Control algorithms, On/off control, Control algorithms 220 – Watlow PPC-2000 User Manual
Page 248: On/off control 220, Figure 6.1—on/off control 220
Chapter 6: Tuning and Control
PPC-2000 User’s Guide
220
Watlow Anafaze
Doc.# 30002-00 Rev 2.3
Control
Algorithms
The next sections explain the different methods for controlling
a loop.
On/Off Control
On/Off control is the simplest way to control a process; a
controller using On/Off control turns an output on or off when
the process variable reaches limits around the desired setpoint.
This limit is adjustable; Watlow Anafaze controllers use an
adjustable spread.
For example, if the set point is 1000°F, and the spread is 20°F,
the heat output switches On when the process variable drops
below 980°F and Off when the process rises above 1000°F. A
process using On/Off control cycles around the set point. Figure
6.1 illustrates this example.
Figure 6.1
On/Off Control
Heat off
Heat on
SP = 1000°F
SP-Spread = 980°F
PV
On
Heat off
Output
Off