Patent ID: 7694560

Claim:
Apparatus for measuring the level of liquid in a container comprising: a substrate having a flat upper surface; a plurality of piezoelectric elements mounted spaced apart directly on the lower surface of said substrate in a pattern such as to allow the bottom wall of containers of different sizes and structural configurations placed on said substrate flat upper surface to reside over at least a part of at least one of said plurality of piezoelectric elements; a layer of a dry material on said substrate flat upper surface overlying all of said plurality of piezoelectric elements for coupling ultrasonic energy to the bottom of a container placed on said substrate over at least a part of one of said piezoelectric elements; and a circuit for providing electrical signals to all of said plurality of piezoelectric elements for conversion to ultrasonic energy to be transmitted upwardly through said substrate and said layer of dry coupling material to the bottom of a container placed on and supported by said substrate flat upper surface and into the container, receiving electrical signals produced by at least one piezoelectric element in response to ultrasonic energy reflected back from the liquid/air interface within the container and transmitted though said layer of dry coupling material and said substrate to said at least one piezoelectric element, and measuring the time between transmission and reception of the ultrasonic energy by said at least one piezoelectric element.