Watlow CLS200 - Manual (Page 147)

CLS200 Series User’s Guide Chapter 6: Enhanced Features
Doc.# 0600-3050-2000 Watlow Anafaze 131
Differential Control
Differential control is a simple application of the ratio con-
trol option, used to control one process (ratio loop) at a dif-
ferential, or offset, to another (master loop). To use
differential control, set the ratio value to 1.0 to provide the
desired offset.
Differential Control Example: Thermoforming
A thermal forming application requires that the outside
heaters operate at a higher temperature than the center
heaters. The differential control point is determined by the
master loop which is using infrared (IR) sensors for temper-
ature feedback. Secondary loops use thermocouples for
feedback.
The loop using the IR sensor as an input is assigned to the
master loop in the SETUP LOOP RATIO CONTROL menu.
The secondary loop is the differential control loop. Setting
the setpoint differential (SP DIFF) to the desired offset will
produce the desired offset between the secondary and mas-
ter loops.
For example, the master loop can be controlled at 325º F
and the secondary loop at 375º F by using a differential of
50º F.
Loop 1 must be set up for PID control of the setpoint at
325º F.
To set up this application, you would do the following:
1. Change the display to loop 2, and then enter the setup
parameters. Go to the first screen in Table 6.5.
2. Follow the steps in Table 6.5 to configure the process
variable retransmit option.