Example of Two Position Control:

A system which is using a two position controller is displays in Figure.

Figure: Two Position Control System

The controlled procedure is the volume of water in the tank. Controlled variable is the level in the tank. It is measured through a level detector which sends information to the controller. The outcome of the controller is sent to the final control element that is a solenoid valve that controls the flow of water inside the tank.

As the water level reduces initially, a point is reached where the measured variable drops below the setpoint. This makes a positive error signal. The controller opens the last control element fully. Water is then injected into the tank and the water level rises. As quickly the water level rises above the setpoint, a negative error signal is built. The negative error signal causes the controller to shut the last control element. This opening and closing of the last control element concluded within a cycling feature of the measured variable.