DCP200 Profile Controller & Recorder -Product Manual
51-52-25-150, Issue 1 –April 2009 Manual Tuning Page 77
Fine Tuning.A separate cycle time adjustment parameter is provided for the Primary and Secondary
control when using time proportioning control outputs.
Note:
Adjusting the cycle time affects the controllers operation; a shorter cycle time gives control
that is more accurate, but mechanical components such as relays will have a reduced life
span.
1. Increase the width of the proportional band if the process overshoots or oscillates
excessively.
2. Decrease the width of the proportional band if the process responds slowly or fails to
reach setpoint.
3. To find the optimum value for the 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.
Note:
Allow enough time for the controller and process to adjust between changes.
4. Initially add Derivative at a value between 1/4th and 1/10th of the Integral Time value.
5. Increase the Derivative Time if the process overshoots/undershoots, increase its value a
little at a time, if the process becomes unstable, 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.
Note:
When controlling a modulating valve, it is recommended that Derivative is set to OFF to
avoid excessive valve activity. Derivative can cause process instability in these processes.
6. After making all other adjustments, if an offset exists between the setpoint and the process
variable use the Bias (manual reset) to eliminate the error:
Below setpoint -use a larger value
Above setpoint - use a smaller value.