Fundamentals of Automatic Control

Automatic process control involves the maintenance of a desired value of a measured or estimated quantity (controlled variable) within prescribed limits (deviations, errors), without the direct action of an operator. Generally, this involves three steps  

Comparing the measurement with the desired value (set point). 

Adjusting some other variable (manipulated variable), which has influence on the controlled variable, until the set point is reached. 

The most important reasons for applying process control are as follows  

Successful design of a process control system requires the following steps  

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