Used for monitoring the level of conductive liquids in tanks and wells. It connects with suspended-type electrodes and is installed on a panel rail.

Its operation is based on measuring the resistance of the liquid between the electrodes, with the ability to adjust the measured conductivity from 5 - 50KΩ. The relay is activated when the liquid level reaches the upper electrode and deactivates when the level "falls" below the middle electrode.

The lower of the three electrodes serves as a reference and can be replaced by the ground when the tank is metallic. The use of safe low alternating voltage between the electrodes prevents the phenomenon of electrolysis.