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

Figure 24.
Diagram showing axial strain gage placement for half-bridge type I.

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

Figure 25.
Diagram showing bending strain gage placement for 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 mV out/ V EX input.

Half-Bridge Type I Circuit Diagram

Figure 26.
Circuit diagram for half-bridge type I with resistor designations.

The following symbols apply to the circuit diagram:

  • R 1 is the half-bridge completion resistor.
  • R 2 is the half-bridge completion resistor.
  • R 3 is the active strain gage element measuring compression due to the Poisson effect (–ε).
  • R 4 is the active strain gage element measuring tensile strain (+ε).
  • V EX is the excitation voltage.
  • R L is the lead resistance.
  • V CH is the measured voltage.

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

Figure 27.
Equation for converting voltage ratio to strain for half-bridge type I.

where V r is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation, GF is the gage factor, v is the Poisson's ratio, R L is the lead resistance, and R g is the nominal gage resistance.