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National Instruments SCXI-1581 User Manual

National Instruments SCXI-1581 User Manual

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SCXI
TM
SCXI-1581 User Manual
April 2006
323074C-01

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  • Page 1 SCXI SCXI-1581 User Manual April 2006 323074C-01...
  • Page 2 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 ©...
  • Page 3 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.
  • Page 4 Conventions 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 <3..0>. » The » symbol leads you through nested menu items and dialog box options to a final action.

  • Page 5: Table Of Contents

    What You Need to Get Started ..................1-1 National Instruments Documentation ................1-2 Installing Application Software, NI-DAQ, and the E/M Series DAQ Device ....1-3 Installing the SCXI-1581 Module into the SCXI Chassis.......1-4 Verifying the SCXI-1581 Installation................1-4 Configuring the SCXI System Software ............1-4 Calibrating the SCXI-1581 ....................1-5...
  • Page 6 Appendix C Common Questions Glossary Index Figures Figure 1-1. SCXI-1581 to DMM Connections ............1-4 Figure 3-1. Block Diagram of SCXI-1581 .............. 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.
  • Page 7 Table 2-1. Front Signal Pin Assignments ..............2-2 Table 2-2. Signal Descriptions................2-3 Table 2-3. Rear Signal Pin Assignments ..............2-4 Table 2-4. SCXI-1581 Communication Signals .............2-5 Table 4-1. Platinum RTD Types................4-12 Table C-1. SCXI-1581 Digital Signals..............C-3 © National Instruments Corporation SCXI-1581 User Manual...

  • Page 8: About The Scxi-1581

    About the SCXI-1581 The SCXI-1581 module provides 32 channels of 100 µA current excitation. You can use the SCXI-1581 in any application that requires 100 µA 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.

  • Page 9: National Instruments Documentation

    Phillips screwdriver National Instruments Documentation 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: •...

  • Page 10: 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...

  • Page 11: Installing The Scxi-1581 Module Into The Scxi Chassis

    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 configurable settings in MAX for use with either NI-DAQmx or Traditional NI-DAQ (Legacy).

  • Page 12: Calibrating The Scxi-1581

    Calibrating the SCXI-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.

  • Page 13: Connecting Signals

    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...

  • Page 14: Table 2-1. Front Signal Pin Assignments

    EX18+ EX19– EX19+ EX20– EX20+ EX21– EX21+ EX22– EX22+ EX23– EX23+ EX24– EX24+ EX25– EX25+ EX26– EX26+ EX27– EX27+ EX28– EX28+ EX29– EX29+ NC means no connection CGND EX30– EX30+ RSVD means reserved RSVD EX31– EX31+ SCXI-1581 User Manual ni.com...

  • Page 15: Table 2-2. Signal Descriptions

    24 and 33, provides a separate ground reference for the communication signals. SERDATIN, SERDATOUT, DAQD*/A, SLOT0SEL*, 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.

  • Page 16: Table 2-3. Rear Signal Pin Assignments

    DIG GND — 39 40 — AI HOLD COMP, 41 42 AI HOLD 43 44 45 46 SER CLK — 47 48 — — 49 50 — — — — — SYNC — — — — SCXI-1581 User Manual ni.com...

  • Page 17: Table 2-4. Scxi-1581 Communication Signals

    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...
  • Page 18 Chapter 2 Connecting Signals Table 2-4. SCXI-1581 Communication Signals (Continued) NI-DAQmx Traditional NI-DAQ SCXI Device Signal (Legacy) Device Signal Name Name Signal Name Direction Description SCAN CLK AI HOLD COMP, SCANCLK Input Scan clock—a rising AI HOLD edge indicates to the...

  • Page 19: Theory Of Operation

    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 CH 0 + Buffer CH 0 –...

  • Page 20: Scanning Other Scxi Modules Through The Scxi-1581

    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.

  • Page 21: Using The Scxi-1581

    The current sources on the SCXI-1581 continuously provide 32 channels of 100 µA 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.

  • Page 22: 4-Wire Configuration

    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.

  • Page 23: 2-Wire Configuration

    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 (V ) is introduced into the measurement equal to the excitation current (I ) times the sum of the two lead resistances, R .

  • Page 24: 3-Wire Resistive Sensor Connected In A 2-Wire Configuration

    The resulting measurement error is: 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 CH0+ terminal. SCXI-1581...

  • Page 25: Lead-Resistance Compensation Using A 3-Wire Resistive Sensor And Two Matched Current Sources

    Note 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.

  • Page 26: Lead-Resistance Compensation Using A 3-Wire Resistive Sensor And Two Differential Amplifiers

    Chapter 4 Using the SCXI-1581 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.

  • Page 27: Configuring Sensors In Software

    RTD type—refer to Table 4-1 for a list of RTD types. • —the nominal resistance value of the RTD. • Configuration—how the RTD is connected. • source—select External when connected to an SCXI-1581. value (A)—100 µ when connected to the SCXI-1581. • © National Instruments Corporation SCXI-1581 User Manual...

  • Page 28: Creating A Thermistor Virtual Channel Using Ni-Daqmx

    • source—select External when connected to an SCXI-1581 value (A)—100 µ when connected to the SCXI-1581. • • Configuration—the wire configuration of the sensor. Click the device tab and set any device specific properties that are applicable for the measurement device.

  • Page 29: Measuring Temperature With Resistive Transducers

    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.

