Basics Manual 2 4 www ni com Installing and Configuring Your National Instruments Device Some DAQ devices have jumpers to set analog input polarity input mode analog output reference and so on Before you install your device refer to your hardware user manuals to check if your device has jumpers and find out how to change its settings You then can determine whether you need to change any jumper settings Record any jumper settings that you change so that you can enter the information correctly in the configuration utility The next step depends on what version of NI DAQ you have Go to the appropriate section below to continue the configuration of your devices Installing and Configuring Your DAQ Device Using NI DAQ 5 x 6 x Refer to the online help for specific instructions on how to install and configure your DAQ device If you are using Windows with NI DAQ 6 5 or higher refer to the help file for Measurement amp Automation
303. s 2D Array of signed 32 bit integers Cluster File Refnum About This Manual LabVIEW Data Acquisition Basics Manual xxii www ni com Related Documentation The following documents contain information you might find helpful as you read this manual LabVIEW QuickStart Guide LabVIEW User Manual G Programming Reference Manual LabVIEW Function and VI Reference Manual LabVIEW Online Reference available online by selecting Help Online Reference LabVIEW Online Tutorial which you launch from the LabVIEW dialog box Windows Application Note 025 Field Wiring and Noise Considerations for Analog Signals Application Note 046 Measuring Temperature with RTDs A Tutorial The user manuals for the data acquisition boards you use National Instruments Corporation I 1 LabVIEW Data Acquisition Basics Manual Part I Before You Get Started This part of the manual contains all the information you should know before you start learning about data acquisition with LabVIEW Part I Before You Get Started contains the following chapters Chapter 1 How to Use This Book explains how this manual is organized Chapter 2 Installing and Configuring Your Data Acquisition Hardware explains how to set up your system to use data acquisition with LabVIEW and your data acquisition hardware Chapter 3 Basic LabVIEW Data Acquisition Concepts explains key concepts in
304. s pH pH electrodes Table 19 1 Phenomena and Transducers Continued Phenomena Transducer Chapter 19 Things You Should Know about SCXI National Instruments Corporation 19 3 LabVIEW Data Acquisition Basics Manual Figure 19 1 shows some common types of transducers signals and the required signal conditioning for each Figure 19 1 Common Types of Transducers Signals and Signal Conditioning Transducers Signals Thermocouples RTDs Strain Gauges Common Mode or High Voltages Loads Requiring AC Switching or Large Current Flow Signals with High Frequency Noise Signal Conditioning Current Excitation Four Wire and Three Wire Configuration Linearization Amplification Linearization and Cold Junction Compensation Voltage Excitation Bridge Configuration and Linearization Isolation Amplifiers Optical Isolation Electromechanical Relays or Solid State Relays Lowpass Filters DAQ Device Chapter 19 Things You Should Know about SCXI LabVIEW Data Acquisition Basics Manual 19 4 www ni com Amplification The most common type of signal conditioning is amplification Amplifying electrical signals improves the accuracy of the resulting digitized signal and reduces noise For the highest possible accuracy amplify the signal so the maximum voltage swing equals the maximum input range of the ADC or digitizer Your system should amplify low level signals at the DAQ device or at the SCXI module
305. s 6 5 to 6 8 hardware timed control loops 6 6 to 6 7 improving performance 6 7 to 6 8 overview 6 5 software timed control loops 6 5 to 6 6 Analog IO Control Loop HW timed VI 6 6 to 6 7 Analog IO Control Loop VI 6 5 to 6 7 analog multiplexers AMUX 5 9 See also AMUX 64T devices analog output buffered overview 10 1 to 10 2 stored in 2D arrays 3 15 to 3 16 buffered waveform generation 12 1 to 12 3 examples 12 1 to 12 3 circular buffered waveform generation 12 3 to 12 4 eliminating errors 12 4 multiple immediate updates 11 2 SCXI analog output application example 22 17 single immediate updates 11 1 to 11 2 single point output choosing between single point or multiple point generation 4 4 overview 10 1 analog output SCXI modules application example 22 17 multiplexed mode 20 6 analog triggering description 8 5 to 8 6 diagram 8 5 examples 8 7 to 8 8 timeline for post triggered data acquisition figure 8 6 analog to digital converter ADC See ADC AO Clear VI circular buffered output 12 4 simultaneous buffered waveform acquisition and generation 14 1 waveform generation 12 3 AO Config VI analog output SCXI example 22 17 circular buffered output 12 3 to 12 4 simultaneous buffered waveform acquisition and generation 14 1 waveform generation 12 2 AO Continuous Gen VI 12 3 AO Generate Waveforms VI 12 1 AO Group Config VI 22 17 AO Hardware Config VI 22 17 AO Single Update VI analog output S
306. s For the fastest performance in parallel mode you can use the appropriate onboard port numbers instead of the SCXI channel string syntax in the digital VIs Refer to the hardware tables in Appendix B Hardware Capabilities in the LabVIEW Function and VI Reference Manual for the digital ports used in parallel mode on each DAQ device or refer to the LabVIEW Online Reference by selecting Help Online Reference Note If you are using a 6507 6508 DIO 96 an AT MIO 16D or an AT MIO 16DE 10 device you also can operate a digital module in parallel mode using the digital ports on the second half of the NB5 or R1005050 ribbon cable lines 51 100 Therefore the DIO 96 can operate two digital modules in parallel mode one module using the first half of the ribbon cable lines 1 50 and another module using the second half of the ribbon cable lines 51 100 Chapter 20 Hardware and Software Setup for Your SCXI System LabVIEW Data Acquisition Basics Manual 20 8 www ni com SCXI Software Installation and Configuration After you assemble your SCXI system you must run Measurement amp Automation Explorer or the configuration utility to enter your SCXI configuration LabVIEW needs the configuration information to program your SCXI system correctly Refer to Chapter 2 Installing and Configuring Your Data Acquisition Hardware National Instruments Corporation 21 1 LabVIEW Data Acquisition Basics Manual 21 Special Programming C
307. s how to connect your counter and device to generate a continuous pulse train If you use counter 0 an internal source is counted to generate the output signal If you use counter 1 or 2 you will need to connect your own source to the CLK pin You obtain the continuous pulse train for your external device from the counter OUT pin Figure 25 8 External Connections Diagram from the Front Panel of Cont Pulse Train 8253 VI The block diagram of the Cont Pulse Train 8253 VI located in labview examples daq counter 8253 llb shows how to use the Generate Pulse Train 8253 VI to generate a continuous pulse train When using counter 0 with this VI you can specify the desired frequency The actual frequency shows the closest frequency to your desired frequency that the counter was able to achieve The actual duty cycle will be as close to 0 5 as possible for your actual frequency When using counter 1 or counter 2 you specify the divisor factor N to be used to divide your supplied source You optionally can enter the user supplied timebase if you want the VI to calculate your actual frequency and actual duty cycle When you click the STOP button the While Loop stops and a call to ICTR Control resets the counter stopping the generation For a complete description of this example refer to the information found in Windows Show VI Info Generating a Finite Pulse Train How you generate a finite pulse varies depending upon which counter chip your
308. s in LabVIEW You can find the Data Acquisition VIs in the Functions palette from your block diagram in LabVIEW When you put your cursor over each of the icons in the Functions palette LabVIEW displays the palette name you are about to access at the top of the Functions palette The Functions Data Acquisition palette contains six subpalettes that contain the different classes of DAQ VIs The DAQ VIs are classified as follows Analog Input VIs Analog Output VIs Digital I O VIs Counter VIs Calibration and Configuration VIs Signal Conditioning VIs DAQ VI Organization Most of the DAQ VI subpalettes arrange the VIs in different levels according to their functionality You can find some of the following four levels of DAQ VIs within the DAQ VI subpalettes Easy VIs Intermediate VIs Utility VIs Advanced VIs Chapter 3 Basic LabVIEW Data Acquisition Concepts LabVIEW Data Acquisition Basics Manual 3 4 www ni com Figure 3 1 shows an example of a DAQ subpalette that contains all of the available levels of DAQ VIs Figure 3 1 Analog Input VI Palette Organization Easy VIs The Easy VIs perform simple DAQ operations and typically reside in the first row of VIs in the DAQ palettes You can run these VIs from the front panel or use them as subVIs in basic applications You need only one Easy VI to perform each basic DAQ operation Unlike intermediate and advanced l
