Float switch for water level sensing, can be used to design water tank overflow alarm system. This sensor has a moving ring on a cylindrical body. A reed switch is housed inside the central cylinder which senses the movement of outer ring under the influence of buoyant force of raising water level. This is NO type switch which closes on sensing of raising water level.
This version of sensor comes with a counter weight so it can be simply hanged into the water tank at different levels, the position of the sensor will be maintained under the buoyant force of water because of the counter weight. This type if sensor is useful when multiple level sensing is required or it is not possible to find a mounting hole in the tank body.