NI PXIe-4330/4331 User Manual
Contents
1. 2 32 Figure 2 23 Window 2 32 Tables Table 2 1 Front Connector Signal Pin Assignments 2 22 Table 2 2 Connector Signal Descriptions esee 2 23 Table 3 1 PXIe DSTAR Line Descriptions 3 2 Table 3 2 3 3 National Instruments Corporation Vii NI PXle 4330 4331 User Manual Getting Started The NI PXIe 4330 4331 provides eight simultaneously sampled input channels for interfacing to strain gage bridges and other Wheatstone bridge based sensors These modules have 24 bit resolution and support the following sample rates e NI PXIe 4330 up to 25 6 kS s e NI PXIe 4331 up to 102 4 kS s You can configure all settings on a per channel basis in software The channels support the following features e Connecting sensors of all bridge configurations including quarter half and full bridge Setting the DC voltage excitation between 0 625 V and 10 V e Selecting 120 Q 350 Q and 1 quarter bridge completion resistors Programmable bridge offset null and shunt calibration e Analog and digital filtering to reject out of band signals e Remote sense of bridge excitation Installation Refer to the NI SC Express 4330 4331 Installation Guide and Terminal Block Specifications for step by step software and hardware installation instructions Module Specifications Refer to the NI PX2. Figure 2 3 Quarter Bridge Type Measuring Axial and Bending Strain A quarter bridge type I configuration has the following characteristics A single active strain gage element is mounted in the principal direction of axial or bending strain NI 4330 4331 User Manual 2 4 ni com Chapter 2 Using the Module e passive quarter bridge completion resistor R3 is required in addition to half bridge completion resistors R3 of these resistors are provided by the NI PXIe 4330 4331 module e Sensitivity 0 5 u V V per ue for GF 2 0 4330 4331 Set Bridge Configuration to Transducer TB 4330 Quarter Bridge i R WW ANG a 3 e gage SC vwe Figure 2 4 Quarter Bridge Circuit Diagram The following symbols apply to the circuit diagram and equations e R Half bridge completion resistors located inside the NI PXIe 4330 4331 e R Quarter bridge completion resistor located inside the NI PXIe 4330 4331 must be equal to the nominal resistance of the active gage e Rs Shunt calibration resistor located inside the NI PXIe 4330 4331 e R4 Active element measuring tensile strain You provide this element e R Lead resistance The resistance in EX and QTR SC field wiring should match e GF Gage Factor speci
3. 100 5 5 EX L Quarter Bridge Shunt Calibration Completion ia Resistors T TEDS T Interface x 8 Channels Figure 2 18 NI PXle 4330 4331 Signal Conditioning Block Diagram The bridge output voltage is sensed through the AI and AI pins and then amplified and filtered before being fed into the ADC input The ADC then performs a ratiometric measurement of the input signal versus the reference signal to determine the actual deflection of the bridge or sensor The NI PXIe 4330 4331 supports half quarter and full bridge measurements When performing a quarter bridge measurement you can configure the NI PXIe 4330 4331 to select between internal 120 350 and 1 kQ quarter bridge completion resistors In addition you can enable programmable shunt calibration resistors individually or in parallel to provide three different possible shunt calibration resistor values Each channel also provides a transducer electronic data sheet TEDS interface This interface can read the TEDS information from supported sensors to provide plug and play identification of the sensor and scaling information NI 4330 4331 User Manual 2 24 ni com Chapter 2 Using the Module Figure 2 19 shows how the ADCs from each channel are connected through to the PXI Express bus Data from the ADCs are adjusted in hardware to remove offset and gain errors Then if required the data is filtered a
4. Figure 2 10 Half Bridge Type II Circuit Diagram The following symbols apply to the circuit diagram and equations e and R Half bridge completion resistors located inside the NI PXIe 4330 4331 e R Active element measuring compressive strain e R Shunt calibration resistor located inside the NI PXIe 4330 4331 e R4 Active element measuring tensile strain e R Lead resistance e GF Gage Factor specified by the gage manufacturer e Vcy Measured voltage of the bridge e Vry Excitation voltage provided by the NI PXIe 4330 4331 V Offset compensated ratiometric bridge output defined by the following equation m Vex Note The ratio of the bridge output voltage and the excitation voltage is done internally on the NI PXIe 4330 4331 National Instruments Corporation 2 11 NI PXle 4330 4331 User Manual Chapter 2 Using the Module To convert module readings to strain use the following equation 2y strain lt GF Full Bridge Type This section provides information for the full bridge strain gage configuration type I The full bridge type I only measures bending strain Figure 2 11 shows how to position strain gage resistors in a bending configuration Figure 2 12 shows the full bridge type I circuit wiring diagram Rejects Axial Measures Bending Figure 2 11 Full Bridge Type Rejecting Axial and Measuring Bending Strain A f
5. rights reserved Important Information Warranty The NI PXIe 4330 4331 is warranted against defects in materials and workmanship for a period of one year from the date of shipment as evidenced by receipts or other documentation National Instruments will at its option repair or replace equipment that proves to be defective during the warranty period This warranty includes parts and labor The media on which you receive National Instruments software are warranted not to fail to execute programming instructions due to defects in materials and workmanship 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 e
6. SC RS RS 21 20 DGND TO Tl 20 idm um 19 T3 TO T1 18 o 18 T3 T2 T2 No 17 o 17 DGND T4 5 Channel 16 o o o 16 T7 T4 T5 15 15 T7 T6 T6 14 3 o o 14 AIGND AI 12 lo o o 13 QTR SC EX AI 4 o eo 12 QTR SC RS RS 10 o 11 AIGND AI 9 E 10 QTR SC EX AI 5 7 9 QTR SC RS o o 8 AIGND AI O 7 QTR SC EX AI 6 4 6 QTR SC RS RS 3 o o sl cse e 5 AIGND Al 1 o o 4 QTR SC EX AI 7 3 QTR SC RS RS RSVD is reserved 2 RSVD DGND RSVD No 1 RSVD RSVD RSVD Channel NI 4330 4331 User Manual 2 22 ni com Chapter 2 Using the Module 1 0 Connector Signal Description Table 2 2 describes the signals found on the I O connector Table 2 2 1 0 Connector Signal Descriptions Signal Names Direction Description AIGND Analog Input Ground lt 0 7 gt AI lt 0 7 gt Input Analog Input Channels 0 to 7 AI and AI are the positive and negative inputs of the differential analog input QTR SC lt 0 7 gt These pins provide the connection point for quarter bridge completion and shunt calibration EX lt 0 7 gt lt 0 7 gt Provides the differential bridge excitation voltage 5 lt 0 7 gt RS lt 0 7 gt Input Remote sense input The remote sense pins s
7. declaration of conformity This system affords the user protection for electromagnetic compatibility EMC and product safety You can obtain the DoC for your product by visiting ni com certification e Calibration Certificate If your product supports calibration you can obtain the calibration certificate for your product at ni com calibration If you searched ni com and could not find the answers you need contact your local office or NI corporate headquarters Phone numbers for our worldwide offices are listed at the front of National Instruments Corporation B 1 NI PXle 4330 4331 User Manual Appendix B Technical Support and Professional Services this manual You also can visit the Worldwide Offices section of ni com niglobal to access the branch office Web sites which provide up to date contact information support phone numbers email addresses and current events NI PXle 4330 4331 User Manual B 2 ni com
8. of the modules in your system to receive their sync pulse from the sync pulse master module This will ensure all ADCS are running in lockstep Choose one module to be the start trigger master This does not have to be the same module you chose in step 3 depending on your application Configure the rest of the modules in your system to receive their start trigger from the start trigger master module This ensures that all modules will begin returning data on the same sample Set the synchronization type of the Start Trigger slaves at DAQmx Trigger Advanced Synchronization Synchronization Type to Slave and that of the Master to Master Also query DAQmx Timing More Synchronization Pulse Synchronization Time on all modules being synchronized choose the maximum value and set that as the DAQmx Timing More Synchronization Pulse Minimum Delay To Start on all modules Commit all of the sync pulse slave module tasks using the DAQmxTaskControl VI Function This sets them up to expect the sync pulse from the master Commit the sync pulse master module task using the DAQmxTaskControl VI Function This will issue the sync pulse Start all of the start trigger slave module tasks This sets them up to expect the start trigger from the master 10 Start the start trigger master module task You can now acquire data Consider using a Multi Device task when synchronizing multiple devices at the same rate Refer to Multi Device Synch Analog Inp
