Chapter 2
Using the Module
©
National Instruments Corporation
2-5
•
A passive quarter-bridge completion resistor (R
3
) is required in addition to half-bridge
completion resistors (R
1
and R
2
). All of these resistors are provided by the
NI PXIe-4330/4331 module.
•
Sensitivity ~ 0.5
μ
V/V per
με
, for GF = 2.0.
Figure 2-4.
Quarter-Bridge I Circuit Diagram
The following symbols apply to the circuit diagram and equations:
•
R
1
and R
2
—Half-bridge completion resistors located inside the NI PXIe-4330/4331.
•
R
3
—Quarter-bridge completion resistor located inside the NI PXIe-4330/4331.
–
R
3
must be equal to the nominal resistance of the active gage (R
4
).
•
R
S
—Shunt calibration resistor located inside the NI PXIe-4330/4331.
•
R
4
—Active element measuring tensile strain (+
ε
). You provide this element.
•
R
L
—Lead resistance. The resistance in the EX+ and QTR/SC field wiring should match.
•
GF
—Gage Factor, specified by the gage manufacturer.
•
V
CH
—Measured voltage of the bridge.
•
V
EX
—Excitation voltage provided by the NI PXIe-4330/4331.
•
V
r
—Offset compensated ratiometric bridge output defined by the following equation:
PXIe-4330/4331 Set Bridge
Configuration to
Quarter Bridge
+
–
+
–
V
CH
AI+
EX+
R
L
R
L
R
L
QTR
/SC
Shunt
Cal A
TB-4330
R
1
R
2
R
3
R
4
(gage)
V
EX
+
Transducer
R
S
V
r
V
CH
strained
(
)
V
CH
unstrained
(
)
–
V
EX
---------------------------------------------------------------------------------
=
