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.