United States Patent [19]
`Freeman
`
`[54] DIGITAL PHASE LOCKED LOOP SIGNAL
`PROCESSING FOR CORIOLIS MASS FLOW
`METER
`
`[75] Inventor: Belvin S. Freeman, Asheville, NC.
`
`[73] Assignees: Schlumberger Industries, Inc.,
`Norcross, Ga.; Continuum Technology
`Corp., Fletcher, NC.
`
`[21] Appl. No.: 748,477
`
`NOV‘ 8’ 1996
`Flled:
`[22]
`Int. Cl.6 ...................................................... .. G01F 1/84
`[51]
`[52] US. Cl. ..................................... .. 73/86L356; 364/510
`[58] Field of Search ..................... .. 73/861355, 861.356,
`73/861357; 364/510
`
`[56]
`
`References Cited
`
`U-S~ PATENT DOCUMENTS
`Re_ 31 450 11/1983 Smith _
`4J422Z338 12/1983 Smith _
`4,491,025
`1/1985 Smith et al. _
`4,757,39O
`7/1988 Mehrgardt et al. ................... .. 358/310
`4,852,410
`8/1989 COlWOIl et al- -
`49347196 6/1990 Romano -
`2,218,869
`6/1992 Purlnmer .................................. .. 83/629
`,429,002
`7/199 CO man.
`5,469,748 11/1995 Kalotay ............................ .. 73/861356
`5,555,190
`9/1996 Derby et a1. ..
`.. 73/861356
`5,578,764 11/1996 Yokoi et al. ..................... .. 73/861356
`
`USOO5804741A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,804,741
`Sep. 8, 1998
`
`OTHER PUBLICATIONS
`
`SpitZer, Davd A.; “Industries FloW Measurement”; pp.
`197—210; 1990 USA.
`DeCarlo, Joseph P.; Fundamentals of FloW Mesurement; pp.
`208—220; 1984 USA.
`
`Primary Examiner—George M. Dombroske
`Assistant Examiner—Harshad Patel
`Attorney, Agent, or Firm—Dority & Manning, PA
`[57]
`ABSTRACT
`
`A Coriolis-type ?uid ?oW rate measuring system uses phase
`locked loop-based signal processing to estimate a tube
`vibration signal and maintain Optimum tube vibrations
`Analog Sinusoidal Sensor Signals from the ?ow meter are
`digitiZed and processed through heterodyne mixing as part
`of phase locked loop tracking of the fundamental vibration
`or oscillation frequency. Digital signal processing is used to
`implement ?ltering and signal manipulation so as to respec
`tively determine phase and frequency estimates for both of
`the tWo digitiZed signals. Frequency estimate data is used to
`adjust the tracker frequency mixed With the respective
`sensor signals. Digitally obtained phase and frequency esti
`mate data are used to determine an optimized drive signal for
`continuing tube vibration. Phase estimate information for
`the tWo respective sensor signals is used to determine phase
`Shift data, used in turn to determine a ?uid ?ow rate through
`the ?ow meter‘
`
`29 Claims, 6 Drawing Sheets
`
`[v 40
`
`HETERODYNE
`MIXER
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`FREQUENCY
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`TRACKER FREQ.
`
`140
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`142
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`1
`
`Micro Motion 1054
`
`

`
`U.S. Patent
`
`Sep.8,1998
`
`Sheet 1 of6
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`5,804,741
`
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`U.S. Patent
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`U.S. Patent
`
`Sep.8,1998
`
`Sheet 3 of6
`
`5,804,741
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`CHANNEL 1
`CHANNEL 2
`
`VOLTAGE
`
`-24 KHz
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`U.S. Patent
`
`Sep.8,1998
`
`Sheet 4 of6
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`U.S. Patent
`
`Sep.8,1998
`
`Sheet 5 of6
`
`5,804,741
`
`RELATIVE
`RESPONSE
`(dB)
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`

`
`U.S. Patent
`
`Sep.8,1998
`
`Sheet 6 of6
`
`5,804,741
`
`RELATIVE
`RESPONSE
`(dB)
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`
`7
`
`

`
`1
`DIGITAL PHASE LOCKED LOOP SIGNAL
`PROCESSING FOR CORIOLIS MASS FLOW
`METER
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates in general to an improved
`Coriolis mass ?oW meter arrangement and in particular to a
`digital signal processing technique for maintaining optimum
`tube vibrations during meter use.
