llllllllllllllllllllllllllIllll|||||Illll||||||||||||||||l|I|||l||lll|||||
`
`US0057341 12A
`
`United States Patent
`
`[191
`
`[11]
`
`Patent Number:
`
`5,734,112
`
`Mar. 31, 1998
`Bose et al.
`[45] Date of Patent:
`
`63-191024
`
`8/1988
`
`Japan ................................73/361.357
`
`Primary Examiner-—George M. Dombroske
`Assistant Examiner—Paul D. Amrozowicz
`Attorney; Agent, or Firm—Duft. Graziano & Forest, RC.
`
`[57]
`
`ABSTRACT
`
`A method for determining pressure in an operating Coriolis
`effect mass flowmeter. The Coriolis flowmeter flow tubes are
`vibrated in both a bending mode (as is normal for measuring
`mass flow rate) and in a twisting mode. The ratio of the
`fundamental frequencies at which the flow tubes vibrate in
`each of the two vibration modes is proportional to the
`pres sure within the flow tubes. In the preferred embodiment.
`a sum/difierence method initially isolates the superposed
`sinusoids representing the fundamental frequencies of the
`two vibrational modes. Fast conjugate gradient (FCG) digi-
`tal filters are then used to rapidly estimate the fundamental
`frequencies in each of the two vibration modes. The esti-
`mated frequencies are then used by filter chains including
`digital notch and band pass filters as well as recursive
`maximum likelihood (RML) digital filter techniques to
`enhance the bending mode and twisting mode fundamental
`frequency estimates. The enhanced bending mode and twist-
`ing mode frequency estimates are used to determine the
`pressure within the flow tubes as a function of the ratio of the
`two frequencies as well as to center the notch and band pass
`filter chains used to enhance the bending mode frequency of
`the two vibration sensor channels for mass flow rate com-
`putations. The pressure so determined may then be used to
`correct mass flow rate computations or for other pressure
`measurement purposes per se.
`
`[54]
`
`[75]
`
`METHOD AND APPARATUS FOR
`MEASURING PRESSURE IN A CORIOLIS
`MASS FLOWMETER
`
`Inventors: Tamal Bose, Denver; Howard Vincent
`Derby. Boulder. both of Colo.; Andrew
`Keith Levien. Cranberry Township. Pa.;
`Anthony William Pankratz.
`Westminster. Colo.
`
`[73]
`
`Assignee: Micro Motion, Inc., Boulder. Colo.
`
`[21]
`
`Appl. No.: 689,339
`
`[22]
`
`Filed:
`
`Aug. 14, 1996
`
`Int. C1.° ........................................................ G01F 1/84
`U.S. Cl. ...................................... .. 73/861.56
`
`Field of Search ....................... 731861.355. 861.356.
`73/861.357. 861.354
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4/1989 Cage et al. ........................... 73/861.38
`4,823,613
`6/1990 Romano ........
`....... 73/861.38
`4,934,196
`5,054,326 10/1991 Mattar
`73/861.355
`....
`5,301,557
`4/1994 Cage et al.
`..... 73/861.355
`5,347,874
`9/1994 Kalotay et al.
`73/861.857
`5,373,745
`12/1994 Cage .............
`73/861.37
`5,423,225
`6/1995 Cage .............
`73/861.37
`5,448,921
`9/1995 Cage et al.
`73/861.38
`5,473,949 12/1995 Cage et al.
`..... .. 73/861.38
`5,555,190
`9/1996 Derby et al.
`. 73/861.356 X
`..
`5,576,500
`11/1996 Cage et al.
`......................... 73/861.357
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`[5 1]
`[52]
`[5 3]
`
`[56]
`
`W0 92/14123
`
`8/1992 European Pat. OE. .
`
`27 Claims, 11 Drawing Sheets
`
`MASS FLOW
`INSTRUMENTATION
`
`Micro Motion 1017
`
`1
`
`Micro Motion 1017
`
`

`
`U.S. Patent
`
`Mar. 31, 1998
`
`Sheet 1 of 11
`
`5,734,112
`
`2
`
`

`
`U.S. Patent
`
`Mar. 31, 1993
`
`Sheet 2 of 11
`
`5,734,112
`
`ommzo:<._:3<o
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`
`3
`
`
`
`

