LABVIEW BASICS I
Contents
1. Auto Indexing Loops If you wire an array to the input tunnel of a For Loop or While Loop you can read and process every element in that array by enabling auto indexing When you wire an array from an external node to an input tunnel on the loop border and enable auto indexing on the input tunnel elements of that array enter the loop one at a time starting with the first element When auto indexing is disabled the entire array is passed into the loop Right click the tunnel at the loop border and select Enable Indexing or Disable Indexing from the shortcut menu to enable or disable auto indexing Auto indexing for While Loops is disabled by default The loop indexes scalar elements from 1D arrays 1D arrays from 2D arrays and so on The opposite occurs at output tunnels Scalar elements accumulate sequentially into 1D arrays 1D arrays accumulate into 2D arrays and so on If you enable auto indexing on an array wired to a For Loop input terminal LabVIEW sets the count terminal to the array size so you do not need to wire the count terminal Auto Indexed output Array 03 04 2009 03 04 2009 Shift Registers 12 S Shift Register amp Feedback N Use shift registers with For Loops or While Loops to transfer values from one loop iteration to the next A shift register appears as a pair of terminals directly opposite each other on the vertical sides of the loop border The terminal on the right side of the loop contains an up2. for use with Express VIs Most other Vis and functions that ship with LabVIEW do not accept this data type To use a built in VI or function to analyze or process the data the dynamic data type includes you must convert the dynamic data type 1D array of waveforms 1D array of scalars 1D array of scalars most recent value 1D array of scalars single channel 2D array of scalars columns are channels 2D array of scalars rows are channels Single scalar Single waveform Simulate Signal Loops and Structures Structures are graphical representations of the loops and case statements of text based programming languages Use structures on the block diagram to repeat blocks of code and to execute code conditionally or in a specific order Like other nodes structures have terminals that connect them to other block diagram nodes execute automatically when input data is available and supply data to output wires when execution completes Each structure has a distinctive resizable border to enclose the section of the block diagram that executes according to the rules of the structure The section of the block diagram inside the structure border is called a subdiagram The terminals that feed data into and out of structures are called tunnels A tunnel is a connection point on a structure border For Loop Executes a subdiagram a set number of times or if you add a conditional terminal until a Boolean con
3. LabVIEW User Manual A VI contains the following three components Front panel Serves as the user interface Block diagram Contains the graphical source code G language that defines the functionality of the VI Icon and connector pane identifies the VI so that you can use the It in another VI A VI within another VI is called subVI A subVI corresponds to a subroutine in text based programming languages NI_MABase vlib Basic Function Generator vi The Icon identifies the VI so you can use offset it in another VI reset signal signal type The connector pane is a set of terminals frequency ae n that corresponds to the controls and amplitude anpa indicators of that VI similar to the connecta pang ESN piae mo out parameter list of a function call in text f jj ae based programming languages The connector pane defines the inputs and square wave duty cyde l l outputs you can wire to the VI Creates an output waveform based on signal type 03 04 2009 introduction to VI LabVIEW data types In LabVIEW there are 32 different data types The color and symbol of each terminal indicate the data type of the corresponding control or indicator In the following table the 9 most common are reported control indicator O Description OOOO Float Double precision floating point numeric Integer 32 bit signed integer numeric Boolean Stores Boolean TRUE FALSE values String Provides a platform independent for
4. a graph chart or file for a report Signal Conditioning A signal is classified as analog or digital by the way it conveys information e A digital or binary signal has only two possible discrete levels high level on or low level off e An analog signal on the other hand contains information in the continuous variation of the signal with respect to time A breakdown of the main signal types is shown in the following figure PCI and PCI Express PCMCIA Of Ji On OFF TTL Line State Digital J t Configuration Measurement and Automation MAX DAQ Assistant and So On Pulse Train Counters Rate Driver Engines Timmer Signals 0 985 NI DAQmx NI 488 2 D C Abc DAT Level A Oe slow Application Programming Interface API NI DAQmx NI VISA or Other API Analog4 Time Domain ADC DAC UAn Shape 7 SA fast Application Software Freq LabVIEW LabWindows CVI Measurement Studio or Other Programming Environments Frequency ADC fast Content Domain Analysis Your Measurement Application Analog Connection considerations To measure analog signals you need to know the signal source grounded or floating You also must consider the measurement system differential referenced single ended or nonreferenced single ended You can measure floating signal sources with both differential and single ended measurement systems In the case of the differential measurement system however make sure
