United States Patent
`
`[19]
`
`[11] Patent Number:
`4,733,569
`Kelsey et al.
`[45] Date of Patent: Mar. 29, 1988
`
`MASS FLOW METER
`
`4,559,833 12/1985 Sipin.
`
`Inventors: Newton D. Kelsey, Dallas, Tex.;
`Martin Kane, Atlantic City, N.J.;
`Wayne Pratt, Scottsdale, Ariz.
`K-Flow Division of Kane Steel Co.,
`Inc., Millville, N.J.
`Appl. No.: 809,658
`Filed:
`Dec. 16, 1985
`Int. Cl.4 .............................................. .. G01F 1/84
`U.S. C1. ...............
`............... .. 73/861.38
`Field of Search ..... ..
`73/861.37, 861.38
`References Cited
`
`
`
`Assignee:
`
`[54]
`[75]
`
`[73]
`
`[21]
`[22]
`[51]
`[52]
`[58]
`[56]
`
`FOREIGN PATENT DOCUMENTS
`149900 11/1961 U.S.S.R.
`.
`146982
`4/1964 U.S.S.R.
`.
`0732672
`5/1980 U.S.S.R.
`......................... .. 73/861.38
`
`OTHER PUBLICATIONS
`
`Alan M. Young, “Corio1is—Based Mass Flow Meter”,
`Dec. 1985—Sensors Magazine.
`E. Dahlin, A. Young, R. Blake, C. Guggenheim, S.
`Kaiser and A. Levien, “Mass Flow Meter”—Measure-
`ment and Controls magazine.
`W. Bye, “Mass Flow Measured with Vibration Genera-
`tors”, Feb. l957—Fluid Handling magazine.
`Danfoss Co., “MASSFLO”.
`Exac Corp., Digital Precision Mass Flow Meter.
`Smith Meter Co., “S—MASS”, 1985.
`Micro Motion, Model D25.
`Instrument Engineers Handbook (Rev. Ed.), Mass
`Flow Meters (pp. 87-90), 1982.
`
`Primary Examiner——Herbert Goldstein
`Attorney, Agent, or Fz’rm—Seide1, Gonda, Goldhasmmer
`& Abbott
`
`[57]
`
`ABSTRACT
`
`A mass flow meter for placement in line within a pre-
`existing process line. The flow meter having a conduit
`forming a substantially free floating spiral or circular
`loop which is symmetrical about the axis line defined by
`the process line. A driving transducer extending radi-
`ally from a bracket on a support beam which is posi-
`tioned along the axis line and attached to the inlet and
`outlet end of the conduit. The driver imparting an alter-
`nating deflection to the loop which is substantially per-
`pendicular to the fluid flow within the loop and parallel
`to the axis line. Sensing transducers are positioned along
`the periphery of the loop, displaced equidistant from the
`driving transducer along‘ its circumference for deter-
`mining the deflection signature of the loop. The deflec-
`tion of the loop in response to the fluid reaction forces
`is measured without reference to a specific fixed axis or
`position of the loop. This acceleration signature is cor-
`related to the mass flow rate of the fluid through the
`conduit.
`
`14 Claims, 8 Drawing Figures
`
`.
`
`.
`.
`
`U.S. PATENT DOCUMENTS
`Smith .
`Re. 31,450 11/1983
`Pearson .
`1/1953
`2,624,198
`Powers .
`11/1957
`2,81 1,854
`11/1957
`Altfillisch et al.
`2,813,423
`White .
`1/1958
`2,819,437
`1/1958
`Altfillisch et a1.
`2,821,084
`4/1958
`Altfillisch et al.
`2,831,349
`5/1958
`Jones et a1.
`.
`2,834,209
`Roth .
`12/1958
`2,865,201
`Roth .
`4/1963
`3,087,325
`Henderson .
`10/1963
`3,108,475
`Roth .
`5/1964
`3, 132,512
`11/1965
`3,218,851
`Sipin .
`7/1966
`3,261,205
`Sipin .
`Roth .
