ESIE07-05
Functional Control
Part 2 – Functional Description
2–73
3
2
4
5
1
Graph 2
The derivative part of the logic controls how the temperature reaches the setpoint. If it is getting closer
– increases the time between intervals, or if it is far from the setpoint – decreases the time between
intervals. The result is having the controller act differently whenever the water temperature changes.
If the derivative time is increased, the control will be more sensitive to temperature changes. For
example: the derivative time can be increased when a chiller is working with a very variable load. The
integral time stores the memory on how the P+1 controls the temperature.
Evap water leaving
Pulse time
Minimum loading pulse
time
Pulse
stand-by
Max loading pulse
time
If temperature is
far from set-point
If temperature is
close to set-point
ESIE07-05.book Page 73 Friday, December 21, 2007 3:21 PM
