EP0577679A1 - Debitmetre acoustique - Google Patents

Debitmetre acoustique

Info

Publication number
EP0577679A1
EP0577679A1 EP19920907504 EP92907504A EP0577679A1 EP 0577679 A1 EP0577679 A1 EP 0577679A1 EP 19920907504 EP19920907504 EP 19920907504 EP 92907504 A EP92907504 A EP 92907504A EP 0577679 A1 EP0577679 A1 EP 0577679A1
Authority
EP
European Patent Office
Prior art keywords
signal
signals
generate
frequency
acoustic
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP19920907504
Other languages
German (de)
English (en)
Inventor
Lawrence Anthony Endress + Hauser Limited Jones
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Endress and Hauser Ltd
Original Assignee
Endress and Hauser Ltd
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 and Hauser Ltd filed Critical Endress and Hauser Ltd
Publication of EP0577679A1 publication Critical patent/EP0577679A1/fr
Withdrawn legal-status Critical Current

Links

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
    • G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating 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 signal is detected by a transducer which is of course also sensitive to acoustic noise propagating through the flow.
  • a transducer which is of course also sensitive to acoustic noise propagating through the flow.
  • Unfortunately it is generally the case that large acoustic disturbances are generated in pipes through which fluids are flowing and this background noise can be sufficient to swamp the acoustic signal which is deliberately propagated through the flow.
  • acoustic flowmeters must be capable of operating with very low signal to noise ratios and as a result practical systems must rely upon complex signal processing techniques. These techniques can only be implemented at considerable cost and as a result acoustic flowmeters have not been widely used. It would be possible to improve the signal to noise ratio by introducing a band pass filter into the signal processing system.
  • the sort of frequencies that have been proposed for use in flowmeters are typically from a few hundred Hertz to a few thousand Hertz. The reason for this is that provided the acoustic wave length is larger than the diameter of the pipe through which the monitored flow is passing the performance of the flowmeter is independent of the flow profile.
  • the Weaver method relies upon the use of low pass filters to reject unwanted sidebands. It is an object of the present invention to apply low pass filters to the problems outlined above with regard to the signal to noise ratio encountered in acoustic flowmeters.
  • an acoustic flowmeter comprising an acoustic signal source, means for launching a signal output from the source into a flow path, means for detecting the signal after transmission through the flow path, means for measuring the time taken for the signal to be transmitted through the flow path, and means for calculating the rate of flow within the flow from the measured transmission time
  • the signal to noise ratio of the eighth signal is very much larger than the signal to noise ratio of the first signal as a result of rejection of unwanted signal components in the low pass filters.
  • low pass filters having the required filter characteristics.
  • commercial low pass elliptic switched capacitor filters are readily available.
  • the system in accordance with the invention may be regarded as a translation of the low pass filter to the frequency of the second signal together with a mirroring of the low pass filter characteristic around the second frequency.
  • the result is equivalent in performance to the provision of a band pass filter with its centre frequency at the frequency of the second signal and a band width equal to twice the cut off frequency of the low pass filters.
  • the eighth signal is applied to a phase locked oscillator to provide in effect a memory the content of which is available in the event of a temporary loss of signal.
  • Figure 1 is the acoustic spectrum of noise in a pipe through which a fluid is flowing and into which a signal at 316.25 Hz has been launched;
  • Figure 2 illustrates the signal to noise ratio achieved using a simple acoustic pick up to detect the signal represented in Figure 1;
  • Figure 3 illustrates the improvement in the signal to noise ratio which can be achieved using a narrow band-pass filter;
  • Figure 4 illustrates an embodiment of the present invention which enables characteristics such as those illustrated in Figure 3 to be achieved;
  • Figure 5 illustrates the characteristic performance of low pass filters illustrated in Figure 4 and the equivalent band-pass filter characteristics achieved by the use of low pass filters in Figure 4;
  • Figure 6 illustrates a circuit for generating the fixed frequency signals utilised in the embodiment of Figure 4; and
  • Figure 7 illustrates results obtained with an embodiment of the present invention.
  • this illustrates the acoustic spectrum of noise in a pipe together with a signal of 316.25 Hz launched into that pipe.
