United States Patent [19]
`Kalotay et a].
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,009,109
`Apr. 23, 1991
`
`ABSTRACT
`[57]
`[54] FLOW TUBE DRIVE CIRCUIT HAVING A
`121%? OUTPUT FOR USE IN A CORIOLIS A drive circuit for providing bursts, rather than contin
`uously alternating amounts, of energy for use in driving
`a flow tube (conduit) in a Coriolis meter and methods
`for use in such a circuit. Speci?cally, the drive circuit
`provides a pre-de?ned burst of energy to a drive coil
`af?xed to a flow conduit at an appropriate point during
`:CYCIF
`°s<=iillft°ryg°éi°nf°tithe cgllldtuit in Offer
`ornam
`epe ampiu e0 eosc aoryrnoion
`substantially within a prescribed range. This burst can
`be applied at a pre-defined point, illustratively the peak,
`in each cycle of the oscillatory motion with no energy
`
`[75] Inventors: Paul Knlotay, Lafayette; Robert
`Bruck, Boulder; Arnold Emch, Estes
`Park; Donald Marten!’ Louisville, 311
`of C010-
`[73] Assignee: Micro Motion, Inc., Boulder, Colo.
`[21] APPI- No-i 446,614
`[22] Filed;
`Dec_ 5 1939
`51
`In Cl 5
`’
`
`G0 1F 1 84
`
`[58]
`
`[56]
`
`pulse occurs in order to reduce the amount of electrical
`energy applied to the drive coil. Alternatively, to fur
`ther reduce this energy, a burst need not be applied
`during every such cycle but rather only at those pre
`References Cited
`de?ned points, e. g. the peaks, within those cycles where
`U'S_ PATENT DOCUMENTS
`the velocity of the ?ow conduit is less than a pre
`'
`‘
`4,9l2,962 4/1990 Kawaguchi ...................... .. 73/32 A de?ned limit vahm
`Primary Examiner-Herbert Goldstein
`Attorney. Agent, or Firm—Peter L. Michaelson
`
`
`
`
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`' 33’1/15'4 155 65’
`’
`’
`
`15 Claims, 6 Drawing Sheets
`
`130'
`
`195
`
`1851
`
`SIGNAL
`VELOCITY SIGNAL
`
`165“ 165L
`
`ANALOG 8 DIGITAL
`PROCESS OUTPUT SIGNALS
`
`1
`
`Micro Motion 1008
`
`

`

`US. Patent
`
`Apr. 23, 1991
`
`Sheet 1 of 6
`
`5,009,109
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`US. Patent
`
`Apr. 23, 1991
`
`Sheet 3 of 6
`
`5,009,109
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`U.S. Patent
`
`Apr. 23, 1991
`
`Sheet 4 of 6
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`5,009,109
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`US. Patent
`
`Apr. 23, 1991
`
`Sheet 5 of 6
`
`5,009,109
`
`F I 6. 5
`
`Em
`
`DRIVE cmcun
`PggPE
`
`INSTRUCT TIMER/COUNTER 550 TO
`_ DELIVER INITIAL DRIVE PULSE (‘v.01 SEC)
`TO FLOM CONOUITS TO BEGIN
`OSCILLATORY MOVEMENT
`
`4-.-
`
`I620
`
`INITIATE OMA TRANSFER FROM I/O SPACE
`TO MEMORY ARRAY TO TRANSFER A REOUISITE
`NUMBER OF SAMPLES TO CHARACTERIZE ONE
`PERIOD OF FLOM CONOUIT MOTION
`
`645
`
`640 f
`PROCESS 'NON-ORIVE'
`RELATED METER FUNCTIONS
`
`650
`I
`DETERMINE MAXIMUM S MINIMUM VALUES OF SAMPLES IN ARRAY;
`CALCULATE ABSOLUTE VALUE OF PEAK, IVpeak I; and
`DETERMINE APPROXIMATE RESONANT FREOUENCY OF FLOM
`CONOUIT MOTION AND STORE FOR USE DURING NEXT
`OMA TRANSFER FROM I/O SPACE
`
`590/“
`
`APPLY SUITABLE LEVEL CHANGE TO
`GATE INPUT OF TIMER/COUNTER
`550 TO ACTIVATE ITS PULSE \
`HIDTH nouuuneu
`675
`OUTPUT
`
`585
`\
`
`680
`\
`.
