CA1210611B

CA1210611B - Method and structure for flow measurement

Info

Publication number: CA1210611B
Application number: CA000488475A
Authority: CA
Inventors: James E. Smith
Original assignee: Micro Motion Inc
Current assignee: Micro Motion Inc
Priority date: 1977-07-25
Filing date: 1985-08-09
Publication date: 1986-09-02
Also published as: GB2001759B; CH641277A5; GB2001759A; IL55212A; NL7807846A; DE2833037C2; ES471982A1; HK59684A; SG29384G; ZA784189B; SE7808094L; IT7850465A0; SE447161B; MX145013A; BE869206A; FR2399007A1; DE2833037A1; JPS5452570A; IL55212A0; CA1106636A

Abstract

ABSTRACT

Apparatus and method for mass flow measurement utilizing a substantially "U" shaped conduit mounted in a cantilevered manner at the legs thereof, 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 conduit around an axis substantially symmetrical to the legs of the conduit. The force moment is measured by sensing incipient movement around the axis, and generating and measuring a nulling force. In preferred embodiments, the oscillating means are mounted on a spring arm having a natural frequency substantially equal to that of the "U"
shaped conduit, and in a particularly preferred embodiment the measuring sensors are mounted on the "U"
shaped conduit and adapted to measure, with proper direction sense, the time differential between the leading and trailing portions of the "U" shaped conduit passing through the plane of the "U" shaped conduit at substantially the midpoint of the oscillation thereof.

Description

- 12~
. .-~ 1 .
The present invention relates generally to a flow measuring device and more particularly to a flow measuring device in the form of a "U" shaped conduit mounted in beam-like, cantilevered, fashion and arranged to determine the density of a fluid material in the conduit, the mass flow rate therethrough, and accordingly other dependent flow parameters.
Heretofore, 1OW meters of the general type with 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 principle. Viewed in a simplified manner, Coriolis forces involve 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 perpendicular to the instantaneous radial movement. Such forces are responsible for precession in gyroscopes. The prior attempts to measure mass flow in this manner involved pressure sensitive bellows or other such mechanical pivoting means.
Several specific approaches have been taken in utilizing Coriolis forces to measure mass flow. For instance, the early Roth U.S. Letters Patent 2,865,201 and 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 Patent 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.

~2~
-~ 2 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 straight forward, practical results in the way of accurate flow measurement have proven elusive.
For instance, the Roth flow meters utilize transducers or gyroscopic coupling as readout means. The gyroscopic 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 involves first driving or oscillating a conduit structure through a rotational movement around an axis, and then measuring the additional energy required to drive such conduit as fluid flows through the conduit. Unfortunately, the 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 line 11 through column 8, line 16, of U.S. Letters Patent 3,485,09~. 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 worthwhile information obtained by such measurements, velocity sensors require measurement of a minute differential velocity superimposed upon the very large pipe oscillation velocities. Thus an entirely accurate determination of the gyroscopic force must deal with velocity measurements under limited and specialized conditions as discussed below. Mathematical analysis .
-~l21~

confirms that velocity measurements provide at bestmarginal results.
The present invention, which provides a heretofore unavailable improvement o~er previous mass flow measuring devices, comprises a support, a "U" shaped, continuous conduit solidly mounted at the open end of the "U" to the support and extending therefrom in a nonarticulated, cantilevered fashion, means for oscillating the conduit relative to the support on either side of the static plane of the "U" shaped conduit and about a first oscillation axis, and means to measure the Coriolis forces tending to elastically distort the "U" shaped conduit around a second deflection axis positioned substantially equidistant between the side legs of the "U" shaped conduit and through the oscillation axis thereof.
Preferably, the oscillator is mounted on a separate arm having a natural frequency substantially that of the "U" shaped tube. Accordingly, the two members oscillate in opposite phase similar to the man~er 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 leading and trailing edges of the conduit to pass through the nominal central point of oscillation as a result of distortion by the Coriolis forces. This arrangement avoids the need to control the frequency and/or amplitude of oscillation.
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 conduit.
Thus rather than compromising the accuracy of the flow meters by measuring but one of the opposing forces, the ~21~6~

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 .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 accomplished free of pressure sensitive, separate pivot means.
Accordingly, an advantage of the present invention lS is to provide a new and improved apparatus and method for measuring mass flow which provides highly accurate measurement with simple, low cost construction.
Another advantage of the present invention is to provide a new and improved apparatus for measuring mass flow which is substantially insensitive to pressure differences between ambient pressure and the fluid being measured.
Accordingly, this invention provides a flow meter for flowable materials comprising:
(1) a support;
~2) a curved, continuous conduit which (i) is free of pressure sensitive joints, (ii) is fixedly attached to the support at inlet and outlet ends of the conduit, (iii) extends from the support in a cantilevered fashion, whereby it is oscillatable relative to the support about an oscillation axis which is substantially located at the sites of solid mounting; (iv) is mounted about a deflection axis located substantially midway between inlet and outlet legs of the conduit; and (v) exhibits a different resonant fre~uency about each of the respective axes;
(3) a driver for oscillating the conduit about said oscillation axis; and ,~

(4) sensor means to measure the Coriolis forces tending to elastically distort the conduit about said deflection axis.
In the Drawings:
FIGUR~ 1 is a perspective view of a fluid flow meter according to one embodiment of the present invention;
FIGURE 2 is an end view of the flow meter of FIGURE
1 illustrating oscillation at midpoint under no flow conditions;
FIGURE 3 is an end view of the flow meter of FIGURE
1 illustrating oscillation at midpoint in the up direction under flow conditions;
FIGURE 4 is an end view of the flow meter of FIGURE
1 illustrating oscillation at midpoint in the down direction under flow conditions;
FIGURE S is a block diagram drawing of the drive circuit of the flow meter of FIGURE l;
FIGURE 6 is a logic diagram of the readout circuit of the flow meter of FIGURE l;
FIGURE 7 is a timing diagram of the readout signals of the flow meter of FIGURE 1 under no flow conditions;
FIGURE 8 is a timing diagram of the readout signal of the flow meter of FIGURE 1 with flow through the conduit;
FIGURE 9 is a simplified perspective view of a fluid flow meter according to another embodiment of the present invention;
FIGURE 10 is a circuit diagram of the drive and readout portion of the flow meter of FIGURE 9, with the exception of the distortion sensing portion of the circuit;
FIGURE 11 is a circuit diagram of one distortion sensing arrangement suitable to generate the signal labeled B in FIGURE 10;
FIGURE 12 is another circuit diagram for a purpose identical to that of FIGURE 11;
FIGURE 13 is yet another circuit diagram for a purpose identical to that of FIGURE 11; and , ~Zl~
~ 6 FIGURE 14 is a typical circuit diagram of the synchronous demodulator of FIGURES 10, 1~ and 13.
Turning now to the drawings, wherein like components are designated by like reference numerals throughout the various figures, a flow meter device according to a first embodiment of the present invention is illustrated in Figure 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 contemplated. 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, substantial deviations from the ideal configuration, i.e. 5 convergence or divergence do not appreciably compromise results. Operable results may be obtained with even gross deviations on the order of 30 or 40, but, since little is to be gained from such deviations in the embodiment 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 of a continuous 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 Figure 1 which permits distortion that the resonant frequency around axis W-W be different than that around axis O-O, and most preferably that the resonant frequency 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 -_ 7 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 conduit 14 at its natural frequency around axis W-W in an oscillating manner. Though "U" shaped conduit 14 is mounted in a beam-like fashion to support 12, the fact that it is oscillated at resonant frequency permits appreciable amplitude to be attained in the "beam" oscillation made around axis W-W. "U" shaped conduit 14 essentially pivots around axis W-W at inlet 15 and outlet 16.
As a preferable embodiment, first sensor 43 and second sensor 44 are supported at the intersections of base leg 19 and inlet leg 18 and outlet leg 20, respectively. Sensors 43 and 44 which are preferably optical sensors, but generally proximity or center crossing sensors, are activated as "U" shaped conduit 14 passes through a nominal reference p~ane 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 understood with reference to Figures 2, 3 and 4, which, in a simplified manner, illustrate the basic 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 Figure 2, base leg 19 maintains a constant angular position around axis O-O throughout the oscillation. However, 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 perpendicular to axis W-W while flow in the outlet leg 20 generates a second Coriolis force again perpendicular to the radial ~Z~6~

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 Figure 3, as base leg 19 passes through the mid-point of the oscillation, the Coriolis forces generated in inlet leg 18 and outlet leg 20 impose a force couple on "U" shaped conduit 14 thereby rotating base leg 19 angularly around axis O-O.
The distortion is both a beam bending 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 conduit 14, essentially all of the resistive force to the Coriolis force couple is in the nature of a resilient spring distortion, thereby obviating the need to and complication of measuring velocity drag restorative forces and inertial opposing forces. Given a substantially constant frequency and amplitude, measurement of the angular distortion of base leg 19 around axis O-O at the nominal midpoint of the oscillation, provides an accurate ind-ication 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 midpoint plane around axis O-O in terms of the time difference between the instant the leading leg, i.e., the inlet leg in the case of Figure 3, passes through the midpoint plane and the trailing leg, i.e., the outlet leg in the case of Figure 3, passes such plane, avoids the necessity of maintaining constant frequency and amplitude since variations in amplitude are accompanied by compensating variations in the velocity of base leg 19. Accordingly, by merely driving "U" shaped conduit 14 at its resonant frequency, time measurement may be made in a manner which will be discussed in further detail below, without concern for concurrent regulation of frequency and amplitude. However, if measurements are made in but one direction, i.e., the up direction in Figure 3, it would be necessary to maïntain an accurate angular alignment of ~2~
~ g 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 Figure 3, and in the down direction shown in Figure 4. As is readily recognized by one s~illed in the art, movement in the down direction, as in Figure 4, reverses the direction of the Coriolis force couple and accordingly, as shown in Figure 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 O-O 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 measu~ements may be made by direct measurement of distortion, i.e, strobe lighting the base leg 19 at the midpoint of oscillation with, for instance, an analogue scale fixed adjacent to end portions and a pointer carried by base leg 19, a preferred mode of measurement involves determining the time difference between the 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 distortions in the time measurement mode, anomalies resulting 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 discussion of the purposes of the invention - electronic aspects of the invention will be more readily understood with reference to Figures 5 through 8.

-` 10 As shown in Figure 5, drive circuit 27 is a simple means for detecting the signal generated by movement of magnet 25 in sensor coil 23. Detector 39 compares the voltage produced 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 conduit 14 and spring arm 22 are permitted to oscillate at their resonant frequencies, frequency control is not required.
The circuitry of Figure 5 provides additional information. 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 frequency is a function of the change in density of the fluid flowing through the conduit. Thus, since the time period of the oscillation can be determined, it is a simple matter to count a fixed frequency oscillator during the time period to determine a density actor. Once generated, 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 determinable function thereof.
Should a direct readout ~e desired, 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 Figure 6, and the related timing diagrams of Figure 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 ~2~

approximately the midpoint of plane A-A the oscillation of "U" shaped conduit 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 amplifier 49 and inverter 50. Line 52, the output from inverter 50, provides, as a result of the double inversion, a positive signal to the set side of flip-flop 54. Similarly, line 56 provides the 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 positive 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 provices the output of inverter amplifier 49 to reset side of flip-~lop 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 A~D gate 64, to line 68 and thus to the downcount side of up~down counter 70O 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.
Thus, in function, readout circuit 33 provides a 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 upcount 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 xeadout circuit 33 will be more readily appreciated with reference to the timing diagram of Figure 7 and Figure 8. In Figure 7, wave forms are illustrated for the condition in which "U" shaped conduit 14 is oscillated in a noflow 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 upstroke, 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. However, when the outputs from flip-flops 54 and 60 are analysed and considering further that these flip-flops provide either downcount or upcount signals respectively to updown counter 70, it will be seen that flip-flop 54, operating on the positive or leading edge of the signals of sensors 43 and 44, provides a~ output on the up stroke, while, in view of the unc~anged orientation of flags 45 and 46, flip-flop 60 provides a similar output on the downstroke. Accordingly, over a co~.plete cycle, the up-down counter 70 is first downcounted a finite number of counts by the output of flip-flop 54, through gate 64, and then upcounted an equal amount by the output of flip-flop 60 through gate 66. Accordingly, the resulting count in up-down counter 70 is zero, representative of the no-flow condition.
On the other hand, under flow conditions as shown in Figure 8, sensor 43 is activated earlier than in Figure 7 as a result of the distortion of base leg 19 by the Coriolis force couple resulting from fluid flow, as discussed above. Similarly, sensor 44 is activated later for an identical reason. Thus, on the upstroke, flip-flop 54 is activated for a substantially longer period than in the condition of Figure 7 since the misalignment of flags 45 and 46 is added to the distortion of base leg 19 by the Coriolis force couple in the up movement. On the other hand, upon down movement, ~Z3L~

i.e., generating the negative or trailing edge of the signals from sensors 43 and 44, the Coriolis force couple is reversed thus causing sensor 43 to be deactivated earlier and sensor 44 to be deactivated later.
Accordingly, flip-flop 60 is activated for a diminished period of time. As is clear from the relative times of activation of the two flip-flops, the downcount period of updown counter 70 is substantially longer than the upcount period resulting from activation of flip-flop 60.
The resulting increased count in the downcount side of up-down counter 70 is an accurate indication of the flow over a period of oscillation. The count in up-down counter 70 after a given number of oscillations is directly proportional to mass flow in "U" shaped conduit 14 during that time period. The number of oscillations may be determined by, for instance, counting the number of activations of, as a typical example, flip-flop 54 at downcounter 71 connected to the output of flip-flop 54 by line 72. Thus, upon the occurrence of "N" outputs from flip-flop 54, downcounter 71 is activated and, in turn, activates logic sequencer 74. Logic sequencer 74 is connected to oscillator 67, and at the frequency of oscillator 67, first latches latch decoder driver 77 through line 78 and then resets updown counter 70 through line 75. Thus until logic sequencer 74 is again activated after "N" outputs from flip-flop 54, display 80 indicates the accumulated count of up-down counter 70 at the time of interrogation thereof, and accordingly displays mass flow rate for the period of "N"
oscillations.
Total mass flow for a selected reset period is similarly provided in that the output from up-down counter 70 is supplied to digital integrator 82 which is also connected to crystal oscillator 84. Thus the counts from updown counter 70 are integrated with regard to time, i.e., the fixed, stable frequency of oscillator 84, and the intergal provided to latch decoder driver 85 which in turn is connected to display 87 to provide a total mass flow readout for the period from last ,,, ~l2~?6 activation of reset 88, i.e., a switch connected to digital integrator 82.
As described above, the density factor may also be determined independent of mass flow measurements by activating flip-flop 90 at the clock frequency of the output of flip-flop 54 through line 92. The output of flip-flop 90 is provided to AND gate 94 which, upon activation of flip-flop 90 provides the count of crystal oscillator 84 to counter latch driver 96. Thus, with time information in terms of the counts from crystal oscillator 84, and with the period of oscillation datum from flip-flop 90 available the count in counter latch driver 96 is a function of density of the fluid in "U"
shaped conduit 14, and accordingly, the readout at display 98 provides the density factor discussed above.
Since the density factor is not a linear function of the period of oscillation of "U" shaped conduit 14, the readout at display 98 must be further processed, either manually through a graph or through a microprocessor for density or specific gravities per se~;~
Summarily, it will be recognized that the most preferred embodiment of flow meter lO of the present invention, provides, as desired, instantaneous mass flow rate, cumulative flow rate over any given period, density 2S information as to the fluid, and volumetric flow rate if desired, i.e., by dividing mass flow rate by density.
This is accomplished, according to empirical tests, at accuracies of 0.1 or 0.2 percent and will, for instance, measure gas flow at quite low rates in an accurate manner. There is no need to regulate the amplitude of the frequency of flow meter lO in the preferred embodiment, i.e., when measuring the time period between output of one sensor until the output of the other sensor.
Another embodiment of the invention is shown in Figure 9, wherein mass flow meter lO0, which is similar in many respects to flow meter device lO, is illustrated.
As shown, flow meter lQ0 includes a base 102 and "U"
shaped conduit 104 extending therefrom in a substantially ~2~q,~6~1 solidly mounted, i.e., free of pivoting devices, manner.
"U" shaped conduit 104 includes inlet 105 and outlet 106 which communicate with inlet leg 108 and outlet leg lO9, respectively. Legs 108 and 109 are arranged to pivot at points 112 and 114 along axis W'-W' to permit oscillation of "U" shaped conduit 104 around axis W'-W'. This may be facilita~ed by, for instance, a thinning in the walls of "U" shaped conduit 104 at pivots 112 and 114, but such pivot points are continuous areas of "U" shaped conduit 104 and may be unaltered tubes. Base leg 116 connects inlet leg 108 and outlet leg 109 thus completing "U"
shaped conduit 104.
Con~rary to the preferred arrangement of flow meter lO, "U" shaped conduit 104 may advantageously have less resistance to bending around the Coriolis force distortion axis than around oscillation axis W'-W' since Coriolis force distortion is nulled. Magnets 118 carried on base leg 116 by supports ll9 interact with drive coil 120 to oscillate "U" shaped conduit 104. Preferably, drive coil 120 is carried on cantilevered spring leaf 122 which is pivotally mounted adjacent axis W'-W' and of a natural frequency substantially equivalent to that of "U"
shaped conduit 104 carrying the contemplated fluid therein. Of course, the mounting of magnet 118 and force coil 120 may be reversed, i.e., on conduit 104 and leaf spring 122, respectively. Also, leaf spring 122 may be dispensed with entirely when base 102 is of substantial mass compared to the mass of "U" shaped conduit 104 and the fluidized material flowed therethrough. However, in most instances, it is preferred to oscillate "U" shaped conduit 104 and leaf spring 122 at a common frequency but 180 out of phase to internally balance the forces within flow meter 100 and avoid vibration of base lQ2.
Base leg 116 carries magnets 125 and 126 which depend downwardly therefrom. Magnet 125 is disposed within sense coil 128 mounted to base 102, while magnet 126 is similarly disposed within sense coil 129 also mounted on base 102. Magnet 125 extends within force coil 131 arranged symmetrically with sense coil 128, ~2~3~1 while magnet 126 extends within force coil 134 similarly mounted relative to sense coil 129. Deflection sensing means 133 and 134, which are shown in a simplified manner in Figure 9, but in more detail in Figures 11 through 13, are positioned adjacent the intersection of inlet legs 108 and 109 and base leg 116.
Turning now to Figure 10 which sets forth the circuit details not shown in Figure 9, it should be noted that sense coils 128 and 129 are connected in series in such a manner that the movement of magnets 125 and 126 into sense coils 128 and 129 will generate a sinusoidal signal "A" with an amplitude proportional to the velocity of the "U" shaped conduit 104. This signal, the magnitude of which is proportional to the speed of movement of magnets 125 and 126, and accordingly a function of the amplitude of oscillation of "U" shaped conduit 104, is provided to AC amplifier 135, and to diode 136 which permits only the positive portion of the sinusoidal signal to charge capacitor 137. Accordingly, the input from diode 136 and capacitor 137 to differential amplifier 138 is determined by the magnitude of the sinusoidal signal. Differential amplifier 138 compares such input with reference voltage VRl. Thus, if the voltage of capacitor 137 exceeds VRl, amplifier 138 outputs a stronger signal. The output from AC amplifier 135, which is of course a sinusoidal signal in phase with the oscillation of "U" shaped tube 104 and of a magnitude determined by the gain control outputted by differential amplifier 138, drives coil 120 to maintain the desired oscillation of "U" shaped tube 104. Signal A is also supplied to a bridge formed of resistors 140, 141, 142 and photoresistor 143. Resistor 144 is included in a feedback loop between resistors 140 and 142, and the output from the interconnection of resistors 140, 142 and 144 is connected to, for instance, the minus input of differential amplifier 145. A variable light source, such as LED 147, is connected through resistor 148 to the output of servo amplifier 150. Servo compensator 152 is a conventional expedient in servo systems as described in .~

