MTS Series 793 - Manual (Page 126)

MTS Series 793 Tuning and Calibration
Shunt Calibration
Calibration Procedures 126
Shunt Calibration
You can verify the calibration accuracy of a DC sensor/conditioner pair through
shunt calibration. Shunt calibration works by shunting a precision resistor across
one arm of the sensor’s Wheatstone bridge. The resulting imbalance provides a
reference value that is recorded on the calibration data sheet that accompanies the
sensor.
Note With systems that use Series 494 hardware, you can use the HWI Editor
application to select the arm of the bridge where the shunt calibration
resistor willl be applied.
A current shunt calibration value, taken before a test, should be compared to the
shunt calibration reference value recorded when the sensor was last calibrated. If
the reference value and the current value differ too greatly, the sensor/conditioner
pair should be recalibrated to establish a new shunt reference value.
Significant variations between current and reference values may occur if the
excitation voltage has drifted, or the sensor has been damaged or has changed if
some other way. It is possible to adjust excitation to compensate for small to
moderate changes in the shunt calibration value.
When to use shunt
calibration
You should perform a shunt calibration check when:
• You start a new test.
• You move a sensor to a different DC conditioner.
• You swap a DC conditioner module.
• You recalibrate a DC sensor.
• You change the sensor cable (resistance may differ).
Note Shunt calibration can not be used to compensate for different length
cables.
Note You cannot check shunt calibration of a sensor being used with the
active control mode when hydraulic pressure is on.
Note Shunt calibration does not compensate for changes in the sensor
sensitivity over time.