`10/1966
`3,276,257
`7/1967
`3,329,019
`Sipin .
`12/1967
`3,355,944
`Sipin .
`8/1968
`Souriau .
`3,396,579
`7/1969
`Brockhaus .
`3,456,491
`12/1969
`3,485,098
`Sipin .
`7/1975
`Hunter et al.
`3,896,619
`12/1975
`Pavlin et al.
`3,927,565
`Smith .
`8/1978
`4,109,524
`Cox et al.
`11/1978
`4, 127,028
`Smith .
`2/1980
`4,187,721
`.
`3/1980
`Cox et al.
`4,192,184
`2/1981
`Smith et a1.
`4,252,028
`1/1982
`Cox et al.
`.
`4,3 1 1,054
`Shiota .
`5/1983
`4,381,680
`Smith .
`12/1983
`4,422,338
`Smith .
`4/1984
`4,444,059
`Hamel .
`9/1984
`4,470,294
`Ruesch .
`1/1985
`4,49 1,009
`1/1985
`Smith et al.
`4,491,025
`
`.
`
`.
`
`.
`
`.
`
`.
`
`
`
`Micro Motion’ 1026 A
`
`1
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`Micro Motion 1026
`
`

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`U.S. Patent V Mar. 29, 1988U.S. Patent V Mar. 29, 1988
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`U.S. PatentU.S. Patent
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`% Mar.29,1988% Mar.29,1988
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`sheet 2 of3sheet 2 of3
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` U.S. Patent Mar. 29, 1988 U.S. Patent Mar. 29, 1988
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`1
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`MASS FLOW METER
`
`4,733,569
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`l3RIEF SUMMARY OF THE INVENTION
`This invention relates to a mass flow meter which
`measures Coriolis or gyroscopic type reaction forces to
`determine the mass flow of a fluid or slurry within a
`conduit. Paricularly this invention incorporates a con-
`duit loop having an inlet end and an outlet end posi-
`tioned substantially along a single axis which is typi-
`cally defined by a line of existing piping. The loop is
`alternately deflected in a direction orthogonal to the
`flow within the conduit. The alternating deflections or
`oscillations of the conduit imparts a transverse angular
`momentum to the fluid flowing through the loop. The
`fluid reacts with a repetitive and measurable force
`against the wall of the conduit causing a transverse
`deflection of the loop. The reaction of the fluid on the
`conduit is proportional to the magnitude and direction
`of the fluid mass flow;
`
`BACKGROUND OF THE INVENTION
`
`The invention relates to a mass flow metering device
`which operates within a defined fluid stream. Such
`metering devices are desirably constructed without
`internal moving parts which may be contaminated by
`the fluid within the stream. The principle of the inven-
`tion is based on the known fact that a fluid flowing
`through a conduit or tube which experiences an acceler-
`ation orthoginal to the direction of its flow, will interact
`with the conduit wall with a reaction force which is
`directly proportional
`to the mass flow of the fluid
`within the conduit. The reaction force generated by the
`fluid against the conduitpis generally referred to as a
`Coriolis force.
`Various issued patents describe mass flow meters
`which utilized the measurement of the fluid reaction
`forces to determine the mass flow rate. These patents
`teach various conduit designs and configurations, vari-
`ous means for measuring the reaction forces and various
`ways of determing the mass flow.
`Roth, U.S. Pat. No. 2,865,201, teaches a gyroscopic
`type flow meter which directly measures the magnitude
`of the reaction forces on the conduit. Since these forces
`are created by a continuous oscillation of the conduit,
`the Roth design is impractical. Similar conduit designs
`are found in Roth, U.S. Pat. No. 3,276,257, and Hender-
`son, U.S. Pat. No. 3,108,475. The sensitivity of the reac-
`tion force measurement in all of these conduit designs is
`greatly influenced by the oscillatory fluctuations of the
`meter conduit and by environmental vibrations.
