Chapter 2
Using the Module
2-10
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:
Half-Bridge Type II
This section provides information for the half-bridge strain-gage configuration type II. The
half-bridge type II only measures bending strain. Figure 2-9 shows how to position
strain-gage resistors in a bending configuration. Figure 2-10 shows the half-bridge type II
circuit wiring diagram.
Figure 2-9.
Half-Bridge Type II Rejecting Axial and Measuring Bending Strain
A half-bridge type II configuration has the following characteristics:
•
Two active strain-gage elements. One strain-gage element is mounted in the direction of
bending strain on one side of the strain specimen (top) while the other is mounted in the
direction of bending strain on the opposite side (bottom).
•
Half-bridge completion resistors (R
1
and R
2
) are provided by the NI PXIe-4330/4331.
•
Sensitive to bending strain.
•
Rejects axial strain.
•
Sensitivity ~ 1
μ
V/V per
με
, for GF = 2.0.
strain
ε
( )
4
V
r
–
GF
1
ν
+
(
)
2
V
r
ν
1
–
(
)
–
[
]
---------------------------------------------------------------
=
R
4
(– )
(+ )
R
3
R
3
R
4
Rejects Axial
Measures Bending