-` 12:~C~

Feedback Control Systems, Analysis and Synthesis, by D'Azo and Hopuis, published by McGraw Hill, 1966, forms the feedback loop between one input of servo amplifier 150 and the output therefrom. Signal B, which is a DC
signal proportional to the small, unnulled distortion of "U" shaped conduit 104 generated as described below with regard to Figures 11, 12 and 13, is connected through resistor 153 to an input of servo amplifier 150. The output of servo amplifier 150 is referenced to voltage VR2 and connected through resistor 148 to LED 147. Thus, as a function of the magnitudP of signal B with respect to VR2 driving servo amplifier 150, the intensity of LED
147 is regulated. For instance, the resistivity of photoresistor 143 decreases upon an increase in intensity of LED 147, thereby decreasing the signal supplied to the positive input of differential amplifier 145 relative to that through resistors 140 and 142 to the negative input thereof. Thus, the output of differential amplifier 145 is 180 out of phase with signal A, since the positive input thereto is decreased while the negative input is not. In summary, as signal B increases, LED 147 is dimmed and photoresistor 14 increases in resistivity, this causes the output of differential amplifier 145 in phase with signal A to increase. The output of differential amplifier 145 is connected to force coils 131 and 132 which, as described above, are supported on base 102 and connected in series and out of phase. Thus, current through force coils 131 and 132 creates, with reference to Figure 9, a torque by attracting, for instance, magnet 125 and repelling magnet 126, both of which are connected to base leg 116. This torque across base leg 116 nulls distortion of base leg 116 as a result of Coriolis forces generated by flow through "U" shaped conduit 104.
Resistors 155, 156 or 157 are connectable, by means of switch 159 and, to force coils 131 and 132 thereby providing a selectable load to adjust the scale factor and provide for greater or lesser torque on base leg 116.
The output from series connected force coils 131 and 132 12~

are also connected as one input to synchronous demodulator 162, which will be described in more detail with reference to Figure 14. The output of synchronous demodulator 162 is a DC signal proportional to mass flow rate, and accordingly provides a measurement of mass flow rate. A DC volt meter (not shown) may be connected to the output of synchronous demodulator 162 to provide a visual reading of mass flow rate through "U" shaped conduit 104, or the DC signal may be directly employed in, for instance, a control loop to other equipment.
As shown in Figure 11, deflection sensors 133 and 134 may comprise, for instance, left flag 164 and right flag 165 which depend from conduit 104. Fixed left flag 166 and fixed right flag 167 are mounted on base 102.
Accordingly, as base leg 116 oscillates, flags 164 and 165 will preclude light from light sources 169 and 170 from reaching photosensors 181 and 182, respectively.
Preferably, the point at which flags 164 and 166, and 165 and 167 intersect to block light is about at the midpoint Of oscillation of base leg 116, but ~e set of flags may be offset somewhat from the other with regard to the interference point. It will be recognized that in the event of distortion of base leg 116 angularly relative to base 102 as a result of Coriolis forces generated by flow through "U" shaped conduit 104, a change in time lapse will exist between the occulting by flags 164 and 166 and flags 165 and 167. At a fixed oscillating rate of base leg 116, the time difference and sense thereof will be dependent upon the Coriolis forces generated and the direction of oscillation. Photosensor 181 is connected to flip-flop 185 at the reset side and 186 at the reset side, with the connection to flip-flop 186 being through inverter 188. Differentiating capacitors 191 and 192 are included in reset input. Similarly, photosensor 182 is connected to the set side of flip-flop 185 and, through inverter 189 to the set side of flip-flop 186 with differentiating capacitors 193 and 194 similarly included in the inputs. Thus, as flags 164 and 166 close, a positive signal is generated by photosensor 181 which . ..~.

