Figure 2-10. shunt circuit, Figure 2-10, Shunt circuit -30 – National Instruments SCXI-1121 User Manual
Page 45
Chapter 2
Configuration and Installation
© National Instruments Corporation
2-29
Figure 2-10. Shunt Circuit
The shunting resistors R
SCAL
are socketed so that you can replace them with
a resistor of another value to achieve the required changes. The R
SCAL
resistors on your terminal block have a 301 k
Ω
±1% value.
Assuming a quarter-bridge strain-gauge configuration with a gauge factor
of GF = 2, the equivalent strain change introduced by the R
SCAL
shunting
resistor is –199 µ
ε
. Determine the change as follows:
1.
Determine the change caused by the shunting resistor using the
following formula:
2.
Using the appropriate strain-gauge strain formula, and assuming that
you have no static voltage, determine the equivalent strain that the
R
SCAL
should produce. For example, R
SCAL
= 301 k
Ω
and a
quarter-bridge 120
Ω
strain gauge with a gauge factor of GF = 2 and
V
exc
= 3.333 V and R = 120
Ω
produces the following result:
V
change
= 0.3321 mV
Replacing the strained voltage with V
change
in the quarter-bridge strain
equation produces an equivalent –199 µ
ε
of change.
SCAL
EX+
R
CH+
EX–
R
SCAL
SCXI-1321
R
g
R
R
CH–
V
change
V
exc
R
d
R
SCAL
R
g
+
(
)
R
SCAL
R
d
R
SCAL
R
g
+
(
)
+
-----------------------------------------------------------
V
exc
2
----------
–
=