Capacitive Limit Switches

An insulated metal probe mounted in a metal container forms a capacitor together with the metal wall whose capacitance continually increases as the medium level increases. Hence, for capacitive measurements a medium with a constant permittivity is required.
The simple and robust construction (as rod or rope sensor) allows level measurement of liquids, granular solids, conductive and non-conductive media.

The metal container wall and measuring sensor form the two electrodes of a capacitor. The capacitance changes as the level increases due to the dielectric constant of the medium.