  • the launched signal is detected by a conventional transducer and if the output of that transducer is not further processed the signal to noise ratio is very poor due to the high level of the noise floor as illustrated in Figure 2.
  • Figure 3 illustrates how the signal to noise ratio could be greatly enhanced if it was possible to provide a narrow band pass filter centred on the wanted signal frequency of 316.25 Hz.
  • the improvement in the signal to noise ratio is a corollary of the narrow band noise floor.
  • the signals illustrated in Figures 1 and 2 are those which are obtained using conventional acoustic flowmeter techniques in a noisy environment.
  • the conditions illustrated in Figure 3 are unfortunately not achievable at sensible cost as it is not possible to produce a band pass filter with a suitably sharp narrow pass band. At the frequencies shown typically a pass band of only 6 Hertz would be required.
  • FIG 4 this illustrates an embodiment of the invention in which the wanted signal that is launched into the monitored flow is at a frequency of 1758 Hz.
  • the signal is received by a loudspeaker configured as a microphone and the output of that transducer is applied as a first signal to an input 1.
  • the first signal is the combination of the wanted signal at 1758 Hz and the accompanying acoustic noise.
  • the detector circuitry illustrated in Figure 4 comprises a local oscillator the output of which is at a frequency 1762 Hz and is applied to input 2.
  • the local oscillator signal is applied to a phase shifter 3 having outputs 4 and 5 to which signals at 1762 Hz are applied in quadrature. That is to say there is a 90° phase shift between the signals appearing on outputs 4 and 5.
  • the signal on output 4 represents a second signal which is multiplied in a mixer 6 with the first signal to generate a third signal that is applied to a low pass filter 7.
  • the signal on output 5 represents a fourth signal which is applied to a mixer 8 with the first signal so as to produce a fifth signal that is applied to a low pass filter 9.
  • the mixers 6 and 8 may be for . example LM1596/LM1496 balanced modulator - demodulators available from National Semiconductor Corporation and the filters 7 and 9 may be LTC1064-1 low noise, eighth order, clock sweepable elliptic low pass filters available from Linear Technology.
  • the low pass filters receive a clock signal applied to input 10 at 439.5 Hz which gives the filters a cut ⁇ off frequency of 4.395 Hz.
  • the outputs of the mixers 6 and 8 carry signals at the frequency of the sum and difference of the signals applied to inputs 1 and 2.
  • the difference (beat) frequencies are passed by the filters 7 and 9 and the other signals are rejected.
  • the outputs of filters 7 and 9 are at 4 Hz.
  • the output of the filter 7 is applied to a mixer 11 with the second signal appearing on the output 4 of the phase shifter 3.
  • the output of the filter 9 is applied to a mixer 12 with the fourth signal appearing at the output 5 of the phase shifter 3.
  • the outputs of the mixers 11 and 12 can be considered as sixth and seventh signals which are combined to form an eighth signal. This occurs in an amplifier 13 to produce a reconstituted version of the original signal without the noise.
  • a phase locked oscillator 14 is then locked onto this signal.
  • the output of the phase locked oscillator is at 1758 Hz, that is the frequency of the wanted signal.
  • the circuit operates to translate the low pass filters in frequency such that the low pass filter characteristics are mirrored about the frequency of the local oscillator.
  • the result is effectively a band pass filter with its centre frequency at the frequency of the local oscillator.
  • the filters are of the switched capacity type and cannot respond to DC signals the local oscillator frequency is also suppressed.
  • the good signal to noise ratio characteristics enable acoustic systems to operate on relatively low power levels.
  • An embodiment of the invention has been tested measuring a gas flow of 36 metres per second in a four inch pipe with only 62 mW of power launching the signal into the gas flow. Results obtained are illustrated in Figure 7. It will be seen that the acoustic velocity (the output of the meter embodying the invention) accurately tracks the reference velocity (the velocity of the flow determined by other means) Earlier acoustic gas flow measurement systems have used much higher power to overcome the signal to noise ratio problem, for example 70 watts.
  • the switched capacitor filters that are used avoid phase drifts since the clock signal is derived from a crystal. Furthermore, switched capacitor filters have added immunity from noise due to the use of sampling. Finally, the use of a phase locked oscillator that is locked to the transmitting frequency means that the stability of the whole circuit is only dependent on the stability of the 10.245 MHz crystal.

