`
`United States Patent
`
`[19]
`
`[11] E
`
`Re. 31,450
`
`Smith
`[45] Relssued Nov. 29, 1983
`
`
`[54] METHOD AND STRUCTURE FOR FLOW
`MEASUREMENT
`
`[75]
`Inventor:
`James E. Smith, Boulder, Colo.
`[73] Assignee, Micro Motion,1..c.,soumer, Colo.
`[21] Appl. No.: 348,071
`
`[22] Filed:
`
`Feb. 11, 1982
`
`Related US. Patent Documents
`
`Reissue of:
`[64]
`Patent No.2
`Issued:
`AP” ”0*
`'
`.
`F‘led'
`,U.S, Applications:
`[63]
`Continuation-impart of Ser. No. 818,475, Jul. 25, 1977,
`abandoned.
`
`4,187,721
`Feb. 12, 1980
`”“68
`Ju1.20, 1978
`
`Int. Cl.3 ................................................ G01F 1/86
`[51]
`[52] U.S. Cl. .................................... 73/861.38; 73/434
`[58] Field of Search .......... 73/32 A, 434, 505, 861.18,
`73/861.35, 861.37, 861.38
`
`[56]
`
`References Cited
`
`7/1962 .Knauth .................................. 73/434
`3,044,302
`8/1962 Alspach et al.
`.
`3,049,917
`8/1962 Roth ...................................... 73/228
`3,049,919
`3,080,750 3/ 1963 Wiley et al.
`.
`3:832:32 371323 $222,':1::::::::::::::::::::::::::::::::x7325:
`3,108,475 10/1963 Henderson .
`3,132,512
`5/1964 Roth .
`3,138,955
`6/1964 Uttley .
`.
`3,164,017
`1/1965 Karlby et a1.
`3,167,691
`1/1965 Halista ................................. 317/157
`3,218,851 11/1965 Sipin ‘
`3,232,110
`2/1966 Li
`.
`3,251,226
`5/1966 Cushing ....................... 73/861.63 x
`3,261,205
`7/1966 Sipin ‘
`3232223 1311322 1"“?
`.
`,
`0w ey .
`3,298,221
`1/1967 Miller et al.
`............................ 73/32
`
`3,303,705
`2/1967 Dostal .......
`73/505
`
`-------- 73/32
`3,320,791
`5/1967 Banks
`3,329,019 7/ 1967 Sipin .
`3,339,400 9/1967 Banks ...................................... 73/32
`3,344,666 10/1967 Rilett
`.
`3,349,604 10/1967 Banks ...................................... 73/32
`313501936 11/1967 Li
`-
`3.355.944 12/1967 Sipin -
`3,385,104
`5/1968 Banks .
`3,396,579
`8/1968 Sourian .
`3,449,940
`6/1969 Banks ...................................... 73/32
`
`. 73/32
`3,449,941 6/ 1969 Banks ..........................
`3,456,491 7/ 1969 Brockhaus .............................. 73/32
`3,481,509 12/1969 Marhauer .
`3,485,098 12/1969 SiPin ‘
`3,533,285 10/1970 Dee .
`3,555,900
`1/1971 Bauer et al.
`3,575,052
`4/1971 Lenker .
`3,584,508
`6/1971 Shiba .
`3,589,178
`6/1971 Germann .
`3,608,374 9/1971 Miller .
`3,613,451 10/1971 Scott
`.
`3,625,055 12/1971 LaFourcade .
`3,677,086
`7/1977 Corey .
`-
`3.688.574 9/1972 Arutunian et a1.
`3,728,893 4/1973 Janssen .................................... 73/32
`3,740,586
`6/1973 Banks et al.
`.
`3,762,217 10/1973 Hagen .
`3,839,915 10/1974 Schlitt
`.
`3,842,681 10/1974 Mumme.
`.
`3,876,927 4/1975 Gee et al.
`3,897,766
`8/1975 Pratt, Jr. et a1.
`3.927565 12/1975 Pavlin Cl 31-
`-
`
`.
`
`.
`
`U’S' PATENT DOCUMENTS
`2,624,198
`1/ 1953 Pearson .
`2,635,462 4/1953 Poole et al.
`............................. 73/32
`2,753,173
`7/1956 Barnaby et a1.
`...........
`.. 264/1
`
`.. 73/32
`2,754,676
`7/1956 Poole et al.
`..
`9/1957 Brown ................................... 73/228
`2,804,771
`2,811,854 11/1957 Powers .
`2,813,423 11/1957 Altfillisch et al.
`2,821,084
`1/1958 Altfillisch et al.
`2,831,349 4/1958 Altfillisch et al.
`2,834,209
`5/1958 Jones et al.
`.
`2,865,201 12/1958 Roth .
`2,877,649
`3/1959 Powers .
`2,889,702
`6/1959 Brooking ................................ 73/32
`2,897,672
`8/1959 Glasbrenner et a1.
`73/228
`2,914,945 12/1959 Cleveland .
`2,923,154
`2/1960 Powers et al.
`2,934,951
`5/1960 Li
`.
`2,943,476
`7/1960 Bernstein ................................ 73/32
`2,943,487
`7/1960 Potter .
`2,956,431 10/1960 Westerheim
`3,039,310
`6/1962 Copland et al.
`
`.
`.
`.
`
`.
`
`73/32
`...................... 73/434
`
`1
`
`Mlcro Motlon 1005
`
`1
`
`Micro Motion 1005
`
`

