The full-bridge type I configuration only measures the bending strain.

Figure 11.
Diagram showing invalid strain gage placement for full-bridge type I.

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

Figure 12.
Diagram showing bending strain gage placement for full-bridge type I.

Full-bridge type I strain gage configurations have the following characteristics:

  • Four active strain gage elements, two mounted in the direction of bending strain on the top side of the strain specimen and the other two mounted in the direction of bending strain on the bottom side.
  • High sensitivity to bending strain.
  • Rejection of axial strain.
  • Compensation for temperature.
  • Compensation for lead resistance.
  • Sensitivity at 1000 µε is ~ 2.0 mV out / V EX input.

Full-Bridge Type I Circuit Diagram

Figure 13.
Circuit diagram for full-bridge type I with resistor designations.

The following symbols apply to the circuit diagram:

  • R 1 is the active strain gage element measuring compressive strain (–ε).
  • R 2 is the active strain gage element measuring tensile strain (+ε).
  • R 3 is the active strain gage element measuring compressive strain (–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 full-bridge type I configurations.

Figure 14.
Equation for converting voltage ratio to strain for full-bridge type I.

where V r is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation, and GF is the gage factor.