Device for capacitive level measurement

Claim 1

A capacitance type measuring device for measuring the level of liquid in a container, comprising: (a) first, second and third electrodes arranged in said container to be in contact with said liquid, said electrodes being coextensive over a height (H) embracing at least the possible level variations of said liquid; (b) said second electrode (F 1 ) being opposed to part of said first electrode for forming therewith a first measuring condenser having said liquid as a dielectric and having its capacitance responsive to the level and dielectric constant of said liquid; (c) said third electrode (F 2 ) being opposed to another part of said first electrode and forming therewith a second measuring condenser having said liquid as a dielectric and having its capacitance responsive to the level and dielectric constant of said liquid; (d) at least one of said second and third electrodes having its width varying over its height, and the dependence of the width from the height being different in said second and third electrodes; (e) a means for applying electrical signals to said first and second measuring condensers and for obtaining therefrom first and second output signals responsive to the capacitances of said first and second condensers, respectively, which in turn are differently responsive to the level and dielectric constant of said liquid owing to said different dependence of width from height; and (f) means for processing said first and second output signals together so as to obtain at least one of a measuring signal responsive only to said liquid level irrespective of said dielectric constant and a measuring signal responsive only to said dielectric constant irrespective of said level.