Apparatus for measuring the level of a liquid, in particular a flammable liquid

Claim 1

Apparatus for measuring the level of a flammable liquid, in particular a cryogenic liquid, contained in a closed receptacle, the apparatus comprising: a vertical elongate plunger freely suspended at its top end from a thread so as to be partially immersed in the liquid; a housing mounted at the top of the receptacle and containing a pulley which is rotatable through no more than one-fourth of a turn, the pulley serving to wind the plunger suspension thread and being connected to a counterweight in such a manner that the pulley-counterweight assembly serves to compensate for the weight of the plunger as reduced by the Archimedes displacement thrust exerted on the plunger by the liquid, with the angular position of the pulley-counterweight assembly varying as a function of the depth to which the plunger is immersed, and consequently as a function of the depth of the liquid in the receptacle; and means for measuring and digitizing the angular position of the pulley, said means comprising a binary encoded disk mounted outside the housing in which the pulley-counterweight assembly is housed, together with light-emitting means and light-receiving means between which the disk moves, and a magnetic coupling for transmitting motion from the pulley to the disk through the housing, wherein the interval between successive sectors constituting the binary coding on the disk decrease as a function of the angle of rotation, in accordance with a mathematical law which is selected so that the said interval varies in such a manner as to compensate for the non-linearity due to the inclination of the counterweight as it moves, such that the digitized data available at the output from the light-receiving means varies linearly with the level of the liquid in the receptacle.