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National Instruments Corporation

4-1

SCXI-1503 User Manual

4

Theory of Operation

This chapter provides a brief overview and a detailed discussion of the
circuit features of the SCXI-1503 module. Refer to Figure 4-1 while
reading this section.

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Summary of Contents for Module SCXI-1503

Page 1: ...SCXI TM SCXI 1503 User Manual March 2007 374271A 01...

Page 2: ...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...

Page 3: ...t 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...

Page 4: ...t 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 t...

Page 5: ...nals 2 2 Connecting Resistive Devices to the SCXI 1503 2 2 4 Wire Configuration 2 3 2 Wire Configuration 2 4 3 Wire Resistive Sensor Configuration 2 5 Lead Resistance Compensation Using a 3 Wire Resis...

Page 6: ...4 11 Resistance Temperature Characteristic of Thermistors 4 12 Chapter 5 Using the SCXI 1503 Developing Your Application in NI DAQmx 5 1 Typical Program Flowchart 5 1 General Discussion of Typical Fl...

Page 7: ...e Resistive Sensor Configuration 2 5 Figure 2 4 3 Wire Configuration Using Matched Current Sources 2 6 Figure 4 1 Block Diagram of SCXI 1503 4 2 Figure 4 2 2 Wire RTD Measurement 4 6 Figure 4 3 Resist...

Page 8: ...signments 2 10 Table 2 4 SCXI 1503 50 Pin Rear Connector Signals 2 11 Table 4 1 Platinum RTD Types 4 8 Table 5 1 NI DAQmx Voltage Measurement Properties 5 4 Table 5 2 NI DAQmx RTD Measurement Properti...

Page 9: ...he SCXI 1503 can programmatically connect each input to ground which greatly improves its accuracy by enabling a self calibration of each input to reduce offset drift errors You can multiplex several...

Page 10: ...CXI 1503 User Manual Terminal block installation guide Documentation for your software Tools Wire cutter Wire stripper Flathead screwdriver Phillips screwdriver National Instruments Documentation The...

Page 11: ...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...

Page 12: ...adio Frequency Interference document before removing equipment covers or connecting or disconnecting any signal wires Installing the SCXI 1503 Module into the SCXI Chassis Refer to the SCXI Quick Star...

Page 13: ...3 User Manual Verifying the SCXI 1503 Installation Refer to the SCXI Quick Start Guide for details about testing the SCXI chassis and module installation in software Refer to Chapter 3 Configuring and...

Page 14: ...output connected to pins A3 and or A4 CJ SENSOR is also filtered and multiplexed to the module output buffer The differential input signal range of an SCXI 1503 module input channel is 10 V when using...

Page 15: ...a bias resistor is not recommended as this can result in noisy readings Connecting Resistive Devices to the SCXI 1503 You can connect resistive devices to the SCXI signal conditioning system in a 4 2...

Page 16: ...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 result...

Page 17: ...s 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 er...

Page 18: ...over the 2 wire measurement by connecting the device as shown in Figure 2 3 In this configuration very little current flows through RL3 and therefore RL2 is the only lead resistance that introduces a...

Page 19: ...rces 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 2 4 Figure 2 4 3 Wire...

Page 20: ...he differential amplifier eliminating their effect on the voltage measured across RT Note RL1 and RL2 are assumed to be equal The effectiveness of this method depends on the matching of the current so...

Page 21: ...IEX1 22 NC IEX2 IEX2 21 NC IEX3 IEX3 20 RSVD IEX4 IEX4 19 RSVD IEX5 IEX5 18 NC IEX6 IEX6 17 NC IEX7 IEX7 16 GND AI8 AI8 15 GND AI9 AI9 14 GND AI10 AI10 13 GND AI11 AI11 12 NC AI12 AI12 11 NC AI13 AI1...

Page 22: ...sis Ground Connects to the SCXI chassis B24 B17 B8 B1 IEX 0 7 IEX 8 15 Negative Excitation Connects to the channel ground reference This is the return path for the corresponding IEX channel C24 C17 C8...

Page 23: ...6 NC NC 7 8 NC NC 9 10 NC NC 11 12 NC NC 13 14 NC NC 15 16 NC NC 17 18 NC NC 19 20 NC NC 21 22 NC NC 23 24 DIG GND SER DAT IN 25 26 SER DAT OUT DAQ D A 27 28 NC SLOT 0 SEL 29 30 NC NC 31 32 NC DIG GND...

Page 24: ...50 Pin Rear Connector Signals Pin SCXI Signal Name NI DAQmx Device Signal Name Direction Description 1 2 AI GND AI GND Analog input ground connects to the analog input ground of the DAQ device 3 AI 0...