`The basic construction and operation of a variety of
`conventional Coriolis-type mass ?oW rate meters are Well
`knoWn to those skilled in the art and readily commercially
`available. One such arrangement relates to a Coriolis-type
`?oW meter of the type having at least tWo analog sensor
`channels (sensor signals) and an electromagnetically-driven
`vibrating-tube design. Generally speaking, a pair of shaped
`parallel ?oW conduits are driven to oscillate, such as at a
`resonant frequency associated With the tubes (and their
`contents). Analysis of the sensor signals describing the
`vibration of the tWo ?oW paths, using knoWn equations,
`relationships, and techniques, may result in derivation of the
`?uid ?oW through the ?oW meter.
`Generally speaking, such a conventional arrangement
`operates such that the tWo sensors, When displaced sym
`metrically from the electromagnet, respond to its oscillation
`With phases Which are different due to an excited Coriolis
`acceleration in the ?oWing ?uid. As is knoWn, such phase
`difference is related to the ?uid ?oW rate in a manner such
`that the actual ?uid ?oW rate itself may be derived from the
`measured phase difference (coupled With knoWing certain
`other information regarding the arrangement).
`The basic construction and theory of operation for such a
`Coriolis-type ?oW meter (of the type having at least tWo
`analog sensor channels and electromagnetically-driven
`vibrating-tube design) are fully disclosed and explained in
`commonly assigned US. patents to Colman (US. Pat. No.
`5,429,002) and CorWon, et al. (US. Pat. No. 4,852,410). The
`complete disclosures of both such ’002 and ’410 US.
`patents are fully incorporated herein by reference.
`The analog sensor outputs under the above circumstances
`are primarily sinusoidal. Their primary frequency is typi
`cally substantially equal to the resonant frequency of the
`tube vibrations. Since the tubes are mechanical devices, they
`do not have perfectly linear response to their vibration
`excitation. Such fact causes a number of harmonic frequen
`cies to be present at multiples of the fundamental frequency.
`The harmonic multiples are generally odd.
`Still further, there may be a number of other sources of
`interference, groWing from either electrical or mechanical
`sources.
`Generally speaking, a Coriolis-type mass ?oW rate meter
`is a high precision instrument. In such context, it is to be
`understood that the measurement accuracy of any ?oW meter
`may be degraded from its full potential if interference
`signals (regardless of source) are not adequately addressed
`(i.e., ?ltered). Such fact is equally true regardless of the
`electronic stage of the signal processing being considered
`(i.e., Whether it is during a ?oW rate calculation segment or
`an operational segment).
`Additional background references regarding Coriolis
`type ?uid ?oW rate measuring devices include Smith (US.
`Pat. No. Re. 31,450); Smith (US. Pat. No. 4,422,338);
`Smith, et al. (US. Pat. No. 4,491,025); and Romano (US.
`Pat. No. 4,934,196), the complete disclosures of Which are
`fully incorporated herein by reference.
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`2
`SUMMARY OF THE INVENTION
`
`The present invention recogniZes and addresses various of
`the foregoing draWbacks, and others, concerning Coriolis
`type mass ?oW rate meters. Thus, broadly speaking, one
`main object of the present invention is improved apparatus
`and methodology regarding the use of Coriolis-type mass
`?oW rate meters.
`It is another principal object of the present invention to
`provide improved apparatus and corresponding methodol
`ogy for operating a Coriolis-type ?oW meter of the type
`having at least tWo analog sensor channels and a vibrating
`tube design. It is a more particular present object to provide
`digitally implemented signal processing associated With
`such a device for improved generation of an optimiZed tube
`vibration drive signal.
`It is another object of the present invention to provide a
`digitally-based signal processing arrangement Which incor
`porates phase locked loop tracking of sensor signals for
`estimating and generating an optimiZed tube vibration sig
`nal. In such context, it is a present object to provide an
`improved drive signal, obtained With very high levels of
`accuracy, noise insensitivity, and harmonic rejection, all in
`an efficiently operable implementation.
