A control loop is a process management system designed to maintain a process variable at a desired set point.

Each step in the loop works in conjunction with the others to manage the system. Once the set point has been established, the control loop operates using a four-step process.

Control Loop

The Control Loop Steps :

Sense :

Measure the current condition of the process using a sensor, which can be a thermocouple or RTD transmitter.

Compare :

Evaluate the measurement of the current condition against the set point using an electronic PID controller.

Respond :

Reacts to any error that may exist between the measured temperature value and the temperature set point by generating a corrective pneumatic signal.

Affect :

Actuate the control valve that will produce a change in the process variable.

The loop continually cycles through the steps, affecting the process variable (water temperature) in order to maintain the desired temperature set point.

Understanding a Control Loop :

Heat Exchanger Control Loop Example