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.