Abstract: The apparatus comprises a vertical elongate plunger (2) which is freely suspended by its top end from a thread (3) so as to be partially immersed in the liquid. A housing (1') mounted at the top of the recipient houses a pulley (4) capable of rotating through not more than one-fourth of a turn, said pulley serving to wind the plunger suspension thread and being fixed to a counterweight (5) so that the angular position of the pulley and counterweight assembly varies as a function of the depth of plunger immersion, and consequently as a function of the depth of liquid in the recipient. A mechanism is provided for measuring and digitizing the angular position of the pulley and includes, in particular, a code disk (11) outside the housing (1') and a magnetic coupling for transmitting motion from the pulley (4) to the code disk (11) through said housing.

Abstract: The head for the hydrostatic detection of a liquid level includes a main enclosure which is divided by a membrane into two chambers, one of which communicates with a supply of air under pressure, while the other is joined to a probe that is immersed deeply into the liquid. That connection is made, in this case, by the intermediary of an auxiliary enclosure that also contains a primary chamber that communicates with the inlet of the air under pressure, and a secondary chamber which is separated from the primary chamber by a membrane. That membrane forms one piece with a valve mounted between the chamber and a small connecting conduit connected with a probe, which prevents any ill-timed rise of the liquid inside the device, in the case of the disappearance of the compressed-air supply, and which makes it possible, at the same time, to install the detector head above the tank.