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SCXI-1520 User Manual

1. Chapter 2 Connecting Signals Table 2 1 Front Signal Pin Assignments Front Connector Diagram Pin Number Column A Column B Column C 32 SCBO S0 S0 Col mn 31 SCBO RS0 RSO A B C 30 SCBI P0 PO m 32 o o o 29 SCBI SCAO SCAO 31 o o o 28 RSVD S1 S14 30 Io Wes dm 27 RSVD RSI RS1 29 o 26 RSVD P1 Ple 28 27 o o o 25 RSVD SCA1 SCAI 26 oO o o 24 SCB2 S2 S2 25 9 9 o 23 SCB2 RS2 RS2 ee 22 SCB3 P2 P2 23 21 SCB3 SCA2 SCA2 22 o 24 a o o 20 RSVD S3 S34 20 0 o o 19 RSVD RS3 RS34 ig o o o 18 RSVD P3 P3 18 17 RSVD SCA3 SCA3 17 o o ele uw 6 16 SCB4 S4 S4 15 o o o 15 SCB4 RS4 RS4 1 4 o o o 14 SCB5 P4 P4 13 o o o 13 SCB5 SCA4 SCA4 12 o o o 12 RSVD S5 S5 11 ilo o o 11 RSVD RS5 RS5 9o o o 10 RSVD P5 P5 8 o o 9 RSVD SCA5 SCAS x 2 8 8 SCB6 S6 S6 6 7 SCB6 RS6 RS6 5 o 42 de ae we 6 SCB7 P6 P6 3 o o o 5 SCB7 SCA6 SCA6 2 0 o o 4 RSVD S7 S7 T e cimi 3 RSVD RS7 RS7 2 RSVD P7 P7 1 RSVD SCA7 SCA7 National Instruments Corporation 2 11 SCXI 1520 User Manual Chapter 2 Connecting Signals The rear signal connector is a 50 pin male cable connector used for analog signal connectivity and communication between the SCXI 1520 and the connected E M Series DAQ device The rear signal connector is shown in Ta
2. lt l nA Switch break down voltage x60 VDC Power Consumption ME iet tet ole terae ba 18 5 to 25 VDC 170 mA max ME ideni pH perio E OUR 18 5 to 25 VDC 170 mA max dM 4 75 to 5 25 VDC 50 mA max Half bridge completion is performed inside the module and configured under software control The quarter bridge completion resistor is in the SCXI 1314 terminal block and is socketed Resistors shipped with the SCXI 1314 are 120 Q and 350 Q default value RN 55 style standard 1 4 W size The tolerance is 0 1 and the temperature coefficient is 10 ppm C max Shunt calibration resistors are in the SCXI 1314 terminal block and are socketed Resistors shipped with the SCXI 1314 are 100 kQ RN 55 style standard 1 8 W size The tolerance is 0 1 and the temperature coefficient is 10 ppm C max SCXI 1520 User Manual A 6 ni com Appendix A Specifications Physical Difnensliorns eec eoe esent tenet 3 0 x 17 2 x 20 3 cm 1 2 x 6 9 x 8 0 in Weight uem Ded ass 750 g 1 Ib 10 4 oz Maximum Working Voltage Maximum working voltage refers to the signal voltage plus the common mode voltage Channel to earth Either the SX or SX input should remain within 10 V of ground Both inputs should be within 10 V of one another Measurement Category I Channel to channel Either the SX or SX input should rema
3. Allowable Settings AI Parameter VI Float In Boolean In or Value In Software Configurable Parameter Setting Name Value Data Type Values Shunt A SCXI Shunt A 25 Boolean In T F TRUE turns switch ON Enable Enabled FALSE turns switch OFF Shunt B SCXI Shunt B 26 Boolean In T F TRUE turns switch ON Enable Enabled FALSE turns switch OFF An example of using the AI Parameter VI to control an SCXI 1520 is shown in Figure 5 4 National Instruments Corporation 5 23 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 input limits Allowable voltage settings Allowable filter settings in Hz Sets bridge type 0 000 0 625 1 125 1 875 D no filtering 9 Quarter Bridge pum 2 500 3125 3750 4 375 10 10 Half Bridge B 5 000 5 625 6 125 6 875 100 11 Full Bridge H 7 500 8 125 8 750 9 375 1000 10 00 10000 exis vitu 1 0 number between 4 number between and 127 with 62 and 4095 with 2048 TRUE turns switch ON TRUE turns switch ON at mid scale at mid scale FALSE turns switch OFF FALSE turns switch OFF Coarse Pot ost Shunt A switch Shunt B switch Param Param Param a pte MAMAKKEEEKRO CN NR nas MERE Is SCXI Coarse Potentiometer Y A SEXI Fine Potentiometer 23 SCXI Shunt A Enabled 7 SCXI Shunt B Enabled waveform graph Al H idi Above settings become active when this Al Start is executed 1080 gt
4. eee 2 4 Figure 2 4 Half Bridge Type II Circuit Diagram see 2 5 Figure 2 5 Full Bridge Type I Circuit Diagram see 2 6 Figure 2 6 Full Bridge Type II Circuit Diagram see 2 7 Figure 2 7 Full Bridge Type III Circuit Diagram eee 2 8 Figure 2 8 Remote Sense Circuit Diagram a aaasssssssssssssssssss 2 9 Figure 4 1 Basic Wheatstone Bridge Circuit Diagram see 4 1 Figure 4 2 Quarter Bridge Type I Measuring Axial and Bending Strain 4 4 Figure 4 3 Quarter Bridge I Circuit Diagram seen 4 5 Figure 4 4 Quarter Bridge Type II Measuring Axial and Bending Strain 4 7 Figure 4 5 Quarter Bridge II Circuit Diagram eee 4 7 Figure 4 6 Half Bridge Type I Measuring Axial and Bending Strain 4 0 Figure 4 7 Half Bridge Type I Circuit Diagram eee 4 9 Figure 4 8 Half Bridge Type II Rejecting Axial and Measuring Bending Strain 4 11 Figure 4 9 Half Bridge Type II Circuit Diagram see 4 11 Figure 4 10 Full Bridge Type I Rejecting Axial and Measuring Bending Strain 4 13 Figure 4 11 Full Bridge Type I Circuit Diagram e 4 13 Figure 4 12 Full Bridge Type II Rejecting Axial and Measuring Bending Strain 4 15 Figure 4 13 F
5. Figure 5 4 Using the Al Parameter VI to Set Up the SCXI 1520 Performing Offset Null Compensation Using Traditional NI DAQ Legacy in LabVIEW The SCXI 1520 provides offset null compensation to adjust signal voltages to remove an initial signal voltage offset from the Wheatstone bridge sensor If you are measuring strain you can use the strain virtual channel in Traditional NI DAQ Legacy to perform offset null compensation shunt calibration and to properly scale strain measurements The offset null compensation and shunt calibration are performed during configuration of the strain virtual channel Refer to Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later for more information about creating a strain virtual channel in MAX SCXI 1520 User Manual 5 24 ni com Chapter 5 Using the SCXI 1520 After you have created a strain virtual channel simply use a DAQ channel control or constant to select the strain virtual channel from a list of all the virtual channels you have configured in MAX You can find the DAQ channel constant in the function subpalette Data Acquisition Analog Input You can find the DAQ channel control in the control subpalette I O If you are using a strain virtual channel you cannot perform offset null compensation dynamically in your application If you need to dynamically perform an offset null compensation in your application you must use SCXI channel strings For more inf
6. National Instruments Corporation 2 7 SCXI 1520 User Manual Chapter 2 Connecting Signals Full Bridge Type lll This section provides information for connecting the full bridge strain gauge configuration type I The full bridge type III only measures axial strain Figure 2 7 shows the full bridge type III circuit wiring diagram SCXI 1520 Set Bridge Transducer SCXI 1314 Configuration to Full Bridge S i L5 H You gt e go P i i s u C s g SCA e i jS I Cal A eS AN lS i Hg Figure 2 7 Full Bridge Type III Circuit Diagram The following symbols apply to the circuit diagram and equations Rjisan active element measuring compressive Poisson effect v Roisan active element measuring tensile strain R is an active element measuring compressive Poisson effect v Ry is an active element measuring the tensile strain e Very is the excitation voltage R isthe lead resistance Vcgis the measured voltage s Note As shown in Figure 2 7 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short SCXI 1520 User Manual 2 8 ni com Cha
7. dummy D S R A ae e R BA i WA el g R i Shunt i Cal A A S N NIU R i Hs Figure 2 2 Quarter Bridge Il Circuit Diagram The following symbols apply to the circuit diagram and equations R and R are half bridge completion resistors Rg is the quarter bridge temperature sensing element dummy gauge Ry is the active element measuring tensile strain e Vygyis the excitation voltage e R 1s the lead resistance Vc is the measured voltage s Note S and QTR are left unwired National Instruments Corporation 2 3 SCXI 1520 User Manual Chapter 2 Connecting Signals Half Bridge Type This section provides information for connecting the half bridge strain gauge configuration type I Figure 2 3 shows the half bridge type I circuit wiring diagram s Note S is left unwired SCXI 1520 Set Bridge Transducer SCXI 1314 Configuration to Half Bridge JL U i VeH _ P C DR i x Oe i R 2 e o SCA o i i Shunt i i Cal A i e SCA AA i i Rs Figure 2 3 Half Bridge Type I Circuit Diagram The following symbols apply to the circuit diagram and equations R and R are half bridge completion resistors R3isthe active element measuring compression from Poisson effect
8. 27 DAQ D A PO 1 DIO1 Input Board data address line this signal taps into the SCXIbus D A line to indicate to the module whether the incoming serial stream is data or address information SCXI 1520 User Manual 2 14 ni com Table 2 3 SCXI 1520 Communication Signals Continued Chapter 2 Connecting Signals Pin SCXI Signal Name NI DAQmx Device Signal Name Traditional NI DAQ Legacy Device Signal Name Direction Description 29 SLOTOSEL P0 2 DIO2 Input Slot 0 select this signal taps into the SCXIbus INTR line to indicate whether the information on MOSI is being sent to a module or Slot 0 36 SCANCLK AI HOLD COMP AI HOLD SCANCLK Input Scan clock a rising edge indicates to the scanned SCXI module that the E M Series DAQ device has taken a sample and causes the module to advance channels 37 SER CLK EXTSTROBE EXTSTROBE Input Serial clock this signal taps into the SCXIbus SPICLK line to clock the data on the MOSI and MISO lines 46 HOLD TRIG PFI 7 AISAMP CLK AI SAMP PFI7 START SCAN Input Hold trigger this signal is used by the MIO to set the track and hold state of the module National Instruments Corporation 2 15 SCXI 1520 User Manual Configuring and Testing This chapter discusses configuring the SCXI 1520 in MAX for use with either NI D
9. AI Bridge Cfg Specifies the sensor Wheatstone bridge type Analog Input General Properties Signal Conditioning Bridge Shunt Cal Shunt Cal Enable AI Bridge ShuntCal Enable Specifies whether to place the shunt calibration resistor across one arm of the bridge Analog Input General Properties Signal Conditioning Bridge Shunt Cal Shunt Cal Select AI Bridge ShuntCal Select Specifies which calibration switch es to enable Configuration Analog Input General Properties ALExcit Val Specifies the amount Signal Conditioning Excitation of excitation in volts Value Analog Input Strain Strain Gage AIL StrainGage Cfg Specifies the strain gauge configuration type Analog Input General Properties Signal Conditioning Bridge Nominal Resistance AI Bridge NomResistance Specifies in ohms the resistance of the bridge in an unloaded condition Analog Input Strain Strain Gage Gage Factor AI StrainGage GageFactor Specifies the sensitivity of the strain gauge Analog Input Strain Strain Gage Poisson Ratio AI StrainGage PoissonRatio Specifies the ratio of lateral strain to axial strain in the specimen material SCXI 1520 User Manual 5 6 ni com Chapter 5 Table 5 1 NI DAQmx Properties Continued Using the SCXI 1520 Property Short Name Description Analog Input General Properties Signal Conditio
10. Patents For patents covering National Instruments products technology refer to the appropriate location Help Patents in your software the patents txt file on your media or the National Instruments Patent Notice at ni com patents WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS 1 NATIONAL INSTRUMENTS PRODUCTS ARE NOT DESIGNED WITH COMPONENTS AND TESTING FOR A LEVEL OF RELIABILITY SUITABLE FOR USE IN OR IN CONNECTION WITH SURGICAL IMPLANTS OR AS CRITICAL COMPONENTS IN ANY LIFE SUPPORT SYSTEMS WHOSE FAILURE TO PERFORM CAN REASONABLY BE EXPECTED TO CAUSE SIGNIFICANT INJURY TO A HUMAN 2 IN ANY APPLICATION INCLUDING THE ABOVE RELIABILITY OF OPERATION OF THE SOFTWARE PRODUCTS CAN BE IMPAIRED BY ADVERSE FACTORS INCLUDING BUT NOT LIMITED TO FLUCTUATIONS IN ELECTRICAL POWER SUPPLY COMPUTER HARDWARE MALFUNCTIONS COMPUTER OPERATING SYSTEM SOFTWARE FITNESS FITNESS OF COMPILERS AND DEVELOPMENT SOFTWARE USED TO DEVELOP AN APPLICATION INSTALLATION ERRORS SOFTWARE AND HARDWARE COMPATIBILITY PROBLEMS MALFUNCTIONS OR FAILURES OF ELECTRONIC MONITORING OR CONTROL DEVICES TRANSIENT FAILURES OF ELECTRONIC SYSTEMS HARDWARE AND OR SOFTWARE UNANTICIPATED USES OR MISUSES OR ERRORS ON THE PART OF THE USER OR APPLICATIONS DESIGNER ADVERSE FACTORS SUCH AS THESE ARE HEREAFTER COLLECTIVELY TERMED SYSTEM FAILURES ANY APPLICATION WHERE A SYSTEM FAILURE WOULD CREATE A RISK OF HARM TO PROPERTY OR PERSONS INCLUDING THE RISK OF BODILY INJURY AN
11. The output of a system with a zero volt input The provision in strain gauge signal conditioning hardware to remove the unwanted offset voltage present at the output of a strain gauge bridge when no strain is applied Maximum voltage that does not cause hardware damage SCXI 1520 User Manual Glossary P parallel mode passband PFI Poisson s ratio pole port pp ppm psi PX PX PXI Q QTR quarter bridge quarter bridge completion resistor SCXI 1520 User Manual A type of SCXI operating mode in which the module sends each of its output channels directly to a separate analog input channel of the E M Series DAQ device connected to the module The range of input frequencies that are passed to the filter output without attenuation See HOLD TRIG The negative ratio of transverse strain to longitudinal axial strain A term used to describe the quality of a lowpass filter In general the more poles a lowpass filter has the better it attenuates frequencies beyond the cutoff frequency 1 A digital port consisting of multiple I O lines on a E M Series DAQ device 2 a serial or parallel interface connector on a PC peak to peak parts per million pounds per square inch a negative excitation output terminal a positive excitation output terminal PCI eXtensions for Instrumentation An open specification that builds on the CompactPCI specification by adding instrumentation specific features
12. cutoff frequency 3 7 SCXI 1520 User Manual Chapter 3 Configuring and Testing 11 Ensure that you have selected the strain channel s you wish to calibrate in the Channel List box Click Calibration to calibrate the strain channel s 12 On the screen that appears choose to enable offset nulling and or shunt calibration Enter the shunt calibration resistor information Click Next 13 Measure and Calibrate displays information specific to the strain channel s Click Measure to acquire a signal from the strain channel s and Reset Data to reset the values to default Click Calibrate to calibrate the strain channel s When you have completed calibrating the strain channel s click Finish 14 If you are creating a task and want to set timing or triggering controls enter the values in the Task Timing and Task Triggering tabs Creating a Custom Voltage with Excitation Global Channel or Task Use the Custom Voltage with Excitation NI DAQmx Task or Global Channel when measuring load force torque pressure or other bridge based sensors To create an NI DAQmx Custom Voltage with Excitation Task or NI DAQmx Global Channel complete the following steps 1 Double click Measurement amp Automation on the desktop 2 Right click Data Neighborhood and select Create New 3 Select NI DAQmx Global Channel or NI DAQmx Task and click Next 4 Select Analog Input then select Custom Voltage with Excitation 5 If you are creatin
13. self temperature compensating strain gauge Has a resistive temperature coefficient that counteracts the thermal expansion coefficient of the material to which the gauge is bonded thus makes the system insensitive to changes in temperature The fractional deformation of a body under an applied force is usually given in the units of microstrain where one microstrain represents a deformation of 10 or 0 0001 negative signal input terminal for channel X positive signal input terminal for channel X Synchronization pulse for scanning only used with modules featuring simultaneous sample and hold A measure of the amount of noise seen by an analog circuit or an ADC when the analog inputs are grounded SCXI 1520 User Manual Glossary T TEDS tensile strain track and hold TRIGO TTL typ U UL unipolar V V VDC VI virtual channels voltage excitation V r rms SCXI 1520 User Manual Transducer Electronic Data Sheets Strain that results from an object being stretched has a positive value See simultaneous sample and hold trigger 0 Transistor Transistor Logic typical Underwriters Laboratory A voltage range that only spans positive voltages volts volts direct current Virtual Instrument 1 A combination of hardware and or software elements typically used with a PC that has the functionality of a classic stand alone instrument 2 A LabVIEW software module VI which consis
14. ve Ry is the active element measuring tensile strain 8 Very is the excitation voltage eR is the lead resistance Vo is the measured voltage s Note As shown in Figure 2 4 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short SCXI 1520 User Manual 2 4 ni com Chapter 2 Connecting Signals Half Bridge Type Il This section provides information for connecting the half bridge strain gauge configuration type II Figure 2 4 shows the half bridge type II circuit wiring diagram s Note S is left unwired SCXI 1520 Set Bridge Transducer SCXI 1314 Configuration to Half Bridge R S V V VV is 1 Von pes x R WA Es Q D R e R gauge out Vout C Vex R i gauge P R We e R I SCA H WW Shunt L i J Cal A SCA n AA O AA e i R Hs i i Figure 2 4 Half Bridge Type II Circuit Diagram The following symbols apply to the circuit diagram and equations R and R are half bridge completion resistors e R3isthe active element measuring compressive strain Ry is the active element mea
15. Chapter 5 Using the SCXI 1520 Traditional NI DAQ Legacy in LabVIEW LabVIEW is a graphical programming environment for test and measurement application development with built in easy to use tools for data acquisition analysis and display You can use functional graphical blocks called subVIs to easily create a custom application that fully utilizes the SCXI 1520 programmable functionality Traditional NI DAQ Legacy provides several standard data acquisition subVIs as well as subVIs specifically for use with the SCXI 1520 For applications using Traditional NI DAQ Legacy in LabVIEW there are two typical methods of addressing SCXI 1520 channels virtual channels specifically strain virtual channels and SCXI channel strings Depending on the needs of your application you choose one of these channel addressing methods to use in your LabVIEW application The strain virtual channel provides scaling for strain gauges provides an easy interface for offset null compensation and shunt calibration and allows you to select any name for the SCXI 1520 strain channel that you choose without additional code When you use virtual channels the maximum number of channels per E Series DAQ device is 512 in multichassis systems NI recommends using the strain virtual channel for ease of use Refer to Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later for more information on how to create a strain virtual channel
16. Terminal for connection to a quarter bridge completion resistor A Wheatstone bridge consisting of one active strain gauge and three passive fixed valued resistors The bridge completion resistor in series with the active strain gauge in a quarter bridge configuration the quarter bridge completion resistor must have the same nominal resistance value as the strain gauge G 10 ni com R remote sense rms rolloff Rs RS RS RSC RSVD RTI RTO RTSI RTSI bus National Instruments Corporation G 11 Glossary The method of compensating for voltage drops in bridge excitation leads by remotely measuring the voltage applied to the bridge gauge resistance line resistance Return Material Authorization root mean square The square root of the average value of the square of the instantaneous signal amplitude a measure of signal amplitude The ratio that a system attenuates signals in the stopband with respect to the passband usually defined in decibels per octave shunt calibration resistance remote sense terminal negative input remote sense terminal positive input Rear Signal Connector reserved bit pin or signal Referred To Input Calculates a specification relative to the input range Referred To Output Real Time System Integration Real Time System Integration bus The NI timing bus that connects an E M Series DAQ device directly by means of connectors on top of the devices for precise synchroni
17. RSX and RSX You can run separate wires from the bridge to these terminals so that the amplifiers obtain feedback directly from the bridge thereby forcing bridge voltage to equal the desired setting Excitation voltage originates from two excitation output buffers per channel One output buffer generates the positive excitation voltage and the other output buffer generates the negative excitation voltage Since each channel is controlled independently a short circuit across the excitation terminals of one channel has no effect on the excitation of another channel PX is always positive with respect to ground and PX is always negative with respect to ground The inverting amplifier X1 forces the voltage at PX to equal the negative of the voltage at PX For example if you set the module output for 5 V PX is at 42 5 V with respect to ground and PX is at 2 5 V with respect to ground The excitation setting originates from an internal digital to analog converter DAC You can set the excitation voltage in a near continuous range using NI DAQmx and between 0 V and 10 V in 0 625 V increments using Traditional NI DAQ Legacy You can power a 350 Q full bridge at 10 V without exceeding the maximum power rating of the excitation source The excitation outputs are protected with 4 22 ni com Chapter 4 Theory of Operation surge suppressors that prevent either excitation output terminal from exceeding 6 V with respect to chassis grou
18. ReadMe First Safety and Radio Frequency Interference DAQ Getting Started Guide S CXI Quick Start Guide SCXI 1520 User Manual Documentation for your hardware Documentation for your software The optional accessories listed in Table 1 1 are available for the SCXI 1520 Table 1 1 Accessories Available for the SCXI 1520 Accessory Description SCXI 13147 Screw terminal block Mounts on the front of the SCXI 1520 module It includes connections and sockets for two shunt calibration resistors and a quarter bridge completion resistor per channel SCXI 1314T RJ 50 terminal block Mounts on the front of the SCXI 1520 module It features eight RJ 50 10 position 10 conductor 10p10c modular plugs for connection to hardware TEDS smart sensors SCXI 1520 User Manual 1 2 ni com Chapter 1 About the SCXI 1520 Table 1 1 Accessories Available for the SCXI 1520 Continued Accessory Description SCXI 1310 Connector and shell assembly The SCXI 1310 provides 96 eyelet type terminals for easy hook and solder signal connection and custom mass termination connectivity TBX 96 DIN rail mounted terminal block with 96 generic screw terminals One of the following cables is required to connect the TBX 96 to an SCXI module SH96 96 shielded cable 1 m R96 96 unshielded ribbon cable 1 m You must wire a shunt resistor between the pins that correspond to the SCA on th
19. The SCXI channel string allows you to combine large numbers of channels into fewer scan list entries to measure the signal voltage level directly for custom scaling and to dynamically perform an offset null compensation in your application NI recommends using SCXI channel strings for more advanced applications In LabVIEW an array of these channel strings configures multiple modules for scanning When using SCXI channel strings you can scan up to 3 072 channels in a multichassis system using a single DAQ device Refer to Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later for more information about using SCXI channel strings s Note You cannot mix virtual channels with the SCXI channel strings within the same channel string array To use virtual channels enter the name of a virtual channel into the analog input channel string If using multiple virtual channels enter them in a different index in the channel string array or separate them using a comma National Instruments Corporation 5 19 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Since you can randomly scan analog input virtual channels you can enter the virtual channels you want to scan in any order or repeatedly in a channel string array Typical Program Flow After you have determined how you want to address the channels and whether you want to configure the SCXI 1520 in MAX or LabVIEW you can design your application using a typ
20. When the switch is closed a socketed shunt calibration resistor in the SCXI 1314 connects across a leg of a Wheatstone bridge For more detailed information about the operation of any of these circuitry stages refer to the Bridge Configuration and Completion section the Excitation section the Gain section the Filter Bandwidth and Cutoff Frequency section the Offset Null Compensation section the Shunt Calibration section the Simultaneous Sample and Hold section and the Modes of Operation section Bridge Configuration and Completion You can configure the SCXI 1520 for use with Wheatstone bridge sensors that require bridge completion Bridge completion is necessary for quarter or half bridge sensors You can set the SCXI 1520 for quarter half or full bridge configuration to match the configuration completion requirements of each sensor When quarter or half bridge configuration is selected Terminal SX where X is a particular channel is disconnected from the front signal connector and internally connected to a half bridge completion network When quarter bridge configuration is selected a socketed quarter bridge completion resistor in the terminal block is internally connected between PX and the QTR terminal You then field wire the quarter bridge sensor between PX and QTR Make sure that the value of the precision quarter bridge completion resistor matches the nominal gauge resistance of the quarter bridge sensor The quarter
21. s Note As shown in Figure 2 5 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short SCXI 1520 User Manual 2 6 ni com Chapter 2 Connecting Signals Full Bridge Type Il This section provides information for connecting the full bridge strain gauge configuration type II Figure 2 6 shows the full bridge type II circuit wiring diagram SCXI 1520 Set Bridge Transducer SCXI 1314 Configuration to Full Bridge Figure 2 6 Full Bridge Type II Circuit Diagram The following symbols apply to the circuit diagram and equations Rjisan active element measuring compressive Poisson effect v Rj is an active element measuring tensile Poisson effect ve Rg is an active element measuring compressive strain Ry is an active element measuring tensile strain Very is the excitation voltage Rjisthe lead resistance Vcg is the measured voltage 3 Note As shown in Figure 2 6 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short
22. s Note Refer to the Read Me First Radio Frequency Interference document before removing equipment covers or connecting or disconnecting any signal wires Installing the SCXI 1520 Module into the SCXI Chassis Refer to the SCXI Quick Start Guide to install your SCXI 1520 module Connecting the SCXI 1520 in an SCXI Chassis to an E M Series DAQ Device for Multiplexed Scanning Refer to the SCXI Quick Start Guide to install the cable adapter and connect the SCXI modules to the DAQ device If you have already installed the appropriate software refer to Chapter 3 Configuring and Testing to configure the SCXI 1520 module s Connecting the SCXI 1520 in a PXI SCXI Combination Chassis to an E M Series DAQ Device for Multiplexed Scanning Refer to the SCXI Quick Start Guide to connect the SCXI modules to the DAQ device If you have already installed the appropriate software refer to Chapter 3 Configuring and Testing to configure the SCXI 1520 module s National Instruments Corporation 1 5 SCXI 1520 User Manual Chapter 1 About the SCXI 1520 Verifying the SCXI 1520 Installation in Software Refer to the SCXI Quick Start Guide for information on verifying the SCXI installation Installing SCXI Using NI DAQmx in Software Refer to the SCXI Quick Start Guide for information on installing modules using NI DAQmx in software Manually Adding Modules in NI DAQmx If you did not auto detect the SCXI modules you must manually ad
23. select None 3 Click the Channel tab Select the appropriate gain filter voltage excitation and bridge configuration setting for each channel If you want to configure all the channels at the same time select the Channel drop down menu scroll to the bottom and select All Channels Refer to the SCXI 1520 Software Configurable Settings section for a detailed description of each setting Click Apply 4 Click Accessory Select the accessory you connected to the module When configuration is complete click OK The Traditional NI DAQ Legacy chassis and SCXI 1520 should now be configured properly If you need to change the module configuration right click the module and repeat steps 1 through 4 Test the system following the steps in the Troubleshooting the Self Test Verification section of Chapter 1 About the SCXI 1520 SCXI 1520 User Manual 3 10 ni com Chapter 3 Configuring and Testing Creating a Strain Virtual Channel To create a strain virtual channel complete the following steps DU OY Ub ode e desde Right click Data Neighborhood and select Create New Select Traditional NI DAQ Virtual Channel and click Finish Click Add Channel Select Analog Input from the drop down menu and click Next Enter the Channel Name and Channel Description and click Next Select Strain Gauge from the drop down menu and click Next Enter the following information a Bridge type from the drop down menu b V initin volts Lead Resist
24. the eight conditioned analog output signals at the rear signal connector of the SCXI 1520 shown in Figure 4 16 are connected directly to the eight analog input channels on the DAQ device When the SCXI 1520 operates in parallel mode the DAQ device performs multiplexed scans of the SCXI 1520 parallel outputs The SCXI 1520 module does not multiplex the channels Traditional NI DAQ Legacy driver software can only control the SCXI 1520 module in multiplexed mode NI DAQmx can operate the SCXI 1520 in both multiplexed and parallel mode In parallel mode SCXI 1520 channels 0 through 7 conditioned outputs are passed directly to DAQ device channels 0 through 7 The DAQ device channels should be configured for differential input mode Scanning remote sense channels is not possible when operating the SCXI 1520 in parallel mode operation This is because RSX and RSX terminals are not connected to the 50 pin rear signal connector of the SCXI 1520 as shown in Figure 4 16 but instead are only connected internally to the analog multiplexer The NI DAQmx driver can still scan the remote sense channel to utilize for strain task and channel calibration National Instruments Corporation 4 35 SCXI 1520 User Manual Chapter 4 Theory of Operation and scaling in MAX However during operation in your application you cannot monitor the remote sense channels if the SCXI 1520 is operating in parallel mode N Note The remote sense hardware control loop