`

`Re. 31,450
`
`Page 2
`
`
`
`73/32 A
`
`[57]
`
`ABSTRACI‘
`
`5/1976 Catherall
`3,955,401
`.
`4,051,723 10/1977 Head et al.
`4,056,976 11/1977 Hildebrand .
`4,109,524
`8/1978 Smith .
`4,127,028 11/1978 Cox et a1.
`
`......................... 73/861.38
`
`FOREIGN PATENT DOCUMENTS
`
`2249269 4/1974 Fed. Rep. of Germany .
`2145387
`2/1975 France .
`32-6595
`8/1957 Japan .
`44—18531
`8/1969 Japan .
`46—19827
`6/1971
`Japan .
`117091
`5/1958 U,S.S.R.
`146982
`4/1961 U.S.S.R.
`149900 11/1961 U.S.S.R.
`159673 12/1963 U.S.S.R.
`171651
`5/1965 U.S.S.R.
`400838 10/1973 U.S.S.R.
`426170 4/1974 U.S.S.R.
`486247
`9/1975 U.S.S.R.
`
`.
`.
`.
`.
`.
`.
`.
`.
`
`OTHER PUBLICATIONS
`
`A. Treatise; Continuous Measurement of Unsteady Flow,
`by G. P. Katys, translated from the Russian by D. P.
`Barrett, MacMillan Company, New York, 1964.
`
`Primary Examiner—Jerry W. Myracle
`Attorney, Agent, or Firm—Irons & Sears
`
`Apparatus and method for mass flow measurement
`utilizing a substantially “U” shaped conduit mounted in
`a cantilever manner at the legs thereof, [means for
`oscillating the conduit, and means for measuring] so
`that, when the conduit is oscillated, sensors mounted on the
`conduit can measure the Coriolis force by measurement
`of the force moment or the angular motion of the con-
`duit around an axis substantially symmetrical to the legs
`of the conduit. The force moment is measured by sens-
`ing incipient movement around the axis, and generating
`and measuring a nulling force. In preferred embodi-
`ments, the oscillating means are mounted on a spring
`am having a natural frequency substantially equal to
`that of the “U” shaped conduit, and in a particularly
`preferred [displacement] embodiment the measuring
`[means are sensors] sensors are mounted on the “U”
`shaped conduit and adapted to measure, with proper
`direction sense, the time differential between the lead-
`ing and trailing portions of the “U” shaped conduit
`passing through the plane of the “U” shaped conduit at
`substantially midpoint of the oscillation thereof.
`
`55 Claims, 14 Drawing Figures
`
`2
`
`

