SCC-SG Series Strain-Gauge Modules User Guide
36
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Using Shunt Calibration to Correct for Gain Error
1.
Calculate the voltage change expected from the introduction of the
shunt-calibration resistor using the following formula:
where
R
SCAL
is the value of the shunt-calibration resistor.
R
4
is the nominal active strain-gauge element value.
R
3
is either the value of a completion resistor or a second active
strain-gauge element nominal value.
V
EX
is the excitation voltage.
For example, for a quarter-bridge configuration where
R
4
=
120
Ω
R
3
=
120
Ω
R
SCAL
=
301 k
Ω
V
EX
=
2.5 VDC
Offset Voltage
=
0 VDC,
then
∆
V
EXPECTED
= 0.2491 mV.
Note
Before completing step 2, null the system offset voltage. Refer to the
section for information on how to null the system offset voltage.
2.
Enable the shunt-calibration circuit and measure the resulting voltage
change (
∆
V
MEASURED
). Use the following equation to calculate a
correction factor that compensates for the DAQ system gain error:
where
∆
V
EXPECTED
is the expected change in voltage.
∆
V
MEASURED
is the measured change in voltage.
F
C
is the correction factor.
3.
Multiply subsequent voltage measurements by the correction factor
F
C
to correct for any gain error present in the DAQ system.
∆
V
EXPECTED
R
3
V
EX
R
SCAL
(
R
4
)
+
R
4
R
SCAL
+
R
3
R
SCAL
(
R
4
)
+
--------------------------------------------------------------
V
EX
2
---------
–
=
∆
V
EXPECTED
∆
V
MEASURED
--------------------------------
F
C
=
