SCXI-1581 User Manual - National Instruments
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1. eee 4 0 The Relationship Between Resistance and Temperature In RTDS Re ERR eR EE Pe ete 4 10 National Instruments Corporation V SCXI 1581 User Manual Contents Theftnistots z cedet UIN nee ER HR 4 13 Thermistor Measurement Circuits pp 4 15 Resistance Temperature Characteristic of Thermistors 4 16 Appendix A Specifications Appendix B Removing the SCXI 1581 Appendix C Common Questions Glossary Index Figures Figure 1 1 SCXI 1581 to DMM Connections eene 1 4 Figure3 1 Block Diagram of SC XI 138 3 1 Figure 4 1 4 Wire Resistive Sensor Connected in a 4 Wire Configuration 4 2 Figure 4 2 2 Wire Resistive Sensor Connected in a 2 Wire Configuration 4 3 Figure 4 3 3 Wire Resistive Sensor Connected in a 2 Wire Configuration 4 4 Figure 4 4 3 Wire Configuration Using Matched Current Sources 4 5 Figure 4 5 3 Wire Configuration Using Two Differential Amplifiers 4 6 Figure 4 6 2 Wire RTD e emen 4 10 Figure 4 7 Resistance Temperature Curve for a 100 Platinum RTD U 000985 ree Reemi e ev 4 11 Figure 4 8 Resistance Temperature Curve for a 2 252 Q Thermistor 4 14 Figure 4 9 Thermistor Measurement with Constant Current Excitation 4 15 Figure A 1 SCXI 15812. Ru i SCXI 1300 SCXI 1581 WW R EXO V L2 1 1 rr 6 Ris EX0 e WW i SCXI 1300 SCXI 1102 Ria CHO gt WW e CHO and are not required to be equal one Figure 4 1 4 Wire Resistive Sensor Connected in a 4 Wire Configuration SCXI 1581 User Manual 4 2 ni com Chapter 4 Using the SCXI 1581 2 Wire Configuration The basic 2 wire configuration is shown in Figure 4 2 In this configuration an error voltage is introduced into the measurement equal to the excitation current Igy times the sum of the two lead resistances Rz and If we assume equal lead resistances the magnitude of the error voltage is Vg 28 This is the most commonly used configuration for connecting thermistors to a signal conditioning system because the large sensitivity of thermistors usually results in the introduction of a negligible error by the lead resistances RTDs typically have a much smaller sensitivity and nominal resistance than thermistors therefore a 2 wire configuration usually results in the introduction of larger errors by the lead resistance Ry SOXI 1300 SCXI 1581 WW F i 4 Rio EX0 WW 7 m gt SCXI 1300 SCXI 1102 Add These _ Connections CHOL gt
3. SCXI 1581 User Manual April 2006 NATIONAL 323074C 01 D 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 2001 2006 National Instruments Corporation All rights reserved
4. 5 1 CHO In this configuration the lead resistance due to R Rj can introduce measurement error ES NET Figure 4 2 2 Wire Resistive Sensor Connected in a 2 Wire Configuration National Instruments Corporation 4 3 SCXI 1581 User Manual Chapter 4 Using the SCXI 1581 3 Wire Resistive Sensor Connected in a 2 Wire Configuration If you are using a 3 wire resistive sensor you can reduce the error voltage by one half over the 2 wire measurement by connecting the device as shown in Figure 4 3 In this configuration very little current flows through R 3 and therefore is the only lead resistance that introduces an error into the measurement The resulting measurement error is VE Riley An advantage of this configuration is that it only requires a single jumper wire from the SCXI 1581 EX0 terminal to the SCXI 1102B C terminal R SCXI 1300 SCXI 1581 L1 i gt 6 1 1 0 Rip i EX0 e Add This Connection i i SCXI 1300 SCXI 1102 Ria Runs gt CHo i In this configuration the lead resistance due to 4 can introduce measurement error t 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Figure 4 3 3 Wire Resistive Sensor Connected in a 2 Wire Configuration SCXI 1581 User Manual 4 4 ni com Chapter 4 Using the SCXI 1581 Lead Resistance Compe
5. A 2 Figure B 1 Removing the SCXTI 138 es B 2 SCXI 1581 User Manual vi ni com Contents Tables Table 2 1 Front Signal Pin Assignments 2 2 Table 2 2 Signal Descriptions i e eta ee de ata e died 2 3 Table 2 3 Rear Signal Pin Assignments pe 2 4 Table 2 4 SCXI 1581 Communication Signals pe 2 5 Table 4 1 Platinum see espe e teneo et 4 12 Table C 1 SCXI 1581 Digital Signals eene C 3 National Instruments Corporation SCXI 1581 User Manual About SCXI 1581 The SCXI 1581 module provides 32 channels of 100 current excitation You can use SCXI 1581 in any application that requires 100 fixed current excitation For example you can use the SCXI 1581 to provide excitation to resistive transducers such as RTDs and thermistors This enables other input devices such as the SCXI 1102 B C to measure the output of the transducers What You Need to Get Started To set up and use the SCXI 1581 you need the following items Hardware SCXI 1581 module of the following terminal blocks e SCXI 1300 front mount terminal block with screw terminal connectivity e SCXI 1310 custom kit for custom connectivity e BNC 2095 rack mount terminal block for BNC connectivity TBX 96 DIN EN mount terminal block with screw terminal connectivity SCXI or PXI SCXI combo chass
6. 1 3 Installing the SCXI 1581 Module into the SCXI 15 1 4 Verifying SCXI 1581 Installatigon esee eene 1 4 Configuring the SCXI System Software 1 4 Calibrating the SCXI I581 reget pere eedem eae 1 5 Chapter 2 Connecting Signals Pin Assigninehts aio er certe deese Tee en eque pe dean cedar Pe 2 1 Chapter 3 Theory of Operation Scanning Other SCXI Modules Through the SCXI 1581 pe 3 2 Chapter 4 Using the SCXI 1581 Operation of the Current Sources enne eere etre 4 1 Connecting Resistive Devices to the SCXI 1581 sess 4 1 4 Wire Configuration cedet eth etri Ee Wand pe eae 4 2 2 Wire Configuratioh atento t edid 4 3 3 Wire Resistive Sensor Connected in a 2 Wire Configuration 4 4 Lead Resistance Compensation Using a 3 Wire Resistive Sensor and Two Matched Current 4 5 Lead Resistance Compensation Using a 3 Wire Resistive Sensor and Two Differential Amplifiers essere 4 6 Configuring Sensors in 4 7 Creating an RTD Virtual Channel Using NI DAQmx ses 4 7 Creating a Thermistor Virtual Channel Using NI DAQmx 4 8 Measuring Temperature with Resistive Transducers see 4 0 RP Eo I Ou 4 0 RTD Measurement
7. 13 NC 19 EX19 o 12 NC EX20 EX20 De 11 21 21 10 NC 22 EX22 8 e 9 NC EX23 EX23 6 8 24 24 ae 7 EX25 EX25 4 o 6 NC EX26 EX26 3 sl o 5 NC EX27 EX27 1 4 EX28 EX28 mm 3 NC 29 EX29 NC means no connection 2 CGND EX30 EX30 RSVD means reserved 1 RSVD EX31 EX31 SCXI 1581 User Manual 2 2 ni com Chapter 2 Connecting Signals Table 2 2 Signal Descriptions Pin Signal Name Description Al A19 A20 RSVD Reserved this pin is reserved Do not connect 25 28 any signal to this pin A2 CGND Chassis Ground connects to the SCXI chassis 1 32 lt 0 31 gt Negative Excitation connects to the channel ground reference This is the return path for the corresponding EX channel C1 32 EX lt 0 31 gt Positive excitation connects to the positive current output of the channel The rear signal connector shown in Table 2 3 is used for analog signal connectivity and communication between the SCXI 1581 and the E M Series DAQ device Grounding signals AIGND and OUTREF provide reference signals needed in the various analog input referencing modes on the E M Series DAQ device In multiplexed mode the CHO signal pair is used for sending analog signals from other modules to the connected E M Series DAQ device If the module is directly connected to t
