WO1994009342A1 - Debitmetre acoustique - Google Patents

Debitmetre acoustique Download PDF

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Publication number
WO1994009342A1
WO1994009342A1 PCT/GB1993/001504 GB9301504W WO9409342A1 WO 1994009342 A1 WO1994009342 A1 WO 1994009342A1 GB 9301504 W GB9301504 W GB 9301504W WO 9409342 A1 WO9409342 A1 WO 9409342A1
Authority
WO
WIPO (PCT)
Prior art keywords
acoustic
flow
flowmeter
tubes
passageways
Prior art date
Application number
PCT/GB1993/001504
Other languages
English (en)
Inventor
Lawrence Anthony Jones
Original Assignee
Endress + Hauser Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Endress + Hauser Limited filed Critical Endress + Hauser Limited
Priority to AU45789/93A priority Critical patent/AU4578993A/en
Publication of WO1994009342A1 publication Critical patent/WO1994009342A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
    • G01F1/662—Constructional details
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters

Definitions

  • the present invention relates to an acoustic flowmeter.
  • Acoustic flowmeters are used to measure the rate of flow of, for example, a gas within a pipe. Such flowmeters use conventional techniques to launch an acoustic signal into the flow from a suitable transducer and to detect the signal after it has traversed a predetermined path through the flow.
  • the traditional method of acoustic gas flow measurement uses ultrasonic transducers positioned to transmit a signal back and forth across the pipe at an angle to the direction of flow. The transit times for signals propagating with and against the flow within the pipe are then measured. This data is then used to calculate the rate of flow within the pipe.
  • the disadvantage of this technique is that the measured flow is at variance with the average flow. Techniques exist for negating this error but additional transducers must be used which is disadvantageous.
  • the characteristic plane wave frequency for an acoustic signal can be determined from the following two expressions:
  • A the wavelength of the acoustic signal
  • the characteristic plane wave frequency is derived from the value of the wavelength calculated from the above expressions in the normal way
  • the characteristic plane wave frequency is approximately twice that when an asymmetric disturbance is used.
  • inspection of equation 2 reveals that for a pipe with a diameter of 2.5 cm, the characteristic plane wave frequency is 16.6 KHz.
  • the acoustic signal frequency which must be used falls within the audio spectrum for a pipe of about 2.5 cm diameter or above. This creates two problems. Firstly, the transducer required to generate the signal of the required frequency would have to be a moving coil, which does not possess the necessary rigidity to withstand the harsh industrial environments encountered in many applications. Secondly, the acoustic signal is audible which is undesirable and could violate environmental legislation.
  • an acoustic flowmeter for measuring the rate of flow of a fluid through the flowmeter from an inlet to an outlet
  • the flowmeter comprising an acoustic signal transmitter, an acoustic signal receiver, the transmitter and receiver being spaced apart along the direction of flow from the inlet to the outlet, and means for measuring the transit time of signals from the transmitter to the receiver to determine the rate of flow
  • the transmitter has a transmission frequency above audible
  • the flowmeter defines a plurality of passageways through which the metered flow passes substantially in parallel between the transmitter and receiver, each passageway being dimensioned to have a characteristic plane wave frequency higher than the transmission frequency.
  • the present invention therefore provides an acoustic flowmeter in which an acoustic frequency beyond the audible range can always be used, regardless of the dimensions of the pipe etc through which the fluid flows before entering or after leaving the meter.
  • above audible range refers to an acoustic signal of sufficiently high frequency not to cause a significant audible nuisance.
  • the signal would not necessarily have to be beyond the audible range of any human ear, although this would be preferable. For instance, in many cases it would be sufficient for the signal to be of such a frequency that its audibility is sufficiently low to be acceptable to the average human ear, or to meet environmental "egislation.
  • audible is to be construed accordingly throughout the specification.
  • the said passageways may be defined by a plurality of tubes interconnected at respective ends thereof by means of manifolds which define the inlet and outlet of the meter.
  • the passageways are defined by a plurality of tubes supported within a fluid channel, the longitudinal axis of each tube extending substantially parallel with the longitudinal axis of the channel.
  • the channel could be a pipe the fluid flow through which is to be metered.