309. s the data into the buffer When your VI tries to read data from the buffer that has not yet been collected LabVIEW waits for the data your VI requested to be acquired and then returns the data If your VI does not read the data from the circular buffer fast enough the VI sends back an error advising you that the data that you retrieved from the buffer is overwritten data Continuously Acquiring Data from Multiple Channels You can acquire time sampled data continuously from one or more channels with the Intermediate VIs An example using these VIs is the Acquire amp Process N Scans VI found in labview examples daq anlogin anlogin llb Open this VI and examine its block diagram There are inputs for setting the channels size of the circular buffer scan rate and the number of samples to retrieve from the circular buffer each time This VI defaults to a input buffer size of 2 000 samples and 1 000 number of scans to read at a time which means the VI reads in half of the buffer s data while the VI fills the second half of the buffer with new data Note The number of scans to read can be any number less than the input buffer size If you do not retrieve data from the circular buffer fast enough your unread data will be overwritten by newer data You can resolve this problem by adjusting one of these three parameters the input buffer size the scan rate or the number of scans to read at a time If your program overwrites data in the
310. sics Manual 27 Measuring Frequency and Period This chapter describes the various ways you can measure frequencies and periods of TTL signals using the counters on your DAQ device One cycle of a signal known as the period is measured in units of time usually seconds The inverse of period is frequency which is measured in cycles per second or hertz Hz The rate of your signal and the type of counter on your DAQ device determine whether you use frequency or period measurement An example of when you would want to know the frequency of a signal is if you need to monitor the shaft speed of a motor Knowing How and When to Measure Frequency and Period A common way to measure the frequency of a signal is to measure the number of pulses that occur during a known time period Figure 27 1 illustrates the measurement of a pulse train of an unknown frequency fs by using a pulse of a known width TG The frequency of the waveform equals the count divided by the known pulse width frequency count TG The period is the reciprocal of the measured frequency period 1 fs You typically use frequency measurement for high frequency signals where the signal to be measured is approaching or faster than the chosen internal timebase Chapter 27 Measuring Frequency and Period LabVIEW Data Acquisition Basics Manual 27 2 www ni com Figure 27 1 Measuring Square Wave Frequency TIO ASIC DAQ STC Am9513 For period measurement you count t
311. sics Manual A LabVIEW Data Acquisition Common Questions This appendix lists answers to questions frequently asked by LabVIEW users Where is the best place to get up to speed quickly with data acquisition and LabVIEW Read this manual and look at the run_me llb examples in labview examples daq run_me llb included with LabVIEW In Windows run Measurement amp Automation Explorer or the DAQ Channel Wizard and the DAQ Solution Wizard from LabVIEW What is the easiest way to address my AMUX 64T device with my MIO device Set the number of AMUX devices used in Measurement amp Automation Explorer Windows or NI DAQ control panel Macintosh Then in the channel string inputs specify the onboard channel For example with one AMUX 64T device the channel string 0 1 will acquire data from AMUX channels 0 through 7 and so on What are the advantages disadvantages of reading AI Read s backlog rather than a fixed amount of data Reading the backlog is guaranteed not to cause a synchronous wait for the data to arrive However it adds more delay until the data is processed because the data was available on the last call and it can require constant reallocation or size adjustments of the data acquisition read buffer in LabVIEW What is the easiest way to verify that my device works and is acquiring data from my signals Run one of the examples in the labview examples daq folder or run the test panel for your device in Measure
312. simplify the programming needed to measure your signal LabVIEW configures the hardware with the appropriate input limits and gain and performs cold junction compensation amplifier offsets and scaling for you To measure a channel using a channel name you can use the Easy VIs or the Continuous Transducer VI located in labview examples daq solution transduc llb Enter the name of your configured channel in the channels input The device input value is not used by LabVIEW when you use channel names The acquired data is in the physical units you specified in the DAQ Channel Wizard The remainder of this section describes how to measure temperature with the SCXI 1100 and SCXI 112x modules using thermocouples when you do not use the DAQ Channel Wizard The temperature examples below use both cold junction measurements and amplifier offsets In SCXI analog input examples you cannot set the scaling constants with the Easy VIs determined by the amplifier offset With the Intermediate VIs you can change the scaling constants before acquisition begins and the Advanced VIs include functions that are not necessary to accurately measure temperature with SCXI modules The examples described in this section use Intermediate VIs along with transducer specific VIs First you should learn how to measure temperature using the SCXI 1100 with thermocouples You can use the example SCXI 1100 Thermocouple VI located in labview examples daq scxi scxi_ai llb Op
313. slope on an incoming analog signal Triggering can be set to occur at a specified voltage on either an increasing or a decreasing signal positive or negative slope AO Analog output array Ordered indexed set of data elements of the same type B BCD Binary coded decimal bipolar A signal range that includes both positive and negative values for example 5 to 5 V buffer Temporary storage for acquired or generated data Glossary National Instruments Corporation G 3 LabVIEW Data Acquisition Basics Manual C cascading Process of extending the counting range of a counter chip by connecting to the next higher counter channel Pin or wire lead to which you apply or from which you read the analog or digital signal Analog signals can be single ended or differential For digital signals you group channels to form ports Ports usually consist of either four or eight digital channels channel clock The clock controlling the time interval between individual channel sampling within a scan Boards with simultaneous sampling do not have this clock channel name A unique name given to a channel configuration in the Data Neighborhood in Measurement amp Automation Explorer circular buffered I O Input output operation that reads or writes more data points than can fit in the buffer When LabVIEW reaches the end of the buffer LabVIEW returns to the beginning of the buffer and continues to transfer data clock Ha
314. ss devices postriggering The technique you use on a DAQ device to acquire a programmed number of samples after trigger conditions are met pretriggering The technique you use on a DAQ device to keep a continuous buffer filled with data so that when the trigger conditions are met the sample includes the data leading up to the trigger condition pulse trains Multiple pulses pulsed output A form of counter signal generation by which a pulse is outputted when a counter reaches a certain value PXI PCI eXtensions for Instrumentation A modular computer based instrumentation platform Glossary LabVIEW Data Acquisition Basics Manual G 12 www ni com R read mark Points to the scan at which a read operation begins Analogous to a file I O pointer the read mark moves every time you read data from an input buffer After the read is finished the read mark points to the next unread scan Because multiple buffers are possible you need both the buffer number and the scan number to express the position of the read mark read mode Indicates one of the four reference marks within an input buffer that provides the reference point for the read This reference can be the read mark the beginning of the buffer the most recently acquired data or the trigger position referenced signal sources Signal sources with voltage signals that are referenced to a system ground such as earth or a building ground Also called grounded signal sou
