Closed Loop Control System Block Diagram and Working Principle

There are two basic types of control systems - open-loop control system and closed-loop control system. An open-loop control system has only a forward path from the input to output and there is no feedback path but a closed-loop system is the combination of an open-loop system with a feedback path from the output to input. The closed-loop control system is also known as a feedback control system. In this article, we are going to see the Block Diagram of Closed Loop System and its working principle. 

The main objective of a closed-loop system is to accept the input signal and generate the output signal by integrating the input signal and feedback signal. A closed-loop system always monitors its output signals. The closed-loop control system works with the one-time instruction or commands as the first time input, after that it uses the feedback signal as its input and works continuously until a stop command is given. For example, an automatic light on/off using an LDR circuit works in a closed-loop system. So, when darkness occurs the light will turn on automatically, and when the light is available the bulb will be turned off automatically.

Closed-Loop Control System Block Diagram

Here, you can see each block of the closed-loop control system with proper terms and identification.

Closed Loop Control System Block Diagram, Block diagram of Closed Loop Control System


Initially, the closed-loop control system takes the input as an open-loop control system and removes noise, distortions. Once the system start working, it may be or may not require the main input signal. It takes the feedback signal as the input and processes them. If a closed-loop system takes both input signal and feedback signal then first it integrates those two signals and sends for further processing.
The input signal can be provided by a transducer, switching device, or a programmable device.


The controlling part of the closed-loop system integrates the both input and output signal and it decides which part of the signal is to be allowed for the processing and which part of the signal is to be rejected. The controller controls the process flow, speed, integration, etc.

Feedback Element

A closed-loop control system has one or multiple feedback paths. The feedback element is that which takes the output signal of the system as its input and generates the feedback signal as its output. The feedback element may be a transducer or sensor. For example limit switch, thermostat are can be the feedback element of a closed-loop control system. In an automatic heating system, the thermostat continuously measures the operating temperature, once the temperature exceeds the preset limit, it will generate a feedback signal and fed to the control system to turn of the heater.

How does a Closed Loop Control System Works?

The basic working principle of a closed-loop system is that it takes the main input signal as the starting instruction and once it starts working, it continuously takes the feedback signal as its input and works without any interruption until the stop command is given to the system. A closed-loop system can work even the main input signal is removed.

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Closed Loop Control System Block Diagram and Working Principle Closed Loop Control System Block Diagram and Working Principle Reviewed by Author on 11/08/2021 Rating: 5
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