5. arrow and stores data on the completion of an iteration LabVIEW transfers the data stored in the right terminal of the shift register to the left terminal The loop then uses the data from the left terminal as the initial values for the next iteration This process continues until all iterations of the loop execute After the loop executes the terminal on the right side of the loop returns the last value stored in the shift register Create a shift register by right clicking the left or right border of a loop and selecting Add Shift Register from the shortcut menu You can add more than one shift register to a loop If you have multiple operations that use previous iteration values within a loop use multiple shift registers to store the data values from those different processes in the structure as shown in the following block diagram Initializing a shift register resets the value the shift register passes to the first iteration of the loop when the VI runs If you do not initialize the shift register the loop uses the value written to the shift register when the loop last executed or if the loop has never executed the default value for the data type Use an uninitialized shift register to preserve state information between subsequent executions of a VI Stacked shift registers let you access data from previous loop iterations Stacked shift registers remember values from multiple previous iterations and carry those values to the next iterations To cre
6. the common mode voltage level of the signal with respect to the measurement system ground remains in the common mode input range of the measurement device A variety of phenomena for example the instrumentation amplifier input bias currents can move the voltage level of the floating source out of the valid range of the input stage of a DAQ device Ground A grounded signal source is best measured with a differential or an nonreferenced single ended measurement system If you use an RSE measurement system with a grounded source the result is typically a noisy measurement system often showing power line frequency 60 Hz components in the readings Ground loop introduced noise can have both AC and DC components introducing offset errors and noise in the measurements The potential difference between the two grounds causes a current to flow in the interconnection This current is called ground loop current However you can still use an RSE measurement system if the signal voltage levels are high and the interconnection wiring between the source and the measurement device has a low impedance In this case the signal voltage measurement is degraded by ground loop but the degradation may be tolerable You must observe the polarity of a grounded signal source before connecting the signal to a ground referenced measurement system because the signal source can be short circuited to ground which can Ground damage the signal source 12 03 04
7. 2009 Analog Connection considerations Signal Source Type Floating Signal Source Not Connected to Building Ground Grounded Signal Source Examples Ungrounded thermocouples signal conditioning Example Instruments with nonisolated with isolated outputs battery devices Differential DIFF A differential measurement system has neither of its inputs tied to a fixed reference such as earth or building ground A differential measurement system is similar to a floating signal source in that the measurementis made with respect to a floating ground that is different from the measurement system ground Ground Referenced Single Ended RSE Note AI GND is shared as a reference for all RSE channels Referenced and nonreferenced single ended measurement systems are similar to grounded sources in that the measurement is made with respect to ground A referenced single ended RSE measurement system measures voltage with respect to the ground AIGND in the figure which is directly connected to the measurement system ground Ground loop losses Vg ane added to measured signal Nonreferenced Single Ended NRSE Note AI SENSE is shared as a reference for all NRSE channels In an NRSE measurement system all measurements are still made with respect to a single node analog input sense AISENSE but the potential at this node can vary with respect to the measurement system ground Pseudodifferential Pseudodifferential input configurat