315. st be configured for the same DAQ device If you configure channels with names of temperature and pressure both of which are measured by the same DAQ device you can specify a list of channels in a single element by separating them by commas for example temperature pressure In specifying channel names spelling and spaces are important but case is not Figure 3 4 Channel String Controls Using channel names you do not need to wire the device input limits or input config input parameters LabVIEW always ignores the device input when using channel names LabVIEW configures your hardware in terms of your channel configuration Tip Unless you need to overwrite your channel name configuration do not wire input limits or input config Allow LabVIEW to set them up for you In addition LabVIEW orders and pads the channels specified in channel list as needed according to any special device requirements Chapter 3 Basic LabVIEW Data Acquisition Concepts LabVIEW Data Acquisition Basics Manual 3 10 www ni com Channel Number Addressing If you are not using channel names to address your channels you can address your channels by channel numbers in the channel list parameter The channel list can be an array of strings or as with the Easy VIs a scalar string control If you have a channel list array you can use one channel entry per array element specify the entire list in a single element or use any combination of these two methods F
316. string array LabVIEW also assigns all the channels listed in a channel string array element the same settings in the corresponding limit settings cluster array element Figure 3 6 illustrates one case of this Figure 3 6 Limit Settings Case 1 In this example channels 0 1 2 and 3 are assigned limits of 10 00 to 10 00 Channel 4 has limits of 5 00 to 5 00 Channels 5 6 and 7 have limit settings of 1 00 to 0 00 If the limit settings cluster array has fewer elements than the channel string array LabVIEW assigns any remaining channels the limit settings contained in the last entry of the limit settings cluster array Figure 3 7 illustrates this case Chapter 3 Basic LabVIEW Data Acquisition Concepts National Instruments Corporation 3 13 LabVIEW Data Acquisition Basics Manual Figure 3 7 Limit Settings Case 2 In this example channels 0 1 2 and 3 have limits of 10 00 to 10 00 There are more channels left but the limit settings cluster array is exhausted Therefore the remaining channels 4 5 6 and 7 are also assigned limits of 10 00 to 10 00 The Easy Analog Input VIs have only one pair of input limits This pair forms a single cluster element If you specify the default limit settings all channels scanned with these VIs will have identical limit settings The Easy Analog Output VIs do not have limit settings All the Intermediate VIs both analog input and output have the channel string array and the
317. sure temperature with thermocouples and RTDs and strain with strain gauges using the SCXI 1100 SCXI 1101 SCXI 1102 SCXI 1112 SCXI 1121 SCXI 1122 SCXI 1125 SCXI 1127 SCXI 1141 SCXI 1142 and SCXI 1143 modules If you are not measuring temperature or pressure you still can gain basic conceptual information on how to measure voltages with an analog input module Three other analog input modules the SCXI 1140 SCXI 1530 and SCXI 1531 are simultaneous sampling modules All the channels acquire voltages at the same time which means you can preserve interchannel phase relationships After all channel voltages are sampled by going into hold mode the software reads one channel at a time When a scan of channels is done the module returns to track mode until the next scan period Both of these operations are performed by the analog input VIs You can use any of the DAQ VIs located in the labview examples daq anlogin anlogin llb or the Getting Started Analog Input VI found in labview examples daq run_me llb to acquire data from the SCXI 1140 SCXI 1530 or SCXI 1531 module For analog output you will learn how to output voltage or current values using the SCXI 1124 module For digital I O you will learn how to input values on the SCXI 1162 1162HV modules and output values on the SCXI 1160 SCXI 1161 and SCXI 1163 1163R modules Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 2 www ni com Analog
318. sy 9513 VI 28 6 Count Time Easy DAQ STC VI 28 5 Count Time Int 9513 VI 28 6 to 28 7 Count Time Int DAQ STC VI 28 6 counter addressing for VIs 3 8 to 3 11 counter chips used in National Instruments devices 24 4 to 24 6 See also 8253 54 counter AM9513 counter DAQ STC counter TIO ASIC counter Counter Read VI controlling pulse width measurement 26 5 to 26 6 counting events Am9513 28 4 DAQ STC 28 3 counting time Am9513 28 7 DAQ STC 28 6 measuring frequency and period high frequency signals 27 5 low frequency signals 27 8 Counter Start VI continuous pulse train generation 25 8 controlling pulse width measurement 26 5 counting events Am9513 28 4 DAQ STC 28 3 counting time Am9513 28 7 DAQ STC 28 6 dividing frequencies 29 2 finite pulse train generation 25 10 to 25 11 measuring frequency and period high frequency signals 27 5 low frequency signals 27 8 single square pulse generation 25 6 Counter Stop VI controlling pulse width measurement 26 6 counting events Am9513 28 4 DAQ STC 28 3 counting time Am9513 28 7 DAQ STC 28 6 dividing frequencies 29 2 finite pulse train generation 25 10 measuring frequency and period high frequency signals 27 5 low frequency signals 27 8 stopping counter generations 25 14 Index LabVIEW Data Acquisition Basics Manual I 8 www ni com counters accuracy of counters 25 13 to 25 14 basic functions 24 1 to 24 6 capabilities 24 1 choosing between
319. t but you can use frequency measurement for a pulse train and take the inverse to get the period The Measure Frequency lt 1 kHz 8253 VI located in labview examples daq counter 8253 llb measures frequency and calculates the period for you National Instruments Corporation 28 1 LabVIEW Data Acquisition Basics Manual 28 Counting Signal Highs and Lows This chapter describes the various ways you can count TTL signals using the counters on your DAQ device Counters can count external events such as rising and falling edges on the SOURCE CLK input pin They also can count elapsed time using the rising and falling edges of an internal timebase An example of counting events is calculating the output of a production line An example of counting time is calculating how long it takes to produce one item on a production line Connecting Counters to Count Events and Time Figure 28 1 shows typical external connections for counting events In the figure your device provides the TTL signal to be counted and it is connected to the SOURCE CLK of counter The number of events counted is determined by reading the count register of counter Figure 28 1 External Connections for Counting Events Figure 28 2 shows typical external connections for counting elapsed time In the figure your device provides a pulse to the GATE of counter While the gate pulse is high counter counts a known internal timebase Dividing the count by the internal ti
320. t and temperature sensor measurement are the channel string and the input limits If you set the temperature sensor in mtemp mode the most common mode you access the temperature by using mtemp If you set the temperature sensor in dtemp mode you read the corresponding DAQ device onboard channel Make sure you use the temperature sensor input limits which are different from your acquisition input limits To read from a temperature sensor based on an IC sensor or a thermistor set the input limit range from 2 to 2 V Chapter 22 Common SCXI Applications LabVIEW Data Acquisition Basics Manual 22 8 www ni com Figure 22 2 Measuring Temperature Sensors Using the Acquire and Average VI After determining the average amplifier offset and cold junction compensation you can acquire data using the Intermediate VIs as shown in Figure 22 3 This example continually acquires data until an error occurs or the user stops the execution of the VI For continuous hardware timed acquisition you need to set up a buffer In this case the buffer is 10 times the number of points acquired for each channel Before you initiate the acquisition with the AI Start VI you need to set up the binary to voltage scaling constants by using the Scaling Constant Tuner VI This VI which you can find in Functions Data Acquisition Signal Conditioning passes the amplifier offset to the DAQ driver so that LabVIEW accounts for the amplifier offset as the AI Read VI retri