`It is a further object of the present invention to provide
`improved Coriolis-based ?uid ?oW rate measuring Which
`more broadly and fully than heretofore practiced obtains
`digital signal processing advantages of stability,
`repeatability, and ?exibility.
`It is yet another present object to provide both apparatus
`and methodology Which afford the above-referenced advan
`tages While also being compatible With existing analog
`sensor and tube vibration driver interfaces, for improved
`resonant excitation response in existing and current tech
`nology ?oW meter tubes.
`Still further, it is a present object more broadly to provide
`such improved methodology and apparatus Which is also
`suitable for practice With a variety of meter designs, having
`in common at least the use of tWo ?oW meter output
`channels carrying sinusoidal analog signals describing tube
`vibration phenomenon, and having an associated driver
`arrangement (for example, an electromagnetically-driven
`device).
`Yet another broad present object is to use digitally imple
`mented phase locked loop analysis techniques for consider
`ing sensor outputs, resulting in a minimum of signal deg
`radation due to any potential sources of interference. In such
`context, it is a present object to digitally implement and
`obtain such advantages and operations With a highly ef?cient
`processing methodology, preferably utiliZing programmable
`controllers Which are operated With select algorithms,
`capable of running in real time and responding extremely
`rapidly to changing conditions in ?uid ?oW, and While
`providing very high levels of noise and interference ?ltering
`to maintain ultimately highest accuracy in the resulting ?oW
`rate estimation.
`It is another present object to provide an improved ?oW
`rate apparatus and corresponding methodology Which pro
`vides very high precision ?uid ?oW rate metering capability
`over a Wide variety of ?oW rates and With a Wide variety of
`?oWing materials (including materials in either one of liquid
`or gaseous state or through state changes).
`Additional objects and advantages of the invention are set
`forth in, or Will be apparent to those of ordinary skill in the
`art from, the detailed description herein. Also, it should be
`further appreciated that modi?cations and variations to the
`
`8
`
`

`
`3
`speci?cally illustrated and discussed features and steps or
`materials and devices hereof may be practiced in various
`embodiments and uses of this invention Without departing
`from the spirit and scope thereof, by virtue of present
`reference thereto. Such variations may include, but are not
`limited to, substitution of equivalent means and features,
`materials, or steps for those shoWn or discussed, and the
`functional or positional reversal of various parts, features,
`steps, or the like.
`Still further, it is to be understood that different
`embodiments, as Well as different presently preferred
`embodiments, of this invention may include various com
`binations or con?gurations of presently disclosed features,
`steps, elements, or their equivalents (including combinations
`of features or steps or con?gurations thereof not expressly
`shoWn in the ?gures or stated in the detailed description).
`One exemplary such embodiment of the present invention
`relates to an improved Coriolis-type system for measuring a
`?uid ?oW rate, comprising ?rst and second ?uid ?oW
`conduits, driver means for oscillating such conduits, ?rst and
`second sensor means associated With such conduits, means
`for digitiZing certain analog sensor signals, and means for
`processing such digitiZed signals in accordance With the
`subject invention.
`In the foregoing arrangement, the ?rst ?uid ?oW conduit
`preferably has respective inlet and outlet portions Which are
`substantially coaxial With a ?rst oscillation axis thereof. The
`second ?uid ?oW conduit likeWise has preferably respective
`inlet and outlet portions Which are substantially coaxial With
`a second oscillation axis thereof and Which are parallel to the
`?rst oscillation axis. Still further, such second conduit is
`preferably formed so as to be physically similar to the ?rst
`conduit, and both conduits are mounted so as to be parallel
`to each other betWeen their respective end portions (When
`the How meter is not in use, i.e., When there are no driven
`tube vibrations and no ?uid ?oW therethrough).
`The above referenced driver means is preferably respon
`sive to a driver signal input for oscillating the ?rst and
`second conduits relative to each other about their respective
`oscillation axes. Such oscillation generates a corresponding
`relative oscillatory motion thereof, Which thereby causes
`oscillating Coriolis accelerations to act on respective ?uid
`?oWs through the conduits.