Page 25: ...into the SCXIbus INTR line to indicate whether the information on MOSI is being sent to a module or Slot 0 36 SCAN CLK AI HOLD COMP AI HOLD Input Scan clock a rising edge indicates to the scanned SCXI...

Page 26: ...ettings 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 u...

Page 27: ...improves the accuracy of the measurement With auto zero enabled the inputs of the SCXI 1503 are internally grounded The driver makes a measurement when the task begins and then subtracts the measured...

Page 28: ...odule to make the following types of measurements Voltage input Thermocouple RTD Thermistors Creating a Global Channel or Task To create a new voltage temperature or current input NI DAQmx global task...

Page 29: ...you set the minimum and maximum range of NI DAQmx Task or NI DAQmx Global Channel the driver selects the best gain for the measurement You also can set it through your application 10 If you are creat...

Page 30: ...tart button 8 After you have completed verifying the channels click the Stop button You have now verified the SCXI 1503 configuration and signal connection Note For more information on how to further...

Page 31: ...Corporation 4 1 SCXI 1503 User Manual 4 Theory of Operation This chapter provides a brief overview and a detailed discussion of the circuit features of the SCXI 1503 module Refer to Figure 4 1 while...

Page 32: ...onnector Rear Signal Connector 32 to 1 Mux Input Protection and Lowpass Filter Switch Switch Switch Mux Inst Amp AI 0 AI 0 AI 0 AI 0 Lowpass Filter Buffer Buffer Inst Amp Gain 31 Gain 0 Lowpass Filter...

Page 33: ...e connects the rear signal connector to the SCXIbus allowing a DAQ device to control the SCXI 1503 module and the rest of the chassis Digital Control Circuitry The digital control circuitry consists o...

Page 34: ...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 1503 The...

Page 35: ...l 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 a single channel on the DAQ device Measuring Temperature...

Page 36: ...he voltage drop across the lead resistances labeled RL adds an error voltage to the measured voltage Figure 4 2 2 Wire RTD Measurement For example a lead resistance of 0 3 in each wire adds a 0 6 erro...

Page 37: ...0 is the resistance of the RTD at 100 C R0 is the resistance of the RTD at 0 C For example a 100 platinum RTD with 0 003911 has a resistance of 139 11 at 100 C Figure 4 3 displays a typical resistance...

Page 38: ...dar 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 Temperature Coefficient...

Page 39: ...ed across the RTD V0 you can solve for T as follows where V0 is the measured RTD voltage IEX is the excitation current US Industrial Standard American 3911 100 A 3 9692 10 3 B 5 8495 10 7 C 4 233 10 1...

Page 40: ...exhibit temperature coefficients of 10 k C or more In comparison a 100 platinum RTD has a sensitivity of only 0 4 C Also the physically small size and low thermal mass of a thermistor bead allows a ve...

Page 41: ...n thermistor stability accuracy and interchangeability have prompted increased use of thermistors in a variety of applications Thermistor Measurement Circuits This section details information about th...

Page 42: ...issipation constant depends heavily on how easily heat is transferred away from the thermistor so the dissipation constant can be specified for different media in still air water or oil bath Typical d...

Page 43: ...4 13 SCXI 1503 User Manual where T K is the temperature in degrees Kelvin equal to T C 273 15 RT is the resistance of the thermistor a b and c are coefficients obtained from the thermistor manufactur...

Page 44: ...or global channel in unlicensed mode These messages continue to appear until you install version 8 1 or later of an NI ADE This section describes how to configure and use NI DAQmx to control the SCXI...

Page 45: ...te a Task Programmatically Create Task in DAQ Assistant or MAX No Hardware Timing Triggering Create Task Using DAQ Assistant No Yes No Yes Configure Channels Further Configure Channels Start Measureme...

Page 46: ...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 usin...

Page 47: ...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...

Page 48: ...age from every sample The SCXI 1503 supports None or Once Yes Analog Input General Properties Advanced Input Configuration Coupling AI Coupling Specifies the input coupling of the channel The SCXI 150...

Page 49: ...such as 2 wire 3 wire or 4 wire Yes Table 5 3 NI DAQmx Thermistor Measurement Properties Property Short Name Description DAQ Assistant Accessible Analog Input Temperature Thermistor R1 AI Thrmistr R1...

Page 50: ...rful analysis toolsets for each NI ADE to help you perform advanced analysis on the data without requiring you to have a programming background After you acquire the data and perform any required anal...

Page 51: ...configure the channels of the SCXI 1503 If you need more information or for further instructions select Help VI Function How To Help from the LabVIEW menu bar Note Except where otherwise stated the V...

Page 52: ...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 Start Measurement DAQmx Start Task vi Read Measurement D...

Page 53: ...operties Note If you do not use Active Channels the properties are set on all of the channels in the task 6 Right click ActiveChans and select Add Element Left click the new ActiveChans box Navigate t...

