Campbell Scientific 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules - Manual (Page 36)

4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules (TIM)
31: Sample (P70)^16425
1: 16 Reps
2: 52 Loc [ uStrain01 ]
32: Do (P86)
1: 20 Set Output Flag Low (Flag 0)
33: End (P95)
End Program
4.4.2 Shunt Calibration Lead Compensation for 3-Wire, ¼ Bridge Strain
Although the following may seem complicated, the process of
performing a Shunt calibration is simple when using the
Calibration Wizard utility found in CSI’s software packages. NOTE
Another method to compensate for sensitivity errors, and to calibrate the
system (adjust system scaling), is to do a shunt calibration. This entails
shunting a resistor across one of the arms of the bridge. The premise of a shunt
calibration is that the shunted arm undergoes a reduction in resistance creating
a simulated strain. The difference in strain reported by the system is checked
against the actual simulated strain. Variance between the reported strain and
the simulated strain can be corrected through adjusting the strain gauge’s Gage
Factor (GF).
4.4.2.1 Three Wire Gage Circuit with Shunt
There are two methods for performing a shunt calibration on a 3-Wire ¼ bridge
strain circuit. The first is to shunt across the active gage remotely, and the
second is to shunt across the Dummy resistor or Dummy Gage (dependant on
which is employed in the circuit) back at the datalogger.
For either shunt method, the Dummy resistor should be a 0.02% precision or
better resistor to insure that its resistance is the nominal resistance of the active
gauge. In addition it should have a low Temperature Coefficient of Resistance
(TCR) to limit the errors introduced by the change in its resistance due to
temperature variations. The Shunt resistor should also have a precision of
0.02% or better and a low TCR.
4.4.2.1.1 Three Wire Gage Circuit with Remote Shunt across the Active Gage
A 3-wire quarter bridge strain circuit with a Shunt calibration resistor ready to
shunt across the arm that holds the strain gauge is shown in figure 4.4-2.
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