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SCXI-1521/B User Manual

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1. T g LeS LH IXOS yoolg jeuiuue ZLEL IXOS Figure 4 4 Block Diagram of SCXI 1317 and SCXI 1521 B Combination ni com 4 6 SCXI 1521 B User Manual Chapter 4 Theory of Operation The SCXI 1521 B input terminals consist of three terminals per channel for direct connectivity to 3 wire resistive strain gauges EX connects to the voltage excitation QTR connects to the SCXI 1521 B quarter bridge completion resistor and AI connects to the SCXI 1521 B AI input amplifier Figure 4 4 shows the block diagram of the SCXI 1521 B The input amplifier stage provides amplification and presents a high input impedance to external signals The offset null compensation circuitry is used to null offset voltages that result from initial imbalances in the strain gauge bridge connection The input amplification stage is followed by an additional amplification and lowpass filter stage before reaching the output multiplexer The 5 1521 has a fixed lowpass filter with a 3 dB cutoff of 10 Hz The SCXI 1521 B has a fixed gain of 42 V V The signal then passes to the multiplexer stage The modes of operation are determined by the multiplexer stage The signal is routed to the E M Series DAQ device channel 0 if the SCXI 1521 B is the cabled module and or to the SCXI backplane through the SCXIbus connector Note 5 1521 does support parallel mode The multiplexer stage is controlled
2. SCXI 1521 B User Manual March 2006 NATIONAL 373749B 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 0 662 45 79 90 0 Belgium 32 0 2 757 00 20 Brazil 55 11 3262 3599 Canada 800 433 3488 China 86 21 6555 7838 Czech Republic 420 224 235 774 Denmark 45 45 76 26 00 Finland 385 0 9 725 725 11 France 33 0 1 48 14 24 24 Germany 49 0 89 741 31 30 India 91 80 41190000 Israel 972 0 3 6393737 Italy 39 02 413091 Japan 81 3 5472 2970 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 3390150 Portugal 351 210 311 210 Russia 7 095 783 68 51 Singapore 1800 226 5886 Slovenia 386 3 425 4200 South Africa 27 0 11 805 8197 Spain 34 91 640 0085 Sweden 46 0 8 587 895 00 Switzerland 41 56 200 51 51 Taiwan 886 02 2377 2222 Thailand 662 278 6777 United Kingdom 44 0 1635 523545 For further support information refer to the Signal Conditioning 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 2004 2006 National Instruments Corporation rights reserved
3. National Instruments Corporation Task myTask new NationalInstruments DAQmx Task myTaskName MyTask CreateStrainGageChannel SClModl ai0 System String physicalChannelName strainO0 System String nameToAssignChannel 0 001 System Double minVal 5 11 SCXI 1521 B User Manual Chapter 5 Using the SCXI 1521 B 0 001 System Double maxVal AIStrainGageConfiguration QuarterBridgeI AIStrainGageConfiguration strainGageConfiguration AIExcitationSource Internal AIExcitationSource excitationSource 3 3 Sys 2 0 Sys 0 0 Sys 120 0 3 Sys 0 0 Sys AIStrainUni cem cem cem cem cem ts S AIChannel myChannel Double excitationValue Double gageFactor Double initialBridgeVoltage 0 System Double normalGageResist Double poissonRatio Double leadWireResist train AIStrainUnits units setting attributes after the channel is created myTask AIChannels strain0 Notes You can create and configure the strain task in MAX and load it into your application with the function call NationalInstruments DAQmx DaqSystem Local LoadTask Refer to NI Measurement Studio Help for more information about creating NI DAQmx tasks in LabWindows CVI and NI DAQmx property information 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 about
4. Appendix A Specifications Excitation te ete eode Constant voltage 0 0 to 5 0 V in 1 023 steps EOT 20 mV 0 390 max Maximum output current 2 mA Load regulation open to 240 0 0896 Temperature 0 00259 30 u V C max Prot ction a iet Surge arrestors in parallel with excitation terminals shunt to ground short circuit protected Bridge Completion SCXI T52T tenons 350 Q 0 1 2 ppm C max SCXI 1521 long term stability SCXI 1521B SCXI 1521 B long term stability Shunt Calibration National Instruments Corporation 3 55 mW at 50 C 0 02 yr 120 Q 0 1 2 ppm C max 55 mW at 50 C 0 02 yr Shunt across quarter bridge completion resistor Fixed 100 kQ 0 1 10 ppm C 150 mW 15 Q max 7 5 Q typ SCXI 1521 B User Manual Appendix A Specifications Power Requirements from SCXI Backplane 18 5 to 25 VDC 170 mA min M LU EE 18 5 to 25 VDC 170 mA min H5 V ascocvessosssnctecvesvoceteceesssocteseaseosncedeeseopee 4 75 to 5 25 VDC 50 mA min Physical 3 0 cm 1 2 in gt 18 8 cm t 7 4 in gt Figure 1 SCXI 1521 B Dimensions 748 gm 26 4 oz 5 1521 User Manual 4 ni com Appendix A
5. Figure B 1 Removing the SCXI 1521 B 2 ni com Common Questions This appendix lists common questions related to the use of the SCXI 1521 B Which version of NI DAQ works with SCXI 1521 B and how I get the most current version of NI DAQ You must have NI DAQmx 7 3 or later Go to ni com and click Download Software Next click Drivers and Updates In the search field enter 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 1521 B yet I still cannot correctly test and verify that my 5 1 1521 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 that requires you to call or email a technical support representative who can often suggest 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 Signal Conditioning Technical Support Information document In NI DAQmx can I use channels of different measurement types in the same task Yes You can create channels of various measurement types programmatically in your application using create channel With NI DAQmx 7 3 or later you can create a task in MAX that has multiple measurement types Will MAX allow me to configure t
6. Important Information Warranty The SCXI 1521 and SCXI 1521B are 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 Nati
7. selection of channels 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 saved to the task configuration The next time you load the task the task uses the settings originally configured in the DAQ Assistant 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
8. 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 limit Advanced Range High of the input range Analog Input General Properties ALRng Low Specifies the lower limit Advanced Range Low of the input range Analog Input General Properties Signal Conditioning Bridge Shunt Cal Shunt Cal Enable AIL Bridge ShuntCal Enable Specifies whether to place the shunt calibration resistor across one arm of the bridge Analog Input General Properties ALExcit Val Specifies the amount of Signal Conditioning Excitation excitation in volts Value Analog Input General Properties AI Bridge NomResistance Specifies in ohms the Signal Conditioning Bridge resistance of the bridge in Nominal Resistance an unloaded condition SCXI 1521 B User Manual 5 4 ni com Table 5 1 NI DAQmx Properties Continued Chapter 5 Using the SCXI 1521 B Property Short Name Description Analog Input Strain Strain Gage Gage Factor Al StrainGage GageFactor Specifies the sensitivity of the strain gauge Analog Input Strain Strain Gage Poisson Ration Al StrainGage PoissonRatio Specifies the ratio of lateral strain to axial strain in
9. you can verify each module in the SCXI chassis To test the successful installation of each module complete the following steps 1 Verify that the chassis is powered on and correctly connected to an E M Series DAQ device 2 Launch MAX 3 Display the list of devices and interfaces by clicking the next to the Devices and Interfaces icon 4 From the list that appears locate the chassis with the module you want to test 5 Display the list of modules in the chassis by clicking the next to the chassis with the module you want to test Right click the module you want to test and select Test Panels If the Error Details box reads No Errors you have successfully installed the module The SCXI system should now 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 troubleshoot the SCXI configuration of NI DAQmx e Ifyou 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 1521 B 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 in
10. 4 RSVD QTR 22 AI22 20 3 RSVD QTR 23 AI23 2 RSVD 22 RSVD 1 RSVD EX 23 RSVD SCXI 1521 B User Manual 2 2 ni com 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 1521 B and the connected E M Series DAQ device Table 2 2 shows the rear signal connector and lists the pin assignments for the SCXI 1521 B Grounding signals AI GND and OUT REF provide reference signals needed in the various analog input referencing modes on the E M Series DAQ device National Instruments Corporation 2 3 SCXI 1521 B User Manual Chapter 2 Connecting Signals Table 2 2 Rear Signal Pin Assignments Rear Connector Diagram Signal Name Pin Number Pin Number Signal Name AI GND 1 2 AIGND 3 4 AIO 5 6 112 m 7 8 E 314 516 9 10 718 11 12 9110 13 14 11 12 13 14 15 16 m 15 16 7 18 17 18 19 20 19 20 21 22 _ 21 22 23 24 25 26 23 24 DIG GND 27 28 SER DAT IN 25 26 DAT OUT DAQ D A 27 28 31 32 33 34 SLOT 0 SEL 29 30 35 36 31 32 m 37 38 39 40 DIG GND 33 34 41 42 35 36 AI HOLD COMP AI HOLD 43 44 SER CLK 37 38 45 46 47 48 39 40 49 50 m 4
