Nonintrusive acoustic liquid level sensor

A method for determining the location in a tank of the surface of a quantity of liquid in the tank from a position outside the tank, the method comprising the steps of

• (a) directing a pulse of sound energy essentially vertically through a bottom wall of the tank and through liquid in the tank from a selected place on the bottom of the tank,
• (b) receiving at substantially the same place on the tank bottom an echo of a sound energy pulse from the liquid surface and generating an echo signal in response thereto,
• (c) determining from the echo signals associated with a series of sound pulses of differing frequency an optimum frequency of sound pulse for use with the liquid in the tank and thereafter performing directing step (a) with pulses of said optimum frequency,
• (d) ascertaining the velocity of sound through liquid in the tank and through the tank wall,
• (e) measuring the time between direction of a sound pulse into the tank and the liquid and receipt of an echo of the pulse from the liquid surface,
• (f) computing the distance of the liquid surface above said place on the bottom of the tank, and
• (g) developing a representation of the computed distance.

A method for determining the location in a tank of the surface of a quantity of liquid in the tank, the method comprising the steps of

• (a) directing pulses of sound energy form a source thereof in an essentially vertical direction toward a liquid surface in the tank and detecting substantially at said source echoes of the pulses from the liquid surface,
• (b) for each pulse, measuring the time between direction of the pulse and the detection of the echo thereof,
• (c) providing information about the speed at which sound travels from the sound pulse source to the liquid surface,
• (d) using said information and the time measurements to determine the distance from the sound pulse source to the liquid surface, thereby to determine the location of the liquid surface, and
• (e) for subsequent sound pulses, disregarding for determination of source-to-surface distance any sound pulse echo which does not have an origin within a defined range of distances above and below the liquid surface.