Watlow CPC400 - Manual (Page 71)

CPC400 Series User’s Guide Chapter 3: Operation and Setup
Doc. 0600-2900-2000 Watlow Anafaze 57
Setting Up Closed-Loop Control
Closed-loop control is used to control an output based on
feedback from a sensor or other signal.
Feedback
The controller receives electrical signals, or feedback, from
a sensor or other device. The input parameters determine
how the controller interprets the signal. The controller in-
terprets or scales the input signal in engineering units such
as °C or °F.
Control Algorithm
When the controller is in automatic control mode and a set
point is supplied, the controller determines the appropriate
output signal.
The controller calculates the output signal based on the
feedback and the control algorithm. Each loop may use ei-
ther on/off control or any combination of proportional, inte-
gral and derivative (PID) control. See the Tuning and
Control chapter for information about these control modes.
TRU-TUNE+™
When the controller is in the adaptive control mode, it de-
termines the appropriate output signal and, over time, ad-
justs the control parameters to optimize responsiveness
and stability. This function is available only for heat and
cool outputs not using on/off control
Control Output Signal Forms
The output level calculated by the controller is represented
by a percentage (0 to 100 percent) of power to be applied.
That value is applied on a digital or analog output accord-
ing to the user-selected output type. See Heat/Cool Output
Type on page 116 for more information about the output
types available.
Heat and Cool Outputs
In some applications, two outputs may be controlled ac-
cording to one input. For example, a loop with both heat
and cooling water flow might be controlled according to
feedback from one thermocouple.
In such systems, the control algorithm includes provisions
to avoid switching too frequently between the heat and cool
outputs. The on/off algorithm uses a hysteresis parameter.
The PID algorithms use both a hysteresis parameter and