  • Page 30: The Relationship Between Resistance And Temperature In Rtds

    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 kΩ. Refer to Appendix A, Specifications, for the maximum ratings.
  • Page 31 Chapter 4 Using the SCXI-1581 where is the resistance of the RTD at 100 °C. is the resistance of the RTD at 0 °C. For example, a 100 Ω platinum RTD with α = 0.003911 has a resistance of 139.11 Ω at 100 °C.

  • Page 32: Table 4-1. Platinum Rtd Types

    Chapter 4 Using the SCXI-1581 where is the resistance of the RTD at temperature T. 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.

  • Page 33: Thermistors

    Chapter 4 Using the SCXI-1581 For temperatures above 0 °C, coefficient C equals 0, reducing this equation to a quadratic. If you pass a known current, I , through the RTD and measure the output voltage developed across the RTD, V...
  • Page 34 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.

  • Page 35: Thermistor Measurement Circuits

    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 × R...

  • Page 36: Resistance/Temperature Characteristic Of Thermistors

    Chapter 4 Using the SCXI-1581 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.
  • Page 37 Specifications This appendix lists the specifications for the SCXI-1581 modules. These specifications are typical at 25 °C unless otherwise noted. Stability Recommended warm-up time ....10 minutes Excitation Channels..........32 single-ended outputs Current output ........100 µA Accuracy ..........±0.05% Temperature drift ........

  • Page 38: Appendix A Specifications

    Humidity ..........10 to 90% RH, noncondensing Maximum altitude........2,000 meters Pollution Degree (indoor use only) ..2 Physical 3.0 cm (1.2 in.) 17.2 cm (6.8 in.) 18.8 cm (7.4 in.) Figure A-1. SCXI-1581 Dimensions Weight ............731 gm (25.8 oz) SCXI-1581 User Manual ni.com...
  • Page 39 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: • IEC 61010-1, EN 61010-1 • UL 61010-1 • CAN/CSA-C22.2 No. 61010-1 For UL and other safety certifications, refer to the product label or visit...

  • Page 40: Appendix B Removing The Scxi-1581

    Removing the SCXI-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: Expand Devices and Interfaces.
  • Page 41 Power off the chassis. Do not remove the SCXI-1581 module from a chassis that is powered on. If the SCXI-1581 is the module cabled to the E/M Series DAQ device, disconnect the cable. Remove any terminal block that connects to the SCXI-1581.
  • Page 42 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 have NI-DAQ 7.0 or later. Visit the NI Web site at ni.com...

  • Page 43: Appendix C Common Questions

    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 µA? No. Do not attempt to modify any circuitry in the SCXI-1581.

  • Page 44: Table C-1. Scxi-1581 Digital Signals

    Does short-circuiting a current-output channel do any damage to the SCXI-1581? No. The SCXI-1581 delivers 100 µA into any load from 0 Ω to 100 kΩ. Does open-circuiting a current-output channel damage the SCXI-1581? What is the open-circuit voltage level? No.
  • Page 45 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.
  • Page 46 ° degree Ω ohms +5 V (signal) +5 VDC source signal amperes application development environment such as LabVIEW, LabWindows/CVI, Visual Basic, C, and C++ analog input AIGND analog input ground signal © National Instruments Corporation SCXI-1581 User Manual...
  • Page 47 Examples are E/M Series data acquisition devices. DAQD*/A the data acquisition device data/address line signal used to indicate whether the SERDATIN pulse train transmitted to the SCXI chassis contains data or address information SCXI-1581 User Manual ni.com...
  • Page 48 EXTCLK external clock signal gain the factor by which a signal is amplified, sometimes expressed in decibels © National Instruments Corporation SCXI-1581 User Manual...
  • Page 49 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 SCXI-1581 User Manual ni.com...
  • Page 50 Glossary not connected (signal) NI-DAQ the driver software needed in order to use National Instruments E/M Series DAQ devices and SCXI components NI-DAQmx The latest NI-DAQ driver with new VIs, functions, and development tools for controlling measurement devices. output voltage...
  • Page 51 (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. transducer a device capable of converting energy from one form to another SCXI-1581 User Manual ni.com...
  • Page 52 (2) a LabVIEW software module (VI), which consists of a front panel user interface and a block diagram program virtual channels channel names that can be defined outside the application and used without having to perform scaling operations watts © National Instruments Corporation SCXI-1581 User Manual...
  • Page 53 A-1 about, C-4 front connector, pin assignments (table), 2-2 CE compliance specifications, A-3 common questions, C-1 connecting resistive devices to SCXI-1581 2-wire configuration, 4-3 installation, into SCXI chassis, 1-4 3-wire resistive sensor connected in 2-wire configuration, 4-4 4-wire configuration, 4-2 lead-resistance compensation Measurement &...
  • Page 54 CE compliance, A-3 electromagnetic compatibility, A-3 rear signal connector, communications environment, A-2 signals, 2-3 excitation, A-1 removing the SCXI-1581 from Measurement physical, A-2 & Automation Explorer, B-1 power requirements from SCXI resistive devices, connecting to SCXI-1581 backplane, A-1 2-wire configuration, 4-3...
  • Page 55 4-13 4-wire configuration, 4-2 resistance/temperature lead resistance compensation characteristics, 4-16 using 3-wire resistive sensor and two resistance-temperature curve differential amplifiers, 4-6 (figure), 4-14 using 3-wire resistive sensor and two matched current sources, 4-5 © National Instruments Corporation SCXI-1581 User Manual...

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