Electrical Engineering ⇒ Topic : Closed Loop Systems
Closed Loop System:- A closed loop system is one in which control action is somehow dependent on the output. In this case the controlled output is feedback through a feedback element and compared with the reference input. Thus the actuating signal is the difference of desired output and reference input.
Closed Loop Systems
If controlling actions of a system are somehow dependent on output or on changes in output, such system is called a closed loop system.
Figure (a) depicts a closed loop system
Figure (a) Closed loop system.
In Figure (a), r (t) is reference input, e(t) is error signal, u (t) is actuating signal, c (t) is controlled output
For positive feedback signal, we can write
e(t) = r(t) + b(t) ............. (1)
For negative feedback signal, we can write
e(t) = r(t) b(t) (24.4) ............. (2)
This error e(t) is applied to the controller. The controller gives the activating signal m(t) for the process. The controlled output will be driven by the action of the controller in such a manner that e(t) will be reduced to zero.
Practical examples of closed loop system are given below:
Automatic electric iron, railway reservation status, display motor speed controlled by tachogenerator feedback, servo voltage stabilizer, etc. Water level controller, missile launching system, temperature control system, voltage stabilizer, etc.
Figure (2) depicts the closed loop control of automatic electric irons. An automatic iron regulates the temperature of iron in such a way that the temperature for a specific cloth remains in specified range.
Figure (a) Automatic electrical iron.
If anybody moves away from desired road with opening eyes, it is an example of closed loop system.
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