Measurement Computing DBK Part 2 - Manual (Page 30)

DBK43A & DBK43B, pg. 10 899892 DBK Option Cards and Modules
A formula used to calculate the shunt-cal resistance value is:
R
Shunt
= [R
Gage
/ F
G
( ε) ] - R
Gage
Where:
R
Shunt
= the shunt calibration resistor value
R
Gage
= the resistance of the gage
F
G
= the gage factor
ε =
the strain value of the gage
Example:
An engineer wants to know the shunt calibration resistor value for a strain gage with the following
parameters.
resistance: 120 Ω
gage factor: 2.0
strain: 5000 micro-strain, i.e., 5000 x 10
-6
Plugging the values into the equation, we get:
R
Shunt
= [R
Gage
/ F
G
( ε) ] - R
Gage
= [120 / 2.0(5000 x 10 -6 )] - 120
= [120 / .01] – 120
= 12000 – 120
= 11,880 Ω
In all cases, the resistance of the solid-state switch will be negligible when compared to the shunt
resistance. Changing the CAL/NORM switch (on the rear panel) to the CAL position while reading the
bridge will activate the shunt-calibration resistors. After reading the offset, return the switch to the NORM
position for normal bridge readings.