A liquid level sensor using the absorption of guided acoustic waves

This liquid level sensor consists of a vertically movable 10-cm-long hollow cylinder with an impedance matching conic section suspended at one end of a few-meters-long magnetorestrictive wire. The wire is automatically wound up or unwound such that the cylindrical sensor element at the bottom of the wire is immersed by just a small and measurable distance into the liquid whose level is sought. Acoustic waves are launched in the wire by a pulse of current in a coil and are transmitted to the hollow cylinder through the cylindrical horn. The carrier frequency of the wave trains and the thickness of the tube are chosen so that the elastic waves strongly leak into the liquid when the hollow cylinder is immersed. The level is then determined by measuring the time-of-flight of the echo reflected at the junction between the wire and the horn, followed by taking into account a small correction term computed from the attenuation of the end echo.<>