8. 9 Click the device tab and set any device specific properties that are applicable for the measurement device To test the NI DAQmx RTD virtual channel click the Test button You have finished creating the NI DAQmx virtual channel You can access the channel by expanding Data Neighborhood NI DAQmx Channels For more information about incorporating the virtual channel into a task with the application refer to the user manual of the analog input device to which the sensor connects Creating a Thermistor Virtual Channel Using NI DAQmx To create an thermistor virtual channel using NI DAQmx complete the following steps 5 1581 User Manual 1 2 3 4 5 oY Launch MAX Right click Data Neighborhood and select Create New Select NI DAQmx Global Virtual Channel and click Next Select Analog Input Temperature Iex Thermistor Select the analog input device and channel to which the sensor connects and click Next Enter a name for the virtual channel and click Finish In the configuration window that opens set the following properties e Signal input range set the min and max to correspond to the measurement range of your application in terms of units that you select under Scaled Units C these scaling coefficients are obtained from the thermistor manufacturer or calculated resistance versus temperature curves 5 lt External when connected to an SCXI 1581 e I valu
9. a b and c are coefficients obtained from the thermistor manufacturer or calculated from the resistance versus temperature curve 4 16 ni com Specifications Stability Excitation This appendix lists the specifications for the SCXI 1581 modules These specifications are typical at 25 C unless otherwise noted Recommended warm up time 10 minutes Channels eng 32 single ended outputs Current output 100 pA ritiro ec ate 0 05 Temperature 5 ppm C Output voltage compliance 10 V Maximum resistive load 100 Overvoltage 40 VDC Measurement Category CATI Power Requirements From SCXI Backplane usi atenta E HERE HS 18 5 to 25 VDC 75 mA Maeva eb otis ed cr 18 5 to 25 VDC 23 mA p 4 75 to 5 25 VDC 20 2 mA National Instruments Corporation A 1 SCXI 1581 User Manual Appendix A Specifications Environmental Operating temperature to 50 C Storage 20 to 70 C Humidity iiiter ertet 10 to 90 RH noncondensing Maximum altitude ssss 2 000 meters Pollution Degree indoor use only 2 Physical 3 0 cm 1 2 in gt E e o o Lo DI
10. Important Information Warranty The SCXI 1581 is warranted against defects in materials and workmanship for a period of one year from the date of shipment as evidenced by receipts or other documentation National Instruments will at its option repair or replace equipment that proves to be defective during the warranty period This warranty includes parts and labor The media on which you receive National Instruments software are warranted not to fail to execute programming instructions due to defects in materials and workmanship for a period of 90 days from date of shipment as evidenced by receipts or other documentation National Instruments will at its option repair or replace software media that do not execute programming instructions if National Instruments receives notice of such defects during the warranty period National Instruments does not warrant that the operation of the software shall be uninterrupted or error free A Return Material Authorization RMA number must be obtained from the factory and clearly marked on the outside of the package before any equipment will be accepted for warranty work National Instruments will pay the shipping costs of returning to the owner parts which are covered by warranty National Instruments believes that the information in this document is accurate The document has been carefully reviewed for technical accuracy In the event that technical or typographical errors exist National Instruments
11. 18 8 cm lt 9 7 4 in Figure 1 SCXI 1581 Dimensions ite neret rene tias 731 gm 25 8 oz SCXI 1581 User Manual A 2 ni com Appendix A Specifications Safety The SCXI 1581 is designed to meet the requirements of the following standards of safety for electrical equipment for measurement control and laboratory use e 61010 1 EN 61010 1 e UL61010 1 e CAN CSA C22 2 No 61010 1 5 Note For UL and other safety certifications refer to the product label or visit ni com certification search by model number or product line and click the appropriate link in the Certification column Electromagnetic Compatibility EMISSIONS EN 55011 Class A at 10 m FCC Part 15A above 1 GHz Trrimiinity EN 61326 1997 A2 2001 Table 1 CE C Tick and FCC Part 15 Class A Compliant i Note For EMC compliance operate this device with shielded cabling CE Compliance The SCXI 1581 meets the essential requirements of applicable European Directives as amended for CE marking as follows Low Voltage Directive safety 73 23 EEC Electromagnetic Compatibility 89 336 3 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 lin
12. Lead Resistance Compensation Using a 3 Wire Resistive Sensor and Two Differential Amplifiers If the accuracy obtained by using a 3 wire device and matched current sources is not sufficient for your application you can eliminate the error due to the mismatch of the current sources by using only one current source and two differential amplifiers The 3 wire 2 amplifier configuration is illustrated in Figure 4 5 Add These Connections R SCXI 1300 SCXI 1581 L1 1 TN i CZ i EXO Rie gt SCXI 1300 T SC c e e Ri3 CHO i p CH0 Ver e le 5 1581 User Manual Figure 4 5 3 Wire Configuration Using Two Differential Amplifiers In this configuration two separate measurements are taken the first labeled V in Figure 4 5 is the sum of the voltage drops across the lead resistance and the resistive device If the voltage drop across Rz and Rr is denoted as and respectively the expression for V becomes Vi Var 4 6 ni com Chapter 4 Using the SCXI 1581 The second measurement labeled V gt in Figure 4 5 is equal to the voltage drop across the lead resistance R gt denoted as 2 therefore V Vy If the lead resistances and are assumed equal you can remove in software the error voltages due to the lead resistances by subt
13. error to the resistance measurement For a platinum RTD at 0 C with a 0 00385 the lead resistance equates to an error of approximately DD 0 385 Q C The Connecting Resistive Devices to the SCXI 1581 section describes different ways of connecting resistive devices to the SCXI system The Relationship Between Resistance and Temperature in RTDs Compared to other temperature measurement devices the output of an RTD is relatively linear with respect to temperature The temperature coefficient called alpha o differs between RTD curves Although various manufacturers specify alpha differently alpha is most commonly defined as the change in RTD resistance from 0 to 100 C divided by the resistance at 0 C divided by 100 C Ro Ro OCC SOOO TC 0 4 10 ni com Chapter 4 Using the SCXI 1581 where Rjoo is the resistance of RTD at 100 C Ro is the resistance of the RTD at 0 C For example a 100 Q platinum RTD with a 0 003911 has a resistance of 139 11 at 100 C Figure 4 7 displays a typical resistance temperature curve for a 100 Q platinum RTD 480 400 320 Resistance Q 240 160 80 0 80 160 240 320 400 480 560 640 720 800 880 960 Temperature C Figure 4 7 Resistance Temperature Curve for a 100 Platinum RTD a 0 00385 Although the resistance temperature curve is relatively linear accurately
