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Ideal settings for these systems are very dependent on the
application; and are often best determined by experiment.
The following general points may prove useful for initial
consideration:
1. A common characteristic is that there is a considerable
difference between the system response to the input of heating
and of cooling energy.
2. In general, both channels can be set independently using the
tuning guidelines for settings for Proportioning Time and
Proportioning Band, and where it is known that one channel
has a dominating and rapid effect on system temperature, the
employment of narrow hysteresis ON/OFF settings for this may
give excellent results.
3. Where both setpoints are required to be set close together
(small deadband), wide proportioning or hysteresis band
settings will overlap allowing simultaneous operation of outputs,
which may give the best overall control.
Where a given application cannot be tuned to give acceptable
results over the required range of process temperatures and
conditions, it is possible that better results may be obtained with
Proportional, Derivative and Approach Control terms only.
5.8 HEATING AND COOLING
5.8.1 General Considerations
5.8.2 Cool Strategy for Heat-Cool Applications
Cool strategy: A change in load causes integral to move the linked
heat and cool prop bands. Refer to Figure 5-9.
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