`A series of patents, U.S. Pat. Nos. 3,261,205,
`3,329,019 and 3,355,944, to Sipin teach the measurement
`of the fluid reaction forces due to an imparted trans-
`verse vibration on a straight conduit, a curved conduit
`and a U-shaped conduit. The earlier conduit designs in
`this series attempt
`to directly measure the reaction
`forces on the conduit and, therefore, were subject to the
`same substantial sensitivity deficiencies due to external
`vibrational influences found in the patents discussed
`above. In the curved and U-shaped conduit designs, the
`imparted oscillation creates a torsional bending moment
`about an, ideally, fixed axis. In the U-shaped design the
`sensors were required to be referenced to the actual
`motion of the tube and to a fixed or stationary position.
`In a working environment each of the Sipin conduit
`designs are extremely noisy in operation and, basically,
`ineffective due to inacuracies created by vibrations of
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`the flow meter and the references of the sensors tube
`unrelated to the fluid reaction force. The drivers, which
`impart the oscillatory motion to the conduit, are at-
`tached to an external casing of the meter. The internal
`and external vibrational effects causes substantial output
`deficiencies in the reaction force sensing means and,
`therefore, greatly effect the calculation of the mass flow
`rate.
`_
`In Smith, U.S. Pat. No. 4,109,524, an attempt was
`made to separate the oscillation means from the force
`measurement system. The flow meter disclosed in this
`patent is cumbersome in application and does not effec-
`tively reduce the vibrational effects on the reaction
`force sensing means.
`The first patent to recognize the need for vibrational
`and noise immunity on the sensing means is Cox et al,
`U.S. Pat. No. 4,127,028. In Cox each reaction force
`sensor is referenced to two adjacent cantalevered tubes.
`The two tubes are oscillated simultaneously in opposite
`relative directions and, ideally, at the same resonance.
`The external vibrational influences on the two tubes are
`intended to be self-cancelling when viewed by the sen-
`sors referenced to both tubes. However, the driving
`means in this design is mounted on a long cantilever arm
`and includes a large weight at the end of the arm. This
`structure produces an extremely low vibrational reso-
`nance and greatly limits the ability of the cantalevered
`tube to oscillate about a fixed reference axis. Environ-
`mentally induced vibrations, as well as vibrational ef-
`fects of the driving means continue to influence the Cox
`measurement sensitivity by affecting the positioning of
`the tubes differently.
`The same deficiencies found in Cox ’028 in its reac-
`tion force sensing are found in the Smith, U.S. Pat. No.
`4,187,721 and its corresponding Reissue No. 31,450.
`Smith, U.S. Pat. No. 4,422,338, attempts to enhance the
`sensitivity of the meter by using a frame which sur-
`rounds the oscillating tube to act as a fixed sensor refer-
`ence. In addition, the Smith ’338 design utilizes velocity
`type sensors to create an adjoining reference system
`such that the zero or reference position of linear type
`sensors, which record thetube motion due to the fluid
`reaction forces,
`is continually adjusted in response to
`vibrational influences on the meter. However, since the
`rotational axis of the cantalevered flow meter tube and
`mounting frame is not stationary, due to the vibrational
`effects on the meter structure. The effect of adjusting
`the reference plane of the reaction force sensors, there-
`fore, is minimal. Commonly assigned copending appli-
`cation Ser. No. 809,659 submitted to the Patent Office
`on Dec 16, 1985 teaches a conduit design which is not
`cantilevered and is driven preferably directly along the
`axial line of the pipeline of the defined fluid stream. The
`structure of this invention overcomes many of the prior
`art deficiencies in sensing.
`It is important to note that in all of the known flow
`meter designs, as long there is an increasing gradient of
`transverse velocity from the entrance of the flow meter
`tube to a point of maximum velocity and a decreasing
`transverse velocity gradient from the maximum point to
`the outlet, that there will be a decreasing transverse
`reaction or Coriolis force gradient in one direction from
`the inlet to the point of maximum deflection or velocity
`and a transverse force gradient in the opposite direction
`from the maximum point to the outlet. The measure-
`ment or sensing of these reaction forces created by the
`
`5
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`

`

`3
`Coriolis reaction of the fluid maybe correlated to the
`mass flow rate within the tube.