  • the tubes are supported within the channel by a supporting body which prevents fluid flow through the channel except through the tubes. This ensures that all the flow is directed along the tubes and that therefore the resultant measurements are independent of the flow profile within the channel.
  • each tube is as large as possible whilst maintaining a characteristic plane wave frequency beyond the audible range.
  • Using as large a bore tube as possible minimises the pressure drop across the meter.
  • each tube has a diameter of 1.25 cm. This gives a characteristic plane wave frequency of 33.2 KHz which is above the audible range.
  • the acoustic signal transmitter and receiver are wide band piezo horn tweeters.
  • the tweeters are positioned so that a symmetric disturbance is generated in the or each tube.
  • a symmetric disturbance maximises the characteristic plane wave frequency of the tube.
  • the tweeters could be arranged such that the direction of vibrational displacement of the tweeters lies generally parallel with the longitudinal axis of the tubes.
  • the tweeters may be positioned such that the direction of vibrational displacement of the tweeters lies generally perpendicular to the direction of the longitudinal axis of the tubes. In this case an asymmetric disturbance is produced which results in a lower characteristic plane wave frequency.
  • the tweeters could simply be fixed to the sides of the channel upstream and downstream of the meter.
  • the present invention thus provides a flowmeter which utilises acoustic signals above the audible range regardless of the dimensions of a channel which contains the flow before and after passing through the meter.
  • Meters of various sizes can be provided by including more or less tubes and if necessary reducing the diameter of the tubes.
  • the flowmeter In addition to measuring the rate of flow the flowmeter according to the present invention also functions as a flow conditioner which removes the curl from any circulating velocity fields within the tubes.
  • Figure 1 is a schematic illustration of a flowmeter according to the present invention
  • Figure 2 is a schematic illustration of a variation of the flowmeter of Fig.l;
  • Figure 3 illustrates test apparatus used to test the performance of the flowmeter of Figure 1;
  • FIGS 4 to 7 show results obtained using the test apparatus of Figure 3.
  • the illustrated flowmeter comprises three relatively small diameter tubes 1 arranged in parallel and supported within a relatively large diameter pipe 2 by means of a support body 3. Fluid, eg gas, flows along pipe 2 in the direction indicated by the arrows.
  • the tubes 1 are arranged so as to lie parallel to the axis of the pipe 2.
  • the support body 3 is sealed with respect to the pipe 2 and the tubes 1 so that all fluid flowing along the pipe 2 is diverted through the tubes 1.
  • Wide band piezo horn tweeters 4 and 5 are secured to the external surface of the pipe 2 at locations upstream and downstream of the tubes 1 respectively.
  • the tweeter 4 In use, the tweeter 4 generates an acoustic signal which is transmitted through the flowing fluid through the tubes 1 which act as wave guides. The signal is then detected downstream of the tubes 1 by the tweeter 5. The time taken for the signal to propagate through the flowing fluid between the two tweeters 4 and 5 is measured and the measured results used to calculate the flow rate of the fluid in accordance with known techniques.
  • the characteristic plane wave frequency of the meter is determined by the positioning of the tweeters 4 and 5 and the diameter of the tubes 1 and not by the diameter of the pipe 2.
  • the tubes 1 have a diameter of 1.25cm and the pipe 2 has a diameter of 10cm.
  • the positioning of the tweeter 4 generates an asymmetric disturbance in the pipe 2 and thus the characteristic plane wave frequency can be found using equation (1) above. Applying this equation reveals the characteristic plane wave frequency of the tubes 1, and therefore of the pipe 2 with the tubes 1 in place, to be 16KHz whereas the characteristic plane wave frequency for the pipe 2 in the absence of the tubes would be 2KHz.
  • acoustic signals up to 16Khz can be used.
  • FIG. 2 A modification of the above described flowmeter in which the tweeters 4 and 5 are arranged to produce a symmetric disturbance is shown in Figure 2.
  • the same reference numerals are used to denote features common to both arrangements.
  • Fluid flowing through the pipe 2 is diverted through a section of pipe 6 via an inlet 7 and an outlet 8.
  • the pipe section 6 extends beyond the location of the inlet 7 and outlet 8 and has closed ends.
  • the tubes 1 are located within the pipe section 6 between the inlet 7 and the outlet 8.
  • the tweeters 4 and 5 are secured to the closed ends of the pipe section 6 upstream and downstream of the tubes 1 respectively. This configuration is necessary to produce a symmetric disturbance.
  • the internal surface of the pipe section 6 between respective tweeters 4 and 5 and the support body 3 is lined with an acoustically absorbent material 9 which reduces unwanted acoustic reflections within the meter.
