DCP200 Profile Controller & Recorder -Product Manual
51-52-25-150, Issue 1 –April 2009 Manual Tuning Page 75
Dual Control Tuning (PID with Primary and Secondary Outputs)This tuning technique balances the need to reach setpoint quickly, with the wish to limit
setpoint overshoot at start-up and during process changes. It determines values for the
Primary Proportional Band, Secondary Proportional Band, Integral and Derivative time
constants that allow the PID control algorithm to give acceptable results in most applications
that use dual control (e.g. Heat & Cool).
CAUTION:
This technique is suitable only for processes that are not harmed by large
fluctuations in the process variable.
1. Tune the controller using only the Primary Control output as described in the Single
Control Tuning section above.
2. Set the Secondary Proportional Band to the same value as the Primary Proportional Band
and monitor the operation of the controller in dual control mode. If there is a tendency to
oscillate as the control passes into the Secondary Proportional Band, increase its value. If
the process appears to be over-damped (slow to respond) in the region of the Secondary
Proportional Band, decrease its value.
3. When the PID tuning values have been determined, if there is a disturbance to the
process variable as control passes from one proportional band to the other, set the
Overlap/Deadband parameter to a positive value to introduce some overlap. Adjust this
value by trial and error until satisfactory results are obtained.
PI Tuning (Valve, Damper & Speed Controllers)This tuning technique is used when controlling a damper, a modulating valve or motor speed
controller. It determines values for the Primary Proportional Band, and Integral Time
Constant. The Derivative Time Constant is normally set to OFF. This type of control (known
as PI Control) minimises valve/motor wear whilst giving optimal process control.
CAUTION:
This technique is suitable only for processes that are not harmed by large
fluctuations in the process variable.
1. Set the setpoint to the normal operating process value (or to a lower value if overshoot
beyond this value is likely to cause damage).
2. Set controller to On/Off Control mode (i.e. set Primary Proportional Band to the minimum
value).
3. Set the Integral Time Constant to OFF.
4. Set the Derivative Time Constant to OFF.