To measure the electrical conductivity of a liquid, or the concentration of a solution, an insulated combination of two transformers each of which has an annular core is immersed in the liquid such that the two transformers are electromagnetically coupled by a coil of the liquid which passes through...http://www.google.com/patents/US5268642?utm_source=gb-gplus-sharePatent US5268642 - Method and apparatus for measuring electrical conductivity of liquid