321. t external hookups by substituting the channel string with calgnd as the channel number For other modules you need to wire the positive and negative channel inputs together at the terminal block and wire them to the chassis ground 4 Use the AI Single Scan VI to take several readings and average them for greater accuracy Set the DAQ device gain settings to match the settings you plan to use in your application If you are using an AT MIO 16F 5 AT MIO 64F 5 or AT MIO 16X use the MIO Configure VI to enable dithering which makes your averaged data more accurate The dither mode is always enabled on E series devices By using the AI Start and AI Read VIs instead of the AI Single Scan VI you can average over an integral number of 60 Hz or 50 Hz power line cycles sine waves to eliminate line noise You now have your first volt binary measurement volt 0 0 or the applied voltage at your input channel and binary is your binary reading or binary average Chapter 23 SCXI Calibration Increasing Signal Measurement Precision LabVIEW Data Acquisition Basics Manual 23 6 www ni com 5 Use the SCXI Cal Constants VI with your volt binary measurement from step 4 as the Volt Amp Hz 1 and Binary 1 inputs in your VI respectively These input names may vary depending on your application setup For example if your volt binary measurement from step 4 was 0 00 V and 2 enter the values into your front panel controls as shown in the following il
322. techniques discussed in these chapters also apply to VME eXtension for Instrumentation Signal Conditioning VXI SC What Is Signal Conditioning Transducers can generate electrical signals to measure physical phenomena such as temperature force sound or light Table 19 1 lists some common transducers Table 19 1 Phenomena and Transducers Phenomena Transducer Temperature Thermocouples Resistance temperature detectors RTDs Thermistors Integrated circuit sensor Light Vacuum tube photosensors Photoconductive cells Sound Microphone Force and pressure Strain gauges Piezoelectric transducers Load cells Chapter 19 Things You Should Know about SCXI LabVIEW Data Acquisition Basics Manual 19 2 www ni com To measure signals from transducers you must convert them into a form that a DAQ device can accept For example the output voltage of most thermocouples is very small and susceptible to noise Therefore you may need to amplify and or filter the thermocouple output before digitizing it The manipulation of signals to prepare them for digitizing is called signal conditioning The following are some common types of signal conditioning Amplification Isolation Filtering Transducer excitation Linearization Position displacement Potentiometers Linear voltage differential transformer LVDT Optical encoder Fluid flow Head meters Rotational flowmeters Ultrasonic flowmeter
323. ted in labview examples daq anlog_io anlog_io llb and examine its block diagram Although this VI is similar to the Simul AI AO Buffered E Series MIO VI described previously it is more advanced because it uses a hardware trigger The waveform acquisition trigger is set up with the trigger type input to the AI Start VI set to digital A start and by default this trigger is expected on the PFI0 pin Hardware triggering for waveform generation requires an additional VI The AO Trigger and Gate Config VI is an advanced analog output VI for E Series boards only The trigger parameters are set using three inputs The trigger or gate source is used to choose the source of your trigger such as a PFI pin or a RTSI pin The trigger or gate source specification is used in conjunction with the trigger or gate source to choose which PFI or RTSI pin number to use such as 0 through 9 for a PFI pin The trigger or gate condition is used to select a rising or falling trigger edge The default analog output trigger for this example is a rising edge on PFI0 Because this is the same pin as the analog input trigger the waveform acquisition and generation starts simultaneously However they are not controlled by independent counter timers so you can run them at different rates For a complete description instructions and I O connections for this VI select Windows Show VI Info from the front panel of the VI Chapter 14 Simultaneous Buffered Waveform Acqu
324. tem ground such as earth or a building ground Also called referenced signal sources group A collection of input or output channels or ports that you define Groups can contain analog input analog output digital input digital output or counter timer channels A group can contain only one type of channel however You use a task ID number to refer to a group after you create it You can define up to 16 groups at one time H handshaked digital I O A type of digital acquisition generation where a device or module accepts or transfers data after a digital pulse has been received Also called latched digital I O hardware triggering A form of triggering where you set the start time of an acquisition and gather data at a known position in time relative to a trigger signal hex Hexadecimal Hz Hertz The number of scans read or updates written per second I IEEE Institute of Electrical and Electronic Engineers Glossary LabVIEW Data Acquisition Basics Manual G 8 www ni com immediate digital I O A type of digital acquisition generation where LabVIEW updates the digital lines or port states immediately or returns the digital value of an input line Also called nonlatched digital I O input limits The upper and lower voltage inputs for a channel You must use a pair of numbers to express the input limits The VIs can infer the input limits from the input range input polarity and input gain s Similarly if you wire th
325. ter generations 25 14 supplying external test clock 13 2 Get DAQ Device Information VI 2 1 Get Timebase 8253 VI 26 5 27 6 Getting Started Analog Input example VI reading amplifier offset 22 5 temperature sensor 22 4 grounded signal sources 5 2 to 5 3 H handshaking latched digital I O 17 1 to 17 8 buffered handshaking 17 6 to 17 8 circular buffered examples 17 7 to 17 8 iterative buffered examples 17 7 simple buffered examples 17 6 choosing between non latched or latched digital I O 4 5 connecting signal lines digital input figure 17 3 digital output figure 17 4 DAQ devices supporting digital handshaking 17 1 defined 15 2 multiple ports 17 2 to 17 4 non buffered handshaking 17 5 overview 17 1 to 17 2 hardware See also installation and configuration SCXI modules debugging connection errors 30 1 relationship between LabVIEW NI DAQ and DAQ hardware figure 2 3 hardware triggering 8 1 to 8 8 analog description 8 5 to 8 6 examples 8 7 to 8 8 digital description 8 2 to 8 3 examples 8 4 to 8 5 overview 8 1 hardware timed analog input output control loops 6 6 to 6 7 I IBF Input Buffer Full line 17 2 ICTR Control VI counting events 28 5 determining pulse width 26 5 measuring frequency and period 27 6 stopping counter generations 25 15 ICTR Control Int VI 28 6 to 28 7 ICTR Timebase Generator VI 25 12 immediate digital I O See nonlatched digital I O Index LabVIEW Dat
326. tes or processes output values one at a time However remember that software timing is not as accurate as hardware timed analog output For more information on hardware timed analog output refer to Chapter 6 One Stop Single Point Acquisition National Instruments Corporation 12 1 LabVIEW Data Acquisition Basics Manual 12 Buffering Your Way through Waveform Generation This chapter shows you which VIs to use in LabVIEW to perform buffered analog updates Buffered Analog Output You can program single buffered analog output in LabVIEW using an Easy Analog Output VI AO Generate Waveforms VI This VI writes an array of output values to the analog output channels at a rate specified by update rate For example if channels consists of two channels and the waveforms 2D array consists of two columns containing data for the two channels LabVIEW writes values from each column to the corresponding channels at every update interval After LabVIEW writes all the values in the 2D array to the channels the VI stops The signal level on the output channels maintains the value of the final value row in the 2D array until another value is generated If you use channel names configured in the DAQ Channel Wizard in channels waveforms is relative to the units specified in the DAQ Channel Wizard Otherwise waveforms is relative to volts Easy VIs contain error handling If an error occurs in the AO Generate Waveforms VI a dialog box appears displ