14. questions about C 4 C CE compliance specifications A 3 common questions C 1 connecting resistive devices to SCXI 1581 2 wire configuration 4 3 3 wire resistive sensor connected in 2 wire configuration 4 4 4 wire configuration 4 2 lead resistance compensation using 3 wire resistive sensor and two differential amplifiers 4 6 and two matched current sources 4 5 connectors rear signal connector communication signals 2 3 conventions used in the manual viii current output channels questions about C 1 C 3 current sources operating 4 1 National Instruments Corporation D DAQ device accessing unused analog input channels C 2 digital signals unavailable with DAQ device connected table C 3 E electromagnetic compatibility specifications A 3 environment specifications A 2 excitation specifications A 1 F front connector pin assignments table 2 2 installation into SCXI chassis 1 4 Measurement amp Automation Explorer removing the SCXI 1581 B 1 multiplexed scanning scanning other SCXI modules through SCXI 1581 3 2 NI DAQ version required C 1 SCXI 1581 User Manual Index 0 operation of current sources 4 1 P physical specifications A 2 pin assignments front connector table 2 2 power requirements from SCXI backplane A 1 Q questions and answers 1 R rear signal connector communications signals 2 3 removing the SCXI 1581 from Measurement amp
15. Automation Explorer 1 resistive devices connecting to SCXI 1581 2 wire configuration 4 3 3 wire resistive sensor connected to 2 wire configuration 4 4 4 wire configuration 4 2 lead resistance compensation using 3 wire resistive sensor and two differential amplifiers 4 6 using 3 wire resistive sensor and two matched current sources 4 5 RTDs resistive temperature detectors measurement errors 4 9 overview 4 9 relationship between resistance and temperature 4 10 resistance temperature curve figure 4 11 5 1581 User Manual 2 5 safety specifications A 3 SCXI 1303 terminal block C 4 SCXI 1581 common questions C 1 digital signals unavailable signals with DAQ device connected table C 3 removing figure B 2 removing from SCXI chassis B 1 taking measurements See measurements signal connections front connector pin assignments table 2 2 software NI DAQ version required C 1 specifications CE compliance A 3 electromagnetic compatibility A 3 environment A 2 excitation 1 physical A 2 power requirements from SCXI backplane 1 safety A 3 stability A 1 stability specifications A 1 ni com T taking measurements See measurements temperature measurement with resistive transducers 4 9 connecting resistive devices to SCXI 1581 4 1 2 wire configuration 4 3 3 wire resistive sensor connected in 2 wire configuration 4 4 4 wire configuration 4 2 lead resistance compensation usin
16. 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 NOT LIMIT
17. Series DAQ device or ground No The SCXI 1581 does not contain any isolation circuitry All current outputs are referenced to chassis ground If you require isolated current outputs consider the SCXI 1124 module instead Can I modify the SCXI 1581 circuitry to generate current at a level different than 100 pA No Do not attempt to modify any circuitry in the SCXI 1581 Are there any user serviceable parts inside the SCXI 1581 No There are no fuses potentiometers switches socketed resistors or jumpers inside the module Disassembly of the module for any reason can void its warranty and nullify its accuracy specification Can I access the unused analog input channels of the E M Series DAQ device if it is directly cabled to the SCXI 1581 in a single chassis system Yes E M Series DAQ device channels 1 through 7 are available to measure unconditioned signals Use an SCXI 1180 or the 50 pin breakout connector on the SCXI 1346 or SCXI 1349 cable adapter to route signals to these channels C 2 ni com Appendix C Common Questions Which digital lines are unavailable on the E M Series DAQ device if I am cabled to an SCXI 1581 module Table C 1 shows the digital lines that are used by the SCXI 1581 for communication and scanning These lines are unavailable for general purpose digital I O if the SCXI 1581 is connected to the DAQ device Table C 1 SCXI 1581 Digital Signals DAQ SCXI 50
18. advantage of the thermistor is its relatively high resistance Thermistors are available with base resistances at 25 C ranging from hundreds to millions of ohms This high resistance diminishes the effect of inherent resistances in the lead wires which can cause significant errors with low resistance devices such as RTDs For example while RTD measurements typically require 3 or 4 wire connections to reduce errors National Instruments Corporation 4 13 SCXI 1581 User Manual Chapter 4 Using the SCXI 1581 caused by lead wire resistances 2 wire connections to thermistors are usually adequate The major trade off for the high resistance and sensitivity of the thermistor is its highly nonlinear output and relatively limited operating range Depending on the type of thermistor the upper range is typically limited to around 300 C Figure 4 8 shows the resistance temperature curve for a 2 252 thermistor The curve of a 100 RTD is also shown for comparison 10M 1M Thermistor T 2 252 Q at 25 C 10k lt Resistance 0 10 1 200 150 100 50 0 50 100 150 200 250 300 350 400 Temperature C Figure 4 8 Resistance Temperature Curve for a 2 252 Thermistor The thermistor has been used primarily for high resolution measurements over limited temperature ranges However continuing improvements in
19. current going out of specification output reference signal parts per million PCI eXtensions for Instrumentation an open specification that builds on the CompactPCI specification by adding instrumentation specific features lead resistance Return Material Authorization reserved bit pin or signal resistance temperature detector seconds samples SCXI 1581 User Manual Glossary scan SCANCLK SCXI SCX Ibus sensor SERCLK SERDATIN SERDATOUT signal conditioning Slot 0 SLOTOSEL SPICLK T thermistor Traditional NI DAQ Legacy transducer 5 1581 User Manual 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 scan clock signal used to increment to the next channel after each E M Series DAQ device analog to digital conversion 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 type of transducer that converts a physical phenomenon into an electrical signal serial clock signal used to synchronize digital data transfers over the SERDATIN and SERDATOUT lines serial data input signal serial data output signal the manipulation of signals to
20. prepare them for digitizing refers to the power supply and control circuitry in the SCXI chassis slot 0 select signal serial peripheral interface clock signal a thermally sensitive resistor An upgrade to the earlier version of NI DAQ Traditional NI DAQ Legacy has the same VIs and functions and works the same way as NI DAQ 6 9 x You can use both Traditional NI DAQ Legacy and NI DAQmx on the same computer which is not possible with NI DAQ 6 9 x a device capable of converting energy from one form to another G 6 ni com UL VAC VDC virtual channels Glossary Underwriters Laboratory volts volts alternating current 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 watts National Instruments Corporation G 7 SCXI 1581 User Manual Index Numerics 2 wire configuration of resistive devices 4 3 3 wire resistive sensor connected in 2 wire configuration 4 4 lead resistance compensation with two differential amplifiers 4 6 with two matched current sources 4 5 4 wire configuration of resistive devices 4 2 BNC 2905 rack mount accessory
