It is used to control the level of conductive liquids in tanks and wells. It is connected with hanging electrodes and installed on a panel rail.
Its operation is based on the measurement of the resistance of the liquid between the electrodes, with the possibility of adjustment, 5 – 50KΩ, of the measured conductivity. The relay is activated when the liquid level reaches the upper electrode and is deactivated when the level falls below the middle electrode. The lowest of the three electrodes serves as the reference and can be replaced by ground when the tank is metallic. The use of safe low alternating voltage between the electrodes prevents the phenomenon of electrolysis.