25. 0 25 Q The nominal values of R3 and Ry equal R SCXI 1520 User Manual 4 10 ni com Half Bridge Type Il Chapter 4 Theory of Operation This section provides information for the half bridge strain gauge configuration type II The half bridge type II only measures bending strain Figure 4 8 shows how to position strain gauge resistors in an axial configuration Figure 4 9 shows the half bridge type II circuit wiring diagram Figure 4 8 Half Bridge Type II Rejecting Axial and Measuring Bending Strain A half bridge type II configuration has the following characteristics Two active strain gauge elements One is mounted in the direction of bending strain on one side of the strain specimen top the other is mounted in the direction of bending strain on the opposite side bottom Completion resistors provide half bridge completion Sensitive to bending strain Rejects axial strain Compensates for temperature Sensitivity at 1000 ue is 1 mVou Vex input s Note S is left unwired National Instruments Corporation Figure 4 9 Half Bridge Type II Circuit Diagram 4 11 SCXI 1520 User Manual Chapter 4 Theory of Operation The following symbols apply to the circuit diagram and equations R and R are half bridge completion resistors R isthe active strain gauge element measuring compressive strain Ry is the active strain gauge element measuring tensile s
26. 02 of FSR 0 35 of setting at RSC 0 1 of the value returned by driver software SCXI 1520 User Manual Specifications Appendix A A amp oeznooe WOD tU MSI 0Z IXOS A 10 Kovnooe ojn osqe ou oje no e OL A 0 O1 19S SI uonejroxq s sueos 00Z SI seSv1oAe Jurod 001 10J 391 ueos pue ZH QT sr Sumes uprapueg 19 eUis sr ISA USIUA O cc JO cp pue medu o npour IYI uooA1oq oouoJogip o1edoduio st 7 oou yiq 1 sffO x L x a8uvy x flu up x L WIA oy PPL DO SE 01 cp BUR oq oprsino 3jup od0n3e1oduroj Jo 3999 IP pn our ol SION 191SK 404 13 J sffO Suipvay fo x Sulpvay 2801104 SI Kov1nooe ojn osqy D SE 01 I Aournooe ojn osqy n SF 0 0F ANZ Au 007 Av O 0S TOF 00001 AW Q OT SF 0 0F AN 07 AN 002 Av Q 0c TOF 0 0Zr AW 0 81 SF 0 0F Avs Av 006 Au 0 0S TOF 0 007 AW 0 0S SF 0 0 ATl 001 Al 0 O0I A 0 0S TOF 0 00T AUI Q O0T SF 0 0 AN 0 07 AU TO AT O SLF OF OTt AUI 0 081 SF 0 0F AN 00S AUI 0 Au 00S 1 TOF ooz AW 0 00S STF 0 0F AW T O AW O T AUI x TOF 0 OI A OTF STF 0 0F AW CO AW 02 AUI Cox TOF Cv ASI STF 0 0 AUI 0 AUI O S AU CT TOF 07 A 0 S STF 0 0F AUI QT AUI O OI AUI 0 TOF 0 A 0 01 O A 29 25 IZLIV juroq 8uts noie Surpeay yuresy yosuey WSO Jua ures jutod 001 Jo d 111249 JeuruoN yuq 24nj roduio WSIS Lad 9SION Ul9jS S aheyon ajqey Aoe1no23y ajajduio ni co
27. 1520 refer to the DAQ device help file for more information Can I measure TEDS load cells with the SCX1 1520 You can use the SCXI 1314T terminal block to read TEDS load cells Refer to ni com for more information about TEDS sensors and accessories D 6 ni com Glossary Symbol Prefix Value p pico 10 12 n nano 10 u micro 10 6 m milli 10 3 k kilo 10 M mega 106 G giga 109 T tera 1012 Numbers Symbols percent positive of or plus _ negative of or minus plus or minus lt less than gt greater than per degree strain E simulated strain v Poisson s ratio National Instruments Corporation G 1 SCXI 1520 User Manual Glossary Q 5V signal A A A D absolute accuracy AC acquisition time ADC ADE Al AI HOLD AI HOLD COMP AI SAMP AI SAMP CLK amp amplification ANSI SCXI 1520 User Manual ohms 5 VDC source signal Amperes Analog to Digital The maximum difference between the measured value from a data acquisition device and the true voltage applied to the input typically specified as voltage Alternating Current The time required by a sample and hold system to switch from hold mode back to tracking a signal Analog to Digital Converter An electronic device often an integrated circuit that converts an analog voltage to a digital number Application Development Environment such as L
28. DAQ device Table D 1 Digital Signals on the SCXI 1520 E M Series Traditional DAQ Device NI DAQmx SCXI NI DAQ Legacy 50 Pin 68 Pin I Signal Name Signal Name SCXI Signal Name Connector Connector Direction DIOO P0 0 SER DAT IN 25 52 Output DIO4 P0 4 SER DAT OUT 26 19 Input DIO1 P0 1 DAQ D A 27 17 Output DIO2 P0 2 SLOTOSEL 29 49 Output SCANCLK AI HOLD COMP SCAN CLK 36 46 Output AI HOLD SCXI 1520 User Manual D 2 ni com Appendix D Table D 1 Digital Signals on the SCXI 1520 Continued Common Questions E M Series Traditional DAQ Device NI DAQmx SCXI NI DAQ Legacy 50 Pin 68 Pin Signal Name Signal Name SCXI Signal Name Connector Connector Direction PFI 7 AI SAMP PFI 7 HOLD TRIG 46 38 Input CLK AI SAMP CLK AI SAMP EXTSTROBE EXTSTROBE SER CLK 37 45 Input With respect to the E M Series DAQ device National Instruments Corporation D 3 In LabVIEW can I use different input limits for the same SCXI 1520 channel if I repeat the channel in the SCXI channel string array No The SCXI 1520 cannot dynamically change the gain settings during scanning Therefore group channels with similar input ranges together in the channel string array Make sure that repeated channels in different indices of the channel string array have the same input limits in the corresponding input limits array In LabVIEW can I use a VI to change my SCXI
29. Legacy refer to the Developing Your Application in NI DAQmx section or the Developing Your Application in Traditional NI DAQ Legacy section respectively of Chapter 5 Using the SCXI 1520 Parallel mode operation acquisition rates have limitations that are determined based on the DAQ device you are using and SS H Refer to the Simultaneous Sample and Hold section for equations that can help you determine maximum acquisition rates with SS H enabled If SS H is disabled and the system is configured for parallel mode operation the maximum sampling rate is determined by the maximum sample rate of the DAQ device The 333 kHz maximum SCXI multiplexing rate is not a limitation in parallel mode operation Therefore if the DAQ device can sample more quickly than 333 kHz the SCXI 1520 configured for parallel mode operation is not the limiting factor 4 36 ni com Using the SCXI 1520 This chapter makes suggestions for developing your application and provides basic information regarding calibration A Caution Electrostatic discharges ESD of 4 kV or greater may cause the SCXI 1520 to stop responding resulting in a lost or erroneous reading As a result a software reset may be required to enhance immunity by restoring functionality in such a condition A software reset can be accomplished by calling the DAQmx Reset Device function The DAQmx Reset VI is located in the Measurement I O NI DAQmx Dev Config palette on the LabVIEW Block Diagram
30. Mode Use the following formula to calculate the maximum SS H sample rate in parallel mode where National Instruments Corporation SR AT NoC 1 x MST yo TT SR is sample rate frequency of acquisition of all channels HT is hold time the time between holding all the SS H channels and the first A D conversion NoC is number of channels the total number of channels being sampled in the scan list SS H or not MST mo is minimum settle time of MIO inverse of maximum sample rate of the MIO also minimum interchannel delay TT is track time the minimum time between the last AD conversion of the current scan and engaging the hold signal of SS H channels of next scan 4 31 SCXI 1520 User Manual Chapter 4 Theory of Operation Table 4 4 shows some example values used to determine the SR using the general equation Table 4 4 NI DAQmx Values Used to Determine Maximum Sample Rate in Parallel Mode DAQmx SR Device Default Required for Device Max NI DAQmx Maximum MIO Accuracy Sample HT MSTwo TT SR Parallel Accuracy Device Bits Rate S s us NoC us us Hz Hz NI 6070E 12 1250000 3 8 0 8 7 64103 64103 NI 6023E 12 200000 3 8 5 7 22222 22222 NI 6221 16 250000 3 8 4 7 26316 12346 68 Pin NI 6254 16 1000000 3 8 1 7 58824 16667 3 16 1 7 40000 14706 NI 6289 18 625000 3 8 1 6 7 47170 15576 3 16 1 6 7 29412 12987 These are the defaul
31. Properties ALExcit Val Specifies the amount of Signal Conditioning Excitation excitation in volts Value Analog Input Strain Strain Gage ALStrainGage Cfg Specifies the strain gauge configuration type Analog Input General Properties Signal Conditioning Bridge Nominal Resistance AI Bridge NomResistance Specifies in ohms the resistance of the bridge in an unloaded condition Analog Input Strain Strain Gage Gage Factor AI StrainGage GageFactor Specifies the sensitivity of the strain gauge Analog Input Strain Strain Gage Poisson Ratio AI StrainGage PoissonRatio Specifies the ratio of lateral strain to axial strain in the specimen material Analog Input General Properties Signal Conditioning Bridge Initial Bridge Voltage AI Bridge Initial Voltage Specifies in volts the output voltage of the bridge in the unloaded condition Analog Input Strain Units AlLStrain Units Specifies the units to use to return strain measurements from the channel Analog Input General Properties AI Gain Specifies a gain factor Advanced Gain and Offset to apply to the signal Gain Value conditioning portion of the channel National Instruments Corporation 5 17 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Table 5 3 NI DAQmx Properties Continued Property Short Name Description Analog Input General Properties ALAutoZeroMode
32. SCXI 1520 Channel Significant Possible Setting NI DAQ Function to Use Parameters Parameters Values Gain SCXI Set Gain f64 gain 1 1 15 1 3 1 5 1 8 gain setting 2 2 2 2 4 2 7 3 1 3 6 4 2 5 6 6 5 7 5 8 7 10 11 5 13 15 18 20 22 24 27 31 36 42 56 65 75 87 100 115 130 150 180 200 220 240 270 310 360 420 560 650 750 870 1000 Bandwidth SCXI Configure Filter 116 filterMode 0 Bypass the filter filter configuration 1 Set filter cutoff mode frequency to freq f64 req 10 0 100 0 1000 0 filter cutoff 10 000 0 Hz frequency if filterMode 1 Excitation SCXI Set Excitation 116 2 DC voltage Voltage excitationType specified in units of type of excitation to set 32 excitationValue new value for the specified excitation parameter volts 0 0 625 1 25 1 875 2 5 3 125 3 75 4 375 5 0 5 625 6 25 6 875 7 5 8 125 8 75 9 375 10 0 National Instruments Corporation SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Table 5 6 NI DAQ Functions Used to Configure SCXI 1520 Continued Channel Significant Possible Setting NI DAQ Function to Use Parameters Parameters Values Bridge SCXI Configure Connection il6 4 Quarter bridge Configuration connectionType 5 Half bridge type of sensor 6 Full bridge connected to the specified channel Shunt SCXI_Calibrate_Setup 116 calop O0 turn off shunts Calibr
33. Specifies when to Advanced High Accuracy Settings measure ground Auto Zero Mode NI DAQmx then subtracts the voltage either on every sample or only once depending on the setting Analog Input Measurement Type AlI MeasType Indicates the measurement to take with the analog input channel s Note This is not a complete list of NI DAQmx properties and does not include every property you may need to configure your application It is a representative sample of important properties to configure for strain and Wheatstone bridge measurements For a complete list of NI DAQmx properties and more information on NI DAQmx properties refer to your ADE help file Developing Your Application in Traditional NI DAQ Legacy 3 Note Ifyou are not using an NI ADE using an NI ADE prior to version 7 0 or are using an unlicensed copy of an NI ADE additional dialog boxes from the NI License Manager appear allowing you to create a task or global channel in unlicensed mode These messages continue to appear until you install version 7 0 or later of an NI ADE This section describes how to configure and use Traditional NI DAQ Legacy to control the SCXI 1520 in LabVIEW LabWindows CVI Measurement Studio and other text based ADEs These NI ADEs provide greater flexibility and access to more settings than MAX but you can use ADEs in conjunction with MAX to quickly create a customized application SCXI 1520 User Manual 5 18 ni com
34. The Reset Device function is usually used at the beginning or end of a program If the Reset Device is used in the middle of a program it will immediately abort all active tasks associated with a device disconnect any routes and return the device to an initialized state Aborting a task immediately terminates the currently active operation such as a read or a write Aborting a task puts the task into an unstable but recoverable state To recover the task in DAQmx use DAQmx Start to restart the task or use DAQmx Stop to reset the task without starting it The task cannot be recovered in Traditional DAQ so the task will need to be completely re setup For more information on these functions please see the DAQmx Traditional DAQ help files Developing Your Application in NI DAQmx s Note If you are not using an NI ADE using an NI ADE prior to version 7 0 or are using an unlicensed copy of an NI ADE additional dialog boxes from the NI License Manager appear allowing you to create a task or global channel in unlicensed mode These messages continue to appear until you install version 7 0 or later of an NI ADE This section describes how to configure and use NI DAQmx to control the SCXI 1520 in LabVIEW LabWindows CVI and Measurement Studio These ADEs provide greater flexibility and access to more settings than MAX but you can use ADEs in conjunction with MAX to quickly create a customized application National Instruments Corporation 5 1
35. Values Used to Determine Maximum Sample Rate in Multiplexed Mode Device Maximum SR MIO Accuracy Device Maximum HT MSTyyo MSTgx TT Traditional NI DAQ Device Bits Sample Rate S s us NoC us us us Legacy Multiplexed NI 6070E 12 1250000 3 8 1 3 7 30961 NI 6070E 12 1250000 3 32 1 3 7 9243 NI 6023E 12 200000 3 8 3 3 4 18640 NI 6023E 12 200000 3 32 5 3 7 5166 NI 6052bE 16 333333 3 8 3 10 T 11047 NI 6052E 16 333333 3 32 3 10 d 2932 NI 6032E 16 100000 3 8 10 10 7 8324 NI 6032E 16 100000 3 32 10 10 7 2176 National Instruments Corporation 4 33 SCXI 1520 User Manual Chapter 4 Theory of Operation Modes of Operation SCXI 1520 User Manual The SCXI 1520 provides two modes of operation for passing the conditioned signals to the digitizing DAQ device multiplexed mode and parallel mode Theory of Multiplexed Mode Operation In multiplexed mode all input channels of an SCXI module are multiplexed into a single analog input channel of the DAQ device Multiplexed mode operation is ideal for high channel count systems Multiplexed mode is typically used for performing scanning operations with the SCXI 1520 The power of SCXI multiplexed mode scanning is its ability to route many input channels to a single channel of the DAQ device The multiplexing operation of the analog input signals is performed entirely by multiplexers in the SCXI modules not inside the
36. a particular STC number As shown in Figure 4 15 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short The nominal values of Rj Ro Rs and Ry equal R SCXI 1520 Theory of Operation This section includes a brief overview and a detailed discussion of the circuit features of the module Refer to Figure 4 16 while reading this section SCXI 1520 User Manual 4 18 ni com Theory of Operation Chapter 4 SCXIbus Connector Rear Signal Connector eovyiaju reu amp ig JoUoD pue 10002 4exejdninig Y 90 5 ueos lt J lt 4exejdninig Bojeuy lt 0HO H i Groa Sas B iucripuoo eub gt J 0D N 2 LF e e N Paw ai 1 enoge ses Buruonipuoo reubis Y gt D fe SESS 2 j gt D 1 1 a feo P gt ewm i g eo 1unus I 1 gt D i i M 1 L Jee gt ewm S9U9IIMS uoreJqie unus v leo Unys s4 D i 1 1 A D i vvv AD
37. also can set the value through your application The default filter cut off frequency in NI DAQmx is 10 kHz Input signal range configure the input signal range using either NI DAQmx Task or NI DAQmx Global Channel When you set the minimum and maximum range of NI DAQmx Task or NI DAQmx Global Channel the driver selects the best gain for the measurement You also can set it through your application The default gain setting in NI DAQmx is 1 0 This setting corresponds to an input range of 10 V e Calibration settings null potentiometer settings and control shunt calibration switches only using Strain NI DAQmx Task Strain NI DAQmx Global Channel or your application The Custom Voltage with Excitation NI DAQmx Task or NI DAQmx Global Channel cannot adjust calibration settings in MAX Adjust calibration 3 6 ni com Chapter 3 Configuring and Testing settings in your application The default configuration settings set the null potentiometers at their midpoint 62 for the coarse potentiometer and 2 047 for the fine potentiometer The default state of the shunt calibration switches is open This state leaves the shunt calibration resistor disconnected from the circuit Modes of operation configure only using chassis installation in software Refer to Chapter 1 About the SCXI 1520 for more information on chassis installation The default setting in NI DAQmx is multiplexed Simultaneous sample and hold settings configure only usi
38. as bridge configuration voltage excitation level filter bandwidth gain input signal range and calibration settings in the following two ways Task or global channel in MAX e Functions in your application s Note All software configurable settings are not configurable both ways This section only discusses settings in MAX Refer to Chapter 4 Theory of Operation for information on using functions in your application SCXI 1520 User Manual These sections describe settings that you can change in MAX and where they are located Strain and custom voltage with excitation are the most commonly used NI DAQmx Task or NI DAQmx Global Channel types with the SCXI 1520 Use the Custom Voltage with Excitation NI DAQmx task or global channel when measuring load force torque pressure or other bridge based sensors Bridge configuration configure using the settings tab of NI DAQmx Task or NI DAQmx Global Channel and functions in your application Channel properties override module properties The default bridge configuration for NI DAQmx is full bridge e Voltage excitation configure using either NI DAQmx Task or NI DAQmx Global Channel You also can set the voltage excitation level through your application In NI DAQmx you can choose from contiguous voltages between 0 and 10 V The default voltage excitation in NI DAQmx is 0 V Filter bandwidth configure the Device tab using either NI DAQmx Task or NI DAQmx Global Channel You
39. box This icon denotes a note which alerts you to important information This icon denotes a caution which advises you of precautions to take to avoid injury data loss or a system crash When this symbol is marked on a product refer to the Read Me First Safety and Radio Frequency Interference for information about precautions to take Bold text denotes items that you must select or click in the software such as menu items and dialog box options Bold text also denotes parameter names Italic text denotes variables emphasis a cross reference or an introduction to a key concept Italic text also denotes text that is a placeholder for a word or value that you must supply Text in this font denotes text or characters that you should enter from the keyboard sections of code programming examples and syntax examples This font is also used for the proper names of disk drives paths directories programs subprograms subroutines device names functions operations variables filenames and extensions Bold text in this font denotes the messages and responses that the computer automatically prints to the screen This font also emphasizes lines of code that are different from the other examples Italic text in this font denotes text that is a placeholder for a word or value that you must supply Contents Chapter 1 About the SCXI 1520 What Yo Need to Get Started uuu k d emeret ghe edente 1 1 National Instruments Docume
40. bridge completion resistor is socketed for easy replacement National Instruments Corporation 4 21 SCXI 1520 User Manual Chapter 4 Theory of Operation s Note When using the SCXI 1520 and SCXI 1314 configured for quarter bridge completion do not wire the sensor or any signal to SX Excitation SCXI 1520 User Manual Refer to the Configurable Settings in MAX section of Chapter 3 Configuring and Testing for more information about programmatically setting bridge completion in MAX For more information about programmatically setting bridge completion in NI DAQmx and Traditional NI DAQ Legacy refer to the Developing Your Application in NI DAQmx section or the Developing Your Application in Traditional NI DAQ Legacy section respectively of Chapter 5 Using the SCXI 1520 The SCXI 1520 provides DC excitation voltage for a Wheatstone bridge sensor For half and full bridge applications the excitation voltage is available at terminal block connections PX and PX For quarter bridge applications PX is not used instead wire to terminals PX and QTRX Terminal QTRX internally connects to PX Excitation voltage originates from two output buffers dedicated to each channel Since each channel is controlled independently a short circuit across the excitation terminals of one channel has no effect on the excitation of another channel The output buffers have negative feedback connections at the terminal block remote sense terminals
41. channel strings for different uses Verifying the Signal Using Strain Virtual Channel If you have already created a virtual channel complete the following steps to verify the signal 1 2 3 Right click the strain virtual channel you want to verify and select Test In Channel Names select the channel you want to verify When you have completed verifying the channel click Close Using the Strain Calibration Wizard in NI DAQmx When using NI DAQmx you can perform an automated strain calibration on one or more channels in your task using the Strain Calibration Wizard in MAX E Note All channels must be strain channels to use the Strain Calibration Wizard Complete the following steps to perform calibration using the Calibration Wizard 1 UAE op oo SCXI 1520 User Manual Expand the list of devices by clicking the next to Data Neighborhood Click the next to NI DAQmx Tasks to expand the list of tasks Select the strain task you previously created Click the Device tab Select the Auto Zero Mode and Lowpass Filter Cutoff Frequency from the dropdown lists Click the Calibration button and follow the onscreen instructions 3 14 ni com Theory of Operation This chapter discusses strain gauge concepts and the theory of operational measurement concepts Strain Gauge Theory This section discusses how to arrange connect and scale signals from bridge based sensors especially strain gauge
42. eet er e eR u ee 2 5 Pull Bridge Type sic oe Ret aS usa S E 2 6 Full Bridg Type Ia asas a cei pa ie eh dete a 2 7 Pull Brid ge Type TIL u a ret tradet dettes eto 2 8 Remote Sense beo t bear Sta as 2 9 Pin ASSIgHments 2 eee ert bee i E e ede e ERI ER aa eee bs des 2 10 National Instruments Corporation V SCXI 1520 User Manual Contents Chapter 3 Configuring and Testing SCXI 1520 Software Configurable Settings eese Common Software Configurable Settings eese Bridge Configuration cingere tpi Excitation Level ste eR et eie rts Filter Bandwidth teet eniin Gain Input Range nce etre bei Bass Null Potentiom ters tete ettet ee Pret Shunt Calibration Switches essen Modes of Operation tereti e teil inpet een Simultaneous Sample and Hold sse Configurable Settings in MAX sess eene nennen eene nennen NEDA Qitnx siete n Ee NINH Nos Creating a Strain Global Channel or Task Creating a Custom Voltage with Excitation Global Channel Traditional NI DAQ Legacy Configuring Module Property Pages in Traditional NI DAQ Verifying the Signal tne etit een p RH ERO Ea yere eres Verifying the Signal in NI DAQmx Using a Task or Global Channel Verifying the Signal in Traditional NI DAQ Leg
43. ft of 24 AWG copper wire has a lead resistance of 0 25 Q The nominal value of R is equal to R SCXI 1520 User Manual 4 8 ni com Half Bridge Type Chapter 4 Theory of Operation This section provides information for the half bridge strain gauge configuration type I The half bridge type I measures either axial or bending strain Figure 4 6 shows how to position strain gauge resistors in an axial and bending configurations Figure 4 7 shows the half bridge type I circuit wiring diagram Figure 4 6 Half Bridge Type Measuring Axial and Bending Strain A half bridge type I has the following characteristics Two active strain gauge elements One is mounted in the direction of axial strain the other acts as a Poisson gauge and is mounted transverse perpendicular to the principal axis of strain Completion resistors provide half bridge completion Sensitive to both axial and bending strain Compensates for temperature Compensates for the aggregate effect on the principle strain measurement due to the Poisson s ratio of the specimen material Sensitivity at 1000 ue is 0 65 MV oy Vex input s Note S is left unwired National Instruments Corporation Figure 4 7 Half Bridge Type I Circuit Diagram 4 9 SCXI 1520 User Manual Chapter 4 Theory of Operation The following symbols apply to the circuit diagram and equations R and R are half bridge completion resistor
44. gauges load cells pressure sensors or torque sensors dynamically in your LabVIEW application use the AI Parameter VI to programmatically engage and disengage the shunt calibration As with all settings that are controlled by the AI Parameter VI the switch settings take effect when the next AI Start VI is encountered in your software not at the time the AI Parameter VI is called Either insert a 500 ms delay in your code or discard the first 500 ms of data after the switches are closed since the filters in the SCXI 1520 are not fully stabilized until 500 ms have elapsed You can find the AI Parameter VI in the function subpalette Data Acquisition Analog Input Advanced Analog Input An example of using the AI Parameter VI to control an SCXI 1520 is shown in Figure 5 4 NI recommends acquiring a buffer of 1000 samples of a channel with the shunt resistors engaged then using the average of this buffer in the shunt calibration calculations After you have measured a buffer of data with the shunt resistors engaged you can calculate the gain adjust factor to use to adjust measurements on that channel If you are performing shunt calibration on a strain gauge you can use the equations for simulated strain found in the Strain Gauge Theory section of Chapter 4 Theory of Operation for the shunt calibration calculations After you have determined the correct gain adjust factor multiply each measurement in your application by the gain adjust facto
45. i uonejduio uon lduoo eBpug eyeno ebpug su rN HeH 1 1 gt D t 1 Bumes gt i p So D 1 UORneyox3 1 i pas 1 1 t 4 1 M y o 1 1 O 1 1J 1X PIOH EE OSX 01 1X E xsi oe gt D pue yora ssedmo7 ureo ejqeueA ssedwo1 duy su Pee gt D 0SH i Lf somos t H is pp MM uU EI yoo Buiuonipuo euis JeuiuJe VLEL IXOS 9INPOW O2SL IXOS mn o o ogos ogos 0vOS 0vOS 0SH ulo Bui platy o1 S euiuJe MaS 0d 0SY 0S Figure 4 16 Block Diagram of SCXI 1314 SCXI 1520 Combination SCXI 1520 User Manual 4 19 National Instruments Corporation Chapter 4 Theory of Operation SCXI 1520 User Manual The analog input signal from the strain gauge or bridge sensor connects to SX and SX of the terminal block The signal passes through the terminal block to an electronic four position switch in the module Figure 4 16 shows the switching stage that controls the input of to the signal conditioning circuitry and the E M Series DAQ device In the switching stage there are four positions In the first position where SX and SX inputs connect directly to an instrumentation amplifier This position is for full bridge connections or general purpose analog input The second position connects the negative input to the internal voltage divider between the excitation terminals The internal voltage divider functions as bridge completi
46. more information on calibrating the SCXI 1520 download the SCXI 1520 Calibration Procedure from ni com calibration Internal Calibration Procedure The SCXI 1520 incorporates internal calibration paths that allow routing channel inputs to ground or to an onboard reference voltage NI software disconnects the channel inputs from the front signal connector and reconnects the inputs to ground or to an onboard reference when performing an internal calibration You need not change any input connections for an internal calibration National Instruments Corporation 5 37 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Internal Calibration Using LabVIEW Note NI recommends that you internally calibrate the DAQ device before you internally calibrate the SCXI 1520 SCXI 1520 User Manual For internal calibration using LabVIEW complete the following steps using the LabVIEW SCXI Calibrate VI found in LabVIEW at NI Measurements Data Acquisition Calibration and Configuration 1 Enter the DAQ device and the SCXI channel string for the channel you want to calibrate 2 Select internal calibration as the calibration operation you are going to perform The driver software takes a few seconds to perform the calibration After completion the module has new calibration constants stored for all gain settings You must repeat the procedure to calibrate other channels in the module Internal Calibration Using a C Based ADE For intern
47. multiplexed mode with two different E M Series DAQ devices No National Instruments Corporation D 1 SCXI 1520 User Manual Appendix D Common Questions If the SCXI 1520 module is not cabled directly to a E M Series DAQ device can I measure conditioned signals for channels 0 through 7 at the rear connector for example using a scope DMM or custom acquisition system NI does not support or recommend this usage In multiplexed mode simultaneous sample and hold would cause glitches in the scope and would likely average glitches in the DMM giving inaccurate measurements Can I use the unused analog input channels of the E M Series DAQ device if I am directly cabled to the SCXI 1520 for example with the SCXI 1180 feedthrough No E M Series DAQ device channels 1 through 7 connect to the conditioned analog outputs of SCXI 1520 channels 1 through 7 Can I configure the SCXI 1520 for use in parallel mode You can configure the SCXI 1520 for parallel mode using NI DAQmx Refer to Chapter 4 Theory of Operation for more information You cannot configure the SCXI 1520 for parallel mode using Traditional NI DAQ Legacy Which digital lines are unavailable on the E M Series DAQ device if it is cabled to an SCXI 1520 module Table D 1 shows the digital lines that are used by the SCXI 1520 for communication and scanning These lines are unavailable for general purpose digital I O if the SCXI 1520 is connected to the E M Series