`APPLY SUITABLE LEVEL CHANGE TO
`BATE INPUT OF TIMER/COUNTER 55o
`TO OEACTIVATE ITS PULSE MIOTH
`MOOULATEO OUTPUT
`
`6
`
`

`

`US. Patent
`
`Apr. 23, ‘1991
`
`Sheet 6 of 6
`
`5,009,109
`
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`

`1
`
`5,009,109
`
`FLOW TUBE DRIVE CIRCUIT HAVING A BURSTY
`OUTPUT FOR USE IN A CORIOLIS METER
`
`25
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The invention relates to apparatus for a drive circuit
`that provides bursts, rather than continuously alternat
`ing amounts, of energy for use in driving a ?ow tube
`(conduit) in a Coriolis meter and to methods for use in -
`such a circuit.
`2. Description of the Prior Art
`Currently, Coriolis meters are ?nding increasing use
`as an accurate way to measure the mass ?ow rate and
`/or density of various process ?uids in many applica
`tions.
`_ Generally speaking, a Coriolis mass ?ow rate meter,
`such as that described in Us. Pat. No. 4,491,025 (issued
`to J. E. Smith et al on Jan. 1, 1985), contains one or two
`20
`parallel conduits, each typically being a U-shaped ?ow
`conduit or tube. Each ?ow conduit is driven to oscillate
`about an axis to create a rotational frame of reference.
`For a U-shaped ?ow conduit, this axis can be termed
`the bending axis. As process ?uid flows through each
`oscillating ?ow conduit, movement. of the ?uid pro
`duces reactionary Coriolis forces that are orthogonal to
`both the velocity of the ?uid and the angular velocity of
`the conduit. These reactionary Coriolis forces, though
`quite small when compared to the force at which the
`30
`conduits are driven, nevertheless cause each conduit to
`twist about a torsional axis that, for a U-shaped ?ow
`conduit, is normal to its bending axis. The amount of
`twist imparted to each conduit is related to the mass
`?ow rate of the process ?uid ?owing therethrough.
`This twist is frequently measured using velocity signals
`obtained from magnetic velocity sensors that are
`mounted to one or both of the ?ow conduits in order to
`provide a complete velocity pro?le of the movement of
`each ?ow conduit with respect to either the other con
`duit or a ?xed reference. In dual tube meters, both ?ow
`40
`conduits are oppositely driven such that each conduit
`oscillates (vibrates) as a separate tine of a tuning fork.
`This “tuning fork” operation advantageously cancels
`substantially all undesirable vibrations that might other
`wise mask the Coriolis force.
`In such a Coriolis meter, the mass ?ow rate of a ?uid
`that moves through the meter is proportional to the
`time interval that elapses between the instant one point
`situated on a side leg of a ?ow conduit crosses a pre
`determined location, e.g. a respective mid-plane of os
`cillation, until the instant a corresponding point situated
`on the opposite side leg of the same ?ow conduit,
`crosses its corresponding location, eg its respective
`mid-plane of oscillation. For parallel dual conduit Cori
`olis mass ?ow rate meters, this interval is equal to the
`phase difference between the velocity signals generated
`for both ?ow conduits at the fundamental (resonant)
`frequency at which these ?ow conduits are driven. In
`addition, the resonant frequency at which each ?ow
`conduit oscillates depends upon the total mass of that
`conduit, i.e. the mass of the conduit itself, when empty,
`plus the mass of any ?uid ?owing therethrough. Inas
`much as the total mass varies as the density of the ?uid
`?owing through the tube varies, the resonant frequency
`likewise varies with any changes in ?uid density and as
`such can be used 'to track changes in ?uid density.
