Magnetic Level Controller MNR 7 / 4074 has a magnetic equipment, a guiding stem with built-in Reed contact, fitting and head housing. 
Magnetic equipment includes 2 fixed magnets and between a float with a built-in magnet. Magnets are all covered by PTFE, non-porous quality. 
Magnetic equipment is designed to keep the float close to lower magnet in atmosphere or gas fluids. Fixed magnets allow floating action even with fluids of low specific weight. 
As the liquid is rising and lifting the float, the mobile magnet switches the Reed contact. Reverse operation is when liquid level is lowering. 

MNR 7 / 4074 is a sensor for acquiring liquid fill-levels which are subject to category 1 (zone 0) conditions. Detection of liquefied gases, level controller for liquids such as fuels, hydrocarbons fluids, water, refrigerating oils, chemicals. Fluid viscosity must be < 100 cSt .Liquids must be free of solids or/and magnetic particles; they may not become resinous or sticky, or to crystallise.

MNR 7/4074 has to be mounted like any passive 2 poles device, free of potential, connected to safe zone through a intrinsically safe switching amplifier in conformity with protection class EEx ia IIC or EEx ib IIC, for use as category 1 (zone 0).
Relay RDN 11, data-sheet 251-01 is convenient for MNR 7/4074