8. ASICS II Eng Salvatore La Malfa Eng Salvatore La Malfa PhD Student D I E E S Department of Electrical Electronic and Systems Engineering University of Catania Faculty of Engineering V le A Doria 6 95125 Catania Italy Tel 39 095 7382341 Fax 39 095 330793 e mail salvatore lamalfa diees unict it 11 03 04 2009 Measurements Fundamentals NI measurement devices and application software are packaged with NI DAQ driver software to program all the features of your NI measurement device such as configuring acquiring and generating data from and sending data to NI measurement devices Using NI DAQ saves you from having to write these programs yourself Application software such as LabVIEW LabWindows CVI and Measurement Studio sends the commands to the driver such as acquire and return a thermocouple reading and then displays and analyzes the data acquired Physical Phenomena Sensors and transducers detect physical phenomena Light Pressure Temperature and So On z ae od oat 3 Signal conditioning components condition physical phenomena so that the Sensors and Transducers measurement device can receive the data The computer receives the data through the measurement device Software controls the measurement system telling the measurement device when and from which channels to acquire or generate data Software also takes the raw data analyzes it and presents it in a form you can understand such as
9. Sais eee T muin mman LABVIEW BASICS Eng Salvatore La Malfa Eng Salvatore La Malfa PhD Student D I E E S Department of Electrical Electronic and Systems Engineering University of Catania Faculty of Engineering V le A Doria 6 95125 Catania Italy Tel 39 095 7382341 Fax 39 095 330793 e mail salvatore lamalfa diees unict it Introduction to VI Waveforms LabVIEW data types Express VI amp Dynamic Data 1 VI Block diagram nodes Loops amp Structures ntrod uction to unnels amp Indexing Built in Functions Array amp Clusters Shift Register amp Feedback N LabVIEW programs are called virtual instruments VI because their appearance and operation imitate physical instruments such as oscilloscopes and multimeters Every VI uses functions that manipulate input from the user interface or other sources and display that infromation or move to other file or other computers LabVIEW User Manual A VI contains the following three components Front panel Serves as the user interface defines the functionality of the VI VI within another VI is 1 subroutine in t You build the front panel with controls and indicators which are the interactive input and output terminals of the VI respectively Controls are knobs push buttons dials and other input devices Indicators are graphs LEDs and other displays Controls simulate instruments input devices and supply data to the
10. at sequences you do not need to use sequence locals to pass data from frame to frame in the Flat Sequence structure Since the Flat Sequence structure displays each frame on the block diagram you can wire from frame to frame without sequence locals and without hiding code 44 Eira 10 03 04 2009 Introduction to VI Waveforms Event Structure edback N Use the Event structure to handle events in a VI The Event structure works like a Case structure with a built in Wait on notification function The Event structure can have multiple cases each of which is a separate event handling routine You can configure each case to handle one or more events but only one of these events can occur at a time l When the Event structure executes it waits until one of the configured events occur then executes the corresponding case for that event l The Event structure completes execution after handling exactly one event It does not implicitly loop to handle multiple events Like a Wait l on Notification function the Event structure can time out while waiting for notification of an event When this occurs a specific Timeout i case executes e The Event Selector Label at the top of the Event structure indicates which events cause the currently displayed case to execute View other event cases by clicking the down arrow next to the case name and selecting another case from the shortcut menu e The Timeout Terminal at the top left corne
11. ate a stacked shift register right click the left terminal and select Add Element from the shortcut menu Feedback Node Use Feedback Node with For Loops or While Loops to transfer values from one loop iteration to the next The feedback Node operates similarly to shift registers in loops The Feedback Node stores data from only the previous iteration To initialize a Feedback Node when a loop executes right click the initializer terminal and select Move Initializer One Loop Out or Move Initializer One Loop In from the shortcut menu to move the initializer terminal The Feedback Node then initializes before the first iteration of each execution of the loop You must wire an initial value to the initializer terminal if you move it to the left edge of a loop If the initializer terminal is on the edge of the outermost or innermost loop LabVIEW dims the corresponding option to Move Initializer One Loop Out or Move Initializer One Loop In in the shortcut menu If you do not move the initializer terminal to the left edge of a loop the Feedback Node globally initializes You can use a Feedback Node that globally initializes anywhere in a block diagram If a Feedback Node globally initializes and you set an initial value the Feedback Node initializes to that value on the first call of the VI in an execution If you do not wire an input value to the initializer terminal the initial input of the Feedback Node for the first execution is the default va
