MTS Series 793 - Manual (Page 40)

MTS Series 793 Tuning and Calibration
About Tuning
Introduction 40
Other Tuning Considerations
Tuning with a dummy
specimen
Specimens can be very expensive. A dummy specimen is an inexpensive material
that has similar characteristics to the specimen selected for testing. The most
important specimen characteristic is its spring rate.
The advantage of a dummy specimen is that it can simulate how your testing
system reacts to real specimen. You can establish a more precise level of tuning
with a dummy specimen.
Tuning with a real
specimen
If you do not have a dummy specimen or if a dummy specimen is not practical,
review the following recommendations if you must use a real specimen:
• Start your PIDF controls at minimum settings.
• Do not use a square waveform for a massive specimen or a specimen prone
to vibrations.
• Adjust rate to minimize any oscillation, overshoot, or ringing in the
waveform.
• Be very conservative by beginning with a ramp waveform to establish initial
control. Then use a waveform that resembles the test waveform to provide a
precise level of control.
Tuning without any
specimen
A specimen is required to tune force and strain control modes. Initial force tuning
may be accomplished with the actuator up against the force sensor. The actuator
acts as a specimen reacting against the force sensor. Review the following
recommendations if you must tune without a specimen:
• If you are using a load frame, adjust the load unit crosshead so the actuator
can reach the force sensor.
• Carefully adjust the actuator using a tuned length control mode so it contacts
the force sensor.
• Switch to force control before you proceed with initial tuning.