Chapter 4
Theory of Operation
©
National Instruments Corporation
4-15
Full-Bridge Type II
This section provides information for the full-bridge type II strain-gauge
configuration. The full-bridge type II only measures bending strain.
Figure 4-12 shows how to position strain-gauge resistors in a bending
configuration. Figure 4-13 shows the full-bridge type II circuit wiring
diagram.
Figure 4-12.
Full-Bridge Type II Rejecting Axial and Measuring Bending Strain
A full-bridge type II configuration has the following characteristics:
•
Four active strain-gauge elements. Two are mounted in the direction of
bending 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).
•
Rejects axial strain.
•
Compensates for specimen temperature variation.
•
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
µε
is
∼
1.3 mV
out
/
V
EX
input.
Figure 4-13.
Full-Bridge Type II Circuit Diagram
R
2
R
1
R
4
R
3
R
4
(+ )
R
1
(– )
R
3
(– )
R
2
(+ )
Axial
Bending
R
2
R
1
(– )
(+ )
+
–
–
+
V
EX
V
CH
R
4
(+ )
R
3
(– )
