Closed Loop Control System

Control systems are classified as either open loop or closed loop. In an open loop system, there is no feedback. In this case, the controller must independently determine the signal to be send to the final control element or the actuator. In this case, the controller can’t determine if the actuator correctly did what it was directed to do. The diagram below shows a representation of open loop control system:

In a closed loop control system, also known as a feedback control system, the output of the process is constantly monitored by a sensor. The sensor samples the system output and passes this information back to the controller. The diagram below shows a representation of closed loop control system:

Because the controller knows what the system is actually doing, it can make any adjustments necessary to keep the output in the right place. This self-correcting feature of a closed loop control loop makes it preferred over open loop control in many applications.

The Controller is an analog or digital circuit that accepts data from the sensors then makes a decision before sending the appropriate commands to the final control element or the actuator. The controller works to keep the Controlled variable like the liquid level, position or velocity at a set point (SP). A closed control system or feedback control system accomplishes this by looking at the error (E) signal which is the difference between where the controlled variable is and where it is supposed to be. Based on the error signal, the controller decides the magnitude and the direction of the signal to the actuator.

Don't miss out on key updates, join our newsletter list here.