MTS WIFT Mini Transducer Interface - Manual (Page 22)

SWIFT ® Mini TI 22
Calibration
Hardware Overview
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 attached to the back of each TI box.
The calibration file is loaded into the TI non-volatile memory by MTS before the
transducer is shipped. A copy of the file is also provided on a disk.
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.
Note For SWIFT transducers designed to operate with the previous generation
low-profile TI, shunt cables A and B must be connected prior to
performing a shunt check.
Shunt verification
Shunt verification is good for verifying the SWIFT electrical system. A shunt
verification that fails should be investigated because the calibration will likely be
affected. However, a shunt passing does not guarantee the system load accuracy
so other checks should be done to verify load accuracy.
At the end of the calibration process, a shunt check is performed. During a shunt
check, 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.