`

`US. Patent
`
`Nov. 29, 1983
`
`Sheet I 0f4
`
`Re. 31,450
`
`
`
`3
`
`

`

`
`
`US. Patent
`
`Nov. 29, 1983
`
`Sheet 2 of4
`
`Re. 31,450
`
`
`
` PEAK
`DETECTOR
`8 HLTER
`
`
`h--—-—-———_———_-—-____—--————————-
`
`
`
`CRYSTAL
`I
`osc.
`
`DISPLAY
`9‘5
`COUNTER
`so
`. LATCH —————— RELATIVE
`93
`DRIVER
`DENSITY
`____________________FIE—6"""mh""u"—
`
`I
`
`l I
`
`.
`,
`i
`',
`.
`l
`I
`I
`
`__.._-_______...__._____.___.‘__._.____..._ -_-_
`
`69
`
`70
`UP-DOWN
`LATCH
`DISPLAY
`DECODER
`MASS
`COUNTER 'I‘IVER FLOW RATE
`77
`88
`so
`78
`0 H"
`
`“Tc"
`DIGITAL
`INTEGRATDR"°§.%?,%ER _’
`32
`as
`
`DISPLAY
`731%;
`87
`
`94
`
`SENSOR 44
`
`UPCOUNT
`
`SE N50? 44
`Dovmcoum
`UPCOUNT
`
`'
`
`'
`
`'
`
`‘
`
`'
`
`IIIl I IlIl
`
`I ;
`
`4
`
`

`

`U.S. Patent
`
`Nov. 29, 1983
`
`Sheet 3 of4
`
`Re. 31,450
`
`
`
`FLOW RATE
`
`SYNCHRONOUS
`DEMODULATOR
`
`D.C. OUTPUT
`PROPORTIONAL TO MASS
`
`5
`
`

`

`US. Patent
`
`Nov. 29, 1983
`
`Sheet 4 of4
`
`Re. 31,450
`
`I88
`
`6
`
`

`

`1
`
`METHOD AND STRUCTURE FOR FLOW
`MEASUREMENT
`
`Re. 31,450
`
`Matter enclosed in heavy brackets [ ] appears in the
`original patent but forms no part of this reissue specifica-
`tion; matter printed in italics indicates the additions made
`by reissue.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present
`invention relates generally to a flow
`measuring device, and more particularly to a flow mea-
`suring device in the form of a “U" shaped conduit
`mounted in beamlike, cantilevered,
`fashion and ar-
`ranged to determine the density of a fluid material in the
`conduit, the mass flow rate therethrough, and accord-
`ingly other dependent flow parameters.
`2. Description of the Prior Art
`type with
`Heretofore, flow meters of the general
`which the present invention is concerned have been
`known as gyroscopic mass flow meters, or Coriolis
`force mass flow meters. In essence, the function of both
`types of flow meters is based upon the same [princi-
`pal] principle.
`Viewed in a simplified manner, Coriolis forces in-
`volve the radial movement of mass from a first point on
`a rotating body to a second point. As a result of such
`movement, the peripheral velocity of the mass changes,
`i.e., the mass is accelerated. The acceleration of the
`mass generates a force in the plane of rotation and per-
`pendicular to the instantaneous radial movement. Such
`forces are responsible for precession in gyroscopes.
`Several approaches have been taken in utilizing Cori-
`olis forces to measure mass flow. For instance, the early
`Roth U.S. Letters Pat. Nos. 2,865,201 and [3,312,512]
`3,132,512 disclose gyroscopic flow meters employing a
`full loop which is continuously rotated (DC type) or
`oscillated (AC type).
`Another flow meter utilizing substantially the same
`forces but avoiding reversal of flow by utilizing a less
`than 180° “loop” is described in Sipin U.S. Letters Pat.
`No. 3,485,098. In both instances, the devices are of the
`so called AC type, i.e., the conduit is oscillated around
`an axis and fluid flowing through the conduit flows first
`away from the center of rotation and then towards the
`center of rotation thus generating Coriolis forces as a
`function of the fluid mass flow rate through the loop.
`Since there is but one means of generating Coriolis
`forces, all of the prior art devices of the gyroscopic and
`Coriolis force configurations generate the same force,
`but specify various means for measuring such forces.
`Thus, though the concept is simple and straightforward,
`practical results in the way of accurate flow measure-
`ment have proven elusive.
`For instance, the Roth flow meters utilize transducers
`or gyroscopic coupling as readout means. The gyro-
`scopic coupling is described in Roth as being complex,
`and transducers are defined as requiring highly flexible
`conduits, such as bellows. The latter mentioned Roth
`patent is primarily concerned with the arrangement of
`such flexible bellows.
`Another classical approach for measuring the force
