Open-loop controller: Difference between revisions

Revision as of 18:42, 26 October 2017

Revision as of 18:43, 26 October 2017

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[[File:Electromechanicaltimer.JPG|thumb|right|An electromechanical timer, normally used for open-loop control based purely on a timing sequence, with no feedback from the process.]]

Fundamentally, there are two types of control loop: open loop (associated with feedforward) control, and closed loop (feedback) control.

In open loop control, the control action from the controller is independent of the "process output" (or "controlled process variable"). A good example of this is a central heating boiler controlled only by a timer, so that heat is applied for a constant time, regardless of the temperature of the building. The control action is the switching on/off of the boiler, but the controlled variable should be the building temperature, but is not as this is open-loop control of the boiler, which does not give closed-loop control of the temperature.