Omron SRM1 - PROGRAMING 02-2001, Руководство по программированию

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7-18 Section Data Control Instructions
431
Direction of Action 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.
Manipulated
variable
Reverse Action
Low
temperature
SV
High
temperature
Forward Action
100%
0%
SV
100%
0%
Proportional
band
Manipulated
variable
Proportional
band
Low
temperature
High
temperature
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 required for stabilization
(settlement time), but it is important not to cause overshooting, then enlarge
the proportional band.
SV
Control by measured PID
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
Control by measured PID
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.
Control by measured PID
(when loose hunting occurs)
Enlarge I or P.
SV