9. provided by the NI PXIe 4330 4331 e V Offset compensated ratiometric bridge output defined by the following equation y und Vix Note The ratio of the bridge output voltage and the excitation voltage is done internally on the NI PXIe 4330 4331 National Instruments Corporation 2 7 NI PXle 4330 4331 User Manual Chapter 2 Using the Module To convert module readings to strain use the following equation 4V strain 27 Half Bridge Type This section provides information for the half bridge strain gage configuration type I The half bridge type I measures either axial or bending strain Figure 2 7 shows how to position strain gage resistors in an axial and bending configurations Figure 2 8 shows the half bridge type I circuit wiring diagram Figure 2 7 Half Bridge Type Measuring Axial and Bending Strain A half bridge type I has the following characteristics e Two active strain gage elements One strain gage element is mounted in the direction of axial strain while the other acts as a Poisson gage and is mounted perpendicular to the principal axis of strain e Half bridge completion resistors and are provided by the NI PXIe 4330 4331 e Sensitive to both axial and bending strain e Sensitivity 0 65 u V V per ue for GF 2 0 NI 4330 4331 User Manual 2 8 ni com Chapter 2 Using the Module PXle 4330 4331 Set Bridge Transducer TB 4330 Co
10. to the specimen and is usually mounted perpendicular to the principal axis of strain e Completion resistors and R3 provide half bridge completion These resistors are provided by the NI PXIe 4330 4331 module e Sensitivity 0 5 u V V per pe for GF 2 0 NI PXle 4330 4331 User Manual 2 6 ni com Chapter 2 Using the Module PXle 4330 4331 Set Bridge Configuration Transducer TB 4330 to Quarter Bridge II or Half Bridge o Al Ven L RS 6 O Wf te R 3 e gage 1 0 5 1 Ry 2 gage Ro Shunt un o Cal A m SHW As i Figure 2 6 Quarter Bridge Il Circuit Diagram The following symbols apply to the circuit diagram and equations e R Half bridge completion resistors located inside the NI PXIe 4330 4331 e R Quarter bridge completion resistor located in close proximity to the active gage must be equal to the nominal resistance of the active gage e R Shunt calibration resistor located inside the NI PXIe 4330 4331 e R4 Active element measuring tensile strain 5 e Ry Lead resistance e GF Gage Factor specified by the gage manufacturer e voltage of the bridge e Vey Excitation voltage
11. 0 4331 To convert module readings to strain use the following equation E strain v Full Bridge This section provides information for the full bridge strain gage configuration type III The full bridge type III only measures axial strain Figure 2 15 shows how to position strain gage resistors in an axial configuration Figure 2 16 shows the full bridge type III circuit wiring diagram R Measures Axial Rejects Bending Figure 2 15 Full Bridge Type 111 Measuring Axial and Rejecting Bending Strain A full bridge type III configuration has the following characteristics e Four active strain gage elements Two strain gage elements are mounted in the direction of axial strain with one on one side of the strain specimen top while the other is on the opposite side bottom The other two act together as a Poisson gage and are mounted transverse perpendicular to the principal axis of strain with one on one side of the strain specimen top and the other on the opposite side bottom e Rejects bending strain e Sensitivity 1 3 u V V per ue for GF 2 0 NI 4330 4331 User Manual 2 16 ni com Chapter 2 Using the Module PXle 4330 4331 Set Bridge Transducer TB 4330 Configuration to Full Bridge Al s V 1 CH 1 Lr i
12. 4330 4331 to any other module that can trigger its acquisitions using the NI PXIe 4330 4331 SampleClock Reference Clock Synchronization With reference clock synchronization master and slave modules generate their ADC oversample clock from the shared 100 MHz reference clock from the PXIe backplane PXIe CLK100 The backplane supplies an identical copy of this clock to each peripheral slot In addition multiple chassis can be synchronized by using a timing and synchronization board to lock the 100 MHz clock across chassis When you acquire data from multiple modules within the same NI DAQmx task NI DAQmx will automatically handle all of the Reference Clock Synchronization details required to synchronize the modules within the task This is known as a Multi Device Task National Instruments Corporation 2 33 NI PXle 4330 4331 User Manual Chapter 2 Using the Module To perform Reference Clock Synchronization when using multiple NI DAQmx tasks that are acquiring at the same rate complete the following steps to synchronize the hardware 1 Specify 100 as reference clock source for all modules to force all the modules to lock to the reference clock on the PXIe chassis Choose an arbitrary NI PXIe 4330 4331 master module to issue a sync pulse on one of the PXIe Trigger lines The sync pulse resets the ADCs and oversample clocks phase aligning all the clocks in the system to within nanoseconds Configure the rest
13. ISK OF HARM TO PROPERTY OR PERSONS 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 Contents Chapter 1 Getting Started Tristall Ati 1 1 Module Specifications E et e tient estes Wheat REIP ee eee 1 1 Module Accessories and 1 1 Chapter 2 Using the Module Connecting Sigmals cn dene S d Pe 2 1 Wheatstone Bridges eoo et eer t E er E He 2 1 Connection Options to Correct for Resistance 2 2 Remote Sensing sss ote ett ped
14. Ie 4330 4351 Specifications document for module specifications Module Accessories and Cables Refer to the NI SC Express 4330 4331 Installation Guide and Terminal Block Specifications document for information about supported accessories and cables National Instruments Corporation 1 1 NI PXle 4330 4331 User Manual Using the Module This chapter describes how to connect Wheatstone bridge sensors to the NI PXIe 4330 4331 in quarter half and full bridge configurations and for remote sensing It also provides the I O connector signal pin assignments of the module Connecting Signals This section includes a brief description of a general Wheatstone bridge and discusses how to connect the signals of supported strain gage configuration types It also discusses connecting leads for remote sensing and shunt calibration Refer to NI SC Express 4330 4331 Installation Guide and Terminal Block Specifications for more signal connection information Wheatstone Bridges Many sensors including strain gages load cells pressure sensors and torque sensors are based on the concept of a Wheatstone bridge There are four elements or legs in a Wheatstone bridge In general these elements can be resistive or reactive but in the majority of bridge based sensors the elements are resistive Most Wheatstone bridge based sensors use all four legs of the bridge as active sensing elements However common strain gage configurations include
15. NI SC Express NI PXle 4330 4331 User Manual April 2010 NATIONAL 373029 01 instruments Worldwide Technical Support and Product Information ni com National Instruments Corporate Headquarters 11500 North Mopac Expressway Austin Texas 78759 3504 USA Tel 512 683 0100 Worldwide Offices Australia 1800 300 800 Austria 43 662 457990 0 Belgium 32 0 2 757 0020 Brazil 55 11 3262 3599 Canada 800 433 3488 China 86 21 5050 9800 Czech Republic 420 224 235 774 Denmark 45 45 76 26 00 Finland 358 0 9 725 72511 France 01 57 66 24 24 Germany 49 89 7413130 India 91 80 41190000 Israel 972 3 6393737 Italy 39 02 41309277 Japan 0120 527196 Korea 82 02 3451 3400 Lebanon 961 0 1 33 28 28 Malaysia 1800 887710 Mexico 01 800 010 0793 Netherlands 31 0 348 433 466 New Zealand 0800 553 322 Norway 47 0 66 90 76 60 Poland 48 22 328 90 10 Portugal 351 210 311 210 Russia 7 495 783 6851 Singapore 1800 226 5886 Slovenia 386 3 425 42 00 South Africa 27 0 11 805 8197 Spain 34 91 640 0085 Sweden 46 0 8 587 895 00 Switzerland 41 56 2005151 Taiwan 886 02 2377 2222 Thailand 662 278 6777 Turkey 90 212 279 3031 United Kingdom 44 0 1635 523545 For further support information refer to the Technical Support and Professional Services appendix To comment on National Instruments documentation refer to the National Instruments Web site at ni com info and enter the Info Code feedback 2010 National Instruments Corporation
