Basics of Control loop


Control loop is consist of all the elements necessary to move the final control elements.
Different types of final control elements are Valve,Motor,Fan etc… Final control elements allows to keep controlled variable on target.
Process measuring elements sends a signal to the controller.At the same time the already determined setpoint is compared with the signal coming from measuring device.
The error detector makes a comparison between the signal from process and the setpoint signal.
If there is a difference between this an error signal is sent to the control logic that changes the position of final control device. The change in the Final control device will cause a change in process.This process will continue until the setpoint is maintained.

Elements of Control loop are
1.Measuring Device
3.Final control device

Terms used are.

Process Variable
Manipulated Variable
Controller Error
Set point

How to read simple control loops on a PFD (Process flow diagram)