Abstract: A flow measuring apparatus has a meter pipe through which the medium being metered flows, at least two ultrasonic transducers being disposed on said pipe for transmitting and receiving a beam running obliquely to the longitudinal axis of the meter pipe. The pipe wall is provided with recesses the beam to pass through from the transmitting transducer into the medium and from the medium to the receiving transducer. Sound-conducting bodies are disposed between the transducers and the medium, the beam passing perpendicularly through the boundary surfaces of said bodies with the medium and said bodies having an acoustic impedance no more than fifteen times the acoustic impedance of the medium.

Abstract: An apparatus for measuring small liquid and particle currents on the high-frequency ultrasonic Doppler principle, has three sound transducers (5, 6, 7) directed jointly either in or against the direction of flow (2), distributed over the circumference of the measuring tube (1). One transducer (5) is a transmitter and the two others (6, 7) are receivers. Two mixers (16, 17) are inserted between the transmitter and the two receivers for producing a differential signal from the master frequency and receiving frequency. A third mixer (18) is provided for producing a signal from the differential signal from the first mixer (16) and the differential signal from the second mixer (17).