MTS Series 793 - Manual (Page 82)

MTS Series 793 Tuning and Calibration
How to Manually Tune the Control Loop
Tuning Procedures 82
Tuning the Strain Control Mode
A strain control mode typically uses the feedback signal from an extensometer.
You need a specimen installed to tune a strain control mode.
Guidelines • Use a triangle waveform for the initial tuning.
• Do not use a square waveform for tuning. A square wave can cause the
extensometer to move or fall off the specimen, which can cause the system
to go unstable.
• If gain is too low, the system may be sluggish or unresponsive with large
static offsets; or it may be uncontrollable.
• If you observe a noisy extensometer feedback signal, use the FL Filter
setting to help suppress any unwanted mechanical resonance.
When to tune
A strain control mode usually only needs to be tuned once. However, you may
want to retune a strain control mode if:
• The type of specimen has changed.
• Any changes are made in the force train.
• Any time hydraulic system potential has changed, such as after servovalve,
hose, or pump replacement.
• You want to fine tune the control mode.
• You deem it necessary as a result of scheduled system calibration or you feel
system response should be improved or reduced.
Prerequisites Be sure the following items are completed before you begin tuning the strain
control mode:
• The specimen is installed (you may choose to use a broken specimen).
• You have created a station configuration file.
• You have created a station parameter set.
Tuning procedure
This basic strain tuning procedure should work for most applications—consider
it a guideline. You should be familiar with the background information presented
in this chapter so you can modify the following procedure for your specific
system.
1. Select an access level of Tuning.