| 摘要 |
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).
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