A hydrostatic level sensor is used to measure the pressure created by a liquid. The greater the height of the liquid, the greater the pressure. The sensor needs to be close to the bottom of the tank and either fitted on the outside via a thread or a flange, or entering into the top of the tank and then attached to the bottom. The pressure creates movement of a flexible piece of metal or ceramic, known as a diaphragm, a bit like a drum, and the position of the diaphragm is measured and a signal is produced that relates to the level of liquid in the tank.
