Omron CVM1D Operation Manual page 328

PID and Related Instructions
Reverse Action
100%
Manipulated
variable
0%
Low
temperature
Adjusting PID Parameters
• 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.
SV
• 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.
SV
• 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.
SV
• If the period is short and hunting occurs, it may be that the control system re-
sponse is quick and the derivative action is too strong. In that case, set the de-
rivative action lower.
SV
Forward Action
100%
Manipulated
variable
0%
Low
temperature
Control by measured PID
When P is enlarged
When P is narrowed
Control by measured PID
Control by measured PID
(when loose hunting occurs)
Enlarge I or P.
Control by measured PID
(when hunting occurs in a short period)
Lower D.
Section 5-24
Proportional
band
High
temperature
SV
323