Note: Descriptions are shown in the official language in which they were submitted.
~l~ h~
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.
v Heretofore, flow meters of the general type with which
the present invention is concerned have been known as gyro-
10 scopic mass flow meters, or Coriolis force mass flow meters.
In essence, the function of both ~ypes of flow meters is
based upon the same principal. 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 accelera-
tion 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.
20 The prior attempts to measure mass flow in this manner
involved pressure sensitive bellows or other such mechanical
pivoting meansO
Several sp~cific approaches have been taken in utilizing
Coriolis forces to measure mass flow. For instance, the
early Roth U.S. Letters Patents 2,865,201 and 3,312,512
dicclose 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
30 than 180 "loop" is described in Sipin U~S. ~etters 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 thxough 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 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 trans-
ducers are defined as requiring highly flexible conduits,
such as bellows. ~he latter mentioned Roth patent is pri-
marily concerned with the arrangement of such flexible
bellows.
Another classical approach for measuring the force
proportional to mass flow involve 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 is flowed through the conduit~
Unfortunatelyr the Coriolis forces are quite small compared
; to the driving forces and, accordingly, it is quite diffi~
cult to accurately measure such small forces in the context
of the larye driving force.
Still another measurement means is described by Sipin
--3--
at column 7, lines l through 23 of U.S. Letters Patent
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 worthwhile
information obtained by such measurements, velocity sensors
require measurement of a mlnute differential velocity super-
imposed upon .he very large pipe oscillation velocities.
Thus an entirely accurate determinate of the gyroscopic
force must deal with velocity measurernents under limited and
specialized conditions as discussed below. Mathematical
analysis confirms that velocity measurements provide at best
marginal results.
The present invention, which provides a heretofore
unavailable improvement over 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~ canti-
levered 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 dis-
tort the 1'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 i5 mounted on a separa~e arm
having a natural requency substantially that of the "U"
shaped tube. Accordingly, ~he two members oscillate in
opposite phase similar to the manner in which the tines of a
~ ...
tuniny fork oscillate and like a tuning fork, canc~l vibr~-
tions at the suppo~t. In a particul~rly preferred embodi-
ment, 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 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 oscilla-tion.
~he cantilevered beam-like mounting of the "U" shaped
conduit is of more than passing significance. In the in-
stance in which distortion is measured, such mounting pro-
vides for the distortion resulting from the Coriolis forces
to be offset substantially entirely by resilient deformation
~ 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 method and apparatus of the present
invention is specfically s~ructured to minimize or obviate
the forces generated by the two non-measured opposing forces,
i.e., velo~ity drag and acceleration of mass. This effort
has been successful to the point whexe such forces are
present in cumulative quan~ities 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.
Accordinglyy an advantage of the present invention is
--5--
to provide a new and improved apparatus and me'chod ~or
measuring mass flow which provides highly accurate measure-
ment with simple, low cost construction.
Another advantage of the present invention is to pro-
vide a new and improved apparatus for measuring mass flow
which is substantially insensitive to pressure difference
between ambient pressure and the fluid being measured.
In the Drawings:
FIGURE 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 Elow meter of FIGURE 1
illustrating oscillation at midpoint under no flow condi-
tions;
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
illustratin~ oscillation at midpoint in the down direction
under flow conditions;
E`IGURE 5 is a block diagram drawing of the drive cir-
cuit of the flow meter of FIGURE l;
FIGURE 6 is a logic diagram o 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 FIGU~E 1 undar 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 simpliied perspec~ive view of a fluid
flo~ meter according to another embodim~nt of the present
invention.
EIGURE 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 purpo~e
identical to that of FIGURE 11; and
FIGU~E 14 is a typical circuit diagram of the synchro-
nous demodulator of FIGURES 10, 12 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
met~r 10 includes fixed support 12 having "U" shaped conduit
14 mounted thereto in a cantilever, beam-like fashion. i'U"
shaped conduit 14 i5 preferably of a tubular material having
resiliency such as is normally found in such materials such
a5 beryllium, copper, tempered aluminum, steel, plastics,
etc. Though de~cribed as "U shapedl', conduit 14 may have
legs which converge, diverge, or are skewed su~stantially.