Page 54: ...he 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 6 NET and C to c...

Page 55: ...nChannel System Double minVal System Double maxVal To actually create and configure the channel you would enter something resembling the following example code Task myTask new NationalInstruments DAQm...

Page 56: ...503 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 EEPR...

Page 57: ...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 is recommende...

Page 58: ...Input coupling DC Input signal ranges 100 mV gain 100 or 10 V gain 1 Input overvoltage protection Powered on 42 VDC Powered off 25 V Inputs protected AI 0 15 CJ sensor input protection 15 VDC powered...

Page 59: ...point average 1 C of autozero temperature Table A 1 RTD Measurement Accuracy Measured Temperature C 100 Max C 100 Typ C 1000 Max C 1000 Typ C 100 to 0 0 60 0 23 1 09 0 46 0 to 25 0 62 0 23 1 11 0 47...

Page 60: ...interval per channel any gain 0 012 accuracy 3 s 0 0061 accuracy 10 s 0 0015 accuracy 20 s Noise characteristics RTI Gain 1 10 Hz to 1 MHz 100 Vrms Gain 100 10 Hz to 1 MHz 1 Vrms 0 1 to 10 Hz 0 5 Vp...

Page 61: ...ift 5 ppm C Output voltage compliance 10 V Maximum resistive load 100 k Overvoltage protection 40 VDC Measurement Category CAT I Power Requirements From SCXI Backplane V 18 5 to 25 VDC 170 mA V 18 5 t...

Page 62: ...ual Physical Figure A 1 SCXI 1503 Dimensions Weight 745 g 26 3 oz Maximum Working Voltage Maximum working voltage refers to the signal voltage plus the common mode voltage Signal common mode Each inpu...

Page 63: ...up 1 Class A CE C Tick ICES and FCC Part 15 Emissions Class A Note For EMC compliance operate this device according to product documentation CE Compliance This product meets the essential requirements...

Page 64: ...ick Yes to continue deleting the module or chassis or No to cancel this action Note Deleting the SCXI chassis deletes all modules in the chassis All configuration information for these modules is also...

Page 65: ...ey are loose but do not completely remove the thumbscrews Remove the SCXI 1503 by pulling steadily on both thumbscrews until the module slides completely out Figure B 1 Removing the SCXI 1503 1 Cable...

Page 66: ...pport representative often suggests troubleshooting measures If requesting technical support by phone have the system nearby so you can try these measures immediately NI contact information is listed...

Page 67: ...ate current at a level different than 100 A No Do not attempt to modify any circuitry in the SCXI 1503 Are there any user serviceable parts inside the SCXI 1503 No There are no fuses potentiometers sw...

Page 68: ...t channel do any damage to the SCXI 1503 No The SCXI 1503 delivers 100 A into any load from 0 to 100 k Does open circuiting a current output channel damage the SCXI 1503 What is the open circuit volta...

Page 69: ...k kilo 103 M mega 106 Numbers Symbols percent positive of or plus negative of or minus plus or minus less than per degree ohms 5 V signal 5 VDC source signal A A amperes ADE application development e...

Page 70: ...Data Address DAQ 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 a...

Page 71: ...drivers driver software software that controls a specific hardware device such as an E M Series DAQ device E EMC electromagnetic compliance EMI electromagnetic interference excitation a voltage or cur...

Page 72: ...asure 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 MISO master in slave out signal MOSI master out slave in signal multiplex to r...

Page 73: ...ion RSVD reserved bit pin or signal RTD resistance temperature detector S s seconds S samples scan one or more analog samples taken at the same time or nearly the same time Typically the number of inp...

Page 74: ...supply and control circuitry in the SCXI chassis SLOT 0 SEL slot 0 select signal SPI CLK serial peripheral interface clock signal T thermistor a thermally sensitive resistor Traditional NI DAQ Legacy...

Page 75: ...ents 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 v...

Page 76: ...d presenting 5 7 completing 5 8 LabVIEW 5 8 program flowchart figure 5 2 programmable properties 5 13 specifying channel strings 5 11 C cables custom 2 1 calibration SCXI 1503 5 13 CE compliance speci...

Page 77: ...nput characteristics specifications A 1 installation into SCXI chassis 1 4 L LabVIEW developing an application 5 8 programming a task table 5 8 using a NI DAQmx channel property node 5 10 LabWindows C...

Page 78: ...resistive sensor connected to 2 wire configuration 2 5 4 wire configuration 2 3 lead resistance compensation using 3 wire resistive sensor and two matched current sources 2 6 RTD measurement propertie...

Page 79: ...t sources 2 6 RTDs measurement errors 4 6 overview 4 5 relationship between resistance and temperature 4 6 resistance temperature curve figure 4 7 thermistors measurement circuits 4 11 overview 4 10 r...

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