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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 or process "set point". An open-loop system cannot engage in [[machine learning]] and also cannot correct any errors that it could make. It will not compensate for disturbances in the process being controlled.
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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. The process output is the building temperature.
In closed loop control, the control action from the controller is dependent on the process output. In the case of the boiler analogy this would include a thermostat to monitor the building temperature, and thereby feed back a signal to ensure the controller maintains the building at the temperature set on the thermostat. A closed loop controller therefore has a feedback loop which ensures the controller exerts a control action to give a process output the same as the "reference input" or "set point". For this reason, closed loop controllers are also called feedback controllers.<ref
The definition of a closed loop control system according to the British Standard Institution is "a control system possessing monitoring feedback, the deviation signal formed as a result of this feedback being used to control the action of a final control element in such a way as to tend to reduce the deviation to zero."<ref>{{cite book|title= The Origins of Feedback Control|last=Mayr|first= Otto| author-link= Otto Mayr| year= 1970
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==See also==
* [[Cataract (beam engine)|Cataract]], the open-loop speed controller of early [[beam engine]]s▼
* [[Control theory]]
* [[Controller (control theory)]]
* [[Feed forward (control)|Feed-forward]]
* [[PID controller]]▼
* [[Process control]]
▲* [[PID controller]]
▲* [[Cataract (beam engine)|Cataract]], the open-loop speed controller of early [[beam engine]]s
==References==
{{Reflist}}
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