It is used to control the level of conductive liquids in tanks and wells. It has an adjustable sensitivity (5-50 kΩ) which allows it to be used in liquids other than water. It is connected with hanging electrodes. Its operation is based on measuring the change in resistance between the electrodes. The relay is activated when the liquid level reaches the upper electrode and is deactivated when the level drops 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.