48. scanned SCXI 1520 module is not directly cabled to the DAQ device the module sends its signals through the SCXIbus to the cabled module The cabled module whose routing is controlled by the SCXI chassis routes 4 34 ni com Chapter 4 Theory of Operation the SCXIbus signals to the DAQ device through the CH 0 pin on its rear signal connector If the DAQ device scans the cabled module the module routes its input signals through the CH 0 pin on its rear signal connector to the DAQ device CH 0 Multiplexed mode scanning acquisition rates have limitations that are determined based on the hardware in the system the mode of operation and SS H Refer to the Simultaneous Sample and Hold section for equations that can help you determine maximum acquisition rates with SS H enabled If SS H is disabled and the system is configured for multiplexed mode operation the maximum sampling rate is determined by the slower of the maximum sample rate of the DAQ device and the maximum multiplexing rate of SCXI The maximum multiplexing rate of SCXI is 333 KHz If the DAQ device can sample more quickly than 333 kHz then the maximum multiplexing rate of SCXI is the limiting factor If the DAQ device can sample at 333 kS s then the DAQ device s sample rate is the limiting factor on the maximum acquisition rate of the system in multiplexed mode operation Theory of Parallel Mode Operation Parallel mode is ideal for high speed acquisitions In parallel mode
49. set up the hardware system use either your application software documentation or the NI DAQ documentation to help you write your application If you have a large complex system it is worthwhile to look through the software documentation before you configure the hardware One or more of the following help files for software information Start Programs National Instruments NI DA Q NI DAQmx Help Start Programs National Instruments NI DA Q Traditional NI DAQ User Manual Start Programs National Instruments NI DA Q Traditional NI DAQ Function Reference Help e NI strain gauge application notes or tutorials NI has additional material about strain gauges and strain measurements available at ni com support You can download NI documents from ni com manuals To download the latest version of NI DAQ click Download Software at ni com SCXI 1520 User Manual 1 4 ni com Chapter 1 About the SCXI 1520 Installing Application Software NI DAQ and the E M Series DAQ Device Refer to the DAQ Getting Started Guide packaged with the NI DAQ software to install your application software NI DAQ driver software and the DAQ device to which you will connect the SCXI 1520 NI DAQ 7 0 or later is required to configure and program the SCXI 1520 module If you do not have NI DAQ 7 0 or later you can either contact a NI sales representative to request it on a CD or download the latest NI DAQ version from ni com
50. single chassis system the obx specifier is optional and causes the gains on the module and E Series DAQ device to be automatically set to fit the input limits parameter When this specifier is omitted the default gain on the DAQ device usually the lowest gain is used but the SCXI 1520 gain is adjusted to fit the input limits NI recommends using the obx specifier Repeating channels or having channels out of sequence in a scan list is not supported on all SCXI modules Refer to the manual of each module for information on this feature which is referred to as flexible scanning or random scanning For more information about using SCXI channel string refer to the LabVIEW Measurements Manual and SCXI 1520 shipping examples Special SCXI 1520 Channel Strings There are two special channel strings you can use with the SCXI 1520 to acquire signals from alternative locations rather than the signal inputs on the channels the remote sense and calibration ground channel strings This section describes the use of these channels SCXI 1520 User Manual B 2 ni com Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later Remote Sense Channel String You can scan the remote sense terminals to monitor the excitation voltage while simultaneously acquiring data from analog input channels This is useful for scaling the measurements by exactly the excitation voltage that is applied to the bridge sensor To scan
51. still functions regardless of the mode of operation correcting the excitation voltage level at all times even though you cannot always scan the remote sense channels SCXI 1520 User Manual When SS H is enabled the parallel output signals are held while the channels are scanned by the DAQ device The T H circuit of each channel is in hold mode during this time This appears as glitches on the parallel outputs as the SCXI 1520 is sampled by the digitizing DAQ device Due to these signal events NI recommends that you not scan the SCXI 1520 channels with a DAQ device while simultaneously measuring their parallel outputs with any other analog input device such as an oscilloscope unless you disable SS H It is possible to enable and disable SS H programmatically in NI DAQmx although NI recommends that you leave SS H enabled for most applications Disabling SS H for one module disables this feature for all modules in all chassis that are controlled by the same DAQ device SS H should only be disabled if your application does not require simultaneous sampling and requires higher acquisition rates than are possible with SS H enabled Refer to the Developing Your Application in NI DAQmx section of Chapter 5 Using the SCXI 1520 for more information about programmatically enabling and disabling SS H using NI DAQmx in your application For more information about programmatically performing offset null compensation in NI DAQmx and Traditional NI DAQ
52. switches After you engage a shunt resistor across an element of the bridge sensor wait until the voltage settles then take a buffer of samples and average them Determine what the resultant voltage offset should be Calculate a gain adjust factor by dividing the ideal or simulated output by the measured output and then use the gain adjust factor by multiplying each 5 34 ni com Chapter 5 Using the SCXI 1520 future measurement by the gain adjust factor Remember to disengage the shunt switches before continuing your application For more information regarding the operation of SCXI Calibrate Setup refer to the Traditional NI DAQ Function Reference Help installed by default in Start Programs National Instruments NI DAQ Performing Acquisition Using Traditional NI DAQ Legacy C API There are several NI DAQ functions you can use to take measurements Usually in SCXI the preference is to take multiple samples from multiple channels using the SCAN Op function SCAN Op performs a synchronous multiple channel scanned data acquisition operation SCAN Op does not return until Traditional NI DAQ Legacy acquires all the data or an acquisition error occurs MIO AI and DSA devices only For this reason it is sometimes useful to use SCAN Op in conjunction with the function Timeout Config which establishes a timeout limit synchronous functions to ensure that these functions eventually return control to your application After acquiring data us
53. the next to Data Neighborhood Click the next to NI DAQmx Tasks to expand the list of tasks Click the task Add or remove channels if applicable in the Channel List Click the Add Channels button shown at left and select the type of channel you want to add a Inthe window that appears expand the list of channels by clicking the next to the module of interest b Select the channel s you want to verify You can select a block of channels by holding down the lt Shift gt key or multiple channels by holding down the Ctrl key Click OK Enter the appropriate information on the Settings tab Click the Device tab and enter the appropriate information on the Device tab Click the Test button to open the test panel Click the Start button if necessary After you have completed verifying the channels close the test panel window You have now verified the SCXI 1520 configuration and signal connection 3 12 ni com Chapter 3 Configuring and Testing s Note For more information on how to further configure the SCXI 1520 or how to use LabVIEW to configure the module and take measurements refer to Chapter 4 Theory of Operation Verifying the Signal in Traditional NI DAQ Legacy This section discusses how to verify the signal in Traditional NI DAQ Legacy using channel strings and virtual channels Verifying the Signal Using Channel Strings The format of the channel string is as follows obx scy md
54. the positive remote sense terminal of the nth channel use the channel string obx scy mdz p pos n To scan the negative remote sense terminal of the nth channel use the channel string obx scy mdz p neg n s Note To measure the total excitation voltage across the bridge you must take the difference between p pos n and p neg n nth channel bridge excitation voltage reading from p pos n reading from p neg n 3 Note If no wires are connected to the remote sense terminals RS and RS the voltages measured are the voltages on excitation output terminals P and P Internal 1 kQ resistors connect RS to P and RS to P Calibration Ground Channel String The SCXI 1520 has a special calibration feature that enables LabVIEW to ground the module amplifier inputs so that you can read the amplifier offset For the other SCXI analog input modules you must physically wire the terminals to ground The measured amplifier offset is for the entire signal path including the SCXI module and the E Series DAQ device To read the grounded amplifier on the SCXI 1520 use the standard SCXI string syntax in the channels array with calgndz substituted for the channel number where z is the appropriate SCXI channel needing grounding For example use the SCXI channel string ob0 sci md1 calgndO to read the grounded channel 0 signal of the module in Slot 1 of SCXI chassis 1 The resulting measurement should be very c
55. to bridge selections in MAX and the LabVIEW Convert Strain Gauge Reading VI You find this VI on the function subpalette Data Acquisition Signal Conditioning Using this VI you wire the SCXI 1520 analog input reading to Vs the initial analog input reading with the system unstrained to Vj and the excitation voltage to Vgyx If you are measuring strain you can use the strain virtual channel in Traditional NI DAQ Legacy to perform offset null compensation shunt calibration and to properly scale strain measurements If you are measuring any other kind of bridge sensor such as load cell pressure sensor or torque sensor and the measurement must be displayed in units of interest for the sensor you cannot use the strain virtual channel This is because the scaling provided by the strain virtual channel returns measurements in units of microstrain u rather than the units of interest for the sensor If you require alternative scaling you can either use an analog input voltage virtual channel with a custom scale configured in MAX or SCXI channel strings and provide scaling in your LabVIEW application National Instruments Corporation 5 27 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 If you are using SCXI channel strings you can easily convert the SCXI 1520 voltage signal measurements in your application into scaled units of interest such as strain pounds or newtons LabVIEW has some common conversion scaling functions suc
56. to select a lowpass filter cutoff frequency You can choose 10 Hz 100 Hz 1 kHz 10 kHz or filter bypass mode If your application requires other cutoff frequencies refer to Chapter 4 Theory of Operation SCXI 1520 User Manual 3 2 ni com Chapter 3 Configuring and Testing Gain Input Range Gain input range is a software configurable setting that allows you to choose the appropriate amplification to fully utilize the range of the E M Series DAQ device In most applications NI DAQ chooses and sets the gain for you determined by the input range This feature is described in Chapter 4 Theory of Operation Otherwise you should determine the appropriate gain using the input signal voltage range and the full scale limits of the SCXI 1520 output signal For common strain gauge configurations where the Gauge Factor is 2 0 the maximum input signal in microvolts is quarter bridge max strain x excitation voltage x 0 5 uV V ue half bridge max strain x excitation voltage x 1 0 un V V ug full bridge max strain x excitation voltage x 2 0 L V V u When you have determined the input signal voltage you can use the following equation to determine the appropriate gain aine SCXI 1520 output voltage range x 10 V Bue input signal voltage If you are using a bridge based sensor use the manufacturer specified sensitivity usually expressed in the units of millivolts per volt to determine the maximum input signal The m
57. troubleshoot the SCXI configuration Troubleshooting in NI DAQmx National Instruments Corporation If you get a Verify SCXI Chassis message box showing the SCXI chassis model number Chassis ID x and one or more messages stating Slot Number x Configuration has module SCXI XXXX or 1520 hardware in chassis is Empty take the following troubleshooting actions Make sure the SCXI chassis is powered on Make sure all SCXI modules are properly installed in the chassis Refer to the SCXI Quick Start Guide for proper installation instructions Make sure the cable between the SCXI chassis and E M Series DAQ device is properly connected nspect the cable connectors for bent pins Make sure you are using the correct NI cable assembly Testthe DAQ device to verify it is working properly Refer to the DAQ device help file for more information If you get a Verify SCXI Chassis message box showing the SCXI chassis model number Chassis ID x and the message Slot Number x Configuration has module SCXI XXXXOor 1520 hardware in chassis is SCXI YYYY 1520 or Empty complete the following troubleshooting steps to correct the error Expand the list of NI DAQmx devices by clicking the next to NI DAQmx Devices 2 Right click the SCXI chassis and click Properties to load the chassis configurator 3 Under the Modules tab ensure that the cabled module is listed in the correct slot 1 7 SCXI 1520 Use
58. you also can manually set or retrieve the potentiometer settings using the AI Parameter VI The shunt calibration switches are exclusively controlled using the AI Parameter VI D 4 ni com Appendix D Common Questions How do I control the gain excitation voltage filter setting bridge configuration potentiometer settings and shunt calibration switches in C based application environments You must use the NI DAQ functions listed in Table 5 6 NI DAQ Functions Used to Configure SCXI 1520 For an SCXI 1520 channel to take a voltage measurement from a sensor that is not in a bridge configuration are there any special considerations You should set the excitation voltage to zero and the bridge configuration to full bridge This is because the SCXI 1520 input offset correction constants stored in the EEPROM are obtained with the excitation voltage set to zero With the excitation voltage not at zero error voltages from the auto nulling circuits can increase offset error beyond the limits given in the specifications What should I take into consideration when I take measurements from sensors with external excitation Set the SCXI 1520 internal excitation to the closest value to match the external excitation level If you want to perform offset null compensation you must set the excitation level to a value other than zero If I am powering my bridge based transducers with an external voltage source what voltage setting should I
59. 1 7 D 1 ni com
60. 1520 configuration settings Yes You can use the AI Parameter VI to change all the SCXI 1520 configuration settings You also can change the configuration settings in NI DAQmx using NI DAQmx Tasks Refer to Chapter 5 Using the SCXI 1520 for more information Some SCXI modules permit flexible scanning Does the SCXI 1520 module permit flexible scanning Yes Flexible scanning is described in Chapter 3 Configuring and Testing but you cannot use flexible scanning when you are using C and Traditional NI DAQ Legacy When using C you can scan only consecutive channels using traditional SCXI channel programming Refer to the NI DAQ Function Reference Help for more details on SCXI scanning Are there any cabling restrictions when using an SCXI 1520 module with a plug in E M Series DAQ device Yes If a chassis contains an SCXI 1520 SCXI 1530 1531 or SCXI 1140 module at least one of these modules must be the cabled module A cabled module is the module connected directly to the E M Series DAQ device This ensures that a timing signal is available for use by all simultaneous sampling SCXI modules in the chassis SCXI 1520 User Manual Appendix D Common Questions SCXI 1520 User Manual Can I use the SCXI 1520 with a version of NI DAQ that works under the Macintosh Operating System Mac OS No as of NI DAQ 6 6 1 Check the release notes of later versions of NI DAQ at ni com for updates Is a register level programming manual a
61. 4 27 signal connections digital signals table D 2 front connector pin assignments table 2 11 SCXI 1520 User Manual Index software NI DAQ version required D 1 specifications amplifier A 4 analog input A 1 bridge completion A 6 dynamic A 4 electromagnetic compatibility A 8 environmental A 7 excitation A 5 filter A 4 maximum working voltage A 7 null compensation A 5 physical A 7 power requirements from SCXI backplane A 6 regulatory compliance A 8 safety A 8 shunt calibration A 6 stability A 5 track and hold A 4 transfer A 1 stability specifications A 5 strain gauge connections full bridge configuration I 2 6 4 13 full bridge configuration II 2 7 4 14 full bridge configuration III 2 8 4 16 half bridge configuration I 2 4 4 9 half bridge configuration II 2 5 4 11 quarter bridge configuration I 2 1 4 4 quarter bridge configuration II 2 2 4 6 SCXI 1520 User Manual questions about D 5 remote sense 2 9 T taking measurements See measurements TBX 96 terminal block 1 3 TEDS D 6 theory of operation block diagram 4 19 excitation 4 22 null compensation 4 25 shunt calibration 4 27 track and hold specifications A 4 transfer specifications A 1 triggering analog D 6 digital D 6 external D 6 troubleshooting incorrect test and verification D 1 questions and answers D 1 self test verification 1 7 V verifying and self testing the configuration troubleshooting
62. 7 Simultaneous Sample and Hold sese 4 28 Maximum Simultaneous Sample and Hold Sample Rate Using NEDAQNIx e te ete dee ied n eed eus 4 30 Maximum Simultaneous Sample and Hold Using Traditional NEDAOQ Eeg86y u a ia eie ete t Reese das HR eS diane 4 32 Modes of Operation eret erp e e egt 4 34 Theory of Multiplexed Mode Operation sees 4 34 Theory of Parallel Mode Operation esee 4 35 Chapter 5 Using the SCXI 1520 Developing Your Application in NI DAQmx eene 5 1 Typical Program Flowchart eio etre eripe 5 2 General Discussion of Typical Flowchart eese 5 4 Creating a Task Using DAQ Assistant or Programmatically 5 4 Adjusting Timing and Triggering e 5 4 Configuring Channel Properties eese 5 5 Performing Offset Null Compensation eee 5 7 Performing Shunt Calibration eee 5 8 Acquiring Analyzing and Presenting eee 5 8 Completing the Application sse 5 9 Developing an Application Using LabVIEW sese 5 9 Using a DAQmx Channel Property Node in LabVIEW 5 11 Specifying Channel Strings in NI DAQmx eee 5 12 Text Based ADES tirer ag ie pas 5 14 Measurement Studio Visual Basic NET and C 5 14 Pro
63. A 5 theory of operation 4 25 null potentiometers coarse and fine control codes table 4 26 configuring 3 4 questions about D 4 0 operation of SCXI 1520 See theory of operation P physical specifications A 7 pin assignments front connector table 2 11 terminal assignments 2 10 potentiometers See null potentiometers power requirements from SCXI backplane A 6 power up state of SCXI 1520 D 4 PXI combination chassis 1 5 Q quarter bridge configuration I 2 1 4 4 quarter bridge configuration II 2 2 4 6 questions and answers D 1 R random scanning D 3 regulatory compliance specifications A 8 remote sense 2 9 National Instruments Corporation F3 Index removing SCXI 1520 from Measurement amp Automation Explorer C 1 from SCXI chassis C 1 S safety specifications A 8 SCXI chassis connecting SCXI 1520 to DAQ device 1 5 removing SCXI 1520 C 1 SCXI 1200 D 2 SCXI 1310 connector and shell assembly 1 3 SCXI 1314 terminal block 1 2 D 5 SCXI 1314T terminal block 1 2 D 6 SCXI 1520 block diagram 4 19 calibration 5 37 common questions D 1 configuration settings 3 1 digital signals table D 2 specifications A 1 taking measurements See measurements theory of operation excitation 4 22 null compensation 4 25 shunt calibration 4 27 SCXI 1600 D 2 self test verification troubleshooting 1 7 D 1 shunt calibration questions about D 4 specifications A 6 theory of operation
64. A passive quarter bridge completion resistor dummy resistor is required in addition to half bridge completion Temperature variation in specimen decreases the accuracy of the measurements Sensitivity at 1000 ue is 0 5 mV out Vgy input s Note S is left unwired Figure 4 3 Quarter Bridge Circuit Diagram The following symbols apply to the circuit diagram and equations R and R are half bridge completion resistors R is the quarter bridge completion resistor dummy resistor R is the active strain gauge element measuring tensile strain Vex is the excitation voltage Ry is the lead resistance Vcg is the measured voltage To convert voltage readings to strain units use the following equation trai 4V 1 xt strain GF 2V TRE where National Instruments Corporation R is the nominal gauge resistance of the sensor Rz is the lead resistance GF is the Gauge Factor 4 5 SCXI 1520 User Manual Chapter 4 Theory of Operation To simulate the effect on strain of applying a shunt resistor across R5 use the following equation AU _ GF 1 4U Notes The value of the quarter bridge completion resistor dummy resistor must equal the nominal resistance of the strain gauge NI recommends using a 0 1 precision resistor To minimize temperature drift errors the strain gauge must have a self temperature compensation STC number that corresponds to th
65. AQmx or Traditional NI DAQ Legacy creating and testing a virtual channel global channel and or task SCXI 1520 Software Configurable Settings This section describes how to set the bridge configuration voltage excitation level filter bandwidth and gain input signal range as well as how to use configuration utilities in MAX to programmatically perform offset null compensation and shunt calibration It also describes how to perform configuration of these settings for the SCXI 1520 in NI DAQmx and Traditional NI DAQ Legacy For more information on the relationship between the settings and the measurements and how to configure settings in your application refer to Chapter 4 Theory of Operation Common Software Configurable Settings This section describes the most frequently used software configurable settings for the SCXI 1520 Refer to Chapter 4 Theory of Operation for a complete list of software configurable settings Bridge Configuration Bridge configuration is a software configurable setting that allows you to connect quarter half or full bridge configuration Wheatstone bridge sensors easily When quarter or half bridge configuration is selected Terminal SX where X is a particular channel is disconnected from the front signal connector and internally connected to a half bridge completion network Implementing quarter bridge completion also involves making field wiring connections to the quarter bridge completion re
66. Application in NI DAQmx section or the Developing Your Application in Traditional NI DAQ Legacy section respectively of Chapter 5 Using the SCXI 1520 The SCXI 1520 has two independent shunt calibration circuits available for each channel at terminal sets SCAX and SCBX on the terminal block Each shunt calibration circuit consists of a resistor in series with a switch The SCXI 1520 shunt calibration switch is a long life solid state switch The electronic switch is galvanically isolated from ground therefore you can connect the switch across any external bridge element National Instruments Corporation 4 27 SCXI 1520 User Manual Chapter 4 Theory of Operation s Notes You can control an individual shunt calibration switch or combination of multiple shunt calibration switches using NI DAQ software The shunt calibration resistors in series with each switch are housed in the SCXI 1314 terminal block The shunt calibration resistors are socketed for easy replacement The resistors are RN 55 style standard 1 4 W precision resistors For resistor replacement instructions refer to the SCXI 1314 Universal Strain Terminal Block Installation Guide Perform an offset null compensation just before you perform a shunt calibration Performing a shunt calibration before an offset null compensation causes improper gain adjustment because the offset signal voltage is compensated multiple times Simultaneous Sample and Hold SCXI 1520 User Manua
67. D 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 Conventions lt gt bold italic monospace monospace bold monospace italic The following conventions are used in this manual Angle brackets that contain numbers separated by an ellipsis represent a range of values associated with a bit or signal name for example AO lt 3 0 gt The symbol leads you through nested menu items and dialog box options to a final action The sequence File Page Setup Options directs you to pull down the File menu select the Page Setup item and select Options from the last dialog
68. DAQ device or SCXI chassis In multiplexed mode the SCXI 1520 scanned channels are kept by the NI DAQ driver in a scan list Immediately prior to a multiplexed scanning operation the SCXI chassis is programmed with a module scan list that controls which module sends its output to the SCXIbus during a scan through the cabled SCXI module The list can contain channels in any physical order and the multiplexer can sequence the channel selection from the scan list in any order The ordering of scanned channels need not be sequential Channels can occur multiple times in a single scan list The scan list can contain an arbitrary number of channels for each module entry in the scan list limited to a total of 512 channels per DAQ device This is referred to as flexible scanning random scanning Not all SCXI modules provide flexible scanning The module includes first in first out FIFO memory for storing the channel scan list defined in your application code NI DAQ drivers load the FIFO based on the channel assignments you make in your application You need not explicitly program the module FIFO as this is done automatically for you by the NI DAQ driver When you configure a module for multiplexed mode operation the routing of multiplexed signals to the DAQ device depends on which module in the SCXI system is cabled to the DAQ device There are several possible scenarios for routing signals from the multiplexed modules to the DAQ device If the
69. DAQmx although NI recommends that you leave SS H enabled for most applications Disabling SS H for one module disables this feature for all modules in all chassis that are controlled by the same DAQ device You should only disable SS H if your application does not require simultaneous sampling and requires higher acquisition rates than are possible with SS H enabled Refer to the Developing Your Application in NI DAQmx section of Chapter 5 Using the SCXI 1520 for more information about National Instruments Corporation 4 29 SCXI 1520 User Manual Chapter 4 Theory of Operation programmatically enabling and disabling SS H using NI DAQmx in your application Maximum Simultaneous Sample and Hold Sample Rate Using NI DAQmx When using NI DAQmx you can use the SCXI 1520 in multiplexed or parallel mode Multiplexed Mode Use the following formula to calculate the maximum SS H sample rate in multiplexed mode SR 1 HT NoC 1 x Maximum of either MST uro or MST scx TT where SR is sample rate frequency of acquisition of all channels HT is hold time the time between holding all the SS H channels and the first A D conversion NoC is number of channels the total number of channels being sampled in the scan list SS H or not MST yro is minimum settle time of MIO inverse of maximum sample rate of the MIO also minimum interchannel delay MSTscx is minimum settle time of SCXI inverse of maximum m
70. IlChannel myChannel myTask AIChannels strain0 myChannel LowpassCutoffFrequency 10 0 myChannel LowpassEnable true myChannel AutoZeroMode ATAutoZeroMode Once You can change any of the properties at a later time For example to change the filter settings of myChannel1 enter the following lines AIChannel myChannel myTask AIChannels strain 0 myChannel LowpassCutoffFrequency 10 0 myChannel LowpassEnable true National Instruments Corporation 5 15 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Modify the example code above or the code from one of the shipping examples as needed to suit your application Refer to the Other Application Documentation and Material section for the location of program examples Notes You can create and configure the strain task in MAX and load it into your application with the function call Nationallnstruments DAQmx DaqgSystem Local LoadTask Refer to the NI Measurement Studio Help for more information on creating NI DAQmx tasks in LabWindows CVI and NI DAQmx property information Programmable NI DAQmx Properties All of the different ADEs that configure the SCXI 1520 access an underlying set of NI DAQmx properties Table 5 3 provides a list of some of the properties that configure the SCXI 1520 You can use this list to determine what kind of properties you need to set to configure the device for your application For a complete list of NI DAQmx propertie
