NI WSN-3214 User Guide and Specifications
25
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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 ~ 1.0
μ
V/V per
με
, for GF = 2.0,
ν
= 0.
Figure 24.
Full-Bridge Type III Circuit Diagram
The following symbols apply to the circuit diagram and equations:
•
R
1
—Active element measuring compressive Poisson effect (–
νε
).
•
R
2
—Active element measuring tensile strain (+
ε
).
•
R
3
—Active element measuring compressive Poisson effect (–
νε
).
•
R
4
—Active element measuring the tensile strain (+
ε
).
•
GF
—Gage Factor, specified by the gage manufacturer.
•
ν
—Poisson’s ratio, defined as the negative ratio of transverse strain to axial strain (longitudinal)
strain. Poisson’s ratio is a material property of the specimen you are measuring.
•
V
CH
—Measured voltage of the bridge.
•
V
EX
—Excitation voltage provided by the NI WSN-3214.
•
V
r
—Offset compensated ratiometric bridge output defined by the following equation:
V
CH
V
EX
R
1
(
–
ν
ε
)
R
2
(+
ε
)
R
3
(
–
ν
ε
)
R
4
(+
ε
)
+
–
NI W
S
N-
3
214
R
COMP
/EX–
AI+
AI–
EX+
R
S
–
R
S
+
+
–
Vr
VCH
VEX
------------
Shunt Calibration
×
Offset Null
–
=
