Types of Control Systems

Open Loop and Closed Loop Control Systems

Open Loop Control

Open Loop Control is a type of control in which the output is not given as feedback to the controller.  The Input is totally independent of the output of the controller.   Thus the control regulates the process without taking into account the state of the output.  Examples of Open Loop controls are Traffic signals at intersections, Bread toaster, Volume control in a Television set, etc

Closed Loop Control

Closed Loop control is one in which the output is given as feedback to the input. Thus the input is increased or decreased depending on the output.  This ensures that a set point is maintained.  Examples of Closed Loop Controls are Automatic temperature control in an air conditioner, level controller in boiler, a voltage stabilizer, etc. 

Manual and Automatic Systems

Manual Control System

A Manual Control System is one in which the process is manually controlled to achieve the set point.  An example would be a tank with a pump.  If a person switches on the pump every day to fill the tank to a particular level and stops the pump once the level in the tank has been reached, it is called manual control

Automatic Control System

In Automatic control, the process is automatically controlled.  If the pump has a timer which switches on the pump for 15 minutes every day to reach a certain level in the tank, the control system can be said to be automatic. 

Both open loop and closed loop control systems can be manual or automatic.