21. 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 5 RIGHT TO RECOVER DAMAGES CAUSED BY FAULT OR NEGLIGENCE ON THE PART OF NATIONAL INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER NATIONAL INSTRUMENTS WILL NOT BE LIABLE FOR DAMAGES RESULTING FROM LOSS OF DATA PROFITS USE OF PRODUCTS OR INCIDENTAL OR CONSEQUENTIAL DAMAGES EVEN IF ADVISED OF THE POSSIBILITY THEREOF This limitation of the liability of National Instruments will apply regardless of the form of action whether in contract or tort including negligence Any action against National Instruments must be brought within one year after the cause of action accrues National Instruments shall not be liable for any delay in performance due to causes beyond its reasonable control The warranty provided herein does not cover damages defects malfunctions or service failures caused by owner s failure to follow the National Instruments installation operation or maintenance instructions owner s modifi
22. to within 0 0025 C year RTDs are sometimes difficult to measure because they have relatively low nominal resistance commonly 100 that changes only slightly with temperature less than 0 4 2 To accurately measure these small changes in resistance you must use special configurations that minimize measured errors caused by lead wire resistance RTD Measurement Errors Because the RTD is a resistive device you must pass a current through the device and monitor the resulting voltage However any resistance in the lead wires that connect the measurement system to the RTD adds error to the readings For example consider a 2 wire RTD element connected to a measurement system that also supplies a constant current Igy to excite the RTD As shown in Figure 4 6 the voltage drop across the lead resistances labeled R adds an error voltage to the measured voltage National Instruments Corporation 4 9 SCXI 1581 User Manual Chapter 4 Using the SCXI 1581 SCXI 1581 User Manual lex RL 0 Vo RL VVW Figure 4 6 2 Wire RTD Measurement The maximum resistance of the thermistor is determined from the current excitation value and the maximum voltage range of the input device When using the SCXI 1581 with an SCXI 1102 B C the maximum measurable resistance is 100 kQ Refer to Appendix A Specifications for the maximum ratings For example a lead resistance of 0 3 in each wire adds a 0 6
23. transferred away from the thermistor so the dissipation constant can be specified for different media in still air water or oil bath Typical dissipation constants range anywhere from less than 0 5 mW C for still air to 10 mW C or higher for a thermistor immersed in water A 2 252 thermistor powered by a 100 uA excitation current dissipates PR 100 pA x 2252 Q 0 0225 mW If this thermistor has a dissipation constant of 10 mW C the thermistor self heats 0 00225 C so the self heating from the 100 uA source of the National Instruments Corporation 4 15 SCXI 1581 User Manual Chapter 4 Using the SCXI 1581 5 1581 User Manual SCXI 1581 is negligible for most applications It is still important to carefully read self heating specifications of the thermistors Resistance Temperature Characteristic of Thermistors The resistance temperature behavior of thermistors is highly dependent upon the manufacturing process Therefore thermistor curves are not standardized to the extent that thermocouple or RTD curves are standardized Typically thermistor manufacturers supply the resistance versus temperature curves or tables for their particular devices You can however approximate the thermistor curve relatively accurately with the Steinhart Hart equation 1 TCK AE o a b In R c In A7 where T K is the temperature in degrees Kelvin equal to T C 273 15 Rr is the resistance of the thermistor
24. 0 CH x corresponds to EX x Likewise CH x corresponds to EX x You cannot use any screw terminals in the SCXI 1300 other than CH x CH x and chassis ground Can I use the BNC 2095 as an accessory for the SCXI 1581 Yes However you must set all the slide switches on the back of the BNC 2095 for no bias resistor connections to ground and no pull up resistor connections to 5 V In other words set all switches on the rear of the BNC 2095 to the OFF down position When using an SCXI 1300 or BNC 2095 with the SCXI 1581 can I read the CJC sensor on these accessories No Can I use an SCXI 1303 terminal block as an accessory for the SCXI 1581 NI does not recommend this combination The SCXI 1303 is optimized for temperature measurement using thermocouples The SCXI 1303 works with the SCXI 1581 but only if you remove all of the resistor packs Refer to the SCXI 1303 32 Channel Isothermal Terminal Block Installation Guide for more information As with the SCXI 1300 and BNC 2095 you cannot measure the CJC sensor 4 ni com Glossary Symbol Prefix Value u micro 10 6 milli 10 3 k kilo 103 M mega 106 Numbers Symbols percent positive of or plus negative of or minus plus or minus lt less than per 3 degree ohms 5 V signal 5 VDC source signal A A amperes ADE application development environment such as LabVIEW LabWindows CVI V
25. 32 34 SLOT 0 SEL 29 30 35 36 31 32 37 198 DIG GND 33 34 39 40 41 42 35 36 AI HOLD COMP 43 44 AI HOLD 45 46 SER CLK 27 38 47 48 39 40 49 50 41 42 43 44 45 46 SYNC 47 48 49 50 5 1581 User Manual 2 4 ni com Chapter 2 Connecting Signals The communication signals between the DAQ device and the SCXI system are listed in Table 2 4 If the DAQ device is connected to the SCXI 1581 these digital lines are unavailable for general purpose digital I O Table 2 4 SCXI 1581 Communication Signals SCXI Pin Signal Name NI DAQmx Device Signal Name Traditional NI DAQ Legacy Device Signal Name Direction Description 24 33 DIG GND D GND DGND Digital ground these pins supply the reference for E M Series DAQ device digital signals and are connected to the module digital ground 25 SER DAT IN P0 0 DIOO Input Serial data in this signal taps into the SCXIbus MOSI line to send serial input data to a module or Slot 0 26 SER DAT OUT P0 4 DIO4 Output Serial data out this signal taps into the SCXIbus MISO line to accept serial output data from a module 27 DAQ D A PO 1 DIO1 Input Board data address line this signal taps into the SCXIbus D A line to indicate to the module whether the incoming serial stream is data or address information 29 S
26. 40 SCXI 1520 SCXI 1530 or SCXI 1531 In that case you must cable to a simultaneous sampling module Can the SCXI 1581 current outputs be interactively controlled in MAX or programmatically controlled using NI DAQ function calls LabVIEW or Measurement Studio No The current output level 15 100 uA as long as the chassis is powered on You cannot power off or adjust the current output using MAX NI DAQ function calls or an ADE such as LabVIEW or Measurement Studio If you require this functionality consider using an SCXI 1124 module or NI 670X device instead Can I create virtual channels for an SCXI 1581 current output channel No As discussed above you cannot programmatically control the current outputs National Instruments Corporation C 1 SCXI 1581 User Manual Appendix C 5 1581 User Manual Common Questions Can I connect N current output channels in parallel to create a precision current source that provides N x 100 Yes you can connect the current output in parallel When connecting the output in parallel connect the appropriate EX terminals together and the corresponding EX terminals together Can I connect N current output channels in series to achieve a higher terminal voltage compliance limit No Each current source is ground referenced Therefore you cannot place multiple current outputs in series Are the SCXI 1581 current output channels isolated with respect to each other the E M
