| 摘要 |
PCT No. PCT/FI95/00168 Sec. 371 Date Mar. 14, 1997 Sec. 102(e) Date Mar. 14, 1997 PCT Filed Mar. 29, 1995 PCT Pub. No. WO95/28619 PCT Pub. Date Oct. 26, 1995An acoustic measurement method of flow measurement for determinating fluid flow velocity or other variables in a measurement pipe section by determining over an exactly determined length (+/-a+/-b) the downstream propagation time TD and upstream propagation time TU for naturally occurring or artificially generated acoustic wave modes propagating upstream and downstream in the pipe section in the form of plane wavefronts at a low frequency. Pairwise opposed transducers mounted on the pipe are configured by delaying, scaling and summing the signals into at least two direction-discriminating filters, of which one eliminates signals related to downstream acoustic waves while the other eliminates signals related to the upstream acoustic waves in the pipe. The output signals of direction-discriminating filters performing filtering in the same direction are compared with each other by forming a symmetrical equilibrium function with respect to their delay variable from (a) the cross correlation function, (b) the time integral of the squared difference, or (c) the time integral of the squared sum, of the output signals, whereby one of the alternative functions is computed for acoustic waves in both downstream and upstream directions. These equilibrium functions are maximally symmetrical with respect to their maxima or minima when the direction-discriminating filtering is properly made, and the correct values of the acoustic wavefront propagation times TD and TU for use in the computation of both the measurement result given by the method and the values of the delay time variables employed in the direction-discriminating filters are determined from these maximally symmetrical equilibrium functions.
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