Open-loop controller: Difference between revisions

Revision as of 20:07, 7 December 2020

Revision as of 18:09, 21 May 2021

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{{more footnotes|date=January 2015}}

In an '''open-loop controller''', also called a '''non-feedback controller''', the control action from the controller is independent of the "process output", which is the process variable that is being controlled.<ref name="auto">"Feedback and control systems" - JJ Di Steffano, AR Stubberud, IJ Williams. Schaums outline series, McGraw-Hill 1967</ref> It does not use [[feedback]] to determine if its output has achieved the desired goal of the input command or process "set point".

There are many open-loop controls, such as on/off switching of valves, machinery, lights, motors or heaters, where the control result is known to be approximately sufficient under normal conditions without the need for feedback. The advantage of using open-loop control in these cases is the reduction in component count and complexity. However, an open-loop system cannot correct any errors that it makes or correct for outside disturbances, and cannot engage in [[machine learning]].

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== Applications ==

[[File:Electric Clothes dryer.jpg|thumb|Electric clothes dryer, which is open-loop controlled by running the dryer for a set time, regardless of clothes dryness.]]

An open-loop controller is often used in simple processes because of its simplicity and low cost, especially in systems where feedback is not critical. A typical example would be an older model domestic [[clothes dryer]], for which the length of time is entirely dependent on the judgement of the human operator, with no automatic feedback of the dryness of the clothes.

For example, an [[irrigation sprinkler]] system, programmed to turn on at set times could be an example of an open-loop system if it does not measure [[soil]] [[moisture]] as a form of feedback. Even if rain is pouring down on the lawn, the sprinkler system would activate on schedule, wasting water.

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{{Electric machines}}

{{Authority control}}

[[Category:Classical control theory]]