6~
, 19 activates the reset side of flip-flop 185 and as flags 165 and 167 close, a positive signal is similarly generated by photosensor 182 to activate the set side of flip-flop 185. Accordingly, flip-flop 185 is activated for the period between the closing of such sets of flags.
On the other hand, the opening of flags 164 and 166, and 165 and 167, generates a falling edge, or negative signal, from photosensors 181 and 182, respectively, which similarly activate flip~flop 186 through inverters 188 and 189. Accordingly, flip~flop 186 is activated for the period between the opening of one set of such flags and the other set. The outputs frc)m flip-flop 185 and 186 are provided, through resistors 195 and 196, respectively, to the inputs of dif~erential integrator 198. Integrating capacitor 200 is provided in association with resistor 195, while integrating capacitor 201 is provided in association with resistor 196 at such inputs to provide integrating capacity.
Output signal B from differential integrator 198 thus depends on the periods of activation of flip-flops 185 and 186. In the event that base leg 116 is merely oscillating without distortion, the time difference between the opening and closing of the flags will be substantially constant and the inputs to differential integrator 198 essentiaIly identical, thereby providing no signal B. On the other hand, in the event Coriolis forces are generated, base leg 116 will be distorted in a clockwise direction on one stroke of the oscillation, and in a counter clockwise direction on the other stroke.
Thus, the closing on one side of the flags will be early on one stroke and late on the other, while the other set of flags will be late on the first stroke and early on the other. The activation of flip-flops 185 and 186 therefore will not be for equal lengths of time, and differential integrator 198 will output an appropriate DC
signal B of a desired plus or minus sense depending upon the phase of the distortion of base leg 116 relative to the up/down stroke.

- ~z~ p Another arrangement to provide the same result is shown in Figure 12. As shown, strain gages 204 and 205 are mounted adjacent the intersection of inlet leg 108 and base leg 116, and outlet leg 109 and base leg 116, respectively. Strain gages 204 and 205, which may be viewed as variable resistors dependent upon the distortion of the adjacent portion of "U" shaped conduits 104, are connected with resistors 207 and 208 to form a bridge circuit communicating with a voltage source as indicated, and connected to AC differential amplifier 210. In the case of simple oscillation of "U" shaped conduit 104, the resistivity of strain gages 204 and 205 vary equally thereby providing essentially identical inputs to AC differential amplifier 210. However, in the event of distortion due to Coriolis forces r one of strain gages 204 and 205 will increase in resistivity while the other decreases thereby providing diffexent inputs to AC
differential amplifier 210 and providing an output in the form of an AC signal proportional in magnitude and sense to the different strains imposed upon strain gages 204 and 205.
The output from AC differential amplifier 210 is provided to synchronous demodulator 211, which, in conjunction with signal A, provides a DC output proportional in magnitude and sense to the distortion of "U" shaped conduit 104 as a result of Coriolis forces.
Synchronous demodulator 211 is similar to above-described synchronous demodulator 162, which will be described in more detail with reference to Figure 14.
A somewhat similar arrangement for generating signal B is illustrated in Figure 13. In this instance, however, pivot member 215 is mounted centrally on base leg llÇ and carries inertia bar 217 which is free to rotate around pivot member 215 and balanced thereon.
Crystals 219 and 220 are connected between inertia bar 217 and base leg 116. Thus, if base leg 116 undergoes simple oscillation, inertia bar 217 merely follows the oscillation without a tendency to rotate around pivot member 215. However, in the event of distortion of "U"

~2~

shaped conduit 104 as a result of Coriolis forces, base leg 116 tends to rotate relative to inertia bar 217, thereby imposing forces in opposite directions upon crystals 219 and 220 and thus generating, as a result of piezoelectric effect, signals from crystals 219 and 220.
The outputs from crystals 219 and 220 are connected to AC
differential amplifier 222, which in turn is connected to synchronous demodulator 224 to provide, in conjunction with signal A, a DC signal B of a magnitude and sense proportional to the distortion of "U" shaped conduit 104.
It is to be understood, of course, that a voltage source and strain gages could be conveniently employed in place of crystals 219 and 220.
Synchronous demodulator 162, described~above with reference to Figure 10, and accordingly, similar to synchronous demodulators 211 and 224, is described in more detail at Figure 14. As shown, input signal in the form of an AC signal is provided at input line 225 to the primary winding 227 of a transformer. Secondary windings 228, having a common ground, are, as ~ndicated by the polarity, wound in opposite directions. Thus, the output from the opposed ends of secondary windings 228 will be out of phase ~y 180. Switching means, in the form of FET transistors 230 and 231 are provided in the outputs from secondary windings 228. Comparator 233, which is connected to signal A, outputs positive or negative signals depending upon the relationship of signal A to reference voltage VR3. The output of comparator 233 thus is a square wave signal of positive or negative sense, and is provided to inverter 235 which inverts the signal.
Thus, one portion of the square wave signal turns on switching means 230 while switching means 231 is turned off, and the other portion turns on switching means 231 while switching means 230 is off. Accordingly, the portion of input signal 225 which is in phase with signal A is provided to RC circuit 237 formed of resistor 238 and capacitor 239 which outputs a DC signal which is proportional to the root mean square of the input, to filter 237. This DC output constitutes the readout as ~Z~63~

