On-off or two-position action

This is the simplest and most commonly experienced type of control. A typical example is the thermostatically controlled domestic immersion heater. Depending on the temperature of the water in the tank, the power supply to the heater is either on or off.

  • Advantage

Advantage of this type of control action is that it is inexpensive and extremely simple.

  • Disadvantage

The disadvantage mainly lies in the oscillatory nature of the control, which makes it suitable only for those applications where it can be used alone and close control is not essential.Note that it is impractical to use on-off control when trying to regulate a flowrate.

It is necessary to have some sort of capacity available. This can be illustrated by means of an experiment which uses as a scenario someone taking a shower.

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