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2.4 Temperature Control Loop Adjustment
In most applications, the default PID settings in the controller with give good temperature control. If it
is found necessary to change these, then it is recommended that the Zeigler-Nichols manual tuning
method is adopted.
NOTICE! This method requires the system to be operating under typical load conditions
and will initially cause the control loop to temporarily become unstable with wide
temperature swing oscillations. It is important to ensure that this will not cause any
damage to the equipment being cooled.
Log-on at Engineering level will be required to make the necessary changes.
1. Set the Integral Reset Time and Derivative Reset Time (Configuration – Temperature Control
screens P311 & P312) to 0 seconds.
2. Increase the Proportional Band (Configuration – Temperature Control screen P310) to a higher
value from the default, e.g. 20°C
3. Check that secondary supply temperature (T2) stabilises. Note: temperature will stabilise at a
higher temperature than the current set point. This offset will be eradicated once the Integral
reset time is added back in.
4. If temperature control is un-stable, raise the Proportional Band to a higher value until
temperature stabilises, otherwise gradually decrease the Proportional Band in 1°C steps until
the supply temperature (T2) starts to oscillate at a constant rate.
5. Measure the frequency of the oscillation time (peak to peak) in seconds (t).
2.4.1 PI Control
For systems that have reasonably steady or slow changing heat loads, PI control only should be
sufficient:-
1. Set the Proportional Band to 2.2 x the Proportional Band setting at which the system became
unstable.
2. Set the Integral Reset Time to 0.83 x the oscillation time (t).
3. Leave the Derivative Reset Time at 0.
2.4.2 PID Control
For systems that will see high or sudden changing heat loads, PID control will generally be preferable:
-
1. Set the Proportional Band to 1.67 x the Proportional Band setting at which the system became
unstable.
2. Set the Integral Reset Time to 0.5 x the oscillation time (t).
Set the Derivative Reset Time to 0.125 x the oscillation time (t).
2.5 Alarm Management
When an alarm occurs, a flashing alarm bell icon will immediately break through at the top right-hand
corner of the Home screen, with the number of active alarms stated below.
CDU Operating & Maintenance Guide
Neptune DWC RM100 in-rack Coolant Distribution Unit
28
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