`proportional to mass flow involve first driving or oscil-
`lating a conduit structure through a rotational move-
`ment around an axis, and then measuring the additional
`energy required to drive such conduit as fluid [is
`flowed] flows through the conduit. Unfortunately, the
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4O
`
`45
`
`50
`
`55
`
`6O
`
`65
`
`2
`Coriolis forces are quite small compared to the driving
`forces and, accordingly, it is quite difficult to accurately
`measure such small forces in the context of the large
`driving force.
`Still another measurement means is described by
`Sipin at column 7,
`lines [1 through 23] I] through
`Column 8, line 16 of US. Letters Pat. No. 3,485,098. In
`this arrangement velocity sensors independent of the
`driving means are mounted to measure the velocity of
`the conduit as a result of the distortion of the conduit
`
`caused by Coriolis forces. While there may be worth-
`while information obtained by such measurements, ve-
`locity sensors require measurement of a minute differen-
`tial velocity superimposed upon the very large pipe
`oscillation velocities. Thus an entirely accurate [deter-
`minate] determination of the gyroscopic force must
`deal with velocity measurements under limited and
`specialized conditions as discussed below. Mathemati-
`cal analysis confirms that velocity measurements pro-
`vide at best marginal results.
`If the Coriolis force is not to produce movements of
`great amplitude, clearly, as a basic precept of physics, a
`reactive force, or forces, must oppose the Coriolis
`force. Put simply, the Coriolis force, particularly in the
`flow meter arrangements permitting distortion of the
`conduit (a qualification which will be explained below),
`is opposed by, stated simply, the spring resistance of the
`conduit itself as it distorts, plus velocity forces resulting
`from movement of the conduit, i.e., air drag, etc. —usu-
`ally a small component ——and an inertial component
`resulting from the acceleration of the mass of the con-
`duit. It is a complex endeavor to concurrently measure
`and sum all three of these opposing forces. Accord-
`ingly, it is understandable that Sipin measures but one of
`the forces,
`i.e., velocity[, forces]. Given the rather
`involved and marginally accurate conventional mass
`flow measuring devices utilizing, for instance, indepen-
`dent densities and flow [velocities] velocity sensors, it
`is understandable that measurement of a single opposing
`force such as velocity by Sipin would produce useful
`though compromised information. If only velocity re-
`lated reactive forces are to be measured, the other nor-
`mally more substantially reactive forces should be mini—
`mized. This is not the case in the apparatus illustrated by
`Sipin. No discussion of this critical consideration is to
`be found.
`Another approach to the problem of measuring the
`small Coriolis forces is described in my US. Letters
`Patent Application Ser. No. 591,907, for “METHOD
`AND APPARATUS FOR MASS FLOW MEA-
`SUREMENT”, filed June 30, 1975 now US Pat. No.
`[4,109,529] 4,109,524.
`In an embodiment of my prior approach, rather than
`attempting to measure the opposing forces to the Corio-
`lis forces, all of which are dependent upon displacement
`of the conduit, I describe an arrangement in which a
`mechanical nulling force, i.e., an opposing force which
`precludes displacement, is produced. Accordingly, any
`infinitesimal incremental displacement of the conduit is
`sensed and opposing force generated. By measuring the
`opposing force, which replaces the inherent opposing
`forces described above, an accurate measurement of the
`mass flow may be made, though at the complication of
`avoiding spurious measurements of forces resulting
`from driving the conduit. My application described two
`independent means for avoiding such complicating
`forces, i.e., balancing the forces on opposite sides of a
`
`7
`
`