71. Node 5 Configure your channels The initial ActiveChan item allows you to specify exactly what channel s you want to configure If you want to configure several channels with different properties separate the lists of properties with another Active Channels box and assign the appropriate channel to each list of properties s Note If you do not use Active Channels the properties are set on all of the channels in the task National Instruments Corporation 5 11 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 6 Right click ActiveChan select Add Element and left click in the new ActiveChan box Navigate through the menus and select the property you wish to define 7 Change the property to read or write to either get the property or write a new value Right click the property go to Change To and select Write Read or Default Value 8 After you have added the property to the property node right click the terminal to change the attributes of the property add a control constant or indicator Figure 5 2 LabVIEW Channel Property Node with Filtering Enabled at 10 kHz and SS H Disabled 9 To add another property to the property node right click an existing property and left click Add Element To change the new property left click it and select the property you wish to define Note Refer to the LabVIEW Help for information about property nodes and specific NI DAQmx properties Specifying Cha
72. Q Assistant or Programmatically When creating an application you must first decide whether to create the appropriate task using the DAQ Assistant or programmatically in the ADE Developing your application using DAQ Assistant gives you the ability to configure most settings such as measurement type selection of channels bridge configuration excitation voltage signal input limits task timing and task triggering You can access the DAQ Assistant through MAX or your NI ADE Choosing to use the DAQ Assistant can simplify the development of your application NI recommends creating tasks using the DAQ Assistant for ease of use when using a sensor that requires complex scaling or when many properties differ between channels in the same task If you are using an ADE other than an NI ADE or if you want to explicitly create and configure a task for a certain type of acquisition you can programmatically create the task from your ADE using functions or VIs If you create a task using the DAQ Assistant you can still further configure the individual properties of the task programmatically with functions or property nodes in your ADE NI recommends creating a task programmatically if you need explicit control of programmatically adjustable properties of the DAQ system Programmatically adjusting properties for a task created in the DAQ Assistant overrides the original or default settings only for that session The changes are not automatically s
73. Qmx section or the Developing Your Application in Traditional NI DAQ Legacy section respectively of Chapter 5 Using the SCXI 1520 4 26 ni com Chapter 4 Theory of Operation Shunt Calibration Shunt calibration is a process used to obtain a gain adjust factor which is used to correct for system gain error and discrepancies between nominal Gauge Factor and actual Gauge Factor of the strain gauge The gain adjust factor is derived using theoretical simulated signal levels that should result from engaging a shunt resistor across one leg of a bridge sensor and the measured signal levels with the shunt resistor actually engaged Use the following formula to calculate the gain adjust factor simulated signal level gain adjust factor i n measured signal level with shunt resistor engaged The gain adjust factor is then multiplied by each future measurement to obtain highly accurate measurements that are adjusted for any gain errors or any discrepancies in the nominal Gauge Factor Refer to the Configurable Settings in MAX section of Chapter 3 Configuring and Testing for more information about performing shunt calibration automatically in global channels using NI DAQmx in MAX or strain virtual channels using Traditional NI DAQ Legacy and tasks For more information about programmatically performing shunt calibration switches in NI DAQmx and Traditional NI DAQ Legacy refer to the Developing Your
74. SCXI SCXI 1520 User Manual May 2009 7 NATIONAL 372583F 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 Information Document To comment on National Instruments documentation refer to the National Instruments Web site at ni com info and enter the info code feedback 2001 2009 National Instruments Corporation All rights reserved Impo
75. SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Typical Program Flowchart Figure 5 1 shows a typical program flowchart for creating a task to configure channels take a measurement analyze the data present the data stop the measurement and clear the task SCXI 1520 User Manual 5 2 ni com Chapter 5 Using the SCXI 1520 Yes Create Task Using No Create Task in DAQ Assistant or MAX DAQ Assistant Y Create a Task Programmatically Create Strain or Custom Voltage with Excitation Channel Create Another Channel Further Configure Channels Configure Channels Hardware Timing Triggering No Y Start Measurement Read Measurement Bridge Null Operation Perform Shunt Y Calibration SS Display Data Shunt Calibration Display Tools Operation Continue Sampling Stop Measurement Y Clear Task National Instruments Corporation Figure 5 1 Typical Program Flowchart 5 8 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 General Discussion of Typical Flowchart SCXI 1520 User Manual The following sections briefly discuss some considerations for a few of the steps in Figure 5 1 These sections are meant to give an overview of some of the options and features available when programming with NI DAQmx Creating a Task Using DA
76. Table 4 1 Strain Gauge Configurations 00 0 lees eeecseceeeseeeeeeeeeseeaeeneeeaeenes 4 2 Table 4 2 Control Codes for Coarse and Fine Offset Null Potentiometers 4 26 Table 4 3 NI DAQmx Values Used to Determine Maximum Sample Rate in Multiplexed Mode 2 icr tte tieu 4 31 Table 4 4 NI DAQmx Values Used to Determine Maximum Sample Rate 1 Parallel Mode aed ner o e et ERR 4 32 Table 4 5 Traditional NI DAQ Legacy Values Used to Determine Maximum Sample Rate in Multiplexed Mode 4 33 Table 5 1 NI DAQMX Properties n tret eter epe tete tt 5 5 Table 5 2 Programming a Task in LabVIEW sees 5 9 Table 5 3 NE DAOmx Properties iet te oe quite tee 5 16 Table 5 4 Settings for Configuring the SCXI 1520 Through the AI Parameter 5 22 Table 5 5 Configuration Functions ssesseseseeeeeeeenee eene ren enne 5 31 Table 5 6 NI DAQ Functions Used to Configure SCXI 1520 5 33 Table D 1 Digital Signals on the SCXI 1520 sese D 2 SCXI 1520 User Manual X ni com About the SCXI 1520 The SCXI 1520 module is an eight channel module for interfacing to strain gauge bridges and other Wheatstone bridge based sensors s Note Descriptions in this chapter explicitly refer to the first channel channel 0 however the same descriptions are applicable to channels lt 1 7 gt You can configure all settings on a per channe
77. Vgxis the excitation voltage R isthe lead resistance Vcgis the measured voltage 3 Note The value of the quarter bridge completion resistor R4 must equal the nominal resistance of the strain gauge NI recommends using a 0 146 precision resistor Quarter Bridge Type II This section provides information for connecting the quarter bridge strain gauge configuration type II Figure 2 2 shows the quarter bridge type II circuit wiring diagram SCXI 1520 User Manual 2 2 ni com Chapter 2 Connecting Signals B Note The quarter bridge type II configuration is often confused with the more commonly used half bridge type I configuration In the half bridge type I configuration the R3 element is active and bonded to the strain specimen to measure Poisson s ratio while in the quarter bridge type II configuration the R element does not actively measure strain but is in close thermal contact with the strain specimen In quarter bridge type II configuration the R5 element is not bonded to the specimen Typically it is either physically close to the specimen or mounted on the same type material at the same temperature but is not under strain SCXI 1520 Set Bridge Transducer SCXI 1314 Configuration to Quarter Bridge Ro WA E Ven _ R s gt i R R gauge i i s e x Ne R3 i T
78. W Table 5 2 Programming a Task in LabVIEW Flowchart Step VI or Program Step Create Task in DAQ Assistant Create aDAQmx Task Name Constant located on the Controls All Controls I O DA Qmx Name Controls subpalette right click it and select New Task DAQ Assistant Create a Task Programmatically optional DAQmx Create Task vi tThis Vl is optional if you created and configured your task using the DAQ Assistant However if you use itin LabVIEW any changes you make to the task will not be saved to a task in MAX National Instruments Corporation 5 9 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Table 5 2 Programming a Task in LabVIEW Continued Flowchart Step VI or Program Step Create AI Strain Channel optional or Create AI Custom Voltage with Excitation Channel optional DAQmx Create Virtual Channel vi AI Voltage by default to change to a strain gauge channel click AI Voltage and select Analog Input Strain Strain Gage This VI is optional if you created and configured your task and channels using the DAQ Assistant Any channels created with this VI are not saved in the DAQ Assistant They are only available for the present session of the task in LabVIEW Adjust Timing Settings optional DAQmx Timing vi Sample Clock by default This VI is optional if you created and configured your task using the DAQ Assistant Any timing settings
79. abVIEW LabWindows CVI Visual Basic C and C analog input Scan clock signal used to increment to the next channel after each E M Series DAQ device analog to digital conversion See AI HOLD See HOLD TRIG See HOLD TRIG amplifier A type of signal conditioning that improves accuracy in the resulting digitized signal by increasing signal amplitude relative to noise American National Standards Institute G 2 ni com bandwidth bias current bipolar bit bridge completion resistors Butterworth filter CE CFR CH channel chassis CLK CMRR CMV common mode noise National Instruments Corporation G 3 Glossary The range of frequencies present in a signal or the range of frequencies to which a measuring device can respond The small input current flowing into or out of the input terminals of an amplifier A voltage range spanning both negative and positive voltages One binary digit either 0 or 1 Fixed valued resistors used to complete a Wheatstone bridge when fewer than four of the bridge elements are working strain gauges A lowpass filter whose characteristics are optimized for maximum flatness in the passband Celsius European emissions control standard Code of Federal Regulations channel Pin or wire lead to which you apply or from which you read an analog or digital signal Analog signals can be single ended or differential For digital signals channels are grouped to form po
80. acquisition board data address line signal used to indicate whether the SER DAT IN pulse train transmitted to the SCXI chassis contains data or address information A data acquisition device decibel The unit for expressing a logarithmic measure of the ratio of two signal levels dB 20log o V1 V2 for signals in volts Direct Current A plug in data acquisition board module card or pad that can contain multiple channels and conversion devices G 4 ni com DIFF differential amplifier differential input DGND DIG GND DIN DIO drivers driver software droop rate E EEPROM EMC EMI excitation EXTCLK external trigger EXTSTROBE National Instruments Corporation G 5 Glossary differential input configuration An amplifier with two input terminals neither of which are connected to a ground reference whose voltage difference is amplified The two terminal input to a differential amplifier digital ground signal See DGND Deutsche Industrie Norme German Industrial Standard Digital Input Output Software that controls a specific hardware device such as an E M Series DAQ device The rate that a sample and hold circuit in hold mode deviates from the true hold value expressed in millivolts per second Electrically Erasable Programmable Read Only Memory ROM that can be erased with an electrical signal and reprogrammed Some SCXI modules contain an EEPROM to store measurement correction
81. acy Verifying the Signal Using Channel Strings Verifying the Signal Using Strain Virtual Channel Using the Strain Calibration Wizard in NI DAQmx eee Chapter 4 Theory of Operation Stram Gauge Pheopysae uere tee ee oreet rr Spese i qe cun Wheatstone Bridges Jte mtt et ette ete Strain Gauges x eb died da i ote t eg Acronyms Formulas and Variable Definitions Software Scaling and Equations essere Quarter Bridge Type L s ed tede ee Re eri e PEERS Quarter Bridge Type lI a ns isa E i er ene ete e eee eR Ray Halt BrudgesType l gettin eee upas ua Half Brdge Type IL 62 ana e thea died tiie deem hte Fu ll Bridge Type Du 8 e e t E teet t ted SCXI 1520 User Manual vi ni com Contents Full Bridge Type Dua saan ahua al en te antares 4 14 Full Bridge Type ID u eee dote ee teet tran 4 16 SCXI 1520 Theory of Operation as 4 18 Bridge Configuration and Completion esee 4 21 Excit tiQno i acie E e RO e D eee cus 4 22 Remote Sense aan sn sasha asinus 4 23 Gaius sanu Pn yas 4 24 Filter Bandwidth and Cutoff Frequency eee 4 25 Offset Null Compensation eese nennen a 4 25 Shunt Calibration rrr ttt reet Ee vegies 4 2
82. ain gauge configuration type I The full bridge type I only measures bending strain Figure 4 10 shows how to position strain gauge resistors in a bending configuration Figure 4 11 shows the full bridge type I circuit wiring diagram Bending Figure 4 10 Full Bridge Type Rejecting Axial and Measuring Bending Strain A full bridge type I configuration has the following characteristics Four active strain gauge elements Two are mounted in the direction of bending strain on one side of the strain specimen top the other two are mounted in the direction of bending strain on the opposite side bottom e Highly sensitive to bending strain Rejects axial strain Compensates for temperature Compensates for lead resistance Sensitivity at 1000 ue is 2 0 mV out Vgy input Figure 4 11 Full Bridge Type Circuit Diagram National Instruments Corporation 4 13 SCXI 1520 User Manual Chapter 4 Theory of Operation The following symbols apply to the circuit diagram and equations e Rjisan active strain gauge element measuring compressive strain R isan active strain gauge element measuring tensile strain e R is an active strain gauge element measuring compressive strain R isan active strain gauge element measuring tensile strain Vyyis the excitation voltage e R is the lead resistance Vc is the measured voltage To con
83. al NI DAQ Legacy CAP u aaah tc pte eret eR tede 5 34 Performing Acquisition Using Traditional NI DAQ Legacy C API 5 35 Performing Scaling Analysis and Display sess 5 35 Other Application Documentation and Material sese 5 36 Traditional NI DAQ Legacy CVI Examples eene 5 36 Traditional NI DAQ Legacy Measurement Studio Examples 5 36 Calibrating the Strain System eese tenente tnnt treten nnne 5 37 Calibrating the SCXI 1520 eite tet te te eerta d 5 37 Internal Calibration Procedure see 5 37 Internal Calibration Using LabVIEW see 5 37 Internal Calibration Using a C Based ADE aa 5 38 External Calibration iter tente 5 38 Calibrating the System tette eite i tee a ace i 5 39 Offset Null Compensation esee 5 39 Shunt Calibration tico mener tein 5 39 Appendix A Specifications Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later Appendix C Removing the SCXI 1520 SCXI 1520 User Manual viii ni com Contents Appendix D Common Questions Glossary Index Figures Figure 2 1 Quarter Bridge I Circuit Diagram eere 2 2 Figure 2 2 Quarter Bridge II Circuit Diagram eee 2 3 Figure 2 3 Half Bridge Type I Circuit Diagram
84. al calibration using a C based ADE complete the following steps using the NI DAQ function SCXI Calibrate 1 Enter the DAQ device DAQ channel module slot and module channel 2 Select internal calibration 0 as the operation you are going to perform The SCXI 1520 takes a few seconds to perform the calibration After completion the module has new calibration constants stored for all gain settings You must repeat the procedure to calibrate other channels in the module External Calibration For instructions on how to perform an external calibration on the SCXI 1520 refer to the SCXI 1520 Calibration Procedure available by going to ni com calibration and clicking Manual Calibration Procedures NI recommends you perform an external calibration once a year 5 38 ni com Chapter 5 Using the SCXI 1520 Calibrating the System You should perform offset null compensation or shunt calibration on transducers in the system to improve accuracy This is considered system or end to end calibration Offset Null Compensation Performing an offset null compensation removes offset in the measurement system Factors such as imperfections in the strain gauge electrical offset in the measurement system signal leads with significant lead resistance as well as other system variables can create offset Refer to the Offset Null Compensation section of Chapter 4 Theory of Operation for information about how to perform offset null compensatio
85. ance in Q a Nominal Gauge in Q e Gauge Factor f Range min in ug g Range max in ue Click Next Enter the following information What DAQ hardware will be used from the drop down menu What channel on your DAQ hardware from the drop down menu c Which analog input mode will be used from the drop down menu d What is the Excitation Voltage s source and value from the drop down menu e Voltage in volts 10 Click Finish Calibrating a Strain Virtual Channel To calibrate a strain virtual channel complete the following steps 1 National Instruments Corporation Right click the virtual channel you want to calibrate and select Properties Click Calibration Select the Engineering Units from the drop down menu 3 11 SCXI 1520 User Manual Chapter 3 Configuring and Testing 6 Enter the Calibration Data and click Update Make the selections in Shunt Cal Circuit A and Operation and click Start After the calibration is completed click Exit Verifying the Signal This section describes how to take measurements using test panels in order to verify signal and configuring and installing a system in NI DAQmx and Traditional NI DAQ Legacy Verifying the Signal in NI DAQmx Using a Task or Global Channel You can verify the signals on the SCXI 1520 using NI DAQmx by completing the following steps SCXI 1520 User Manual 1 Expand the list of tasks and virtual channels by clicking
86. ation calibration 4 turn on shunt A operation to be on all channels performed 5 turn on shunt B on all channels Performing Offset Null Compensation Using Traditional NI DAQ Legacy C API After configuring the system settings and module properties you can perform an offset null compensation programmatically using SCXI Strain Null This function takes measurements and adjusts the coarse and fine offset null potentiometers to minimize or eliminate any electrical offset for a channel You can repeat this process for each channel by calling the SCXI Strain Null function in a loop You can use the resulting imbalance in your application as a software correction factor by determining the residual voltage from the imbalance and subtracting this residual offset from each future measurement For more information regarding the operation of SCXI Strain Null refer to the Traditional NI DAQ Function Reference Help installed by default in Start Programs National Instruments NI DAQ Performing Shunt Calibration Using Traditional NI DAQ Legacy C API SCXI 1520 User Manual After performing an offset null compensation you can perform a shunt calibration programmatically This process is described in the Shunt Calibration section of Chapter 4 Theory of Operation You can use SCXI Calibrate Setup With the parameter CalOp set to 4 to engage SCA set to 5 to engage SCB and set to 0 to disengage the shunt resistor of both
87. aved to the task configuration The next time you load the task the task uses the settings originally configured in the DAQ Assistant Refer to the NI DAQmx Help for information on programmatically saving tasks Adjusting Timing and Triggering There are several timing properties that you can configure through the DAQ Assistant or programmatically using function calls or property nodes If you create a task in the DAQ Assistant you can still modify the timing properties of the task programmatically in your application 5 4 ni com Chapter 5 Using the SCXI 1520 When programmatically adjusting timing settings you can set the task to acquire continuously acquire a buffer of samples or acquire one point at a time For continuous acquisition you must use a While Loop around the acquisition components even if you configured the task for continuous acquisition using MAX or the DAQ Assistant For continuous and buffered acquisitions you can set the acquisition rate and the number of samples to read in the DAQ Assistant or programmatically in your application By default the clock settings are automatically set by an internal clock based on the requested sample rate You also can select advanced features such as clock settings that specify an external clock source internal routing of the clock source or select the active edge of the clock signal Configuring Channel Properties All ADEs used to configure the SCXI 1520 access an underlying se
88. aximum input signal is max input signal voltage sensor sensitivity X excitation voltage x maximum input sensor full scale input For example if you have a 0 to 500 psi pressure sensor with 3 0 mV V sensitivity an excitation voltage of 10 V and a maximum pressure of 200 psi the maximum signal is 3 0 mV V x 10 V x 200 psi 500 psi 12mV National Instruments Corporation 3 3 SCXI 1520 User Manual Chapter 3 SCXI 1520 User Manual Configuring and Testing If you are using a DAQ device that has a maximum analog input range of x10 V and you have a maximum input to the SCXI 1520 of 12 mV set the gain to the setting closest to 833 10V 12 mV but less than 833 A larger gain setting saturates the DAQ device input for a 12 mV signal In this example the closest lesser gain setting for the SCXI 1520 is 750 Null Potentiometers Coarse and fine null potentiometers are software configurable settings that allow you to remove unwanted offset voltage In most cases you do not explicitly set the null potentiometers but instead allow driver software to automatically adjust them for you However if you want to explicitly set the null potentiometers you can write an application program that adjusts the null potentiometers settings Refer to Chapter 4 Theory of Operation for more information Shunt Calibration Switches Shunt calibration switches A and B are software control settings that allow you to e
89. ble 2 2 The rear signal connector allows the DAQ device to access all eight differential analog output signals from the SCXI 1520 The positive terminal of each analog output is named CHX and the negative terminal CHX SCXI 1520 User Manual 2 12 ni com Table 2 2 Rear Signal Pin Assignments Chapter 2 Connecting Signals Rear Connector Diagram Signal Name Pin Number Pin Number Signal Name CHO 3 4 CH0 CH1 5 6 CH 1 1 2 CH2 7 8 CH2 3 4 CH3 9 10 CH3 5 6 718 CH4 11 12 CH4 9 10 CH5 13 14 CH5 11 12 13144 CH6 15 16 CH6 15 16 CH7 17 18 CH7 17 18 i gt 19 20 21 22 21 22 23 24 23 24 DIG GND 25 26 27 28 SER DAT IN 25 26 SER DAT OUT 29 30 DAQ D A 27 28 31 32 33 34 SLOT 0 SEL 29 30 35 36 31 32 37 38 DIG GND 33 34 39 40 41 42 35 36 AI HOLD COMP AI HOLD 43 44 SER CLK 37 38 45 46 47 48 32 a9 isi 49 50 Al 42 43 44 45 46 SYNC 47 48 49 50 In parallel output mode channel 0 is selected at the output multiplexer and is connected to CH 0 The seven other channels are directly connected to CH 1 through CH 7 respectively on the rear connector National Instruments Corporation 2 13 SCXI 1520 User Manual Chapter 2 Connecting Signal
90. c eu obo Convert the scaling National Instruments Corporation 5 29 SCXI 1520 User Manual Chapter 5 SCXI 1520 User Manual Using the SCXI 1520 8 Analyze and display the data 9 Clear the acquisition Reset Hardware Perform Offset Null Yes Configure Acquisition Settings No Perform Offset Null Compensation lt Configure Module Settings Perform Shunt Yes Configure Acquisition Settings Configure Module Settings t Acquire and Coa t Gain Adjust Factor Perform Acquisition Yes Acquire Engage Shunts Configure Acquisition Settings Continue Sampling Analyze Present Clear and Complete Acquisition Configure Module Settings Figure 5 5 Offset Null and Shunt Calibration Flowchart 5 30 ni com Chapter 5 Using the SCXI 1520 Configuring System Settings Using Traditional NI DAQ Legacy C API Start the configuration of the acquisition by ensuring that the SCXI 1520 module and SCXI chassis are in their default states and that the driver software configuration matches the states the actual physical hardware configuration After setting the hardware and software to the defaults of the module s you can configure any module settings that vary from the default configuration settings You also should configure the acquisition para
91. ced by the offset null potentiometers changes by the same amount and the offset null is maintained The offset null potentiometers are controlled digitally using control codes The control codes of the offset null potentiometers are set in software using integer values The coarse potentiometer ranges from 0 to 127 and the fine potentiometer from 0 to 4095 The span of correction the voltage nulling range for each potentiometer depends on the channel gain setting Table 4 2 summarizes the nulling range and scale of the control codes Table 4 2 Control Codes for Coarse and Fine Offset Null Potentiometers Approximate Module Correction Offset Null Range Channel Gain Span at Analog Potentiometer Integer Values Mid Scale Settings Input Coarse 0 to 127 62 220 Vex 10 lt 20 2x Vex Fine 0 to 4095 2047 220 Vgx 364 20 Vex 18 SCXI 1520 User Manual In most cases you do not explicitly set the offset null potentiometers but instead allow the NI DAQ driver software to automatically adjust them for you You can do this either through MAX or in your application Refer to the Configurable Settings in MAX section of Chapter 3 Configuring and Testing for more information about programmatically performing offset null compensation in MAX For more information about programmatically performing offset null compensation in NI DAQmx and Traditional NI DAQ Legacy refer to the Developing Your Application in NI DA
92. coefficients ElectroMagnetic Compliance ElectroMagnetic Interference Supplying a voltage or current source to energize an active sensor or circuit external clock signal A voltage pulse from an external source that causes a DAQ operation to begin See SER CLK SCXI 1520 User Manual Glossary FIFO filtering flexible scanning FSR full bridge gain gain accuracy gain error Gauge Factor GF H half bridge hold mode settling time hold step SCXI 1520 User Manual 1 Fahrenheit a temperature measurement scale 2 farad a measurement unit of capacitance First In First Out memory buffer A type of signal conditioning that allows you to remove unwanted frequency components from the signal you are trying to measure The hardware capability to sequence through channels in a scan list in any order Full Scale Range A Wheatstone bridge in which all four elements are active strain gauges The factor by which a signal is amplified sometimes expressed in decibels A measure of deviation of the gain of an amplifier from the ideal gain See gain accuracy For a given strain gauge is the fractional resistance change relative to the strain that caused the resistance change Thus Gauge Factor is a measure of strain gauge sensitivity See Gauge Factor A Wheatstone bridge consisting of two active strain gauges and two passive fixed valued resistors The time it takes for a sample and hold ci
93. cts bending strain Compensates for the aggregate effect on the principle strain measurement due to the Poisson s ratio of the specimen material Compensates for lead resistance Sensitivity at 1000 ue is 1 3 mV Vgy input Figure 4 15 Full Bridge Type III Circuit Diagram The following symbols apply to the circuit diagram and equations R is an active strain gauge element measuring compressive Poisson effect ve R3 is an active strain gauge element measuring tensile strain 8 National Instruments Corporation 4 17 SCXI 1520 User Manual Chapter 4 Theory of Operation R is an active strain gauge element measuring compressive Poisson effect ve R isan active strain gauge element measuring the tensile strain Vyyis the excitation voltage e R isthe lead resistance Vc is the measured voltage To convert voltage readings to strain units use the following equation 2V strain GF v 1 V v D where GF is the Gauge Factor v is the Poisson s ratio To simulate the effect on strain of applying a shunt resistor across R5 use the following equation 4U GF v 1 U 1 N Notes Full bridge type III is sometimes used for axial strain measurement R and Ry are positioned along the beam axis and on opposite sides of the beam and R and R are positioned transverse to the beam axis and on opposite sides of the beam Strain gauges need not have
94. d each of the modules Refer to the SCXI Quick Start Guide to manually add modules N Note NI recommends auto detecting modules for the first time configuration of the chassis Installing SCXI Using Traditional NI DAQ Legacy in Software Refer to the SCXI Quick Start Guide for information on installing modules using Traditional NI DAQ Legacy in software Manually Adding Modules in Traditional NI DAQ Legacy If you did not auto detect the SCXI modules you must manually add each of the modules Refer to the SCXI Quick Start Guide to manually add modules 3 Note NI recommends auto detecting modules for the first time configuration of the chassis Verifying and Self Testing the Installation The verification procedure for the SCXI chassis is the same for both NI DAQmx and Traditional NI DAQ Legacy To test the successful installation for the SCXI chassis refer to the SCXI Quick Start Guide Verify that the chassis is powered on and correctly connected to an E M Series DAQ device SCXI 1520 User Manual 1 6 ni com Chapter 1 About the SCXI 1520 After verifying and self testing the installation the SCXI system should operate properly with your ADE software If the test did not complete successfully refer to Chapter 3 Configuring and Testing for troubleshooting steps Troubleshooting the Self Test Verification If the Self Test Verification did not verify the chassis configuration complete the steps in this section to