16. The NI PXIe 4330 4331 can be used with force sensors such as load cells pressure sensors or torque sensors that have the following characteristics e Wheatstone bridge based Unamplified mV V or V V output These sensors typically use a full bridge configuration with a 350 nominal bridge resistance but other configurations and nominal bridge resistances can be used Figure 2 17 shows the force pressure torque sensor circuit diagram PXle 4330 4331 Set Bridge Transducer TB 4330 Configuration to Full Bridge Alt R RS Vor e ie at el C Vex 2 8 aP o B ue Shunt i i Rs Figure 2 17 Force Pressure and Torque Sensor Circuit Diagram 1 Sensors that measure force pressure or torque through other means for example piezoelectric force sensors cannot be used with the NI PXIe 4330 4331 Sensors that contain a built in voltage or current amplifier cannot be used with the NI PXIe 4330 4331 NI 4330 4331 User Manual 2 18 ni com Chapter 2 Using the Module The following symbols apply to the circuit diagram and equations e through R Active elements of the bridge located inside the sensor e R Shunt calibration resistor located inside the NI PXIe 4330 4331 e R Lead resistance Vcg Measured voltage sensor outp
17. V NI PXle 4330 4331 User Manual Contents Chapter 3 Timing anid Sample Clock Timebase eese External Clock nete HE Digital Trigeeritt8 e ENDE SEES anaes Analog E I E PEG Triggering and Filter Delay eene Synchronization e Ie ein m E Er dp rege epo anaes c e Haee ud Reference Clock Synchronization Configuring and Using TEDS in Software sss Accessory NI SC Express Considerations NI SC Express Clock and Trigger 12 esee Appendix A PXIesCLDK100 uc ore te t ERE EE PXIe SYNGIOO eite e teo moe etat tele n eerte tette te e tete e te uberi EE et STAR e oH tete IS PXIe DSTAR AuG inu sail latent eee Pepe Trgser ee rrr e et aer tt e eod Pa Mete iere vint Offset Nulling Bridge Balancing Appendix B Technical Support and Professional Services Figures Figure 2 1 Basic Wheatstone Bridge Circuit Diagram esee Figure 2 2 Connecting Remote Sense Wires to the NI PXIe 4330 4331 Figure 2 3 Quarter Bridge Type I Measuring Axial and Bending Strain Figure 2 4 Quarter Bridge I Circuit Diagram eee Figure 2 5 Quarter Bridge Type II Measuring Axial and Bend
18. a sigma ADC is free from the differential nonlinearity DNL and associated noise inherent in high resolution ADCs using other conversion techniques NI 4330 4331 User Manual 2 26 ni com Chapter 2 Using the Module Analog Input Filters The NI PXIe 4330 4331 uses a combination of analog and digital filtering to provide an accurate representation of in band signals while rejecting out of band signals The filters discriminate between signals based on the frequency range or bandwidth of the signal The three important bandwidths to consider are the passband the stopband and the alias free bandwidth The NI PXIe 4330 4331 accurately represents signals within the passband as quantified primarily by passband flatness and phase nonlinearity signals that appear in alias free bandwidth are either unaliased signals or signals that have been filtered by at least the amount of the stopband rejection Anti Alias Filters A digitizer or ADC might sample signals containing frequency components above the Nyquist limit The undesirable effect of the digitizer modulating out of band components into the Nyquist bandwidth is aliasing The greatest danger of aliasing is that you cannot determine whether aliasing occurred by looking at the ADC output If an input signal contains several frequency components or harmonics some of these components might be represented correctly while others contain aliased artifacts Lowpass filtering to el
19. ance in the wiring to the sensor and remote sense can not be used Refer to Figure 2 4 for a diagram of this setup The NI PXIe 4330 4331 shunt calibration circuitry consists of precision resistors and software controlled switches The shunt calibration resistors are built into the module and referenced to Refer to the software help for information about enabling the shunt calibration resistors on the NI 1 4330 4331 Shunt calibration involves simulating the input of strain by changing the resistance of an arm in the bridge by some known amount This is accomplished by shunting or connecting a large resistor of known value across one arm of the bridge creating a known change in the bridge output You can then measure the output of the bridge and compare it to the expected bridge output value You can use the results to correct gain errors in the entire measurement path or to simply verify general operation to gain confidence in the setup Strain Gage Sensor Configurations This section describes the configurations and signal connection of various supported strain gage configuration types Quarter Bridge Type This section provides information for the quarter bridge strain gage configuration type I The quarter bridge type I measures either axial or bending strain Figure 2 3 shows how to position a strain gage resistor in an axial and bending configuration Figure 2 4 shows the quarter bridge type I circuit wiring diagram
20. ations On SC Express modules the eight PXI trigger signals are synonymous with RTSI lt 0 7 gt In a PXI chassis with more than eight slots the PXI trigger lines may be divided into multiple independent buses Refer to the documentation for your chassis for details PXI STAR Trigger In a PXI Express system the Star Trigger bus implements a dedicated trigger line between the system timing slot and the other peripheral slots The Star Trigger can be used to synchronize multiple modules or to share a common trigger signal among modules A system timing controller can be installed in the system timing slot to provide trigger signals to other peripheral modules Systems that do not require this functionality can install any standard peripheral module in this system timing slot An SC Express module receives the Star Trigger signal PXI STAR from a System timing controller PXI STAR can be used as a trigger signal for input operations An SC Express module is not a System timing controller An SC Express module can be used in the system timing slot of a PXI system but the system will not be able to use the Star Trigger feature PXle DSTAR A C PXI Express devices can provide high quality and high frequency point to point connections between each slot and a system timing slot These connections come in the form of three low voltage differential star triggers that route between a PXI Express system timing controller and a peripheral devic
21. between 2 V The majority of full bridge sensors are balanced between the upper and lower arms of the bridge resulting in a common mode voltage equal to one half the excitation voltage when connected to a single ended excitation voltage or 0 V when connected to a balanced differential excitation voltage Since the NI PXIe 4330 4331 has a balanced differential excitation voltage source the common mode voltage for balanced sensors is equal to 0 V However some full bridge sensors are unbalanced between the upper and lower arms Common mode imbalances are often given as a voltage relative to a single ended voltage excitation source To convert a common mode voltage that is specified relative to a single ended excitation to a common mode voltage driven by a balanced differential excitation use the following equation 1 x 2r 1 Where is ratio of common mode voltage of sensor divided by excitation as listed in sensor specifications NI 4330 4331 User Manual 2 20 ni com Chapter 2 Using the Module For instance if a sensor is specified to have a 3 V common mode voltage with a 10 V single ended excitation is equal to 0 3 resulting in common mode voltage of 2 V when connected to a balanced differential 10 V excitation voltage supply For this case 2 V is within the common mode range of the NI PXIe 4330 4331 If the common mode voltage was outside of the range of the NI PXIe 4330 4331 it wou
22. d Vibration Measurement Suite often provide an excellent alternative to external clocking in encoder and tachometer applications Visit ni com soundandvibration for more information about the Sound and Vibration Measurement Suite National Instruments Corporation 2 29 NI PXle 4330 4331 User Manual Chapter 2 Using the Module Digital Triggering You can configure the NI PXIe 4330 4331 modules to start an acquisition in response to a digital trigger signal from one of the PXI Express backplane trigger lines The trigger circuit can respond either to a rising or a falling edge In addition the trigger circuit provides a programmable filter useful for debouncing noisy trigger signals Analog Triggering Analog triggering allows you to trigger your application based on an input signal and trigger level you define You can configure the analog trigger circuitry to monitor any input channel acquiring data Choosing an input channel as the trigger channel does not influence the input channel acquisition capabilities The analog trigger signal can be used as a reference trigger only In a reference triggered acquisition you configure the module to acquire a certain number of pre trigger samples and a certain number of post trigger samples The analog trigger on the NI PXIe 4330 4331 cannot be used as a start trigger This restriction 15 a result of the way the module compensates for the filter group delay When using an analog reference trigg
