On-Off Control

System to control room temperature is shown below. A heater and a thermometer are placed inside the room. The controller turns the heater on or off depending on the temperature readings from the thermometer.

For example, suppose we want to keep the room temperature between 25 to 28 degrees. On-off control does the following:

With this approach, the room temperature fluctuates between 25 and 28 degrees as shown below: