A high Precision Acoustic Current Sensor,
BROWN (NEIL) INSTRUMENT SYSTEMS INC CATAUMET MA
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This paper describes an acoustic differential travel time method of sensing fluid flow e.g. ocean currents. For each axis of the sensor array a pair of acoustic transducers is simultaneously and repetitively connected to the same output of a crystal oscillator typically 0.5 to 3mHz to produce pairs of continuous wave bursts travelling in opposite directions. Before the acoustic signals arrive, each transducer is simultaneously connected to receiving circuits which then compare the phase of the arriving signals. The phase difference is directly proportional to the fluid flow velocity component parallel to a line joining the two transducers. Although this concept is not new, the method of processing the discontinuous received signals is novel and yields results which are essentially identical to truly continuous wave operation. The impossible problem of distinguishing simultaneously transmitted and received signals of the same frequency is avoided while superior zero ability and noise performance are achieved.