12. block diagram of the VI Indicators simulate instrument output devices and display data the block diagram acquires or generates 03 04 2009 03 04 2009 Introduction to VI Introduction to VI LabVIEW programs are called virtual instruments VI because their appearance and operation imitate physical instruments such as oscilloscopes and multimeters Every VI uses functions that manipulate input from the user interface or other sources and display that infromation or move to other file or other computers LabVIEW User Manual A VI contains the following three components Front panel Serves as the user interface Block diagram Contains the graphical source code G language that defines the functionality of the VI Icon and connector pane Identifies the VI so that you can use the in another VI A VI within another VI is called subVI A subVI corresponds to a subroutine in text based programming languages After you build the front panel you add code using graphical representations of functions to control the front panel objects The block diagram contains this graphical source code Introduction to VI LabVIEW programs are called virtual instruments VI because their appearance and operation imitate physical instruments such as oscilloscopes and multimeters Every VI uses functions that manipulate input from the user interface or other sources and display that infromation or move to other file or other computers
13. by hand You can automate these measurements by using a PC to control the GPIB instruments The GPIB protocol categorizes devices as controllers talkers or listeners to determine which device has active control of the bus Each device has a unique GPIB primary address between 0 and 30 The Controller defines the communication links responds to devices that request service sends GPIB commands and passes receives control of the bus Controllers instruct Talkers to talk and to place data on the GPIB You can address only one device at a time to talk The Controller addresses the Listener to listen and to read data from the GPIB You can address several devices to listen The GPIB is a digital 24 conductor parallel bus The GPIB uses an 8 bit parallel byte serial asynchronous data transfer scheme which means that whole bytes are sequentially handshaked across the bus at a speed that the slowest participant in the transfer determines Because the unit of data on the GPIB is a byte the messages transferred are frequently encoded as ASCII character strings Refer to the GPIB documentation for more information about the hardware specifications of GPIB devices You can obtain faster data rates with HS488 devices and controllers HS488 is an extension to GPIB that most NI controllers support Input analogico Numero di canali Frequenza di campionamento Risoluzione Campionamento simultaneo Intervallo massimo di tensione Intervallo di accuratezza I
14. dition or an error occurs While Loop Executes a subdiagram until a Boolean condition or an error occurs Case structure Contains multiple subdiagrams only one of which executes depending on the input value passed to the structure Sequence structure Contains one or more subdiagrams that E execute in sequential order Event structure Contains one or more subdiagrams that run time Diagram Disable structure Contains one or more sopooDoUooOoOoOoO 10000000000 execute when events are generated by user interaction Timed structures Execute one or more subdiagrams with ume bounds and delays Flat sequence Stacked sequence Conditional Disable structure Contains one or more geen E subdiagrams exactly one of which compiles and executes at subdiagrams exactly one of which compiles and executes at run time For Loop A For Loop executes a subdiagram a set number of times eThe count terminal is an input terminal whose value indicates how many times to repeat the subdiagram Set the count explicitly by wiring a value from outside the loop to the left or top side of the count terminal or set the count implicitly with auto indexing The iteration termina is an output terminal that contains the number of completed iterations The iteration count always starts at zero Both the count and iteration terminals are 32 bit signed integers If you wire a floating point or fixed point number to the count terminal LabVIEW ro