`
`U.S. Patent
`
`Mar. 31, 1998
`
`Sheet 3 of 11
`
`5,734,112
`
`
`
`1:"
`
`F’G- 4
`
`TWIST MODE
`VIBRATION
`
`4
`
`

`
`U.S. Patent
`
`3
`
`m_m<=n_%E5:9:we__w$558Sm
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`_____
`
`5
`
`
`

`
`U.S. Patent
`
`Mar. 31, 1993
`
`Sheet 5 of 11
`
`5,734,112
`
`_
`
`_
`
`_
`
`_
`
`_5:“.
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`E5:__EENS_Sm_.__mam_
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`
`

`
`U.S. Patent
`
`Mar. 31, 1998
`
`Sheet 6 of 11
`
`5,734,112
`
`
`
`
`
`DELAY_RML_BEND
`e
`DELAY_RML_TW|ST
`é- 100
`
`
`
`K‘ 700
`
`FIG. 7
`
`(OTHER INITIALIZATION)
`
`
`
`DELAY_RML_BEND
`(:
`100
`
`710
`
`
`
`
`
`
`
`‘71 4
`
`NOTCHED_TW|ST (-
`ANF (DIFF, BEND_FRECI)
`
`
`
`
`
`
`
`TW|ST__FRE(1 €-
`FCG (N0TCHED_TW|ST)
`
`716
`
`DELAY_RML_BEND
`(__.
`100
`
`720
`
`
`
`
`7
`
`

`
`U.S. Patent
`
`Mar. 31, 1998
`
`Sheet 7 of 11
`
`5,734,112
`
`
`
`BP_BEND
`C
`
`FIG. 8
`
`BP (BEND, BEND_FREO)
`
`
`
`A 724
`
`
`
`ENH_BEND_FREO
`<———
`
`726
`
`
`
`RML (ENH_BEND)
`
`
`
`
`
`COPY RML COEFFICIENT
`FROM FCG COEFFICIENT
`
`(ENH_BEND_FREQ
`V 6-
`BEND_FFlEO)
`
`DELAY__RML_BEND
`C
`
`
`
`730
`
`732
`
`DELAY__RML_BEND - 1
`
`
`
`
`
`736
`
`
`
`ENH__BEND_FREO
`(__
`
`740
`
`HML (ENH_TW|ST)
`
`
`
`
`COPY RML COEFFICIENT
`FROM FCG COEFFICIENT
`
`
`(ENH_TWlST_FREQ
`(-
`
`742
`
`TW|ST__FREO)
`
`
`
`
`DELAY_RML_TW|ST
`(_
`DELAY_RML__TW|ST - 1
`
`
`
`
`
`8
`
`

`
`U.S. Patent
`
`Mar. 31, 1993
`
`Sheet 8 of 11
`
`5,734,112
`
`FIG. 9
`
`\ 744
`
`
`
`
`
`
`
`ENH_LEFT
`(-
`BP (NF (LEFT, ENH_TWlST_FREQ),
`ENH_BEND_FREQ)
`
`
`
`ENH_R|GHT
`
`(-
`
`
`
`BP (NF (RIGHT, ENH_TW|ST_FREO),
`ENH_BEND_FREO)
`
`/a 743
`
`\ 746
`
`755
`
`
`
`PRESSURE
`(._
`g (AVG_ENH_TW|ST_FREQ /
`ENH_BEND_FREQ)
`
`758
`
`
`
`UPDATE GOEFITZEL FILTERS
`FROM ENH_LEFT AND
`ENH_R|GHT
`
`
`
`AVG_ENH_TWlST_FREQ
`e-
`
`
`
`750
`
`MASS_FLOW_RATE
`<_
`h (At, PRESSURE)
`
`AVG(ENH_TW|ST_FREO);
`AVG_ENH_BEND_FREO
`S
`
`AVG(ENH_BEND_FREQ)
`
`» 752
`
`750
`-
`
`UTILIZE PRESSURE
`AND MASS_FLOW_RATE
`
`
`
`
`
`
`
`
`HANNING
`WINDOW
`
`(HALF wmnow)
`
`
`COMPLETE
`
`At
`
`+-
`1 (GOERTZEL (ENH_LEFT).
`GOERTZEL (ENH_R|GHT))
`
`
`
`754
`
`N0
`
`752
`
`o
`
`RESET GOERTZEL FILTER AND
`
`FREQUENCY AVERAGE
`COMPUTAT|ONS
`
`?
`
`
`
`YES
`
`
`
`
`
`9
`
`