11. 5 12 shunt calibration questions about C 4 specifications A 3 theory of operation 4 9 common questions C 1 configuration troubleshooting self test verification 1 6 configuration settings excitation level 3 1 gain 3 2 null potentiometers 3 2 conventions used in the manual iv National Instruments Corporation D DAQ devices cabling restrictions with plug in E Series DAQ devices C 3 connecting to SCXI 1521 B for multiplexed scanning in PXI combination chassis 1 4 unavailable digital lines C 2 digital settings unavailable with DAQ device connected table C 2 dynamic specifications A 2 E electromagnetic compatibility specifications A 6 environmental specifications 5 excitation questions about C 4 setting excitation voltage level 3 1 specifications A 3 theory of operation 4 8 F filters questions about C 4 specifications A 2 front connector pin assignments table 2 2 5 1521 User Manual Index gain configuration 3 2 questions about C 4 installation connecting to DAQ device for multiplexed scanning in PXI combination chassis 1 4 removing SCXI 1521 B from Measurement amp Automation Explorer B 1 from SCXI chassis B 1 software installation 1 4 internal calibration See calibration L LabVIEW software questions about C 3 Macintosh operating system C 3 maximum working voltage specifications A 5 Measurement amp Automation Explorer removing SCXI 1521 B
12. B 1 self test verification troubleshooting 1 6 measurements calibrating SCXI 1521 B 5 12 pin assignments terminal assignments 2 1 multiplexed mode operation connecting to SCXI 1521 B for DAQ device in PXI combination 1 4 questions about C 3 SCXI 1521 B User Manual 1 2 N NI DAQ software C 1 3 null compensation specifications A 2 theory of operation 4 8 null potentiometers coarse and fine control codes table 4 8 configuring 3 2 questions about C 4 0 operation of SCXI 1521 B See theory of operation P physical specifications A 4 pin assignments front connector table 2 2 terminal assignments 2 1 potentiometers See null potentiometers power requirements from SCXI backplane A 4 power up state of SCXI 1521 B C 4 PXI combination chassis 1 4 0 quarter bridge configuration I 4 3 questions and answers C 1 R random scanning C 3 regulatory compliance specifications A 6 removing SCXI 1521 B from Measurement amp Automation Explorer B 1 from SCXI chassis B 1 ni com 5 safety specifications A 5 SCXI chassis installing SCXI 1521 B 1 4 removing SCXI 1521 B B 1 SCXI 1310 connector and shell assembly 1 2 SCXI 1317 terminal block C 4 SCXI 1502 dimensions figure A 4 SCXI 1521 B block diagram 4 6 calibration 5 12 common questions C 1 configuration settings 3 1 digital signals table C 2 installation 1 4 specifications A 1 taking measurements See measurements th
13. 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 3 4 ni com Chapter 3 Configuring and Testing 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 Verifying the Signal in NI DAQmx Using a Task or Global Channel Complete the following steps to verify the SCXI 1521 B signals 1 Open channel or task you created in the Creating a Strain Global Channel or Task section 2 Click the Test button National Instruments Corporation 3 5 SCXI 1521 B User Manual Theory of Operation This chapter discusses strain gauge concepts and the theory of operational measurement concepts Strain Gauge Theory This section describes how to arrange connect and scale signals from bridge based sensors especially strain gauges 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 an active sensing element 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 and R compose one voltage divider circuit and R4 and R5 compose the s
14. Null Potentiometers esses 4 8 Table 5 1 NLEDAQOmd Properties ote aba es 5 4 Table 5 2 Programming a Task in sese 5 7 Table C 1 Digital Signals on the SCXI 1521 B eee C 2 National Instruments Corporation SCXI 1521 B User Manual About the SCXI 1521 B This chapter introduces the SCXI 1521 B module and explains how to install the software and hardware Note Descriptions in this chapter explicitly refer to first channel channel 0 but these descriptions also are applicable to the remaining 23 channels The SCXI 1521 and SCXI 1521B modules are 24 channel modules for interfacing to quarter bridge strain gauges and are configured using Measurement amp Automation Explorer MAX or through NI DAQmx property nodes The SCXI 1521 has 350 Q completion resistors while the SCXI 1521B has 120 Q completion resistors The 5 1521 includes the following functionality DC voltage excitation between 0 and 5 V in 1023 steps Programmable offset nulling circuitry 10 Hz lowpass filter Analog input gain of 42 V V Software controllable shunt calibration What You Need to Get Started To set up and use the SCXI 1521 B you need the following National Instruments Corporation Hardware SCXI 1521 B module SCXI 1317 terminal block SCXI or PXI SCXI combo chassis Computer if using an SCXI chassis Cabling cable adapter and sensors as requi
15. Read Me First Safety and Radio Frequency Interference document shipped with the product for precautions to take When symbol is marked on a product it denotes a warning advising you to take precautions to avoid electrical shock When symbol is marked on a product it denotes a component that may be hot Touching this component may result in bodily injury 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 SCXI 1521 B refers to both the SCXI 1521 and SCXI 1521B module unless otherwise noted Contents Chapter 1 About the SCXI 1521 B What You Need to Get Started 1 1 National Instru
16. Specifications Maximum Working Voltage Maximum working voltage refers to the signal voltage plus the common mode voltage Channel to earth esses Input should remain within x11 V of ground Measurement Category I Channel to channel Input should remain within x11 V of ground Measurement Category I Caution Do use for measurements within Measurement Categories II or IV Environmental Operating 0 to 50 C Storage temperature 20 to 70 C H nmudity 10 to 90 RH noncondensing Maximum altitude pp 2 000 m Pollution Degree indoor use only 2 Safety The SCXI 1521 B is designed to meet the requirements of the following standards of safety for electrical equipment for measurement control and laboratory use e TEC 61010 1 EN 61010 1 e UL 61010 1 e CAN CSA C22 2 No 61010 1 Note For UL and other safety certifications refer to product label or visit ni com certification search by model number or product line and click the appropriate link in the Certification column National Instruments Corporation 5 SCXI 1521 B User Manual Appendix A Specifications Electromagnetic Compatibility EN 55011 Class at 10 Part 15A above 1 GHz 1 etri rt Rr eres EN 61326 1997 A2
17. a register level programming manual available for the SCXI 1521 B NI does not support register level programming for the SCXI 1521 B SCXI 1521 B User Manual Appendix SCXI 1521 B User Manual Common Questions Whatis the power on state of the SCXI 1521 B 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 1521 B module Refer to Chapter 1 About the SCXI 1521 B for more information How do I control the excitation voltage filter setting potentiometer settings and shunt calibration switches from LabVIEW Refer to Chapter 3 Configuring and Testing for more information What should I take into consideration when I take measurements from sensors with external excitation Set the Excitation Source Property to external and Excitation Value Property to the closest value that matches the external excitation level Does the SCXI 1317 terminal block contain a CJC temperature sensor No Are there any user serviceable parts inside the SCXI 1521 B No There are no fuses multiturn potentiometers DIP switches slide switches socketed resistors or jumpers inside the module Disassembly of the module for any rea
18. chassis When using the PXI 1011 combination chassis you can only control the SCXI modules through the backplane Parallel mode operation is not available with the PXI 1011 chassis and is not supported by the SCXI 1521 B 1 Make sure the appropriate software is already installed or install it 2 Ifthe E M Series DAQ device for controlling the SCXI system is not installed in the right most slot of the PXI 1010 combination chassis install it 3 Power on the SCXI portion of the PXI combination chassis Refer to Chapter 3 Configuring and Testing to configure the SCXI 1521 B Verifying and Self Testing the Installation To test the installation of the SCXI chassis complete the following steps 1 Verify that the chassis is powered on and correctly connected to an E M Series DAQ device 2 Launch MAX 3 Display the list of devices and interfaces by clicking the next to the Devices and Interfaces icon 4 From the list that appears locate the chassis you want to test Right click the chassis and select Test 5 Ifthe SCXI chassis is installed properly a message indicating successful verification appears Click OK The SCXI system should now operate properly with your ADE software If the test did not complete successfully refer to Chapter 3 Configuring and Testing for troubleshooting steps National Instruments Corporation 1 5 SCXI 1521 B User Manual Chapter 1 About the SCXI 1521 B If you are using NI DAQmx
