The PZ-831 relay is used to detect the presence of electrically conductive liquids at the levels of installed flood probes. In a dry state (all probes open) all relay contacts are open. Shorting the COM base probe and the next level probe with liquid will close the contact of the relay assigned to the given probe, e.g. when the first level probe R1 is flooded (short circuit of the COM base probe and the R1 level probe) the contact 11-12 will be closed. Similarly for level probes R2 and R3. Lowering the liquid level below the level probe (opening of the COM probe and the level probe) will open the contact assigned to the given probe.