Watlow CLS200 - Table 5.2 - Application Example: Setting up Cascade Control

CLS200 Series User’s Guide
Chapter 5: Enhanced Features
106
Table 5.2 — Application Example: Setting Up Cascade Control
DISPLAY USER INPUT
ALARM
SETUP LOOP 02
CASCADE?
Press YES to set up the cascade parameters with loop 2 as
the secondary loop.
ALARM
02 CASCADE
PRIM. LOOP? 01
Enter 01 for loop 1 process variable. Press ENTER.
ALARM
02 CASCADE
BASE SP? 150
The base setpoint corresponds to the 0% level output of the
primary loop. Enter the base setpoint of the secondary loop.
For this example, we will assume a base setpoint of 150°F,
which is the desired water temperature. Press ENTER.
ALARM
02 CASCADE
MIN SP? -350
Enter the minimum setpoint of the secondary loop. For this
example, we will use a minimum setpoint of -350°F. Press
ENTER.
ALARM
02 CASCADE
MAX SP? 1400
Enter the maximum setpoint of the secondary loop. For this
example, we will use a maximum setpoint of 1400°F. Press
ENTER.
ALARM
02 CASCADE
HT SPAN? 40
Enter the heat span of the secondary loop. This is the span
over which the primary output from 0 to 100% is used to
change the setpoint. The desired setpoint range is 150 to
190°F. We will assume a linear rise in setpoint, so the heat
span is 40°F. Press ENTER.
ALARM
02 CASCADE
CL SPAN? 0
Enter the cool span of the secondary loop. For this example
we will assume no low-side adjustment to the setpoint, so the
cool span is 0°F. Press ENTER.
3. Press BACK several times until the normal loop display appears. The output percentage of
loop 1 will now control 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 setpoint 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 setpoint should equal 190 (BASE SP +
HT SPAN).