MTS Series 793 - Manual (Page 35)

About Tuning
MTS Series 793 Tuning and Calibration Introduction 35
Creating a Tuning Program
The purpose of a tuning program is to produce a command that reflects the most
demanding system response expected from a test.
Note The Function Generator is very useful for quickly setting up a tuning
program. If you use the same tuning program on a regular basis you may
wish to create and save your tuning procedure using Basic TestWare™
or by using the optional MultiPurpose TestWare™ application.
Initial tuning is best done with a waveform that has abrupt changes. This excites
the system at frequencies likely to be unstable with excessive gain. Square and
ramp waveforms are preferred. Final tuning can be done with the actual program
command for the test.
Note Always monitor the sensor feedback or error signal to evaluate the
control accuracy. See
“Monitoring Waveforms While Tuning” on page 42.
Command waveforms
A typical tuning program is a low-amplitude (5% to 10% of full-scale), low-
frequency (1 Hz to 2 Hz) square waveform.
The amplitude, frequency, and waveform type of a tuning program can be
selected to reflect the capabilities of the testing system or the testing
requirements.
Square and tapered
square waveform
A square waveform requires the servovalve to open rapidly to a large opening. It
is the most demanding waveform because it requires the maximum response
from the servoloop system. It also places a large acceleration on the test system
and specimen.
Tapered square waves taper from 0% to 100% amplitude at the beginning of
execution, and from 100% to 0% at the end of execution.
• A square waveform is most useful for tuning displacement.
• A square waveform has an infinite velocity command.
• Do not use a square waveform when tuning a control mode that uses an
extensometer. The large accelerations can cause the extensometer to move
or fall off the specimen, which can cause the system to go unstable.
• Monitor the feedback or error signal to evaluate the system stability.