23. dware automatically compensates for its group delay such that data from this module will line up closely in time with the occurrence of the trigger event However the group delay affects how long it takes to receive data after the trigger event For example after a digital start trigger you can not read data for the first sample in software until the filter group delay has elapsed Refer to the NI PXIe 4330 4351 Specifications document for details regarding the group delay at different sample rates Synchronization Some applications require tight synchronization between input and output operations on multiple modules Synchronization is important to minimize skew between channels or to eliminate clock drift between modules in long duration operations You can synchronize the analog input operations on two or more NI PXIe 4330 4331 modules to extend the channel count for your measurements In addition the NI PXIe 4330 4331 can synchronize with certain other DSA modules such as the NI PXIe 449x modules using Reference Clock Synchronization You can also synchronize modules that support external timing to the NI PXIe 4330 4331 by routing the SampleClock output from the NI PXIe 4330 4331 to the external device The SampleClock toggles every time that the NI 4330 433 1 acquires a sample and it toggles at the point in time that the input signal was valid at the NI PXIe 4330 4331 ADC input pins This means that you can synchronize the NI PXIe
24. e Using multiple connections simplifies the creation of applications because of the increased routing capabilities Table 3 1 describes the three differential star DSTAR lines and how they are used Table 3 1 DSTAR Line Descriptions Trigger Line Purpose DSTARA DSTARB Distributes high speed high quality clock signals from the system timing slot to the peripherals input Distributes high speed high quality trigger signals from the system timing slot to the peripherals input DSTARC Sends high speed high quality trigger or clock signals from the peripherals to the system timing slot output NI PXle 4330 4331 User Manual 3 2 ni com Chapter 3 NI SC Express Considerations The DSTAR lines are only available for PXI Express devices when used with a PXI Express system timing module For more information refer to the PXI Express Specification at Www pxisa org Trigger Filters You can enable a programmable debouncing filter on each PXI Trig PXIe DSTAR or PXI STAR signal When the filters are enabled your module samples the input on each rising edge of a filter clock This filter clock is generated using the onboard oscillator The following example explains how the filter works for low to high transitions of the input signal High to low transitions work similarly Assume that an input terminal has been low for a long time The input terminal then changes
25. eference to its analog to digital converter ADC In this way variations in the excitation voltage are compensated for and the module returns data as a ratio of the bridge output voltage and the excitation voltage Connection Options to Correct for Resistance Errors The basic Wheatstone bridge in Figure 2 1 shows the excitation voltage impressed directly across the bridge However field wiring used to connect sensors to measurement devices have non zero resistance and this resistance can create errors in bridge circuit measurements The NI PXIe 4330 4331 provides two mechanisms to correct for these errors remote sensing and shunt calibration Remote Sensing Remote sensing continuously and automatically corrects for errors in excitation leads and generally is most appropriate for half and full bridge sensors Moreover its use is most critical in applications that employ long wires and or small gauge wires as these have greater resistance The resistance in the wires that connect the excitation voltage to the bridge causes a voltage drop which is a source of gain error The NI PXIe 4330 4331 includes remote sensing to compensate for this gain error Connect remote sense inputs of the NI PXIe 4330 4331 to the excitation voltage wires of the sensor as close to the bridge circuit as possible Refer to the full bridge diagram in Figure 2 2 for an illustration of how to connect remote sense wires NI 4330 4331 User Manual 2 2 ni c
26. ense the actual voltage applied to the bridge lt 0 7 gt Input Output TEDS sensor digital communication lines lt 0 7 gt Negative reference for TEDS communication Internally connected to the module digital ground RSVD These pins are reserved for communication with the accessory DGND Digital ground these pins supply the reference for module digital signals and are connected to the module digital ground NI PXle 4330 4331 Block Diagram Figure 2 18 shows the analog input circuitry block diagram of the NI PXIe 4330 4331 The programmable excitation block provides the excitation voltage for the bridge or sensor The voltage level is configurable on a per channel basis This excitation voltage is sensed locally or remotely via the remote sense terminals 5 and RS and fed back to ADC Analog to Digital Converter reference through a programmable gain amplifier The gain applied when sensing the excitation voltage is automatically selected based on the selected excitation voltage level National Instruments Corporation 2 23 NI 4330 4331 User Manual Chapter 2 Using the Module Connector Programmable Excitation RS Gain 1 RS AAA er 0 25 EX AI Analog Reference G 10 Anti Alias ADC Al Filter gg E ME SC pa H 1200 350 Q 1kQ 50
27. er the module first waits for the specified number of pre trigger samples to be acquired Once enough pre trigger samples are acquired the reference trigger will occur the next time the analog trigger condition is met You also can route the resulting reference trigger event to the NI PXIe trigger bus to synchronize the triggering of other modules in the system During repetitive triggering on a waveform you might observe jitter because of the uncertainty of where a trigger level falls compared to the actual digitized data Although this trigger jitter is never greater than one sample period it might be significant when the sample rate is only twice the bandwidth of interest This jitter usually has no effect on data processing and you can decrease this jitter by sampling at a higher rate You can use several analog triggering modes with the NI PXIe 4330 4331 modules for instance analog edge analog edge with hysteresis and window triggering NI 4330 4331 User Manual 2 30 ni com Chapter 2 Using the Module Analog Edge Triggering For analog edge triggering configure the module to detect a certain signal Level and slope either rising or falling Figure 2 20 shows an example of rising edge analog triggering The analog comparison becomes true when the signal starts below Level and then crosses above Level 3 2 mVN gar aa Level lt Level and Slope of Signal Initiates Data Capt
28. es above 4 2 mV V as shown in Figure 2 22 42mVN cats Hysteresis 3 2 mV V Level laid ees Analog Comparison Reference Trigger Figure 2 22 Analog Edge Triggering with Hysteresis on Falling Slope Window Triggering A window trigger occurs when an analog signal either passes into enters or passes out of leaves a window defined by two levels Specify the levels by setting a value for the top and bottom window boundaries Figure 2 23 demonstrates a trigger that acquires data when the signal enters the window You can also program the trigger circuit to acquire data when the signal leaves the window Window Top Window Bottom Analog Comparison Reference Trigger Figure 2 23 Window Triggering NI 4330 4331 User Manual 2 32 ni com Chapter 2 Using the Module Triggering and Filter Delay The NI PXIe 4330 4331 can use a digital trigger signal from the backplane as either a start trigger initiating an acquisition or a reference trigger in the middle of an acquisition The NI PXIe 4330 4331 can also generate an analog trigger event from its digitized ADC data As a result of the way the NI PXIe 4330 4331 modules adjust for its digital filter group delay analog triggers can only act as reference triggers In all cases the NI PXIe 4330 4331 interprets triggers based on where they occur in time The har
29. et e reete dies 2 2 Shunt Calibration 5 eed aee aee ie iet tee tiun 2 4 Strain Gage Sensor Configurations esee 2 4 Quarter Bridge 2 4 Quarter Bridge Type 2 6 Halt Bridge l i eere eer pd 2 8 Halt Bridge Type Il diete rtr 2 10 F ll Bridge ie tutte tte EE 2 12 Full Bridge Type IE ne tte RERO 2 14 Full Bndge Type III etaient tete eene tede 2 16 Force Pressure and Torque Sensor Configurations esses 2 18 Common Mode Voltage Considerations eee 2 20 Shielding and Grounding Considerations eee 2 21 dod a 2 21 Connector Signal 2 23 NI PXIe 4330 4331 Block 2 23 Signal Acquisition 2 25 Software Scaling and Equations 2 26 Nyquist Frequency and Nyquist 2 26 AD tantu ute eet AGEs o t ted ae 2 26 Anal g rer ete oe rrr terete tees 2 27 Ant Alias Putters eet eee ens 2 27 P ssband eb 2 28 Stop aid ui e P E tes ee eee 2 28 Alias Free Bandwidth e etre tiere 2 28 Filter Gro up Delay 5 3 ep Pee ed eaedem 2 28 Supported Data Rates ie tete t ee np Pee en etg 2 29 National Instruments Corporation
