Watlow Series D8 - Manual (Page 119)

Series D8 User’s Guide Chapter 4: Operation and Setup
Doc. 0600-3120-2000 Watlow Anafaze 101
Figure 4.9 Secondary Set Point When Primary
Loop Has Heat and Cool Outputs
Figure 4.10 Secondary Set Point When Primary
Loop Has Heat Output Only
Proportional-Only Control on the Primary Loop
The PID parameters of the primary loop must be tuned to pro-
duce the desired effect on the set point of the secondary loop.
The primary loop typically uses proportional-only control.
Disabling the integral and derivative components of PID
makes the secondary set point a predictable function of the
primary loop’s process variable.
The proportional band is selected so that the set point of the
secondary loop has the desired relationship to the process
variable of the primary loop. For an example, see Cascade
Control Example: Water Tank on page 102.
Set Point of Secondary Loop
(Engineering Units)
High Set Point
Low Set Point
-100%
Output of Primary Loop (Percent of Full Scale)
100%
Set Point of the Secondary Loop
(Engineering Units)
High Set Point
Low Set Point
0%
Output of Primary Loop (Percent of Full Scale)
100%