MTS Series 793 - Manual (Page 19)

About Tuning
MTS Series 793 Tuning and Calibration Introduction 19
About Tuning
Tuning is adjusting your test system so that its servo loop responds accurately to
its command signal. When you tune, you are setting the response and stability of
the servo control loop. Proper tuning improves the performance of your test
system just like setting the timing on an automobile improves its performance.
It is not necessary for you to always have every control mode of every control
channel perfectly tuned. Tune whenever necessary to whatever extent needed to
have your test system behave the way you want it to.
The controller system software includes several tuning controls. You do not need
to use all of the controls to properly tune your system. In fact, most testing can be
accomplished with just the proportional gain adjustment. The other adjustments
introduce a signal to the command to compensate for specific situations.
Note Throughout this chapter the terms gain, rate, and reset represent
proportional gain, rate derivative, and reset integration respectively.
Control loop elements
The control loop of your test system basically has three elements:
• The command, which is really demanding,
“I want you do this.”
• The feedback, which is responding,
“I’m actually doing this at the present time.”
• The error, which is complaining, “You two are out of agreement by this
much.”
Summing junction
This means that Error = Command - Feedback. This is the summing junction.
You want to get the summing junction to drive the error to zero, and to do it
smoothly and efficiently.
Consequences of a
large degree of error
While precise tuning is not usually necessary, inaccurate tuning increases the
error and phase lag between the command and the feedback. If the error is large,
it can reduce control accuracy and repeatability, and prevent the full program
command from being applied to the specimen.