Controllers Fitted With Primary And Secondary Outputs; Manual Fine Tuning - WEST P8700 User Manual

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Controllers Fitted With Primary and Secondary Outputs

Before starting to tune a controller, check that the Setpoint Upper Limit ( :-=+ ) and Setpoint
Lower Limit ( :-++ ) are set to safe levels.
The following simple technique may be used to determine values for the Primary Proportional
Band ( -6B- ), Secondary Proportional Band ( -6B: ), Integral Time Constant ( 59:# ) and
Derivative Time Constant ( 05#; ).
CAUTION:
This technique is suitable only for processes that are not harmed by large
fluctuations in the process variable. It provides an acceptable basis from which to
start fine-tuning for a wide range of processes.
1. Tune the controller using only the Primary Control output as described in the previous
section.
2. Set -6B: to the same value as -6B- and monitor the operation of the controller in dual
output mode. If there is a tendency to oscillate as the control passes into the Secondary
Proportional Band, increase the value of -6B: . If the process appears to be over-damped
in the region of the Secondary Proportional Band, decrease the value of -6B: .
3. When the PID tuning term values have been determined, if there is a kick to the process
variable as control passes from one output 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.

Manual Fine Tuning.

A separate cycle time adjustment parameter is provided for each time proportioning control
output.
Note:
Adjusting the cycle time affects the controllers operation; a shorter cycle time gives more
accurate control but electromechanical components such as relays 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.
59305, Issue 5 – March 2005
- DIN Controllers & Indicators - Product Manual
Manual Tuning Page 91