MTS Series 793 - Manual (Page 195)

Extensometer Calibration
MTS Series 793 Tuning and Calibration Calibration Procedures 195
Extensometer Calibration
An extensometer is a sensor attached to a specimen that measures a dimensional
change (gage length or strain) that occurs in the specimen during testing. It works
by means of precision resistance-type strain gages bonded to a metallic element
to form a Wheatstone bridge circuit.
Extensometers require special test fixtures to aid in calibration.
Prerequisites
Be sure the items described in “Pre-Calibration Considerations” on page 123 are
true.
An extensometer requires DC excitation, which requires either a dedicated DC
conditioner or a digital universal conditioner (DUC) configured in the DC mode.
You must know which conditioner is connected to the extensometer.
Note If you are recalibrating a sensor, use the existing calibration values as a
starting point.
Initial calibration
If you are calibrating a sensor for the first time, you may find it necessary to:
• Perform an initial tuning of the sensor channel before calibration.
• Perform the procedure twice.
Recalibration
If you are recalibrating a sensor, use the existing calibration values as a starting
point.
Considerations for full-
range conditioners
Full-range conditioners allow you to choose Gain/Delta K or Gain/Linearization
for calibrating extensometers. The mV/V Pos Tension and mV/V Pos Comp
calibration types are typically not used for controllers equipped with full-range
conditioners.
• During calibration, Manual Offset should always be set to zero.
• During calibration, ensure that Electrical Zero Lock is checked on the
Offset/Zero tab of the Inputs panel.
• After calibration, do not change the electrical zero adjustment.
Readjustment of electrical zero after calibration will change the point at
which linearization takes place, disturbing other calibration settings
(especially Delta
K).