Liquid level sensing devices

Claim 1

A liquid-level sensing device comprising, in combination: an elongate member adapted to be partially submerged in a liquid, with one end out of said liquid; transmitting means in contact with a portion of said member which is out of said liquid for inducing sinusoidal motion along said member in opposite directions from said portion; means mounted on said member for absorbing said motion travelling from said portion toward said one end of the member; flexure wave receiving means in contact with said member in spaced relation to said portion thereof beyond the level of the liquid for receiving the motion induced by said transmitting means; means connected both to said transmitting means and to said receiving means for detecting and comparing the phase of the motion at the transmitting means with the phase at the receiving means so as to obtain a phase difference measurement representative of the transit time of motion induced by said transmitting means and detected by said receiving means; and means for converting said obtained phase difference measurement into a form indicating the extent to which said elongate member is immersed in said liquid.