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Tuning
Tuning the controller, as with any PID loop, requires tuning each para-
meter separately and in sequence. To achieve good PID control manu-
ally, you can use the trial and error method explained below.
Tune the Proportional Band
Set Integral Time = 0 (off)
Set Derivative Time = 0 (off)
Start with a large Proportional Band value which gives very sluggish
control with noticeable offset and tighten by decreasing the value in
half. Analyze the process variable. If the control is still sluggish, tighten
by decreasing the value in half again. Continue with the same proce-
dure until the process starts to oscillate at a constant rate. Widen the
Proportional Band by 50%, or multiply the setting 1.5 times. From a cold
start, test and verify that the Proportional Band allows maximum rise to
setpoint while maintaining minimum overshoot and offset. If not com-
pletely satisfied, fine-tune the value, up or down, as needed and test
until correct. The Proportional Band is now tuned.
Add Integral Time
Start with a large Integral Time value which gives very sluggish
response to process offset and tighten by decreasing the value in half.
Analyze the process variable. If the response to process offset is still
sluggish, tighten by decreasing the value in half again. Continue with
the same procedure until the process starts to oscillate at a constant
rate. Increase the Integral Time value by 50%, or multiply the setting 1.5
times. From a cold start, test and verify that the Integral Time allows
maximum elimination of offset with minimum overshoot. If not complete-
ly satisfied, fine-tune the value, up or down, as needed and test until
correct. The Integral Time is now tuned.