  • the advantage gained by using a symmetric disturbance to produce the required acoustic signal, as oppose to an asymmetric disturbance, is that the characteristic plane wave frequency of the flowmeter is approximately doubled. For instance if 1.25cm diameter tubes 1 are used the characteristic plane wave frequency for a symmetric disturbance is 33.2KHz (from equation (2) above) compared with 16KHz for an asymmetrical disturbance. This allows higher frequencies to be used or alternatively allows larger bore tubes 1 to be used whilst maintaining a characteristic plane wave frequency above the audible range. The advantage in using larger bore tubes 1 is that the pressure drop across the tubes 1 is reduced. Furthermore, with the arrangement of Figure 2 the diameter of the pipe section 6 is not limited by the diameter of the pipe 2.
  • the effective overall diameter of the flowmeter is not limited by the diameter of the pipe through which the gas is flowing as is the case with the arrangement of Figure 1. This gives greater freedom of scope for selection of the diameter of the tubes 1 and allows relatively large dimension tweeters to be used. For instance, by maximising the diameter of the pipe section 6 and the tubes 1 the pressure drop across the tubes can be minimised.
  • the number of tubes 1 used may be varied for any given application. For instance, it may be desirable to use only two tubes 1 if the diameter of the pipe 2 or the pipe section b prevent the use of further tubes. Conversely, the use of a greater number of tubes 1 would be desirable for larger diameter pipes 2 and pipe sections 6 where use of only two tubes 1 ⁇ .HIV result in an unacceptable pressure drop across the meter.
  • the tubes 1 may be arranged in other, al ternative, dispositions within the pipe section 6.
  • t he tubes 1 may be " bundled" in a generally annular array about the axis of the pipe section 6.
  • Such an arrangement improves the flow conditioning effect of the meter and reduces the acoustic noise produced. The latter feature allows the signal processing equipment to be simplified.
  • FIG. 3 A test assembly used to test the perf ormance of the flowmeter of Figure 1 is illustrated in Figure 3. Air is drawn through a pipe 10 bv a centrifugal fan 1 1 which is controlled by an inverter and provides a very stable air flow. The air enters the pipe 10 through an inlet 12 and passes through a flow conditioner 13 before reaching the acoustic flowmeter which is installed within a test section 14 of the pipe 10. The tubes i are located within the pipe 10, in the manner described above, between tweeters 4 and 5. The air flow then passes through the fan 11 and through a vortex flowmeter 15 before being expelled from the pipe 10 via outlet 16. Measurements taken from the acoustic flowmeter and vortex meter 15 are fed to processing equipment 17 at which the results are analyzed and compared in accordance with standard techniques. A differential pressure meter (not shown) is used to measure the pressure drop across the meter.
  • the basic purpose of the assembly is to compare the air flow rate figures obtained from the acoustic flowmeter with those obtained from the reference vortex meter 15 over a range of flow rates.
  • a vortex meter is used as the reference meter as such meters are known to give very accurate results for flow rates above around 5m/s.
  • Figure 4 is a plot of results obtained from both meters over a range of flow rates.
  • the frequency of the signal used for the acoustic flowmenter was 17KHz.
  • the points + represent the respective meter readings for a number of flow rates. Where the readings taken from the two meters agree the points + lie on the straight line 19.
  • the results show that the results closely agree for flow rates above approximately 6m/s which corresponds with the accurate working range of vortex meter. The fact that the results do not agree below approximately 6m/s indicates that the acoustic meter may well be more accurate over this range.
  • Figures 5 and 6 show the percentage error distribution of the results obtained from the acoustic flowmeter as compared with results obtained from the vortex meter for a range of flow rates.
  • Figure 5 show the results for an undisturbed flow whereas Figure 6 combines these results with those for a disturbed flow.
  • the plots show that the error distribution is very small, being within 0.5% for the undisturbed flow and within 1% of the disturbed flow.
  • the results show that the performance of the acoustic flowmeter is little effected by the presence of disturbances in the flow.
  • Figure 7 shows measured results for the pressure drop across the acoustic meter for a range of flow rates. The results show that even for a relatively rapid flow of around 20m/s the pressure drop is in the region of lOmbar which is negligible. More precisely, a pressure drop of 12.25mbar was measured at a flow rate of 21.71m/s.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Volume Flow (AREA)

