MTS SWIFT 30 Sensor - Manual (Page 29)

Calibration
SWIFT 30 Sensors Hardware Overview 29
Calibration
Each transducer is calibrated by MTS before shipment. The transducer and TI
may be returned to MTS for repair and recalibration as required.
Calibration is performed at MTS on a special fixture that is capable of applying
multiple loads to the transducer. During calibration, raw signals are measured.
The calibration gains and cross talk compensation values are computed from this
raw data. These gains are recorded in a calibration file.
A unique calibration file is supplied for each transducer. The serial number of the
TI associated with the transducer is listed at the top of the calibration file. A label
with the serial number of the TI box (and the SWIFT sensor with which it was
originally calibrated) is located at the back of each TI box.
The calibration file is loaded into the TI non-volatile RAM by MTS before the
transducer is shipped. A copy of the file is also provided on a diskette.
MTS verifies the calibration by applying loads to the transducer, measuring the
main outputs and checking for accuracy. Final calibration reports are provided
with each transducer.
Shunt calibration At the end of the calibration process, a shunt calibration is performed. During a
shunt calibration, a resistance is introduced into the bridge circuit. The difference
between the shunted and unshunted voltage is the delta shunt reference value for
each bridge. That value is saved in the calibration file, which is downloaded from
a PC or laptop computer and stored in non-volatile memory in the TI.
At any time afterward, pressing the Shunt button on the front of the TI causes
each of the strain gage bridges to be shunted in sequence, and the measured shunt
voltage (delta shunt measured value ) is compared to the reference value.
An acceptable tolerance range is also loaded into the TI memory during system
calibration. One tolerance value is used for all bridges. This value is loaded as a
percentage of allowable deviation from the delta shunt values. For example, if the
FX1 bridge has a shunt delta reference value of –3.93, and the tolerance is set at 2
(percent), the acceptable range for the measured value would be –3.85 to –4.01.