Omron CPM1 Programming Manual page 428

Direction of Action
Reverse Action
100%
Manipulated
variable
0%
Low
temperature
Adjusting PID Parameters
When using PID action, select either of the following two control directions. In
either direction, the MV increases as the difference between the SV and the PV
increases.
• Forward action: MV is increased when the PV is larger than the SV.
• Reverse action: MV is increased when the PV is smaller than the SV.
Proportional
band
High
SV
temperature
The general relationship between PID parameters and control status is shown
below.
• When it is not a problem if a certain amount of time is required for stabilization
(settlement time), but it is important not to cause overshooting, then enlarge
the proportional band.
Control by measured PID
SV
When P is enlarged
• When overshooting is not a problem but it is desirable to quickly stabilize con-
trol, then narrow the proportional band. If the proportional band is narrowed too
much, however, then hunting may occur.
When P is narrowed
SV
Control by measured PID
• When there is broad hunting, or when operation is tied up by overshooting and
undershooting, it is probably because integral action is too strong. The hunting
will be reduced if the integral time is increased or the proportional band is en-
larged.
Control by measured PID
(when loose hunting occurs)
SV
Enlarge I or P.
Forward Action
Proportional
band
100%
Manipulated
variable
0%
Low
High
temperature
temperature
SV
Section 7-26