`
`U.S. Patent
`
`Mar. 31, 1998
`
`Sheet 9 of 11
`
`5,734,112
`
`
`BALANCED
`OP-AMP
`
`CIRCUIT
`
`
`
`158
`
`FIG. 10
`
`10
`
`

`
`U.S. Patent
`
`Mar. 31, 1993
`
`Sheet 10 of 11
`
`5,734,112
`
`«mmP
`
`33¢
`
`s_<EoE
`
`28
`
`2GE
`
`11
`
`25%IE5I
`
`F2:
`
`5.
`
`11
`
`
`

`
`U.S. Patent
`
`Mar. 31, 1998
`
`Sheet 11 of 11
`
`5,734,112
`
`1 300
`
`
`
`:o._.o<u_=o:s....__._<uEms.
`
`150
`
`200
`
`250
`
`300
`
`350
`
`400
`
`450
`
`500
`
`AVERAGE METER PRESSURE (PSI)
`
`FIG. 13
`
`PRESSURE (PSI)
`
`FIG. 14
`
`12
`
`
`

`
`1
`METHOD AND APPARATUS FOR
`MEASURING PRESSURE IN A CORIOLIS
`MASS FLOWMETER
`
`FIELD OF THE INVENTION
`
`The present invention relates to pressure measurment in
`association with Coriolis effect mass flowmeters and in
`particular to a method and apparatus for deriving material
`pressure information in response to the operation of the
`Coriolis effect mass flowmeter and for deriving precision
`mass flow information in response to the operation of the
`flowmeter.
`
`PROBLEM
`
`It is known to use Coriolis effect mass flowmeters to
`measure mass flow and other information for materials
`flowing through a conduit. Such flowmeters are disclosed in
`U.S. Pat. Nos. 4.109.524 of Aug. 29. 1978. 4.491.025 of Jan.
`1. 1985. and Re. 31.450 of Feb. 11. 1982. all to J. E. Smith
`et al. These flowmeters have one or more flow tubes of
`straight or curved configuration. Each flow tube configura-
`tion in a Coriolis mass flowmeter has a set of natural
`vibration modes. which may be of a simple bending, tor-
`sional or coupled type. Each flow tube is driven to oscillate
`at resonance in one of these natural modes. Material flows
`into the flowmeter from a connected conduit on the inlet side
`of the flowmeter. is directed through the flow tube or tubes.
`and exits the flowmeter through the outlet side. The natural
`vibration modes of the vibrating material filled system are
`defined in part by the combined mass of the flow tubes and
`the material flowing within the flow tubes.
`When there is no flow through the flowmeter. all points
`along the flow tube oscillate with identical phase due to an
`applied driver force. As material begins to flow. Coriolis
`accelerations cause each point along the flow tube to have a
`difierent phase. The phase on the inlet side of the flow tube
`lags the driver. while the phase on the outlet side leads the
`driver. Sensors are placed on the flow tube to produce
`sinusoidal signals representative of the motion of the flow
`tube. The phase difference between two sensor signals is
`proportional to the mass flow rate of material through the
`flow tube.
`
`A complicating factor in this measurement is that the
`density of typical process materials vary. Changes in density
`cause the frequencies of the natural modes to vary. Since the
`flowmeter’s drive control system maintains the flow tubes
`vibrating in resonance. the oscillation frequency varies in
`response to changes in density. Mass flow rate in this
`situation is proportional to the ratio of phase dilference and
`oscillation frequency.
`The above-mentioned U.S. Pat. No. Re. 31.450 to Smith
`discloses a Coriolis flowmeter that avoids the need for
`measuring both phase diflerence and oscillation frequency
`when measuring mass flow rate. Phase difference is deter-
`mined by measuring the time delay between level crossings
`of the two sinusoidal signals of the flowmeter. When this
`method is used. the variations in the oscillation frequency
`cancel. and mass flow rate is proportional to the measured
`time delay. This measurement method is hereinafter referred
`to as a time delay or At measurement.
`Information regarding the characteristics of material
`flowing in a Coriolis mass flowmeter is typically derived by
`instrumentation which measures the phase or time delay