`
`The prior art of this type flow meter exhibits signifi-
`cant deficiencies in their determination of the fluid reac-
`tion on the tube. These deficiencies are directly related
`to the geometry of the meter and its sensing technique.
`It is difficult to isolate the oscillating motion of the flow
`meter tube created by the fluid reaction forces due ‘to
`the environmental vibrations encountered by the con-
`duit (or vibrations created by the meter itself).
`The typical industrial environment in which the flow
`meter operates is subject to substantial vibrational influ-
`ences due to the presence of rotating machinery within
`the process line in which the meter is located. External
`temperature influences, as well as, internal pressure and
`temperature fluctuations adversely affect the reliability
`and the sensitivity of the known meter designs.
`Additional problems which effect the sensitivity of
`this type flow meter relate to the utilization of these
`instruments “on line” within an existing piping system
`in an industrial process. Impedance of the fluid flow
`caused by the flow meter may significantly hamper the
`efficiency of the industrial process.
`Furthermore, flow meters of this type have a ten-
`dency to become complex, bulky and expensive, all of
`which adversely affect the applicability of the Coriolis
`or gyroscopic measurement
`technique in many in-
`stances.
`
`_
`
`OBJECT OF THE INVENTION
`It is therefore an object of this invention to provide a
`.. mass flow meter that overcomes some of the deficien-
`cies of the prior art and which may be easily positioned
`“on-line” within an existing pipe or process line.
`It is also the object of this invention to provide a flow
`meter
`structure which effectively increases
`the
`measurablility of the fluid reaction force on the conduit
`. while eliminating environmental and structural limita-
`H‘ tions that affect the reaction force sensing and its corre-
`N_. lation to the mass flow rate.
`Q
`I It is a further intent of the present invention to pro-
`,__,vide a mass flow meter that is substantially insensitive to
`"temperature and pressure fluctuations and to typical
`industrial environmental vibrations.
`
`SUMMARY OF THE INVENTION
`
`The preferred embodiment of the present invention
`incorporates. a flow meter conduit or tube positioned
`within a pre-existing pipe line or defined fluid stream
`having an inlet and an outlet end arranged axially along
`the pipe line of the fluid stream. Intermediate between
`the inlet and outlet, the flow meter tube is spiraled sym-
`metrically about the axis line such that the conduit
`forms a substantially free floating loop. In one embodi-
`ment of the invention the loop lies in a plane substan-
`tially perpendicular to the first axis (the plane being
`defined by the “Z” and the “Y” axes). The loop is free
`floating having no defined axis of rotation and is rela-
`tively free of restrictions or constraints along all points
`of its periphery.
`A fluid stream enters through the inlet of the meter,
`proceeds around the loop (such that it is traveling in a
`direction perpendicular to the axis of its input flow),
`exits the loop through the outlet and returns into the
`defined fluid stream. A support beam, lying substan-
`tially along the first axis and passing through the geo-
`metric center of the loop is secured adjacent to the inlet
`and outlet ends of the flow meter conduit. A mounting
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`bracket secured to the support beam incorporates radi-
`ally extending arms which position a single or, in the
`alternative, a pair of driving transducer(s) on the pe-
`riphery of the loop. Each driver imparts an oscillating
`deflection to the loop in a direction substantially per-
`pendicular to the flow within the loop and parallel to
`the X-axis. Sensing transducers may be mounted radi-
`ally from the bracket and positioned adjacent to the
`outside edge of the loop. Sensors may also be mounted
`directly onto the periphery of the loop without support
`from the brackets. Two or more sensors on opposite
`sides of the center oscillation are used to process and
`correlate the information relating to the deflection sig-
`nature of the conduit loop due to the reaction forces of
`the fluid on the conduit.
`The radially positioned sensing transducers produce
`serial information as to the specific displacement cycle
`of the conduit resulting from the fluid reaction forces.
`This information can be correlated in the microproces-
`sor in any convenient manner to provide an accurate
`determination of the mass flow rate.
