MTS Series 793 - Manual (Page 24)

MTS Series 793 Tuning and Calibration
About Tuning
Introduction 24
At first, it may seem desirable to make proportional gain as large as possible.
After all, we want the system to react quickly and positively. One sign of a
system with insufficient proportional gain is that it is sluggish.
There is only one problem with having proportional gain higher than necessary:
it is very difficult to keep the car on the road. It flies off, we overcontrol trying to
correct it, and the cycle continues. A servo loop can do that too; it is said to be
ringing. It is unstable. There is nothing subtle about an unstable loop—you will
hear it. If the test fixture is large enough, you will feel it too.
So as a general rule, the gain should be as high as possible without causing the
loop to go unstable. General principles to remember are:
• With a given error signal, increasing the gain increases the input to the
servovalve.
• Increasing the input to the servovalve opens it more.
• Opening the servovalve more moves the oil faster into the actuator.
• Moving oil faster makes the loop respond quicker, reducing the error faster.
More about
Proportional gain
Proportional gain is used for all tuning situations. It introduces a control factor
that is proportional to the error signal. Proportional gain increases system
response by boosting the effect of the error signal on the servovalve.
Keep in mind:
• As proportional gain increases, the error decreases and the feedback signal
tracks the command signal more closely.
• Higher gain settings increase the speed of the system response.
• Too much proportional gain can cause the system to become unstable, while
too little proportional gain can cause the system to become sluggish.
• Gain settings for different control modes may vary greatly. For example, the
gain for force may be as low as 1 while the gain for strain may be as high as
10,000.