27. CXI 1581 User Manual Appendix B Removing the SCXI 1581 1 Power off the chassis Do not remove the SCXI 1581 module from a chassis that is powered on 2 Ifthe SCXI 1581 is the module cabled to the E M Series DAQ device disconnect the cable 3 Remove any terminal block that connects to the SCXI 1581 4 Rotate the thumbscrews that secure the SCXI 1581 to the chassis counterclockwise until they are loose but do not completely remove the thumbscrews Remove the SCXI 1581 by pulling steadily on both thumbscrews until the module slides completely out 1 Cable 3 SOXI 1581 5 SCXI Chassis Power Switch 2 SCXI Module Thumbscrews 4 Terminal Block 6 SCXI Chassis Figure B 1 Removing the SCXI 1581 SCXI 1581 User Manual B 2 ni com Common Questions This appendix lists common questions related to the use of the SCXI 1581 Which version of NI DAQ works with the SCXI 1581 and how do I get the most current version of NI DAQ You must NI DAQ 7 0 or later Visit the NI Web site at ni com and select Download Software Drivers and Updates Search Drivers and Updates Enter the keyword NI DAQ to find the latest version of NI DAQ for your operating system Can the SCXI 1581 be the cabled module when there are also multiplexed analog input modules in the chassis Yes unless one or more of the multiplexed analog input modules in the same chassis feature simultaneous sampling such as the SCXI 11
28. Digital Interface and Control 10090000 National Instruments Corporation Figure 3 1 Block Diagram of SCXI 1581 3 1 SCXI 1581 User Manual Chapter 3 Theory of Operation Scanning Other SCXI Modules Through the SCXI 1581 When connected as the cabled module in an SCXI chassis the SCXI 1581 can route the multiplexed signals from other SCXI modules to the E M Series DAQ device The SCXI 1581 routes multiplexed signals from other SCXI modules to the E M Series DAQ device even though the SCXI 1581 does not have any analog input channels Refer to the user manuals for your other SCXI modules for details about scanning those modules in multiplexed mode SCXI 1581 User Manual 3 2 ni com Using the SCXI 1581 This chapter makes suggestions for developing your application Operation of the Current Sources The current sources on the 5 1581 continuously provide 32 channels of 100 current excitation These current sources are on whenever the SCXI chassis is powered on The current sources on the SCXI 1581 are designed to be accurate to within 0 05 of the specified value with a temperature drift of no more than 5 ppm C The high accuracy and stability of these current sources makes them especially well suited to measuring resistance to a high degree of accuracy Connecting Resistive Devices to the SCXI 1581 You can connect resistive devices to the SCXI signal cond
29. ED 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 AX N bold italic monospace monospace bold The following conventions are used in this manual Angle brackets that contain numbers separated by an ellipsis represent a range of values associated with a bit or signal name for example AO lt 3 0 gt The symbol leads you through nested menu items and dialog box options to a final action The sequence File Page Setup Options directs you to pull down the File menu select the Page Setup item and select Options from the last dialog box This icon denotes a note which alerts you to important information This icon denotes a caution which advises you of precautions to take to avoid injury data loss or a system crash When this symbol is marked on the product refer to the Read Me First Safety and
30. LOT 0 SEL P0 2 DIO2 Input Slot 0 select this signal taps into the SCXIbus INTR line to indicate whether the information on MOSI is being sent to a module or Slot 0 National Instruments Corporation 2 5 SCXI 1581 User Manual Chapter 2 Connecting Signals Table 2 4 SCXI 1581 Communication Signals Continued NI DAQmx Traditional NI DAQ SCXI Device Signal Legacy Device Pin Signal Name Name Signal Name Direction Description 36 SCAN CLK AI HOLD COMP SCANCLK Input Scan clock a rising AI HOLD edge indicates to the scanned SCXI module that the E M Series DAQ device has taken a sample and causes the module to advance channels 37 SER CLK EXT STROBE EXTSTROBE Input Serial clock this signal taps into the SCXIbus SPICLK line to clock the data on the MOSI and MISO lines 5 1581 User Manual 2 6 ni com Theory of Operation This chapter provides a brief overview and a detailed discussion of the circuit features of the SCXI 1581 module Refer to Figure 3 1 while reading this section SCXI 1300 Terminal Block SCXI 1581 Module CHO CHO Screw Terminals to Field Wiring CH31 O lt lt CH31 Buffer gt CHO To Analog Bus Analog Bus euBIS Switch t
31. Pin 68 Pin Signal Name Signal Name Connector Connector Direction DIOO SERDATIN 25 52 Output DIO4 SERDATOUT 26 19 Input DIO1 DAQD A 27 17 Output DIO2 SLOTOSEL 29 49 Output SCANCLK SCANCLK 36 46 Output I With respect to the Series device National Instruments Corporation C 3 Does short circuiting a current output channel do any damage to the SCXI 1581 No The SCXI 1581 delivers 100 uA into any load from 0 to 100 Does open circuiting a current output channel damage the SCXI 1581 What is the open circuit voltage level No An SCXI 1581 current output channel is not damaged if no load is connected The open circuit voltage is 12 4 VDC How can I tell if the SCXI 1581 is working Disconnect all loads from the channel you are testing Measure the current output value using an ammeter If the ammeter has a fuse ensure that the fuse is not blown before performing the measurement Alternatively place a known resistance R 100 kQ across the current output and use a voltmeter to measure the voltage drop across it If the current output is functioning you should measure V 100 x 10A x R where R is given in Q SCXI 1581 User Manual Appendix C Common Questions 5 1581 User Manual How does the screw terminal labeling on the SCXI 1300 relate to the front signal connector on the SCXI 1581 In other words if I want to use current output channel x where do I connect wires in the SCXI 130
32. 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 and code excerpts 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 Contents Chapter 1 About the SCXI 1581 What You Need to Get Started ee 1 1 National Instruments Documentation rennen 1 2 Installing Application Software NI DAQ and the Series Device
33. ble settings in MAX for use with either NI DAQmx or Traditional NI DAQ Legacy To verify the functionality of the SCXI 1581 complete the following steps while referring to Figure 1 1 1 Connect a high precision DMM to each Ex x and Ex x channel configured in current measurement mode 2 Verify that the output is 100 uA and is within the specifications listed in Appendix A Specifications 3 If any channel is not within specifications ensure that the SCXI chassis is functioning properly 4 Ifthe module is still not within specifications contact NI for further technical assistance NI contact information is listed in the Technical Support Information document DMM SCXI 1581 Current In Ex x COM GND Figure 1 1 5 1581 to DMM Connections Configuring the SCXI System Software Refer to the SCXI Quick Start Guide and the user manuals of the modules in your application to configure and verify them in software 5 1581 User Manual 1 4 ni com Chapter 1 About the 5 1581 Calibrating the 5 1581 The SCXI 1581 is within the specifications described in Appendix A Specifications when it is shipped You can verify that the SCXI 1581 is within the specification using a DMM of appropriate accuracy for your application If a current source on the SCXI 1581 drifts out of specification over time a subcomponent has likely failed If the SCXI 1581 fails to op
