MTS Series 793 - Manual (Page 30)

MTS Series 793 Tuning and Calibration
About Tuning
Introduction 30
More about Feed
Forward Gain
Feed forward (F/F2 Gain) introduces a derivative of the command signal. It
anticipates how large a valve opening is needed to reach the required response
and adds that to the valve command—like compensating for phase lag.
F Gain vs. F2 Gain
F Gain is applied to the current control mode before the forward loop filter. F2
Gain is applied after the forward loop filter.
When your forward loop filters are set to low frequencies it tends to limit the
effectiveness of F Gain. F2 Gain may work better in this situation.
You would tend to use F Gain when there are frequencies you do not wish to
excite. Using F Gain allows the forward loop filter to filter out these frequencies.
F/F2 Gain
• Does not compensate for normal changes during testing (such as
temperature changes, servovalve droop, and so forth).
• May be used to minimize phase lag.
• Should be used like derivative gain. However, F Gain applies to the test
command signal while derivative gain applies to the feedback signal.
• Feed forward gain helps the servo-control loop react quickly to an abrupt
change in the command.
• Is needed when testing a soft specimen in force control.
Stabilization Gain (S Gain)
Stabilization gain allows a second signal to be integrated into the composite
command signal as a stabilizing factor. It enhances stability for systems that
move large masses at high speeds. The second signal is generated by a special
transducer such as
ΔP (differential pressure) or accelerometer.
Stabilization controls will be available only if a stabilization resource was added
to the control channel.
Feed Forward Command
Original Command
Original Feedback
Adjusting F Gain or F2
Gain causes the command
signal to start sooner. This
causes the feedback signal
to track the original
command signal more
closely.