described above, i.e., a DC signal proportional to the mass flow through "U" shaped conduit 104.
In summary, flow meter 100 described above, utilizes deflection sensors 133 and 134 to detect the magnitude and sense of small, incipient deflections of "U" shaped conduit 104 due to Coriolis force and generate a DC
signal of a sense and magnitude proportional to such deflection. The DC signal, signal B, is in essence a feedback signal which regulates the nulling force generated by force coils 131 and 132 to-produce a counterforce thus preventing appreciable distortion beyond the incipient sensed distortion. Sense coils 128 and 129, in addition to maintaining the frequency of oscillation of "U" shaped conduit 104 through the drive circuit described above, also provides signal A, a signal in phase with the Coriolis forces thus providing for proper modulation of force coils 131 and 132, proper synchronization of the output of AC amplifier 135 to drive "U" shaped conduit 104 and proper demodulation of the synchronous signal of force coils 131 and 132 to produce a DC output proportional to mass flow rate.
Though the two generally preferred means for measuring the Coriolis forces are described in detail above, i.e., allowing resilient deflection of the conduit and measuring the deflection, or nulling the force to preclude deflection and measuring the nulling force, numerous other generally less desirable means exist. In any event, by using a solidly mounted "U" shaped conduit essentially free of pressure sensitive joints or pivot means, oscillation and deflection may be readily accomplished and mass flow determined over wide pressure ranges.
Although only limited preferred embodiments of the invention have been illustrated and described, it is anticipated that various changes and modifications will be apparent to those skilled in the art, and that such changes may be made without departing from the scope of the invention as defined by the following claims.

Claims

1. A flow meter for flowable materials comprising:
(1) a support;
(2) a curved, continuous conduit which: (i) is free of pressure sensitive joints, (ii) is fixedly attached to the support at inlet and outlet ends of the conduit, (iii) extends from the support in a cantilevered fashion, whereby it is oscillatable relative to the support about an oscillation axis which is substantially located at the sites of solid mounting, (iv) is mounted about a deflection axis located substantially midway between inlet and outlet legs of the conduit; and (v) exhibits a different resonant frequency about each of the respective axes;
(3) a driver for oscillating the conduit about said oscillation axis; and (4) sensor means to measure the Coriolis forces tending to elastically distort the conduit about said deflection axis.

2. The flow meter as set forth in claim 1 in which the conduit is oscillated about said oscillation axis at constant frequency and amplitude and said sensor means to measure Coriolis forces comprise means to measure the angular deflection of the conduit as a result of elastic deformation of the conduit about the deflection axis.

3. The flow meter as set forth in any of claims 1 or 2 in which the resonant frequency of the conduit about the oscillation axis is lower than the resonant frequency of the conduit about the deflection axis.

4. The flow meter as set forth in claim 1 in which the driver for oscillating the conduit comprises a magnet mounted on the conduit, a sensor coil mounted adjacent the magnet, a force coil mounted adjacent the magnet, and a power source to supply an electrical current to the force coil in response to a signal determined by moving the magnet past the sensor coil.

5. The flow meter as set forth in claim 4 in which the driver further comprises a detector to identify the peak amplitude of the signal generated by the sensor coil as a result of relative movement between the sensor coil and the magnet and to output current to the coil force such that a preselected amplitude of oscillation is maintained.

6. The flow meter as set forth in claim 1 in which there is attached to the support a reciprocating member having a natural resonant frequency substantially that of the conduit and capable of oscillating in opposite phase with said conduit.

7. The flow meter as set forth in claim 6 in which a sensor coil and force coil are carried on the reciprocating member or the conduit, and a magnet positioned adjacent both the sensor coil and force coil is carried on the other of the reciprocating member or conduit, with the magnet, sensor coil and force coil in conjunction with an amplifier and peak detector comprising the driver for oscillating the conduit about the oscillation axis.

8. The flow meter as set forth in claim 1 in which first and second sensor means are mounted adjacent the conduit at symmetrical positions, each sensor means being adapted to output a signal as the adjacent portion of the conduit passes through a preselected point of its oscillation, and further including a timer for measuring the time lag between signal outputs by the two sensors whereby the rate of mass flow through the conduit is determined as a directly proportional function of said time lag.

9. The flow meter as set forth in claim 8 in which a timer subtracts the time lags in one direction of oscillation from that of the other direction of oscillation.

10. The flow meter as set forth in claim 8 in which the outputs from the first and second sensor means are each electrically connected to a pair of inverters in series, the outputs of the first inverters in each series are connected one each to the set and reset inputs of a first flip-flop, the output from the first flip-flop is connected to one input of the first logic gate and the output of the second flip-flop is connected to one input of a second logic gate, the other inputs of both the first and second logic gates are connected to an oscillator, the output of the first logic gate is connected to one clock input of an up-down counter, and the output of the second logic gate is connected to the other input of the up-down counter, whereby the up-down counter is activated as a function of the time differential of activation of the first and second sensors with up-count being provided in one direction of conduit oscillation and the down-count being provided in the opposite direction of conduit oscillation.

11. The flow meter as set forth in claim 10 further including a readout for transferring and displaying the output from the up-down counter to a display register upon the occurrence of "N" oscillations of the conduit as a readout of the mass flow rate therethrough and also including a signal generator for resetting the up-down counter after transfer of the up-down counter output to the display register.