95. djustment factor 2R Gain Adjusting Factor 1 8 This gain adjust factor is used in your application to compensate for the voltage drop across the leads as follows V meas x Gain Adjusting Factor The SCXI 1520 has multiple gain stages to provide optimal overall signal gains appropriate for fully utilizing the range of the digitizing E M Series DAQ device The first gain stage the instrumentation amplifier stage provides gains of either 1 or 20 The second gain stage provides many discrete settings between 1 and 50 Together these two gain stages combine for 49 overall gain settings with overall gains between 1 and 1000 For overall module gain settings equal to or greater than 20 the gain of the first stage is set to 20 so that the noise and offset drift of later stages is small in comparison to this stage The instrumentation amplifier stage uses operational amplifiers with very low temperature drift and noise characteristics If overall module gain is less than 20 the first stage is set to 1 and the appropriate second stage gain is applied In normal operation of the SCXI 1520 you need not set the gain since NI DAQ sets the gain based on the range of your virtual channel task or global channel or the input limits set in LabVIEW In NI DAQmx the default setting is 1 0 and in Traditional NI DAQ Legacy the default gain setting is 100 00 4 24 ni com Chapter 4 Theory of Operation Refer to the Configurable S
96. e SCXI 1314 and the appropriate legs of the bridge sensor Refer to Chapter 4 Theory of Operation for more information Ti The SCXI 1314T only supports SCA It does not support SCB There are no quarter bridge completion resistors in the SCXI 1314T If you are connecting a quarter bridge sensor to an SCXI 1520 using an SCXI 1314T you must place an external resistor between the pins that correspond to PX and SX on the terminals Refer to Chapter 2 Connecting Signals for more information There are no quarter bridge completion resistors in the SCXI 1310 or TBX 96 If you are connecting a quarter bridge sensor to an SCXI 1520 using an SCXI 1310 or TBX 96 you must place an external resistor between the pins that correspond to PX and SX on the terminals Refer to Chapter 2 Connecting Signals for more information National Instruments Documentation The SCXI 1520 User Manual is one piece of the documentation set for data acquisition DAQ systems You could have any of several types of manuals depending on the hardware and software in the system Use the manuals you have as follows Getting Started with SCXI This is the first manual you should read It gives an overview of the SCXI system and contains the most commonly needed information for the modules chassis and software e SCXI or PXI SCXI chassis manual Read this manual for maintenance information on the chassis and for installation instructions The DAQ Ge
97. e sides of the beam and R and R are positioned transverse to the beam axis and on opposite sides of the beam Strain gauges need not have a particular STC number As shown in Figure 4 13 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short The nominal values of Rj Ro Rs and Ry equal R Full Bridge Type lll SCXI 1520 User Manual This section provides information for the full bridge strain gauge configuration type III The full bridge type III only measures axial strain Figure 4 14 shows how to position strain gauge resistors in an axial configuration Figure 4 15 shows the full bridge type III circuit wiring diagram 4 16 ni com Chapter 4 Theory of Operation Figure 4 14 Full Bridge Type III Measuring Axial and Rejecting Bending Strain A full bridge type III configuration has the following characteristics Four active strain gauge elements Two are mounted in the direction of axial strain with one on one side of the strain specimen top the other on the opposite side bottom The other two act together as a Poisson gauge 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 Compensates for temperature Reje
98. e thermal expansion coefficient of the material under test STC gauges have a temperature sensitivity that counteracts the thermal expansion coefficient of the test specimen The STC number approximately equals the thermally induced change in strain with change in temperature and is expressed in units of microstrain per degree Fahrenheit For example if the test specimen is aluminum use a gauge with an STC number of 13 0 If the test specimen is steel use a gauge with an STC number of 6 0 To minimize temperature drift errors in the wiring use the three wire connection shown in Figure 4 3 The wires connected to terminals S and QTR carry the same current and are on opposite sides of the same element of the bridge Therefore any temperature related changes in voltage drop across R caused by temperature variation of the leads cancel out leaving Vc unchanged The voltage drop across the lead resistance on a quarter bridge type I configuration is uncompensated in hardware It is important to accurately determine the gauge lead resistance and enter it in MAX or in the application software equation so the software can compensate for the voltage drop You can neglect lead resistance Ry of the wiring if shunt calibration is performed or if lead length is very short 10 ft depending on the wire gauge For example 10 ft of 24 AWG copper wire has a lead resistance of 0 25 Q Quarter Bridge Type II This section provides information for the qua
99. e with shielded cabling CE Compliance C This product meets the essential requirements of applicable European Directives as follows 2006 95 EC Low Voltage Directive safety 2004 108 EC Electromagnetic Compatibility Directive EMC Online Product Certification Refer to the product Declaration of Conformity DoC for additional regulatory compliance information To obtain product certifications and the DoC for this product visit ni com certification search by model number or product line and click the appropriate link in the Certification column SCXI 1520 User Manual A 8 ni com Appendix A Specifications Environmental Management Dx NI is committed to designing and manufacturing products in an environmentally responsible manner NI recognizes that eliminating certain hazardous substances from our products is beneficial to the environment and to NI customers For additional environmental information refer to the NI and the Environment Web page at ni com environment This page contains the environmental regulations and directives with which NI complies as well as other environmental information not included in this document Waste Electrical and Electronic Equipment WEEE EU Customers At the end of the life cycle all products must be sent to a WEEE recycling center For more information about WEEE recycling centers and National Instruments WEEE initiatives visit ni com environment weee AF Ra mis R
100. eory of Operation The following symbols apply to the circuit diagram and equations R and R are half bridge completion resistors R is the quarter bridge temperature sensing element dummy gauge e Ry is the active strain gauge element measuring tensile strain 8 Vey is the excitation voltage e R is the lead resistance Vcgis the measured voltage To convert voltage readings to strain units use the following equation train 2 x 1 ANNS GPA EZY Rg where R is the nominal gauge resistance Ri is the lead resistance GF is the Gauge Factor To simulate the effect on strain of applying a shunt resistor across R3 use the following equation e U GF 1 4U Notes The dummy gauge element must always be unstrained and mounted to the same type of material as the active gauge but not strained The dummy gauge temperature must closely track the temperature of the active gauge Gauges need not have a STC number corresponding to the material type of the test specimen As shown in Figure 4 5 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short You can neglect lead resistance Ry of the wiring if shunt calibration is performed or if lead length is very short 10 ft depending on the wire gauge For example 10
101. et the control codes of the potentiometers in Traditional NI DAQ Legacy use the LabVIEW AI Parameter VI An example of using the AI Parameter VI to control an SCXI 1520 is shown in Figure 5 4 For more information and example programs for setting the offset null potentiometers go to ni com info and use these info codes rd1520 rdnull and rdxi15 National Instruments Corporation 5 25 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Performing Shunt Calibration Using Traditional NI DAQ Legacy in LabVIEW SCXI 1520 User Manual Shunt calibration is a process used to obtain a gain adjust factor which corrects system gain error and discrepancies between nominal Gauge Factor and actual Gauge Factor of the strain gauge If you are measuring strain you can use the strain virtual channel in Traditional NI DAQ Legacy to perform offset null compensation shunt calibration and to properly scale strain measurements The offset null compensation and shunt calibration are performed during configuration of the strain virtual channel Refer to Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later for more information about creating a strain virtual channel in MAX Refer to the Shunt Calibration section of Chapter 4 Theory of Operation for more information on the process and calculations required for shunt calibration in your application To perform shunt calibration for bridge sensors such as strain
102. ettings in MAX section of Chapter 3 Configuring and Testing for more information about programmatically setting gain using range settings in MAX For more information about programmatically setting gain using range settings in NI DAQmx and Traditional NI DAQ Legacy refer to the Developing Your Application in NI DAQmx section or the Developing Your Application in Traditional NI DAQ Legacy section respectively of Chapter 5 Using the SCXI 1520 Filter Bandwidth and Cutoff Frequency The SCXI 1520 provides two filtering stages with an overall response of a four pole Butterworth filter You can control the cutoff frequency of the filter through software You can choose 10 Hz 100 Hz 1 kHz 10 kHz or filter bypass mode For additional flexibility in cutoff frequency settings and for greater suppression NI recommends combining the hardware filtering provided by the SCXI 1520 with digital filtering NI recommends using the Advanced Analysis functions of LabVIEW LabWindows CVI or Measurement Studio By combining hardware anti aliasing with digital filtering you can choose any cutoff frequency The Advanced Analysis functions are only available in LabVIEW Full or Professional Development Systems and LabWindows CVI Base or Full Development Systems Refer to the Configurable Settings in MAX section of Chapter 3 Configuring and Testing for more information about programmatically setting the cutoff frequency of the filter in MAX For more in
103. for DAQ device channel 0 in a single chassis system In a multichassis or remote chassis system the DAQ device channel x corresponds to chassis number n 1 where DAQ device channel x is used for scanning the nth chassis in the system scy is the SCXI chassis ID where y is the number you chose when configuring the chassis mdz is the slot position where the module is located with z being the particular slot number The slots in a chassis are numbered from left to right starting with 1 National Instruments Corporation B 1 SCXI 1520 User Manual Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later channels is the list of channels that are scanned for module z It can have several formats obx scy mdz nx where nxis a single input channel obx scy mdz n0 n2 where n0 n2 are individual input channels that are not necessarily sequential obx scy mdz n0 n3 where n0 and n3 represent an ascending sequential list of input channels inclusive obx scy mdz n0 n2 n3 n4 n1 n5 n2 where n0 n2 and n5 represent single channels not necessarily sequential and n3 and n4 represent the endpoints of an ascending sequential list of channels inclusive In this case channels n1 and n2 are explicitly repeated in the channel list ik Notes Using parentheses surrounding multiple channels in a channel string is important for correct scanning operation of the SCXI channels In a
104. formation about programmatically setting the cutoff frequency of the filter in NI DAQmx and Traditional NI DAQ Legacy refer to the Developing Your Application in NI DAQmx section or the Developing Your Application in Traditional NI DAQ Legacy section respectively of Chapter 5 Using the SCXI 1520 Offset Null Compensation The SCXI 1520 provides offset null compensation to adjust signal voltages to proper levels when the strain gauge or bridge sensor is at rest unstrained For most sensors offset null compensation is used to remove an initial voltage offset from the Wheatstone bridge Many strain gauge signal conditioning devices use a manually adjusted multi turn screw potentiometer for offset null compensation In the SCXI 1520 offset null compensation is performed electronically using software controlled electronic potentiometers National Instruments Corporation 4 25 SCXI 1520 User Manual Chapter 4 Theory of Operation Two offset null potentiometers are used one for coarse adjustments and the other for fine adjustments The sum of the two potentiometer signals is added to the analog input path to adjust the signal voltage to remove the offset which nulls the strain gauge channel The voltage input to the potentiometers is a voltage proportional to the excitation voltage setting Therefore if the excitation voltage changes by a small amount due to changes such as temperature and sensor loading the correction signal produ
105. g a channel you can select only one channel If you are creating a task select the channels to add to the task You can select a range of channels by holding down the Shift key while selecting the channels You can select multiple individual channels by holding down the lt Ctrl gt key while selecting channels Click Next Select the name of the task or channel and click Finish In the Channel List box select the channel s you want to configure You can select a range of channels by holding down the lt Shift gt key while selecting the channels You can select multiple individual channels by holding down the lt Ctrl gt key while selecting channels 8 Enter the specific values for your application in the Settings tab Context help information for each setting is provided on the right side of the screen SCXI 1520 User Manual 3 8 ni com Chapter 3 Configuring and Testing Click the Device tab and select the autozero mode and lowpass filter cutoff frequency If you are applying custom scaling select the Create New drop down and follow the onscreen wizard If you are creating a task and want to set timing or triggering controls enter the values in the Task Timing and Task Triggering tabs Traditional NI DAQ Legacy In Traditional NI DAQ Legacy you can configure software settings such as bridge configuration voltage excitation level filter bandwidth gain input signal range and calibration settings in the f
106. generate code for a strain task You can then use the appropriate function call to modify the task To create a configurable channel or task in LabWindows CVI complete the following steps 1 Launch LabWindows CVI 2 Open a new or existing project 3 From the menu bar select Tools Create Edit DAQmx Tasks 4 Choose Create New Task In MAX or Create New Task In Project to load the DAQ Assistant 5 Configure the NI DAQm x strain task following the instructions in the Creating a Strain Global Channel or Task section of Chapter 3 Configuring and Testing 6 The DAQ Assistant creates the code for the task based on the parameters you define in MAX and the device defaults To change a property of the channel programmatically use the DAQmxSetChanAt tribute function s Note Refer to the NJ LabWindows CVI Help for more information on creating NI DAQmx tasks in LabWindows CVI and NI DAQmx property information Measurement Studio Visual Basic NET and C SCXI 1520 User Manual When creating a strain task in Visual Basic NET and C follow the general programming flow in Figure 5 1 You can then use the appropriate function calls to modify the task This example creates a new task and configures an NI DAQmx strain channel on the SCXI 1520 You can use the same functions for Visual Basic NET and C In this example an analog input channel object is used since reading the voltage from a Wheatstone bridge configuration is an analog
107. grammable NI DAQmx Properties esee 5 16 Developing Your Application in Traditional NI DAQ Legacy 5 18 Traditional NI DAQ Legacy in LabVIEW 5 19 Typical Program Flow esee 5 20 Configuring the SCXI 1520 Settings Using Traditional NI DAQ Legacy in LabVIEW sii oer tet tr HEP ERE 5 22 National Instruments Corporation vii SCXI 1520 User Manual Contents Performing Offset Null Compensation Using Traditional NI DAQ Legacy 1n Lab VIEW rer tne rtr dedos 5 24 Performing Shunt Calibration Using Traditional NI DAQ Legacy inLab VIEW sonion oii tt Dt ep ed tr e o eh iui 5 26 Configure Start Acquisition and Take Readings Using Traditional NI DAQ Legacy in LabVIEW aa aa aq emere emen 5 27 Converting Scaling Using Traditional NI DAQ Legacy in LabVIEW 5 27 Analyze and Display Using Traditional NI DAQ Legacy in LabVIEW 5 28 Traditional NI DAQ Legacy in Text Based ADEs 5 28 Low Level DAQ Functions nennen nnne ennt 5 29 Configuring System Settings Using Traditional NI DAQ Legacy C API 5 31 Configuring Module Settings Using Traditional NI DAQ Legacy C API 5 32 Performing Offset Null Compensation Using Traditional NI DAQ Legacy CAPI nig qunqa a peri ere eds 5 34 Performing Shunt Calibration Using Tradition
108. h as the Convert Strain Gauge Reading VI in the function subpalette Data Acquisition Analog Input Signal Conditioning You also can use an Expression Node or Formula Node to convert voltage signal measurements into whatever units your application requires You can find an Expression Node in the function subpalette Numeric You can find Formula Nodes in the Function subpalettes Analyze Mathematics Formula For more information about using the Expression Node or Formula Node refer to the LabVIEW User Manual You also can use the LabVIEW Help for more detailed information about how to use these nodes to perform mathematical calculations such as scaling conversions Analyze and Display Using Traditional NI DAQ Legacy in LabVIEW In LabVIEW you can easily analyze SCXI 1520 measurements with a variety of powerful analysis functions that you can find in the function subpalettes Analyze Waveform Conditioning and Analyze Signal Processing You can perform post acquisition processing such as waveform comparisons harmonic analysis and digital filtering For more information about these VIs refer to the LabVIEW Analysis Concepts manual You also can use the LabVIEW Help for more detailed information about how to use the analysis VIs In LabVIEW you also can easily display SCXI 1520 measurements with a variety of graphical waveform graphs numeric slides gauges and other indicators You can find useful graphical controls and indicators for
109. he SCXI 1520 NI provides powerful analysis toolsets for each NI ADE to help you perform advanced analysis on the data without requiring you to have a programming background After you acquire the data and perform any required analysis it is useful to display the data in a graphical form or log it to a file NI ADEs provide easy to use tools for graphical display such as charts graphs slide controls and gauge indicators NI ADEs have tools that allow you to easily save the data to files such as spread sheets for easy viewing ASCII files for universality or binary files for smaller file sizes Completing the Application After you have completed the measurement analysis and presentation of the data it is important to stop and clear the task This releases any memory used by the task and frees up the DAQ hardware for use in another task s Note In LabVIEW tasks are automatically cleared Developing an Application Using LabVIEW This section describes in more detail the steps shown in the typical program flowchart in Figure 5 1 such as how to create a task in LabVIEW and configure the channels of the SCXI 1520 If you need more information or for further instructions select Help gt VI Function amp How To Help from the LabVIEW menu bar s Note Except where otherwise stated the VIs in Table 5 2 are located on the Functions All Functions NI Measurements DAQmx Data Acquisition subpalette and accompanying subpalettes in LabVIE
110. he SCXI 1520 Module into the SCXI Chassis section If the module is installed in the correct slot power off the chassis remove the module as specified in Appendix C Removing the SCXI 1520 and verify that no connector pins are bent on the rear signal connector Reinstall the module as described in the Installing the SCXI 1520 Module into the SCXI Chassis section ensuring the module is fully inserted and properly aligned in the slot After checking the preceding items return to the Troubleshooting the Self Test Verification section and retest the SCXI chassis If these measures do not successfully configure the SCXI system contact NI Refer to the Technical Support Information document for contact information National Instruments Corporation 1 9 SCXI 1520 User Manual Connecting Signals This chapter describes how to connect Wheatstone bridge sensors to the SCXI 1520 in quarter half and full bridge configurations and for remote sensing It also provides the front and rear signal pin assignments of the module Connecting Bridge Sensor Signals This section discusses how to connect the signals of supported strain gauge configuration types as well as full bridge sensors such as load force torque and pressure sensors It also discusses connecting leads for remote sensing and shunt calibration Refer to Chapter 4 Theory of Operation for a discussion of strain gauge concepts Refer to the SCXI 1314 Installation Guide f
111. he strain gauge or bridge sensor is at rest unstrained For most sensors offset null compensation removes an initial voltage offset from the Wheatstone bridge If you are measuring strain you can use a strain task or global channel to perform offset null compensation The offset null compensation can be performed during the configuration of the global channel s or programmatically using the DAQmx Offset Null function in LabVIEW use Dagmx Perform Bridge Offset Nulling National Instruments Corporation 5 7 SCXI 1520 User Manual Chapter 5 3 SCXI 1520 User Manual Using the SCXI 1520 Calibration vi in CVI use the DAQmxPerformBridgeOffsetNullingCal function Refer to the Creating a Strain Global Channel or Task section of Chapter 3 Configuring and Testing for information about offset null compensation when in MAX If you are not measuring strain or would like to adjust the Offset to an arbitrary voltage you can manually adjust the coarse and fine potentiometer settings using properties For more information about offset null compensation refer to the Offset Null Compensation section of Chapter 4 Theory of Operation Performing Shunt Calibration Shunt calibration is a process used to obtain a gain adjust factor which corrects for system gain error and discrepancies between the nominal gauge factor and actual gauge factor of the strain gauge If you are measuring strain you can use a strain task or global channel to perfor
112. heatstone Bridge Based Transducer Figure C 1 Removing the SCXI 1520 SCXI 1520 User Manual C 2 ni com Common Questions This appendix lists common questions related to the use of the SCXI 1520 Which version of NI DAQ works with the SCXI 1520 and how do I get the most current version of NI DAQ You must have NI DAQ 7 0 or later Visit the NI Web site at ni com and select Download Software Drivers and Updates Search Drivers and Updates Enter the keyword NI DAQ to find the latest version of NI DAQ for your operating system I have gone over the Verifying and Self Testing the Installation section of Chapter 1 About the SCXI 1520 yet I still cannot correctly test and verify that my SCXI 1520 is working What should I do now Unfortunately there is always the chance that one or more components in the system are not operating correctly You may have to call or email a technical support representative The technical support representative often suggests additional troubleshooting measures If requesting technical support by phone have the system nearby so you can try these measures immediately NI contact information is listed in the Technical Support Information document In NI DAQmx can I use channels of different measurement types in the same task Yes you can set up your channels programmatically or through the DAQ Assistant Will MAX allow me to configure two SCXI 1520 modules that are in the same chassis in
113. ical program flow such as the one shown in Figure 5 3 SCXI 1520 User Manual 5 20 ni com Chapter 5 Using the SCXI 1520 Use Virtual Channel or SCXI Channel String Virtual Channel SCXI Channel String Configure Acquisition Settings Create Virtual Channel in MAX Configure Mode Properties Yes Perform Offset Null SCXI Strain Null vi No Shunt Calibration Procedure Perform Shunt Calibration e y Start Acquisition 4t Take Measurements Continue Sampling No Scale Analyze and Display Clear Acquisition Error Handling Figure 5 3 Typical SCXI 1520 Program Flow with Traditional NI DAQ Legacy National Instruments Corporation 5 21 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Configuring the SCXI 1520 Settings Using Traditional NI DAQ Legacy in LabVIEW You can configure SCXI 1520 settings perform offset null compensation and perform shunt calibration in MAX using the strain virtual channel To configure and control the SCXI 1520 from LabVIEW use the AI Parameter VI You can find AI Parameter VI in the function subpalette Data Acquisition Analog Input Advanced Analog Input A parameter changed by the AI Parameter VI takes effect in hardware when AI Start VI is called not when AI Parameter VI is called The AI parameter VI me
114. in within 10 V of ground Both inputs should be within 10 V of one another Measurement Category I A Caution Do not use for measurements within Categories II II or IV Environmental Operating temperature 0 to 50 C Storage temperature 20 to 70 C Humidity endete ete 10 to 90 RH noncondensing Maximum altitude 2 000 m Pollution Degree indoor use only 2 National Instruments Corporation A 7 SCXI 1520 User Manual Appendix A Specifications Safety This product meets the requirements of the following standards of safety for electrical equipment for measurement control and laboratory use ITEC 61010 1 EN 61010 1 e UL 61010 1 CSA 61010 1 s Note For UL and other safety certifications refer to the product label or the Online Product Certification section Electromagnetic Compatibility This product meets the requirements of the following EMC standards for electrical equipment for measurement control and laboratory use e EN 61326 IEC 61326 Class A emissions Basic immunity e EN 55011 CISPR 11 Group 1 Class A emissions e AS NZS CISPR 11 Group 1 Class A emissions e FCC 47 CFR Part 15B Class A emissions ICES 001 Class A emissions iy Note For the standards applied to assess the EMC of this product refer to the Online Product Certification section N Note For EMC compliance operate this devic
115. ing SCAN Op the resultant data is not organized by channel so you should demultiplex the data using SCAN Demux SCAN_Demux rearranges or demultiplexes data acquired by SCAN Op into row major order meaning each row of the array holding the data corresponds to a scanned channel for easier access by C applications BASIC applications need not call SCAN Demux to rearrange two dimensional arrays since these arrays are accessed in column major order For more information regarding each acquisition function refer to the Traditional NI DAQ Function Reference Help installed by default in Start Programs National Instruments NI DAQ Performing Scaling Analysis and Display After acquiring raw voltage data from the acquisition functions most applications require adjustment by device calibration constants for accuracy scaling measured voltage analysis and graphical display The SCXI 1520 has stored software calibration constants loaded on the module EEPROM that are used to achieve the absolute accuracy specifications SCXI Scale scales an array of binary data acquired from an SCXI channel to voltage using the stored software calibration constants when it scales the data You must call SCAN Demux before SCXI Scale if you have multiple channels in the scan For more information regarding SCXI_Scale refer to the Traditional NI DAQ Function Reference Help installed by default in Start Programs National Instruments NI DAQ National I
116. input operation The following text is a function prototype example void AIChannelCollection CreateStrainGageChannel System String physicalChannelName System String nameToAssignChannel System Double minVal 5 14 ni com Chapter 5 Using the SCXI 1520 System Double maxVal AIStrainGageConfiguration strainGageConfiguration AIExcitationSource excitationSource System Double excitationValue System Double gageFactor System Double initialBridgeVoltage System Double normalGageResist System Double poissonRatio System Double leadWireResist AIStrainUnits units To actually create and configure the channel you would enter something resembling the following example code Task myTask new NationalInstruments DAQmx Task myTaskName MyTask CreateStrainGageChannel SC1Mod1 ai0 System String physicalChannelName strain0 System String nameToAssignChannel 0 001 System Double minVal 0 001 System Double maxVal AIStrainGageConfiguration FullBridgeIII AIStrainGageConfiguration strainGageConfiguration AIExcitationSource Internal AIExcitationSource excitationSource 3 3 System Double excitationValue 2 0 System Double gageFactor 0 0 System Double initialBridgeVoltage 120 0 System Double normalGageResist 0 3 System Double poissonRatio 0 0 System Double leadWireResist AIStrainUnits Strain AIStrainUnits units setting attributes after the channel is created A