327. that you use to scan the AMUX 64T channels Refer to Appendix B Hardware Capabilities of the LabVIEW Function and VI Reference Manual or select Help Online Reference for more information about addressing AMUX 64T channels Refer to the AMUX 64T User Manual for more information about the external multiplexer device Important Terms You Should Know The following are some definitions of common terms and parameters that you should remember when acquiring your data A scan is one acquisition or reading from each channel in your channel string Number of scans to acquire refers to the number of data acquisitions or readings to acquire from each channel in the channel string Number of samples is the number of data points you want to sample from each channel The scan rate determines how many times per second LabVIEW acquires data from channels scan rate enables interval scanning a longer interval between scans than between individual channels comprising a scan on devices that support this feature channel clock rate defines the time between the acquisition of consecutive channels in your channel string Refer to Chapter 9 Letting an Outside Source Control Your Acquisition Rate for more information about scan and channel clock rates Refer to Chapter 14 Introduction to the LabVIEW Data Acquisition VIs in the LabVIEW Function and VI Reference Manual or select Help Online Reference for specific information about the Anal
328. the measuring system will add error to your readings If you are using lead Chapter 22 Common SCXI Applications National Instruments Corporation 22 11 LabVIEW Data Acquisition Basics Manual lengths greater than 10 feet you will need to compensate for this lead resistance RTDs also are classified by the type of metal they use The most common metal is platinum For more information about how the lead wires affect RTD measurements as well as general RTD information refer to Application Note 046 Measuring Temperature with RTDs A Tutorial You can find this note on the National Instruments web site www ni com Signal conditioning is needed to interface an RTD to a DAQ device or an SCXI 1200 module Signal conditioning required for RTDs include current excitation for the RTD amplification of the measured signal filtering of the signal to remove unwanted noise and isolation of the RTD and monitored system from the host computer Typically you would use the SCXI 1121 module with RTDs because it easily performs all the signal conditioning listed previously You must set up the excitation level gain and filter settings on the SCXI 1121 module with jumpers as well as in your system s configuration utility For information on how to connect and configure the RTD with the SCXI 1121 module look at the Getting Started with SCXI manual or the RTD application note mentioned previously The SC 2042 RTD is a signal conditioning device des
329. the DAQ STC the Am9513 or the 8253 54 chip Typically 660x devices use the TIO ASIC chip E Series devices for example the AT MIO 16E 1 use the DAQ STC chip Legacy type MIO devices for example the AT MIO 16 use the Am9513 chip Low cost Lab 1200 type devices for example the Lab PC 1200 use the 8253 54 chip If you are not sure which chip your device uses refer to your hardware documentation Figure 24 1 Counter Gating Modes 1 GATE Counter Value 2 SOURCE 4 3 5 7 6 8 count rising SOURCE edge Falling Edge Gating 1 GATE Counter Value 2 SOURCE 4 3 5 7 6 8 10 9 count rising SOURCE edge Rising Edge Gating 1 GATE Counter Value 2 SOURCE 4 3 5 6 count rising SOURCE edge High Level Gating 1 GATE Counter Value 2 SOURCE 4 3 5 6 count rising SOURCE edge Low Level Gating Chapter 24 Things You Should Know about Counters National Instruments Corporation 24 5 LabVIEW Data Acquisition Basics Manual TIO ASIC You can configure the TIO ASIC to count either low to high or high to low transitions of the SOURCE input The counter has a 32 bit count register with a counting range of 0 to 232 1 It can be configured to increment or decrement for each counted edge Furthermore you can use an external digital line to control whether the count register increments or decrements which is useful for encoder applications Of the gating modes shown in Figure 24 1 t
330. the digital data transfer based on several different types of events These devices also feature the RTSI bus PCI and AT version and PXI trigger bus PXI to synchronize digital and timing signals with other devices 8255 Family Many digital I O boards use the 8255 programmable peripheral interface PPI This PPI controls 24 bits of digital I O and has three 8 bit ports A B and C Each port can be programmed as input or output Ports A and B always are used for digital I O while port C can be used for I O or handshaking Most boards have from 3 to 12 8 bit ports A port width must be a multiple of 8 bits with a maximum of 32 bits These boards perform immediate or handshaked digital I O E Series Family E Series boards have one port of eight digital I O lines The direction of each line is software programmable on a per line basis The digital input circuitry has an 8 bit register that can read back outgoing digital signals and read incoming signals These boards perform immediate I O Some E Series boards have an additional 24 digital I O lines provided through an 8255 PPI For discussions in this document these boards can be thought of as belonging to both the E Series and 8255 families National Instruments Corporation 16 1 LabVIEW Data Acquisition Basics Manual 16 Immediate Digital I O This chapter focuses on transferring data across a single port The most common way to use digital lines is with nonlatched immediate
331. to 22 20 sending out multiple digital values 17 2 to 17 4 types of digital acquisition generation 15 2 digital ports and lines 15 1 digital SCXI application examples digital input 22 17 to 22 18 digital output 22 19 to 22 20 digital SCXI modules multiplexed mode for digital and relay modules 20 6 parallel mode 20 7 digital signals vs analog signals 4 3 digital triggering defined 8 2 description 8 2 to 8 3 diagram of signal connections 8 2 examples 8 4 to 8 5 timeline for post triggered data acquisition figure 8 3 DIO Port Config VI 22 18 Disable Indexing option 3 15 Display and Output Acq d File scaled VI 12 4 to 12 5 dividing frequencies 29 1 to 29 3 documentation about the manual xix conventions used in manual xix xx data types for LabVIEW xxi flowchart for finding information 4 2 how to use this book 1 1 to 1 4 related documentation xxii Index National Instruments Corporation I 11 LabVIEW Data Acquisition Basics Manual down counter 29 1 Down Counter or Divide Config VI 29 2 to 29 3 E E series MIO boards hardware triggered 14 2 simultaneous buffered waveform acquisition and generation 14 1 to 14 2 software triggered 14 1 to 14 2 Easy Counter VI continuous pulse train generation 25 8 finite pulse train generation 25 9 to 25 10 single square pulse generation 25 6 Easy VIs See also VIs addressing OUT and IN pins on DIO 32F board A 2 continuous pulse train generation 25 8
332. tosh systems configuring DAQ devices 2 4 to 2 6 NI DAQ driver files 2 3 SCXI software configuration 2 8 to 2 10 manual See documentation maximum sampling rate per channel 7 4 Meas Buffered Pulse Period DAQ STC VI 26 6 to 26 7 Measure Frequency lt 1kHz 8253 VI 27 8 Measure Frequency gt 1kHz 8253 VI 27 6 Measure Frequency Dig Start gt 1kHz 8253 VI 27 6 Measure Frequency Easy 9513 VI 27 4 Measure Frequency Easy DAQ STC VI 27 4 Measure Period Easy 9513 VI 27 7 Measure Period Easy DAQ STC VI 27 7 Measure Pulse Easy 9513 VI 26 4 Measure Pulse Easy DAQ STC VI 26 2 Measure Pulse Width or Period VI determining pulse width Am9513 26 4 DAQ STC 26 2 to 26 3 measuring low frequency signals 27 7 Measure Short Pulse Width 8253 VI 26 4 to 26 5 measurement system choosing 5 4 to 5 6 differential measurement system 5 9 to 5 11 nonreferenced single ended measurement system 5 13 to 5 14 referenced single ended measurement system 5 12 Microsoft Windows See Windows environment MIO boards E series MIO boards 14 1 to 14 2 legacy MIO boards 14 3 Multi Board Synchronization VI 18 2 multiple channel single point analog input 6 2 to 6 4 multiple immediate updates 11 2 multiple waveform acquisition choosing between single point and multi point acquisition 4 4 procedure for acquiring 7 3 to 7 4 multiplexed mode SCXI analog input modules 20 5 analog output modules 20 6 channel addressing 21