`between two output signals of the sensors of the flowmeter.
`These measurements must be made with great accuracy
`since it is often a requirement that the derived flow rate
`
`5,734,112
`
`2
`
`information have an accuracy of at least 0. 15% of reading.
`These flowmeter output signals are sinusoidal and are dis-
`placed in time or phase by an amount determined by the
`Coriolis forces generated by the meter through which the
`material flows. The signal processing circuitry which
`receives these sensor output signals measures this phase
`dilference with precision and generates the desired charac-
`teristics of the flowing process material to the required
`accuracy of at least 0.15% of reading.
`U.S. Pat. No. 5.473.949 of Dec. 12. 1995 to Cage et al..
`describes a method of determining pressure and density in a
`Coriolis mass flowmeter. The Cage patent teaches the exci-
`tation of a vibrating conduit in two dilferent modes. Fluid is
`caused to flow in the conduit and measurements are made of
`the two modes of vibration at a “working point” of the
`flowmeter. The pressure and density of the material flowing
`in the flowmeter is then determined through the simulta-
`neous solution of two equations as provided by the Cage
`patent.
`
`Digital signal processing (DSP) techniques improve the
`accuracy of processing the signals from the Coriolis flow-
`meter sensors. DSP techniques and apparatus measure the
`phase difierence between the sensor signals without intro-
`ducing phase shifts between the two signals through the
`measurement process. Any phase shift (delay) induced by
`the DSP operation is identical for the two sensor signals. In
`addition. DSP techniques can more effectively filter the
`signals to extract the data from the ambient noise signals
`induced on the signals by the environment in which the
`flowmeter is operated.
`It is known that changes in pressure within the flow tubes
`of the flowmeter can affect the accuracy of the mass flow
`measurements. Changes in the pressure of the material
`flowing within the flow tubes can change the stilfness of the
`flowmeter’s flow tubes. This changes the resonant frequency
`of the flow tubes and causes errors in the mass flow
`measurement. To
`the effects of pressure changes
`on resonant frequency and mass flow measurements. it is
`common to stiffen the walls of the flow tubes. However.
`increasing the stiffness of the flow tubes to decrease the
`effects of pressure changes may increase costs of the flow-
`meter and also decreases the sensitivity of the flowmeter.
`Decreased sensitivity due to pressure effects may limit the
`usable range for application of the flowmeter.
`It is known in the art to use a pressure meter in conjunc-
`tion with the flowmeter to measure the instantaneous mate-
`
`rial pressure and to use the measured pressure values in the
`correction of the mass flow rate measurements. However.
`the addition of an independent pressure meter adds com-
`plexity (and associated costs) to the flow measurement
`apparatus.
`
`SOLUTION
`
`invention solves the above and other
`The present
`problems. thereby advancing the useful arts. by providing
`methods and apparatus for measuring the pressure within a
`Coriolis mass flowmeter without the addition of an inde-
`pendent pressure meter. A pressure measurement derived
`from the operation of a Coriolis eflect mass flowmeter is
`used to correct the mass flow measurements of the flowme-
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`ter. The pressure measurement may be utilized directly in the
`controlled process for other purposes requiring pressure
`measurements in a conduit. The methods and apparatus of
`the present invention operate the Coriolis efiect mass flow-
`meter by vibrating the flow tubes in both a bending mode
`and in a twisting mode. Each mode of vibration has a
`
`13
`
`13
`
`

