SCC-SG Series Strain-Gauge Modules User Guide and

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Transcript of SCC-SG Series Strain-Gauge Modules User Guide and

  • USER GUIDE

    SCC-SG Series Strain Gage Modules

    This document discusses all of the mechanical, electrical, and scaling considerations of each strain gage configuration type supported by NI. The SCC-SG Series strain-gage input modules (SCC-SGXX) allow you to take quarter-, half-, and full-bridge configuration strain measurements. Use them as follows:

    SCC-SG01 for 120 quarter-bridge configurations. SCC-SG02 for 350 quarter-bridge configurations. SCC-SG03 for half-bridge configurations.

    SCC-SG04 for full-bridge configurations.

    SCC-SG24 for at least 350 full-bridge configurations.

    Each module consists of two strain-gage input channels, offset-nulling circuitry for each channel, and an excitation circuit. Each input channel includes an instrumentation amplifier with differential inputs and a fixed gain of 100.

    The SCC-SG11 is a shunt calibration module. It contains two pairs of switches and resistors that you connect across strain gage elements where you want to perform shunt calibration.

    ContentsConventions ............................................................................................ 4What You Need to Get Started ............................................................... 5Device Specific Information ................................................................... 6

    Installing the Module ....................................................................... 6Connecting Strain Gage Input Signals............................................. 6Panelettes ......................................................................................... 7

    SCC-SG0X and SCC-SG24 .................................................................... 7Variable Definitions......................................................................... 7

  • SCC-SG Series Strain Gage Modules User Guide 2 ni.com

    SCC-SG01/02 Quarter-Bridge Connection ......................................7Quarter-Bridge Type I ...............................................................8

    SCC-SG03 Half-Bridge Connection ................................................10Half-Bridge Type I ....................................................................10Half-Bridge Type II...................................................................11Quarter-Bridge Type II..............................................................12

    SCC-SG04/24 Full-Bridge Connection............................................14Full-Bridge Type I.....................................................................14Full-Bridge Type II ...................................................................15Full-Bridge Type III ..................................................................16

    Calibration ........................................................................................18Using Shunt Calibration to Correct for Gain Error ...................18Shunt Calibration Using the SCC-SG11 ...................................19

    Replacing Resistors .................................................................................23Replacing the Quarter-Bridge Completion Resistors .......................23Replacing the Nulling Resistors .......................................................24Replacing the Shunt Resistors ..........................................................24

    Using the SCC-SGXX..............................................................................25Converting Voltage Measurements to Units of Strain .....................25Strain Equations................................................................................26

    Formulas and Variable Definitions ...........................................27Quarter-Bridge Type I ...............................................................27Quarter-Bridge Type II..............................................................28Half-Bridge Type I ....................................................................28Half-Bridge Type II...................................................................28Full-Bridge Type I.....................................................................29Full-Bridge Type II ...................................................................29Full-Bridge Type III ..................................................................29

    Specifications...........................................................................................30SCC-SG0X Strain Gage Input Modules ...........................................30

    Strain Gage Bridge Configuration.............................................30Analog Input..............................................................................30Transfer Characteristics.............................................................30Amplifier Characteristics ..........................................................31Excitation ..................................................................................31Strain Gage Bridge Completions...............................................31Completion Accuracy................................................................31Power Requirements .................................................................32

    SCC-SG24 Strain Gage Input Module .............................................32Analog Input..............................................................................32Transfer Characteristics.............................................................32Amplifier Characteristics ..........................................................33Dynamic ....................................................................................33Stability .....................................................................................33

  • National Instruments Corporation 3 SCC-SG Series Strain Gage Modules User Guide

    Null Compensation ................................................................... 33Excitation.................................................................................. 34Power Requirements................................................................. 34

    SCC-SG11 Shunt Calibration Module............................................. 34Digital I/O................................................................................. 34Shunt Calibration ...................................................................... 34Power Requirements................................................................. 35

    SCC-SGXX Strain Gage Input Modules ......................................... 35Maximum Working Voltage..................................................... 35Physical..................................................................................... 35Environmental .......................................................................... 36

    Safety ............................................................................................... 36Electromagnetic Compatibility ........................................................ 36CE Compliance ................................................................................ 36

    SCC-SGXX Module Pin Assignments .................................................... 37Theory of Operation................................................................................ 39

    Strain Gage Theory.......................................................................... 39Wheatstone Bridges .................................................................. 39Strain Gages.............................................................................. 40Quarter-Bridge Type I .............................................................. 41Quarter-Bridge Type II ............................................................. 42Half-Bridge I............................................................................. 43Half-Bridge II ........................................................................... 44Full-Bridge Type I .................................................................... 45Full-Bridge Type II................................................................... 46Full-Bridge Type III ................................................................. 47

    Signal Conditioning Theory............................................................. 48Filtering .................................................................................... 48Amplification............................................................................ 48Excitation.................................................................................. 48Bridge Completion ................................................................... 49

    Theory of Calibration....................................................................... 49Offset Nulling Adjustment ....................................................... 49Nulling Range Adjustment ....................................................... 49

  • SCC-SG Series Strain Gage Modules User Guide 4 ni.com

    ConventionsThe following conventions are used in this guide:

    Angle brackets that contain numbers separated by an ellipsis represent a range of values associated with a bit or signal namefor example, AI .

    The symbol leads you through nested menu items and dialog box options to a final action. The sequence FilePage SetupOptions 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 Radio-Frequency Interference document, shipped with the product, for precautions to take.

    When symbol is marked on a product it den