117. ion voltage 20 000 counts of resolution 80 000 ue offset null compensation range 4 We resolution for quarter bridge GF 2 0 Excitation Type ue HR iad Constant voltage Settings uei cv ect bs 0 0 to 10 0 V in 0 625 V increments Error decode ete 20 mV 0 3 of nominal setting 0 1 of value returned by driver software Maximum operating current In all anges zoe ist ets 29 mA Short circuit protection Yes R eul tion aii suis ceased eee US No load to 120 2 load With remote sense 0 003 Without remote sense 0 08 Temperature drift 0 005 C 30 uV C max National Instruments Corporation A 5 SCXI 1520 User Manual Appendix A Specifications Noise DC to 10 KHzZ 200 uV Remote sense seen Error less than 0 02 per ohm of lead resistance both leads Protection aU EE Surge arrestors in parallel with excitation terminals shunt to ground Bridge Completion Halt bnidge exeun Two precision resistors 5 kQ each 0 196 ratio matching Quarter bridge sess Socketed resistor inside the SCXI 1314 terminal block Shunt Calibration TY c p haha Two independent points Resistor aaa ete eene recae Socketed inside the SCXI 1314 terminal block Switch resistance 32 Q typ 50 Q max Switch off leakage
118. ions Continued Function Description SCXI SCAN Setup Initializes multiplexing circuitry for a scanned data acquisition operation Initialization includes storing a table of the channel sequence and gain setting for each channel to be digitized MIO and AI devices only You cannot repeat channels or use nonsequential channels when using the SCXI SCAN Setup function SCXI MuxCtr Setup Programs the E Series DAQ device with the correct number of channels multiplexed per scan This number must match the total number of channels programmed in SCXI SCAN Setup s Note NI strongly recommends monitoring the built in error status of each NI DAQ function The NI DAQ C API provides the NIDAQErrorHandler function which ensures that a specified NI DAQ function executed properly and assists in handling error messages and reporting Configuring Module Settings Using Traditional NI DAQ Legacy C API After configuring the hardware for acquisition you must load the various channel attributes such as filter gain bridge configuration and excitation appropriate for your application explicitly using the NI DAQ function calls shown in Table 5 6 For more information regarding each setting refer to the Traditional NI DAQ Function Reference Help installed by default in Start Programs National Instruments NI DAQ SCXI 1520 User Manual 5 32 ni com Table 5 6 NI DAQ Functions Used to Configure SCXI 1520 Chapter 5 Using the
119. isa SED ChE ROHS rhRE ZEP1 National Instruments 764 P E E TIRA d rp i db T e 3 58 Rd ROHS XT National Instruments F El RoHS GHEE TS ni com environment rohs china For information about China RoHS compliance go to ni com environment rohs china National Instruments Corporation A 9 SCXI 1520 User Manual Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later s Note This appendix is not applicable if you use the virtual channels to configure and measure the SCXI channels Virtual channels are configured using MAX If you use virtual channels you address the SCXI channels by specifying the channel name s in the channel string input When using LabVIEW Measure and Visual Basic the SCXI channel string determines which SCXI channels are scanned and the scanning sequence The SCXI channel string allows you to take measurements from several channels on one module with only one channel string entry An array of these channel string entries configures multiple modules for scanning When the application program runs the channel string is used for programming the channel information into the SCXI system The format of the channel string is as follows obx scy mdz channels where obx is the onboard E Series DAQ device channel with x representing a particular channel where the multiplexed channels are sent This value is 0
120. l Simultaneous sample and hold SS H signal conditioning allows multiplexing MIO DAQ devices to return synchronized samples of all channels with negligible skew time between channels SS H signal conditioning is performed on the SCXI 1520 with track and hold T H circuitry The outputs of the T H amplifiers follow their inputs also called tracking the inputs until they receive a hold signal from the DAQ device All channels with T H circuitry hold their signal at the same time even if they are on different SCXI modules The DAQ device then digitizes the signal of each channel giving you simultaneous sampling between channels since no time elapsed between the holding of each signal All signals are then released and the T H circuitry output returns to tracking the input signal For accurate measurements you can use the SS H equations to calculate the maximum sample rate when scanning SCXI systems with at least one SS H module in the scan list Figure 4 17 shows and example of a signal during a SS H sampling 4 28 ni com Chapter 4 Theory of Operation Volts CHO CH 1 CH 2 i A s Time Hold r Line Convert o Ee 1 2 3 1 HoldTime 2 Max Min Settle Time of MIO Min Settle Time of SCXI 3 TrackTime Figure 4 17 Signal During Simultaneous Sample and Hold Sampling It is possible to enable and disable SS H programmatically in NI
121. l NI DAQ Legacy section of Chapter 3 Configuring and Testing and change the configuration of the cabled module in the system from Connected to None to Connected to Device x If you get the message Failed to find followed by the module codes and the message Unable to communicate with chassis take the following troubleshooting actions Make sure the SCXI chassis is powered on Make sure the cable between the SCXI chassis and E Series DAQ device is properly connected nspect the cable connectors for bent pins Make sure you are using the correct NI cable assembly Testthe DAQ device to verify it is working properly Refer to the DAQ device help file for more information 1 8 ni com Chapter 1 About the SCXI 1520 If you get the message Failed to find followed by module codes and the message Instead found module with ID OXxx refer to the Traditional NI DAQ Legacy section of Chapter 3 Configuring and Testing and make sure the correct module is in the specified slot Delete the incorrect module as described in Appendix C Removing the SCXI 1520 and add the correct module as described in the Traditional NI DAQ Legacy section of Chapter 3 Configuring and Testing If you get the message Failed to find followed by a module code and the message Slot x is empty make sure the configured module is installed in the specified slot If not install the module by following the instructions in the Installing t
122. l basis in software The SCXI 1520 is configured using Measurement amp Automation Explorer MAX or through NI DAQmx property nodes With the SCXI 1520 and the accessory SCXI 1314 terminal block you can do the following Connect sensors of all bridge configurations including quarter half and full bridge Set the DC voltage excitation between 0 and 10 V increments dependent upon the driver software Programmatically offset null bridge circuits connected to the SCXI 1520 Set the analog input lowpass filter cut off frequency to 10 Hz 100 Hz 1 kHz 10 kHz or bypass Set the analog input gain between 1 and 1000 at any one of 49 settings Implement shunt calibration using two independent circuits Connect the bridge for remote sense voltage excitation What You Need to Get Started To set up and use the SCXI 1520 you need the following CL Hardware National Instruments Corporation SCXI 1520 module One of the following terminal blocks SCXI 1314 terminal block SCXI 1314T terminal block 1 1 SCXI 1520 User Manual Chapter 1 About the SCXI 1520 SCXI or PXI SCXI combo chassis E M Series DAQ device Computer if using an SCXI chassis Cabling cable adapter and sensors as required for your application C Software NI DAQ 7 0 or later Application software such as LabVIEW LabWindows CVI Measurement Studio or other programming environments C Documentation
123. le 2 11 full bridge configuration I 2 6 4 13 full bridge configuration II 2 7 4 14 full bridge configuration III 2 8 4 16 gain configuration 3 3 4 24 questions about D 4 H half bridge configuration I 2 4 4 9 half bridge configuration II 2 5 4 11 installation connecting to DAQ device for multiplexed scanning in PXI combination chassis 1 5 in SCXI chassis 1 5 into SCXI chassis 1 5 removing SCXI 1520 from Measurement amp Automation Explorer C 1 from SCXI chassis C 1 internal calibration See calibration SCXI 1520 User Manual L LabVIEW software internal calibration of SCXI 1520 5 37 questions about D 3 Macintosh operating system D 4 maximum working voltage specifications A 7 Measurement amp Automation Explorer removing SCXI 1520 C 1 self test verification troubleshooting 1 7 measurements calibrating SCXI 1520 5 37 pin assignments terminal assignments 2 10 strain gauge connections full bridge configuration I 2 6 4 13 full bridge configuration II 2 7 4 14 full bridge configuration III 2 8 4 16 half bridge configuration I 2 4 4 9 half bridge configuration II 2 5 4 11 quarter bridge configuration I 2 6 4 13 quarter bridge configuration II 2 7 4 14 remote sense 2 9 multiplexed mode operation connecting to SCXI 1520 for DAQ device in PXI combination 1 5 in SCXI chassis 1 5 questions about D 3 ni com N NI DAQ software D 1 D 4 null compensation specifications
124. lose to 0 V The AI Start VI grounds the amplifier before starting the acquisition The AI Clear VI removes the grounds from the amplifier after the acquisition completes You can specify a range of channels also The string calgnd0 7 grounds the amplifier inputs for channels 0 through 7 and reads the offset for each amplifier National Instruments Corporation B 3 SCXI 1520 User Manual Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later Use the SCXI Calibrate VI available on the Functions Data Acquisition Calibration and Configuration palette to automatically perform a self calibration and modify the scaling constants on the module to adjust for any amplifier offset Refer to the Calibrating the Strain System section of Chapter 5 Using the SCXI 1520 for more information about how to use SCXI Calibrate VI with the SCXI 1520 SCXI 1520 User Manual B 4 ni com Removing the SCXI 1520 This appendix explains how to remove the SCXI 1520 from MAX and an SCXI chassis Removing the SCXI 1520 from MAX To remove a module from MAX complete the following steps after launching MAX 1 Expand Devices and Interfaces 2 Expand the list of installed chassis by clicking the next to NI DAQmx and or Traditional NI DAQ Devices 3 Expand the list of installed modules by clicking the next to the appropriate chassis Right click the module or chassis you want to delete and click Delete A confi
125. ly in your application using the voltage to strain conversion equations provided in this document for each configuration type Finally there are voltage to strain conversion functions included in LabVIEW NI DAQmx and Traditional NI DAQ Legacy In LabVIEW the conversion function Convert Strain Gauge 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 C C and convert bas for Visual Basic Refer to the Traditional NI DAQ User Manual and the LabVIEW Measurements Manual for more information The names given the strain gauge types in these sections directly correspond to bridge selections in MAX and the LabVIEW Convert Strain Gauge Reading VI Quarter Bridge Type SCXI 1520 User Manual This section provides information for the quarter bridge strain gauge configuration type I The quarter bridge type I measures either axial or bending strain Figure 4 2 shows how to position a strain gauge resistor in an axial and bending configurations Figure 4 3 shows the quarter bridge type I circuit wiring diagram Figure 4 2 Quarter Bridge Type Measuring Axial and Bending Strain 4 4 ni com Chapter 4 Theory of Operation A quarter bridge type I has the following characteristics A single active strain gauge element is mounted in the principle direction of axial or bending strain
126. m A 2 SCXI 1520 User Manual Specifications Appendix A AOCANIOe WOD TU JISIA OcGT IXOS 9u 10 AVINI ojnjosqe oy oje noqeo OL s sueos QZ SI seSe1oAe Jurod 001 10 391 ueos pue ZH QT St Sumes uprapueg 19 eUis sr J9A9uotuA O cc JO cp pue onje1eduroj o npour ou uooA1oq oouoJogirp o1jedoduio st 7 oou fuq 1 sffO x L 23upby x fiq uio x uuo oui ppe Do cc 01 I BUI ou oprsjno Yup enje1eduro Jo SI IP pn our ol 2510N WasKG 404 13 J2S fO Suipvay fo x Sulpvay 2801104 st Koe1noo ojn osqy D SE 01 T Aournooe on osqy TF 0 0 an TOF 3n 3Tl 00007 DOT 0001 3 OSTIF Spug ma pt 0 0 ad cor adc 31l 0000F TOF 0001 31 00 Z oSprrg JTeH g 0 0 an an px 3ni 00008 TOF 0001 31 000r OIF 0 0 anc 3n LF 3ni 00008F TOF 09S 3ni 000LF 08 0 0 an pF 3n ope 3l 00008 TOF 001 3l 0000r spuig 1o1enO 9 an 94 95 990J9AV urod asuey SUPLA ur asuey asplig WSO yug jutoq 001 BUIS sumy Jo Wd ules 9JEMpJEH yuq myndug euisis qeaq 9SION UI9 S S A uoneyoax3 0 2 49 uresg ajqey Asesnooy ajajduiro SCXI 1520 User Manual A 3 National Instruments Corporation Appendix A Specifications Amplifier Dynamic Filter Input impedance DC gt 1 GQ Input impedance DC powered off 5 8 kQ min Input bias current 20 nA max Input
127. m shunt calibration The shunt calibration is performed during the configuration of the global channel s Refer to the Creating a Strain Global Channel or Task section of Chapter 3 Configuring and Testing for information about shunt calibration in MAX To manually perform shunt calibration refer to the Shunt Calibration section of Chapter 4 Theory of Operation Acquiring Analyzing and Presenting After configuring the task and channels you can start the acquisition read measurements analyze the data returned and display it according to the needs of your application Typical methods of analysis include digital filtering averaging data performing harmonic analysis applying a custom scale or adjusting measurements mathematically Some custom scaling applications require the actual excitation voltage applied to the bridge instead of the nominal excitation voltage output by the SCXI 1520 You can scan the remote sense pins RSX and RSX with the DAQmx physical channels DevX pPosXx and DevX pNegx to find the actual excitation voltage Take the difference of the two physical channels to determine the actual excitation applied to the bridge and use this value in the scaling equation Note If RSX and RSX are not wired to the bridge where PX and PX connect pPosX and pNegx only measure the internal excitation Measuring this voltage does not correct for the voltage drop in the excitation leads 5 8 ni com Chapter 5 Using t
128. ments In NI DAQmx you can disable this setting through your application if you require scan rates beyond the maximum allowable with SS H engaged NI recommends leaving SS H engaged 3 Note You cannot change the simultaneous sampling mode in MAX You must use an ADE such as LabVIEW or LabWindows CVI to configure the setting using NI DAQmx Channel Property Node Refer to your ADE help file for more information Configurable Settings in MAX 3 Note Ifyou are not using an NI ADE using an NI ADE prior to version 7 0 or are using an unlicensed copy of an NI ADE additional dialog boxes from the NI License Manager appear allowing you to create a task or global channel in unlicensed mode These messages continue to appear until you install version 7 0 or later of an NI ADE This section describes where you can access each software configurable setting for modification in MAX The location of the settings varies depending on the version of NI DAQ you use Refer to either the NI DAQmx section or the Traditional NI DAQ Legacy section You also canrefer to the DAQ Getting Started Guide and the SCXI Quick Start Guide for more information on installing and configuring the hardware You also can use the DAQ Assistant to graphically configure common measurement tasks channels or scales National Instruments Corporation 3 5 SCXI 1520 User Manual Chapter 3 Configuring and Testing NI DAQmx In NI DAQmx you can configure software settings such
129. meters using the functions in Table 5 5 For additional information such as the function prototypes parameters and usage instructions for each function refer to the Traditional NI DAQ Function Reference Help installed by default in Start Programs National Instruments NI DAQ Table 5 5 Configuration Functions Function Description SCXI Reset Resets the hardware such as the specified module to its default state You also can use SCXI Reset to reset the SCXI chassis Slot 0 scanning circuitry or reset the entire chassis The SCXI 1520 default conditions are Channels configured for full bridge connection e Gain set at 1 0 10 Hz lowpass filter e Excitation set at 0 volts Shunt switches disabled Potentiometers mid ranged SCXI_Load_Config Loads the SCXI chassis configuration information you established in MAX Sets the software states of the chassis and the modules present to their default states This function makes no changes to the hardware state of the SCXI chassis or modules It is possible to programmatically change the configuration you established in MAX using the SCXI Set Config function SCXI Track Hold Setup Establishes the T H behavior of an SS H module and sets up the module for either a single channel operation or an interval scanning operation National Instruments Corporation 5 31 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Table 5 5 Configuration Funct
130. modified with this VI are not saved in the DAQ Assistant They are only available for the present session Configure Channels optional DAQmx Channel Property Node refer to the Using a DAQmx Channel Property Node in LabVIEW section for more information This step is optional if you created and fully configured the channels using the DAQ Assistant Any channel modifications made with a channel property node are not saved in the task in the DAQ Assistant They are only available for the present session Perform Offset Null Compensation Daqmx Perform Bridge Offset Nulling Calibration vi or you can perform offset null compensation when you create and configure your channels using the DAQ Assistant Refer to the Creating a Strain Global Channel or Task section of Chapter 3 Configuring and Testing for information about offset null compensation in MAX Perform Shunt Calibration You can perform shunt calibration when you create and configure your channels using the DAQ Assistant Refer to the Creating a Strain Global Channel or Task section of Chapter 3 Configuring and Testing for information about shunt calibration in MAX Start Measurement DAQmx Start Task vi Read Measurement DAQmx Read vi Analyze Data Some examples of data analysis include filtering scaling harmonic analysis or level checking Some data analysis tools are located on the Functions Signal Analysis subpalette and on the Functio
131. mux NC NI DAQ noise nonlinearity 0 offset error offset null compensation overvoltage protection National Instruments Corporation G 9 Glossary An SCXI operating mode in which analog input channels are multiplexed into one module output so that the cabled E M Series DAQ device has access to the module s multiplexed output as well as the outputs of all other multiplexed modules in the chassis multiplexer A switching device with multiple inputs that sequentially connects each of its inputs to its single output typically at high speeds in order to measure several signals with a single analog to digital converter Not Connected signal The driver software needed in order to use NI E M Series DAQ devices and SCXI components An undesirable electrical signal Noise comes from external sources such as AC power lines motors generators transformers fluorescent lights soldering irons CRT displays computers electrical storms welders radio transmitters and internal sources such as semiconductors resistors and capacitors Noise corrupts signals you are trying to measure For an amplifier a measure of the maximum output deviation from an ideal linear response in units of percent relative to full scale The ideal linear response is taken to be a straight line on a plot of measured output voltage to measured input voltage with the ends of the line connecting the extremes of the plot at the full scale limits
132. n Shunt Calibration Performing shunt calibration removes gain or amplitude errors in the measurement system Factors such as non ideal gauges incorrect strain gauge factor temperature fluctuations as well as other system variables can create these errors Refer to the Shunt Calibration section of Chapter 4 Theory of Operation for information about how to perform shunt calibration National Instruments Corporation 5 39 SCXI 1520 User Manual Specifications This appendix lists the specifications for the SCXI 1520 modules These specifications are typical at 25 C unless otherwise noted Analog Input Number of channels Voltage gain settings Input coupling Overvoltage protection Inputs protected Transfer Nonlinearity eene Gain eITOrF u aa au iain Offset error Gain 220 Gam 204 a eet dee National Instruments Corporation A 1 X1 to X1000 with the following gain settings 1 1 15 1 3 1 5 1 8 2 2 2 2 4 2 7 3 1 3 6 4 2 5 6 6 5 7 5 8 7 10 11 5 13 15 18 20 22 24 27 31 36 42 56 65 75 87 100 115 130 150 180 200 220 240 270 310 360 420 560 650 750 870 1000 DC 35 V powered on 25 V powered off lt 0 7 gt Better than 0
133. n with one on one side of the strain specimen top and the other on the opposite side bottom Rejects axial strain Compensates for temperature Compensates for the aggregate effect on the principle strain measurement due to the Poisson s ratio of the specimen material Compensates for lead resistance Sensitivity at 1000 ue is 1 3 mV out Vgx input Figure 4 13 Full Bridge Type II Circuit Diagram The following symbols apply to the circuit diagram and equations National Instruments Corporation R is an active strain gauge element measuring compressive Poisson effect ve R3 is an active strain gauge element measuring tensile Poisson effect ve 4 15 SCXI 1520 User Manual Chapter 4 Theory of Operation R is an active strain gauge element measuring compressive strain Ry is an active strain gauge element measuring tensile strain Vyyis the excitation voltage e R isthe lead resistance Vc is the measured voltage To convert voltage readings to strain units use the following equation 2V GF 1 v strain where GF is the Gauge Factor v is the Poisson s ratio To simulate the effect on strain of applying a shunt resistor across R3 use the following equation E _ 2U GF 1 v s Notes Full bridge type II is sometimes used for strain measurement of bending beams R and R are positioned along the beam axis and on opposit
134. nd E Note Chassis ground is at the same potential as earth ground when the chassis is plugged into a standard 3 prong AC outlet If PX is connected to earth ground the excitation source does not function properly Refer to the Configurable Settings in MAX section of Chapter 3 Configuring and Testing for more information about programmatically setting the excitation level in MAX For more information about programmatically setting the excitation level in NI DAQmx and Traditional NI DAQ Legacy refer to the Developing Your Application in NI DAQmx section or the Developing Your Application in Traditional NI DAQ Legacy section respectively of Chapter 5 Using the SCXI 1520 Remote Sense The excitation output buffers have negative feedback connections at the terminal block remote sense terminals RSX and RSX You can run separate wires from the bridge to these terminals so that the amplifiers obtain feedback directly from the bridge forcing bridge voltage to exactly equal the desired setting This removes unwanted DC offset in the signal and compensates for changes in lead resistance caused by temperature variation in the lead wires The SCXI 1520 excitation output circuits set the output voltage by monitoring the remote sense terminals Therefore the SCXI 1520 corrects for a voltage J x R drop in the excitation leads between the module and the bridge even if lead resistance changes with temperature You can scan the remote se
135. ng your application The default setting in NI DAQmx engages SS H s Note Referto Chapter 4 Theory of Operation for information on configuring the settings for your application using Traditional NI DAQ Legacy Creating a Strain Global Channel or Task To create a new NI DAQmx strain global task or channel complete the following steps 1 2 3 National Instruments Corporation Double click Measurement amp Automation on the desktop Right click Data Neighborhood and select Create New Select NI DAQmx Task or NI DAQmx Global Channel and click Next Select Analog Input Select Strain If you are creating a task you can select a range of channels by holding down the Shift key while selecting the channels You can select multiple individual channels by holding down the Ctrl key while selecting channels If you are creating a channel you can only select one channel Click Next Name the task or channel and click Finish In the Channel List box select the channel s you want to configure You can select a range of channels by holding down the Shift key while selecting the channels You can select multiple individual channels by holding down the Ctrl key while selecting channels Enter the specific values for your application in the Settings tab Context help information for each setting is provided on the right side of the screen Click the Device tab and select the autozero mode and lowpass filter
136. ngage or disengage the shunt calibration resistors in order to perform gain calibration In most cases you do not explicitly control the shunt calibration switches but instead allow driver software to automatically adjust them for you during the automated shunt calibration procedure However if you want to explicitly control the calibration switches you can write an application program that controls the shunt calibration switches Refer to Chapter 4 Theory of Operation for more information Note The gain adjustment is done for you automatically if you have performed shunt calibration using the NI DAQ driver Refer to the Traditional NI DAQ Legacy section and the NI DAQmx section for more information about how to perform shunt calibration using the driver 3 4 ni com Chapter 3 Configuring and Testing Modes of Operation The SCXI 1520 can operate in multiplexed mode or parallel mode Using NI DAQmx you can operate the SCXI 1520 in either multiplexed or parallel mode In Traditional NI DAQ Legacy only multiplexed mode is supported Refer to the Strain Gauge Theory section of Chapter 4 Theory of Operation for more information on multiplexed and parallel mode operation Simultaneous Sample and Hold When it is critical to measure two or more signals at the same instant in time simultaneous sample and hold SS H is required Typical applications that might require SS H include vibration measurements and phase difference measure
137. ning Bridge AT Bridge Initial Voltage Specifies in volts the output voltage of the Initial Bridge Voltage bridge in the unloaded condition Analog Input General Properties AI Bridge Balance CoarsePot Specifies by how much Signal Conditioning Bridge Balance Coarse Potentiometer Property to compensate for offset in the signal This value can be between 0 and 127 Analog Input General Properties Signal Conditioning Bridge Balance Fine Potentiometer Property AL Bridge Balance FinePot Specifies by how much to compensate for offset in the signal This value can be between 0 and 4095 Analog Input General Properties ALExcit Src Specifies the source of Signal Conditioning Excitation excitation Source Analog Input General Properties AI SampAndHold Enable Specifies whether to enable the sample and hold circuitry of the device Advanced Sample and Hold Enable s Note This is not a complete list of NI DAQmx properties and does not include every property you may need to configure your application It is a representative sample of important properties to configure for strain and Wheatstone bridge measurements For a complete list of NI DAQmx properties and more information about NI DAQmx properties refer to your ADE help file Performing Offset Null Compensation The SCXI 1520 provides offset null compensation circuitry to adjust signal voltages to proper levels when t
138. nnel Strings in NI DAQmx Use the channel input of DAQmx Create Channel to specify the SCXI 1520 channels The input control constant has a pull down menu showing all available external channels You can right click the physical channel input select I O Name Filtering and check Internal Channels This allows you to select the SCXI 1520 excitation channels The strings take one of the following forms single device identifier channel number for example SC1Mod1 ch0 e multiple noncontinuous channels for example SC1Mod1 ch0 SC1Mod1 ch4 SCXI 1520 User Manual 5 12 ni com Chapter 5 Using the SCXI 1520 multiple continuous channels for example SC1Mod1 ch0 4 channels 0 through 4 positive or negative excitation on a particular SCXI 1520 channel for example SC1Mod1 _pPos0 SC1Mod1 _pNeg0 When you have a task containing SCXI 1520 channels you can set the properties of the channels programmatically using the DAQmx Channel Property Node Follow the general programming flowchart or open an example to build a basic strain virtual channel You can use property nodes in LabVIEW to control configure and customize the NI DAQmx task and SCXI 1520 To create a LabVIEW property node complete the following steps 1 2 Launch LabVIEW Create the property node in a new Virtual Instrument VI or in an existing VI Open the block diagram view From the Functions tool bar select NI Measurements DAQmx Data Acquisition and
139. nning of a scan and reverts back to track mode at the end of a scan The signal then passes from the simultaneous sample and hold stage to the multiplexer stage The modes of operation are determined by the multiplexer stage If configured for multiplexed mode operation the multiplexer selects the conditioned analog signal from one of the 4 20 ni com Chapter 4 Theory of Operation eight channels for routing The signal is routed to the E M Series DAQ device channel 0 if the SCXI 1520 is the cabled module and or to the SCXI backplane through the SCXIbus connector If configured for parallel mode operation the signals are routed through the rear signal connector to the digitizing DAQ device The multiplexer stage is controlled by the digital interface and control circuitry The digital interface and control circuitry stores the scan list controls the multiplexer and allows flexible scanning random scanning Two other circuitry stages that are not directly in the signal path are excitation circuitry and shunt calibration switches The excitation stage is stable output with a controlled feedback loop called remote sense The remote sense signal is connected to the analog multiplexer You can scan remote sense when configured in multiplexed mode operation The shunt calibration switches are controlled by the digital interface and control circuity You must connect the SCX terminals to the bridge for shunt calibration to function correctly