`As noted above, these mass ?ow and density relation
`ships inherent in a Coriolis meter require that each ?ow
`
`35
`
`2
`conduit in the meter must be driven to resonantly vi
`brate in order for the meter to properly operate. To
`ensure that proper vibratory motion is initiated in, for
`example a dual tube Coriolis meter, and thereafter main
`tained during operation of the meter, the meter contains
`an appropriate drive mechanism that is mounted to both
`of the ?ow conduits typically between corresponding
`extremities of these conduits. The drive mechanism
`frequently contains any one of many well known ar
`rangements, such as a magnet mounted to one conduit
`and a coil mounted to the other conduit in an opposing
`relationship to the magnet. A drive circuit continuously
`applies a periodic, typically sinusoidally or square
`shaped, drive voltage to the drive mechanism. Through
`interaction of the continuous alternating magnetic ?eld
`produced by the coil in response to the periodic drive
`signal and the constant magnetic ?eld produced by the
`magnet, both ?ow conduits are initially forced to vi
`brate in an opposing sinusoidal pattern which is thereaf
`ter maintained. Inasmuch as the drive circuit tightly
`synchronizes the frequency of the drive signal to essen
`tially match the resonant frequency of the conduits,
`both ?ow conduits are kept in a state of opposing sub
`stantially resonant sinusoidal motion.
`One known drive circuit currently in use today and
`typi?ed by that disclosed in, for example, US. Pat. No.
`4,777,833 (issued to B. L. Carpenter on Oct. 18,
`l988—hereinafter referred to as the ’833 Carpenter
`patent-and currently owned by the present assignee)
`utilizes an analog drive circuit. Speci?cally, this circuit
`utilizes a synchronous analog ampli?er to generate a
`continuous square wave with two analog levels that
`each equally change based upon a simultaneously oc
`curring difference between an analog reference voltage
`and a ?ow conduit position signal. As the magnitude of
`this difference increases (decreases), based upon de
`creasing (increasing) amplitudes of the oscillatory
`movement of the ?ow conduits which results from, for
`example, increases (decreases) in the density in the pro
`cess ?uid that simultaneously ?ows through the ?ow
`conduits, positive and negative drive levels produced
`by the synchronous ampli?er corresponding and
`equally increase (decrease) to once again restore the
`amplitude of the oscillatory ?ow tube movement to its
`proper level. Various analog components, such as inter
`alia ampli?ers, buffers, a phase shifter and an edge de
`tector, are used'to appropriately determine this differ
`ence based upon the analog reference level and one of
`the velocity sensor signals, typically a left velocity sen
`sor signal, produced within the meter.
`Unfortunately, analog drive circuits used in Coriolis
`meters and typi?ed by that described in the ’833 Car
`penter patent suffer from various drawbacks.
`First, analog drive circuits, particularly those which
`provide an alternating square shaped drive signal to the
`coil, do not permit the energy that is applied to the
`drive coil to be precisely controlled by the drive circuit
`itself at any one instant during the signal. With these
`circuits, the drive signal is merely set to alternate be
`tween two levels that are static within any one drive
`cycle. Precise control over the energy supplied to drive
`coil by the drive circuit itself has proven to be particu
`larly important in those applications, such as intended
`use of the meter particularly the mechanical Coriolis
`metering assembly itself in a hazardous environment,
`where a critical need exists to always limit this energy
`to as low a value as is realistically possible. While intrin
`
`45
`
`55
`
`65
`
`8
`
`

`

`3
`sic safety barriers are used in these applications to limit
`the energy that would ?ow to the drive coil located in
`a hazardous area to below a pre-de?ned maximum
`amount and in doing so perform extremely well, it
`would be preferable to further limit the energy at its
`source, if possible, i.e. drive circuit, and rely on the
`barrier as a back-up protective device rather than as a
`main mechanism for limiting the energy.