19. null compensation when in MAX For more information about offset null compensation refer to the Offset Null Compensation section of Chapter 4 Theory of Operation National Instruments Corporation 5 5 SCXI 1521 B User Manual Chapter 5 5 1521 User Manual Using the SCXI 1521 B Perform Shunt Calibration Shunt calibration is a process used to obtain a gain adjust factor which corrects for system gain error You can use a strain task or global channel to perform 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 1521 B NI provides powerful analysis toolsets for each NI ADE t
20. of signal amplitude The ratio that a system attenuates signals in the stopband with respect to the passband usually defined in decibels per octave Reserved bit pin or signal Referred To Input Calculates a specification relative to the input range Seconds Samples Samples Per Second Used to express the rate at which an E M Series DAQ device samples an analog signal G 8 ni com sample sample rate scan scan rate SCXI SCXIbus sensor SER CLK SER DAT IN SER DAT OUT shunt calibration signal conditioning simulated strain Slot 0 SLOT 0 SEL SPI CLK National Instruments Corporation G 9 Glossary An instantaneous measurement of a signal normally using an analog to digital converter in an E M Series DAQ device The number of samples a system takes over a given time period usually expressed in samples per second 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 number of scans a system takes during a given time period usually expressed in scans per second 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 to each other A device that convert
21. programming the SCXI modules for scanning in multiplexed mode 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 1521 B System calibration involves removing potential error causing variables such as offset and verifying the accuracy of the strain element through shunt calibration SCXI 1521 B User Manual 5 12 ni com Chapter 5 Using the SCXI 1521 B Calibrating the SCXI 1521 B The SCXI 1521 B 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 errors in the module External Calibration Most external calibration documents for SCXI modules are available to download from ni com calibration by clicking Manual Calibration Procedures For external calibration of modules not listed there Basic Calibration Service or Detailed Calibration Service 15 recommended You can get information about both of these calibration services from ni com calibration NI recommends performing an external calibration once year Calibrating the System You should perform offset null compensation or shunt calibration on transducers in the system to impro
22. shunt calibration automatically in global channels using NI DAQmx in MAX For more information about programmatically performing shunt calibration in NI DAQmx refer to the Developing Your Application in NI DAQmx section of Chapter 5 Using the SCXI 1521 B Note 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 Modes of Operation The SCXI 1521 B operates in multiplexed mode passing the conditioned signals to the digitizing DAQ device National Instruments Corporation 4 9 SCXI 1521 B User Manual Chapter 4 Theory of Operation SCXI 1521 B User Manual 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 1521 B 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 DAQ device or SCXI chassis In multiplexed mode the SCXI 1521 B scanned channels are kept by the NI DAQ driver in a sca
23. signals to a single output 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 G 6 ni com NI DAQ noise nonlinearity 0 offset error offset null compensation overvoltage protection P passband Poisson s ratio pole port pp National Instruments Corporation G 7 Glossary 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 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
24. 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 General Properties Signal Conditioning Bridge Balance Fine Potentiometer Property AI Bridge Balance FinePot Specifies by how much to compensate for offset in the signal This value can be between 0 and 4 095 Analog Input General Properties Signal Conditioning Excitation Source ALExcit Src Specifies the source of excitation 3 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 measurements For a complete list of NI DAQmx properties and more information about NI DAQmx properties refer to your ADE help file Perform Offset Null Compensation The 5 1521 provides offset null compensation circuitry to adjust signal voltages to proper levels when the strain gauge is at rest unstrained You can use a strain task or global channel to perform offset null compensation The offset null compensation 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 offset
25. to cabled module The cabled module whose routing is controlled by the SCXI chassis routes the SCXIbus signals to device through the pin on its rear signal connector If the DAQ device scans the cabled module the module routes its input signals through the AI 0 pin on its rear signal connector to the DAQ device AI 0 4 10 ni com Using the SCXI 1521 B This chapter makes suggestions for developing your application and provides basic information regarding calibration Developing Your Application in NI DAQmx Note If you are using an ADE prior to version 7 0 using an unlicensed copy of an NI ADE or not using 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 1521 B 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 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 National Instruments Corporation 5 1 SCXI 1521 B User Ma
26. to analog Data Address Digital ground signal 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 A data acquisition device SCXI 1521 B User Manual Glossary DAQD A dB DC device differential amplifier DIN DIO drivers driver software E EEPROM EMC EMI excitation F FIFO filtering flexible scanning SCXI 1521 B User Manual The data 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 Decibel The unit for expressing a logarithmic measure of the ratio of two signal levels dB 201025 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 An amplifier with two input terminals neither of which are connected to a ground reference whose voltage difference is amplified Deutsche Industrie Norme German In
27. 1 42 43 44 45 46 SYNC 47 48 49 50 SCXI 1521 B User Manual 2 4 ni com Chapter 2 Connecting Signals In multiplexed mode the AI 0 signal pair is used for sending all 24 channels of the SCXI 1521 B and analog signals from other modules to the connected E M Series DAQ device If the module is cabled directly to the E M Series DAQ device the other analog channels of the E M Series DAQ device are unavailable for general purpose analog input because they are connected to active signals on the SCXI 1521 B amplifier Table 2 3 lists the communication signals between the E M Series DAQ device and the SCXI system If the E M Series DAQ device is connected to the SCXI 1521 B these digital lines are unavailable for general purpose digital I O Table 2 3 SCXI 1521 B Communication Signals Pin NI DAQmx SCXI Signal Device Signal Name Name Direction Description 24 33 DIG GND D GND 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 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 0 4 Output Serial data out This signal taps OUT into the SCXIbus MISO line to accept serial output data from a module 27 DAQ D A P0 1 Input Board data address line This signal taps i
28. 2001 Table 1 EMC EMII C Tick Part 15 Class Compliant Note For EMC compliance operate this device with shielded cabling CE Compliance The SCXI 1521 B meets the essential requirements of applicable European Directives as amended for CE marking as follows Low Voltage Directive safety 73 23 EEC Electromagnetic Compatibility Directive EM 89 336 EEC Note Refer to the Declaration of Conformity DoC for this product for any additional regulatory compliance information To obtain 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 1521 B User Manual A 6 ni com Removing SCXI 1521 B This appendix explains how to remove the SCXI 1521 B from MAX and an SCXI or PXI SCXI combination chassis Removing the SCXI 1521 B from MAX To remove a module from MAX complete the following steps after launching MAX 1 Display the list of installed devices and interfaces by clicking the next to the Devices and Interfaces icon 2 Click the next to NI DAQmx Devices to display the chassis 3 Click the next to the appropriate chassis to display the installed modules 4 Right click the module or chassis you want to delete and click Delete You are presented with a confirmation window Click Yes to continue deleting the module or cha
29. Input DIO 1 P0 1 27 17 Output DIO 2 P0 2 29 49 Output SCAN CLK AI HOLD 36 46 Output AI HOLD SCXI 1521 B User Manual C 2 ni com Table 6 1 Digital Signals on the SCXI 1521 B Continued Common Questions E M Series DAQ Device NI DAQmx 50 Pin 68 Pin Signal Name SCXI Signal Name Connector Connector Direction PFI 7 PFI 7 46 38 Input START SCAN AI SAMP CLK AI SAMP EXTROBE EXTROBE 37 45 Input With respect to the E M Series DAQ device National Instruments Corporation C 3 In LabVIEW can I use different input limits for the same SCXI 1521 B physical channel Yes Since the SCXI 1521 B has only one gain the same value is programmed each time Some SCXI modules permit flexible scanning Does the SCXI 1521 B module permit flexible scanning Yes Flexible scanning is described in Chapter 4 Theory of Operation Are there any cabling restrictions when using an SCXI 1521 B module with a plug in E M Series DAQ device Yes If a chassis contains an SCXI 1521 B SCXI 1520 8 1 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 Can I use the SCXI 1521 B 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
