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BA C7000 for EC Tower | EN | 01-2019 | 1000755
Instructions for adjusting a PID controller
These instructions answer the following questions, using a G valve as an example. However, the measures can also be transferred to
other components that are controlled by a PID controller:
1.) Why is the G valve too fast?
2.) Why is the G valve too slow?
3.) Why does the G valve oscillate?
1.) PID controller too fast -> I part too large or P part too large
2.) PID controller too low -> I part too small or P part too small
3.) PID controller oscillates -> There are resonances between the PID controller and the system that has to be controlled. This
usually happens when: 1.) the PID controller is too fast.
Adjusting a PID controller:
P part on 1
I part on 1
D part on 0
- increase the P part very slowly until the system begins to oscillate or behaves strangely in another way.
- now reset the P part to 50 % to 70 % of the value that was set before.
- increase the I part very slowly until the actual value is quickly adjusted to the exact setpoint but without oscillations.
- always leave the D part set to 0.
Not only the control parameters have an influence on the control characteristics. The actual water temperature and the actual
compressor speed also have a very significant influence on the G valve.
Therefore, the G valve tends to oscillate with the basic settings when the water is very cold or when the compressor is running slowly
or react a little slowly when the water is very warm and the compressor speed is high.
The basic settings of the G valve are selected so that they work satisfactorily for as many operating states as possible. Optimiza-
tions on one end (control speed) can easily cause significantly worse behavior at the other end (control stability, control accuracy).
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