30. fied by the gage manufacturer e Vcy Measured voltage of the bridge Vyy Excitation voltage provided by the NI PXIe 4330 4331 e Offset compensated ratiometric bridge output defined by the following equation y Honoree Veg r Vgx National Instruments Corporation 2 5 NI PXle 4330 4331 User Manual Chapter 2 Using the Module B Note The ratio of the bridge output voltage and the excitation voltage is done internally on the NI PXIe 4330 4331 To convert module readings to strain use the following equation AV strain 1 2V To compensate for lead resistance errors shunt calibration should be used Quarter Bridge Type II This section provides information for the quarter bridge strain gage configuration type II The quarter bridge type II configuration measures either axial or bending strain Figure 2 5 shows how to position a strain gage resistor in an axial and bending configurations Figure 2 6 shows the quarter bridge type II circuit wiring diagram Figure 2 5 Quarter Bridge II Measuring Axial and Bending Strain A quarter bridge type II has the following characteristics One active strain gage element and one passive quarter bridge element dummy gage used for temperature compensation The active element R4 is mounted in the direction of axial or bending strain The dummy gage R3 is mounted in close thermal contact with the strain specimen but not bonded
31. from low to high but glitches several times When the filter clock has sampled the signal high on N consecutive edges the low to high transition is propagated to the rest of the circuit The value of N depends on the filter setting Refer to Table 3 2 Table 3 2 Filters N Filter Clocks Pulse Width Pulse Width Filter Needed to Pass Guaranteed to Guaranteed to Setting Filter Clock Signal Pass Filter Not Pass Filter None 90 ns 100 MHz 9 90 ns 80 ns short 5 12 us 100 MHz 512 5 12 us 5 11 us medium 2 56 ms 100 kHz 256 2 56 ms 2 55 ms high Custom User Configurable N N timebase N 2 timebase National Instruments Corporation The filter settling for each input can be configured independently At power on the filters are disabled Enabling filters introduces jitter on the input signal The maximum jitter is one period of the timebase These filters work by rejecting any pulse shorter than the specified filter setting For example a 5 12 us filter will reject any pulses shorter than 5 12 us The trigger filters can be used to prevent false triggers from occurring in cases where the trigger signal is noisy or glitchy 3 3 NI PXle 4330 4331 User Manual Offset Nulling Bridge Balancing When you install a bridge based sensor the bridge probably will not output exactly 0 V when not under load Slight variations in resistance among the bridge legs generate some nonze
32. ided by the NI PXIe 4330 4331 e Offset compensated ratiometric bridge output defined by the following equation Vex Note The ratio of the bridge output voltage and the excitation voltage is done internally on the NI PXIe 4330 4331 National Instruments Corporation 2 13 NI PXle 4330 4331 User Manual Chapter 2 Using the Module To convert module readings to strain use the following equation yV r strain GF Full Bridge Type Il This section provides information for the full bridge type II strain gage configuration The full bridge type II only measures bending strain Figure 2 13 shows how to position strain gage resistors in a bending configuration Figure 2 14 shows the full bridge type II circuit wiring diagram Ro v amp Rejects Axial Measures Bending Figure 2 13 Full Bridge Type II Rejecting Axial and Measuring Bending Strain A full bridge type II configuration has the following characteristics e Four active strain gage elements Two are mounted in the direction of bending strain with one on one side of the strain specimen top and the other on the opposite side bottom The other two act together as a Poisson gage and are mounted transverse perpendicular to the principal axis of strain with one on one side of the strain specimen top and the other on the opposite side bottom e Rejects axial strain e Sensitivity 1 3 u V V per pe fo
33. iminate components above the Nyquist frequency either before or during the digitization process can guarantee that the digitized data set is free of aliased components The NI PXIe 4330 4331 modules employ both digital and analog lowpass filters to achieve this protection The NI PXIe 4330 4331 modules include an oversampled architecture and sharp digital filters with cut off frequencies that track the sampling rate Thus the filter automatically adjusts to follow the Nyquist frequency Although the digital filter eliminates almost all out of band components it is still susceptible to aliases from certain narrow frequency bands located at frequencies far above the sampling rate These frequencies are referred to as the ADC alias holes In addition to the digital filtering the NI PXIe 4330 4331 modules feature a fixed frequency analog filter The analog filter removes high frequency components in the analog signal path before they reach the ADC This filtering addresses the possibility of high frequency aliasing from the narrow bands that are not covered by the digital filter While the frequency response of the digital filter directly scales with the sample rate the analog filter 3dB point is fixed The NI PXIe 4330 4331 automatically adjusts its oversample rate to maintain a high level of alias protection regardless of the current sampling rate National Instruments Corporation 2 27 NI PXle 4330 4331 User Manual Chapter 2 Using the Modu
34. ing Strain Figure 2 6 Quarter Bridge II Circuit Figure 2 7 Half Bridge Type I Measuring Axial and Bending Strain Figure 2 8 Half Bridge Type I Circuit Figure 2 9 Half Bridge Type II Rejecting Axial and Measuring Bending Stralis ae Figure 2 10 Half Bridge Type II Circuit Diagram e NI PXle 4330 4331 User Manual vi ni com Contents Figure 2 11 Full Bridge Type I Rejecting Axial and Measuring Bending Strain 2 12 Figure 2 12 Full Bridge Type I Circuit Diagram eee 2 13 Figure 2 13 Full Bridge Type II Rejecting Axial and Measuring Bending Strain 2 14 Figure 2 14 Full Bridge Type II Circuit 2 15 Figure 2 15 Full Bridge Type III Measuring Axial and Rejecting Bending SITAID ERROR 2 16 Figure 2 16 Full Bridge Type III Circuit Diagram ene 2 17 Figure 2 17 Force Pressure and Torque Sensor Circuit Diagram 2 18 Figure 2 18 NI PXIe 4330 4331 Signal Conditioning Block Diagram 2 24 Figure 2 19 NI PXIe 4330 4331 Digital Back End Block Diagram 2 25 Figure 2 20 Analog Level Trigger on Rising 2 31 Figure 2 21 Analog Edge Triggering with Hysteresis on Rising Slope 2 31 Figure 2 22 Analog Edge Triggering with Hysteresis on Falling Slope
35. ld be necessary to reduce the excitation voltage to a level that results in a common mode voltage that is within range To find the maximum excitation voltage that meets this criterion solve the following equation setting Vm equal to 2 V if r lt 0 5 or setting V m equal to 2 V if r 0 5 2 V E eni 2r 1 Shielding and Grounding Considerations iyi Note For proper electromagnetic compatibility EMC performance use shielded wire and connect the shield to the chassis ground Module Pinout This is the pinout represented on the front connector of the NI PXIe 4330 4331 Refer to the I O Connector Signal Description section for definitions of each signal Refer to the terminal block installation guide for signal locations on the terminal block National Instruments Corporation 2 21 NI PXle 4330 4331 User Manual Chapter 2 Using the Module Table 2 1 Front Connector Signal Pin Assignments Front Connector Diagram Pin Number Column A Column B Column C Channel 32 AIGND AI 31 TR SC EX AI A B C 9 a 0 auu 30 QTR SC RS RS 32 ep lite 29 AIGND EX Al 30 28 QTR SC EX AI 1 29 o0 27 QTR SC RS RS w 26 AIGND EX 27 25 QTR SC EX AI 2 26 o 5 o o 24 QTR SC RS RS 24 o 23 AIGND AI 23 22 QTR SC EX AI 3 der amp 21 QTR
36. le Passband The signals within the passband have frequency dependent gain or attenuation The small amount of variation in gain with respect to frequency is called the passband flatness The digital filters of the NI PXIe 4330 4331 adjust the frequency range of the passband to match the sample rate Therefore the amount of gain or attenuation at a given frequency depends on the sample rate Stopband The filter significantly attenuates all signals above the stopband frequency The primary goal of the filter is to prevent aliasing Therefore the stopband frequency scales precisely with the sample rate The stopband rejection is the minimum amount of attenuation applied by the filter to all signals with frequencies within the stopband Alias Free Bandwidth Any signal that appears in the alias free bandwidth of the NI PXIe 4330 4331 is not an aliased artifact of signals at a higher frequency The alias free bandwidth is defined by the ability of the filter to reject frequencies above the stopband frequency and it is equal to the sample rate minus the stopband frequency Filter Group Delay The digital filtering performed by the NI PXIe 4330 4331 produces a delay of many samples worth of time between when an event occurs on the input signal going into the NI PXIe 4330 4331 and when the data associated with that event is available at the output of the acquisition and filtering process This delay is called the group delay In order to simp
