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Difference between open loop and closed loop control system

OPEN-LOOP CONTROL SYSTEMS

Open loop systems are systems in which the output of a system is not used as a variable to control the system. In other words, open loop systems are systems in which input to the system is not controlled by the present output. In an open-loop system, the output of this system is not fed back as input to the system for control or operation. An open system is essentially a feedforward system. The system is an “open” system because it does not have, a feedback loop in its control shown in Figure 1.7 There are many reasons to use open loop control such as simplifying the control system, quicker response of the system, reducing the possibility of oscillation and sometimes lowering the cost.

CLOSED-LOOP CONTROL SYSTEMS

Closed-loop system uses on a feedback loop to control the operation of the system. In closed loop or feedback control, the controller notices what actually takes place at the output end and it drives the plant in such a way as to obtain the desired output. Closed-loop control systems are the type most commonly used because they respond and move the loads they are controlling quicker and with greater accuracy than open-loop systems. The reason for quicker response and greater accuracy is that an automatic feedback system informs the input that the desired movement has taken.

Advantages and disadvantages of closed-loop control system

Advantages

It is a closed loop control with the appropriate sensor which provides much greater stability
It will also give much better repeatability
It overcomes temperature and hysteresis effects
It can perform a task faster than open-loop
Good reliability can be achieved
Optimisation in control is possible.

Disadvantages

Generally, closed-loop control systems are complicated in construction.
The cost of the system is higher.
Sometimes, closed loop control systems may become unstable.

Difference between open loop and closed loop control system

Sr. No.	Open-loop control systems	Closed-loop control systems
1.	Open loop operation dose not uses on a feedback to control the operation of the system.	Closed loop operation uses the feedback system.
2.	The effects of known disturbances alone can be countered. Other disturbances cannot be taken into account.	The effects of disturbances are countered by virtue of negative feedback.
3.	As long as the controlled plant is stable, the control system will not become unstable.	Closed loop operation can be unstable even if the plant is stable.
4.	It is less accurate.	It is more accurate.
5.	It is simple in construction.	It is complicated in construction.
6.	The presence of non-linearities causes malfunctioning.	Usually, it performs accurately even in the presence of non- linearities.
7.	The response is slow because of manual control.	Closed loop control can perform a task faster than open-loop.
8.	Optimisation in control is not possible.	Optimisation in control is possible.
9.	It ensures easy maintenance because of no complex electronic circuits.	It is difficult to maintain and repair.
10 .	The cost of the system is less.	The cost of the system is more.