`The above-referenced ?rst and second sensor means are
`associated With the conduits for generating analog sinusoidal
`outputs in tWo respective predetermined locations in corre
`spondence With the relative motion betWeen the ?rst and
`second conduits at such tWo predetermined locations. The
`means for digitiZing operate on such analog sinusoidal
`outputs and further function for generating corresponding
`?rst and second digitiZed outputs.
`The exemplary means for processing preferably operates
`on such digitiZed outputs to estimate a fundamental fre
`quency thereof, to estimate a phase shift betWeen the digi
`tiZed outputs, and to establish from such frequency and
`phase shift estimates an optimiZed driver signal input for the
`driver means. Still further, such means for processing pref
`erably functions for determining from the phase shift a
`corresponding mass ?oW rate of ?uid ?oWing through the
`?rst and second conduits.
`In accordance With additional features Which may also be
`practiced With the foregoing exemplary embodiment, the
`means for processing may include phase locked loop track
`ing of the digitiZed outputs for the elimination of interfer
`ence and noise distortions in establishing the driver signal
`input for the driver means. Such tracking is preferably
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`accomplished through heterodyne mixing of the respective
`digitiZed outputs With an adjusted phase locked looped
`tracker frequency, and With subsequent ?ltering and pro
`cessing of the respective outputs of the heterodyne mixing
`so as to determine the frequency and phase shift estimates.
`It is to be understood by those of ordinary skill in the art
`that the present invention fully addresses and encompasses
`corresponding methodologies. For example, another present
`exemplary embodiment concerns an improved method of
`operating a Coriolis-type system for measuring a ?uid ?oW
`rate, using and operating the above-brie?y described
`arrangement.
`Yet another method comprising a present exemplary
`embodiment relates to a method of determining ?uid ?oW
`rate through a Coriolis-type ?oW meter of the type having at
`least tWo analog sensor channels and an
`electromagnetically-driven vibrating-tube design.
`In such exemplary method, ?rst, the analog sensor signals
`are digitiZed, and then the digitiZed signals are preferably
`custom ?ltered for rejecting interference and noise. Still
`further, phase locked loop tracking is preferred for dynami
`cally matching the ?ltering operation With the time-varying
`sensor Waveforms.
`In such exemplary methodology, a further step may
`include processing the ?ltered signals for obtaining fre
`quency and phase estimates of a drive signal for optimiZed
`tube vibrations and using such optimiZed drive signal for
`electromagnetically driving such tube vibrations. Also, in
`accordance With such methodology, one may use the phase
`estimates to determine phase shift (i.e., phase difference)
`estimates, and thereafter to determine therefrom a corre
`sponding ?uid ?oW rate through the How meter.
`It is to be further understood that the present invention
`equally encompasses corresponding digital signal apparatus
`for determining ?uid ?oW through a Coriolis-type ?oW
`meter of the type having at least tWo analog sensor channels
`(i.e., signal outputs) and an electromagnetically-driven
`vibrating-tube design.
`In such an exemplary apparatus, analog-to-digital con
`verter means are provided for digitiZing the respective
`analog sensor signals. Thereafter, digital ?ltering means
`?lter the digitiZed signals for rejecting interference and
`noise. Phase locked loop means track the time-varying
`sensor signal Waveforms for dynamically matching opera
`tions of the digital ?ltering means. Means for processing the
`?ltered signals are provided for obtaining frequency and
`phase estimates therefrom and for outputting a drive signal
`based thereon for optimiZed tube vibrations. A driver means
`is responsive to such drive signal for electromagnetically
`generating tube vibrations in accordance With the drive
`signal.
`Thereafter, ?oW rate data means may be used for deter
`mining a corresponding ?uid ?oW rate through the How
`meter based on determining phase shift (phase difference)
`estimates from the phase estimate information otherWise
`obtained through practice of the present invention.