34. cation of the product owner s abuse misuse or negligent acts and power failure or surges fire flood accident actions of third parties or other events outside reasonable control Copyright Under the copyright laws this publication may not be reproduced or transmitted in any form electronic or mechanical including photocopying recording storing in an information retrieval system or translating in whole or in part without the prior written consent of National Instruments Corporation National Instruments respects the intellectual property of others and we ask our users to do the same NI software is protected by copyright and other intellectual property laws Where NI software may be used to reproduce software or other materials belonging to others you may use NI software only to reproduce materials that you may reproduce in accordance with the terms of any applicable license or other legal restriction Trademarks National Instruments NI ni com and LabVIEW are trademarks of National Instruments Corporation Refer to the Terms of Use section on ni com 1egal for more information about National Instruments trademarks Other product and company names mentioned herein are trademarks or trade names of their respective companies 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 REGARDING USE OF
35. configure the hardware e One or more of the following help files for software information Start Programs National Instruments NI DAQ NI DAQmx Help Start Programs National Instruments NI DAQ Traditional NI DAQ User Manual Start Programs National Instruments NI DAQ Traditional NI DAQ Function Reference Help You can download NI documents from ni com manuals To download the latest version of NI DAQ click Download Software at ni com Installing Application Software NI DAQ and the E M Series DAQ Device Refer to the DAQ Getting Started Guide packaged with the NI DAQ software to install your application software NI DAQ driver software and the DAQ device to which you will connect the SCXI 1581 NI DAQ 7 0 or later is required to configure and program the SCXI 1581 module If you do not have NI DAQ 7 0 or later you can either contact an NI sales representative to request it on a CD or download the latest NI DAQ version from ni com National Instruments Corporation 1 8 SCXI 1581 User Manual Chapter 1 About the 5 1581 B Note Refer to the Read Me First Safety and Radio Frequency Interference document before removing equipment covers or connecting or disconnecting any signal wires Installing the SCXI 1581 Module into the SCXI Chassis Refer to the SCXI Quick Start Guide to install your SCXI 1581 module Verifying the SCXI 1581 Installation The SCXI 1581 has no software configura
36. converting measured resistance to temperature requires curve fitting The following Callendar Van Dusen equation is commonly used to approximate the RTD curve R 100 National Instruments Corporation 4 11 SCXI 1581 User Manual Chapter 4 Using the SCXI 1581 where is the resistance of the RTD at temperature T Ro is the resistance of the RTD at 0 C A B and C are the Callendar Van Dusen coefficients shown in Table 4 1 T is the temperature in C Table 4 1 lists the RTD types and their corresponding coefficients Table 4 1 Platinum RTD Types Standard D 100 American Temperature Coefficient of Callendar Van Dusen Standard Resistance TCR PPM Typical Ro Coefficient IEC 751 3851 100 Q 3 9083 x 103 DIN 43760 10809 5775x107 ASTM E1137 C 2 4 183 x 10 12 EN 60751 Low cost vendor 3750 1000 Q 3 81 x 10 compliant B 602x107 C 2 6 0 x 107 JISC 1604 3916 100 Q 3 9739 x 103 5 870 x 10 C 2 44 x 107 US Industrial 3920 100 Q 3 9787 x 103 B 5 8686 x 10 7 C 2 4 167 x 107 US Industrial Standard American 3911 100 Q 3 9692 x 103 5 8495 x 1077 C 2 4 233 x 10 12 ITS 90 3928 1000 3 9888 103 5 915 x 10 3 85 x 10 12 1 No standard Check TCR 5 1581 User Manual 4 12 ni com Thermistors Chapter 4 Using the SCXI 1581 For temperatures above 0 C c
37. e A 100 u when connected to the SCXI 1581 e Configuration the wire configuration of the sensor Click the device tab and set any device specific properties that are applicable for the measurement device To test the NI DAQmx thermistor virtual channel click the Test button You have finished creating the NI DAQmx virtual channel You can access the channel by expanding Data Neighborhood NI DA Qmx Channels 4 8 ni com Chapter 4 Using the SCXI 1581 For more information about incorporating the virtual channel into a task with the application refer to the user manual of the analog input device to which the sensor connects Measuring Temperature with Resistive Transducers This section discusses RTDs and thermistors and describes accuracy considerations when connecting resistive transducers to the signal conditioning system RTDs A resistive temperature detector RTD is a temperature sensing device whose resistance increases with temperature An RTD consists of a wire coil or deposited film of pure metal RTDs are made of different metals and have different resistances but the most popular RTD is made of platinum and has a nominal resistance of 100 at 0 C RTDs are known for their excellent accuracy over a wide temperature range Some RTDs have accuracies as high as 0 01 0 026 C at 0 C RTDs are also extremely stable devices Common industrial RTDs drift less than 0 1 C year and some models are stable
38. e and click the appropriate link in the Certification column National Instruments Corporation A 3 5 1581 User Manual Removing the 5 1581 This appendix explains how to remove the SCXI 1581 from MAX and an SCXI chassis or PXI SCXI combination chassis Removing the SCXI 1581 from MAX To remove a module from MAX complete the following steps after launching MAX 1 Expand Devices and Interfaces 2 Click the next to NI DAQmx and or Traditional NI DAQ Devices to expand the list of installed chassis 3 Click the next to the appropriate chassis to expand the list of installed modules 4 Right click the module or chassis you want to delete and click Delete A confirmation window opens Click Yes to continue deleting the module or chassis or No to cancel this action 5 Note Deleting the SCXI chassis deletes all modules in the chassis 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 1581 from a Chassis Consult the documentation for the chassis and accessories for additional instructions and precautions To remove the SCXI 1581 module from a chassis complete the following steps while referring to Figure B 1 5 Note Figure B 1 shows an SCXI chassis but the same steps are applicable to a PXI SCXI combination chassis National Instruments Corporation B 1 S
39. erate according to the published specifications send it back to NI for repair or replacement For information about contacting NI refer to the Technical Support Information document National Instruments Corporation 1 5 SCXI 1581 User Manual Connecting Signals This chapter discusses signal connections to using the SCXI 1581 module Pin Assignments The pin assignments for the SCXI 1581 front signal connector are shown in Table 2 1 Note Do not make any connections to RSVD pins National Instruments Corporation 2 1 SCXI 1581 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 NC EX0 EX0 Column 3l NC EX1 EX1 A B 30 EX2 EX2 CD 32 29 NC EX3 EX3 31 28 RSVD Ex4 EX4 30 27 RSVD EX5 EX5 29 28 26 RSVD 6 EX6 27 o o 25 RSVD EX7 EX7 ee X 24 NC EX8 EX8 25 23 EX9 EX9 24 23 o o 22 NC EX10 EX10 22 21 EX11 EX11 ce 20 RSVD EX12 EX12 20 19 RSVD EX13 19 ale 18 NC EX14 EX14 17 17 15 EX15 16 o 16 NC EX16 EX16 15 15 NC EX17 EX17 14 13 5 5 14 NC EX18 EX18 12 0
