Functions Of Pid Control; Operation Method; Forward Operation And Reverse Operation - Mitsubishi Electric MELSEC-Q series Programming Manual

4.2

Functions of PID Control

Operation method

The operation methods for PID control with the PID control instructions are the velocity type and process value derivative
type. The following describes the control executed for both of these methods:
Velocity type operation
The velocity type operation calculates amounts of changes in the MVs (manipulated values) during PID operation.
The actual MV is the accumulated amount of change of the MV calculated for each sampling cycle.
Process value derivative type operation
The process value derivative type operation executes PID operations by differentiating the PV (process value).
Because the deviation is not subject to differentiation, sudden changes in the output due to differentiation of the changes in
the deviation generated by changing the set value can be reduced.

Forward operation and reverse operation

Either forward operation or reverse operation can be selected to designate the direction of PID control.
• In forward operation, the MV (manipulated value) increases as the PV (process value) increases beyond the SV (set value).
• In reverse operation, the MV increases as the PV decreases below the SV.
• In forward operation and reverse operation, the MV becomes larger as the difference between the SV and the PV
increases.
• The figure below shows the relationships among forward operation and reverse operation and the MV, the PV, and the SV.
• The figure below shows examples of process control with forward operation and reverse operation:
4 FUNCTIONS OF PID CONTROL
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4.2 Functions of PID Control