`The support beam may be rigidly mounted or have a
`spring damping arrangement
`to reduce vibrations
`which may be translated to and from the mounting
`system. However, due to the radial sensing configura-
`tion contemplated by this invention, the external vibra-
`tion translated to the beam and mounting bracket are
`effectively self cancelling.
`A free floating loop arrangement has the advantage
`of reducing the spring constant of the conduit which
`acts to resists deflection of the loop due to the fluid
`reaction forces. This spring constant reduction in-
`creases the sensitivity of the meter. The sensing capabil-
`ities of the meter are also increased, as compared to the
`known designs, since the flow meter loop is not can-
`talevered or subject to an extreme bending moment
`about a fixed mounting position. The softer spring con-
`stant, also, permits the use of heavier or stronger wall
`materials when designing the flow meter conduit, in-
`creasing longevity and permitting use with higher oper-
`ating pressures and temperatures. The symmetrical po-
`sitioning of the loop also optimizes the center of gravity
`about its central axis.
`
`A free floating loop, as compared to a cantalevered
`U-shaped form, eliminates the need for measurements
`about a fixed rotational axis. The reactions of the flow
`meter conduit, as measured by the sensors, are not refer-
`enced to a specific fixed structure or axis and, therefore,
`vibrations created by the structure or by environmental
`machinery do not alter a fixed reference location. Addi-
`tionally, radial positioning of the drivers and the sensors
`effectively cancel these external vibrations and, there-
`fore, do not create a significant effect on the sensor
`measurements.
`
`The acceleration imparted to the fluid by the driver
`is, desirably, at a maximum at a point along the axis line
`defined fluid stream and is directed parallel to that line.
`Common mode vibrations from the driver are translated
`axially through this system. Additional vibrational in-
`fluences do not substantially affect the fluid flow before
`or after passing through into the flow meter.
`Also, the transverse mounting of the loop is substan-
`tially immune to noise and other translated vibrational
`forces. Transverse mounting with respect to the fluid
`stream creates a very stable plane, such that no one
`portion of the flow meter conduit is subject a to greater
`vibrational effect than another.
`
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`

`5
`In line mounting of the flow meter conduit, also,
`brings the inlet and outlet of the flow meter closer to-
`gether. Therefore,
`the conduit contemplated by this
`invention substantially reduces the size of the meter
`between the inlet and the outlet as well as the size of the
`casting of the covers and mounting brackets required.
`Further objects and advantages will become apparent
`to those skilled in the art by particularly describing the
`preferred embodiments of the invention.
`For the purpose of illustrating the invention, there is
`shown in the drawings a number of forms which are
`presently preferred; it being understood, however, that
`this invention is not limited to the precise arrangements
`and instrumentalities shown.
`
`
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a perspective view of a single loop embodi-
`ment in accordance with the teachings of the present
`invention.
`FIG. 2 is a side view of the embodiment in FIG. 1.
`FIG. 3 is a perspective view of the embodiment in
`FIG. 1 referencing a three-dimensional coordinate sys-
`tem.
`FIGS. 4a and 4b show an alternate sensor embodi-
`ment mounted directly on the flow meter conduit.
`FIG. 5 shows an alternate embodiment of the flow
`meter to that shown in FIGS. 1, 2 and 3.
`FIG. 6 shows a two driver embodiment of the flow
`meter shown in FIG. 1.
`
`FIG. 7 shows the relative reaction forces effecting
`the conduit loop.
`DETAILED DESCRIPTION OF THE
`DRAWINGS
`
`The preferred embodiment of the flow meter of this
`invention comprises a conduit or tube which is gener-
`ally referenced by the numeral 10. This conduit 10 is to
`be positioned “in line” within a defined fluid stream or
`pre-existing pipe line (not shown).