333. trol VI is called to continually read the count register until one of four conditions are met The count register value has decreased but is no longer changing It is finished measuring the pulse The count register value is greater than the previously read value An overflow has occurred An error has occurred Your chosen time limit has been reached After the While Loop the final count is subtracted from the originally loaded count of 65535 and multiplied by the timebase period to yield the pulse width Finally the last ICTR Control VI resets the counter Notice that this VI uses only Counter 0 If Counter 0 has an internal timebase of 2 MHz the maximum pulse width you can measure is 216 0 5 s 32 ms For a complete description of this example refer to the information found in Windows Show VI Info Controlling Your Pulse Width Measurement How you control your pulse width measurement depends upon which counter chip is on your DAQ device If you are uncertain of which counter chip your DAQ device has refer to your hardware documentation TIO ASIC DAQ STC or Am9513 Figure 26 5 shows one approach to measuring pulse width using the Intermediate VIs Pulse Width or Period Meas Config Counter Start Counter Read and Counter Stop You can use these VIs to control when the measurement of the pulse widths begins and ends The Pulse Width or Period Config VI configures a counter to count the number of cycles
334. tstone bridge For more information on how to connect your strain gauge to SCXI refer to the Getting Started with SCXI manual The SCXI 1121 and the SCXI 1122 modules are commonly used with strain gauges because they include voltage or current excitation and internal Wheatstone bridge completion circuits You also can use the signal conditioning device SC 2043SG as an alternative to SCXI modules The device is designed specifically for strain gauge measurements For more information on this device refer to your National Instruments catalog You can set up your SCXI module to amplify strain gauge signals or filter noise from signals For information about setting up the excitation level gain and filter settings refer to your Getting Started with SCXI manual for the necessary hardware configuration and to Chapter 2 Installing and Configuring Your Data Acquisition Hardware for software configuration Rg R1 R2 Physical strain gauge is value at rest Supplied by signal conditioning hardware DC Voltage Excitation Vm R1 R2 Rg Rg Chapter 22 Common SCXI Applications National Instruments Corporation 22 15 LabVIEW Data Acquisition Basics Manual To build a strain gauge application in LabVIEW you can use the Easy I O analog input VIs If you are measuring multiple transducers on several different channels you need to scan the necessary channels as quickly as possible Because the Easy I O VIs reconfigure
335. uffer so you can read and process data from one buffer while the acquisition fills another multiplexed mode An SCXI operating mode in which analog input channels are multiplexed into one module output so that your cabled DAQ device has access to the module s multiplexed output as well as the outputs on all other multiplexed modules in the chassis through the SCXIbus Also called serial mode Glossary LabVIEW Data Acquisition Basics Manual G 10 www ni com multiplexer A set of semiconductor or electromechanical switches with a common output that can select one of a number of input signals and that you commonly use to increase the number of signals measured by one ADC N NB NuBus NI DAQ The NI DAQ software system which contains a driver a configuration utility a suite of electronic documentation and a rich set of examples nodes Execution elements of a block diagram consisting of functions structures and subVIs nonlatched digital I O A type of digital acquisition generation where LabVIEW updates the digital lines or port states immediately or returns the digital value of an input line Also called immediate digital I O nonreferenced signal sources Signal sources with voltage signals that are not connected to an absolute reference or system ground Also called floating signal sources Some common examples of nonreferenced signal sources are batteries transformers or thermocouples Nonreferenced single ended
336. ulses for clock signals and triggers for other DAQ applications You can measure the pulse width of TTL signals You can measure the frequency and period of TTL signals You can count TTL signal transitions edges or elapsed time You can divide the frequency of TTL signals Signal Transitions or Edges 5 V 0 V Chapter 24 Things You Should Know about Counters LabVIEW Data Acquisition Basics Manual 24 2 www ni com Knowing the Parts of Your Counter The following illustration shows a basic model of a counter A counter consists of a SOURCE or CLK input pin a GATE input pin an OUT output pin and a count register In plug in device diagrams and in the LabVIEW Function and VI Reference Manual these counter parts are called SOURCEn or CLKn GATEn and OUTn where n is the number of the counter Signal transitions edges are counted at the SOURCE input The count register can be preloaded with a count value and the counter increments or decrements the count register for each counted edge The count register value always reflects the current count of signal edges Reading the count register does not change its value You can use the GATE input to control when counting occurs in your application You also can use a counter with no gating allowing the software to initiate the counting operation The OUT pin can be toggled according to available counter programming modes to generate various TTL puls
337. ultiple waveform acquisition 7 3 to 7 4 overview 3 5 SCXI temperature measurement examples 22 6 to 22 8 simultaneous buffered waveform acquisition and generation 14 1 single square pulse generation 25 6 single immediate updates 11 1 stopping counter generations 25 14 strain gauge application 22 15 waveform generation 12 3 to 12 4 interval scanning 5 18 isolation of transducer signals 19 5 iterative buffered digital I O examples 17 7 L Lab 1200 boards simultaneous buffered waveform acquisition and generation 14 4 LabVIEW software basic LabVIEW data acquisition concepts 3 1 to 3 16 See also VIs data organization for analog applications 3 14 to 3 16 location of common DAQ examples 3 1 to 3 2 Index National Instruments Corporation I 15 LabVIEW Data Acquisition Basics Manual common questions about LabVIEW A 1 to A 3 data types xxi relationship between LabVIEW NI DAQ and DAQ hardware figure 2 3 latched digital I O See handshaking latched digital I O legacy MIO boards hardware triggered 14 3 simultaneous buffered waveform acquisition and generation 14 3 software triggered 14 3 limit settings considerations for selecting analog input settings 5 7 to 5 8 description 5 6 effect on ADC precision figure 5 6 measurement precision for various device ranges and limit settings table 5 8 SCXI gains 21 3 to 21 4 VI limit settings 3 11 to 3 13 linearizing voltage levels 19 6 M Macin
338. umber of values to acquire or generate Use circular buffered handshaking when you want to acquire or generate data continuously Circular buffered handshaking is similar to simple buffered handshaking in that both types of handshaking place data in a buffer However a circular buffer application returns to the beginning of the buffer when it reaches the end and fills the same buffer again Note Circular buffered handshaking works only on 6533 devices Chapter 17 Handshaked Digital I O LabVIEW Data Acquisition Basics Manual 17 8 www ni com The examples Cont Handshake Input VI and Cont Handshake Output VI show how to read or write data respectively using a circular buffer to implement continuous buffered handshaking These examples are located in labview examples daq digital 653x llb Select Windows Show VI Info for any of these examples for more information about using and testing them National Instruments Corporation 18 1 LabVIEW Data Acquisition Basics Manual 18 Timed Digital I O This chapter describes timed digital I O which is also known as pattern generation or pattern I O Timed digital I O implies reading or writing digital data or patterns at a fixed rate This mode is especially useful when you want to synchronize digital I O with other events For example you might want to synchronize or time stamp digital data with analog data being acquired by another device Digital I O timing can be controlled by one
