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



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



Half-bridge type I strain gage configurations have the following characteristics:
  • Two active strain gage elements, one mounted in the direction of axial strain and the other acting as a Poisson gage and mounted transverse, or perpendicular, to the principal axis of strain.
  • Completion resistors which provide half-bridge completion.
  • Sensitivity to both axial and bending strain.
  • Compensation for temperature.
  • Compensation for the aggregate effect on the principle strain measurement due to the Poisson's ratio of the material.
  • Sensitivity at 1000 µε is ~ 0.65 mVout/ VEX input

Half-Bridge Type I Circuit Diagram

Figure 3. Half-Bridge Type I Circuit Diagram

Half-Bridge Type I Circuit Diagram
The following symbols apply to the circuit diagram:
  • R1—Half-bridge completion resistor.
  • R2—Half-bridge completion resistor.
  • R3—Active strain gage element measuring compressive strain (–ε).
  • R4—Active strain gage resistor measuring tensile strain (+ε).
  • VEX—Excitation voltage.
  • RL—Lead resistance.
  • VCH—Measured voltage.

    • The following equation converts voltage ratios to strain units for half-bridge type I configurations:

    Strain ( ε ) = - 4 V r GF [ ( 1 + ν ) - 2 V r ( ν - 1 ) ] × ( 1 + R L R g )
    where
    • Vr is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation.
    • GF is the gage factor.
    • ν is the Poisson's ratio.
    • RL is the lead resistance.
    • Rg is the nominal gage resistance.