37. lf Bridge Type 11 This section provides information for the half bridge strain gage configuration type II The half bridge type II only measures bending strain Figure 2 9 shows how to position strain gage resistors in a bending configuration Figure 2 10 shows the half bridge type II circuit wiring diagram Rejects Axial Measures Bending Figure 2 9 Half Bridge Type II Rejecting Axial and Measuring Bending Strain A half bridge type II configuration has the following characteristics e Two active strain gage elements One strain gage element is mounted in the direction of bending strain on one side of the strain specimen top while the other is mounted in the direction of bending strain on the opposite side bottom e Half bridge completion resistors and R3 are provided by the NI PXIe 4330 4331 e Sensitive to bending strain e Rejects axial strain e Sensitivity 1 V V per ue for GF 2 0 NI 4330 4331 User Manual 2 10 ni com Chapter 2 Using the Module 4330 4331 Set Bridge Transducer TB 4330 Configuration to Half Bridge R R ma 1 WWW Ext R E gage gt EX WAV Ro maS 3 P iom 4 E L SC d e Mae ekv R Rg
38. lify the process of acquiring data from the NI PXIe 4330 4331 modules and correlating that data with data from other modules the NI PXIe 4330 4331 compensates for this group delay in the following ways e The Sample Clock output from the NI PXIe 4330 4331 is generated at the point in time when the input signal is valid at the ADC input pins When acquiring data the NI PXIe 4330 4331 generates a Sample Clock then waits for the data associated with that Sample Clock to be acquired then returns that data As a result any other acquisitions timed with this Sample Clock line up with the data returned by the NI PXIe 4330 4331 Any triggers generated or received by the NI PXIe 4330 4331 are interpreted based on their relationship to the Sample Clock being generated For example a Start Trigger that starts an acquisition results in data from the next Sample Clock being returned as the first point in the acquisition Refer to the Triggering and Filter Delay section for more details about how this affects analog trigger events NI PXle 4330 4331 User Manual 2 28 ni com Chapter 2 Using the Module e For any on demand software timed acquisition the NI PXIe 4330 4331 waits for the group delay to elapse before returning the sample As a result the data returned aligns closely in time with when the data was requested However as a result you must wait for the group delay to elapse before this sample is available e Similarly for hardware timed ac
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41. nd decimated to match the specified acquisition rate Finally the data is placed into a FIFO where it is transferred through PCI Express to the host computer memory Gain amp Digital UR S Offset Filtering amp FIFO lt Interface Correction Decimation ogic a Analog x Trigger m x 8 o o Timing amp Triggering o w Controller gt w y 5 a DDS Clock Generation 8 o Figure 2 19 NI PXle 4330 4331 Digital Back End Block Diagram Timing and triggering of the acquisition is handled by an onboard timing and triggering controller This controller configures an onboard DDS clock generator to provide an oversample clock to the ADCS in order to acquire data at the specified rate The DDS clock can be generated either using an onboard oscillator or using the 100 MHz backplane clock provided by PXI Express Running the DDS clock from the 100 MHz backplane clock allows for synchronization of multiple NI PXIe 4330 4331 modules In addition to sending and receiving triggers from the PXIe backplane the NI PXIe 4330 4331 can also be configured to generate an Analog Trigger event from the digitized analog data of its ADCs Signal Acquisition Considerations This section contains information about signal acquisition concepts including software scaling and equations Delta Sigma converters Nyqui
42. nfiguration to Half Bridge iom EE L SC d Wf eww R 1 Rs Figure 2 8 Half Bridge Type I Circuit Diagram The following symbols apply to the circuit diagram and equations and R Half bridge completion resistors located inside the NI PXIe 4330 4331 element measuring compression from Poisson effect Rs Shunt calibration resistor located inside the NI PXIe 4330 4331 R Active element measuring tensile strain R Lead resistance Factor specified by the gage manufacturer v Poisson s ratio defined as the negative ratio of transverse strain to axial strain longitudinal strain Poisson s ratio is a material property of the specimen you are measuring Vcgy Measured voltage of the bridge Vey Excitation voltage provided by the NI PXIe 4330 4331 V Offset compensated ratiometric bridge output defined by the following equation lt strained V cy constrained Vix National Instruments Corporation 2 9 NI PXle 4330 4331 User Manual Chapter 2 Using the Module B Note The ratio of the bridge output voltage and the excitation voltage is done internally on the NI PXIe 4330 4331 To convert module readings to strain use the following equation 4AV strain GF 1 v 2V v 1 Ha
43. ng rate of f can represent only signals with frequencies lower than f 2 This maximum frequency is known as Nyquist frequency The bandwidth from 0 Hz to the Nyquist frequency is the Nyquist bandwidth ADC The NI PXIe 4330 4331 ADCs use a conversion method known as delta sigma modulation This approach involves oversampling the input signal at a higher rate and then decimating and filtering the resulting data to achieve the desired sample rate For example if the desired data rate is 100 kS s each ADC actually samples its input signal at 6 4 MS s 64 times the data rate producing 1 bit samples that are sent to a digital filter This filter rejects signal components greater than the Nyquist frequency of 50 kHz The 1 bit 6 4 MS s data stream from the ADC contains all of the information necessary to produce 24 bit samples at 100 kS s The delta sigma ADC achieves this conversion from high speed to high resolution with a technique called noise shaping The ADC adds random noise to the signal so that the resulting quantization noise although large is restricted to frequencies above the Nyquist frequency which is 50 kHz in this case This noise is not correlated with the input signal and is almost completely rejected by the digital filter The resulting output of the filter is a band limited signal with a large dynamic range One of the advantages of a delta sigma ADC is that it uses a 1 bit DAC as an internal reference As a result delt
44. nsor calibration certificates specify the electrical output in mV or V not mV V or V V If this is the case divide the specified electrical output by the excitation voltage at which the calibration was performed National Instruments Corporation 2 19 NI 4330 4331 User Manual Chapter 2 Using the Module The two point linear conversion uses the following equations physical physical electrical electrical b physical m x electrical physical reading mx V b If offset nulling bridge balancing is used to compensate for offset then the zero point of the sensor can be assumed to output exactly 0 V V simplifying these equations physical electrical physical reading mx V When the calibration certificate of the sensor provides a table of more than two calibration points or a polynomial expression table or polynomial scaling can produce more accurate results by compensating for non linearity in the response of the sensor Table scaling requires providing NI DAQmx with a set of electrical values and corresponding physical values Polynomial scaling requires providing NI DAQmx with the forward and reverse coefficients of a polynomial representing the response of the sensor If you only know one set of coefficients you can use the DAQmx Compute Reverse Polynomial Coefficients VI function to determine the other set Common Mode Voltage Considerations The NI PXIe 4330 4331 supports common mode voltages
