Measurement-computing DBK Part 2 Uživatelský manuál Strana 30

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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
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
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.
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