30. NG 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 AND DEATH SHOULD NOT BE RELIANT SOLELY UPON ONE FORM OF ELECTRONIC SYSTEM DUE TO THE RISK OF SYSTEM FAILURE TO AVOID DAMAGE INJURY OR DEATH THE USER OR APPLICATION DESIGNER MUST TAKE REASONABLY PRUDENT STEPS TO PROTECT AGAINST SYSTEM FAILURES INCLUDING BUT
31. 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 AN N bold italic monospace monospace bold SCXI 1521 B 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 0 lt 3 0 gt The gt symbol leads you through nested menu items and dialog box options to a final action The sequence File Page Setup Options directs you to pull down the File menu select the Page Setup item and select Options from the last dialog box This icon denotes a 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 icon is marked on the product refer to the
32. asing signal amplitude relative to noise The range of frequencies present in a signal or the range of frequencies to which a measuring device can respond 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 G 2 ni com channel chassis CLK CMRR CMV common mode voltage compressive strain current excitation cutoff frequency D D A D A D GND DAC DAQ DAQ device National Instruments Corporation 0 3 Glossary 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 ports 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 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
33. ay tools are located on the Controls Numeric Indicators subpalette and Controls 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 SCXI 1521 B User Manual 5 8 ni com Chapter 5 Using the SCXI 1521 B Using a DAQmx Channel Property Node in LabVIEW You can use property nodes in LabVIEW to manually configure the channels To create a LabVIEW property node complete the following steps Launch LabVIEW 2 Create the property node a new VI or in an existing VI 3 Open the block diagram view 4 From the Functions toolbox select Functions NI Measurements DAQmx Data Acquisition and select DAQmx Channel Property Node 5 Left click inside the box labelled Property and select Active Channels This 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 ea
34. 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 The shunt calibration circuitry is comprised of a fixed value shunt resistor in series with a switch The switch is controlled by the digital interface and control circuity When the switch is closed the shunt calibration resistor is connected in parallel with the quarter bridge completion resistor For more detailed information about the operation of any of these circuitry stages refer to the Quarter Bridge Completion Excitation Offset Null Compensation Shunt Calibration and Modes of Operation sections Quarter Bridge Completion Quarter bridge completion resistors are provided on the module The SCXI 1521 has 350 Q resistors while the SCXI 1521B has 120 Q resistors National Instruments Corporation 4 7 SCXI 1521 B User Manual Chapter 4 Theory of Operation Excitation You can set the excitation voltage of the SCXI 1521 B from 0 to 5 V in 1 023 steps The excitation voltage is buffered on a per channel basis to prevent excitation load variation errors from interfering with other channels You can set the excitation voltage in banks of six channels grouped as follows CH lt 0 5 gt CH lt 6 11 gt CH lt 12 17 gt and CH lt 18 23 gt Refer to the Configurable Settings in MAX section of Chapter 3 Configuring and Testing for more i
35. c eerte ree Pe PTS 5 10 LabWindows CVI esee 5 10 Measurement Studio Visual Basic NET and 5 11 Other Application Documentation and Material 5 12 Calibrating the Strain 5 12 Calibrating the 5 152 5 13 External Calibration ait tp eed 5 13 Calibrating the System eto os tede Ne ege 5 13 Offset Null Compensation ene 5 13 Shunt Calibration vis innen e ter er iei eee 5 13 Appendix A Specifications Appendix B Removing the SCXI 1521 B SCXI 1521 B User Manual vi ni com Contents Appendix C Common Questions Glossary Index Figures Figure 4 1 Basic Wheatstone Bridge Circuit Diagram eee 4 1 Figure 4 2 Quarter Bridge Type I Measuring Axial and Bending Strain 4 3 Figure 4 3 Quarter Bridge Type I Circuit 4 4 Figure 4 4 Block Diagram of SCXI 1317 and SCXI 1521 B Combination 4 6 Figure 5 1 Typical Program FlowWwchart eee 5 2 Figure 1 SCXI 1521 B em eene 4 Figure B 1 Removing the 5 152 0 B 2 Tables Table 1 1 Accessories Available for the 5 1521 1 2 Table 2 1 Front Signal Pin Assignments pe 2 2 Table 2 2 Rear Signal Pin Assignments pe 2 4 Table 2 3 SCXI 1521 B Communication Signals ppp 2 5 Table 4 1 Control Codes for Fine
36. ch list of properties 5 Note If you do not use Active Channels properties are set on all of channels in the task 6 Right click ActiveChans and select Add Element Left click the new ActiveChans 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 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 3 Note Refer to LabVIEW Help for information about property nodes and specific NI DAQmx properties National Instruments Corporation 5 9 SCXI 1521 B User Manual Chapter 5 Using the SCXI 1521 B Specifying Channel Strings in NI DAQmx SCXI 1521 B User Manual Use the channel input of DAQmx Create Channel to specify the SCXI 1521 B channels The input control constant has a drop down menu showing all available external channels You can right click the physical channel input select IO Name Filtering and check Internal Channels This allows you to select the SCXI 1521 B excitation channels The strings take one of the fol
37. deformation of 10 6 or 0 000146 A measure of the amount of noise seen by an analog circuit or an ADC when the analog inputs are grounded Strain that results from an object being stretched has a positive value Typical Underwriters Laboratory 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 consists 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 Vex STRAINED X UNSTRAINED G 10 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 National Instruments Corporation G 11 SCXI 1521 B User Manual Index A analog input specifications A 1 block diagram 4 6 bridge completion specifications A 3 bridge configuration overview 3 1 4 7 quarter bridge configuration I 4 3 questions about C 4 C calibration internal calibration overview
38. dustrial Standard Digital input output Software that controls a specific hardware device such as an E M Series DAQ device 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 coefficients Electromagnetic compliance Electromagnetic interference Supplying a voltage or current source to energize an active sensor or circuit 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 G 4 ni com gain gain accuracy gain Gauge Factor GF H half bridge I O ID in input impedance instrumentation amplifier National Instruments Corporation 6 5 Glossary 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 Hertz Cycles per second of a periodic signal Input Ou
39. e nter 4 1 Acronyms Formulas and Variable 4 2 National Instruments Corporation V SCXI 1521 B User Manual Contents Software Scaling and Equations sese 4 3 Quarter Bridge Type L ce tended repete 4 3 SCXI 1521 B Theory of Operation essere 4 5 Quarter Bridge Completion essent 4 7 TIE 4 8 Offset Null 4 8 Shunt Calibration ei ate etur preste ta t e 4 9 Modes of Operation need eer med erp gas 4 0 Theory of Multiplexed Mode Operation sees 4 9 Chapter 5 Using the SCXI 1521 B Developing Your Application in NI DAQmx eere eee 5 1 Typical Program 5 1 General Discussion of Typical Flow 5 3 Creating a Task Using DAQ Assistant or Programmatically 5 3 Adjusting Timing and Triggering seen 5 3 Configuring Channel Properties pp 5 4 Perform Offset Null Compensation eee 5 5 Perform Shunt 5 6 Acquiring Analyzing and Presenting 5 6 Completing the Application sese 5 6 Developing an Application Using LabVIEW sese 5 7 Using a DAQmx Channel Property Node in LabVIEW 5 9 Specifying Channel Strings in NI DAQmx 5 10 Text Based ADES is
40. e with Excitation NI DAQmx Task or NI DAQmx Global Channel cannot adjust calibration settings in MAX Adjust calibration settings in your application The default configuration settings set the fine null potentiometer to 2 048 which is its midrange value The default state of the shunt calibration switches is open This state leaves the shunt calibration resistor disconnected from the circuit Modes of operation refer to Chapter 1 About the SCXI 1521 B for more information about chassis installation The default setting in NI DAQmx is multiplexed 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 Launch MAX Right click Data Neighborhood and select Create New Select NI DAQmx Task or NI DAQmx Global Channel and click Next Select Analog Input 3 8 SCXI 1521 B User Manual Chapter 3 Configuring and Testing 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 box labelled Channel List select the channel s you want to configure You can select a range of channels by holding down t