Landscapes

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

Abstract

Débitmètre acoustique comportant une source de signaux acoustiques servant à lancer un signal de sortie dans une voie d'écoulement et à détecter le signal après son passage dans celle-ci. La mesure de la durée du passage du signal dans la voie d'écoulement permet de calculer le débit de l'écoulement à partir de la durée d'émission du signal ainsi mesurée. Afin d'améliorer le rapport signal/bruit du débitmètre, les signaux acoustiques émis dans la voie d'écoulement génèrent un premier signal qui se mélange à un deuxième signal ayant une fréquence différente afin de générer un troisième signal. Le premier signal se mélange également à un quatrième signal afin de générer un cinquième signal, les deuxième et quatrième signaux ayant la même fréquence et étant en quadrature. Les troisième et cinquième signaux s'appliquent à une paire de filtres passe-bas (79) dont on sélectionne la fréquence de coupure de telle sorte que soient transmis les signaux dont la fréquence est sensiblement égale ou inférieure à la différence de fréquence entre les premier et deuxième signaux. Le troisième signal filtré se mélange au deuxième pour générer un sixième signal, et le cinquième signal filtré se mélange au quatrième signal pour générer un septième signal. Les sixième et septième signaux se mélangent l'un à l'autre pour générer un huitième signal représentant le signal émis dans ladite voie d'écoulement. Le rapport signal/bruit du huitième signal est considérablement plus grand que celui du premier signal en raison du rejet dans les filtres passe-bas des composantes indésirables de signal.
EP19920907504 1991-03-26 1992-03-25 Debitmetre acoustique Withdrawn EP0577679A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9106465 1991-03-26
GB919106465A GB9106465D0 (en) 1991-03-26 1991-03-26 Acoustic flowmeter

Publications (1)

Publication Number Publication Date
EP0577679A1 true EP0577679A1 (fr) 1994-01-12

Family

ID=10692266

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19920907504 Withdrawn EP0577679A1 (fr) 1991-03-26 1992-03-25 Debitmetre acoustique

Country Status (3)

Country Link
EP (1) EP0577679A1 (fr)
GB (2) GB9106465D0 (fr)
WO (1) WO1992017753A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4556253B2 (ja) * 1999-06-24 2010-10-06 パナソニック株式会社 流量計
EP2642256B1 (fr) * 2012-03-23 2018-07-18 ams AG Agencement et procédé de mesure

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3307408A (en) * 1966-08-10 1967-03-07 Int Research & Dev Co Ltd Synchronous filter apparatus in which pass-band automatically tracks signal, useful for vibration analysis
US3949605A (en) * 1974-07-02 1976-04-13 The United States Of America As Represented By The Secretary Of The Navy Acoustic current/flow measuring system
EP0250660B1 (fr) * 1986-06-05 1991-03-27 Moore Products Co. Procédé et dispositif de mesure de la vitesse d'un fluide
GB2205645A (en) * 1987-06-12 1988-12-14 Milan Herman Miessler Fluid flow measurement

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9217753A1 *

Also Published As

Publication number Publication date
GB2267568B (en) 1994-08-03
GB2267568A (en) 1993-12-08
GB9314722D0 (en) 1993-09-29
WO1992017753A1 (fr) 1992-10-15
GB9106465D0 (en) 1991-05-15

Similar Documents

Publication Publication Date Title
US3762221A (en) Measurement of fluid flow rates
Walls et al. Extending the range and accuracy of phase noise measurements
US4011755A (en) Acoustic flowmeter
US5763283A (en) Method and apparatus for phase for and amplitude detection
US7254493B1 (en) Pressure transducer based fluid velocity sensor
Coulthard Ultrasonic cross-correlation flowmeters
US4528857A (en) Phase modulation, ultrasonic flowmeter
EP0577679A1 (fr) Debitmetre acoustique
Busignies et al. Some relations between speed of indication, bandwidth, and signal-to-random-noise ratio in radio navigation and direction finding
GB2066466A (en) Ultrasonic Flow Measurement
JP3459399B2 (ja) ガス濃度測定処理装置
KR0177353B1 (ko) 레이저 도플러 속도 측정 장치
US3653047A (en) Aircraft navigation receiver apparatus
US3165928A (en) Flow meter
RU2225012C2 (ru) Фазометр с гетеродинным преобразованием частоты
JPS6055934A (ja) 超音波血流計
JP2723291B2 (ja) 超音波センサ
JPS5813852B2 (ja) 流速又は流量測定装置
Vandenbussche et al. An FPGA based digital lock-in amplifier implemented using MFIR resonators
JP3248024B2 (ja) 渦流量計
SU1465812A1 (ru) Устройство дл измерени фазового сдвига четырехполюсника
JPS5852487Y2 (ja) 相関技術を利用した流速流量測定装置
Adair et al. Measurement of RF signal generator phase noise using a one-generator delay-line method
JPH055502Y2 (fr)
SU1370596A1 (ru) Устройство дл измерени сдвига фазы

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 19930721

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FR GB IT LI NL

17Q First examination report despatched

Effective date: 19950621

GRAG Despatch of communication of intention to grant

Free format text: ORIGINAL CODE: EPIDOS AGRA

GRAH Despatch of communication of intention to grant a patent

Free format text: ORIGINAL CODE: EPIDOS IGRA

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION HAS BEEN WITHDRAWN

18W Application withdrawn

Withdrawal date: 19970324