Two wires from the relay are connected to a resistance-sensing probe in the pump seal cavity and the grounded motor housing to monitor for seal leakage, applying an ultra-low voltage signal.
If the seal starts to leak, contaminating fluid enters the seal cavity. This lowers the resistance between the internal probe and the common ground. When the resistance drops below the user-adjusted sensitivity setpoint of the relay, the output relay energizes, visualizing the current condition of the seal with an indication LED on the front of the device. The relay output can be used to give an alarm indication of a leaking seal.
The universal 10in1 level controller V4LM4S30 comes with three relay outputs and allows connecting up to four probes at a time.