41. econd voltage divider circuit The output of a Wheatstone bridge is measured between the middle nodes of the two voltage dividers A physical phenomenon such as a change in strain or temperature applied to a specimen changes the resistance of the sensing elements in the National Instruments Corporation 4 1 SCXI 1521 B User Manual Chapter 4 Theory of Operation Wheatstone bridge The Wheatstone bridge configuration is used to help measure the small variations in resistance that the sensing elements produce in response to a physical changes in the specimen Acronyms Formulas and Variable Definitions In the figures and equations in this document the acronyms formulas and variables are defined as is the measured strain e is tensile strain and 8 is compressive 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 is the lead resistance If lead lengths are long can significantly affect 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 R U 4R 2R v is the Poisson s ratio defined as the negative ratio of transverse s
42. ed Vgy To convert voltage readings to strain units use the following equation 4AV 1 R t GENE R where R is the nominal gauge resistance of the sensor Rz is the lead resistance GF is the Gauge Factor 4 4 ni com Chapter 4 Theory of Operation To simulate the effect on strain of applying a shunt resistor across R3 use the following equation ON 5 GF 1 4U hy Notes minimize temperature drift errors the strain gauge must have a self temperature compensation STC number that corresponds to the 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 You can neglect lead resistance 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 of24 AWG copper wire has a lead resistance of 0 25 Q SCXI 1521 B Theory of Operation This section includes a brief overview and a detailed discussion of the circuit features of the
43. eory of operation excitation 4 8 null compensation 4 8 shunt calibration 4 9 self test verification troubleshooting 1 6 C 1 shunt calibration questions about C 4 specifications A 3 theory of operation 4 9 signal connections digital signals table C 2 front connector pin assignments table 2 2 software application development environments supported 1 4 installation 1 4 NI DAQ version required C 1 specifications analog input A 1 bridge completion A 3 dynamic A 2 electromagnetic compatibility A 6 National Instruments Corporation F3 Index environmental A 5 excitation A 3 filter A 2 maximum working voltage A 5 null compensation A 2 physical A 4 power requirements from SCXI backplane A 4 regulatory compliance A 6 safety A 5 shunt calibration A 3 stability A 2 transfer A 1 stability specifications A 2 strain gauge connections quarter bridge configuration I 4 3 T taking measurements See measurements 96 terminal block 1 2 theory of operation block diagram 4 6 excitation 4 8 null compensation 4 8 shunt calibration 4 9 transfer specifications A 1 troubleshooting incorrect test and verification C 1 questions and answers C 1 self test verification 1 6 V verifying and self testing the configuration troubleshooting 1 6 C 1 SCXI 1521 B User Manual
44. er calibration pe 0 1 reading Before calibration 4 096 of reading max Input offset error pp 7 mV max mV typ 1 This is the error after software correction Gain error is taken into account in the software correction coefficients stored in the onboard EEPROM These constants are applied automatically when using NI DAQmx This is the error before software calibration National Instruments Corporation A 1 SCXI 1521 B User Manual Appendix A Specifications Dynamic Filter Stability Minimum scan interval per channel 0 012 accuracy 3us 0 00690 accuracy 10 us 0 001590 accuracy 20 us Noise RTI 0 1 10 10 HZ eee es 2 5 utet ett rms 1 UV 1 MHz bandwidth Lowpass filter type 2 pole Butterworth 12 dB octave rolloff 3 dB bandwidth esses 10 Hz Recommended warm up time 30 minutes 11 ppm C max 4 ppm C typ Offset drift cene es 3 wV C max 1 uV C typ Offset Null Compensation ei 0 45 of excitation voltage Resolution et 4 096 counts of resolution 9 600 ue offset null compensation range 4 4 resolution for GF 2 0 1 Includes excitation voltage noise contribution SCXI 1521 B User Manual A 2 ni com
45. figuration of these settings for the SCXI 1521 B in NI DAQmx For more information about 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 1521 B 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 easily configure the bridge type The SCXI 1521 B only supports the quarter bridge I strain gauge bridge configuration Excitation Level Excitation level is a software configurable setting that allows you to set the excitation voltage level of the module You can choose voltage excitation settings between 0 and 5 V in 1 023 increments Refer to Appendix A Specifications for more information about the excitation voltage settings on the SCXI 1521 B National Instruments Corporation 3 1 SCXI 1521 B User Manual Chapter 3 Configuring and Testing Gain Input Range Gain input range is a software configurable setting that allows you to choose the appropriate amplification for your application The SCXI 1521 B has a fixed gain of 42 V V Additional gain settings available on the digitizer device In most applications NI DAQmx selects the gain for you based on the
46. he Shift key while selecting the channels You can select multiple individual channels by holding down the Ctrl key while selecting channels Note To add channels from another module measuring strain first complete task creation for one module and then in the Channel List select the to add channels to the strain task Add the additional channels to your task To add channels of various measurement types to the same task you must complete this task in your application Refer to the Developing Your Application in NI DAQmx section of Chapter 5 Using the SCXI 1521 B for more information about adding channels 9 10 11 12 13 SCXI 1521 B User Manual 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 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 On the screen that opens choose to enable offset nulling and or shunt calibration Enter the shunt calibration resistor information Click Next 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
47. iguration 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 Bending Figure 4 2 Quarter Bridge Type Measuring Axial and Bending Strain A quarter bridge type I has the following characteristics e single active strain gauge element is mounted in the principle direction of axial or bending strain A passive quarter bridge completion resistor dummy resistor is required in addition to half bridge completion National Instruments Corporation 4 3 SCXI 1521 B User Manual Chapter 4 Theory of Operation SCXI 1521 B User Manual e Temperature variation in specimen decreases the accuracy of the measurements e Sensitivity at 1000 where 2 0 is 0 5 mV out Vgy input Figure 4 3 Quarter Bridge Type I Circuit Diagram The following symbols apply to the circuit diagram and equations R and are half bridge completion resistors R is the quarter bridge completion resistor dummy resistor is the active strain gauge element measuring tensile strain Vex is the excitation voltage R is the lead resistance is the measured voltage 15 the voltage ratio that is used the voltage to strain conversion equations and is defined by the following equation r y cii strain
48. lowing forms e Single device identifier channel number for example SC1Mod1 ch0 e Multiple noncontinuous channels for example SC1Mod1 ch0 SC1Mod1 ch4 e Multiple continuous channels for example SC1Mod1 ch0 4 channels 0 through 4 e Excitation on a particular SCXI 1521 B channel for example SC1Mod1 _Vex0 SC1Mod1 Vex1 Once you have a task containing SCXI 1521 B channels you can set the properties of the channels programmatically using the DAQmx Channel Property Node 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 1521 B LabWindows CVI LabWindows CVI works with the DAQ Assistant in MAX to 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 DAQmx strain task following the instructions in the Creating a Strain Global Channel or Task section 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 5 10 ni com Chapter 5 Using SCXI 1521 B property of the channel
49. ments 1 3 Installing the Application Software NI DAQ and Device 1 4 Installing the SC XI 52 i diee tenete hrec eR 1 4 Connecting the SCXI 1521 B to an E M Series DAQ Device for Multiplexed Scanning a PXI SCXI Combination Chassis 1 4 Verifying and Self Testing the Installation eee 1 5 Troubleshooting the Self Test Verification et 1 6 Chapter 2 Connecting Signals Pin ASSIS melts see ere aee tte ee de peers rer Poen rete due e ea deg 2 1 Chapter 3 Configuring and Testing SCXI 1521 B Software Configurable Settings eee 3 1 Common Software Configurable Settings pe 3 1 Bridge 3 1 Excitation Leyeh iuit ee Cote eee 3 1 Gain Inp t Range 2 tette eit ep 3 2 Fine Null Potentiometer eese 3 2 Shunt Calibration Switches pe 3 2 Modes of Operation tate tege etd 3 2 Configurable Settings in 3 2 NEDAQMX n e ecrit 3 3 Creating a Strain Global Channel or 3 3 Verifying the Signal etie euh aere 3 5 Verifying the Signal in NI DAQmx Using a Task or Global Channel 3 5 Chapter 4 Theory of Operation Stram Gauge Theoty uei ett tt pb deep ceed t tp de pedis 4 1 Wheatstone Bridg