`
`3
`
`4
`
`5,734,112
`
`fundamental frequency associated therewith. Well known
`signal processing techniques are used in conjunction with
`sensors positioned on the flow tubes to derive the mass flow
`rate as a function of the vibrations of the flow tubes. The
`methods of the present invention also make use of the fact
`that the ratio between a first vibration mode frequency of the
`flow tubes (e.g. the twisting mode frequency) and a second
`vibration mode of the flow tubes (e.g.. the bending mode
`frequency) varies as a function of the pressure within the
`flow tubes. The ratio of the two measured frequencies is used
`by signal processing methods and apparatus of the present
`invention to determine the material pressure within the flow
`tubes. The same signal processing apparatus is used both to
`derive the mass flow rate and to determine the pressure
`within the flowmeter flow tubes. This obviates the need for
`
`separate pressure measurement apparatus in many material
`flow measurement applications. Numerous other correction
`factors.
`including flow tube temperature and material
`density. are measured by the signal processing apparatus and
`used to correct both the mass flow rate determination and the
`
`pressure determination. By determining pressure within the
`flow tubes. the mass flow rate measurements may be cor-
`rected to account for the affects of pressure on the mass flow
`rate measurements.
`
`Measuring pressure within the flow tubes and compen-
`sating the measured mass flow rate to correct for the effects
`of pressure changes on the flow tubes vibration character-
`istics permits the flow tube walls to be constnrcted of thinner
`material. The flow tubes need be only thick enough to
`reasonably contain the static material pressure within the
`operating flow tubes. The flow tube walls need not be
`thickened for the sole purpose of reducing the effects of
`pressure changes on mass flow rate measurements. This
`thinner construction permits the flowmeter to maximize its
`sensitivity in flow measurement applications. The thinner
`flow tube walls provide better sensitivity for mass flow
`measurements. In particular. the thinner wall construction
`permits the flowmeter to measure lower mass flow rates such
`as is common in the measurement of mass flow of low
`density materials.
`In accordance with the present invention, the ratio of any
`two vibrational mode frequencies may be used to determine
`the pressure if the two vibrational mode frequencies match
`certain characteristics. The two vibration modes must
`
`respond differently to changes in pressure within the flow
`tubes. Any two vibration mode frequencies which meet this
`criterion may be used to determine pressure within the flow
`tubes from the ratio of the two vibration mode fiequencies.
`Although the description which follows presents the meth-
`ods of the present invention in view of a particular two
`vibrational modes (the first bending mode and the first
`twisting mode) other vibrational modes may satisfy this
`same criterion and may serve equally well for determining
`the pressure within the flowmeter. Also in accordance with
`the present invention. pressure is derived by measuring the
`frequency of a single mode of vibration. This can be done
`when one of the modes is either not subject to or not aifected
`by changes in the mounting conditions. the temperature of
`the flow tubes and the density of the material.
`The present invention drives the flow tubes to vibrate both
`in the first out of phase bending mode (herein the bend mode
`or bending mode) and in the first out of phase twist mode
`(herein the twist mode or twisting mode). Depending on the
`needs of a particular flowmeter application. the flow tubes
`may be driven to vibrate in both modes simultaneously or.
`in the alternative. the tubes may be sequentially and repeti-
`tively driven in the twisting mode followed by the bending
`
`mode. In addition. the tubes may be vibrated continuously in
`the bending mode for normal mass flow measurements and
`periodically simultaneously vibrated in the twisting mode in
`order to periodically determine pressure and mass flow
`corrections therefrom.
`
`Signal processing apparatus samples the output signals of
`sensors attached to the vibrating flow tubes to isolate and
`measure the frequency of each vibration mode. The signal
`processing apparatus determines the mass flow rate from the
`bending mode vibration signal samples as is well known in
`the art. The ratio of bending mode frequency and twisting
`mode frequency varies. in part. as a function of the material
`pressure within the mass flowmeter’s flow tubes. The signal
`processing apparatus computes and utilizes this ratio to
`determine the pressure within the flowmeter. A mass flow
`rate correction factor is then determined using the pressure
`measurement. This correction factor is used by the signal
`processing apparatus to correct the mass flow rate. This
`corrected mass flow rate measurement is then used to control
`or otherwise report information regarding the process flow.
`In addition to correction of the mass flow rate
`measurements,
`the pressure measurement of the present
`invention may be utilized per se to obviate the need for
`independent pressure metering devices. The present inven-
`tion fulfills the need for a pressure measurement device in
`applications of Coriolis flowmeters where pressure measure-
`ments are also required.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 depicts a typical mass flowmeter attached to mass
`flow instrumentation in which the methods of the present
`invention may be advantageously applied;
`FIG. 2 is a block diagram depicting additional details of
`the mass flow instrumentation of FIG. 1;
`
`FIG. 3 is a perspective view of a typical flow tube in the
`bending vibrational mode;
`FIG. 4 is a top view of a typical flow tube in the twisting
`vibrational mode;
`
`FIG. 5 is a block diagram depicting the various digital
`filters applied to isolate and enhance signals processed by
`the programs in the DSP within mass flow instrumentation
`of FIG. 1 using the preferred embodiment sum/difierence
`method of the present invention;
`FIG. 6 is a block diagram depicting the various digital
`filters applied to isolate and enhance signals processed by
`the programs in the DSP within mass flow instrumentation
`of FIG. 1 using the alternative embodiment fourth order
`filter method of the present invention;
`FIGS. 7-9 are flowcharts which describe the methods of
`an embodiment of the present invention operable within the
`DSP of the mass flow instrumentation of FIG. 1;
`
`FIG. 10 is a block diagram of the driver circuit of FIG. 2
`which isolates the desired fundamental frequencies of the
`vibrating flow tubes using a sum/dilference method;
`FIG. 11 is a circuit diagram of the balanced op-amp circuit
`of FIG. 10;
`FIG. 12 is a block diagram which depicts integrated
`circuit devices within the mass flow instrumentation of FIG.
`1;
`
`10
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`FIG. 13 is a graph depicting a typical relationship between
`the calibration factor of a mass flowmeter and the pressure
`within the flowmeter flow tubes; and
`
`65
`
`FIG. 14 is a graph depicting a typical relationship between
`the ratio of twist mode vibration frequency over the bend
`
`14
`
`14
`
`

