MTS Series 793 - Manual (Page 27)

About Tuning
MTS Series 793 Tuning and Calibration Introduction 27
In your attempt to accelerate, you press the gas pedal all the way to the floor—
and hold it there. But now you are going too fast to safely round a curve, so you
slam on the brakes just as you enter the curve, then release them. The brakes
stabilize the trip by restraining the driving action at the time that the car is
changing direction. Consider this: you barely need brakes if going slowly down a
wide, level street. Brakes become more essential the faster you go and the
quicker you change direction. Derivative gain is the same concept. It stabilizes
the system by reducing the error signal when its rate of change is the greatest.
This reduces overshoot and ringing at high proportional gain settings.
So, derivative gain indicates the change in acceleration in the error signal. Or, in
an equation:
Derivative Gain = Gain x (Command - Feedback)'
(The ' symbol in the equation above means “first derivative.”)
Derivative gain looks at the feedback side
of the summing junction. It is the
derivative of that signal, indicating how
fast the feedback is changing.
Here is a signal with a high degree
of proportional gain. Derivative
gain has not been applied yet.
Notice how noisy the signal is. The same high gain signal after
derivative gain has been applied.
The derivative gain tends to damp
out the ringing.
Feedback
Command Error