15. e subdiagrams or frames that execute in sequential order Within each frame of a sequence structure as in the rest of the block diagram data dependency determines the execution order of nodes There are two types of sequence structures eFlat Sequence structure executes frames from left to right and when all data values wired to a frame are available The data leaves each frame as the frame finishes executing This means the input of one frame can depend on the output of another frame Stacked Sequence structure The Stacked Sequence structure shown as follows stacks each frame so you see only one frame at a time and executes frame 0 then frame 1 and so on until the last frame executes The Stacked Sequence structure returns data only after the last frame executes Use the Stacked Sequence structure if you want to conserve space on the block diagram Rely on data flow rather than sequence structures to control the order of execution for example by the use error clusters To take advantage of the inherent parallelism in LabVIEW avoid overusing sequence structures Sequence structures guarantee the order of execution and prohibit parallel operations For example asynchronous tasks that use I O devices such as PXI GPIB serial ports and DAQ devices can run concurrently with other operations if sequence structures do not prevent them from doing so Avoid when possible using stacked sequence structures Use flat sequences instead With fl
16. ions are common in simultaneous sampling and dynamic signal acquisition DSA devices that do not employ a multiplexed signal architecture A pseudodifferential system is well suited for measuring the output of floating or isolated devices under test such as battery powered instruments or most accelerometers NI DAQmx key concepts Virtual channels and tasks are fundamental components of NI DAQmx e Virtual channels or sometimes referred to generically as channels are software entities that encapsulate the physical channel along with other channel specific information range terminal configuration and custom scaling that formats the data e Tasks are collections of one or more virtual channels with timing triggering and other properties A physical channel is a terminal or pin at which you can measure or generate an analog or digital signal A single physical channel can include more than one terminal as in the case of a differential analog input channel or a digital port of eight lines Every physical channel on a device has a unique name for instance SC1Mod4 ai0 Dev2 ao5 and Dev6 ctr3 To create virtual channels use the DAQmx Create Virtual Channel function VI or the DAQ Assistant Virtual channels created with the DAQm x Create Virtual Channel function VI are called ocal virtual channels and can only be used within the task If you create virtual channels with the DAQ Assistant you can use them in other tasks and reference them ou
17. lue for each data type Each time the VI runs after the first execution the initial value is the last value from the previous execution 03 04 2009 Case Structure A Case structure has two or more subdiagrams or cases Only one subdiagram is visible at a time and the structure executes only one case at a time An input value determines which subdiagram executes The Case structure is similar to switch statements or if then else statements in text based programming languages The case selector label at the top of the Case structure contains the name of the selector value that corresponds to the case in the center and decrement and increment arrows on each side Wire an input value or selector to the selector terminal to determine which case executes You must wire an integer Boolean value string or enumerated type value to the selector terminal If you do not specify a default for the Case structure to handle out of range values you must explicitly list every possible input value For example if the selector is an integer and you specify cases for 1 2 and 3 you must specify a default case to execute if the input value is 4 or any other unspecified integer value You can create multiple input and output tunnels for a Case structure Inputs are available to all cases but cases do not have to use each input However you must define each output tunnel for each case Sequence Structure A sequence structure contains one or mor
18. mat for information and data which you can use to create simple text messages pass and store numeric data and so on Array Encloses the data type of its elements in square brackets and takes the color of that data type As you add dimensions to the array the brackets become thicker Cluster Encloses several data types Cluster data types appear brown if all elements in the cluster are numeric or pink if all elements of the cluster are of different types Error code clusters appear dark yellow while LabVIEW class clusters are crimson by default or teal green for Report Generation VIs Dynamic data Express VIs Includes data associated with a signal and the attributes that provide information about the signal such as the name of the signal or the date and time the data was acquired Waveform Carries the data start time and t of a waveform I O Passes resources you configure to I O VIs to communicate with an instrument or a measurement device data types t in Functions Block Diagram No10 es pee iera nodes Clusters Nodes are objects on the block diagram that have inputs and or outputs and perform operations when a VI runs They are analogous to statements operators functions and subroutines in text based programming languages LabVIEW includes the following types of nodes Functions Built in execution elements comparable to an operator function or statement SubV Is Vls used on the block diagram of anothe
