Abstract: The invention concerns a flow metering techniques, which applies acoustic means and/or methods as embodied for an acoustic flow metering arrangement according to the invention. The flow metering can be implemented with an acoustic flow meter arrangement, which comprises a measuring section (1) provided with a sound source, at least two sound sensors and a reflector, being arranged so that the sound source of the acoustic flow meter arrangement and at least two sound sensors are arranged to mutual pre-defined distances in the measuring section. So, the determination of the sound velocity at rest (c) and the flow velocity (v), from the known distance between the sound source and the sensors, is obtainable from the values for sum (TSUM) and difference (TDIF) of the upstream and downstream transit times of sound between the sensor locations, by utilising the sound as directly propagated and as reflected.

Abstract: Method and device of acoustic flow measurement for measurement of the flow velocities of gases and/or of quantities that can be derived from same. Long-wave sound is transmitted into a measurement pipe (10). The sound signals passing in the gas flow downstream and upstream are detected by means of two sound detectors (14a, 14b) placed in connection with the measurement pipe (10) at a specified distance (L) from one another, the flow velocity (v) of the gas that flows in the measurement pipe (10) being determined by making use of polarity correlation (15;15.sub.1, 15.sub.2) of said signals. The frequency of the sound that is transmitted into the measurement pipe (10) is scanned between a certain minimum and maximum frequency (f.sub.min, . . . f.sub.max). The measurement signals (f.sub.a (t), f.sub.b (t)) arriving from the two sound detectors (14a, 14b) are passed to a narrow-band filter (17a, 17b) or system of filters (17a.sub.1, 17a.sub.2, 17b.sub.1, 17b.sub.2).

Abstract: A method and device for acoustic flow measurement of the flow velocity of gases is disclosed. An acoustic signal is transmitted into the measurement pipe and, under ideal working conditions, the signals are detected both upstream and downstream by means of two sound detectors mounted at a certain distance from each other within the measurement pipe, the flow velocity of the gas in the measurement pipe being determined by means of correlation of the sound signals. A standardized sound speed in the medium at rest is stored in memory, and whenever one of either the upstream or downstream travel times cannot be measured due to a disturbance, the flow velocity is computed from a single travel time, either downstream or upstream, and by means of the sound speed at rest stored in memory.