Change of relative dielectric permittivity

Fundamentals

Free load carriers in the liquid are a prerequisite for the flow of electric power. But even if free load carriers are not available, the liquid will react once it is exposed to an electric field. This effect describes the so-called dielectric properties of a medium and was observed by FARADAYwho made this discovery while experimenting with a liquid-filled condenser.

Orientation polarization and electron polarization

Due to the electrode arrangement of the LUBRICON sensor, it also functions as a condenser and its electric field is influenced by the characteristics of the liquid. A fixed frequency provides a permanent electric potential voltage and the following statements are valid:

  • For a given electric potential, the load of a condenser filled with a non-conductive liquid is always higher than in a vacuum (or in air).
  • The load and, consequently, the capacity of a condenser increases according to the value of the relative permittivity and it also depends on the polarization of the dielectric, a process which, in turn, is determined by two simultaneous effects: orientation polarization andelectron polarization.

Orientation polarization takes place when the liquid consists of molecules which are in themselves structured as permanent dipoles. The molecules of distilled water are a perfect example for this type of molecules.

Electron polarization is a consequence of the fact that every non-conductor consists of atoms: the positive nuclear atom and the negative electrons circling around it. Unlike most metals, non-conductors have no free electrons; the electrons are basically fixed to the nuclear atom. Under the influence of an electric field, however, the positive and the negative molecular particles of such a substance are less firmly attached to one another.