`
`5,734,112
`
`mode vibration frequency and the pressure within the flow-
`meter flow tubes.
`
`5
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Overview—Coriolis Flowmeter Applications
`
`Atypical Coriolis mass flowmeter 10 is illustrated in FIG.
`1 as having two flow tubes 12. 14 aflixed to a manifold body
`30 so as to have substantially identical spring constants and
`moments of inertia about their respective out-of-phase bend-
`ing axes W—W and W'—W‘. One of ordinary skill in the art
`will readily recognize that the cantilever mounted flowmeter
`design depicted in FIG. 1 is intended only as exemplary of
`a Coriolis etfect mass flowmeter in which the methods of the
`present
`invention may be advantageously applied. The
`methods of the present invention are advantageously appli-
`cable to flowmeters having many different flow tube geom-
`etries as well as flowmeters having multiple flow tubes or a
`single flow tube.
`A drive coil and magnet 20 are mounted at a midpoint
`region between the top portion 130 and 130' of flow tubes
`12. 14 to oscillate flow tubes 12. 14 out of phase about axes
`W—W and W'—W‘. This vibration is referred to herein as
`a “bending” vibrational mode or simply “bend mode.” FIG.
`3 is a perspective view of a single flow tube 14 attached to
`a manifold body 30 vibrating in the bend mode about axis W.
`A pair of drive coils and associated magnets 21R and 21L
`are mounted at the right and left sides. respectively. of flow
`tubes 12. 14 to oscillate the flow tubes 12. 14 about the
`center axis of each flow tube. namely. T and T’, respectively.
`out of phase with respect to the left and right sides of the
`flowtubes. This vibration is referred to herein as a “twisting"
`vibrational mode or simply “twist mode.” One of ordinary
`skill in the art will readily recognize that drive coil and
`magnet 20 positioned on top portions 130 and 130' may be
`eliminated if drive coils and magnets 21R and 21L are
`capable of driving the flow tubes 12 and 14 to vibrate in both
`modes. FIG. 4 is a top View of a single flow tube 12 attached
`to a manifold body 30 vibrating in the twist mode about axis
`T. As noted in FIG. 1. each flow tube 12 and 14 is driven to
`vibrate in the twisting mode about its own axis. T and T’.
`respectively.
`Left sensor 16 and right sensor 18 are mounted near the
`respective ends of the top portions of flow tubes 12. 14 to
`sense the relative movement of flow tubes 12. 14. This
`sensing is preferably done by well known techniques apply-
`ing velocity sensors. Flow tubes 12 and 14 have left side legs
`131 and 131' and right side legs 134 and 134'. The side legs
`converge downwardly toward each other and are affixed to
`surfaces 120 and 120' of manifold elements 121 and 121‘.
`Brace bars 140R and 140L are brazed to the legs of flow
`tubes 12. 14 and serve to define the axes W—W and W'—W‘
`about which the flow tubes oscillate out of phase when
`driver 20 is energized over path 156. The position of axes
`W—W and W—W‘ is determined by the placement of brace
`bars 140R and 140L on flow tube side legs 131, 131' and
`134. 134'.
`
`Temperature detector 22 is mounted on side leg 131 of
`flow tube 14 to measure the flow tube’s temperature and the
`approximate temperature of the material flowing therein.
`This temperature information is used to determine changes
`in the spring constant of the flow tubes. Drivers 20. 21R. and
`21L. sensors 16 and 18 and temperature detector 22 are
`connected to mass flow instrumentation 24 by paths 156.
`161. 160. 157. 158 and 159. respectively. Mass flow instru-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`S0
`
`55
`
`65
`