`Still further, present exemplary embodiments relate to
`improved apparatus for operating a Coriolis-type ?oW meter
`of the type having at least tWo analog sensor channels and
`a vibrating tube design, comprising analog-to-digital con
`verter means for digitiZing respective analog sensor signals;
`digital signal processing means, responsive to the digitiZed
`respective sensor signals, for digitally tracking such digi
`tiZed signals using a phase locked loop and for estimating
`from such tracking an optimiZed tube vibration signal; and
`drive means responsive to such optimiZed tube vibration
`
`9
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`5,804,741
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`5
`signal. Through practice of the foregoing advantageous
`arrangement, the How meter tube vibrations may be main
`tained in accordance With the vibration signal, so that
`desired tube vibration is maintained based on digital phase
`locked loop tracking of the sensor signals for improved ?oW
`meter operation.
`Those of ordinary skill in the art Will better appreciate the
`features and aspects of such embodiments, methods, and
`others, upon revieW of the remainder of the speci?cation.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`A full and enabling disclosure of the present invention,
`including the best mode thereof, directed to one of ordinary
`skill in the art, is set forth in the speci?cation, Which makes
`reference to the appended ?gures, in Which:
`FIG. 1 is a side elevational vieW, in partial cutaWay, of an
`exemplary embodiment of a conventional Coriolis-type ?oW
`meter arrangement of the type having at least tWo analog
`sensor channels and an electromagnetically-driven
`vibrating-tube design, such as may be used in practice of the
`present invention;
`FIG. 2 is a schematic block diagram illustration of an
`exemplary embodiment of the present invention, as may be
`used in conjunction With the How meter apparatus otherWise
`represented in present FIG. 1;
`FIG. 3 is an exemplary plot of a pair of analog sinusoidal
`signals as may be output by a pair of sensor means associ
`ated With conduits of a conventional Coriolis-type based
`arrangement as represented in present FIG. 1;
`FIG. 4 is a plot of a tWo-sided frequency spectrum of the
`exemplary signals of present FIG. 3, for representing numer
`ous small imperfections (interference) present in such sig
`nals;
`FIG. 5 is a schematic block diagram representation of
`digital signal processing aspects of an exemplary
`embodiment, and related methodology, in accordance With
`the present invention;
`FIG. 6 is an exemplary plot of the signal frequency
`spectrum subjected to a frequency translation thereof due to
`operation of the heterodyne mixing stage of the exemplary
`embodiment of present FIG. 5;
`FIG. 7 is an exemplary plot of the frequency spectral
`response of the comb ?lter features as represented in the
`exemplary embodiment of present FIG. 5;
`FIG. 8 is an exemplary plot of the resulting signal
`spectrum after operation on a signal passing through the
`comb ?lter features as represented in the present embodi
`ment of FIG. 5;
`FIG. 9 is an exemplary plot of the resulting frequency
`spectrum of a signal after operation of the decimation
`features as represented in the exemplary embodiment of
`present FIG. 5;
`FIG. 10 an exemplary plot representing the three ?lter
`stages of each of the ?nite impulse response (FIR) ?lters per
`such features as represented in the exemplary embodiment
`of present FIG. 5; and
`FIG. 11 is an exemplary plot of frequency offset data
`(horiZontal axis) versus FIR response ratio data (vertical
`axis), as derived from operation of the features represented
`in the exemplary embodiment in present FIG. 5.
`Repeat use of reference characters throughout the present
`speci?cation and appended draWings is intended to represent
`same or analogous features, elements, or steps of the inven
`tion.
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`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`Reference Will noW be made in detail to the presently
`preferred embodiments of the invention (including both
`apparatus and methodology), a complete example of Which
`is fully illustrated and represented in the accompanying
`draWings. It is to be understood that such example is
`provided by Way of an explanation of the invention, not
`limitation of the invention. In fact, it Will be apparent to
`those skilled in the art that various modi?cations and varia
`tions can be made in the present invention. For instance, the
`subject signal processing apparatus and methodology may
`be utiliZed in conjunction With different constructions of
`Coriolis-type mass ?oW meters, so long as generally such
`meters are of the type having at least tWo analog sensor
`channels (outputs) and a vibrating tube design.
`FIG. 1 represents an exemplary such conventional or prior
`art Coriolis-type ?oW rate meter device generally 10. Such
`construction 10 is essentially the same as the devices fully
`disclosed and explained (both construction and theory of
`operation) in commonly assigned US. Pat. Nos. 5,429,002
`and 4,852,410, the complete disclosures of Which are fully
`incorporated herein by reference.