`Second, analog drive circuits generally tend to be
`complex and require a multitude of parts which adds to
`the manufacturing cost of the meter electronics.
`Third, discrete analog components, such as those
`used in a drive circuit, may exhibit undesirable tempera
`ture, aging and/ or drift characteristics any one of which
`might, over time, cause the output produced by such a
`component to vary. These affects can be minimized to a
`certain and usually acceptable extent by using compo
`nents with matched temperature characteristics, appro
`priate temperature compensation circuits and/or suffi
`ciently frequent re-calibration. However, use of
`20
`matched components further increases the cost of the
`meter electronics, while temperature compensation
`circuits often require additional components which
`increase the parts count as well as the manufacturing
`cost of the drive circuit. Re-calibration disadvanta
`25
`geously increases the costs associated with actual use of
`the meter.
`Therefore, a need exists in the art for a simple and
`inexpensive ?ow tube drive circuit particularly suited
`for use in a Coriolis meter that provides substantially
`accurate control over the amount of energy that is to be
`applied to the drive coil at any instant, has a reduced
`parts count and cost over analog drive circuits known
`in the art, and does not appreciably, suffer, if at all, from
`temperature, aging and/or drift affects which are com
`monly associated with analog drive circuits known in
`the art.
`
`4-0
`
`SUMMARY OF THE INVENTION
`An object of the present invention is to provide a
`drive circuit for use in a Coriolis meter that provides
`substantially accurate control over the amount of en
`ergy that is to be applied to the drive coil at any time.
`Another object is to provide such a drive circuit that
`generates a reduced amount of energy to the drive coil,
`45
`as compared to that generated by drive circuits known
`in the art, but which is nevertheless suf?cient to main
`tain the amplitude of the vibratory motion of the ?ow
`conduits at a desired level.
`Another object is to provide such a drive circuit that
`does not appreciably suffer from temperature, drift
`and/or aging affects commonly associated with analog
`drive circuits known in the art.
`Another object is to provide such a drive circuit that
`has a relatively low parts count and is relatively simple
`and inexpensive to manufacture.
`These and other objects are provided in accordance
`with the teachings of our inventive drive circuit which
`provides a pre-de?ned burst of energy to a drive coil
`affixed to a ?ow conduit at an appropriate point during
`a cycle of the oscillatory motion of the conduit in order
`to maintain the peak amplitude of the oscillatory motion
`substantially within a prescribed range. This burst can
`be applied at a pre-de?ned point in each cycle of the
`oscillatory motion with no energy being applied during
`that cycle other than when the burst occurs in order to
`reduce the amount of electrical energy applied to the
`drive coil. Alternatively, to further reduce this energy,
`
`5,009,109
`4
`a burst need not be applied during every such cycle but
`rather only at those pre-de?ned points within those
`cycles where the amplitude of the oscillatory motion of
`the ?ow conduit is less than a pre-defined limit value.
