Omron SYSMAC CS Series Instruction & Reference Manual page 598

3. Instructions
Direction of Action
When using PID control, 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.
Reverse Action
Output
(MV output designation: 50%)
Adjusting PID Parameters
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
(settlement time), but it is important not to
cause overshooting,
proportional band.
Control by measured PID
SV
When P is enlarged
• 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 enlarged.
Control by measured PID
(when loose hunting occurs)
SV
Enlarge I or P.
564
Low SV
High
temperature
temperature
required for stabilization
then enlarge the
Forward Action
Output
Low
temperature
• When overshooting is not a problem but it is
desirable to quickly stabilize control, then
narrow the
proportional band is narrowed too much,
however, then hunting may occur.
When P is narrowed
SV
Control by measured PID
• 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.
CS/CJ/NSJ Series Instructions Reference Manual (W474)
SV High
temperature
proportional band. If the