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without hunting, integral operation to automatically correct any offset, and deriv-
ative operation to speed up the response to disturbances.
PID Operation Output Step Response
PID Operation Output Lamp Response
PID operation
I operation
P operation
D operation
Ramp response
0
0
Deviation
Operation
amount
PID operation
I operation
P operation
D operation
Step response
0
0
Deviation
Operation
amount
Direction of Operation When using PID operation, select either of the following two control directions. In
either direction, the operation amount increases as the difference between the
SV and the PV increases.
•Forward operation: Control amount is increased when the PV is larger than the
SV.
•Reverse operation: Control amount is increased when the PV is smaller than
the SV.
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 operation is too strong. The
Special Math Instructions Section 5-21