`In accordance with the teachings of a preferred em
`bodiment of our invention, our inventive drive circuit
`periodically samples the left velocity sensor signal
`throughout a single cycle of this signal using a pre
`de?ned sampling period. These samples are transferred
`on a direct memory access (DMA) basis, using a well
`known cycle stealing technique, from an input/output
`space into a memory array, both situated within random
`access memory in a microprocessor. Transferring sam
`pled data values in this manner does not adversely and
`appreciably affect the throughput of the microproces
`sor. In response to the samples occurring throughout
`this cycle of the signal, the drive circuit, speci?cally the
`microprocessor contained therein, determines the zero
`crossings and maximum and minimum values of this
`cycle and thereafter calculates the absolute value of the
`peak of the cycle using the maximum and minimum
`values. Using two adjacent zero crossings contained
`within the cycle, the microprocessor also determines
`the approximate frequency of the velocity signal and
`hence the approximate resonant frequency of the ?ow
`conduits. Once these operations have occurred, the
`' microprocessor compares the absolute value of the peak
`against a pre-de?ned limit value, Vref. This comparison
`determines whether the amplitude of the vibratory mo
`tion of the flow conduits has decayed to a suf?ciently
`low value to warrant the addition of a burst of energy to
`the drive coil and therethrough to the ?ow conduits in
`order to appropriately restore this amplitude. Specifi
`cally, in the event the absolute value of the peak is less
`than the limit value, then the microprocessor illustra
`tively gates a timer/counter circuit to generate a burst,
`such as a pulse, having a pre-defmed shape to the drive
`coil within a speci?c window during the remainder of
`the cycle. Alternatively, if the absolute value of the
`peak is greater than the limit value, then no such pulse
`is generated by the timer/ counter and hence no burst of
`energy is applied to the drive coil. Depending upon
`various mechanical characteristics of the ?ow tubes and
`the rate at which the density of the process ?uid ?ow
`ing therethrough changes, several, perhaps quite a num
`ber, of cycles of oscillatory flow tube movement may
`elapse until the absolute value of the peak decays to a
`suf?ciently low value to cause the drive circuit to apply
`a burst of energy to the ?ow tubes. In addition, the
`microprocessor, using the approximate value of the
`frequency of the velocity signal, determines the number
`of samples that need to be obtained during the next
`DMA transfer in order to fully characterize the next
`cycle of oscillatory ?ow tube movement and stores this
`number for use during subsequent initiation of that
`DMA transfer.
`Furthermore, a burst of energy can also be imparted
`to the drive coil at an appropriate point outside the
`window during a cycle(s) in order to remove a ?nite
`amount of vibratory energy from the ?ow conduits and
`thereby effectively retard the peak value of these vibra
`tions, when necessary.
`In accordance with a feature of our invention, the
`drive circuit can adapt its performance to changing
`operating conditions of the Coriolis meter, such as
`changes in the density of the process ?uid ?owing
`through the meter, while imparting relatively minimal
`amounts of energy to the drive coil that are nevertheless
`
`60
`
`65
`
`9
`
`

`

`5
`sufficient to sustain the ?ow tubes in resonant oscilla
`tory motion with a pre-de?ned peak value. Speci?cally,
`the limit value can be changed, e.g. increased, when
`ever the rate of change in the absolute value of the peak
`is suf?ciently high so that bursts of mechanical energy
`can be rapidly added to the vibrating ?ow conduits,
`such as over a larger number of successive cycles than
`would otherwise occur. Adding bursts of energy in this
`fashion quickly compensates for increased attenuation
`that occurs in the peak of the vibratory amplitude of the
`?ow tubes, caused by large rapid increases in the fluid
`density. Moreover, whenever the absolute value of the
`peak amplitude reaches or exceeds the increased limit
`value, the limit value can ‘be appropriately decreased to
`a normal value in order to reduce the rate at which
`mechanical energy will be imparted to the vibrating
`?ow conduits.
`
`i0
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The teachings of the present invention may be clearly
`understood by considering the following detailed de
`scription in conjunction with the accompanying draw
`ings, in which:
`’
`FIG. 1 is an overall diagram of Coriolis mass ?ow
`rate metering system 5;
`25
`FIG. 2 depicts a block diagram of meter electronics
`20 shown in FIG. 1;
`FIG. 3 is a block diagram of a prior art embodiment
`of ?ow tube drive circuit 40;
`‘ FIG. 3A depicts various waveforms associated with
`drive circuit 40 shown in FIG. 3;
`FIG. 4 is a block diagram of a preferred embodiment
`of drive circuit 40 constructed in accordance with the
`teachings of our present invention;
`FIG. 5 depicts a flowchart of drive circuit routine
`600 executed by microprocessor 530 shown in FIG. 4 to
`generate a drive signal in accordance with the teachings
`of our invention;
`FIG. 6 is a waveform depicting two illustrative cy
`cles of the left velocity signal and the temporal relation
`40
`ship between this velocity signal and the occurrence of
`drive signal bursts produced by our inventive drive
`circuit; and
`FIG. 7 depicts various illustrative waveforms each of
`which can be used to produce a drive signal burst.
