Watlow ez-zone pm - Single Set Point Ramping; Cascade Control; Compressor Control

Watlow EZ-ZONE
®
PMI Controller • 198 • Chapter 9 Features
Single Set Point Ramping
Ramping protects materials and systems that cannot tolerate rapid temperature changes.
The value of the ramp rate is the maximum degrees per minute or hour that the system tem-
perature can change.
Select Ramp Action rp (Setup Page, Loop Menu):
off ramping not active.
str ramp at startup.
Stpt ramp at a set point change.
both ramp at startup or when the set point changes.
Select whether the rate is in degrees per minute or degrees per hour with Ramp Scale r.SC.
Set the ramping rate with Ramp Rate r.rt (Setup Page, Loop Menu).
Cascade Control
The PM (PM4/8/9) can be congured for Cascade control with enhanced rmware. Cascade
is used to optimize the performance of thermal systems with long lag times. It utilizes a con-
trol strategy in which one control loop provides the set point for another loop. See Chapter
10 for application examples.
Compressor Control
The PM control can be congured for Compressor control with two loops of control and
enhanced rmware. A typical use scenario for compressor control is for cooling and/or dehu-
midication. The application may have one or two loops of control which utilize the com-
pressor to accomplish the cooling and/or dehumidication (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 make
the determination when it should or should not run. Because you may not turn the compres-
sor off until the loop is in the heat or
humidify region, the input values
(Source Function A and B) to the com-
pressor algorithm must be loop power
(+/- 100%).
The compressor will turn 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
Set Point
Time
Temperature
Temperature ramps to Set Point at a set rate
degrees
per minute
Heating System with Ramping
Set Point
Time
Temperature
Heating System without Ramping
Temperature reaches Set Point quickly
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