`

`Re. 31,450
`
`3
`beam to cancel the forces and measuring the Coriolis
`force at maximum angular velocity when driving accel-
`eration forces and bellows spring forces are zero. The
`balancing approach in conjunction with nulling re-
`quired relatively slow operation to accomodate the
`response time of the mechanical beam.
`In summary, numerous attempts have heretofore
`been made to measure mass flow as a function of the
`Coriolis forces generated by mass flow through an os-
`cillating conduit. However, accurate measurements
`have been possible only when the conduit displacement
`is nulled while balancing [theacceleration] the accel—
`eration forces due to driving the conduit. and only ap-
`proximate measurements made when the conduit
`is
`allowed to distort against inherent restoration forces
`such as spring resistance in the conduit, velocity drag
`factors and inertia while making such measurements.
`SUMMARY OF THE INVENTION
`
`The present invention, which provides a heretofore
`unavailable improvement over previous mass flow mea-
`suring devices, comprises a substantially continuous
`“U“ shaped tube mounted in beam-like fashion,
`i.e.,
`without flexible or separate pivoting sections, means for
`oscillating the conduit and means for measuring the
`resulting Coriolis force by measuring the force moment
`due to the Coriolis forces, or the angular distortion of
`the conduit as a result of such Coriolis forces. Prefera-
`bly, the [oscillatiogn] oscillation means are mounted
`on a separate arm having a natural frequency substan-
`tially that of the “U" shaped tube. Accordingly, the two
`members oscillate in opposite phase similar to the man-
`ner in which the tines of a tuning fork oscillate and like
`a tuning fork, cancel vibrations at the support. In a
`particularly preferred embodiment, the distortion of the
`"U” shaped conduit is measured by sensors positioned
`adjacent the intersections of the base and legs of the
`conduit which measure the time lag between the lead-
`ing and trailing edges of the conduit passing through the
`nominal central point of oscillation as a result of distor-
`tion by the Coriolis forces. This arrangement avoids the
`need to control the frequency and/or amplitude of os—
`cillation.
`The cantilevered beam-like mounting of the “U”
`shaped conduit is of more than passing significance. In
`the instance in which distortion is measured, such
`mounting provides for the distortion resulting from the
`Coriolis forces to be offset substantially entirely by
`resilient deformation forces within the conduit free of
`mechanical pivot means other than flexing of the con-
`duit. By minimizing [draft] drag and inertial inputs,
`measurement of but one of the three opposing forces
`generates highly accurate determinations. Thus rather
`than compromising the accuracy of the flow meters by
`measuring but one of the opposing forces, the method
`and apparatus of the present invention is specifically
`structured to minimize or obviate the forces generated
`by the two non-measured opposing forces, i.e., velocity
`drag and acceleration of mass. This effort has been
`successful to the point where such forces are present in
`cumulative quantities of less than 0.2% of the torsional
`spring force. Also, by mounting the conduit in a beam—
`like fashion, which pivots by beam bending, the need
`for bellows and other such devices which are reactive
`to the differences in pressure between the conduit and
`ambient pressure are entirely avoided. Pivoting is ac—
`complished free of pressure sensitive, separate pivot
`means.
`
`4
`Accordingly, it is an object of the present invention
`to provide a new and improved apparatus and method
`for measuring mass flow which provides highly accu-
`rate measurement with simple, low cost construction.
`Another object of the present invention is to provide
`a new and improved apparatus for measuring mass flow
`which is substantially insensitive to pressure difference
`between ambient pressure and the fluid being measured.
`Yet another object of the present invention is to pro-
`vide a new and improved apparatus and method for
`measuring mass flow which measures substantially all of
`the displacement forces generated by Coriolis forces.
`Still another object of the present
`invention is to
`provide a new and improved apparatus and method for
`measuring fluid mass flow which is capable of accurate
`measurement of the mass flow of gases.
`Yet still another object of the present invention is to
`provide a new and improved apparatus and method for
`measuring mass flow which is capable of accurately
`determining the mass flow of fluidized mixtures of
`solids and gases.
`Still yet another object of the present invention is to
`provide a new and improved apparatus and method for
`measuring fluid flow substantially independent of pres-
`sure, temperature and viscosity variations.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the drawings:
`FIG. 1 is a perspective view of a fluid flow meter
`according to one embodiment of the present invention;
`FIG. 2 is an end view of the flow meter of FIG. 1
`illustrating oscillation at midpoint under no flow condi-
`tions;
`FIG. 3 is an end view of the flow meter of FIG. 1
`illustrating oscillation at midpoint in the up direction
`under flow conditions;
`FIG. 4 is an end view of the flow meter of FIG. 1
`illustrating oscillation at midpoint in the down direction
`under flow conditions;
`FIG. 5 is a block diagram drawing of the drive circuit
`of the flow meter of FIG. 1;
`FIG. 6 is a logic diagram of the readout circuit of the
`flow meter of FIG. 1;
`FIG. 7 is a timing diagram of the readout signals of
`the flow meter of FIG. 1 under no flow conditions;
`FIG. 8 is a timing diagram of the readout signal of the
`flow meter of FIG. 1 with flow through the conduit;
`FIG. 9 is a simplified perspective view of a fluid flow
`meter according to another embodiment of the present
`invention.
`FIG. 10 is a circuit diagram of the drive and readout
`portion of the flow meter of FIG. 9, with the exception
`of the distortion sensing portion of the circuit;
`FIG. 11 is a circuit diagram of one distortion sensing
`arrangement suitable to generate the signal labeled B in
`FIG. 10;
`FIG. 12 is another circuit diagram for a purpose
`identical to that of FIG. 11;
`FIG. 13 is yet another circuit diagram for a purpose
`identical to that of FIG. 11; and
`FIG. 14 is a typical circuit diagram of the synchro—
`nous demodulator of FIGS. 10, 12 and 13.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Turning now to the drawings, wherein like compo-
`nents are designated by like
`reference numerals
`throughout the various figures. a flow meter device
`
`10
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`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`8
`
`