50. module Refer to Figure 4 4 while reading this section National Instruments Corporation 4 5 SCXI 1521 B User Manual Theory of Operation Chapter 4 SCXIbus Connector IonuoD pue Iel6Iq lt sng Ves Rear Signal Connector Jeyng c YLO eos Duiuonipuo jeubis IV 205167 60 E c 1 uoesueduoD 9 1 IN 255 5 f eas 295 1 non Ww S HlO i 10 SIS H reg nys ZH OL SIV ules 1 i 9X3 1 y 2 S euiuue L n 5 5 9195 iL t 2 1 04000 Eas 1 5 8 6 8 5 y W me reo junus 1 5 2 81 36 2 2 81 xa ZH 8110 RIES D gt s 0 N3SI lt 6 0 1 5 x3 gino 1 1 Butuonipuo jeubis
51. n 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 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 scanned SCXI 1521 B module is not directly cabled to the DAQ device the module sends its signals through the SCXIbus
52. nformation about programmatically setting excitation level in MAX For more information about programmatically setting excitation level in NI DAQmx refer to the Developing Your Application in NI DAQmx section of Chapter 5 Using the SCXI 1521 B Offset Null Compensation The SCXI 1521 B provides hardware offset null compensation that removes the offset voltage that exists in the strain gauge when it is unstrained to adjust signal voltages to proper levels Hardware offset nulling is performed programmatically using software The fine null potentiometer is used for offset adjustments The potentiometer signals are 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 potentiometer is a voltage proportional to the excitation voltage setting Therefore if the excitation voltage changes by a small amount due to a changes such as temperature and sensor loading the correction signal produced by the fine null potentiometer changes by the same amount and the offset null is maintained The fine null potentiometer is controlled digitally using control codes The control codes of the fine null potentiometer are set in software using integer values Table 4 1 summarizes the nulling range and scale of the control codes Table 4 1 Control Codes for Fine Null Potentiometers Range Integer Values Mid Scale Bridge Offset Nulling 0 to 4 095 2 048 0 45
53. nto the SCXIbus D A line to indicate to the module whether the incoming serial stream is data or address information 29 SLOT 0 SEL P0 2 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 National Instruments Corporation 2 5 SCXI 1521 B User Manual Chapter 2 Connecting Signals Table 2 3 5 1521 Communication Signals Continued NI DAQmx SCXI Signal Device Signal Pin Name Name Direction Description 36 SCAN CLK AI HOLD COMP Input Scan clock A rising edge AI HOLD 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 EXTROBE Input Serial clock This signal taps into the SCXIbus SPI CLK line to clock the data on the MOSI and MISO lines SCXI 1521 B User Manual 2 6 ni com Configuring and Testing This chapter describes how to configure SCXI 1521 B for use with NI DAQmx It also describes how to create and test a virtual channel global channel and or task SCXI 1521 B Software Configurable Settings This section describes how to set the voltage excitation level 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 con
54. nual Chapter 5 Using the SCXI 1521 B Yes Create Task Using No DAQ Assistant Y Create a Task Programmatically Create Strain or Custom Voltage with Excitation Channel Hardware Timing Triggering Create Task in DAQ Assistant or MAX Create Another Channel Further Configure Channels Adjust Timing Settings Configure Channels Bridge Null Yes Analyze Data Operation po Process Data Display Data Graphical Display Tools Shunt Calibration Operation y Start Measurement Continue Sampling Read Measurement Stop Measurement Clear Task Figure 5 1 Typical Program Flowchart SCXI 1521 B User Manual 5 2 ni com Chapter 5 Using the SCXI 1521 B General Discussion of Typical Flow Chart 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 DAQ 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
55. o 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 5 6 ni com Chapter 5 Using the SCXI 1521 B 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 1521 B If you need more information or for further instructions select Help VI Function amp How To Help from the LabVIEW menu bar iyi Note Except where otherwise stated the VIs in Table 5 2 are located on the Functions Functions NI Measurements DAQmx Data Acquisition subpalette and accompanying subpalettes in LabVIEW Table 5 2 Programming a Task in LabVIEW Flowchart Step o
56. of Vex SCXI 1521 B User Manual 4 8 ni com Chapter 4 Theory of Operation In most cases you do not explicitly set the fine null potentiometer but instead allow the NI DAQ driver software to automatically adjust it 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 refer to the Developing Your Application NI DAQmx section of Chapter 5 Using the SCXI 1521 B Shunt Calibration Shunt calibration is a process used to obtain a gain adjust factor which is used to correct for system gain error 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 gain adjust factor simulated signal level measured signal level with shunt resistor engaged The gain adjust factor is then multiplied by each future measurement to obtain accurate measurements that are adjusted for gain errors Refer to the Configurable Settings in MAX section of Chapter 3 Configuring and Testing for more information about performing
57. on the hardware and software in the system Use the manuals you have as follows National Instruments Corporation SCXI or PXI SCXI chassis manual Read this manual for maintenance information about the chassis and for installation instructions The DAQ Getting Started Guide This document has information about 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 The SCXI hardware user manuals Read these manuals next 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 manuals If you are using accessory products 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 The Series device documentation This documentation has detailed information about the E M Series DAQ device that plugs into or is connected to the computer Use this documentation for hardware installation and configuration instructions specification information about the E M Series DAQ device and ap
58. onal Instruments reserves the right to make changes to subsequent editions of this document without prior notice to holders of this edition The reader should consult National Instruments if errors are suspected In no event shall National Instruments be liable for any damages arising out of or related to this document or the information contained in it EXCEPT AS SPECIFIED HEREIN NATIONAL INSTRUMENTS MAKES NO WARRANTIES EXPRESS OR IMPLIED AND SPECIFICALLY DISCLAIMS ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE CUSTOMER S RIGHT TO RECOVER DAMAGES CAUSED BY FAULT OR NEGLIGENCE ON THE PART OF NATIONAL INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER NATIONAL INSTRUMENTS WILL NOT BE LIABLE FOR DAMAGES RESULTING FROM LOSS OF DATA PROFITS USE OF PRODUCTS OR INCIDENTAL OR CONSEQUENTIAL DAMAGES EVEN IF ADVISED OF THE POSSIBILITY THEREOF This limitation of the liability of National Instruments will apply regardless of the form of action whether in contract or tort including negligence Any action against National Instruments must be brought within one year after the cause of action accrues National Instruments shall not be liable for any delay in performance due to causes beyond its reasonable control The warranty provided herein does not cover damages defects malfunctions or service failures caused by owner s failure to follow the National Instruments installation operation or maintenance instructions o
59. output of a strain gauge bridge when no strain is applied Maximum voltage that does not cause hardware damage The range of input frequencies that are passed to the filter output without attenuation 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 A digital port consisting of multiple I O lines on a E M Series DAQ device Peak to peak SCXI 1521 B User Manual Glossary ppm PXI Q QTR quarter bridge quarter bridge completion resistor rms rolloff RSVD RTI S S s SCXI 1521 B User Manual Parts per million PCI eXtensions for Instrumentation An open specification that builds on the CompactPCI specification by adding instrumentation specific features 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 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
60. p 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 in your task 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 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 Functions All Functions Analyze subpalette Display Data You can use graphical tools such as charts gauges and graphs to display your data Some displ
61. plication 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 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 1 8 SCXI 1521 B User Manual Chapter 1 About the SCXI 1521 B The Start Programs National Instruments NI DAQ NI DAQmx Help files for software information e 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 Installing the Application Software NI DAQ and the 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 1521 B NI DAQmx 7 3 or later is required to configure and program the SCXI 1521 B module If you do not have NI DAQmx 7 3 or later you can either contact an NI sales representative to request it on a CD or download the latest NI DAQ version from com Installing the SCXI 1521 B 5 Note Refer to the Read Me Firs
