Watlow Series D8 - Manual (Page 120)

Chapter 4: Operation and Setup Series D8 User’s Guide
102 Watlow Anafaze Doc. 0600-3120-2000
How To Set Up Cascade Control
1. For the primary cascade loop:
• Configure proportional-only control. For an exam-
ple, see Cascade Control Example: Water Tank on
page 102.
• Enter the desired set point. See Changing the Set
Point on page 84.
2. For the secondary cascade loop:
• Set up PID control as you would for a standard
closed-loop application.
• Set up the parameters in the Cascade menu. See
Cascade Menu on page 149.
NOTE! Cascade control cannot be used on the same
control loop as ratio control.
Cascade Control Example: Water Tank
A tank of water has an inner and outer thermocouple. The out-
er thermocouple is located in the center of the water. The inner
thermocouple is located near the heating element. The desired
temperature of the water is 150° F, which is measured at the
outer thermocouple.
Using cascade control, the outer thermocouple is used on the
primary loop (in this example, loop 1), and the inner thermo-
couple is used on the secondary loop (loop 2). The heater is
controlled by loop 2.
As the temperature of the outer thermocouple drops from 150°
F to 140° F, the set point of the secondary loop should rise
from 150 to 190° F.
Table 4.9 and Table 4.10 show the setup for this application.