45. om Chapter 2 Using the Module 4330 4331 Al Al EX RS Figure 2 2 Connecting Remote Sense Wires to the NI PXle 4330 4331 The actual bridge excitation voltage measured at the bridge is smaller than the voltage sourced atthe and EX connector pins This reduction in voltage is due to the voltage drop across the excitation lead wire resistance If you do not use remote sensing of the actual bridge voltage the resulting reduction in gain is given by the following equations e for half bridge sensors g 2 e for full bridge sensors Re If you connect the remote sense signals directly to the bridge resistors the NI PXIe 4330 4331 senses the actual bridge voltage using high impedance RS leads and eliminates the gain errors caused by the resistance of the EX and EX leads National Instruments Corporation 2 3 NI PXle 4330 4331 User Manual Chapter 2 Using the Module Shunt Calibration Shunt calibration can correct for errors from the resistance of both the excitation wiring and wiring in the individual resistors of the bridge Remote sensing corrects for resistances from the EX leads on the NI PXIe 4330 4331 to the sensor and shunt calibration corrects for these errors and for errors caused by wire resistance within an arm of the bridge Shunt calibration is most useful with three wire quarter bridge sensors because there may be significant resist
46. one two or four active sensing elements Figure 2 1 shows a resistive Wheatstone bridge circuit diagram Figure 2 1 Basic Wheatstone Bridge Circuit Diagram National Instruments Corporation 2 1 NI 4330 4331 User Manual Chapter 2 Using the Module The Wheatstone bridge is the electrical equivalent of two parallel voltage divider circuits and compose one voltage divider circuit and R4 and R4 compose the second voltage divider circuit The output of a Wheatstone bridge is measured between the middle nodes of the two voltage dividers A physical phenomena such as a change in strain or temperature applied to a specimen changes the resistance of the sensing elements in the Wheatstone bridge resulting in a bridge output voltage that is proportional to the physical phenomena The output voltage of the bridge scales with the excitation voltage However the ratio of the bridge output and the excitation voltage remains fixed over variations in excitation voltage and it is this unitless ratio that is of interest To accurately measure the ratiometric output of a bridge based sensor both the bridge output voltage and the excitation voltage must be known Determination of the excitation voltage can be accomplished by either using an accurate voltage source or by measuring it The NI PXIe 4330 4331 uses circuitry that continuously measures the excitation voltage and applies it as a r
47. quisition at very low sample rates you might notice that it takes several seconds for an acquisition to begin This is because during start the ADCs get reset and have to wait many samples before delta sigmas are operational That time is dependent on the sample rate To improve the time it takes an acquisition to begin select a higher sample rate Supported Data Rates The NI PXIe 4330 4331 supports rates of 1 S s to 100 S s in 1 S s increments Rates beyond 100 S s are supported in 100 S s increments up to the maximum rate for the module Timing and Triggering This section contains information about timing and triggering theory of operation Sample Clock Timebase The ADCs require an oversample clock to drive the conversion The oversample clock frequency is greater than the sample rate On the NI PXIe 4330 4331 modules the oversample clock is produced from a DDS clock generation circuit The DDS in turn is run from a 100 reference clock This 100 MHz reference clock can be supplied either by an onboard oscillator or by the PXI backplane 100 MHz clock Multiple modules can be synchronized by selecting the PXI backplane 100 MHz clock as the reference clock source for all the modules Refer to the Reference Clock Synchronization section for more information External Clock The NI 1 4330 4331 ADCs cannot be clocked from external sources such as encoders tachometers However signal processing features in the Sound an
48. r GF 2 0 NI 4330 4331 User Manual 2 14 ni com Chapter 2 Using the Module 4330 4331 Set Bridge Transducer TB 4330 Configuration to Full Bridge m Shunt d Cal A Figure 2 14 Full Bridge Type II Circuit Diagram The following symbols apply to the circuit diagram and equations element measuring compressive Poisson effect v R Active element measuring tensile Poisson effect ve element measuring compressive strain R4 Active element measuring tensile strain R Shunt calibration resistor located inside the NI PXIe 4330 4331 R Lead resistance GF Factor specified by the gage manufacturer v Poisson s ratio defined as the negative ratio of transverse strain to axial strain longitudinal strain Poisson s ratio is a material property of the specimen you are measuring Vcg Measured voltage of the bridge Vey Excitation voltage provided by the NI PXIe 4330 4331 V Offset compensated ratiometric bridge output defined by the following equation y Vix National Instruments Corporation 2 15 NI PXle 4330 4331 User Manual Chapter 2 Using the Module B Note The ratio of the bridge output voltage and the excitation voltage is done internally on the NI PXIe 433
49. ro initial offset voltage Use the DAQmx Perform Bridge Offset Nulling Calibration VI function or the DAQ Assistant to perform an offset nulling calibration which will apply software compensation for the bridge NI DAQmx will measure the bridge while not under load and then use this measurement as the initial bridge voltage when scaling readings from the bridge This method is simple fast and requires no manual adjustments The disadvantage of the software compensation method in contrast to hardware compensation is that software compensation does not physically remove the offset of the bridge If the offset is large enough it limits the amplifier gain you can apply to the output voltage thus limiting the dynamic range of the measurement The NI PXIe 4330 4331 does not have any internal hardware nulling circuitry however its input range is sufficiently wide so that the inputs will not saturate even with a relatively large initial bridge offset National Instruments Corporation A 1 NI PXle 4330 4331 User Manual Technical Support and Professional Services Visit the following sections of the award winning National Instruments Web site at ni com for technical support and professional services e Support Technical support at ni com support includes the following resources Self Help Technical Resources For answers and solutions visit ni com support for software drivers and updates a searchable KnowledgeBase product
50. st frequency and bandwidth timing triggering and synchronization National Instruments Corporation 2 25 NI PXle 4330 4331 User Manual Chapter 2 Using the Module Software Scaling and Equations After you have acquired the signal of interest you can scale this measurement to the appropriate units in software This is done automatically for you in NI DAQmx using a strain task or strain channel You also can scale the measurements manually in your application using the measurement to strain conversion equations provided in this document for each configuration type The NI PXIe 4330 4331 also supports measurements for force pressure torque bridge V V and custom voltage with excitation Finally there are voltage to strain conversion functions included in LabVIEW and NI DAQmx In LabVIEW the conversion function Convert Strain Gage Reading VI is in the Data Acquisition Signal Conditioning subpalette The prototypes for the NI DAQ functions Strain Convert and Strain_Buf_Convert are in the header file convert h for and convert bas for Visual Basic Refer to the LabVIEW Measurements Manual for more information The names given the strain gage types in these sections directly correspond to bridge selections in MAX and the LabVIEW Convert Strain Gage Reading VI Nyquist Frequency and Nyquist Bandwidth Any sampling system such as an ADC is limited in the bandwidth of the signals it can measure Specifically a sampli
51. structions 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 National Instruments respects the intellectual property of others and we ask our users to do the same NI software is protected by copyright and other intellectual property laws Where NI software may be used to reproduce software or other materials belonging to others you may use NI software only to reproduce materials that you may reproduce in accordance with the terms of any applicable license or other legal restriction Trademarks LabVIEW National Instruments NI ni com the National Instruments corporate logo and the Eagle logo are trademarks of National Instruments Corporation Refer to the Trademark Information at ni com trademarks for other National Instruments trademarks Other product and company names mentioned herein are trademarks or trade names of their respective companies Members of the National Instruments Alliance Partner Program are business entities independent from National Instruments and have no age
