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Quarter-Bridge Type I

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    Last Modified: February 16, 2016

    The following figure shows how to position a strain gage resistor in an axial configuration for the quarter-bridge type I.

    The following figure shows how to position a strain gage resistor in a bending configuration for the quarter-bridge type I.

    Quarter-bridge type I strain gage configurations have the following characteristics:
    • A single active strain gage element mounted in the principle direction of axial or bending strain.
    • A passive quarter-bridge completion resistor, known as a dummy resistor, in addition to half-bridge completion.
    • Temperature variation decreasing the accuracy of the measurements.
    • Sensitivity at 1000 µε is ~ 0.5 mVout / VEX input.

    Quarter-Bridge Type I Circuit Diagram

    The following symbols apply to the circuit diagram:
    • R1 is the half-bridge completion resistor.
    • R2 is the half-bridge completion resistor.
    • R3 is the quarter-bridge completion resistor, known as a dummy resistor.
    • R4 is the active strain gage element measuring tensile strain (+ε).
    • VEX is the excitation voltage.
    • RL is the lead resistance.
    • VCH is the measured voltage.

    The following equation converts voltage ratios to strain units for quarter-bridge configurations.

    where Vr is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation, GF is the gage factor, RL is the lead resistance, and Rg is the nominal gage resistance.


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