`

`Re. 31,450
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4O
`
`5
`according to a first embodiment of the present invention
`is illustrated in FIG. 1 and generally designated by
`reference numeral 10. Flow meter 10 includes fixed
`support 12 having “U" shaped conduit 14 mounted
`thereto in a cantilever, beam-like fashion. “U” shaped
`conduit 14 is preferably of a tubular material having
`resiliency such as is normally found in such materials
`such as beryllium, copper, tempered aluminum, steel,
`plastics, etc. Though described as “U shaped", conduit
`14 may have legs which converge, diverge, or are
`skewed substantially. A continuous curve is contem-
`plated. Preferably, “U” shaped conduit 14 includes inlet
`15 and outlet 16 which in turn are connected by inlet leg
`18, base leg 19 and outlet leg 20. Most preferably, inlet
`leg 18 and outlet leg 20 are parallel, and base leg 19 is
`perpendicular to both; but, as mentioned above, sub-
`stantial deviations from the ideal configuration, i.e., 5°
`convergence or divergence do not appreciably compro-
`mise results. Operable results may be obtained with
`even gross deviations on the order of 30° or 40°, but,
`since little is gained from such deviations in the embodi-
`ment of concern, it
`is generally preferred to maintain
`inlet leg 18 and outlet leg 20 in a substantially parallel
`relationship. Conduit 14 may be in the form ofa contin-
`uous or partial curve as is convenient.
`Though the physical configuration of “U” shaped
`conduit 14 is not critical, the frequency characteristics
`are important. It is critical in the embodiment of FIG. 1
`which permits distortion that the [resonent] resonant
`frequency around axis W—W be different
`than that
`around axis 0—0, and most preferably that the reso-
`nant frequency [abut] about axis W—W be the lower
`resonant frequency.
`Spring arm 22 is mounted to inlet and outlet legs 18
`and 20, and carries force coil 24 and sensor coil 23 at the
`end thereof adjacent base leg 19. Magnet 25, which fits
`within force coil 24 and sensor coil 23, is carried by base
`leg 19, Drive circuit 27, which will be discussed in more
`detail below, is provided to generate an amplified force
`in response to sensor coil 23 to drive “U" shaped con-
`duit 14 at its natural frequency around axis W—W in an
`oscillating manner. Though “U” shaped conduit 14 is
`mounted in a beamlike fashion to [supports] support
`12, the fact that it is oscillated at resonant frequency
`permits appreciable amplitude to be attained in the
`“beam" oscillation mode around axis W—W. “U"
`shaped conduit 14 essentially pivots around axis WWW
`at inlet 15 and outlet 16.
`As a preferable embodiment, first sensor [32] 43 and
`second sensor 44 are supported at the intersections of 50
`base leg 19 and inlet leg 18 and outlet leg 20, respec-
`tively. Sensors 43 and 44 which are preferably optical
`sensors, but generally proximity or center crossing sen-
`sors, are activated as “U” shaped conduit 14 passes
`through a nominal reference plane at approximately the
`mid-point of the "beam” oscillation. Readout circuit 33,
`as will be described below, is provided to indicate mass
`flow measurements as a function of the time differential
`of the signals generated by sensors 44 and 43.
`Operation of flow meter 10 will be more readily un-
`derstood with reference to FIGS. 2, 3 and 4, which, in
`a simplified manner,
`illustrate the basic [principal]
`principle of the instant invention. When conduit 14 is
`oscillated in a no flow condition, inlet leg 18 and outlet
`leg 20 bend at axis W——W essentially in a pure beam
`mode, i.e., without torsion. Accordingly, as shown in
`FIG. 2, base leg 19 maintains a constant angular position
`around axis 0—0 throughout the oscillation. However,
`
`45
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`55
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`6S
