Editing Automation (section)

===PID controller===
{{main|PID controller}}
[[File:PID en.svg|thumb|upright=1.5|A [[block diagram]] of a PID controller in a feedback loop, where r(''t'') is the desired process value or "set point", and y(''t'') is the measured process value]]

A proportional–integral–derivative controller (PID controller) is a [[control loop]] [[feedback mechanism]] ([[controller (control theory)|controller]]) widely used in [[industrial control system]]s.

In a PID loop, the controller continuously calculates an ''error value'' <math>e(t)</math> as the difference between a desired [[Setpoint (control system)|setpoint]] and a measured [[process variable]] and applies a correction based on [[Proportional control|proportional]], [[integral]], and [[derivative]] terms, respectively (sometimes denoted ''P'', ''I'', and ''D'') which give their name to the controller type.

The theoretical understanding and application date from the 1920s, and they are implemented in nearly all analog control systems; originally in mechanical controllers, and then using discrete electronics and latterly in industrial process computers.