`Referring to FIGS. 1-3, the conduit 10 is provided
`with an inlet 12 and an outlet 14 at respective ends. The
`inlet 12 and outlet 14 are positioned substantially along
`a single axial line which is defined by the pre-existing
`pipe line and is referenced as the X-axis 16. Intermediate
`of the inlet 12 and outlet 14 the conduit 10 is formed into
`a spiral which, as shown, forms a loop 18. The refer-
`enced coordinate system referred to in this text is shown
`in FIG. 3. The Y-axis is referred to by the numeral 20
`and the Z-axis being 22 in the three dimensional system
`shown.
`The inlet portion 24 of the conduit 10 between the
`inlet 12 and loop 18 and its corresponding outlet portion
`26 from the loop 18 to the outlet 14 are formed through
`the use of gently bent portions which turn the direction
`of the fluid flow approximately 90° (when viewed from
`above the X-Z plane). These inlet and outlet portions
`24, 26 of the spiral design in FIGS. 1, 2 and 3 are formed
`to minimize restriction of the fluid flow through the
`conduit 10. The actual shape of these portions 24, 26
`will vary depending on conduit diameter, the intended
`working fluid and the length of the spiral of the loop
`along the X-axis 16.
`A mounting bracket 28 is positioned at the center of
`the loop 18. Supporting arm 30 extends radially from
`the mounting bracket 28 and is positioned substantially
`along the Y-axis 20 to a position directly adjacent to the
`periphery of the loop 18. A driving transducer 32 is
`mounted on the end of support arm 30. The driver 32
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`4,733,569
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`6
`may be of any conventional design such as an electro-
`magnetic coil excited by an alternating current (See
`FIG. 2). The driver 32 when excited to oscillate the
`loop 18, imparts a deflection to the loop 18 substantially
`parallel to the X-axis 16. The oscillation of the loop 18
`induces the alternating change in the angular momen-
`tum of the fluid within the conduit 10. Alternately,
`driver 32 substantially deflects the loop 18 perpendicu-
`lar to the Y-Z plane and about the Z-axis 22, although
`these references are not critical to the invention.
`The mounting bracket 28 is supported on a beam 36
`which passes through the center of the loop 18 and
`extends substantially along the X-axis 16 and is attached
`to the inlet 12 and the outlet 14. This structure refer-
`ences the driver 32 to a single point which is substan-
`tially at the center of the loop 18.
`The loop 18 is substantially symmetrical about the
`reference beam 36 (and the X-axis 16) and, therefore,
`automatically compensates for thermal expansion of the
`conduit 10 due to temperature variations in the fluid or
`the environment. Expansion or contraction of the con-
`duit loop 18 or the bent portions 24, 26 will result in
`equivalent changes in the loop’s dimensions along its
`periphery and its position with respect to the X-axis 16.
`It should be noted that the plane of the loop 18 need
`not be perpendicular to the X-axis 16 (FIGS. 1, 2 and 3).
`The only limitation is that the driver 32 deflects the
`conduit 10 in a direction which is substantially perpen-
`dicular to the flow within the loop 18 and at the same
`time parallel to the X-axis 16.
`Sensing transducers 38 and 40 may be mounted radi-
`ally from the mounting bracket 28 on support arms 39,
`41, respectively. These sensors 38, 40 are, preferably,
`located at the position adjacent to the maximum mea-
`surable deflection of the loop 18 created by the reaction
`of the fluid to the transverse acceleration created by the
`driver 32. Typically this position is a along the circum-
`ference of the loop 18, approximately 90° from the
`driver 32. These sensors or switches may take any
`known form such as linear, optical, etc.
`In an alternate embodiment of this invention a piezo
`transducer type sensor 38’, 40’ may be directly attached
`to the loop 18 (as shown in FIG. 8) or mounted by a clip
`(not shown) rather than be supported on arms 39, 41.
`Although any type sensing mechanism may be utilized
`these piezo self referencing sensors, which are acceler-
`ometers, are preferred. This type of sensing transducer,
`particularly shown in FIGS. 4a and 4b, converts high
`mechanical vibrational energy into an electrical pulse
`where the relative motion of the loop 18 becomes pro-
`portional to the acceleration of the tube 10 at the refer-
`ence position. The piezo transducer is generally used
`together with a low pass filter to eliminate vibrational
`frequency components in the neighborhood of the natu-
`ral resonance frequency. Such filtering may be per-
`formed simultaneously by a microprocessor while cal-
`culating the mass flow calculations.