`45
`To facilitate understanding, identical reference nu
`merals have been used, where appropriate, to designate
`identical elements that are common to the ?gures.
`
`30
`
`20
`
`5,009,109
`6
`tion, mass ?ow rate information is also provided in
`analog 4-20 mA form over leads 26 for easy Connection
`to downstream process control and/or measurement
`equipment.
`Coriolis meter assembly 10, as shown, includes a pair
`of manifolds 110 and 110'; tubular member 150; a pair of
`parallel ?ow conduits (tubes) 130 and 130'; drive mech
`anism 180; a pair of velocity sensing coils 1601_ and
`160R; and a pair of permanent magnets 1701, and 1703.
`Conduits 130 and 130' are substantially U-shaped and
`have their ends attached to conduit mounting blocks
`120 and 120’, which are, in turn, secured to respective
`manifolds 110 and 110'. Both ?ow conduits are free of
`pressure sensitive joints.
`With the side legs of conduits 130 and 130' ?xedly
`attached to conduit mounting blocks 120 and 120’ and
`these blocks, in turn, ?xedly attached to manifolds 110
`and 110’, as shown in FIG. 1, a continuous closed ?uid
`path is provided through Coriolis meter assembly 10.
`Speci?cally, when meter 10 is connected, via inlet end
`101 and outlet end 101’, into a conduit system (not
`shown) which carries the ?uid that is being measured,
`?uid enters the meter through an ori?ce in inlet end 101
`of manifold 110 and is conducted through a passageway
`therein having a gradually changing cross-section to
`conduit mounting block 120. There, the ?uid is divided
`and routed through ?ow conduits 130 and 130'. Upon
`exiting ?ow conduits 130 and 130’, the ?uid is recom
`bined in a single stream within conduit mounting block
`120' and is thereafter routed to manifold 110'. Within
`manifold 110’, the ?uid flows through a passageway
`having a similar gradually changing cross-section to
`that of manifold 110—as shown by dotted lines 105—to
`an ori?ce in outlet end 101'. At end 101’ the ?uid reen
`ters the conduit system. Tubular member 150 does not
`conduct any ?uid. Instead, this member serves to axially
`align manifolds 110 and 110’ and maintain the spacing
`therebetween by a pre-determined amount so that these
`manifolds will readily receive mounting blocks 120 and
`120’ and ?ow conduits 130 and 130'.
`U-shaped ?ow conduits 130 and 130' are selected and
`appropriately mounted to the conduit mounting blocks
`so as to have substantially the same moments of inertia
`and spring constants about bending axes W-W and
`W’—W', respectively. These bending axes are perpen
`dicularly oriented to the side legs of the U-shaped ?ow
`conduits and are located near respective conduit mount
`ing blocks 120 and 120'. The U-shaped ?ow conduits
`extend outwardly from the mounting blocks in an essen
`tially parallel fashion and have substantially equal mo
`ments of inertia and equal spring constants about their
`respective bending axes. Inasmuch as the spring con
`stant of the conduits changes with temperature, resistive
`temperature detector (RTD) 190 (typically a platinum
`RTD device) is mounted to one of the ?ow conduits,
`here conduit 130’, to continuously measure the tempera
`ture of the conduit. The temperature of the conduit and
`hence the voltage appearing across the RTD, for a
`given current passing therethrough, will be governed
`by the temperature of the ?uid passing through the ?ow
`conduit. The temperature dependent voltage appearing
`across the RTD is used, in a well known method, by
`meter electronics 20 to appropriately compensate the
`value of the spring constant for any changes in conduit
`temperature. The RTD is connected to meter electron
`ics 20 by lead 195.
