Omron SYSMAC CJ - REFERENCE MANUAL 08-2008 Reference Manual page 808

Data Control Instructions
Reverse Action
Output
(MV output designation: 50%)
Adjusting PID Parameters
768
Low
High
SV
temperature
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 stabili-
zation (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
control, then narrow the proportional band. If the proportional band is nar-
rowed 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 propor-
tional band is enlarged.
Control by measured PID
(when loose hunting occurs)
SV
Enlarge I or P.
• If the period is short and hunting occurs, it may be that the control system
response is quick and the derivative action is too strong. In that case, set
the derivative action lower.
Control by measured PID
(when hunting occurs in a short period)
SV
Lower D.
Forward Action
Output
Low
temperature
Section 3-18
High
SV
temperature