Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1997-03-14
1998-06-23
Chilcot, Richard
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
7386127, 7386118, G01F 100
Patent
active
057708061
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an acoustic method of flow measurement for the determination of fluid flow velocity, volumetric flow and/or mass flow rate in a measurement pipe section by way of determining the downstream propagation time T.sub.D and upstream propagation time T.sub.U for naturally occurring and/or artificially generated acoustic wave modes propagating upstream and downstream in a measurement pipe section in the form of plane wavefronts at a low frequency.
Moreover, the invention concerns a measurement apparatus implementing the method according to the invention for the measurement of fluid flow velocity, volumetric flow and/or mass flow rate, said apparatus comprising a measurement pipe section in which the flow under measurement takes place, at least three acoustic transducers suited to convert the acoustic waves propagating in the measurement pipe section into an electrical signal.
With regard to the state of the art, reference is made to Finnish patents FI 76885, FI 88208 and FI 89835 and a plurality of prior-art patents cited therein.
As known in the art, when the frequency of an acoustic wave propagating in a pipe is smaller than a cutoff frequency determined by the pipe dimensions, the speed of sound in the measured medium and the acoustic coupling between the medium and the pipe, only a fundamental mode acoustic wave propagating in the form of a plane wavefront can travel in the pipe without attenuation. Further is known in the art that the phase velocity of such an acoustic piston-mode wavefront can be determined so that to the speed of sound in the medium at rest is added the flow velocity of the medium averaged over the pipe cross section using positive sign to obtain the phase velocity of the downstream wave and using negative sign to obtain the phase velocity of upstream wave, respectively. Hence, the phase velocities of fundamental-mode wavefronts are independent from the flow profile over the pipe cross section, which makes it possible to accomplish Robertson, "Effect of arbitrary temperature and flow profiles on the speed of sound in a pipe", J. Acoust. Soc. Am., Vol. 62, No. 4, pp. 813-818, October 1977, and B. Robertson, "Flow and temperature profile independence of flow measurements using long acoustic waves", Transactions of the ASME, Vol. 106, pp. 18-20, March 1984!. Accurate methods based on the above-described principle for the measurement of the phase velocities of the downstream and upstream fundamental modes have been disclosed in the art.
It is an object of the present invention to further develop the measurement method based on the fundamental modes of acoustic waves and an apparatus implementing the method so as to achieve essential improvements in the accuracy of the method and its insensitivity to disturbance.
To achieve this goal of the invention and others to be described later in the text, the method according to the invention is principally characterized in that configured by delaying, scaling and summing of the signals into at least two direction-discriminating filters of which one filter/one set of filters eliminates related to downstream acoustic waves while the other filter/other set of filters eliminates signals related to the upstream acoustic waves in the measurement pipe section (1); 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 of the filter output signals, b) the time integral of the squared difference of the output signals, or c) the time integral of the squared sum of the output signals, whereby one of the listed alternative functions is computed for acoustic waves in maximally symmetrical with respect to their maxima or minima; and T.sub.U 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 with the help of a ce
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patent: 4831884 (1989-05-01), Drenthen
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patent: 5421212 (1995-06-01), Mayranen et al.
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Chilcot Richard
Noori Max H.
Valtion teknillinen tutkimuskeskus
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