`Very brie?y, FIG. 1 represents a side elevational vieW,
`With partial cross section, of the internal structure of a
`Coriolis-type device 10. Such meter 10 has a generally
`rectangular casing 12 Within Which are contained a pair of
`?uid ?oW conduits. An exemplary one of such conduits 14
`is shoWn by the partial sectional vieW of FIG. 1. Such
`exemplary conduit 14 has an inlet portion generally 16 and
`an outlet portion generally 18, respectively associated With
`inlet and outlet ?uid conduit connections generally 20 and
`22. As understood by those of ordinary skill in the art,
`manifolds or other elements are used to split ?uid ?oW
`entering connection 20 into tWo separate pathWays directed
`to the respective ?uid ?oW conduits. At the outlet end, ?oWs
`from the respective conduits are combined for emerging
`together via connection 22. Hence, the general ?oW direc
`tion Within device 10 is in the direction of arroW 24.
`As further understood by those of ordinary skill in the art,
`?uid ?oW conduit 14 may be generally an omega-shape as
`illustrated, or may assume other shapes. Such particular
`construction aspects of meter 10 form no particular part of
`the present invention.
`As further understood, ?uid ?oW conduit 14 has its
`respective inlet and outlet portions 16 and 18 disposed
`substantially coaxial With a ?rst oscillation axis thereof,
`generally represented by dotted line 26. As further under
`stood by those of ordinary skill in the art, the second ?uid
`?oW conduit (not seen in FIG. 1) likeWise has respective
`inlet and outlet portions Which are substantially coaxial With
`a second oscillation axis thereof, Which axis is parallel to the
`?rst oscillation axis 26. Also, the second conduit is formed
`so as to be physically similar to the ?rst conduit 14. As
`shoWn in more particular detail in the above-referenced ’002
`and ’410 patents incorporated herein by reference, the
`respective conduits are mounted Within casing 12 so as to be
`parallel to each other betWeen their respective end portions
`When not in use (i.e., Whenever the meter is not operated for
`tube vibrations and no ?uid ?oW passes therethrough).
`Still further in accordance With the conventional device
`10, driver means generally 28 may be provided for oscil
`lating the ?rst and second conduits relative to each other
`about their respective oscillation axes. In a conventional
`device, such driver means is responsive to a driver signal
`input. Driver means 28 may comprise an electromagnetic
`
`10
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`

`
`5,804,741
`
`7
`coil device, having a magnetizing Wire coil and movable
`magnetic core element, such as described and illustrated in
`the ’002 patent incorporated herein by reference. When
`operative, driver means causes a corresponding relative
`oscillatory motion of the conduits, for thereby causing
`oscillating Coriolis accelerations to act on respective ?uid
`?oWs through such conduits, all as Well knoWn and under
`stood by those of ordinary skill in the art.
`Still further in accordance With conventional device 10,
`respective ?rst and second sensor means generally 30 and 32
`may be associated With the conduits for generating analog
`sinusoidal outputs from the tWo indicated respective prede
`terrnined locations. With such an arrangement, the relative
`motion of the tWo conduits at such tWo predeterrnined
`locations may be determined through the output signals from
`the respective sensors.
`Lastly, While various arrangements may be practiced,
`FIG. 1 represents preferable use of an electrical connector
`generally 34, and associated electrical signal Wires generally
`36, by Which a driver signal input may be provided to driver
`means 28 and by Which analog sinusoidal outputs may be
`obtained from sensor means 30 and 32. Such sensors may
`comprise electrornagnetic coil devices, similar to driver
`means 28, but operated “in reverse” thereto.
`It is to be understood that particular connections of the
`various electrical Wires 36 With the components 28, 30, and
`32 are not shoWn in detail, for relative clarity. HoWever,
`different arrangements of such Wiring may be practiced,
`interconnections of which form no particular aspect of the
`subject invention.
`FIG. 2 diagrarnrnatically represents Wiring interconnec
`tions of the respective sensor means 30 and 32 relative to
`other electrical components and aspects of the subject inven
`tion. FIG. 2 likeWise is representative of the relationship of
`present electronic components and apparatus With driver
`means 28. As represented, the present invention is cornpat
`ible With receiving the analog sinusoidal outputs from the
`respective sensors 30 and 32 and providing a suitable driver
`signal for input to driver means 28.
