M&M
R
EFRIGERATION
I
NC
. 3-9
Chapter 3: Capacity Control
slowly to control parameter changes. While the control parameter is outside the band-
width values the slide valve is continuously loaded or unloaded.
Long Pulse - This is the longest amount of time used to move the slide valve while
loading or unloading the compressor. This time period is used when the control
parameter differential is equal to the bandwidth value. If the longest pulse is too long
the compressor may overshoot the optimal position. If the value is too short the slide
valve will react slowly to large changes in the control parameter.
Update Time - This is the time interval between computations of slide valve move
time. Once a required move time is calculated the CCS waits the update time interval
before another computation is made. This time is normally greater than or equal to
the long pulse.
The relationship of these parameters can be seen in the time proportional control
strategy diagrams shown below:
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