Method and device for measurement of the flow velocities of gases and/or of quantities that can be derived from same

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). The passband of said filters (17) is scanned synchronously with the frequency scanning of the sound transmission. The duration of the frequency scanning and the width of the passband of said filters (17) are chosen so that, at the moment of the measurement sequence, the measurement signal detected by each sound detector (14a, 14b) has access through its filter (17) substantially without attenuation, as well as so that the interference frequencies substantially different from the mean frequency (f.sub.0) of the filters (17) are attenuated significantly.

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