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Quarter-Bridge Type I

Last Modified: November 16, 2017

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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