`The mechanical structure of a typical accelerometer
`is shown in FIGS. 4a and 4b. A ceramic body piece 42
`is formed with its electrical components 42a, 42b, 42c
`being mounted within a thick film or directly onto the ~
`only surface. The ends of the sensor 38 are mounted to
`the conduit wall 10. The body 42 is provided with a
`central, typically, tungsten filled epoxy mass 46. The
`central mass 46 is mounted to a film which is supported
`on the body 42 by washer 48. The alternating deflec-
`tions of the loop 18 due to the reaction forces of the
`fluid move the central mass 46 in alternating directions
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`placing the piezo element crystal in alternating tension
`and compression modes. The output of this arrange-
`ment produces an electrical signal simulating the deflec-
`tion signature of the fluid reaction forces on the conduit
`10.
`
`It is desired that the physical dimensions of the loop
`be such that its natural resonant frequency does not
`correspond to the resonant frequencies of machinery
`found in the surrounding environment or utilized in the
`process line. Typical industrial machinery operates at a
`resident frequency of 50-60 Hz. The combination of
`these environmental vibrations on the operating flow
`meter may create substantial discrepancies in the mea-
`surements of the sensing transducers 38, 40.
`The alternate embodiments of the invention included
`in FIGS. 5 and 6 show, generally, a loop 18 and 118,
`respectively, formed substantially in a single plane (Y-Z
`plane). The imparted oscillation created by the driver(s)
`32 in these figures is parallel to the X-axis 16, perpendic-
`ular to the fluid flow within the loop 18 and 118 and
`substantially perpendicular to the Y-Z plane. Thus the
`deflections of both sides of the loop are basically away
`from the Y-Z plane although this plane is not particu-
`larly referenced by the sensors.
`The embodiment in FIG. 6 includes a second driver
`32’ which is mounted fromthe bracket 28 by a second
`support arm 30’. The two drivers impart 32, 32’ deflec-
`tions of the single plane loop 18’ such that the loop 18’
`is deflected substantially simultaneously away from the
`'5'_}’;Z-axis 22. Again, this axis is not referenced by the sen-
`_:sors 38’, 40’ for a proper calculation of the mass flow.
`iv Both embodiments of the flow meter in FIGS. 5 and
`->6 utilize the substantially free floating loop design hav-
`ing a reduced spring constant. The torsional bending of
`‘the loop 18' is reduced as compared to the alternate
`embodiment 18 (in FIGS. 1-3) since the conduit is in the
`. same plane and not spiraled about the X-axis.
`FIG. 9 shows the integrated reaction forces (Fm and
`5-Fm’) on the loop 18 in response to the transverse im-
`..-parted deflection (VC). This integrated reaction force
`m) is basically the same for all embodiments shown in
`frthe drawings and creates a torque (Tm) substantially
`about the Y-axis 20.
`
`OPERATION
`
`In operation, a fluid stream is supplied to the inlet 12,
`travels around loop 18, and is returned into the stream
`through the outlet 14. The fluid is subject to an alternat-
`ing transverse acceleration caused to the loop 18 by the
`excitation of the driver 32. A maximum deflection oc-
`curs in one direction and then a reverse deflection oc-
`curs to a similar maximum. The transverse acceleration
`imparted to the fluid flowing in the conduit 10 results in
`reaction force which deflects the loop 18, on opposite
`sides of the driver 32, away from its stationary position.
`The sensors 38, 40 (or 38’, 40’) are preferably positioned
`at points of maximum displacement of the loop 18
`caused by this fluid reaction force.