`Both of these flow conduits are sinusoidally driven in
`opposite directions about their respective bending axes
`
`50
`
`DETAILED DESCRIPTION
`After reading the following description, those skilled
`in the art will readily appreciate that our inventive drive
`circuit can be utilized with nearly any Coriolis meter
`regardless of whether that meter is measuring mass ?ow
`rate, density or other parameter(s) of a process ?uid.
`55
`Nevertheless, for purposes of brevity, the inventive
`drive circuit will be discussed in the context of a meter
`that speci?cally measures mass ?ow rate.
`FIG. 1 shows an overall diagram of Coriolis mass
`?ow rate metering system 5.
`As shown, system 5 consists of two basic compo
`nents: Coriolis meter assembly 10 and meter electronics
`20. Meter assembly 10 measures the mass ?ow rate of a
`desired process ?uid. Meter electronics 20, connected
`to meter assembly 10 via leads 100, illustratively pro
`vides mass ?ow rate and totalized mass ?ow informa
`tion. Mass ?ow rate information is provided over leads
`26in frequency form and in scaled pulse form. In addi
`
`65
`
`10
`
`

`

`0
`
`25
`
`5,009,109
`8
`7
`velocity signals appearing on leads 165L and 165R, re
`and at essentially their common resonant frequency. In
`spectively. Meter electronics 20 also produces, as noted,
`this manner, both ?ow conduits will vibrate in the same
`the alternating drive signal appearing on lead 185.
`manner as do the tines of a tuning fork. Drive mecha~
`nism 180 supplies the sinusoidal oscillatory driving
`Leads 1651,, 165R, 185 and 195 are collectively referred
`to as leads 100. The meter electronics processes both the
`forces to conduits 130 and 130’. This drive mechanism
`left and right velocity signal and the RTD temperature,
`can consist of any one of many well known arrange
`through any one of a number of well known methods,
`ments, such as a magnet mounted to illustratively flow
`to determine the mass ?ow rate and totalized mass ?ow
`conduit 130' and an opposing coil mounted to illustra
`of the ?uid passing through meter assembly 10. This
`tively flow conduit 130 and through which an alternat
`ing current is passed, for sinusoidally vibrating both
`mass ?ow rate is provided by meter electronics 20 on
`associated lines within leads 26 in analog 4—20 mA form.
`?ow conduits at a common frequency. A suitable con
`tinuous alternating drive signal is applied by meter elec
`Mass ?ow rate information is also provided in fre
`quency form (typically with a maximum range of 0-10
`tronics 20, via lead 185, to drive mechanism 180.
`With ?uid ?owing through both conduits while these
`KHz), over an appropriate line within leads 26 for con
`nection to downstream equipment.
`conduits are sinusoidally driven in opposing directions,
`A block diagram of meter electronics 20 is depicted in
`Coriolis forces will be generated along adjacent side
`legs of each of flow conduits 130 and 130' but in oppo
`FIG. 2. Here, as shown, meter electronics 20 consists of
`site directions, i.e. the Coriolis force generated in side
`mass flow rate circuit 30 and flow tube drive circuit 40.
`Mass ?ow rate circuit 30 processes the left and right
`leg 131 will oppose that generated in side leg 131’. This
`velocity signals appearing over leads 1651_ and 165R,
`phenomenon occurs because although the ?uid ?ows
`respectively, along with the RTD signal appearing on
`through the ?ow conduits in essentially the same paral
`lel direction, the angular velocity vectors for the oscil
`lead 195, in a well known manner, to determine the mass
`?ow rate of the ?uid passing through meter assembly
`lating (vibrating) ?ow conduits are situated in opposite
`though essentially parallel directions. Accordingly,
`10. The resulting mass ?ow rate information is provided
`during one-half of the oscillation cycle of both flow
`as a 4-20 mA output signal over lead 263, for easy con
`conduits, side legs 131 and 131' will be twisted closer
`nection to additional downstream process control
`equipment (not shown), and as a scaled frequency signal
`together than the minimum distance occurring between
`these legs produced by just the oscillatory movement of
`over lead 262 for easy connection to a remote totalizer
`the conduits generated by drive mechanism 180. During
`(also not shown). The signals appearing on leads 262
`and 263 form part of the process signals that collec
`the next half-cycle, the generated Coriolis forces will
`twist the side legs 131 and 131’ further apart than the
`tively appear on leads 26 shown in FIG. 1. Inasmuch as
`maximum distance occurring between these legs pro
`the method through which circuit 20 generates mass
`duced by just the oscillatory movement of the conduits
`?ow rate information is well known to those skilled in
`generated by drive mechanism 180.