140. ns All Functions Analyze subpalette SCXI 1520 User Manual ni com Chapter 5 Using the SCXI 1520 Table 5 2 Programming a Task in LabVIEW Continued Flowchart Step VI or Program Step Display Data You can use graphical tools such as charts gauges and graphs to display your data Some display tools are located on the Controls Numeric Indicators subpalette and Controls All Controls Graph subpalette Continue Sampling For continuous sampling use a While Loop If you are using hardware timing you also need to set the DAQmx Timing vi sample mode to Continuous Samples To do this right click the terminal of the DAQmx Timing vi labeled sample mode and click Create Constant Click the box that appears and select Continuous Samples Stop Measurement DAQmx Stop Task vi This VI is optional clearing the task automatically stops the task Clear Task DAQmx Clear Task vi Using a DAQmx Channel Property Node in LabVIEW s Note With the SCXI 1520 you must use property nodes to disable SS H You can use property nodes in Lab VIEW to manually configure the channels To create a LabVIEW property node complete the following steps 1 Launch LabVIEW 2 Create the property node in a new VI or in an existing VI 3 Open the block diagram view 4 From the Functions toolbox select All Functions NI Measurements DAQmx Data Acquisition and select DAQmx Channel Property
141. nse terminals The output multiplexer has input connections to the RSX and RSX terminals You can scan these terminals for monitoring and scaling purposes even if the remote sense terminals are not connected Refer to Chapter 5 Using the SCXI 1520 and Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later for more information Wire the SCXI 1520 for remote sense as shown in Figure 2 8 Remote Sense Circuit Diagram There are no configuration settings you need to change in the software s Note If you use remote sense set R to zero in the MAX configuration of the channel and in your application equations for measured strain National Instruments Corporation 4 23 SCXI 1520 User Manual Chapter 4 Theory of Operation If you leave the remote sense terminal unconnected internal 1 kQ resistors provide feedback to the buffers from the PX and PX terminals Therefore you need not install a jumper wire between RSX and PX or RSX and PX However NI recommends performing a shunt calibration to compensate for the voltage drop across lead resistance N Note NI recommends that you connect remote sense wires to the sensor directly for optimal performance Gain SCXI 1520 User Manual If you are not connecting remote sense and not performing shunt calibration you must scale the measurements to compensate for the excitation voltage drop across the lead resistance You should use the following gain a
142. nstruments Corporation 5 35 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 After you have adjusted the measurement by the appropriate calibration constants using SCXI Scale you can use a function from the NI conversion library convert h to convert a voltage or voltage buffer from a strain gauge to units of strain NI ADEs also provide many powerful analysis functions to perform digital filtering harmonic analysis averaging and complex mathematics on measurements After performing scaling and analysis on the acquired data you can display the measurements in several ways You can use any built in GUI tools in your ADE NI ADEs provide many graphical controls and indicators such as charts graphs gauges slides and plots that you can use to display the data There is also a built in function found in nidagex h called NIDAQPlotWaveform that you can use to generate a simple plot of the data Other Application Documentation and Material Refer to the ADE manual and the DAQ analog input examples that come with your application software for more detailed information on programming the SCXI modules for scanning in multiplexed mode Traditional NI DAQ Legacy CVI Examples Many example programs ship with NI DAQ For more example information on how to create tasks and channels refer to the example programs By default the example programs are installed in C v Program Files NationaliInstruments CVI 7 0 Samples More examples a
143. ntation essere rennen 1 3 Installing Application Software NI DAQ and the E M Series DAQ Device 1 5 Installing the SCXI 1520 Module into the SCXI Chassis 1 5 Connecting the SCXI 1520 in an SCXI Chassis to an E M Series DAQ Device for Multiplexed Scanning eee 1 5 Connecting the SCXI 1520 in a PXI SCXI Combination Chassis to an E M Series DAQ Device for Multiplexed Scanning 1 5 Verifying the SCXI 1520 Installation in Software sss 1 6 Installing SCXI Using NI DAQmx in Software eee 1 6 Manually Adding Modules in NI DAQmx eee 1 6 Installing SCXI Using Traditional NI DAQ Legacy in Software 1 6 Manually Adding Modules in Traditional NI DAQ Legacy 1 6 Verifying and Self Testing the Installation eene 1 6 Troubleshooting the Self Test Verification sese ene 1 7 Troubleshooting in NI DAQmx nennen nnne 1 7 Troubleshooting in Traditional NI DAQ Legacy eee 1 8 Chapter 2 Connecting Signals Connecting Bridge Sensor Signals essere 2 1 Quarter Brdge Type T 3i re e Ee deve e e eto Lese 2 1 Quarter Bridge Type IT ie e en sq ier erre deb Rene 2 2 Halt Bridse Type T see eet ete enn e e RE eR 2 4 Halt Bridge Type ien rn te
144. o each other A device that converts a physical phenomenon into an electrical signal Serial clock signal used to synchronize digital data transfers over the SER DAT IN and SER DAT OUT lines serial data input signal serial data output signal The amount of time required for a voltage to reach its final value within specified accuracy limits G 12 ni com shunt calibration signal conditioning simulated strain simultaneous sample and hold Slot 0 SLOTOSEL SPICLK spot noise STC strain gauge strain Sx SX SYNC system noise National Instruments Corporation G 13 Glossary The method of calibrating the gain of a strain gauge data acquisition channel by placing a resistor of known value in parallel with a bridge element The manipulation of signals to prepare them for digitizing A strain measurement where the change in bridge output voltage is not caused by deformation of the specimen being measured rather it is caused by temporarily connecting a known resistance in parallel with one of the bridge elements while all the strain gauges in the bridge remain unstrained A series of sample and hold circuits that are connected in a matter so as to switch modes in unison Refers to the power supply and control circuitry in the SCXI chassis Slot 0 select signal serial peripheral interface clock signal The rms noise voltage or rms noise current in a frequency band 1 Hz wide at the specified frequency
145. offset current 20 nA max CMRR DC to 60 Hz full bridge setting Gain 320 eee gt 85 dB G in lt 20 eiri gt 60 dB 0 0125 accuracy 3 us 0 006 accuracy 10 us 0 0015 accuracy 20 us Noise RTI gain 200 0 1 to 10 Hz 2 0 LV p Spot noise RTI gain 200 1000 Hz 16 nV Hz Lowpass filter type 4 pole Butterworth 24 dB octave rolloff Lowpass filter settings 10 Hz 100 Hz 1 kHz 10 kHz or bypass Bandwidth filter bypassed 3 dB at 20 kHz Simultaneous Sample and Hold SCXI 1520 User Manual Acquisition time Settle to 0 012 7 us Settle to 0 003 10 us Settle to 0 0015 50 us Hold mode settling time 1 us typ Interchannel skew 200 ns typ A 4 ni com Appendix A Specifications Intermodule skew 200 ns typ Droop tate eee 30 mV s typ 100 mV s max Stability Recommended warm up time 15 minutes Gam drft Jr en ets 40 ppm of reading C max Offset drift Gain 2202 pia hea 2 uV C typ 5 wV C max Galn 20 ederet 10 H V C typ x25 nu V C max Offset Null Compensation Ranges sete eee 4 of excitat
146. ollowing three ways module property pages in MAX virtual channels properties in MAX functions in your ADE s Note Allsoftware configurable settings are not configurable in all three ways This section only discusses settings in MAX Refer to Chapter 4 Theory of Operation for information on using functions in your application Most of these settings are available in module properties and or using virtual channels National Instruments Corporation Bridge configuration configure using module properties virtual channels properties and functions in your application Virtual channel properties override module properties The default bridge configuration for Traditional NI DAQ Legacy is quarter bridge Voltage excitation configure using module properties or virtual channel properties Virtual channel properties override module properties settings You also can set excitation through your application You can choose one of 17 voltage settings between 0 and 10 V The default voltage excitation level for Traditional NI DAQ Legacy is 2 5 V Filter bandwidth configure only using module properties You also can set bandwidth through your application The default filter bandwidth level for Traditional NI DAQ Legacy is 10 Hz Gain input signal range configure gain using module properties When you set the minimum and maximum range of the virtual channel the driver selects the best gain The default gain setting for Traditi
147. on for quarter and half bridge configurations The third switch position connects the amplifier input to a calibration voltage source inside the module for gain calibration and the fourth position grounds both inputs for offset calibration The instrumentation amplifier stage presents a very high input impedance to external signals and passes only the differential signal The offset null compensation circuitry adjusts the signal voltage by a specified offset after an offset null calibration is performed The signal from the instrumentation amplifier stage passes through a lowpass filter stage a variable gain stage another lowpass filter stage and finally a simultaneous sample and hold stage before reaching the output multiplexer for multiplex mode operation The signals S1 through S7 are also directly routed to the rear signal connector for parallel mode operation You can set the cutoff frequencies of the lowpass filter stage to one of five settings You also can bypass the filters for a maximum bandwidth of 20 kHz The variable gain stage allows you to set the gain at many discrete settings between 1 and 50 These settings along with the 1 or 20 setting of the instrumentation amplifier permit the SCXI 1520 to have 49 gain settings between 1 and 1000 The simultaneous sample and hold stage uses track and hold circuitry to perform simultaneous sampling for all channels When enabled track and hold circuitry holds the signal at the begi
148. onal NI DAQ Legacy is 100 3 9 SCXI 1520 User Manual Chapter 3 Configuring and Testing Calibration settings configure null potentiometer settings and control shunt calibration switches only using strain virtual channel or using your application The default configuration settings set the null potentiometers at their midpoint 62 for the coarse potentiometer and 2 047 for the fine potentiometer The default state of the shunt calibration switches is open This state leaves the shunt calibration resistor disconnected from the circuit Modes of operation configure only using module properties The default setting in Traditional NI DAQ Legacy is multiplexed mode Parallel mode is not supported in Traditional NI DAQ Legacy Simultaneous sample and hold settings can modify this setting only using NI DAQmx Ns Note Referto Chapter 4 Theory of Operation for information on configuring the settings for your application using Traditional NI DAQ Legacy Configuring Module Property Pages in Traditional NI DAQ Legacy 1 Right click the SCXI 1520 module you want to configure and select Properties Click General 2 Ifthe module you are configuring is connected to an E Series DAQ device select that device by using Connected to If you want this DAQ device to control the chassis confirm there is a check in the This device will control the chassis checkbox If the module you are configuring is not connected to an DAQ device
149. or more signal connection information iyi Notes The circuits in this section illustrate circuits using the SCXI 1314 terminal block If you are using the SCXI 1314T terminal block refer to the SCXI 1314T TEDS Bridge Sensor Terminal Block Installation Guide for the permitted circuit configuration diagrams Refer to Figure 2 5 and use its wiring diagram for full bridge sensors such as load force torque and pressure sensors Quarter Bridge Type This section provides information for connecting the quarter bridge strain gauge configuration type I Figure 2 1 shows the quarter bridge type I circuit wiring diagram 3 Note S is left unwired National Instruments Corporation 2 1 SCXI 1520 User Manual Chapter 2 Connecting Signals SCXI 1520 Set Bridge Configuration to Transducer SCXI 1314 Quarter Bridge R ig WA e 5 P VH P i I e g i C SCA You must connect e gj the shunt calibration wires externally using SCA I a i the terminal block e VON g Screw connections S I Figure 2 1 Quarter Bridge Circuit Diagram The following symbols apply to the circuit diagram and equations R and R are half bridge completion resistors e R is the quarter bridge completion resistor e Ry is the active element measuring tensile strain
150. ormation about using SCXI channel strings with the SCXI 1520 refer to Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later If you are measuring any other kind of bridge sensor such as a load cell pressure sensor or torque sensor and require the measurement to be displayed in units of interest for the sensor you cannot use the strain virtual channel This is because the scaling provided by the strain virtual channel returns measurements in units of microstrain u rather than the units of interest for the sensor If you require alternative scaling you can either use an analog input voltage virtual channel with a custom scale configured in MAX or SCXI channel strings and provide scaling in your LabVIEW application To perform an offset null compensation for bridge sensors such as strain gauges load cells pressure sensors or torque sensors dynamically in your LabVIEW application use the SCX Strain Null VI You can find the SCXI Strain Null VI in the function subpalette Data Acquisition Analog Input Calibration and Configuration The SCXI Strain Null VI only performs offset null compensation for SCXI channel strings not virtual channels If you want to explicitly set the potentiometers you can write an application program that adjusts the settings of many channels simultaneously or restores a particular null setting between sessions without performing a nulling operation each time To explicitly set or g
151. plications or if you are using an ADE other than an NI ADE you can use the Traditional NI DAQ Legacy C API to call functions from the DAQ driver dynamically linked library dll The Low Level DAQ Functions section outlines the steps for programming with the low level DAQ function calls If you are using LabWindows CVI or Measurement Studio you also can write advanced applications using the same low level DAQ functions guidelines Low Level DAQ Functions Ns Notes If you are anew SCXI 1520 user NI recommends that you use the NI DAQmx API rather than the Traditional NI DAQ Legacy C API NI DAQmx is the second generation data acquisition driver optimized for ease of use and improved performance You can find a complete example using Traditional NI DAQ Legacy C API functions to perform an offset null compensation and shunt calibration with the SCXI 1520 at ni com info using the code rdscaq Use this example program as a guide when developing your Traditional NI DAQ Legacy C API application You can design your SCXI 1520 application using a typical offset null compensation and offset null program flow shown in Figure 5 5 which has the following basic steps 1 Configure the system settings for the offset null compensation operation Perform offset null compensation Configure settings for the shunt calibration operation Perform shunt calibration Configure the settings for acquisition Perform the acquisition pig Uno qus
152. pter 2 Connecting Signals Remote Sense s Note NI recommends using remote sense if your application requires the improved accuracy Refer to Chapter 4 Theory of Operation for more information about using remote sense Wire the SCXI 1520 for remote sense as shown in Figure 2 8 Transducer SCXI 1314 SCXI 1520 Run Separate Wires Between Remote Sense Terminals and Bridge i Reid Prija x x x C Ora r N x x uM x Figure 2 8 Remote Sense Circuit Diagram 3 Note If you use remote sense set R to zero in the equations for measured strain e National Instruments Corporation 2 9 SCXI 1520 User Manual Chapter 2 Connecting Signals Pin Assignments SCXI 1520 User Manual The pin assignments for the SCXI 1520 front signal connector are shown in Table 2 1 The front signal connector is a special 96 pin DIN C male connector through which you make all signal connections The terminal assignments are as follows SX and SX are for analog input RSX and RSX are for remote sense PX and PX are for excitation output SCAX are for shunt calibration circuit A SCBX are for shunt calibration circuit B where X is the channel number The negative terminals are listed in Column B and the positive terminals are listed in Column C The pins labeled RSVD are reserved Do not make any connections to the RSVD pins 2 10 ni com
153. r Manual Chapter 1 About the SCXI 1520 4 Ifthe cabled module is not listed in the correct slot complete the following troubleshooting steps a If the cabled module is not listed in the correct slot and the slot is empty click the drop down listbox next to the correct slot and select the cabled module Configure the cabled module following the steps listed in the SCXI Quick Start Guide Click OK b Ifanother module appears where the cabled module should be click the drop down listbox next to the correct slot and select the cabled module A message box appears asking you to confirm the module replacement Click OK Configure the cabled module following the steps listed in the SCXI Quick Start Guide Click OK Ensure that you have the highest priority SCXI module cabled to the E M Series DAQ device Refer to the SCXI Quick Start Guide to find out which SCXI module in the chassis should be cabled to the DAQ device After checking the preceding items return to the Troubleshooting the Self Test Verification section and retest the SCXI chassis If these measures do not successfully configure the SCXI system contact NI Refer to the Technical Support Information document for contact information Troubleshooting in Traditional NI DAQ Legacy SCXI 1520 User Manual If you get the message Unable to test chassis at this time you have not designated at least one module as connected to a E Series DAQ device Refer to the Traditiona
154. r for maximum absolute accuracy 5 26 ni com Chapter 5 Using the SCXI 1520 Configure Start Acquisition and Take Readings Using Traditional NI DAQ Legacy in LabVIEW After you have performed an offset null compensation shunt calibration and configured the SCXI 1520 settings for your application you can use the intermediate analog input functions AI Config VI AI Start VI AI Read VI and AI Clear VI to create your data acquisition application You can find the intermediate data acquisition Traditional NI DAQ Legacy functions in the function subpalettes Data Acquisition Analog Input NI recommends using the intermediate analog input functions for most SCXI 1520 applications For more information about using the intermediate data acquisition Traditional NI DAQ Legacy functions refer to the LabVIEW Measurements Manual You also can use the LabVIEW Help for more detailed information about the various inputs and outputs of these functions Converting Scaling Using Traditional NI DAQ Legacy in LabVIEW The names given the strain gauge types in Chapter 4 Theory of Operation in Figure 4 3 Quarter Bridge I Circuit Diagram Figure 4 5 Quarter Bridge II Circuit Diagram Figure 4 7 Half Bridge Type I Circuit Diagram Figure 4 9 Half Bridge Type II Circuit Diagram Figure 4 11 Full Bridge Type I Circuit Diagram Figure 4 13 Full Bridge Type II Circuit Diagram and Figure 4 15 Full Bridge Type III Circuit Diagram directly correspond
155. rcuit to switch from sampling mode to hold mode and settle within a given percentage at the true hold value The difference in the true hold value and the measured hold value in a sample and hold circuit G 6 ni com HOLD TRIG Hz I O ICD ID in indirect scanning input bias current input damage level input impedance input offset current instrumentation amplifier interchannel delay interchannel skew intermodule skew National Instruments Corporation G 7 Glossary hold trigger Hertz Cycles per second of a periodic signal Input Output The transfer of data to from a computer system involving communications channels operator interface devices and or data acquisition and control interfaces See interchannel delay identifier inch or inches The measurement that occurs when a signal passes on the SCXIbus from the scanned SCXI module to the cabled SCXI module The current that flows into the inputs of a circuit The highest voltage level that you can apply to the module without damaging it The measured resistance and capacitance between the input terminals of a circuit The difference between the bias current flowing out of the input terminals SX and SX ideally is zero so that no error voltage is generated across the input due to differences in bias current A very accurate differential amplifier with a high input impedance Amount of time that passes between sampling consec
156. re installed by default in C Program Files WNational Instruments NNI DAQNExamples Traditional NI DAQ Legacy Measurement Studio Examples Many example programs ship with NI DAQ For more example information on how to create tasks and channels refer to the example programs By default the example programs are installed in C Program FilesWNationalInstruments Measurement Studio 7 0 More examples are installed by default in c Program Files National InstrumentsNNI DAQN Examples SCXI 1520 User Manual 5 36 ni com Chapter 5 Using the SCXI 1520 Calibrating the Strain System There are two types of calibration important to verifying the accuracy of a strain measurement system Device calibration ensures the accuracy of the SCXI 1520 System calibration involves removing potential error causing variables such as offset and verifying the accuracy of the strain element through shunt calibration Calibrating the SCXI 1520 The SCXI 1520 is shipped with a calibration certificate and is calibrated at the factory to the specifications described in Appendix A Specifications Calibration constants are stored inside the calibration EEPROM and provide software correction values your application development software uses to correct the measurements for offset errors in the module To obtain the highest level of accuracy you should periodically perform an internal calibration You can initiate an internal calibration using NI software For
157. rely changes the configuration in the driver memory When called the AI Start VI reads the configuration settings in the driver memory and then sends the actual control information to the SCXI 1520 module A setting established through AI Parameter VI is only valid for the LabVIEW session and does not change the setting in MAX You can use the AI Parameter VI to configure the SCXI 1520 settings shown in Table 5 4 Table 5 4 Settings for Configuring the SCXI 1520 Through the AI Parameter Allowable Settings AI Parameter VI Float In Boolean In or Value In Software Configurable Parameter Setting Name Value Data Type Values Excitation SCXI DC 17 Float In dbl 0 000 0 625 1 125 1 875 Level Voltage 2 500 3 125 3 750 5 375 Excitation 5 000 5 625 6 125 6 875 71 500 8 125 8 750 9 375 10 00 Filter Filter Setting 14 Float In dbl 0 0 disable filter 10 0 Bandwidth 100 0 1000 0 10000 0 Bridge Type SCXI 19 Value In u16 9 Quarter Bridge Connection 10 Half Bridge Type 11 Full Bridge Coarse SCXI Coarse 24 Float In dbl Any integer between 0 and Potentiometer Potentiometer 127 with 62 at mid scale Fine SCXI Fine 23 Float In dbl Any integer between 0 and Potentiometer Potentiometer 4095 with 2048 at mid scale SCXI 1520 User Manual 5 22 ni com Chapter 5 Using the SCXI 1520 Table 5 4 Settings for Configuring the SCXI 1520 Through the AI Parameter Continued
158. rmation window opens Click Yes to continue deleting the module or chassis or No to cancel this action s Note Deleting the SCXI chassis deletes all modules in the chassis All configuration information for these modules is also lost The SCXI chassis and or SCXI module s should now be removed from the list of installed devices in MAX Removing the SCXI 1520 from a Chassis Consult the documentation for the chassis and accessories for additional instructions and precautions To remove the SCXI 1520 module from a chassis complete the following steps while referring to Figure C 1 3 Note Figure C 1 shows an SCXI chassis but the same steps are applicable to a PXI SCXI combination chassis 1 National Instruments Corporation Power off the chassis Do not remove the SCXI 1520 module from a chassis that is powered on If the SCXI 1520 is the module cabled to the E M Series DAQ device disconnect the cable C 1 SCXI 1520 User Manual Appendix C Removing the SCXI 1520 3 Remove any terminal block that connects to the SCXI 1520 4 Rotate the thumbscrews that secure the SCXI 1520 to the chassis counterclockwise until they are loose but do not completely remove the thumbscrews Remove the SCXI 1520 by pulling steadily on both thumbscrews until the module slides completely out 1 Cable 5 Terminal Block 2 SCXI Module Thumbscrews 6 SCXI Chassis Power Switch 3 SOXI 1520 7 SCXI Chassis 4 Strain Gauge or W
159. rtant Information Warranty The SCXI 1520 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 exist National Instruments reser
160. rter bridge strain gauge configuration type II The quarter bridge type II measures either axial or bending strain Figure 4 4 shows how to position a strain gauge resistor in an axial and bending configurations Figure 4 5 shows the quarter bridge type II circuit wiring diagram SCXI 1520 User Manual 4 6 ni com Chapter 4 Theory of Operation Figure 4 4 Quarter Bridge Type Il Measuring Axial and Bending Strain A quarter bridge type II has the following characteristics One active strain gauge element and one passive temperature sensing quarter bridge element dummy gauge The active element is mounted in the direction of axial or bending strain The dummy gauge is mounted in close thermal contact with the strain specimen but not bonded to the specimen and is usually mounted transverse perpendicular to the principle axis of strain e This configuration is often confused with the half bridge type I configuration with the difference being that in the half bridge type I configuration the R element is active and bonded to the strain specimen to measure the effect of Poisson s ratio Completion resistors provide half bridge completion Compensates for temperature e Sensitivity at 1000 ue is 0 5 mV out Vey input s Note S and QTR are left unwired Figure 4 5 Quarter Bridge II Circuit Diagram National Instruments Corporation 4 7 SCXI 1520 User Manual Chapter 4 Th
161. rts The enclosure that houses powers and controls SCXI modules clock input signal Common Mode Rejection Ratio A measure of the ability of a differential amplifier to reject interference from a common mode signal usually expressed in decibels dB See common mode voltage Noise that appears on both inputs of a differential amplifier SCXI 1520 User Manual Glossary common mode voltage compressive strain current excitation cutoff frequency D D A D A D GND DAC DAQ DAQ D A DAQ device dB DC device SCXI 1520 User Manual Voltage that appears on both inputs of a differential amplifier Strain that results from an object being compressed has a negative value A source that supplies the current needed by a sensor for its proper operation The frequency that defines the upper end of the passband of a lowpass filter Digital to Analog Data Address See DGND D A converter An electronic device often an integrated circuit that converts a digital number into a corresponding analog voltage or current data acquisition 1 Collecting and measuring electrical signals from sensors transducers and test probes or fixtures and processing the measurement data using a computer 2 Collecting and measuring the same kinds of electrical signals with A D and or DIO boards plugged into a computer and possibly generating control signals with D A and or DIO boards in the same computer The data
162. s R is the active strain gauge element measuring compression from Poisson effect v Ry is the active strain gauge element measuring tensile strain Vey is the excitation voltage e R isthe lead resistance Vy is the measured voltage To convert voltage readings to strain units use the following equation trai 4 V 1 j SS XK SPESE or lay 2 i R where R is the nominal gauge resistance R is the lead resistance v is the Poisson s ratio GF is the Gauge Factor To simulate the effect on strain of applying a shunt resistor across R3 use the following equation _ AU _ GF 1 v 2U v 1 Notes In half bridge type I R4 is mounted along the principal axis of the stress field and Rs is mounted transverse to the axis of the stress field Use this configuration in applications where no stress exists along the axis of the transverse strain gauge Strain gauges need not have a particular STC number As shown in Figure 4 9 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short You can neglect lead resistance Rz of the wiring if shunt calibration is performed or if lead length is very short 10 ft depending on the wire gauge For example 10 ft of 24 AWG copper wire has a lead resistance of