40. g 3 wire resistive sensor and two differential amplifiers 4 6 using 3 wire resistive sensor and two matched current sources 4 5 National Instruments Corporation Index RTDs measurement errors 4 9 overview 4 9 relationship between resistance and temperature 4 10 resistance temperature curve figure 4 11 thermistors measurement circuits 4 15 overview 4 13 resistance temperature characteristics 4 16 resistance temperature curve figure 4 14 SCXI 1581 User Manual
41. he E M Series DAQ device the other analog channels of the E M Series DAQ device are available for general purpose analog input because they are not connected to the SCXI 1581 in multiplexed mode The communication signals between the E M Series DAQ device and the SCXI system are SERDATIN SERDATOUT DAQD A SLOTOSEL SERCLK and SCANCLK The digital ground DIGGND on pins 24 and 33 provides a separate ground reference for the communication signals SERDATIN SERDATOUT DAQD A SLOTOSEL and SERCLK are the communication lines for programming the SCXI 1581 The SCANCLK and SYNC signals are the signals necessary for multiplexed mode scanning If the E M Series DAQ device is connected to the SCXI 1581 these digital lines are unavailable for general purpose digital I O National Instruments Corporation 2 3 SCXI 1581 User Manual Chapter 2 Connecting Signals Table 2 3 Rear Signal Pin Assignments Rear Connector Diagram Signal Name Pin Number Pin Number Signal Name AI GND 1 2 AI GND CH0 3 4 CH0 5 6 112 7 8 4 9 10 5 6 7 18 11 12 9 10 13 14 ER 11 12 13 14 16 15 16 17 18 a dl OUT REF 19 20 19 20 21 22 21 22 23 24 DIG GND 25 26 27 28 SER DAT IN 25 26 SER DAT OUT 29 30 DAQ D A 27 28 31
42. is E M Series DAQ device Computer Cabling cable adapter and sensors as required for your application 1 When connected to an SCXI 1581 you cannot measure the onboard temperature sensor National Instruments Corporation 1 1 SCXI 1581 User Manual Chapter 1 About the 5 1581 Software NI DAQ 7 0 or later Application software such as LabVIEW LabWindows CVI Measurement Studio or other programming environments Documentation A Read Me First Safety and Radio Frequency Interference Getting Started Guide 8 Quick Start Guide S CXI 1581 User Manual Documentation for your hardware A Documentation for your software Tools Wire cutter Wire stripper Flathead screwdriver Phillips screwdriver National Instruments Documentation SCXI 1581 User Manual The SCXI 1581 User Manual is one piece of the documentation set for data acquisition DAQ systems You could have any of several types of manuals depending on the hardware and software in the system Use the manuals you have as follows 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 SCXI or PXI SCXI chassis manual Read this manual for maintenance information on the chassis and for installation instr
43. isual Basic C and C Al analog input AIGND analog input ground signal National Instruments Corporation G 1 SCXI 1581 User Manual Glossary bit CE CGND CH channel chassis CLK common mode voltage current excitation D D A D A DAQ DAQ device DAQD A SCXI 1581 User Manual one binary digit either O or 1 European emissions control standard chassis ground signal channel pin or wire lead to which you apply or from which you read an analog or digital signal Analog signals can be single ended or differential For digital signals channels also known as lines are grouped to form ports the enclosure that houses powers and controls SCXI modules clock input signal voltage that appears on both inputs of a differential amplifier a source that supplies the current needed by a sensor for its proper operation digital to analog Data Address 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 devices plugged into a computer and possibly generating control signals with D A and or DIO devices in the same computer a data acquisition device Examples are E M Series data acquisition devices the data acquisition device data address line signal used to indicate whether the SERDATIN pulse
44. itioning system in a 4 2 or 3 wire configuration The SCXI 1102 B C modules are 32 channel analog input modules that are ideally suited for measuring DC or slowly varying voltages Figures 4 1 through 4 5 illustrate various ways to connect sensors for current excitation and voltage measurements using the SCXI 1581 and the SCXI 1102B C modules Refer to the appropriate ADE and SCXI documentation for information concerning setting appropriate voltage gains for the analog inputs You can use the SCXI 1300 terminal block to make signal connections to the SCXI 1581 and SCXI 1102 modules When using the SCXI 1300 terminal block terminals EX lt 0 31 gt and EX lt 0 31 gt map to terminals CH lt 0 31 gt and lt 0 31 gt respectively on the SCXI 1300 terminal block National Instruments Corporation 4 1 SCXI 1581 User Manual Chapter 4 Using the SCXI 1581 4 Wire Configuration The 4 wire configuration also referred to as a Kelvin connection is shown in Figure 4 1 The 4 wire configuration uses one pair of wires to deliver the excitation current to the resistive sensor and uses a separate pair of wires to sense the voltage across the resistive sensor Because of the high input impedance of the differential amplifier negligible current flows through the sense wires This results in a very small lead resistance voltage drop error The main disadvantage of the 4 wire connection is the greater number of field wires required
45. nsation Using a 3 Wire Resistive Sensor and Two Matched Current Sources You can compensate for the errors introduced by lead resistance voltage drops by using a 3 wire resistive sensor and two matched current sources connected as shown in Figure 4 4 Assume Ru i SCXI 1300 zs c Rut Rie LIS hr 5 R EX1 aZ L2 i WW EXO EB gt SCXI 1300 SCXI 1102 Add These _ Connections c e i CHO Figure 4 4 3 Wire Configuration Using Matched Current Sources In this configuration the lead resistance voltage drop across is converted into a common mode voltage that is rejected by the differential amplifier Also the polarity of the lead resistance voltage drops across and are series opposing relative to the inputs of the differential amplifier eliminating their effect on the voltage measured across iy Note and are assumed to be equal The effectiveness of this method depends on the matching of the current sources Each current source on the SCXI 1581 has an accuracy of 0 05 This accuracy results in a worst case matching of 0 1 Refer to the Measuring Temperature with Resistive Transducers section for accuracy considerations of RTDs and thermistors National Instruments Corporation 4 5 SCXI 1581 User Manual Chapter 4 Using the SCXI 1581