339. upports only high level gating For single pulse output the 8253 54 can create only negative polarity pulses For this reason some applications require the use of a 7404 inverter chip to produce a positive pulse The 14 pin 7404 is a common chip available from many electronics stores and can be powered with the 5 V available on most DAQ devices Figure 24 2 shows how to wire a 7404 chip to invert a signal Chapter 24 Things You Should Know about Counters LabVIEW Data Acquisition Basics Manual 24 6 www ni com Figure 24 2 Wiring a 7404 Chip to Invert a TTL Signal For specific information about the Counter VIs in LabVIEW refer to Chapter 14 Introduction to the LabVIEW Data Acquisition VIs in the LabVIEW Function and VI Reference Manual or the LabVIEW Online Reference available by selecting Help Online Reference National Instruments Corporation 25 1 LabVIEW Data Acquisition Basics Manual 25 Generating a Square Pulse or Pulse Trains This chapter describes the ways you can generate a square pulse or multiple pulses called pulse trains using the counters available on your DAQ device with the example VIs in LabVIEW Generating a Square Pulse There are many applications where you may need to generate TTL pulses TTL pulses can be used as clock signals gates and triggers You can use a pulse train of known frequency to determine an unknown TTL pulse width You also can use a single pulse of known duration to determine a
340. urce is set to external These examples are located in labview daq examples digital 653x llb The Change Detection Input VI reads in a fixed number of patterns where each pattern is read in when there is a state transition on one of the data lines Further the line mask parameter can be used to selectively monitor transitions only on certain lines This example is located in labview daq examples digital 653x llb The Multi Board Synchronization VI shows how to synchronize two 6533 devices to acquire data simultaneously This example is located in labview daq examples digital 653x llb Finite Timed I O with Triggering You can use triggering to control the start and or stop of the digital I O process The trigger event can be one of the following Rising edge of a digital pulse Falling edge of a digital pulse Pattern match trigger where the trigger event occurs when data on the lines being monitored matches a specified pattern Pattern not match trigger where the trigger event occurs when data on the lines being monitored differs from a specified pattern The Buffered Pattern Input Trig VI Buffered Pattern Output Trig VI and Start amp Stop Trig VI show how to use the triggering features on the 6533 devices These examples are located in labview daq examples digital 653x llb Continuous Timed Digital I O In this mode digital data is continuously acquired or generated until the user stops the process Th
341. uring Your Data Acquisition Hardware the chapter of this manual that describes your specific application or the NI DAQ User Manual Chapter 30 Debugging Techniques LabVIEW Data Acquisition Basics Manual 30 2 www ni com Windows In the Measurement amp Automation Explorer you can use the NI DAQ Test Panels to verify that your device is operating properly Refer to the NI DAQ online help or Measurement amp Automation Explorer online help for more details VI Construction Errors The various sections below describe methods to find problems with VI construction All the techniques described can be used by themselves or in conjunction with one another Error Handling The best way to determine if your application executed without an error is to use one of the error handler VIs in your application The Error Handler VIs are located in Functions Time amp Dialog You can use these VIs only with Intermediate and Advanced VIs Easy I O VIs already include error handling capabilities within each VI Each Intermediate and Advanced VI has an error input and output cluster named error in and error out respectively The error clusters contain a Boolean that indicates whether an error occurred the error code for the error and the name of the VI that returned the error If error in indicates an error the VI returns the same error information in error out and does not perform any DAQ operations When you use any of the Intermediate or
342. using an earlier version of NI DAQ for Windows you can find the help file in Start Programs LabVIEW NI DAQ Configuration Utility Help If you are using a Macintosh you can find the help file in the Help menu of the NI DAQ Configuration Utility NI DAQ 4 8 x for Macintosh Software Configuration To use SCXI with LabVIEW and NI DAQ 4 8 x you must enter the configuration for each SCXI chassis using NI DAQ Select SCXI Configuration in the NI DAQ menu bar to bring up the SCXI Configuration dialog box as shown in Figure 2 6 Figure 2 6 Accessing the NI DAQ SCXI Configuration Dialog Box Chapter 2 Installing and Configuring Your Data Acquisition Hardware National Instruments Corporation 2 9 LabVIEW Data Acquisition Basics Manual Figure 2 7 shows NI DAQ with the SCXI Configuration dialog box selected Figure 2 7 SCXI Configuration Dialog Box in NI DAQ Follow these steps to configure your SCXI chassis and modules 1 Leave the Chassis control set to 1 if you have only one chassis You will use this number to access the SCXI chassis from your application If you have multiple chassis increment the Chassis control to configure each subsequent chassis 2 Select the appropriate chassis type This activates the remaining fields on the panel 3 If you have only one chassis leave the Address field and the address jumpers on your SCXI chassis set to 0 If you have additional chassis select a unique hardware jumpered address f
343. utput Acq d File scaled VI to generate your data from the file you created This example uses circular buffered output To generate data at the same rate at which it was acquired you must know the rate at which your data was acquired and use that as the update rate National Instruments Corporation 13 1 LabVIEW Data Acquisition Basics Manual 13 Letting an Outside Source Control Your Update Rate DAQ devices use internal counters and timers to determine the rate of data generation However you might encounter times when you need to generate data in synch with other signals in your system For example you might need to output data to a test circuit every time that test circuit emits a pulse In this case internal counter timers are inefficient for your needs You need to control the update rate with your own external source of pulses Externally Controlling Your Update Clock Chapter 12 Buffering Your Way through Waveform Generation mentions that for more control over your analog output applications you can use the Intermediate DAQ VIs This chapter explains how to use these Intermediate VIs to generate data using an external update clock The update clock controls the rate digital to analog conversions occur To control your data generation externally you must supply this clock signal to the appropriate pin on the I O connector of your DAQ device The clock source you supply must be a TTL signal For an example of this proc
344. w VI Info Chapter 26 Measuring Pulse Width LabVIEW Data Acquisition Basics Manual 26 4 www ni com Am9513 Open the block diagram of the Measure Pulse Easy 9513 VI located in labview examples daq counter Am9513 llb This VI uses the Easy VI Measure Pulse Width or Period The Measure Pulse Width or Period VI counts the number of cycles of the specified timebase depending on your choice from the type of measurement menu located on the front panel of the VI The type of measurement menu choices for this VI are shown in Figure 26 4 Figure 26 4 Menu Choices for Type of Measurement for the Measure Pulse Width or Period 9513 VI Either menu choice can be used to measure the width of a single pulse or to measure a pulse within a train of multiple pulses However the pulse must occur after the counter starts Because the counter uses high level gating it might be difficult to measure a pulse within a fast pulse train If the counter is started in the middle of a pulse it measures the remaining width of that pulse The timebase you choose determines how long a pulse you can measure with the 16 bit counter For example the 100 Hz timebase allows you to measure a pulse up to 216 10ms 655 seconds long The 1 MHz timebase allows you to measure a pulse up to 65 ms long Because a faster timebase yields a more accurate pulse width measurement it is best to use the fastest timebase possible without the counter reaching terminal count
