Control loop: Difference between revisions

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{{short description|Fundamental building block of control systems}}

A '''control loop''' is the fundamental building block of [[control system]]s in general [[industrial control system]]s and [[industrial control system]]s in particular. It consists of the process sensor, the controller function, and the final control element (FCE) which controls the process necessary to automatically adjust the value of a measured [[process variable]] (PV) to equal the value of a desired [[set-point (control system)|set-point]] (SP).

There are two common classes of control loop: open loop and closed loop. In an open-loop control system, the control action from the controller is independent of the process variable. An example of this is a central heating boiler controlled only by a timer. The control action is the switching on or off of the boiler. The process variable is the building temperature. This controller operates the heating system for a constant time regardless of the temperature of the building.