FEEDBACK CONTROL SYSTEMS

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ECM2105 - Control Engineering Dr Mustafa M Aziz (2013)________________________________________________________________________________Open-loop control system: utilises an actuating device to control the process (plant) directlywithout using feedback.InputActuatingdeviceProcess orplantOutputClosed-loop control system: uses a measurement of the output and feedback of this signal tocompare it with the desired input (reference or command).R(s)E(s)U(s)G c(s)+ _G(s)Y(s)H(s)Notation:R(s): Laplace transform of the input signal;U(s): Laplace transform of the control or actuating signal;Y(s): Laplace transform of the output signal;E(s): Laplace transform of the error signal;G c (s): Transfer function of the controller;G(s): Transfer function of the process or plant;H(s): Transfer function of the sensor.2
ECM2105 - Control Engineering Dr Mustafa M Aziz (2013)________________________________________________________________________________3. Why Closed-Loop Control?An advantage of the closed-loop control system is the fact that the use of feedback makes thesystem response relatively insensitive to external disturbances (e.g. temperature and pressure) andinternal variations in system parameters (e.g. component tolerances) which are not known orpredicted.3.1. Sensitivity of control systems to parameter variationsSuppose that G(s) changes to G(s)+∆G(s) due to the environment, ageing, etc. For small ∆G(s)
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FEEDBACK CONTROL SYSTEMS

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