`The deflection of the loop is measured with respect to
`time in order to determine the signature of both sides of
`the loop 18 due to the oscilating accelertion force. The
`transverse acceleration of the flowing mass within the
`loop 18 will cause a differential deflection on opposite
`sides of the driver 32. The deflection of the loop 18
`between the inlet portion 24 and the driver 32 will lag
`or lead the deflection between the driver 32 and the
`outlet portion 26 depending on the oscillation direc-
`tions. This is due to the spatial accelerations and decel-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4,733,569
`
`8
`erations of the mass flow in these respective loop 18
`segments. The signature information provided by the
`sensors 38, 40 with respect to this phase motion of the
`loop 18 is fed into a microprocessor. Noise vibrations
`can be removed simultaneously from these signals as
`can an indication of the validity of the signature cycle.
`The sensor data may then be directly correlated to
`determine the mass flow. Each of these calculations and
`electronic filterings can be performed by any suitable
`technique.
`Suitable sensing means can be of either the analog or
`digital type. Analog sensors are used to measure the
`phase difference of the differential deflection of the two
`sides of the loop 18. Information relating to the phase of
`the two simultaneous outputs cancels the effects of
`structural changes in the physical positioning of a loop
`18 with respect to the sensing system. This type sensing
`system dynamically responds to structure variations in
`the flow meter due to the changes in ambient conditions
`and, also,
`to common dynamic continuous or spike
`vibrational effects.
`
`The electrical circuitry utilized to control the energi-
`zation of the driving transducers and to measure the
`loop 18 deflections, its time phase relationship to the
`driving force, and to receive and process the resulting
`signals may be performed in a microprocessor. The
`driver circuit is a conventional mechanical feedback
`multivibrator which runs at the resonant frequency of
`the mass being driven. Typically, A MOSFET bridge
`excites the coil which drives the magnet. Conventional
`coil/acceleometer feedback can be used but a combina-
`tion of piezo/coil or piezo/crystal can be used to elimi-
`nate some electromagnetic common mode noise.
`Since it has become clear that mechanical noise is
`affecting known flow meters, it is desirable to produce
`a narrow band signal
`to eliminate unwanted noise
`caused by vibrations actually sensed by the sensors.
`This is in addition to differential noise cancellation be-
`tween the sensors and the driver. The narrow band
`filters at the output of the piezo x-tal type preamp
`should be very tightly matched in characteristics and
`physically tied together for temperature tracking, so
`that any phase shift in the filters will be identical and the
`integrity of the desired mechanical phase shift is main-
`tained.
`
`In a circular design common industrial environmental
`vibrations effect the loop 18 equally at all locations
`rather than to one portion to a greater extent than an-
`other. The temperature and vibration error, which un-
`equally effect different portions of the apparatus in
`known Coriolis type flow meters, may cause the offset
`zero reading during calibration and use of these known
`meters. The structure of this invention inherently pro-
`vides the, so called, common mode rejection of these
`environmental vibrations and substantially increases the
`sensitivity and accuracy of the meter. The free floating
`design, therefore, permits the application of the inven-
`tion in otherwise normally unacceptable industrial envi-
`ronments.
`
`invention may be embodied in other
`The present
`specific forms without departing from the spirit or es-
`sential attributes thereof and, accordingly, reference
`should be made to the appended claims, rather than to
`the foregoing specification, as indicating the scope of
`the invention.
`We claim:
`1. An apparatus for measuring the mass flow of a fluid
`stream comprising: a conduit having an inlet end and an
`
`8
`
`

`

`9
`outlet end, each said end fixed with respect to one an-
`other and positioned substantially along a single axis; a
`substantially free-floating continuous flow tube forming
`at least one loop spiraled between said inlet and said
`outlet ends, whereby the continuous flow tube is sub-
`stantially free of restrictions or constraints along its
`spiraled length offset from the single axis, and said loop
`being symmetrical about said single axis between said
`fixed inlet and outlet ends; a driving transducer impart-
`ing an oscillation to said loop in a direction perpendicu-
`lar to the flow within said loop and parallel to the single
`axis; and means for sensing the deflections of said loop
`in response to the reaction of the flow to the oscillation
`of said driving transducer, said sensing means posi-
`tioned in opposite radial directions from said driving
`transducer along the perip