Abstract: In an ultrasonic antenna assembly specifically adapted for use in a material level control system and of the type which includes a parabolic reflector and an ultrasonic energy source mounted at the parabolic focus and directed to radiate energy toward the reflector surface from the direction of the parabolic axis, the improvement comprising a sonic absorber of low-density fiberglass disposed at the reflector surface opposite the energy source to absorb energy directed onto said surface from said source, such that multiple reflections between the energy source and the reflector surface are inhibited.In a modified embodiment the parabolic reflector and energy source are adapted to be mounted in the upper portion of a storage tank such that the parabolic axis is substantially horizontal, and a plane reflector is disposed adjacent the parabolic reflector at an angle of forty-five degrees with respect to the parabolic axis.

Abstract: Ultrasonic pulses are transmitted from the top of a tank or bin by a transducer and reflected by the material contained therein and received by the same transducer. In the short range mode, two millisecond pulses at sixty second intervals provide a measurment of from two to twenty one feet. Failure to detect a reflected pulse in the short range mode automatically switches the device to the long range mode utilizing ten millisecond pulses at three hundred millisecond intervals. After a pulse is transmitted the energy received by the receiver is converted to a digital value each millisecond and compared to the highest previously converted digital value so that the time of the largest received reflection signal and consequently the distance to the material surface may be determined.