An open loop control system is the one in which the output signal is NOT fed back to the input of the system. Therefore, an open loop control system is also referred to as a non-feedback control system.

In the case of an open loop control system, the output has NO control over the control action of the system. Thus, the open loop control system follows its input signals regardless of the final results. The input is supplied to the controller, which produces an actuating signal (or control signal). This actuating single is supplied to the plant or processing system, which is to be controlled.

The major disadvantage of an open loop control system is that it is poorly equipped to handle the disturbances, which may reduce its ability to complete the desired task.

E.g. The clothes dryer is one of the examples of the open-loop control system. In this, the control action can be done physically through the operator. Based on the clothing’s wetness, the operator will fix the timer to 30 minutes. So after that, the timer will discontinue even after the machine clothes are wet. The dryer in the machine will stop functioning even if the preferred output is not attained. This displays that the control system doesn’t give feedback. In this system, the controller of the system is the timer.

Closed loop:

A closed-loop control system is the one in which the output signal is fed back to the input of the system. Therefore, in a closed-loop control system, the control action is a function of the desired output signal.

The main components of a closed loop control system are − the controller, plant, error detector or comparator and feedback element, which are connected together. The error detector accepts the input signal and feedback signal to produce an error signal, which is the difference between input and feedback signals. The feedback signal is the sample of the output of the overall system.

Now, the error signal is supplied to the controller to produce an actuating signal that controls the plant or processing system to produce desired results. Therefore, in the closed-loop control system, the input of the system is automatically adjusted to produce the desired response from the system.

The best example of a closed-loop control system is AC or air conditioner. The AC controls the temperature by evaluating it with the nearby temperature. The evaluation of temperature can be done through the thermostat. Once the air conditioner gives the error signal, it is the main difference between the room and the surrounding temperature. So, the thermostat will control the compressor. These systems are accurate, expensive, reliable, and require high maintenance.