Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1996-04-25
1997-07-22
Dombroske, George M.
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
7386127, G01F 100
Patent
active
056505728
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an ultrasound flowmeter having a measurement tube through which a gaseous or liquid medium flows.
DESCRIPTION OF THE RELATED ART
When using ultrasound to measure the flow of moving liquid or gaseous media (fluids), the problem arises that the measurement signal supplied from the receiver the (ultrasound transducer) depends not only on the flow, but also on the respective flow profile in the measurement tube and on the type of fluid flowing through it. Various flow profiles result, depending on the flow rate. The laminar flow profile shown in FIG. 1a in a tube having a quadrilateral cross section occurs at a slow flow rate. The lines which are shown in the interior of the tube indicate areas of identical flow rate. Laminar flow profiles can be described by a parabolic shape, see FIG. 1c. The highest flow rates occur in the tube center. The greater the flow, the greater is the flow rate and the greater the extent to which the flow profile approximates to a box shape. FIG. 1b shows a turbulent flow profile which occurs at high flow rates. The flow rate in the nether regions of the tube remains approximately the same.
The previously known ultrasound transducers have an approximately Gaussian sensitivity distribution. The maximum sensitivity of the ultrasound transducer is at its center. It decreases sharply towards the edge. In addition, the sensitivity is sharply influenced by the tube wall characteristics when the ultrasound is injected through the tube wall.
If an ultrasound transducer is now used to ensonify the moving medium in a flow channel, as is known from German Patent Document DE 40 10 148 A1, in order to determine the flow rate from the sound propagation time or by means of the Doppler effect, then, particularly in the case of a laminar flow profile, the highest flow rate which occurs in the flow channel center is assessed more strongly than the lower flow rate which occurs at the edge of the flow channel. This has the consequence that a specific measurement characteristic is produced for each flow profile and for each fluid, which leads to a complex evaluation unit.
Furthermore, in the case of the flowmeter which is described in German Patent Document DE 40 10 148 A1, it is disadvantageous that the ultrasound signal can propagate, because of the measurement tube design, not only in a w-shape but also on a parasitic v-shaped path, and additional measures are therefore necessary to suppress the signal components resulting therefrom.
The publication "Ultraschall-Durchflu.beta.messung" [Ultrasound flow measurement] by H. Bernard, messen+prufen/automatik [Measurement Testing/automatic system], Issue 5, 1983, pages 258 to 263 discloses a flowmeter having a measurement tube through which a liquid medium flows and in the case of which disturbances of the flow profile are reduced in that measurement beams produced by a plurality of ultrasound transducers are distributed over the tube cross section. The complexity for signal evaluation increases with the number of ultrasound transducers used.
Pages 288 et seqq of the publication "Ultrasonic Measurements for Process Control" Academic Press, San Diego, 1989, by L. C. Linworth describe a flowmeter whose measurement tube is provided with an ultrasound transmitting transducer and an ultrasound receiving transducer. The transmitting and receiving surfaces of the ultrasound transducers are in this case inclined in such a manner that the transmitted sound is reflected, depending on the embodiment, at one, two or four reflection points in the measurement tube.
The U.S. Pat. No. 4,103,551 specifies an ultrasound measurement system for different flow characteristics. The device is used for ultrasound flow measurement in a round tube which has two ultrasound transducers which communicate with one another along an acoustic path in the tube. The acoustic path includes a chord which bisects the tube radius.
A device for determining the flow in a cylindrical tube is disclosed in European Patent Document EP 0 268 3
REFERENCES:
patent: 4103551 (1978-08-01), Lynnworth
patent: 5090252 (1992-02-01), Tschirner
Bernard, "Ultraschall-Durchflubmessung", messen + prufen/automatik, 1993, pp. 258-263.
Nuckel, Flow Applications, Contrapropagating Transmission Applications, pp. 288-295.
Biegel Ron
Dombroske George M.
Siemens Aktiengesellschaft
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