Positive and negative feedback of the control loop
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Dear experts, could anyone tell me the relationship between the forward and reverse effects of a control loop and those of a control valve?
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In a control loop, there is no such thing as positive or negative action; rather, there is positive feedback and negative feedback. Based on the characteristics of the controlled object and whether the control valve operates in open or closed mode, it is necessary to determine the forward or reverse action of the regulator in order to achieve negative or positive feedback in the control loop.
It must be determined based on the specific conditions of the controlled object in the process flow.
Regulation loop? There is only the concept of positive feedback; industrial systems mostly use negative feedback. Regulating valves also do not have any positive or negative actions; there is only the distinction between air-operated open and air-operated closed types. It is the actuator of the regulating valve that determines whether it operates in a positive or negative manner, and it is based on the positive or negative action of the actuator along with the shape of the valve core that it is determined whether the valve operates in air-operated open or air-operated closed mode. The positive and negative actions of a regulator are determined by the relationship between the changes in its input and output. The original poster should read more books on this topic
The positive and negative feedback in the control loop should be related to the source signal of the control valve; that is, when the value of the source signal is higher or lower than the set value, it causes the control valve to move in the direction of opening wider or closing tighter
The direct/indirect action and air-open/air-close type of control valve should be selected based on process safety, material conservation, and environmental protection, but safety comes first. The function of a regulator should be based on negative feedback achieved in a closed-loop system.