46. oefficient C equals 0 reducing this equation to a quadratic If you pass a known current Igy through the RTD and measure the output voltage developed across RTD Vo you can solve for T as follows Vo 2 2 Vo 205 R A RA 4R B Ro 72 E where Vo is the measured RTD voltage Igy is the excitation current A thermistor is a piece of semiconductor made from metal oxides pressed into a small bead disk wafer or other shape sintered at high temperatures and finally coated with epoxy or glass The resulting device exhibits an electrical resistance that varies with temperature There are two types of thermistors negative temperature coefficient NTC thermistors whose resistance decreases with increasing temperature and positive temperature coefficient PTC thermistors whose resistance increases with increasing temperature NTC thermistors are more commonly used than PTC thermistors especially for temperature measurement applications A main advantage of thermistors for temperature measurement is their extremely high sensitivity For example a 2 252 Q thermistor has a sensitivity 100 at room temperature Higher resistance thermistors can exhibit temperature coefficients of 10 kQ C or more In comparison 100 platinum RTD has a sensitivity of only 0 4 2 Also the physically small size and low thermal mass of a thermistor bead allows a very fast response to temperature changes Another
47. posts on a circuit board Jumpers are used on some SCXI modules and terminal blocks to either select certain parameters or enable disable circuit functionality the small resistance of a lead wire The resistance varies with the lead length and ambient temperature If the lead wire carries excitation current this varying resistance can cause measurement error meters 1 Mega the standard metric prefix for 1 million or 10 when used with units of measure such as volts and hertz 2 mega the prefix for 1 048 576 or 220 when used with to quantify data or computer memory master in slave out signal master out slave in signal to route one of many input 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 multiplexed output of the module as well as the outputs of all other multiplexed modules in the chassis G 4 ni com NC NI DAQ NI DAQmx 0 output voltage compliance OUTREF P ppm PXI RMA RSVD RTD National Instruments Corporation G 5 Glossary not connected signal the driver software needed in order to use National Instruments E M Series DAQ devices and SCXI components The latest NI DAQ driver with new VIs functions and development tools for controlling measurement devices the largest voltage that can be generated across the output of a current source without the
48. racting V3 from V In most 3 wire device applications the lead wires are all the same length and made of the same material therefore substantiating the assumption of equal lead resistances Configuring Sensors in Software You can create a virtual channel to convert RTD voltages into temperature readings To create an RTD virtual channel refer to the Creating an RTD Virtual Channel Using NI DAQmx section Creating an RTD Virtual Channel Using NI DAQmx To create an RTD virtual channel using NI DAQmx complete the following steps Launch MAX Right click Data Neighborhood and select Create New Select NI DAQmx Global Virtual Channel and click Next Select Analog Input Temperature RTD Select the analog input device and channel to use and click Next Enter a name for the virtual channel and click Finish cb ons In the configuration window that opens set the following properties e Signal input range set the min and max to correspond to the measurement range of your application in terms of units that you select under Scaled Units e RTD type refer to Table 4 1 for a list of RTD types Ry the nominal resistance value of RTD e Configuration how the RTD is connected e source select External when connected to an SCXI 1581 e value A 100 u when connected to SCXI 1581 National Instruments Corporation 4 7 SCXI 1581 User Manual Chapter 4 Using the SCXI 1581 8
49. thermistor stability accuracy and interchangeability have prompted increased use of thermistors in a variety of applications SCXI 1581 User Manual 4 14 ni com Chapter 4 Using the SCXI 1581 Thermistor Measurement Circuits This section details information about thermistor measurement circuits The most common technique is to use a current source and measure the voltage developed across the thermistor Figure 4 9 shows the measured voltage Vo equals x I m x O Vo 7 Rr Er Thermistor Vo lex X Figure 4 9 Thermistor Measurement with Constant Current Excitation The level of the voltage output signal depends directly on the thermistor resistance and magnitude of the current excitation Do not use a higher level of current excitation in order to produce a higher level output signal because the current causes the thermistor to heat internally leading to temperature measurement errors This phenomena is called self heating When current passes through the thermistor power dissipated by the thermistor equaling heats the thermistor Thermistors with their small size and high resistance are particularly prone to these self heating errors Manufacturers typically specify this self heating as a dissipation constant which is the power required to heat the thermistor 1 C from ambient temperature mW C The dissipation constant depends heavily on how easily heat is
50. train transmitted to the SCXI chassis contains data or address information G 2 ni com device DGND differential amplifier DIN DIO DoC drivers driver software EMC EMI EX EX excitation EXTCLK G gain National Instruments Corporation Glossary a plug in data acquisition device module card or pad that can contain multiple channels and conversion devices SCXI modules are distinct from devices with the exception of the SCXI 1200 which is a hybrid digital ground signal an amplifier with two input terminals neither of which are tied to a ground reference whose voltage difference is amplified Deutsche Industrie Norme German Industrial Standard digital input output Declaration of Conformity software that controls a specific hardware device such as an E M Series DAQ device electromagnetic compliance electromagnetic interference positive excitation channel negative excitation channel a voltage or current source used to energize a sensor or circuit external clock signal the factor by which a signal is amplified sometimes expressed in decibels G 3 SCXI 1581 User Manual Glossary ID in input impedance J jumper L lead resistance MISO MOSI multiplex multiplexed mode 5 1581 User Manual identifier inch or inches the measured resistance and capacitance between the input terminals of a circuit a small rectangular device used to connect two adjacent
51. uctions The DAQ Getting Started Guide This document has information on installing NI DAQ and the E M Series DAQ device Install these before you install the SCXI module The SCXI hardware user manuals Read these manuals for detailed information about signal connections and module configuration They 1 2 ni com Chapter 1 About the 5 1581 also explain in greater detail how the module works and contain application hints Accessory installation guides or manuals Read the terminal block and cable assembly installation guides They explain how to physically connect the relevant pieces of the system Consult these guides when you are making the connections Series DAQ device documentation This documentation has detailed information about the DAQ device that plugs into or is connected to the computer Use this documentation for hardware installation and configuration instructions specification information about the DAQ device and application hints Software documentation You may have both application software and NI DAQ software documentation National Instruments NI application software includes LabVIEW LabWindows CVI and Measurement Studio After you 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
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