Measurement Computing 6224 - Manual (Page 30)

6224 User’s Manual Strain and Pressure/Force 7-5
Half-Bridge I
Half-bridge type I measures either axial or bending strain.
Half-bridge type I has the following characteristics:
Two active strain-gauge elements. One is mounted in the direction of axial strain, the other acts as a Poisson gauge
and is mounted transverse (perpendicular) to the principal axis of strain.
Completion resistors provide half bridge completion.
Sensitive to both axial and bending strain.
Compensates for temperature.
Compensates for the aggregate effect on the principle strain measurement due to the Poisson’s ratio of the specimen
material.
Sensitivity at 1000 is ~ 0.65 mV
out
/ V
EX
input.
The following apply to the above circuit diagram and to the equations provided in the supplemental information.
R1 and R2 are half-bridge completion resistors.
R3 is the active strain-gauge element measuring compression from Poisson effect (– ).
R4 is the active strain-gauge element measuring tensile strain (+ ).
Supplemental Information
Data from strain channels (Half-Bridge I) is converted to strain units using the following equation:
10
6
4 V r
GF 1 ( ) 2 V r 1 ( )
1
R L
R g