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`6
`when flow is initiated, fluid moving radially from axis
`W—W through inlet leg 18 generates a first Coriolis
`force perpendicular to the direction of flow and perpen-
`dicular to axis W—W while flow in the outlet leg 20
`generates a second Coriolis force again perpendicular to
`the radial direction of flow, but in an opposite direction
`to that of the first Coriolis force since flow is in the
`opposite direction. Accordingly, as shown in FIG. 3, as
`base leg 19 passes through the mid-point of the oscilla-
`tion. the Coriolis forces generated in inlet leg 18 and
`outleg leg 20 impose a force couple on “U“ shaped
`conduit 14 thereby rotating base leg 19 angularly
`around axis 0—0. The distortion is both a beam bend-
`ing distortion and a torsional distortion essentially in
`inlet leg 18 and outlet leg 20. As a result of the choice of
`frequencies and the configuration of “U” shaped con-
`duit I4, essentially all of the resistive force to the Corio-
`lis force couple is in the nature of a resilient spring
`distortion, thereby obviating the need to and complica-
`tion of measuring velocity drag restorative forces and
`inertial opposing forces. Given a [sustantially] sub-
`stantially constant frequency and amplitude, measure-
`ment of the angular distortion of base leg 19 around axis
`0—0 at the nominal midpoint of the oscillation, pro-
`vides an accurate indication of mass flow. This provides
`a substantial improvement over the prior art. However,
`as a most significant aspect of the present invention,
`determination of the distortion of base leg 19 relative to
`the nominal undistorted mid-point plane around axis
`O——0 in terms of the time difference between the in-
`stant the leading leg, i.e., the inlet leg in the case of FIG.
`3, passes through the midpoint plane and the trailing
`leg, i.e., the outlet leg in the case of FIG. 3, passes such
`plane, avoids the necessity of maintaining constant fre—
`quency and amplitude since variations in amplitude are
`accompanied by compensating variations in the veloc-
`ity of base leg 19. Accordingly, by merely driving “U"
`shaped conduit 14 at its resonant frequency. time mea-
`surements may be made in a manner which will be
`discussed in further detail below, without concern for
`[conccurrent] concurrent regulation [or] offrequency
`and amplitude. However, if measurements are made in
`but one direction,
`i.e.,
`the up direction in FIG. 3,
`it
`would be necessary to maintain an accurate alignment
`of base leg 19 relative to the nominal midpoint plane.
`Even this requirement may be avoided by, in essence.
`subtracting the time measurements in the up direction
`shown in FIG. 3, and in the down direction shown in
`FIG. 4. As is readily recognized by one skilled in the
`art, movement
`in the down direction, as in FIG. 4,
`reverses the direction of the Coriolis force couple and
`accordingly, as shown in FIG. 4, reverses the direction
`of distortion as a result of the Coriolis force couple.
`Summarily, stated broadly, “U" shaped conduit 14,
`having specified frequency characteristics though only
`general physical configuration characteristics, is merely
`oscillated around axis W—W. Flow through “U”
`shaped conduit 14 induces spring distortion in “U“
`shaped conduit 14 resulting, as a convenient means of
`measurement,
`in angular movement of base leg 19
`around axis 0—0 initially in a first angular direction
`during one phase of the oscillation, and,
`then in the
`opposite direction during the other phase of oscillation.
`Though, by controlling amplitude, flow measurements
`may be made by direct measurement of distortion, i.e.,
`strobe lighting the base leg 19 at the midpoint ofoscilla—
`tion with, for instance, an analogue scale fixed adjacent
`to end portions and a pointer carried by base leg 19. a
`
`9
`
`

