Abstract: An ultrasonic sensor for measuring the level of liquid in a vessel has an elongated tubular probe, a tube within the probe, and a transducer that converts electrical energy to ultrasonic energy mounted at or near one end of the tube to transmit ultrasonic energy along the probe longitudinal axis. A conical reflector that reflects ultrasonic energy is opposite the transducer ultrasonic energy emitting part to reflect ultrasonic energy received from the transducer upwardly in the probe to an air-liquid interface from which it is downwardly reflected to the conical reflector element that directs the energy reflected from the interface back to the transducer for conversion to an electrical signal that is used by an electronic module to measure the liquid level in the probe, which is the liquid level in the vessel, by measuring the round trip travel time of the ultrasonic signal energy.