Patent ID: 6895815

Claim:
An apparatus for fluid level measurement comprising an upright tube extending into a storage tank substantially the full height distance of the tank, an acoustic transducer positioned at the top of the tube and operable to emit a sound pulse to be bounced off the surface of the fluid level within the tube and to receive a reflected pulse, means for measuring the time of arrival of the reflected sound pulse, and an acoustic coupling means for the transducer to shape and increase the amplitude of the pulse emitted from the transducer together with an increase in the amplitude of the voltage produced by the transducer in response to the received reflected pulse wherein the acoustic coupling means comprises a stopper for the upper end of the tube, the stopper having a conical passage axially thereof, the passage having a restricted throat at its upper end and an opening having substantially the same diameter as the tube at its lower end, and wherein the top of the stopper has a recess of shallow depth, the throat of the passage axially entering the bottom of the recess and the transducer sealing off the top of the recess whereby the recess is air-tight except for the throat.