`

`Re. 31,450
`
`7
`preferred mode of measurement involves determining
`the time difference between the [instance] instants in
`which the leading and trailing edges of the base leg 19
`move through the midpoint plane. This avoids the need
`to control amplitude. Further, by measuring the up
`oscillation distortions and the down oscillation distor-
`tions in the time measurement mode, anomalies result—
`ing from physical misalignment of “U" shaped conduit
`14 relative to the midpoint plane are cancelled from the
`measurement results.
`The essentially conventional —given the above dis-
`cussion of the purposes of the invention —electronic
`aspects of the invention will be more readily understood
`with reference to FIGS. 5 through 8.
`As shown in FIG. 5, drive circuit 27 is a simple means
`for detecting the signal generated by movement of mag-
`net 25 in sensor coil 23. Detector 39 compares the volt—
`age provided by sensor coil 23 with reference voltage
`37. As a result, the gain of force coil amplifier 41 is a
`function of the velocity of magnet 25 within sensor coil
`23. Thus, the amplitude of the oscillation of “U” shaped
`conduit 14 is readily controlled. Since “U” shaped con-
`duit 14 and spring arm 22 are permitted to oscillate at
`their resonant frequencies, frequency control
`is not
`required.
`The circuitry of FIG. 5 provides additional informa-
`tion. The output of force coil amplifier 41 is a sinusoidal
`signal at the resonant frequency of “U” shaped conduit
`14. Since the resonant frequency is determined by the
`spring constant and mass of the oscillating system, and
`given the fact that the spring constant is fixed and the
`mass changes only as the density of the fluid flowing
`through the conduit (the conduit mass clearly does not
`change), it will be appreciated that any change in fre-
`quency is a function of the change in density of the fluid
`flowing through the conduit. Thus, since the time per—
`iod of the oscillation can be determined, it is a simple
`matter to count 3 fixed frequency oscillator during the
`time period to determine a density factor. Once gener—
`ated, the density factor can be converted to fluid density
`by, for instance, a chart or graph in that the time period
`is not a linear function of density, but only a determin-
`able function thereof. Should a direct readout be de-
`sired, a microprocessor can be readily programmed to
`convert the density factor directly to fluid density.
`The nature and function of readout circuit 33 will be
`more readily understood with reference to the logic
`circuit illustrated in FIG. 6, and the related timing dia-
`grams of FIGS. 7 and 8. Readout circuit 33 is connected
`to inlet side sensor 43 and outlet side sensor 44 which
`develop signals as flags 45 and 46 carried on base leg 19
`pass by the respective sensor at approximately the mid-
`point of plane A—A the oscillation of “U" shaped con-
`duit 14. As shown, inlet sensor 43 is connected through
`inverter amplifier 47 and inverter 48 while outlet side
`sensor 44 is similarly connected through inverter ampli-
`fier 49 and inverter 50. Line 52, the output from inverter
`50, provides, as a result of the double inversion, a posi-
`tive signal to the set side of flip-flop 54. Similarly, line
`56 provides an output from inverter 48, again a positive
`signal, the reset side of flip-flop 54. Accordingly, flip—
`flop 54 will be set upon output of a positive signal from
`sensor 44, and reset on the subsequent output of a posi—
`tive signal from sensor 43.
`In a similar manner, line 58 provides the inverted
`signal from sensor 43 through inverter amplifier 47 to
`the set side of flip-flop 60, while line 62 provides the
`output of inverter amplifier 49 to the reset side of flip-
`
`IO
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`15
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`20
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`25
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`30
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`35
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`45
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`50
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`55
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`65
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`8
`flop 60. Thus, flip—flop 60 would be set upon the output
`of a negative signal from sensor 43, and reset upon the
`subsequent output of a negative signal from sensor 44.
`The output of flip-flop 54 is connected through line 63
`to a logic gate such as AND gate 64. AND gates 64 and
`66 are both connected to the output of oscillator 67 and,
`accordingly, upon output from flip~flop 54, the signal
`from oscillator 67 is gated through AND gate 64, to line
`68 and thus to the downcount side of up-down counter
`70. Similarly, upon the output of a signal from flip-flop
`60, the output of oscillator 67 is gated through AND
`gate 66 to line 69 connected to the upcount side of
`updown counter 70.
`readout circuit 33 provides a
`Thus,
`in function,
`downcount signal at the frequency of oscillator 67 to
`updown counter 70 for the period during which sensor
`44 is activated prior to activation of sensor 43 during the
`down motion of “U" shaped conduit 14, while an up-
`count signal is provided to up-down counter 70 for the
`period during which sensor 43 is activated prior to
`activation of sensor 44 during the up motion of “U”
`shaped conduit 14.
`The significance of readout circuit 33 will be more
`readily appreciated with reference to the timing dia-
`gram of FIG. 7 and FIG. 8. In FIG. 7, wave forms are
`illustrated for the condition in which “U" shaped con-
`duit 14 is oscillated in a no-flow condition, but in which
`flags 44 and 46 are not precisely statically aligned with
`plane A—A. Thus, as shown in the timing diagram,
`sensor 44 initially switches positive early relative to the
`ideal time represented by the vertical lines on the up-
`stroke, and switches negative late on the down stroke as
`a result of the misalignment of flag 46. On the other
`hand, sensor 43 switches positive late on the upstroke
`and switches negative early on the downstroke. How-
`ever, when the ou