Chapter 4
Theory of Operation
©
National Instruments Corporation
4-9
Half-Bridge Type I
This section provides information for the half-bridge strain-gauge
configuration type I. The half-bridge type I measures either axial or
bending strain. Figure 4-6 shows how to position strain-gauge resistors
in an axial and bending configurations. Figure 4-7 shows the half-bridge
type I circuit wiring diagram.
Figure 4-6.
Half-Bridge Type I Measuring Axial and Bending Strain
A 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
με
is
∼
0.65 mV
out
/
V
EX
input.
Note
S– is left unwired.
Figure 4-7.
Half-Bridge Type I Circuit Diagram
(– )
R
4
(+ )
(+ )
(– )
Axial
Bending
R
3
R
3
R
4
R
1
R
L
+
–
–
+
V
EX
(– )
(+ )
R
L
R
L
R
2
V
CH
R
4
R
3