345. w about Analog Input LabVIEW Data Acquisition Basics Manual 5 2 www ni com Figure 5 1 Types of Analog Signals You might be saying to yourself I know that I have a thermocouple and that the primary information temperature is contained in the level of the analog voltage Now I am ready to go hunting Well you are almost ready to hunt but you first must figure out a few more signal characteristics before you can begin For example what is your signal referenced to How fast does the signal vary with time The rate you sample determines how often the A D conversions take place A fast sampling rate acquires more points in a given time and therefore can often form a better representation of the original signal than a slow sampling rate According to the Nyquist Theorem you must sample at a rate greater than twice the maximum frequency component in that signal to get accurate frequency information about that signal The frequency at one half the sampling frequency is referred to as the Nyquist frequency Refer to the Sampling Considerations section in Chapter 11 Introduction to Analysis in LabVIEW of the LabVIEW User Manual for more information about the Nyquist frequency What Is Your Signal Referenced To Signals come in two forms referenced and non referenced signal sources More often referenced sources are said to be grounded signals and non referenced sources are called floating signals Grounded Signal Sources Ground
346. x examples This font is also used for the proper names of disk drives paths directories programs subprograms subroutines device names functions operations variables filenames and extensions and code excerpts monospace bold Bold text in this font denotes the messages and responses that the computer automatically prints to the screen This font also emphasizes lines of code that are different from the other examples NI DAQ 4 8 x NI DAQ 4 8 x refers to functions supported only on the Macintosh for NuBus DAQ products NI DAQ 5 x NI DAQ 5 x refers to functions supported only on Windows DAQ products NI DAQ 6 x NI DAQ 6 x refers to functions supported only on Windows and PCI based Macintosh DAQ products Platform Text in this font denotes a specific platform and indicates that the text following it applies only to that platform About This Manual National Instruments Corporation xxi LabVIEW Data Acquisition Basics Manual LabVIEW Data Types Each VI description gives a data type picture for each input and output parameter as illustrated in the following table Control Indicator Data Type Signed 8 bit integer Signed 16 bit integer Signed 32 bit integer Unsigned 8 bit integer Unsigned 16 bit integer Unsigned 32 bit integer Single precision floating point number Double precision floating point number Extended precision floating point number String Boolean Array of signed 32 bit integer
347. xamples daq anlog_io anlog_io llb and examine its block diagram The only difference between this example VI and the Simul AI AO Buffered legacy MIO VI described previously is the trigger type input to the AI Start VI is set to digital A start trigger This sets up the waveform acquisition for a digital trigger Because the waveform generation uses the same counter timer as the waveform acquisition it also is dependent on the digital trigger For a complete description instructions and I O connections for this VI select Windows Show VI Info from the front panel of the VI Chapter 14 Simultaneous Buffered Waveform Acquisition and Generation LabVIEW Data Acquisition Basics Manual 14 4 www ni com Using Lab 1200 Boards Lab 1200 boards such as the Lab PC 1200 or the DAQCard 1200 also can perform simultaneous waveform acquisition and generation The approach is similar to the previous descriptions Refer to the examples Simul AI AO Buffered Lab 1200 VI and Simul AI AO Buffered Trigger Lab 1200 VI located in labview examples daq anlog_io anlog_io llb to see how this acquisition and generation is performed National Instruments Corporation IV 1 LabVIEW Data Acquisition Basics Manual Part IV Getting Square with Digital I O This part of the manual describes basic concepts about how to use digital signals with data acquisition in LabVIEW including immediate handshaked and timed digital I O Part IV Getting Squa
348. xecution highlighting data movement is marked by bubbles moving along the wires Refer to Chapter 2 Creating VIs in the LabVIEW User Manual and Chapter 4 Executing and Debugging VIs and SubVIs in the G Programming Reference Manual for more information about execution highlighting Chapter 30 Debugging Techniques LabVIEW Data Acquisition Basics Manual 30 4 www ni com Using the Probe Tool If your VI is producing questionable results you may want to use the Probe tool to check intermediate values in a VI The Probe tool helps you find where the incorrect results are occurring Refer to Chapter 2 Creating VIs in the LabVIEW User Manual and Chapter 4 Executing and Debugging VIs and SubVIs in the G Programming Reference Manual for more information on using the probe Setting Breakpoints and Showing Advanced DAQ VIs Once you have narrowed down the location of an error to a subVI you can set a breakpoint on that subVI to cause VI execution to pause before executing the subVI You can now see what values get passed in or are generated by the Advanced VIs single step through the subVI s execution probe wires to see data or change values of front panel controls Refer to Chapter 2 Creating VIs in the LabVIEW User Manual and Chapter 4 Executing and Debugging VIs and SubVIs in the G Programming Reference Manual for more information on how to set a breakpoint National Instruments Corporation A 1 LabVIEW Data Acquisition Ba
349. xpected This chapter shows you some tips to help learn why your VI is not working With LabVIEW DAQ applications you might find errors in hardware connections software configuration or VI construction The goal of this chapter is to help you narrow down where the problem is in your program flow Hardware Connection Errors When no error occurs but the data is not what you expected you might want to check your hardware connections and jumper settings For example if you have an analog input application make sure your signals are properly grounded For more information on analog input configuration issues refer to Chapter 5 Things You Should Know about Analog Input For SCXI modules verify that gain jumpers are set up properly To verify how a DAQ device gets set to a certain gain or limit setting as noted in the software refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts Another common SCXI hardware error is using digital lines on your DAQ device that are reserved for communication with the SCXI modules To test that your hardware has not been damaged connect a known voltage to the channels you are using To check the location of any hardware connections refer to your hardware user manual Software Configuration Errors As you check hardware connections verify that the NI DAQ software configuration reflects your hardware setup For possible difficulties with software configuration read Chapter 2 Installing and Config
350. y occurs so that the finite pulse train has time to complete before the example can be run again This is useful if the example is used as a subVI where it may get called over and over For a complete description of this example refer to the information found in Windows Show VI Info Counting Operations When All Your Counters Are Used The DAQ STC and Am9513 have counting operations available even when all the counters have been used TIO ASIC and DAQ STC devices feature a FREQ_OUT pin and Am9513 devices feature an FOUT pin You can generate a 0 5 duty cycle square wave on these pins without using any of the available counters The CTR Control VI found in Functions Data Acquisition Counters Advanced Counter AM9513 amp Compatibility enables and disables the FOUT signal and sets the square wave frequency The square wave Chapter 25 Generating a Square Pulse or Pulse Trains National Instruments Corporation 25 13 LabVIEW Data Acquisition Basics Manual frequency is defined by the FOUT timebase signal divided by the FOUT divisor Note If you are using NI DAQ 6 5 or higher National Instruments recommends you use the new Advanced Counter VIs such as Counter Group Config Counter Get Attribute Counter Set Attribute Counter Buffer Read and Counter Control For more information refer to the LabVIEW Online Reference You also can refer to the Generate Pulse Train on FREQ_OUT VI located in examples daq counter DAQ STC llb o

DAQ basics

Contents

Download Pdf Manuals

Related Search

Related Contents