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Chapter 2
Using the Module
2-16
ni.com
Note
The ratio of the bridge output voltage and the excitation voltage is done internally
on the NI PXIe-4330/4331.
To convert module readings to strain use the following equation:
Full-Bridge Type III
This section provides information for the full-bridge strain-gage configuration type III. The
full-bridge type III only measures axial strain. Figure 2-15 shows how to position strain-gage
resistors in an axial configuration. Figure 2-16 shows the full-bridge type III circuit wiring
diagram.
Figure 2-15.
Full-Bridge Type III Measuring Axial and Rejecting Bending Strain
A full-bridge type III configuration has the following characteristics:
•
Four active strain-gage elements. Two strain-gage elements are mounted in the direction
of axial strain with one on one side of the strain specimen (top) while the other is on the
opposite side (bottom). The other two act together as a Poisson gage and are mounted
transverse (perpendicular) to the principal axis of strain with one on one side of the strain
specimen (top) and the other on the opposite side (bottom).
•
Rejects bending strain.
•
Sensitivity ~ 1.3
μ
V/V per
με
, for GF = 2.0.
strain
ε
( )
2
V
r
–
GF
1
ν
+
(
)
--------------------------
=
R
2
(+ )
(+ )
(– )
(– )
R
4
R
3
R
1
R
4
R
3
R
2
R
1
Measures Axial
Rejects Bending