Measurement Computing 6224 - Manual (Page 34)

6224 User’s Manual Strain and Pressure/Force 7-9
Full-Bridge III
Full-bridge type III only measures axial strain.
A Full-bridge type III configuration has the following characteristics:
Four active strain-gauge elements. Two are mounted in the direction of axial strain with one on one side of the strain
specimen (top), the other on the opposite side (bottom). The other two act together as a Poisson gauge and are
mounted transverse (perpendicular) to the principal axis of strain with one on one side of the strain specimen (top),
the other on the opposite side (bottom).
Compensates for temperature.
Rejects bending strain.
Compensates for the aggregate effect on the principle strain measurement due to the Poisson’s ratio of the specimen
material.
Compensates for lead resistance.
Sensitivity at 1000 is ~ 1.3 mV
out
/ V
EX
input.
The following symbols apply to the above circuit diagram and to the equations provided in the supplemental information.
R1 is an active strain-gauge element measuring compressive Poisson effect (– ).
R2 is an active strain-gauge element measuring tensile strain (+ ).
R3 is an active strain-gauge element measuring compressive Poisson effect (– ).
R4 is an active strain-gauge element measuring the tensile strain (+ ).
Supplemental Information
Data from strain channels (Full-Bridge III) is converted to strain units using the following equation:
10
6
2 V r
GF 1 ( ) V r 1 ( )