`the art and does not form any part of the present inven
`During oscillation of the ?ow conduits, the adjacent
`tion, mass flow rate circuit 30 along with its constituent
`side legs, which are forced closer together than their
`electronics will not be discussed in any further detail
`counterpart side legs, will reach the end point of their
`herein. In this regard, the reader is illustratively re
`ferred to US. Pat. Nos. 4,777,833 (issued to B. L. Car
`travel, where their velocity crosses zero, before their
`counterparts do. The time interval which elapses from
`penter on Oct. 18, 1988) or 4,843,890 (issued to A. L.
`the instant one pair of adjacent side legs reaches their
`Samson et al on July 4, 1989) which are both co-owned
`40
`by the present assignee and which describe different
`end point of travel to the instant the counterpart pair of
`side legs, i.e. those forced further apart, reach their
`embodiments of circuits that can be used within a Cori
`respective end point is proportional to the total mass
`olis mass ?ow rate meter to determine mass ?ow rate of
`‘?ow rate of the ?uid ?owing through meter assembly
`a process ?uid.
`Flow tube drive circuit 40, depicted in FIG. 2, pro
`10. The reader is referred to US. Pat. No. 4,491,025
`vides an alternating drive signal, via lead 185, to drive
`(issued to J. E. Smith et. al. on Jan. 1, 1985) for a more
`detailed discussion of the principles of operation of
`mechanism 180. This circuit synchronizes the sine wave
`parallel path Coriolis ?ow meters than that just pres
`drive signal to the left velocity signal which appears on
`leads 165 and 41.
`ented.
`FIG. 3 depicts a block diagram of a well known em~
`To measure the time interval, At, coils 160], and 160;;
`bodiment of flow tube drive circuit 40, shown in FIG. 2.
`are attached to either one of conduits 130 and 130’ near
`Throughout the following discussion of circuit 40, ref
`their free ends and permanent magnets 170], and 170;;
`erence will be made, where appropriate, to various
`are also attached near the free ends of the other one of
`waveforms produced within or by circuit 40 and de
`the conduits. Magnets 170L and 170;; are disposed so as
`picted within FIG. 3A. Accordingly, the reader should
`to have coils 1601_ and 160R located in the volume of
`55
`simultaneously refer to both FIGS. 3 and 3A through
`space that surrounds the respective permanent magnets
`out this discussion. Speci?cally, circuit 40 receives the
`and in which the magnetic flux ?elds are essentially
`uniform. With this con?guration, the electrical signal
`left velocity signal produced by coil 160;, and, in re
`outputs generated by coils 1601_ and 160;; provide a
`sponse thereto, provides a square wave drive signal to
`velocity pro?le of the complete travel of the conduit
`drive coil 180 at a frequency equal to the resonant fre
`60
`quency of the flow conduit and in phase with and hence
`and can be processed, through any one of a number of
`tightly synchronized to its movement. As such, this
`well known methods, to determine the time interval
`drive signal injects mechanical energy into both flow
`and, in turn, the mass ?ow rate of the ?uid passing
`through the meter. In particular, coils 160], and 160;;
`conduits to overcome inherent mechanical losses and
`produce the left and right velocity signals that appear
`thereby ensures that both conduits continuously vibrate
`on leads 1651, and 165R, respectively.
`at substantially, if not exactly, their common resonant
`frequency. Moreover, this circuit automatically adjusts
`