19. minals to functions by using the Positioning tool to drag P o gt xe gt the top or bottom borders of the function up or down respectively Computes the sum of the inputs Detailed help AZ You also can add or remove terminals by right clicking one of the terminals of the function and selecting Add Input Add Output Remove Input or Remove Output from the shortcut menu Depending on the function you can add terminals for inputs outputs or refnum controls The Add Input and Add Output shortcut menu items add a terminal immediately after the terminal you right clicked The Remove Input and Remove Output shortcut menu items remove the terminal you right clicked If you use the shortcut menu items to remove a wired terminal LabVIEW removes the terminal and disconnects the wire Array amp Clusters Use the array and cluster controls and functions to group data Arrays group data elements of the same type Clusters group data elements of mixed types Arrays An array consists of elements and dimensions Elements are the data that make up the array A dimension is the length height or depth of an array You can build arrays of numeric Boolean path string waveform and cluster data types Consider using arrays when you work with a collection of similar data and when you perform repetitive computations Arrays are ideal for storing data you collect from waveforms or data generated in loops where each iteration of a loop produces o
20. ne element of the array Array indexes in LabVIEW are zero based Array elements are ordered An array uses an index so you can readily access any particular element The index is zero based which means it is in the range 0 to n 1 where n is the number of elements in the array An example of an array is a waveform represented as a numeric array in which each successive element is the voltage value at successive time intervals A more complex example of an array is a graph represented as an array of points where each point is a cluster containing a pair of numeric values that represent the X and Y coordinates A 2D array stores elements in a grid It requires a column index and a row index to locate an element both of which are zero based The row index selects the waveform and the column index selects the point on the waveform Index OF 1 2 3 4 5 6 7 8 3 4 volts 0 4 0 9 1 4 08 T 01 077 037 03 7 02 1 04 09 14 08 J01 1 0 1 06 04 02 08 2 16 14 07 05 05 06 02 03 05 0 1 6 X Coord 0 4 2 2 3 3 3 2 24 118 119 Index 1 2 3 4 5 6 Y Coord 0 2 0 5 13 23 26 19 12 03 04 2009 Introduction to VI Waveforms LabVIEW data types Express VI amp Dynamic Data A rray amp CI u ste rs Block diagram nodes Loops amp Structures Built in Functions Tunnels amp Indexing Array amp Clusters Shift Register amp Feedback N Use the array and cluster cont
21. ns in the configuration dialog box that appears when you place the Express VI on the block diagram Instrument I O Vision and Motion Mathematics Signal Processing Data Communication Connectivity Control Design amp Simulation The primary benefit of Express VIs is their interactive configurability Express Vis are useful when you want to give users a VI or library of VIs for building their own applications easily with minimal programming expertise Express VIs do not provide run time interactive configuration for VIs If you need run time reconfiguration build an application with a user interface that contains features similar to a configuration dialog box Express VIs are designed for ease of use If you need an application to run with strict memory restrictions or high execution speeds use standard VIs w Re DAQ Assist Instr Assist a Simulate Sig Sim Arb Sig Fimmel Read Meas File PromptUser File Dialog e NI DMM NL SCOPE NLAFSA Q NI RFSA Spec r vyv yv yv Y Y FS Y Y FY Waveforms Express VI amp Dynamic Data Dynamic Data lok diagram nodes 1 Most Express VI accept and or return the dynamic data type The dynamic data type accepts data from and sends e Hisignal Manipulation data to the following data types where the scalar data type is a floating point number or a Boolean value The dynamic data type is
