Abstract: Apparatus for detecting discontinuities, such as bubbles, in a fluid stream in a tube in which successive bursts of ultrasonic energy are transmitted through the tube and received. Discontinuities are detected by comparing each received signal against a reference level which is set over a longer term by the received signals, the presence of a discontinuity is detected by a reduced amplitude signal which causes an indication to be produced.

Abstract: A transmitting transducer is mounted on the outside wall of a vessel and supplies bursts of ultrasonic energy. If liquid is present, the energy is coupled to the other side of the vessel. Otherwise, the energy is attenuated. A receiving transducer (which may be the same as the transmitting transducer) is positioned to receive the ultrasonic energy if liquid is present. It is gated to be active only when such energy should arrive in the presence of liquid. The receiving transducer therefore generates an electrical signal indicating presence or absence of liquid in the vessel at the level at which the transducers are mounted.

Abstract: Method and apparatus for detecting discontinuities, such as bubbled, in a fluid stream, in which a tube is placed between a transducer transmitting successive bursts of ultrasonic energy and for receiving the bursts. The receiving transducer is connected to a signal processing circuit which keeps an indicator in a first state when signals are received corresponding to the presence of a fluid and in a second state when the bursts of energy are modified by the discontinuity.