What is control loop ? What are the two types of control loop?

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What is a control loop?

Control loop is a group of components working together as a system to achieve and maintain the desired value of a system variable by manipulating the value of another variable in the control loop.
Each control loop has at least one input and an output.

There are two types of Control Loop - Open Loop and Closed Loop

Open Loop Control System

Open loop system includes a controller and controlled device but no means for reporting the value of the process back to the controller. The controlled device acts directly on the process input.
No means is provided to monitor the process output and correct the error.

Closed Loop Control System

Unlike an open loop system, a Closed Loop System provides feedback,that is a means for measuring and correcting the value of the process output. The main advantage of closed loop system is its ability more accurate control of a process,which justifies its use despite its greater tool.