We use many control systems in our daily life, automatic tripping of Air Conditioner, the pressing iron, refrigerator, and many more. Based on the construction of a control system, there are basically two types of control systems. One is the open loop system and the other one is closed-loop control system.
Closed Loop Control System
If feedback generated from the output of the system is used to control the input, then it will be called a closed-loop control system. As these systems use feedback loops, we can name them feedback loop systems.
In a closed-loop control system, input is not applied directly to the system and is set to the controller unit. The controlling unit controls the processing unit to get a desired output. A measuring instrument measured the output of the system and compares it with the desired output of the system. If the output is changed with the desired output, a feedback signal is sent to the control system so that the output can be corrected.
Transfer function of Closed-loop System
A transfer function of a closed-loop system gives the relationships of output signal and the input signal in accordance with all possible value of input signal. Consider we have a closed-loop control system as given below:
In the above system, we have
G(s) = Forward transfer function
H(s) = Feedback Transfer function
X(s) = Input signal
Y(s) = E(s)G(s) = Output signal
B(s) = H(s)Y(s) = Feedback signal
As,
The output of the system is given as,
For negative feedback
Similarly, for positive feedback we get
Example: Electric Iron
In an electric iron, the temperature is set to a reference point by the user. The temperature measuring instrument measures the actual temperature of the iron and sends the signal to the controller. The controller then compares the actual temperature with the desired temperature and gives instructions to the actuator and adjusts the electric supply to the heating element.
Conclusion
If feedback generated from the output of the system is used to control the input, then it will be called a closed-loop control system. A closed-loop control system is a dependent system, as the input of the system depends upon the feedback of the previous output generated by the system.
