App-21
IM 701240-01E
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App
App
Index
Appendix
Note
•
When executing shunt calibration, select an appropriate range so that the measured values
do not exceed the range when the shunt calibration relay circuit is ON. The SL1400 attempts
shunt calibration within the current specified range.
•
If shunt calibration fails (the measured value exceeds the range, for example), an error
message is displayed. In such case, change the range and execute shunt calibration again.
Taking Measures against Noise
Because measurements are made at the
µ
V level, the strain gauge is extremely
susceptible to noise. If the execution of balancing or shunt calibration fails, it may be
due to the effect of noise. Check the following points.
• Because the strain gauge is attached away from the bridge head, it is recommended
that twisted wire be used for extension.
• Use a bridge head with high noise resistance. It is recommended that YOKOGAWA
bridge head (701957/701958) with high noise resistance be used.
Calculation of the Shunt Resistance
To execute shunt calibration, the shunt resistance (Rs) and the expected strain (
ε
) need
to be calculated in advance. Use
ε
as given in the equation below (normally a negative
value). With the SL1400, enter the value into “P2-Y” under the shunt calibration
execution menu. However, when using the general method given for shunt calibration
(the easy method), an error of 1 to 2% can be introduced as the strain value (
ε
)
increases. Therefore, calculate using the detailed method whenever possible. Also, you
must select a setting range value that will not result in an overrange.
Equation for Rs and
ε
When Executing Shunt Calibration
• General Equation
∆
R/R = K
×
ε
(1): Basic Equation of Strain
∆
R = R–R//Rs
(2): Equation of the change in resistance when the shunt
resistance is ON
In this manual, the parallel equation of resistors are expressed as follows:
R//Rs=
=
1
R
R
×
Rs
R+Rs
1
1
Rs
+
ε
:
Strain (strain you wish to generate when the shunt resistance is turned ON)
K: Gauge
factor
R: Bridge
resistance
∆
R: Resistance change
Rs: Shunt resistance (shunt resistance you wish to derive)
If
∆
R is cancelled out from (1) and (2),
Rs=R
×
(1-K
×ε
)/(K
×ε
)
(Equation A): General equation used to calculate the
shunt resistance (includes error)
Appendix 10 Shunt Calibration of the Strain Module