Heat Manager Pro User Manual V1.5 Page 70
When you make use of thyristor modules or solid state relays the cycle time can be set at the
lowest possible value (0.1s) since these modules don’t have mechanical contacts. The control-
ler output can directly drive the modules proportionally which will result in a quick response to
varying process conditions and a more stable and accurate process control.
B.3
W
ORK STEP
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BY
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STEP AND
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BY
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ONE
When you adjust a PID controller by hand, a lot of experience and, as the Germans say:
“fingerspitzen gefuehl” is necessary. We consider this manual adjustment procedure more like
an art than a science.
It is very important that you have a graphic overview of the process values so you can see if
your modifications give improvements (or not, then you need to move in the other direction).
It is always best to first start by setting the I and D factors to 0 and only use the P-action.
When you roughly “feel” how the process reacts to a step like change of the set value, you can
try the addition of the I action to get the process value exactly on the set value.
Later on you add the D action to improve responsiveness.
After that, you start changing the P, I or D values one by one. Try doubling them, or halving
them, and see how the process reacts to it. This procedure must be re-done until you are
satisfied with the new settings.
When you see a process value that is slowly oscillating with a small amplitude and long period
towards the desired set value you are on the right track with these settings.
We know from practice that the D action should be roughly 25% of the I action. Certainly not
more.
