Elements of Automatic Control:

There are the three functional elements required to perform the functions of an automatic control system are:

1.  A measurement element

2.  An error detection element

3.  A final control element

Relationships among these elements and the functions they perform in an automatic control system are displays in Figure. The measuring element performs the measuring function through sensing and evaluating the controlled variable. An error detection element first compares the value of the controlled variable to the desired value and then signals an error if a deviation exists among the actual and desired values. The last control element responds to the error signal through correcting the manipulated variable of the procedure.

Figure: Relationships of Functions and Elements in an Automatic Control System