Figure 4.11 - Example Application Using Cascade Control; Table 4.9 - Parameter Settings For The Primary Loop In The Cascade Example; Table 4.10 - Parameter Settings For The Secondary Loop In The Cascade Example - Watlow D8 Series User Manual

D8 Series User's Guide
Chapter 4: Operation and Setup
Using cascade control, the outer thermocouple is used on the primary loop (in this example,
loop 1), and the inner thermocouple 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.
Figure 4.11 – Example Application Using Cascade Control
Table 4.9 – Parameter Settings for the Primary Loop in the Cascade Example
Table 4.10 – Parameter Settings for the Secondary Loop in the Cascade Example
Water
Loop 1 Input
Process Variable
Outer T/C
Process Variable
Heater
Inner T/C
Power
Controller
MENU PARAMETER
(none)
Set point
Control Ht prop band
Control Ht integral
Control Ht derivative
MENU PARAMETER
Cascade Cascade prim loop
Cascade Cascade low SP
Cascade Cascade high SP
Loop 1: Primary Cascade Loop
Loop 2: Secondary Cascade Loop
Loop 2 Input
D8
VALUE
150°F
10
0
0
VALUE
1
150°F
190°F
Loop 2 PID Output
COMMENT
Desired temperature at the inner
thermocouple.
As the input drops 10°F, the output
increases to 100 percent.
Only proportional control is used.
Only proportional control is used.
COMMENT
Loop 1 is the primary loop.
When the primary loop's output is 0 percent,
the secondary loop's set point is 150°F.
When the primary loop output is 100
percent, the secondary loop set point
is 190°F.
81