Watlow CPC400 - Manual (Page 97)

CPC400 Series User’s Guide Chapter 4: Tuning and Control
Doc. 0600-2900-2000 Watlow Anafaze 83
Figure 4.2 Proportional Control
Proportional and Integral Control (PI)
With proportional and integral control, the integral term
corrects for offset by repeating the proportional band’s er-
ror correction until there is no error. For example, if a pro-
cess tends to settle about 5°F below the set point,
appropriate integral control brings it to the desired setting
by gradually increasing the output until there is no devia-
tion.
Figure 4.3 Proportional and Integral Control
Proportional and integral action working together can
bring a process to set point and stabilize it. However, with
some processes the user may be faced with choosing be-
tween parameters that make the process very slow to reach
set point and parameters that make the controller respond
quickly, but introduce some transient oscillations when the
set point or load changes. The extent to which these oscil-
lations of the process variable exceed the set point is called
overshoot.
Offset
Proportional
Set Point
Process Variable
Band
Proportional
Set Point
Process Variable
Band
Overshoot