Open loop Control system

Open-loop system, referred to as non-feedback system, is a type of continuous control system in which the output has no influence or effect on the control action of the input signal. In other words, in an open-loop control system the output is neither measured nor “fed back” for comparison with the input. Therefore, an open-loop system is expected to faithfully follow its input command or set point regardless of the final result.

Also, an open-loop system has no knowledge of the output condition so cannot self-correct any errors it could make when the preset value drifts, even if this results in large deviations from the preset value.

Another disadvantage of open-loop systems is that they are poorly equipped to handle disturbances or changes in the conditions which may reduce its ability to complete the desired task. For example, the dryer door opens and heat is lost. The timing controller continues regardless for the full 30 minutes but the clothes are not heated or dried at the end of the drying process. This is because there is no information fed back to maintain a constant temperature.

Control characteristics of such systems are :-
Independent of output of the system. The output is neither measured nor feedback for comparison with the Input. Then we can define the main characteristics of an “Open-loop system” as being:

• • There is no comparison between actual and desired values.
• • An open-loop system has no self-regulation or control action over the output value.
• • Each input setting determines a fixed operating position for the controller.
• • Changes or disturbances in external conditions does not result in a direct output change    (unless the controller setting is altered manually).

Advantages of Open loop control system:-
i) Simple and Economic
ii) More Stable

Disadvantages of Open loop control system:-
i) Inaccurate
ii) Affected by system parameter variation and external noise.