`6
`mentation 24 includes at least one microprocessor which
`processes the signals received from sensors 16. 18, and 22
`to determine the mass flow rate of the material flowing
`through flowmeter 10 as well as other measurements. such
`as material density and temperature. Mass flow instrumen-
`tation 24 also applies a drive signal over path 156 to driver
`20 to oscillate flow tubes 12 and 14 in the bend mode
`out-of-phase about axes W—W and W'—W‘. Additionally.
`instrumentation 24 applies a drive signal over paths 160 and
`161 to drivers 21L and 21R. respectively. to oscillate flow
`tubes 12 and 14 in the twist mode about axis W". One of
`ordinary skill in the art will readily recognize that driver 20
`may be eliminated if drivers 21L and 21R are physically and
`electronically capable of simultaneously driving the flow
`tubes 12 and 14 in the desired two vibrational modes.
`Alternatively. the drivers may drive the flow tubes sequen-
`tially in the two dilferent modes—-one mode at a time.
`One of ordinary skill in the art will readily recognize that.
`depending upon flow tube geometric configurations. a single
`driver circuit. properly positioned on the flow tubes. may be
`capable of driving the flow tubes to vibrate in both modes.
`Manifold body 30 is formed of casting 150. 150'. Casting
`elements 150. 150‘ are attachable to a supply conduit and
`exit conduit (not shown). by flanges 103. 103'. Manifold
`body 30 diverts the material flow from the supply conduit
`into flow tubes 12. 14 and then back into an exit conduit.
`When manifold flanges 103 and 103' are connected via inlet
`end 104 and outlet end 104' to a conduit system (not shown).
`carrying the process material to be measured. the material
`enters manifold body 30 and manifold element 110 through
`inlet orifice 101 in flange 103 and is connected by a channel
`(not shown) having a gradually changing cross-section in
`casting element 150 to flow tubes 12. 14. The material is
`divided and routed by manifold element 121 to the left legs
`131 and 131' of flow tubes 12 and 14. respectively. The
`material then flows through the top tubes elements 130. 130'
`and through the right side legs 134 and 134' and is recom-
`bined into a single stream within flow tube manifold element
`121'. The fluid is thereafter routed to a channel (not shown)
`in exit casting element 150' and then to exit manifold
`element 110'. Exit end 104' is connected by flange 103'
`having bolt holes 102' to the conduit system (not shown).
`The material exits through ouflet orifice 101' to return to the
`flow in the conduit system (not shown).
`Mass flow instrumentation 24 analyzes signals received
`on paths 157. 158. and 159 and generates standard output
`signals on path 155 to indicate mass flow rates utilized by a
`control system or operator for monitoring and control of the
`mass flow rate through the associated conduit system (not
`shown). Mass flow instrumentation 24 also generates output
`signals on path 162 indicative of pressure within the mass
`flowmeter. As noted above. the pressure so determined is
`used within the mass flow instrumentation to correct the
`mass flow rate computations and may be used independently
`for other contr'ol purposes requiring pressure measurements.
`
`Overview—Pressure Etfects on Flow Tube
`Vibrations
`
`Mass flow rate within a Coriolis eifect mass flowmeter is
`known to be proporfional to At (the time diiference mea-
`surement discussed above). The mass flow rate may there-
`fore be expressed as:
`m=CFAt
`
`where CF is the calibration factor and m is flow rate.
`However. as pressure increases or decreases within the
`
`15
`
`15
`
`