22. ntervallo minimo di tensione Intervallo di accuratezza Output analogico Numero di canali Velocit di aggiornamento Risoluzione Intervallo massimo di tensione Intervallo di accuratezza Intervallo minimo di tensione Intervallo di accuratezza 1 0 digitale Numero di canali Temporizzazione Livelli di logica Intervallo input massimo Intervallo output massimo Contatori Timer Numero di Contatori Timer Risoluzione Frequenza di origine massima 8 SE 4DI 48 kS s 14 bits No 10 10 V 138 mV 1 1V 150 S s 12 bits 0 5V 7 mV 0 5 V Software TTL 0 5 V 5 MHz Minima ampiezza di impulsi input 100 ns Livelli di logica Intervallo massimo TTL 0 5V 16 SE 8 DI 1 25 MS s 16 bits No 10 10 V 1920 uV 100 100 mV 52 uV 2 86 MS s 16 bits 10 10 V 2080 uV 5 5 V Hardware Software TTL 0 5 V 7DaDO2a BOD Sia National Instruments offers several hardware platforms for data acquisition The most readily available platform is the desktop computer National Instruments offers PCI DAQ boards that plug into any desktop computer In addition NI makes DAQ modules for PX CompactPCl a more rugged modular computer platform specifically for measurement and automation applications For distributed measurements the National Instruments Compact FieldPoint platform delivers modular I O embedded operation and Ethernet communication For portable or handheld measurements National Instruments DAQ device
23. r VI comparable to subroutines Express Vis SubVls designed to aid in common measurement tasks You configure an Express VI using a configuration dialog box Structures Execution control elements such as For Loops While Loops Case structures Flat and Stacked Sequence structures Timed structures and Event structures Formula and Expression Nodes Formula Nodes are resizable structures for entering equations directly into a block diagram Expression Nodes are structures for calculating expressions that contain a single variable Property and Invoke Node Property Nodes are structures for setting or finding properties of a class Invoke Nodes are structures for executing methods of a class Call by Reference Nodes Structures for calling a dynamically loaded VI Call Library Function Nodes Structures for calling most standard shared libraries or DLLs Code Interface Nodes CINs Structures for calling code written in text based programming languages 03 04 2009 Functions Nodes are objects on the block diagram that have inputs and or outputs and perform operations when a VI runs e Functions are the essential operating elements of LabVIEW Function icons on the Functions palette have pale yellow backgrounds and black foregrounds e Functions do not have front panels or block diagrams but do have connector panes e You cannot open or edit a function You can change the number of terminals for some functions You can add ter
24. r of the Event structure specifies the number of milliseconds to wait for an event before timing out The default is 1 which specifies to wait indefinitely for an event to occur If you wire a value to the Timeout terminal you must provide a Timeout case e The Event Data Node behaves similarly to the Unbundle by name function This node is attached to the inside left border of each event case The node identifies the data LabVIEW provides when an event occurs You can resize this node vertically to add more data items and you can set each data item in the node to access any event data element The node provides different data elements in each case of the Event structure depending on which event s you configure that case to handle If you configure a single case to handle multiple events the Event Data Node provides only the event data elements that are common to all the events configured for that case e The Event Filter Node is similar to the Event Data Node This node is attached to the inside right border of filter event cases The node identifies the subset of data available in the Event Data Node that the event case can modify The node displays different data depending on which event s you configure that case to handle By default these items are inplace to the corresponding data items in the Event Data Node If you do not wire a value to a data item of an Event Filter Node that data item remains unchanged iiss ee m CCU N LABVIEW B
25. rols and functions to group data Arrays group data elements of the same type Clusters group data elements of mixed types Cluster Clusters group data elements of mixed types A cluster is similar to a record or a struct in text based programming languages Bundling several data elements into clusters eliminates wire clutter on the block diagram and reduces the number of connector pane terminals that subVIs need The connector pane has at most 28 terminals If your front panel contains more than 28 controls and indicators that you want to pass to another VI group some of them into a cluster and assign the cluster to a terminal on the connector pane Most clusters on the block diagram have a pink wire pattern and data type terminal Error clusters have a dark yellow wire pattern and data type terminal Clusters of numeric values sometimes referred to as points have a brown wire pattern and data type terminal You can wire brown numeric clusters to Numneric functions such as Add or Square Root to perform the same operation simultaneously on all elements of the cluster Anno di nascita The error in and error out clusters include the Cluster persona following components of information ET status is a Boolean value that reports TRUE if an error occurred code is a 32 bit signed integer that identifies the error numerically A nonzero error code coupled with a status of FALSE signals a warning rather than a error source is a string tha
