The product is used to detect the presence of liquid inside a pipe or tank, with a key application being the secondary protection of submersible pumps against "dry run" operation. It connects to a spark plug type electrode.

Its operation is based on measuring the change in resistance between the electrode and ground. When connected to the power supply voltage, the relay is triggered for an adjustable time T. Immediately afterward, it checks for the presence of liquid and remains triggered if present, or turns off the output relay if not.

Using a safe low alternating voltage between the electrode and ground prevents electrolysis phenomena. The complex resistance of the liquid should be less than 20 kΩ.

Note: the PT415L model is also available, which, if it detects a fault (loss of water presence) at the electrode, then disables the relay and "locks" the fault.