User guide

Watlow EZ-ZONE
®
PM PID Controller • 93 • Chapter 9 Features
Cool Output Curve
A nonlinear output curve may improve performance when the response of the output device is nonlinear. If a
cool output uses one of the nonlinear curves a PID calculation yields a lower actual output level than a linear
output would provide.
These output curves are used in plastics extruder applications: curve A for oil-cooled extruders and curve
B for water-cooled extruders.
Select a nonlinear cool output curve with Cool Output Curve [`C;Cr] (Setup Menu, Loop Menu).
Control Methods
Output Configuration
Each controller output can be configured as a heat output, a cool output, an alarm output or deactivated. No
dependency limitations have been placed on the available combinations. The outputs can be configured in any
combination. For instance, all three could be set to cool.
Heat and cool outputs use the set point and Operations parameters to determine the output value. All heat
and cool outputs use the same set point value. Heat and cool each have their own set of control parameters.
All heat outputs use the same set of heat control parameters and all cool outputs use the same set of cool out-
put parameters.
Each alarm output has its own set of configuration parameters and set points, allowing independent op-
eration.
Auto (closed loop) and Manual (open loop) Control
The controller has two basic modes of operation, auto mode and manual mode. Auto mode allows the control-
ler to decide whether to perform closed-loop control or to follow the settings of Input Error Failure [FAiL]
(Setup Page, Loop Menu). The manual mode only allows open-loop control. The EZ-ZONE PM controller is
normally used in the auto mode. The manual mode is usually only used for specialty applications or for trou-
bleshooting.
Manual mode is open-loop control that allows the user to directly set the power level to the controller’s out-
put load. No adjustments of the output power level occur based on temperature or set point in this mode.
In auto mode, the controller monitors the input to determine if closed-loop control is possible. The control-
ler checks to make certain a functioning sensor is providing a valid input signal. If a valid input signal is
present, the controller will perform closed-loop control. Closed-loop control uses a process sensor to determine
the difference between the process value and the set point. Then the controller applies power to a control out-
put load to reduce that difference.
If a valid input signal is not present, the controller will indicate an input error message in the upper dis-
play and [Attn] in the lower display and respond to the failure according to the setting of Input Error Fail-
ure [FAiL]. You can configure the controller to perform a “bumpless” transfer [bPLS], switch power to out-
put a preset fixed level [MAn], or turn the output power off.
Actual Output Power
0
20
40
60
80
100
PID Calculation
Linear
Curve 1
Curve 2
Linear
Curve A
Curve B