Despatch P1400+ Temperature Controller - Manual (Page 62)

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9.4 Manually 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.
3. Increase the automatic reset until the process becomes unstable, then decrease until stability
has been restored.
Note:
Allow enough time for the controller and process to adjust.
4. Initially add rate at a value between 1/4
th
and 1/10
th
of the automatic reset value.
5. Decrease Rate if the process overshoots/undershoots or oscillates excessively.
Note:
When controlling a modulating valve, it is recommended that Rate (Derivative) is set to 0
seconds (OFF) to avoid excessive valve activity.
Rate can cause process instability.
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 bias value
Above setpoint - use a smaller bias value.