163. s Wheatstone Bridges All strain gauge configurations are based on the concept of a Wheatstone bridge A Wheatstone bridge is a network of four resistive legs One or more of these legs can be active sensing elements Figure 4 1 shows a Wheatstone bridge circuit diagram Figure 4 1 Basic Wheatstone Bridge Circuit Diagram The Wheatstone bridge is the electrical equivalent of two parallel voltage divider circuits R and R compose one voltage divider circuit and R4 and R compose the second voltage divider circuit The output of a Wheatstone bridge is measured between the middle nodes of the two voltage dividers National Instruments Corporation 4 1 SCXI 1520 User Manual Chapter 4 Theory of Operation 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 The Wheatstone bridge configuration is used to help measure the small variations in resistance that the sensing elements produce corresponding to a physical changes in the specimen Strain Gauges Strain gauge configurations are arranged as Wheatstone bridges The gauge is the collection of all of the active elements of the Wheatstone bridge There are three types of strain gauge configurations quarter half and full bridge The number of active element legs in the Wheatstone bridge determines the kind of bridge configuration Table 4 1 shows the number of ac
164. s In multiplexed mode the CH 0 signal pair is used for sending all eight channels of the SCXI 1520 and analog signals from other modules to the connected E M Series DAQ device If the module is cabled directly to the DAQ device the other analog channels of the DAQ device are unavailable for general purpose analog input because they are connected to the SCXI 1520 amplifier outputs This means that connecting an SCXI 1180 module to the 50 pin breakout connector of the SCXI 1349 or other cable adapter assembly may cause interference and incorrect measurements when the DAQ device is cabled to the SCXI 1520 The communication signals between the DAQ device and the SCXI system are listed in Table 2 3 If the DAQ device is connected to the SCXI 1520 these digital lines are unavailable for general purpose digital I O Table 2 3 SCXI 1520 Communication Signals NI DAQmx Traditional NI DAQ SCXI Device Signal Legacy Device Pin Signal Name Name Signal Name Direction Description 24 33 DIG GND DGND DGND Digital ground these pins supply the reference for E M Series DAQ device digital signals and are connected to the module digital ground 25 SER DAT IN P0 0 DIOO Input Serial data in this signal taps into the SCXIbus MOSI line to send serial input data to a module or Slot 0 26 SER DAT OUT P0 4 DIO4 Output Serial data out this signal taps into the SCXIbus MISO line to accept serial output data from a module
165. s refer to your ADE help file Table 5 3 NI DAQmx Properties Advanced Range Low Property Short Name Description Analog Input General Properties AILRng High Specifies the upper limit Advanced Range High of the input range on the digitizer device Analog Input General Properties AI Rng Low Specifies the lower limit of the input range on the digitizer device Analog Input General Properties Advanced Sample and Hold Enable AI SampAndHold Enable Specifies whether to enable the sample and hold circuitry of the device Analog Input General Properties Signal Conditioning Bridge Configuration AI Bridge Cfg Specifies whether the sensor is a type of Wheatstone bridge Analog Input General Properties Signal Conditioning Bridge Shunt Cal Shunt Cal Enable AI Bridge ShuntCal Enable Specifies whether to place the shunt calibration resistor across one arm of the bridge SCXI 1520 User Manual ni com Chapter5 Using the SCXI 1520 Table 5 3 NI DAQmx Properties Continued Property Short Name Description Analog Input General Properties AI Bridge ShuntCal Select Specifies which Signal Conditioning Bridge Shunt Cal Shunt Cal Select calibration switch es to enable Configuration Analog Input General Properties ALExcit Src Specifies the source of Signal Conditioning Excitation excitation Source Analog Input General
166. select the type of property node you wish to configure The ActiveChan item allows you to specify what channel s you want to configure If you want to configure several channels with different properties separate the lists of properties with another Active Channels box and assign the appropriate channel to each list of properties Right click ActiveChan and select Add Element Left click the new ActiveChan box Navigate through the menus and select the property you wish to define You must change the property to read or write to either get the property or write a new value Right click the property go to Change To and select Write Read or Default Value After you have added the property to the property node right click the terminal to change the attributes of the property add a control constant or indicator To add another property to the property node right click an existing property and left click Add Element To change the new property left click it and select the property you wish to define Note Refer to the LabVIEW Help for information about property nodes and specific NI DAQmx properties National Instruments Corporation 5 13 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Text Based ADEs You can use text based ADEs such as LabWindows CVI Measurement Studio Visual Basic NET and C to create code for using the SCXI 1520 LabWindows CVI LabWindows CVI works with the DAQ Assistant in MAX to
167. set on the SCXI 1520 Use the closest corresponding value allowed by the SCXI 1520 Do the SCXI 1314 or SCXI 1314T terminal blocks contain a CJC temperature sensor No Are there any user serviceable parts inside the SCXI 1520 No There are no fuses multiturn potentiometers DIP switches slide switches socketed resistors or jumpers inside the module Disassembly of the module for any reason can void its warranty and nullify its calibration Can I use remote sense when powering a Wheatstone bridge based transducer with an external source No Remote sense uses a feedback loop and this feedback loop would be erratic since the SCXI 1520 cannot control the level of the external source National Instruments Corporation D 5 SCXI 1520 User Manual Appendix D Common Questions SCXI 1520 User Manual How do I perform external triggering using the SCXI 1520 For analog triggering use your data acquisition device analog triggering functionality through pin PFI 0 Verify that your E M Series DAQ device supports analog triggering For more information about analog triggering with the SCXI 1520 refer to the Analog Hardware Triggering using SCXI KnowledgeBase by going to ni com info and using the info code rdahtu For digital triggering use your data acquisition device digital triggering functionality through pin PFI 0 All E M Series DAQ devices support digital triggering For more information about digital triggering with the SCXI
168. sistor QTR in the terminal block National Instruments Corporation 3 1 SCXI 1520 User Manual Chapter 3 Configuring and Testing Excitation Level Excitation level is a software configurable setting that allows you to set the voltage excitation level available on PX and PX where X is a particular channel You can choose voltage excitation settings between 0 and 10 V To prevent the module from overheating do not set the excitation voltage greater than resistance connected between the excitation terminals x 29 0 mA s Note You need not include the loading effect of the internal half bridge completion resistors in the above calculation When using internal quarter bridge completion you must include the nominal gauge resistance as well as the quarter bridge completion resistance R Ry Table 3 1 shows the maximum allowable excitation voltages for standard bridge configurations and resistances Table 3 1 Excitation Voltage for Configuration and Gauge Resistances Traditional NI DAQ Configuration NI DAQmx Excitation Legacy Excitation Sensor Resistance Voltage Range Voltage Range Quarter or 120 Q lt 6 96 V 0 to 6 875 V Half Bridge 350 Q Oto 10 V 0to 10 V 1000 Q 0to 10 V 0to10 V Full Bridge or 120 Q lt 3 48 V 0 to 3 125 V Full Bridge Sensor 350 Q 0to 10 V 0to10 V 1000 Q 0to 10 V Oto 10V Filter Bandwidth Filter bandwidth is a software configurable setting that allows you
169. sive strain g is the simulated strain GF is the Gauge Factor which should be specified by the gauge manufacturer R is the nominal gauge resistance which should be specified by the gauge manufacturer R is the lead resistance If lead lengths are long R can significantly impact measurement accuracy R is the shunt calibration resistor value U is the ratio of expected signal voltage to excitation voltage with the shunt calibration circuit engaged Parameter U appears in the equations for simulated strain and is defined by the following equation _ Re U AR 2R v is the 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 is the measured voltage of the signal Vex is the excitation voltage V is the voltage ratio that is used in the voltage to strain conversion equations and is defined by the following equation V ae Vc Vex National Instruments Corporation 4 3 SCXI 1520 User Manual Chapter 4 Theory of Operation Software Scaling and Equations After you have acquired the voltage signal Vcg you can scale this voltage to the appropriate strain units in software This is done automatically for you in NI DAQmx using a strain task or strain channel and in Traditional NI DAQ Legacy using the strain virtual channel You also can scale the voltages manual
170. suring tensile strain e Vygyis the excitation voltage Rjisthe lead resistance Vo is the measured voltage s Note As shown in Figure 2 3 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short National Instruments Corporation 2 5 SCXI 1520 User Manual Chapter 2 Connecting Signals Full Bridge Type This section provides information for connecting the full bridge strain gauge configuration type I Figure 2 5 shows the full bridge type I circuit wiring diagram SCXI 1520 Set Bridge Transducer SCXI 1314 Configuration to Full Bridge x E LS ll Von _ l T P C Cis SCA i i d Shunt I i I Cal A i ymv SoA ANN f I R I Rs Figure 2 5 Full Bridge Type I Circuit Diagram The following symbols apply to the circuit diagram and equations Rjisan active element measuring compressive strain R isan active element measuring tensile strain 8 Rs3isan active element measuring compressive strain Ry is an active element measuring tensile strain Very is the excitation voltage R isthe lead resistance Voy is the measured voltage
171. t D 4 C calibration internal calibration overview 5 37 procedure for 5 37 using C based ADE 5 38 using LabVIEW 5 37 shunt calibration questions about D 4 specifications A 6 theory of operation 4 27 C based environment configuration questions D 5 internal calibration of SCXI 1520 5 38 common questions D 1 National Instruments Corporation l 1 configuration troubleshooting self test verification 1 7 configuration settings excitation level 3 2 filter bandwidth 3 2 4 25 gain 3 3 4 24 null potentiometers 3 4 connecting SCXI 1520 to DAQ device See DAQ devices conventions used in the manual iv D DAQ devices cabling restrictions with plug in E M Series DAQ devices D 3 connecting to SCXI 1520 for multiplexed scanning in PXI combination chassis 1 5 in SCXI chassis 1 5 unavailable digital lines D 2 digital settings unavailable with DAQ device connected table D 2 digital triggering D 6 documentation conventions used in the manual iv dynamic specifications A 4 E electromagnetic compatibility specifications A 8 environmental specifications A 7 excitation maximum allowable voltages table 3 2 questions about D 4 setting excitation voltage level 3 2 SCXI 1520 User Manual Index specifications A 5 theory of operation 4 22 external triggering D 6 F filters bandwidth configuration 3 2 4 25 questions about D 4 specifications A 4 front connector pin assignments tab
172. t of NI DAQmx properties Table 5 1 shows some of these properties You can use Table 5 1 to determine what kind of properties you need to set to configure the module for your application For a complete list of NI DAQmx properties refer to your ADE help file s Note You cannot adjust some properties while a task is running For these properties you must stop the task make the adjustment and re start the application Figure 5 1 assumes all properties are configured before the task is started Table 5 1 NI DAQmx Properties Property Short Name Description Analog Input General Properties ALRng High Specifies the upper Advanced Range High limit of the input range Analog Input General Properties ALRng Low Specifies the lower Advanced Range Low limit of the input range Analog Input General Properties AI Lowpass Enable Enables the lowpass Filter Analog Lowpass Enable filter of the channel National Instruments Corporation 5 5 SCXI 1520 User Manual Chapter 5 Using the SCXI 1520 Table 5 1 NI DAQmx Properties Continued Property Short Name Description Analog Input General Properties Filter Analog Lowpass Cutoff Frequency AI Lowpass CutoffFreq Specifies in hertz the frequency corresponding to the 3 dB cutoff of the filter You can specify 10 100 1000 or 10000 Analog Input General Properties Signal Conditioning Bridge Configuration
173. t values used by DAQmx but these might not be the desired values for your application For DAQ boards with a 16 bit or higher ADC 20 us was used for MSTscx and 50 us for TT SCXI 1520 User Manual Maximum Simultaneous Sample and Hold Using Traditional NI DAQ Legacy When using Traditional NI DAQ Legacy you can only use the SCXI 1520 in multiplexed mode To use parallel mode you must use NI DAQmx 4 32 ni com Chapter 4 Theory of Operation Multiplexed Mode Use the following formula to calculate the maximum SS H sample rate in multiplexed mode 1 jl NoC x Maximum of either MST yo MST cy or HT TT where SR is sample rate frequency of acquisition of all channels HT is hold time the time between holding all the SS H channels and the first A D conversion NoC is number of channels the total number of channels being sampled in the scan list SS H or not MST mo is minimum settle time of MIO inverse of maximum sample rate of the MIO also minimum interchannel delay MSTscx is minimum settle time of SCXI inverse of maximum multiplex rate of SCXI 1 333 k 3 us for 12 bit MIO 1 1000k 10 us for 16 bit MIO TT is track time the minimum time between the last AD conversion of the current scan and engaging the hold signal of SS H channels of next scan Table 4 5 shows some example values used to determine the SR using the general equation Table 4 5 Traditional NI DAQ Legacy
174. tion 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 National Instruments NI ni com and LabVIEW are trademarks of National Instruments Corporation Refer to the Terms of Use section on ni com 1egal for more information about 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 agency partnership or joint venture relationship with National Instruments
175. tive elements in each configuration Table 4 1 Strain Gauge Configurations Configuration Number of Active Elements Quarter bridge 1 Half bridge 2 Full bridge 4 Each of these configurations is subdivided into multiple configuration types The orientation of the active elements and the kind of strain measured determines the configuration type NI supports seven configuration types in software However with custom software scaling you can use all Wheatstone bridge configuration types with any NI hardware product that supports the gauge configuration type The supported strain gauge configuration types measure axial strain bending strain or both While you can use some similar configuration types to measure torsional strain NI software scaling does not support these configuration types It is possible to use NI products to measure torsional strain but to properly scale these configuration types you must create a custom scale in MAX or perform scaling in your software application This document discusses all of the mechanical electrical and scaling considerations of each strain gauge configuration type supported by NI SCXI 1520 User Manual 4 2 ni com Chapter 4 Theory of Operation Acronyms Formulas and Variable Definitions In the figures and equations in this document the acronyms formulas and variables are defined as follows is the measured strain 4 is tensile strain and is compres
176. train Very is the excitation voltage e R isthe lead resistance Voy is the measured voltage To convert voltage readings to strain units use the following equation train x 1 si strain GF R where R is the nominal gauge resistance R is the lead resistance GF is the Gauge Factor To simulate the effect on strain of applying a shunt resistor across R5 use the following equation Es 2U GF Notes Half bridge type II requires one strain gauge to undergo tensile strain while the other strain gauge undergoes compressive strain of the same magnitude This configuration is often used to measure bending strain where the strain gauges are mounted on opposite sides of a beam The strain gauges need not have a particular STC number As shown in Figure 4 7 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short You can neglect lead resistance Rz of the wiring if shunt calibration is performed or if lead length is very short 10 ft depending on the wire gauge For example 10 ft of 24 AWG copper wire has a lead resistance of 0 25 Q The nominal values of R and Ry equal R SCXI 1520 User Manual 4 12 ni com Chapter 4 Theory of Operation Full Bridge Type This section provides information for the full bridge str
177. ts of a front panel user interface and a block diagram program Channel names that can be defined outside the application and used without having to perform scaling operations A source that supplies the voltage needed by a sensor for its proper operation CN Ve X STRAINED Vg X UNSTRAINED volts root mean square G 14 ni com Glossary W W watts Wheatstone bridge A circuit arrangement consisting of four resistive elements in a diamond pattern with excitation voltage applied across two opposing terminals small resistance changes in the elements are easily detected by measuring voltage changes across the remaining two terminals working voltage The highest voltage with respect to ground that should be applied to an input terminal during normal use normally well under the breakdown voltage for safety margin Includes both the signal and common mode voltages National Instruments Corporation G 15 SCXI 1520 User Manual Index A amplifier specifications A 4 analog input specifications A 1 analog triggering D 6 block diagram 4 19 bridge completion specifications A 6 bridge configuration full bridge configuration I 2 6 4 13 full bridge configuration II 2 7 4 14 full bridge configuration III 2 8 4 16 half bridge configuration I 2 4 4 9 half bridge configuration II 2 5 4 11 overview 3 1 4 21 quarter bridge configuration I 2 1 4 4 quarter bridge configuration II 2 2 4 6 questions abou
178. tting Started Guide This document has information on installing NI DAQ and the E M Series DAQ device Install these before you install the SCXI module The SCXI Quick Start Guide This document contains a quick overview for setting up an SCXI chassis installing SCXI modules and terminal blocks and attaching sensors It also describes setting up the SCXI system in MAX National Instruments Corporation 1 8 SCXI 1520 User Manual Chapter 1 About the SCXI 1520 e The SCXI hardware user manuals Read these manuals for detailed information about signal connections and module configuration They also explain in greater detail how the module works and contain application hints Accessory installation guides or manuals Read the terminal block and cable assembly installation guides They explain how to physically connect the relevant pieces of the system Consult these guides when you are making the connections e The E M Series DAQ device documentation This documentation has detailed information about the DAQ device that plugs into or is connected to the computer Use this documentation for hardware installation and configuration instructions specification information about the DAQ device and application hints Software documentation You may have both application software and NI DAQ software documentation National Instruments NI application software includes LabVIEW LabWindows CVI and Measurement Studio After you
179. ull Bridge Type II Circuit Diagram eee cseeeeeeeeeeeeaees 4 15 Figure 4 14 Full Bridge Type III Measuring Axial and Rejecting Bending Strain esee 4 17 Figure 4 15 Full Bridge Type III Circuit Diagram e 4 17 Figure 4 16 Block Diagram of SCXI 1314 SCXI 1520 Combination 4 19 Figure 4 17 Signal During Simultaneous Sample and Hold Sampling 4 29 Figure 5 1 Typical Program Flowchart eese 5 3 Figure 5 2 LabVIEW Channel Property Node with Filtering Enabled at 10 KHz and SS H Disabled 5 12 Figure 5 3 Typical SCXI 1520 Program Flow with Traditional NI DAQ Legacy eene 5 21 National Instruments Corporation ix SCXI 1520 User Manual Contents Figure 5 4 Using the AI Parameter VI to Set Up the SCXI 1520 5 24 Figure 5 5 Offset Null and Shunt Calibration Flowchart esses 5 30 Figure C 1 Removing the SCXI 1520 usineiros ini C 2 Tables Table 1 1 Accessories Available for the SCXI 1520 o oo sss 1 2 Table 2 1 Front Signal Pin Assignments esee 2 11 Table 2 2 Rear Signal Pin Assignments sese 2 13 Table 2 3 SCXI 1520 Communication Signals eee 2 14 Table 3 1 Excitation Voltage for Configuration and Gauge Resistances 3 2
180. ultiplex rate of SCXI 1 333 k 3 us for 12 bit MIO 1 1000 k 10 us for 16 bit MIO TT is track time the minimum time between the last AD conversion of the current scan and engaging the hold signal of SS H channels of next scan Table 4 3 shows some example values used to determine the SR using the general equation SCXI 1520 User Manual 4 30 ni com Chapter 4 Theory of Operation Table 4 3 NI DAQmx Values Used to Determine Maximum Sample Rate in Multiplexed Mode DAQmx SR Device Default Required for Device Max NI DAQmx SR Maximum MIO Accuracy Sample HT MSTyro MSTscxi TT Multiplexed Accuracy Device Bits Rate S s us NoC us us t ut Hz Hz NI 6070E 12 1250000 3 8 0 8 3 Ji 32258 32258 32 0 8 3 7 9709 9709 NI 6023E 12 200000 3 8 5 3 T 22222 22222 32 5 3 7 6061 6061 NI 6221 16 250000 3 8 4 3 7 26316 5181 68 Pin 32 4 3 7 7463 1486 NI 6289 18 625000 3 8 1 6 3 7 32258 5181 32 1 6 3 7 9709 1486 These are the default values used by DAQmx but these might not be the desired values for your application For DAQ boards with a 16 bit or higher ADC 20 1s was used for MST scx and 50 Us for TT Note To use a MSTscx value that is different than the 3 Us default you must explicitly set the AI Convert Clock Rate in DAQmx Refer to your ADE help file for details on setting the AI Convert Clock Rate property Maximum SS H Sample Rates in Parallel
181. user interaction with your application in the controls subpalettes For more information about these VIs refer to the LabVIEW User Manual You also can use the LabVIEW Help for more detailed information about how to use graphical controls and indicators in your application Traditional NI DAQ Legacy in Text Based ADEs SCXI 1520 User Manual NI text based ADEs such as LabWindows CVI Measurement Studio for Microsoft Visual Basic and Measurement Studio for Microsoft Visual C offer help in the development of test and measurement applications These ADEs provide easy data acquisition data analysis graphical display and data logging tools Refer to the ADE user manual for more information about how to use these features 5 28 ni com Chapter 5 Using the SCXI 1520 The high level data acquisition tools provided in LabWindows CVI and Measurement Studio allow you to easily use virtual channels configured in MAX providing easy configuration and programming of the data acquisition systems However some of the more advanced features of the SCXI 1520 are not accessible through this easy to use API For more advanced features or for more explicit control of the programmatic attributes use the low level DAQ functions provided in the Traditional NI DAQ Legacy C API Refer to the ADE user documentation for more information about how to use the high level data acquisition tools that are provided in your NI ADE For more advanced SCXI 1520 ap
182. utive channels The interchannel delay must be short enough to allow sampling of all the channels in the channel list within the scan interval The largest difference in hold mode settling time between two sample and hold circuits on the same module The largest difference in hold mode settling time between two sample and hold circuits on different modules SCXI 1520 User Manual Glossary L line resistance lowpass filter max microstrain min MIO MIO device MISO MOSI multiplex SCXI 1520 User Manual The small but nonzero resistance of a lead wire that varies with the lead length and ambient temperature can cause measurement error if the lead wire carries excitation current A filter that passes signals below a cutoff frequency while blocking signals above that frequency meters 1 Mega The standard metric prefix for 1 million or 10 when used with units of measure such as volts and hertz 2 mega The prefix for 1 048 576 or 220 when used with B to quantify data or computer memory maximum The unit of strain measurement usually denoted by ueg one ue represents a deformation of 10 or 0 000146 1 minutes 2 minimum Multifunction I O Refers to the multifunction I O E M Series DAQ devices that have MIO or 60XX in their names Master In Slave Out signal Master Out Slave In signal To route one of many input signals to a single output G 8 ni com multiplexed mode
183. vailable for the SCXI 1520 NI does not support register level programming for the SCXI 1520 What is the power on state of the SCXI 1520 multiplexer analog bus switches and configuration settings The multiplexer analog bus switches and configuration settings are not in a known state immediately after power on All hardware settings are programmed automatically when beginning an acquisition in LabVIEW or a test panel in MAX Which accessories can I use to connect signals to the front of the SCXI 1520 module Refer to Chapter 1 About the SCXI 1520 for more information How do I control the gain excitation voltage filter setting bridge configuration potentiometer settings and shunt calibration switches from LabVIEW The gain of each SCXI 1520 channel is automatically set based on the channel limits used in setting up the acquisition You usually use the LabVIEW AI Config VI to set the channel limits If the channel limits are not explicitly set the SCXI 1520 defaults to the gain setting entered when the module was configured using MAX Refer to Chapter 3 Configuring and Testing for more information Although excitation voltage filter setting and bridge configuration are usually set using MAX you also can control or change these settings programmatically using AI Parameter VI in LabVIEW Although you usually use the SCXI Strain Null VI to adjust the electronic potentiometers for offset nulling the analog inputs to zero
184. vert voltage readings to strain units use the following equation strain where GF is the Gauge Factor To simulate the effect on strain of applying a shunt resistor across R3 use the following equation e X i GF Ns Notes Strain gauges need not have a particular STC number As shown in Figure 4 11 for greatest calibration accuracy use separate wires between the bridge and the SCA terminals Do not directly connect S or P to the SCA terminals inside the SCXI 1314 terminal block unless the strain gauge cable length is very short The nominal values of Rj Ro R5 and Ry equal A Full Bridge Type Il This section provides information for the full bridge type II strain gauge configuration The full bridge type II only measures bending strain Figure 4 12 shows how to position strain gauge resistors in a bending configuration Figure 4 13 shows the full bridge type II circuit wiring diagram SCXI 1520 User Manual 4 14 ni com Chapter 4 Theory of Operation Figure 4 12 Full Bridge Type II Rejecting Axial and Measuring Bending Strain A full bridge type II configuration has the following characteristics Four active strain gauge 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 gauge and are mounted transverse perpendicular to the principal axis of strai
185. ves 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 instructions owner s modifica
186. z channel where obx is the onboard E Series DAQ device channel with x representing a particular channel where the multiplexed channels are sent This value is 0 for DAQ device channel 0 in a single chassis system In a multichassis or remote chassis system the DAQ device channel x corresponds to chassis number n 1 where DAQ device channel x is used for scanning the nth chassis in the system scy is the SCXI chassis ID where y is the number you chose when configuring the chassis mdz is the slot position where the module is located with z being the particular slot number The slots in a chassis are numbered from left to right starting with 1 channel is the channel that is sampled from module z Use the format obx scy mdz n to verify the signal where n is a single input channel Complete the following steps to use channel strings in verifying the signal 1 Qv D dg s National Instruments Corporation Expand the list of tasks and virtual channels by clicking the next to Devices and Interfaces Click the next to Traditional NI DAQ Devices to expand the device list Right click the appropriate E Series DAQ device Click Test Panels Enter the channel string Enter the input limits 3 13 SCXI 1520 User Manual Chapter 3 Configuring and Testing T 8 Select the Data Mode Select the Y Scale Mode Refer to the LabVIEW Measurements Manual for more information and for proper formatting of
187. zation of functions seconds samples SCXI 1520 User Manual Glossary S s sample sample and hold sample rate SCA scan scan interval accuracy scan rate SCB SCXI SCXIbus Sensor SER CLK SER DAT IN SER DAT OUT settling time SCXI 1520 User Manual Samples per second Used to express the rate at which an E M Series DAQ device samples an analog signal An instantaneous measurement of a signal normally using an analog to digital converter in an E M Series DAQ device A circuit with a sample mode where the output tracks the input and a hold mode where the output remains at the last known input before switching modes The number of samples a system takes over a given time period usually expressed in samples per second Shunt Calibration terminal circuit A One or more analog samples taken at the same time or nearly the same time Typically the number of input samples in a scan is equal to the number of channels in the input group For example one scan acquires one new sample from every analog input channel in the group The minimum interchannel delay needed to achieve a given accuracy The number of scans a system takes during a given time period usually expressed in scans per second Shunt Calibration terminal circuit B Signal Conditioning eXtensions for Instrumentation Located in the rear of an SCXI chassis the SCXIbus is the backplane that connects modules in the same chassis t

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