Watlow CLS200 User Manual
Page 139
CLS200 Series User’s Guide
Chapter 6: Enhanced Features
Doc.# 0600-3050-2000
Watlow Anafaze
123
3.
Press
BACK several times until the normal loop display
appears. The output percentage of loop 1 will now con-
trol the setpoint of loop 2.
To verify that cascade is working as expected, you would
follow these steps:
1.
Set loop 1 to MANUAL and the OUTPUT to 0%. Loop 2 set-
point should equal 150 (BASE SP).
2.
Adjust loop 1 MANUAL OUTPUT to 50%. Loop 2 setpoint
should equal 170 (BASE SP + 50% of HT SPAN)
3.
Adjust loop 1 MANUAL OUTPUT to 100%. Loop 2 set-
point should equal 190 (BASE SP + HT SPAN).
4.
To complete the cascade setup, both loop 1 and loop 2
must be configured for inputs, outputs, and alarms.
In addition, the PID parameters of loop 1 must be tuned to
produce the desired effect for the application on the set-
point of loop 2. For a cascade control application that uses
the secondary loop for PID control, loop 1 typically uses
only proportional mode. This must be set for the amount of
change in the process variable to cause a 100% change in
the output level.
The proportional band is selected so the setpoint of the sec-
ondary loop has the desired relationship to the process
variable of the primary loop. In this application, the pro-
portional band (PB) of the primary loop is set to 10˚ F and
the integral and derivative are turned off.
Figure 6.6 Secondary Loop Setpoint Related
to Primary Loop Output
As the temperature of loop 1 drops, the output of loop 1 goes
up proportionally and the setpoint of loop 2 goes up propor-
tionally. Thus heat is added to the system at the element
190°F
150°F
0%
50%
100%
Secondar
y Loop Setpoint
Process Variable 1
(SP1-PB1)
(SP1)
170°F
150°F
145°F
140°F
Heat Output (%)
(BASE SP + HT SPAN)
(BASE SP)
(eng. units)
SP: Setpoint
PB: Proportional Band
(eng.
units)
Primary Loop Output