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Redundant link is redundant. These are, and always will be, the same thing. |
General review reference added to the first paragraph. "improved rectification of random fluctuations" added as an advantage. |
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A '''closed-loop controller''' or '''feedback controller''' is a [[control loop]] which incorporates [[feedback]], in contrast to an ''[[open-loop controller]]'' or ''non-feedback controller''.
A closed-loop controller uses feedback to control [[state (controls)|states]] or [[Negative feedback#Overview|outputs]] of a [[dynamical system]]. Its name comes from the information path in the system: process inputs (e.g., [[voltage]] applied to an [[electric motor]]) have an effect on the process outputs (e.g., speed or torque of the motor), which is measured with [[sensor]]s and processed by the controller; the result (the control signal) is "fed back" as input to the process, closing the loop.<ref>{{Cite journal |last=Bechhoefer |first=John |date=2005-08-31 |title=Feedback for physicists: A tutorial essay on control |url=https://link.aps.org/doi/10.1103/RevModPhys.77.783 |journal=Reviews of Modern Physics |volume=77 |issue=3 |pages=783–836 |doi=10.1103/RevModPhys.77.783}}</ref>
In the case of linear [[feedback]] systems, a [[control loop]] including [[sensor]]s, control algorithms, and actuators is arranged in an attempt to regulate a variable at a [[Setpoint (control system)|setpoint]] (SP). An everyday example is the [[cruise control]] on a road vehicle; where external influences such as hills would cause speed changes, and the driver has the ability to alter the desired set speed. The [[PID algorithm]] in the controller restores the actual speed to the desired speed in an optimum way, with minimal delay or [[Overshoot (signal)|overshoot]], by controlling the power output of the vehicle's engine.
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* reduced sensitivity to parameter variations
* improved reference tracking performance
* improved rectification of random fluctuations<ref>{{Cite journal |last=Cao |first=F. J. |last2=Feito |first2=M. |date=2009-04-10 |title=Thermodynamics of feedback controlled systems |url=https://link.aps.org/doi/10.1103/PhysRevE.79.041118 |journal=Physical Review E |volume=79 |issue=4 |pages=041118 |doi=10.1103/PhysRevE.79.041118}}</ref>
In some systems, closed-loop and open-loop control are used simultaneously. In such systems, the open-loop control is termed ''[[feed forward (control)|feedforward]]'' and serves to further improve reference tracking performance.
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