Abstract

Un débitmètre acoustique pour mesurer le débit d'un liquide traversant ce débitmètre d'une entrée vers une sortie, comprend un émetteur de signaux acoustiques et un récepteur de signaux acoustiques espacés dans la direction d'écoulement de l'entrée vers la sortie. Des moyens sont prévus permettant de mesurer le temps de transit de signaux entre l'émetteur et le récepteur, pour déterminer le débit. L'émetteur a une fréquence d'émission au-dessus des fréquences audibles et le débitmètre définit une pluralité de passages par lesquels le liquide dont on mesure le débit passe en parallèle entre l'émetteur et le récepteur. Chaque passage est dimensionné pour avoir une fréquence caractéristique d'onde plane (c'est-à-dire une fréquence au-dessous de laquelle uniquement des ondes planes se propagent dans le passage) supérieure à la fréquence d'émission.
PCT/GB1993/001504 1992-10-20 1993-07-16 Debitmetre acoustique WO1994009342A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU45789/93A AU4578993A (en) 1992-10-20 1993-07-16 Acoustic flowmeter

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9222032.6 1992-10-20
GB9222032 1992-10-20

Publications (1)

Publication Number Publication Date
WO1994009342A1 true WO1994009342A1 (fr) 1994-04-28

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AU (1) AU4578993A (fr)
WO (1) WO1994009342A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2713762A1 (fr) * 1993-01-30 1995-06-16 Cambridge Consultants Débitmètre de fluide.
WO1996006333A1 (fr) * 1994-08-23 1996-02-29 Schlumberger Industries S.A. Dispositif de mesure ultrasonore d'une quantite volumique d'un fluide a proprietes acoustiques ameliorees
GB2313910A (en) * 1996-06-07 1997-12-10 Kromschroeder Ag G Acoustic fluid flowmeter
US6338277B1 (en) 1997-06-06 2002-01-15 G. Kromschroder Aktiengesellschaft Flowmeter for attenuating acoustic propagations
GB2395011B (en) * 2001-09-10 2005-06-15 Joseph Baumoel Clamp-on gas flowmeter
EP1612520A1 (fr) * 2003-02-24 2006-01-04 Matsushita Electric Industrial Co., Ltd. Dispositif de mesure de fluides a ultrasons
WO2020054383A1 (fr) * 2018-09-10 2020-03-19 パナソニックＩｐマネジメント株式会社 Débitmètre à ultrasons

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4365518A (en) * 1981-02-23 1982-12-28 Mapco, Inc. Flow straighteners in axial flowmeters
US4523478A (en) * 1983-08-18 1985-06-18 Nusonics, Inc. Sonic flow meter having improved flow straighteners
GB2209217A (en) * 1987-08-28 1989-05-04 Gen Electric Co Plc An ultrasonic fluid flow meter

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4365518A (en) * 1981-02-23 1982-12-28 Mapco, Inc. Flow straighteners in axial flowmeters
US4523478A (en) * 1983-08-18 1985-06-18 Nusonics, Inc. Sonic flow meter having improved flow straighteners
GB2209217A (en) * 1987-08-28 1989-05-04 Gen Electric Co Plc An ultrasonic fluid flow meter

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 9, no. 217 (P-385)(1940) 4 September 1985 *

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2713762A1 (fr) * 1993-01-30 1995-06-16 Cambridge Consultants Débitmètre de fluide.
WO1996006333A1 (fr) * 1994-08-23 1996-02-29 Schlumberger Industries S.A. Dispositif de mesure ultrasonore d'une quantite volumique d'un fluide a proprietes acoustiques ameliorees
FR2724016A1 (fr) * 1994-08-23 1996-03-01 Schlumberger Ind Sa Dispositif de mesure ultrasonore d'une quantite volumique d'un fluide a proprietes acoustiques ameliorees
GB2313910A (en) * 1996-06-07 1997-12-10 Kromschroeder Ag G Acoustic fluid flowmeter
WO1997047950A1 (fr) * 1996-06-07 1997-12-18 G. Kromschröder Aktiengesellschaft Debitmetre
US6338277B1 (en) 1997-06-06 2002-01-15 G. Kromschroder Aktiengesellschaft Flowmeter for attenuating acoustic propagations
GB2395011B (en) * 2001-09-10 2005-06-15 Joseph Baumoel Clamp-on gas flowmeter
EP1612520A1 (fr) * 2003-02-24 2006-01-04 Matsushita Electric Industrial Co., Ltd. Dispositif de mesure de fluides a ultrasons
EP1612520A4 (fr) * 2003-02-24 2007-08-29 Matsushita Electric Ind Co Ltd Dispositif de mesure de fluides a ultrasons
US7360449B2 (en) 2003-02-24 2008-04-22 Matsushita Electric Industrial Co., Ltd. Ultrasonic fluid measurement instrument having a plurality of split channels formed by partition boards
WO2020054383A1 (fr) * 2018-09-10 2020-03-19 パナソニックＩｐマネジメント株式会社 Débitmètre à ultrasons
JP2020041870A (ja) * 2018-09-10 2020-03-19 パナソニックＩｐマネジメント株式会社 超音波流量計

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Publication number Publication date
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