12. The flow meter as set forth in claim 10 wherein the output of the up-down counter is connected to a digital integrator, the digital integrator derives a time base from a fixed frequency oscillator, and the output of the digital integrator is connected to a display readout of total mass flow.

13. The flow meter as set forth in claim 1 including a frequency counter for measuring the time period of oscillation of the conduit and displaying the time period as a related function of the density of a fluid flowing through the conduit.

14. A flow meter as set forth in claim 1 in which the driver for oscillating the conduit causes oscillation at constant frequency and amplitude and the sensor means to measure Coriolis forces comprise:
means to sense distortion of the conduit about the deflection axis;
a torque generating circuit responsive to the distortion detector to generate a counter force to limit the distortion to an incipient distortion; and a measuring device to determine the counterforce whereby the rate of mass flow of the flowable material through the conduit is determined by the magnitude of the counterforce.

15. The flow meter as set forth in claim 14 in which the detector to sense distortion of the conduit about the deflection axis comprises sensors positioned one each adjacent the side legs of the conduit at predetermined points of the oscillation pathway about the oscillation axis.

16. The flow meter as set forth in claim 15 in which the centerline crossing sensors each comprise a pair of flags, one pair fixedly mounted and the other pair attached to the side legs of the conduit and adapted to overlap the fixed flags at the predetermined points of the oscillation pathway, a light source mounted on one side of each pair of flags, and a photosensitive detector mounted on the other side of each pair of flags whereby the centerline crossing may be detected by blocking the light source from the photosensitive detector by the flags.

17. The flow meter as set forth in claim 14 in which the detector to sense distortion of the conduit about the deflection axis comprise a pair of strain gages attached one each to the conduit adjacent each intersection of the side legs and base leg of the conduit, the strain gages forming a bridge circuit having a signal output proportional to the distortion of the conduit about the deflection axis.

18. The flow meter as set forth in claim 14 in which the detector to sense distortion of the conduit about the deflection axis comprise an inertia bar symmetrically and pivotally mounted at about the midpoint of the base leg of the conduit, and a pair of force sensors connected one each between each end of the inertia bar and the adjacent portions of the base leg of the conduit.

19. A method for measuring mass flow rate of a material, comprising:
(1) flowing the material through a curved, continuous conduit free of pressure-sensitive joints, with the inlet and outlet portions thereof solidly mounted in a cantilevered, beam-like fashion to a support, which conduit: (i) is characterized by an oscillation axis substantially at the points of solid mounting, and an axis of symmetry substantially perpendicular to the oscillation axis; and (ii) exhibits a different resonant frequency about each of the respective axes;
(2) oscillating the conduit about the oscillation axis;
(3) generating Coriolis forces in the curved conduit as a result of material flow through the oscillating conduit; and (4) measuring the magnitude of the Coriolis forces tending to deform the conduit about the axis of symmetry.

20. The method for measuring mass rate flow as set forth in claim 19, in which the conduit is oscillated at the resonant frequency of the conduit and material therein and at constant amplitude.

21. The method for measuring mass flow rate as set forth in claim 20 in which the magnitude of Coriolis forces tending to elastically deform the conduit about the axis of symmetry thereof is determined by measuring the angular deflection of the conduit about the axis of symmetry.

22. The method for measuring mass flow rate as set forth in claim 19 in which the mass flow rate is determined as a function of the time differential between passage of one portion of the conduit through a predetermined point of the oscillation pathway, and the passage of a second portion of the conduit through a predetermined point of said oscillation pathway.

23. The method for measuring mass flow rate as set forth in claim 20 in which the deforming forces are measured by sensing incipient distortion of the conduit about the axis of symmetry;
generating a force opposing the deforming forces in response to the sensed incipient distortion; and measuring the opposing force to determine mass flow rate.

24. The method for measuring mass flow rate as set forth in claim 19 in which a reciprocating member having a resonant frequency substantially identical to that of the conduit is attached adjacent to the conduit, and oscillated out of phase with the conduit.

25. The method for measuring mass flow rate as set forth in claim 24 in which the conduit and reciprocating member are oscillated by generating a force between a magnet mounted on one of the conduit and reciprocating member and a force coil mounted on the other of the conduit and reciprocating member.

26. The method for measuring mass flow rate as set forth in claim 23 in which the incipient distortion is detected by measuring the time differential between passage of one portion of the conduit through a predetermined point of the oscillation pathway and the passage of a second portion of the conduit through a predetermined point of the oscillation pathway.

27. The method for measuring mass flow rate as set forth in claim 23 in which the incipient distortion is detected by strain gages mounted on the conduit at positions symmetrical relative to the axis of symmetry.

28. The method for measuring mass flow rate as set forth in claim 23 in which the incipient distortion of the conduit is detected by crystals mounted between the conduit and an inertia bar pivotally mounted to the conduit at the axis of symmetry, the crystals being positioned symmetrically relative to the axis of symmetry of the conduit.