West Control Solutions Pro-EC44 - Manual (Page 114)

Pro-EC44 2-Loop Graphical Profile Controller & Recorder
Pro-EC44 Product Manual - 59540-1 October 2013 Page 107
Integral Time Constant
To find the optimum integral time, decrease its value until the process becomes unstable,
then increase it a little at a time, until stability has is restored. Induce a load disturbance or
make a setpoint change to verify that the process stabilises. If not increase the value some
more and re-test. If the response is too slow, decrease the integral time, but avoid instability.
Integral Time
Too Short: Overshoots and oscillates Too Long: Slow warm up and response
Derivative Time Constant
Initially set the derivative to between 1/4
th
and 1/10
th
of the Integral time value.
Increase the derivative time if the process overshoots/undershoots. Increase it a little at a
time, but if the process becomes unstable, decrease it until the oscillation stops. Induce a
load disturbance or make a setpoint change to verify that the process stabilises. If not
decrease the value some more and re-test.
Derivative Time
Too Long: Oscillates and over corrects
when process disturbed
Too Short: Slow warm up and disturbance
response under-corrects
Note: When controlling a modulating valve, it is usually recommended that
derivative is set to OFF to avoid excessive valve activity. Derivative can cause
process instability in these processes.
Process Disturbance
Process Disturbance