Watlow PM PLUS™ 6
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Chapter 8: Features
Once the Ramp Action is selected, you can go back to the Control Loop List and select whether the rate is in
degrees per minute or degrees per hour at
Operations — Setup - Control Loop - Ramp Scale
and then set the
ramping rate at
Operations — Setup - Control Loop - Ramp Rate
Compressor Control
The PM PLUS can be configured for Compressor control with two loops of control and enhanced firmware,
as frequently used for cooling and/or dehumidification. The application may have one or two loops of con-
trol that utilize the compressor for cooling and/or dehumidification (negative power levels). Because the
compressor is a mechanical device, it is desirable to minimize unwanted starts and stops. Either loop can
attempt to start or stop the compressor, but this algorithm will determine when it should or should not run.
Because you may not turn the compressor off until the loop is in the heat or humidify region, the input val-
ues (Source Function A and B) to the compressor algorithm must be loop power (+/- 100%).
The compressor turns on and off under the following conditions:
Loop 1
Off - When Source A Value >= Input A Turn Off
On - When Source A Value <= Input A Turn On
Loop 2
Off - When Source B Value >= Input B Turn Off
On - When Source B Value <= Input B Turn On
To prevent unwanted on/off cycling and compressor wear, set the Minimum On Time and Minimum Off Time
for the compressor.
The Time Delay setting is used to avoid having the compressor remain on indefinitely if the loop control
modes are set to off, such as when a profile ends. The rule for the Time Delay setting follows:
Off - Source A Value and Source B Value = 0.0% for a period longer than Time Delay
0% Compressor
On Power
Off
On
100%
2%
0%
-100%
Compressor On Delay = 45 Seconds
Compressor Off Delay = 20 Seconds
2% Compressor
Off Power
Time In Seconds
% Power
Heat
Cool
Compressor
Set Point
Time
Temperature
Heating System without Ramping
Temperature reaches Set Point quickly