52. the DAQmx Configure TEDS VI Accessory Auto Detection NI SC Express modules automatically detect compatible accessories or terminal blocks The RSVD pins on the I O connector provide power to the accessories as well as digital communication lines This allows software to detect when accessories are inserted or removed In addition software can automatically identify the specific terminal block as well as access any calibration or scaling information associated with the terminal block Measurement amp Automation Explorer MAX allows you to see what accessories are currently connected to your module In MAX expand Devices and Interfaces and locate your module If a terminal block is connected to your module it will be displayed beneath the module Unsupported terminal blocks appear in MAX with an X next to them NI DAQmx property nodes can be used to programmatically access information about connected accessories in your application Refer to the NI DAQmx Help for documentation about programmatically accessing accessory status Select Start All Programs National Instruments NI DAQ NI DAQmx Help National Instruments Corporation 2 35 NI 4330 4331 User Manual NI SC Express Considerations This chapter details the clock and trigger functionality available through the PXI Express chassis NI SC Express Clock and Trigger Signals PXle CLK100 PXIe CLK100 is a common low skew 100 MHz reference clock used for synchroni
53. ull bridge type I configuration has the following characteristics e Four active strain gage elements Two strain gage elements are mounted in the direction of bending strain on one side of the strain specimen top while the other two are mounted in the direction of bending strain on the opposite side bottom e Highly sensitive to bending strain e Rejects axial strain e Sensitivity 2 uL V V per ue for GF 2 0 NI 4330 4331 User Manual 2 12 ni com Chapter 2 Using the Module 4330 4331 Set Bridge Transducer TB 4330 Configuration to Full Bridge EE T0 10 2 48i 19 49 5 8l 18H WWW g R i WW e D R QTR J Shunt SC Cal A Bv R Rs Figure 2 12 Full Bridge Type I Circuit Diagram The following symbols apply to the circuit diagram and equations e R Active element measuring compressive strain e R Active element measuring tensile strain e R Active element measuring compressive strain e R4 Active element measuring tensile strain e R Shunt calibration resistor located inside the NI PXIe 4330 4331 e R Lead resistance e GF Gage Factor specified by the gage manufacturer e Vcy Measured voltage of the bridge e Vry Excitation voltage prov
54. ure 0 Analog Comparison Reference Trigger Figure 2 20 Analog Level Trigger on Rising Slope Analog Edge Triggering With Hysteresis When you add hysteresis to analog edge triggering you add a window above or below the trigger level This triggering mode often is used to reduce false triggering due to noise or jitter in the signal For example if you add a hysteresis of 1 mV V to the example in Figure 2 20 which uses a level of 3 2 mV V the signal must start at or drop below 2 2 mV V to arm the trigger The analog comparison becomes true when the signal rises above 3 2 mV V and becomes false when it falls below 2 2 mV V as shown in Figure 2 21 3 2 mV V Level S TREE Hysteresis 2 2 mV V Nds co AR NE MR Analog Comparison Reference Trigger Figure 2 21 Analog Edge Triggering with Hysteresis on Rising Slope National Instruments Corporation 2 31 NI PXle 4330 4331 User Manual Chapter 2 Using the Module When using hysteresis with a falling slope the trigger is armed when the signal starts above Level plus the hysteresis value and asserts when the signal crosses below Level For example if you add a hysteresis of 1 mV V to alevel of 3 2 mV V the signal must start at or rise above 4 2 mV V to arm the trigger The analog comparison becomes true as the signal falls below 3 2 mV V and becomes false when it ris
55. ut e Vgy Excitation voltage provided by the NI PXIe 4330 4331 e Offset compensated ratiometric bridge output defined by the following equation _ Vex under load no load Vy X V r Note The ratio of the bridge output voltage and the excitation voltage is calculated internally on the NI PXIe 4330 4331 Converting module readings to physical force pressure or torque readings can be performed using linear table or polynomial scaling In NI DAQmx linear scaling for bridge based force pressure and torque sensors is done based on two points which are specified as pairs of corresponding physical and electrical values electrical physical and electrical physical These should be based on calibration certificate of the sensor if one is available otherwise they can be based on the specifications or data sheet of the sensor Any two points can be used assuming that they are far enough apart to accurately determine the slope of the linear scaling equation For example e physical The zero point of the sensor zero force pressure or torque e electrical The electrical output corresponding to the zero point of the sensor in mV V or V V e physical The maximum physical reading of the sensor or capacity maximum load pressure or torque e electrical The electrical output corresponding to the maximum physical reading of the sensor in mV V or V V Note Some se
56. ut Cont Acq Multi Rate PXIe 433x VI for an example of how to synchronize when acquiring at different rates Consider the following caveat to using Reference Clock synchronization The NI PXIe 4330 4331 automatically compensates for its filter group delay However some other device families do not compensate for their filter delay In this case you might need to compensate for group delay in the waveforms when you synchronize between device families NI PXle 4330 4331 User Manual 2 34 ni com Chapter 2 Using the Module TEDS The NI PXIe 4330 4331 supports communicating with Transducer Electronic Data Sheet TEDS enabled sensors IEEE 1451 4 Class 2 TEDS enabled sensors carry a built in self identification EEPROM containing a table of parameters and sensor information This allows your data acquisition system to automatically detect and configure the sensors TEDS contains information about the sensor such as calibration sensitivity and manufacturer information This information is accessible in Measurement amp Automation Explorer MAX VIs in LabVIEW or by calling the equivalent function calls in a text based ADE For more information about TEDS plug and play sensors refer to ni com pnp Configuring and Using TEDS in Software To manually configure TEDS in MAX right click on the NI PXIe 4330 4331 module within the Configuration tree Then select Configure TEDS from the pop up menu To programmatically configure TEDS call
57. xist 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 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 in
58. zation of multiple modules in a PXI Express measurement or control system The NI PXIe backplane is responsible for generating PXIe CLK100 independently to each peripheral slot in a PXI Express chassis For more information refer to the PXI Express Specification at www pxisa org PXle_SYNC100 PXIe SYNCIOO is a common low skew 10 MHz reference clock with a 10 duty cycle for synchronization of multiple modules in a PXI Express measurement or control system The PXI Express backplane is responsible for generating PXIe SYNCIOO independently to each peripheral slot in a PXI Express chassis For more information refer to the PXI Express Specification at www pxisa org PXI CLK10 PXI_CLK10 is a common low skew 10 MHz reference clock for synchronization of multiple modules in a PXI measurement or control system The PXI backplane is responsible for generating CLK10 independently to each peripheral slot in a PXI chassis Note PXI cannot be used as a reference clock for SC Express modules PXI Triggers A PXI chassis provides eight bused trigger lines to each module in a system Triggers may be passed from one module to another allowing precisely timed responses to asynchronous external events that are being monitored or controlled Triggers can be used to synchronize the operation of several different PXI peripheral modules National Instruments Corporation 3 1 NI 4330 4331 User Manual NI SC Express Consider
59. zo d Al ee We BS 92 o P 5 Shunt 5 1 Cal A 1 16 v Rs Figure 2 16 Full Bridge Type III Circuit Diagram The following symbols apply to the circuit diagram and equations R Active element measuring compressive Poisson effect v R Active element measuring tensile strain R5 Active element measuring compressive Poisson effect v R4 Active element measuring the tensile strain R Lead resistance GF Factor specified by the gage manufacturer v Poisson s ratio defined as the negative ratio of transverse strain to axial strain longitudinal strain Poisson s ratio is a material property of the specimen you are measuring R Shunt calibration resistor located inside the NI PXIe 4330 4331 Vcg Measured voltage of the bridge Vex Excitation voltage provided by the NI PXIe 4330 4331 V Offset compensated ratiometric bridge output defined by the following equation Vex National Instruments Corporation 2 17 NI 4330 4331 User Manual Chapter 2 Using the Module B Note The ratio of the bridge output voltage and the excitation voltage is done internally on the NI PXIe 4330 4331 To convert module readings to strain use the following equation trai m strain GF v 1 V v 1 Force Pressure and Torque Sensor Configurations
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