The mainly used tow types of automatic control systems in industries are closed-loop or feedback control systems and open-loop or feed-forward control systems, and this post or article shows these control system advantages and characteristics.
(I) Closed Loop or Feedback Control System
In this type of system, the control variable is measured and compared with the reference input. And its difference is the input signal.
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That is, the loop in which the main variable is used to control the process/input is called a closed-loop control system.
It is clear from a fig that the main variable is used to automatically regulate steam input. That is, steam is controlled by the main variable (temperature), so it is a closed-loop control system.
Advantages
Only one controller is used to change the entire input.
Characteristics
1. Minimum derivation, following a disturbance.
2. Feedback control cannot give close control when there is a large time delay in measuring price output as when the main variable is a chemical composition, a molecular weight.
(II) Open Loop or Feed Forward Control System
If the main variable is not used to control any input, it is called an open-loop control system. In this, each piece of information is controlled by a separate controller.
It is clear that the pressure inside the jacket is controlled by the pressure controller and the flow is controlled by the flow controller.
It is clear from Fig that the temperature of the kettle which is the primary variable is neither used for pressure control nor liquid flow control nor is it used for temperature control.
The feed-forward control system cannot maintain the C at a set point, So the method is not accurate.
Advantages
1. Simple construction and easy maintenance.
2. No stability problem.
