NI WSN-3214 User Guide and Specifications
22
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Figure 20.
Full-Bridge Type I Circuit Diagram
The following symbols apply to the circuit diagram and equations:
•
R
1
—Active element measuring compressive strain (–
ε
).
•
R
2
—Active element measuring tensile strain (+
ε
).
•
R
3
—Active element measuring compressive strain (–
ε
).
•
R
4
—Active element measuring tensile strain (+
ε
).
•
GF
—Gage Factor, specified by the gage manufacturer.
•
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:
Note
The ratio of the bridge output voltage to the excitation voltage is calculated internally on the
NI WSN-3214. Shunt Calibration is only supported for quarter-bridge. If you are switching from
using a quarter-bridge to a half-bridge or full-bridge configuration, you need to specify 1 for Shunt
Calibration, and then perform Offset Null in the software.
The NI WSN-3214 converts the readings to strain using the following equation:
V
CH
V
EX
R
1
(–
ε
)
R
2
(+
ε
)
R
3
(–
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
–
=
strain
(
ε )
Vr
–
GF
---------
=