26. s for USB and PCMCIA work with laptops or Windows Mobile PDAs In addition National Instruments has launched DAQ devices for PCI Express the next generation PCI O bus and for PXI Express the high performance PXI bus Desktop PXI Rugged and Modular Portable 03 04 2009 14
27. t identifies where the error occurred task channels in Some VIs functions and structures that accept Boolean data also recognize an error cluster For example you can wire an error cluster to the Boolean inputs of the Select Quit LabVIEW or Stop functions If an error occurs the error cluster passes a TRUE value to the function GW Introduction to VI Waveforms a LabVIEW data types Express VI amp Dynamic Data Wavefo rm S Block diagram nodes Loops amp Structures Built in Functions Tunnels amp Indexing Array amp Clusters Shift Register amp Feedback N The waveform data type carries the data start time and delta t of a waveform e You can create a waveform using the Build Waveform function e Many of the Vis and functions you use to acquire or analyze waveforms accept and return waveform data by default e When you wire waveform data to a waveform graph or chart the graph or chart automatically plots a waveform based on the data start time and delta x of the waveform e When you wire an array of waveform data to a waveform graph or chart the graph or chart automatically plots all waveforms ia Tole 0 35 0 4 0 45 0 5 0 55 03 04 2009 Express VI An Express VI is a VI whose settings you can configure interactively through a dialog box Express VIs appear on the block diagram as expandable nodes with icons surrounded by a blue field You can configure an Express VI by setting optio
28. tside the context of a task Because these channels can apply to multiple tasks they are called global virtual channels You can select global virtual channels with the NI DAQmx API or DAQ Assistant and add them to a task Create New Express Task NI DAQ ona DAQmx Create Channel AI Voltage Basic vi Select the measurement type for the x s input terminal configuration task i 3 minimum value A task is a collection of one or more virtual E ing triggerng and other Zounter Input maximum value Digital Inpat A To hava multiple measurement types task in within a single task you must first eraate TEDS the task with ore measurement type After physical channels you create he task rlirk the Add Generate Signale a Channels button to add a new name to assign measurement t type n the task z units error in custom scale name properties Creates channel s to measure voltage If the measurement requires the use of internal excitation or you need excitation to scale the voltage use the AI Custom Voltage with Excitation instance of this VI z Back ten Finish Cancel ly A 13 IEEE 488 2 GPIB GPIB or General Purpose Interface Bus instruments offer test and manufacturing engineers the widest selection of vendors and instruments for general purpose to specialized vertical market test applications GPIB instruments are often used as stand alone benchtop instruments where measurements are taken
29. unds it and coerces it to within range You can add a conditional terminal to configure a For Loop to stop when a Boolean condition or an error occurs A For Loop with a conditional terminal executes until the condition occurs or until all iterations complete whichever happens first For example if you want a loop to execute a set number of times unless an error occurs you can use a For Loop with a conditional terminal and wire an error cluster to the conditional terminal shown as follows 03 04 2009 While Loop Similar to a Do Loop or a Repeat Until Loop in text based programming languages a While Loop executes a subdiagram until a condition occurs The While Loop executes the subdiagram until the conditional terminal an input terminal receives a specific Boolean value The While Loop does not include a set iteration count and runs infinitely if the condition never occurs If a conditional terminal is Stop if True you place the terminal of a Boolean control outside a While Loop and the control is FALSE when the loop starts you cause an infinite loop as shown in the following example You also cause an infinite loop if the conditional terminal is Continue if True and the control outside the loop is set to TRUE The iteration terminal shown as follows is an output terminal that contains the number of completed iterations The iteration count always starts at zero During the first iteration the iteration terminal returns 0
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