62. programmatically use the DAQmxSetChanAttribute function 5 Note Refer to NJ LabWindows CVI Help for more information about creating NI DAQmx tasks in LabWindows CVI and NI DAQmx property information Measurement Studio Visual Basic NET and 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 1521 B You can use the same functions for Visual Basic and Create a new task with the channel object In this example an analog input channel object is used since reading the voltage from a Wheatstone bridge configuration is an analog input operation The following text is a function prototype example void AIChannelCollection CreateStrainGageChannel System String physicalChannelName System String nameToAssignChannel System Double minVal 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 modify the following example code or the code from one of the shipping examples as needed to suit your application
63. r Program Step Create Task in DAQ Assistant Create a DAOmx 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 DAQmx Create Task vi tThis Vl is optional if you created Programmatically and configured your task using the DAQ Assistant However if optional you use it in LabVIEW any changes you make to the task will not be saved to a task in MAX Create AI Strain Channel DAQmx Create Virtual Channel vi AI Voltage by default optional to change to a strain gauge channel click AI Voltage and select Analog Input Strain Strain Gage This VI is optional if Or you created and configured your task and channels using the Create AI Custom Voltage DAQ Assistant Any channels created with this VI are not saved with Excitation Channel in the task in the DAQ Assistant they are only available for the present session Adjust Timing Settings DAQmx Timing vi Sample Clock by default This VI is optional optional if you created and configured your task using the DAQ Assistant Any timing settings modified with this VI are not saved in the task in the DAQ Assistant they are only available for the present session National Instruments Corporation 5 7 SCXI 1521 B User Manual Chapter 5 Using the SCXI 1521 B Table 5 2 Programming a Task in LabVIEW Continued Flowchart Step VI or Program Ste
64. red for your application 1 1 SCXI 1521 B User Manual Chapter 1 About the SCXI 1521 B Software NI DAQmx 7 3 or later of the following software packages e LabVIEW LabWindows CVI Documentation A Read Me First Safety and Radio Frequency Interference Getting Started Guide SCXI Quick Start Guide SCXI 1521 B User Manual SCXI 1317 Terminal Block Installation Guide Documentation for your software The optional accessories listed in Table 1 1 are available for the SCXI 1521 B Table 1 1 Accessories Available for the SCXI 1521 B Accessory Description 5 1317 Screw terminal block Mounts on front of the SCXI 1521 B module and provides easy access to the terminal for field wiring connections SCXI 1310 Connector and shell assembly 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 SCXI 1521 B User Manual 1 2 ni com Chapter 1 About the SCXI 1521 B National Instruments Documentation The SCXI 1521 B User Manual is one piece of the documentation set for data acquisition DAQ systems You could have any of several types of manuals depending
65. ridge completion resistor e X connects to the amplifier terminal The pins labeled RSVD are reserved Do not make any connections to these pins National Instruments Corporation 2 1 SCXI 1521 B User Manual Chapter 2 Connecting Signals Table 2 1 Front Signal Pin Assignments Front Connector Diagram Pin Number Column A Column B Column C 32 EX 0 QTR 0 AIO 31 1 QTR 1 Column 30 EX 2 QTR 2 A B 29 EX 3 QTR 3 AI3 ge 28 RSVD QTR4 14 31 27 RSVD QTR 5 15 20 26 RSVD EX 4 RSVD 298 0 25 RSVD 5 RSVD ae wm 24 EX 6 QTR 6 AI6 26 23 EX 7 QTR 7 AI7 210 22 8 QTR 8 AI8 23 0 21 9 QTR 9 AI9 2 20 RSVD QTR 10 AI10 21 19 RSVD QTR 11 20 48 5 18 RSVD EX 10 RSVD 18 17 RSVD EX 11 RSVD 16 12 QTR 12 AT 12 16 15 13 QTR 13 AI 13 15 14 14 QTR 14 AI 14 13 13 15 QTR 15 115 1210 12 RSVD QTR 16 AI 16 11 RSVD QTR 17 17 10 10 RSVD 16 RSVD o o 9 RSVD 17 RSVD 7 8 18 QTR 18 AI18 7 19 QTR 19 AI 19 5 6 EX 20 QTR 20 120 4 o He 6 D 5 EX 21 21 AI 21 2 o
66. s 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 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 Refers to the power supply and control circuitry in the SCXI chassis Slot 0 select signal Serial peripheral interface clock signal SCXI 1521 B User Manual Glossary STC strain gauge strain system noise T tensile strain typ U UL VDC VI virtual channels voltage excitation V 5 1521 User Manual 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
67. son voids its warranty and nullify its calibration C 4 ni com Glossary Symbol Value u micro 10 6 milli 10 3 k kilo 103 M mega 106 G giga 109 Numbers Symbols Percent Positive of or plus Negative of or minus Plus minus lt Less Degree Strain 5 Simulated strain V Poisson s ratio Q Ohms 5 V signal 5 VDC source signal National Instruments Corporation G 1 SCXI 1521 B User Manual Glossary A A A D absolute accuracy AC ADC ADE Al AI GND AI HOLD COMP AI HOLD amplification bandwidth bridge completion resistors Butterworth filter CE 5 1521 User Manual 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 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 LabVIEW LabWindows CVI Visual Basic C and C Analog input Analog input ground signal Scan clock signal used to increment to the next channel after each E M Series DAQ device analog to digital conversion A type of signal conditioning that improves accuracy in the resulting digitized signal by incre
68. specified input range Fine Null Potentiometer The fine null potentiometer has software configurable settings that allow you to remove unwanted offset voltage In most cases you do not explicitly set the fine null potentiometer but instead allow driver software to automatically adjust it for you However if you want to explicitly set the fine null potentiometer you can write an application program that adjusts the fine null potentiometer settings Refer to Chapter 4 Theory of Operation for more information Shunt Calibration Switches The SCXI 1521 B includes a software controllable shunt calibration switch on each channel of the module that is used to engage or disengage a fixed shunt calibration resistor Sy Note The gain adjustment is done for you automatically if you have performed shunt calibration using the NI DAQ driver Refer to the N DAQmx section for more information about how to perform shunt calibration using the driver Modes of Operation The SCXI 1521 B operates in multiplexed mode only Configurable Settings in MAX Note If you are using NI ADE prior to version 7 0 are using an unlicensed copy of NI ADE or are not using 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 SCXI 1521 B User Manual This section describes where
69. ssis or No to cancel this action hy 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 1521 B from a Chassis Consult the documentation for the chassis and accessories for additional instructions and precautions To remove the SCXI 1521 B module from a chassis complete the following steps while referring to Figure B 1 Note Figure B 1 shows an SCXI chassis but the same steps are applicable to a PXI SCXI combination chassis 1 Power off the chassis Do remove the SCXI 1521 B module from a chassis that is powered on 2 If the SCXI 1521 B is the module cabled to the Series device disconnect the cable National Instruments Corporation B 1 SCXI 1521 B User Manual Removing 5 1521 terminal block that connects to 5 1521 Rotate thumbscrews that secure SCXI 1521 B to chassis counterclockwise until they are loose but do not completely remove the thumbscrews Remove the SCXI 1521 B by pulling steadily on both thumbscrews until the module slides completely out Cable SCXI Module Thumbscrews SCXI 1521 B Strain Gauge RON 5 Terminal Block 6 SCXI Chassis Power Switch 7 SCXI Chassis SCXI 1521 B User Manual
70. stalled in the chassis Make sure the cable between the SCXI chassis and E M Series DAQ device is properly connected nspect the cable connectors for bent pins SCXI 1521 B User Manual 1 6 ni com Chapter 1 About the SCXI 1521 B Make sure you are using the correct NI cable assembly for your application Test the E M Series DAQ device to verify it is working properly Refer to the E M Series DAQ device help file for more information e Ifyou 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 XXXX or 1521 B hardware in chassis is SCXI YYYY 1521 B or Empty complete the following troubleshooting steps to correct the error 1 Expand the list of NI DAQmx devices by clicking 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 4 Ifthe cabled module is not listed in the correct slot complete the following troubleshooting steps a Ifthe 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 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 bo