`
`5,734,112
`
`c1>=1+((K,,,1oo)(P-P.,))
`
`8
`
`where IQ, is a pressure calibration factor (expressed as a
`percentage per psi of pressure). P is the pressure (determined
`as above) within the flow tubes. and P0 is the calibration line
`pressure (i.e.. the nominal pressure used to calibrate the
`flowmeter for normal operation in its intended application).
`Pressure calibration factor KP and calibration line pressure
`P0 are determined through standard factory or in situ cali-
`bration techniques well known to those of ordinary skill in
`the art.
`
`10
`
`7
`flowtubes of the Coriolis efl‘ect mass flowmeter. the stilfness
`of the flow tubes may change. A change in the stiffness of the
`flow tube afl’ects the mass flow rate sensitivity of the
`flowmeter. A change in the stilfness of the flow tube also
`aifects the vibrational frequencies of the flow tubes. The
`ratio between bending mode and twisting mode vibration
`frequencies of the flow tubes changes in response to pressure
`changes in the flow tubes. The frequency ratio is therefore
`related to pressure within the flow tubes (as well as a number
`of other factors).
`FIGS. 13 and 14 are graphs of empirical data from
`operating Coriolis effect mass flowmeters which depict the
`elfects described above. FIG. 13. is a graph depicting typical
`effects of pressure on the flowmeter calibration factor. Graph
`1300 shows meter calibration factor on the y-axis as a
`function of the pressure within the flow tubes on the x-axis.
`The plotted data points 1302. 1304. and 1306 are measured
`data from an operating Micro Motion D300 flowmeter
`(modified to provide additional drive coils for application of
`twisting drive force as well as bending drive force). It can be
`seen in graph 1300 that the calibration factor increases as the
`pressure within the D300 flow tubes increases.
`FIG. 14 is a graph depicting typical effects of pressure on
`the frequency ratio of the flow tubes. Graph 1400 shows the
`frequency ratio of twist mode vibration over bend mode
`vibration on the y-axis as a function of the pressure within
`the flow tubes on the x-axis. Curves 1402 and 1404 are fitted
`to measured data points from an operating Micro Motion
`CMFSOO mass flowmeter (modified to provide additional
`drive coils for application of twisting drive force as well as
`bending drive force). Specifically. curve 1402 is fitted to data
`points measured while flowing water through the CMF300
`flowmeter and curve 1404 is fitted to data points measured
`while flowing corn syrup through the CMF30O flowmeter. It
`can be seen in curves 1402 and 1404 of graph 1400 that the
`frequency ratio is afiected by pressure within the flow tubes
`(as well as by density of the material flowing therein).
`As noted in FIG. 14. material density alfects the frequency
`ratio. Likewise.
`it can be shown that
`temperature and
`mounting parameters of the flow tubes can affect the fre-
`quency ratio determination. These factors can be easily
`characterized and compensated by calibration of the mass
`flowmeter as used in a particular application. The frequency
`ratio with these compensations applied thereto is therefore
`usable as an indirect measure of the pressure within the
`operating mass flowmeter flow tubes. Details of the required
`compensation are provided below.
`Once the frequency ratio has been appropriately adjusted.
`it is used to determine the corresponding pressure within the
`flow tubes. Well known curve fit or table lookup and
`interpolation numerical techniques may be applied to com-
`pute the pressure given the compensated frequency ratio.
`The pressure so determined may be utilized. per se. as a
`direct pressure measurement for applications requiring such
`pressure determinations.
`In addition. the pressure so determined is used to correct
`the calibration factor of the mass flowmeter to thereby
`correct the mass flow rate measurements thereof. The pres-
`sure is used to determine a pressure correction factor which
`is then applied to correct the mass flow determination. The
`mass flow rate within the vibrating flow tubes is therefore
`determined as:
`m=CF CPAt
`
`Overview——Mass Flow Instrumentation
`
`invention comprises digital signal processing
`present
`methods operable within a digital signal processor (DSP)
`chip to perform the computational functions within mass
`flow instrumentation 24. Discrete samples are taken of the
`analog signals generated as output from each of the flow
`tube sensors. The discrete samples from the left and right
`sensors are digitized by use of standard analog to digital
`conversion (AID) devices. Once digitized. further process-
`ing of the samples is performed by digital signal processing
`methods within the DSP chip.
`This digital signal processing software (discussed below)
`is operable on mass flow instrumentation 24 shown in
`greater detail in FIG. 12. Digital signal processor 1200 of
`FIG. 12 is a computing device much like any common
`microprocessor but with special purpose functions tuned for
`application to signal processing tasks. Many such DSP
`processor devices are known to those skilled in the art. One
`example of such a device is the Texas Instruments TMS
`320C3l. This device includes a hardware floating point
`processing unit to enhance the performance of the signal
`processing computations. One of ordinary skill in the art will
`readily recognize that fixed point signal proces