`When considered from the block diagram schernatic rep
`resentation level of present FIG. 2, further represented
`aspects of the present invention include rneans generally 38
`for digitiZing respective analog sinusoidal outputs from
`sensors 30 and 32 and for generating corresponding ?rst and
`second digitiZed outputs. Still further, FIG. 2 represents
`means of the present invention generally 40 for processing
`such digitiZed outputs so as to estimate a fundamental
`frequency thereof, to estimate phases and a phase shift
`betWeen such digitiZed outputs, and to establish from such
`estirnates an optimized driver signal input for the driver
`means 28. Such means for processing may also be opera
`tional for determining from such phase shift estimate a
`corresponding rnass ?oW rate of ?uid ?oWing through the
`?rst and second conduits.
`In greater detail, such means generally 38 for digitiZing
`may operate separately on the ?rst and second channels as
`respectively associated With sensor means 30 and 32. Such
`respective sensors may be interconnected via respective
`lines 42 and 44 With respective sample and hold devices 46
`and 48. In such manner, the integrity of the respective
`outputs from sensor means 30 and 32 are maintained.
`Outputs of the respective sample and hold devices 46 and
`48 may be interconnected via lines 50 and 52 With respective
`analog-to-digital converter means 54 and 56, from Which
`emerge on respective data lines 58 and 60 respective ?rst
`and second digitiZed outputs of the analog sinusoidal outputs
`from lines 42 and 44.
`
`15
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`25
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`35
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`45
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`55
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`65
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`8
`Means generally 40 for processing such digitiZed outputs
`58 and 60 may preferably comprise a prograrnrnably con
`trollable device such as a digital signal processing (DSP)
`rnicroprocessor chip 62. Such DSP chip 62 may comprise
`any of a number of suitable commercially available devices.
`One presently preferred example is the part number 2115
`DSP chip available from Analog Devices. Such chip is in
`essence a self-contained 16 bit rnicroprocessor, operating
`such as at 16 rnHZ.
`Additional details of the operation of exemplary means 40
`for processing (DSP chip 62) are discussed in greater detail
`beloW With reference to present FIG. 5. OtherWise, it is to be
`understood that practice of the subject invention provides
`output data 64 representative of an optimized driver signal
`for driver means 28. Such digital data 64 is converted by
`digital-to-analog converter means 66 into an analog sinu
`soidal signal on line 68, the frequency and phase of Which
`has been determined by operation of processing means 40.
`An arnpli?er means 70 may be utiliZed for establishing a
`signal amplitude for a ?nal driver signal 72 Which is suitably
`matched to the speci?c device comprising driver means 28.
`Selection and operation of such arnpli?er means 70 relative
`to a particular driver means 28 is Well Within the skill of a
`practitioner in this art, and forms no particular details of the
`present invention.
`Obtaining ?oW rate information is a Well knoWn tech
`nique based on calculations starting With phase shift infor
`rnation derived in accordance With this invention from the
`respective analog sinusoidal signals 42 and 44. As Well
`understood, such tWo signals 42 and 44 have respective
`phase differences due to being located (syrnrnetrically
`displaced) on, opposite sides of the central aXis ?oW path
`location (dotted line 26) at Which driver means 28 is
`situated.
`UtiliZing such Well knoWn technique for calculating ?oW
`rate from phase shift data, processing means 40 may be
`provided for outputting deterrnined ?oW rate data on a data
`output line 74. In a practical application, data outputting
`rneans generally 76 may be provided, responsive to the
`determined ?oW rate data output 74, for displaying and
`recording the determined ?oW rate data and cumulative
`amounts of ?uid ?oW. Such an arrangement may be irnple
`rnented in a rnicroprocessor-based device, as Well knoWn to
`those of ordinary skill in the art.
`Alternatively, such device 76 may be provided so as to
`actually calculate or determine the How rate data, deriving
`instead from processing means 40 only the basic phase shift
`data as determined thereby in accordance With this inven
`tion. Such variations of practice of the present invention are
`Within the ordinary skill of those practicing in this art, and
`require no further detailed explanation for an adequate
`underst