71. t Radio Frequency Interference document before removing equipment covers or connecting or disconnecting any signal wires Refer to the SCXI Quick Start Guide to unpack and install the SCXI 1521 B in an SCXI chassis After installing the SCXI 1521 B power on the SCXI chassis Connecting the SCXI 1521 B to an E M Series DAQ Device for Multiplexed Scanning in a PXI SCXI Combination Chassis In this configuration you can multiplex all 24 channels of the SCXI 1521 B into a single channel of the E M Series DAQ device in the right most slot using the PXI backplane in a PXI SCXI combination chassis Consult the PXI SCXI chassis documentation the documentation of other SCXI modules and E M Series DAQ device documentation for additional instructions and cautions You should have already installed your software SCXI 1521 B User Manual 1 4 ni com Chapter 1 About the SCXI 1521 B and inserted the SCXI 1521 B module and any other SCXI modules in the chassis according to the instructions in the SCXI Quick Start Guide To use the SCXI 1521 B module in multiplexed mode with an E M Series DAQ device in a PXI SCXI combination chassis complete the following steps Notes No cables required between SCXI 1521 B and Series device if the E M Series DAQ device is installed in the right most PXI slot You can configure this device to control the SCXI system using an internal bus that connects the PXI chassis to the SCXI
72. the DAQ Assistant you can still modify the timing properties of the task programmatically in your application When programmatically adjusting timing settings you can set the task to acquire continuously acquire a buffer of samples or acquire one point at a National Instruments Corporation 5 8 SCXI 1521 B User Manual Chapter 5 Using SCXI 1521 B 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 can also 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 ADEs used to configure the SCXI 1521 B access an underlying set 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 Note You cannot adjust some properties while a task is running For these properties
73. to 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 the NI DAQmx section for more information about setting locations 3 2 ni com NI DAQmx Chapter 3 Configuring and Testing 5 Note software configurable settings are not configurable both ways This section only discusses settings in MAX Refer to Chapter 4 Theory of Operation for information about using functions in your application Strain and custom voltage with excitation are the most commonly used NI DAQmx task or NI DAQmx Global Channel types with the SCXI 1521 B The following list describes the settings you can use in MAX and where they are located Voltage excitation configure using either NI DAQmx Task or NI DAQmx Global Channel You can also set the voltage excitation level through your application In NI DAQmx you can choose from contiguous voltages between 0 and 5 V The default voltage excitation in NI DAQmx is 0 V 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 Calibration settings fine null potentiometer settings and control shunt calibration switches only using Strain NI DAQmx Task Strain NI DAQmx Global Channel or your application The Custom Voltag
74. tput The transfer of data to from a computer system involving communications channels operator interface devices and or data acquisition and control interfaces Identifier Inch or inches The measured resistance and capacitance between the input terminals of a circuit A very accurate differential amplifier with a high input impedance SCXI 1521 B User Manual Glossary L line resistance lowpass filter max maximum working voltage microstrain min MISO MOSI multiplex multiplexed mode SCXI 1521 B 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 106 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 highest voltage with respect to ground that can be applied to an input terminal without damaging the device Includes both the signal and common mode voltages The unit of strain measurement usually denoted by one represents deformation of 10 6 or 0 000146 1 Minutes 2 Minimum Master in slave out signal Master out slave in signal To route one of many input
75. train to axial strain longitudinal strain Poisson s ratio is a material property of the specimen you are measuring is the measured voltage of the signal Vex 15 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 E Ve X SCXI 1521 B User Manual 4 2 ni com Chapter 4 Theory of Operation Software Scaling and Equations Once you have acquired the voltage signal 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 You can also scale the voltages manually in your application using the voltage to strain conversion equations provided in this document for each configuration type Finally voltage to strain conversion functions are included in LabVIEW and NI DAQmx 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 and convert bas for Visual Basic The names of 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 This section provides information about the quarter bridge strain gauge conf
76. ve 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 compensation Shunt Calibration Performing shunt calibration removes gain or amplitude errors in the measurement system Factors such as non ideal gauge resistance and 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 13 SCXI 1521 B User Manual Specifications Analog Input Transfer This appendix lists specifications for SCXI 1521 B modules These specifications are typical at 25 unless otherwise noted Number of channels 24 VOltage aliit 42 Input coupling eee DC Overvoltage 11 powered on and off Inputs protected esses AI 0 24 Nonlinearity eee 0 0296 max Gain error Aft
77. wner s modification of the product owner s abuse misuse or negligent acts and power failure or surges fire flood accident actions of third parties or other events outside reasonable control Copyright Under the copyright laws this publication may not be reproduced or transmitted in any form electronic or mechanical including photocopying recording storing in an information retrieval system or translating in whole or in part without the prior written consent of National Instruments Corporation National Instruments respects the intellectual property of others and we ask our users to do the same NI software is protected by copyright and other intellectual property laws Where NI software may be used to reproduce software or other materials belonging to others you may use NI software only to reproduce materials that you may reproduce in accordance with the terms of any applicable license or other legal restriction Trademarks National Instruments NI ni com and LabVIEW are trademarks of National Instruments Corporation Refer to the Terms of Use section ni com 1egal for more information about National Instruments trademarks Product and company names mentioned herein are trademarks or trade names of their respective companies Patents For patents covering National Instruments products refer to the appropriate location Help Patents in your software the patents txt file on your CD or ni com patents WARNING REGARDI
78. wo SCXI 1521 B modules that are in the same chassis in the multiplexed mode with two different E M Series DAQ devices No National Instruments Corporation C 1 SCXI 1521 B User Manual Appendix Common Questions If the SCXI 1521 B 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 Can I use the unused analog input channels of the E M Series DAQ device if I am directly cabled to the SCXI 1521 B 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 1521 B channels 1 through 7 Can I configure the SCXI 1521 B for use in parallel mode No The SCXI 1521 B does not support parallel mode Which digital lines are unavailable on the E M Series DAQ device if I am cabled to an SCXI 1521 B module Table C 1 shows the digital lines that are used by the SCXI 1521 B for communication and scanning These lines are unavailable for general purpose digital I O if the SCXI 1521 B is connected to the E M Series DAQ device Table C 1 Digital Signals on the SCXI 1521 B E M Series DAQ Device NI DAQmx 50 Pin 68 Pin Signal Name SCXI Signal Name Connector Connector Direction DIO 0 0 0 25 52 Output DIO 4 P0 4 26 19
79. x appears asking you to confirm the module replacement Click OK Configure the cabled module Click OK e 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 E M Series DAQ device e After checking the preceding items retest the SCXI chassis If these measures do not successfully configure the SCXI system contact NI Refer to the Signal Conditioning Technical Support Information document for contact information National Instruments Corporation 1 7 SCXI 1521 B User Manual Connecting Signals This chapter describes how to connect quarter bridge strain gauges to SCXI 1521 B through the SCXI 1317 It also provides the front and rear signal pin assignments of the module To connect a quarter bridge strain gauge in configuration type I with either a 2 or 3 wire strain gauge refer to the SCXI 1517 Terminal Block Installation Guide Refer to Chapter 4 Theory of Operation for a discussion of strain gauge concepts Pin Assignments The pin assignments for the SCXI 1521 B 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 In the following list of terminal assignments X is the channel number e X connects to the sensor excitation e X connects to the quarter b

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