Chapter 2 Configuration and Installation
© National Instruments Corporation 2-29 SCXI-1121 User Manual
Figure 2-10. Shunt Circuit
The shunting resistors RSCAL are socketed so that you can replace them with
a resistor of another value to achieve the required changes. The RSCAL
resistors on your terminal block have a 301kΩ ±1% value.
Assuming a quarter-bridge strain-gauge configuration with a gauge factor
of GF = 2, the equivalent strain change introduced by the RSCAL shunting
resistor is –199 µε. 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
RSCAL should produce. For example, RSCAL = 301 kΩ and a
quarter-bridge 120 Ω strain gauge with a gauge factor of GF = 2 and
Vexc = 3.333 V and R = 120 Ω produces the following result:
Vchange = 0.3321 mV
Replacing the strained voltage with Vchange in the quarter-bridge strain
equation produces an equivalent –199 µε of change.
SCAL
EX+
R
CH+
EX–
R
SCAL
SCXI-1321
R
g
R
R
CH–
Vchange
VexcRdRSCAL Rg
+()
RSCAL RdRSCAL Rg
+()+
-----------------------------------------------------------Vexc
2
----------–=