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~eO, 5 convergence or divergence do not appreciably com-
promise 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 ley
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 im-
portant. 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 pre-
ferably 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 ~3 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 t~ 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 IlU" shaped conduit 14 is mounted in a beam-
like fashion to supports 12, the fact that it is oscillated
at resonant freguency 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 1~.
As a preerable embodiment, first sensor 43 and second
sensor 44 are supported at the intersectlons of base leg 19
and inlet leg 18 and outlet leg 20, respectively. Sensors
43 and 44 which are preferably optical sensors, but generally
~ ,3~ ~
proximity or center crossing sensors, are activated at "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 clescribed below, is provided
to indicate mass flow measurements as a function of the time
clifferential of the signals generated by sensors 44 and 43.
Operation of flow meter 10 will be more readily under-
stood with reference to FIGURES 2, 3, and 4, which, in a
simplified manner, illustrate the basic principal 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 perpendiculax 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 FIGURE 3, as
base leg 19 passes through the mid-point of the oscillation,
the Coriolis forces generated in inlet leg 18 and ou~let leg
20 impose a force couple on l'U" shaped conduit 14 thereby
rotating base leg lg angularly around axis O-O. The dis-
tortion 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 configura-
tion of "U" shaped conduit 14, essentially all of ~he re-
sistive force to the Coriolis force couple i9 in the nature
of a resilient spring distor-tion, thereby obviating the need
; to and complication of measuring velocity drag restorative
Eorces and inertial opposing forces. Given a substantially
constant frequency and amplitude, measurement of the angular
distortion of base leg l9 around axis O-O at the nominal
midpoint of the oscillation, provides an accurate indication
of mass flow. This provides a substantial improvement over
c the prior art. However, as a most significant aspect of the
present invention, determination of the distortion of base
lO 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
FIGU~E 3, passes through the midpoint plane and the trailing
leg, i.e., the outlet leg in the case of FIGUP~ 3, passes
such plane, avoids the necessity cf maintaining constant
frequency and amplitude since variations in amplitude are
accompanied by compensating variations in the velocity of
base leg l9. Accordingly, by merely driving "U" shaped con-
duit 14 at its resonant frequency, time measurements may be
20 made in a manner which will be discussed in further detail
below, without concern for concurrent regulation of ampli-
tude. However, if measurements are made in but one direc-
tion, i.e., the up direction in FIGURE 3, it would be necessary
to maintain an accurate angular alignment of base leg l9
relative to the nominal midpoint plane. Even this require-
ment 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 recog-
nized by one skilled in the art, movement in the down direc-
30 tion, as in FIGURE 4, reverses the direction of the Coriolis
force couple and accordingly, as shown in FIGURE 4, reverses
--10--
~t;, ~
the direction of distortion as a result of the Coriolis
force couple.
Summarily, s-tated broadly, "U" shaped conduit 14,
having specified frequency charactexistics 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
10 direction during one phase of the oscillation, and, then in
} the opposite direction during the o~her phase of oscillat-on.
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 of oscillation
with, for instance, an analogue scale fixed adjacent to end
portions and a pointer carried by base leg 19, a pr~ferred
mode of measurement involves determining the time difference
between the instance in which the leading and trailing edges
of the base leg 19 move through the midpoint plane. This
20 avoids the need to control amplitude. Further, by measuring
the up oscillation distortions and the down oscillation
distortions in the time measurement mode r anomalies re-
~ulting from physical misalignment of "U" shaped conduit 14
relative to the midpoint plane are cancelled rom the measure-
ment results.
The essentially conventional - given ~he above dis-
cussion of the purposes of the invention - electronic as-
pects of the invention will be more readily understood with
re~erence to FIGUR~S 5 through 8.
As shown in FIGURE 5, dxive circuit 27 is a simple
means for dekecting the signal generated by movement of
maynet 25 in sensor coil 23. Deteetor 39 compares the
voltage produced by sensor coil 23 with reference voltaye
37. As a result, the gain of force coil amplifier 41 is a
function of the velocity of ma~net 25 within sensor coil 23.
Thus, the amplitude of the oseillation of "U" shaped conduit
14 is readily controlled. Sinee "U" shaped conduit 14 and
spring arm 22 are permitted to oscillate at their resonant
frequeneies, frequency eontrol is not required.
The circuitry of FIGURE 5 provides additional informa-
tion. The output of foree eoil amplifier 41 is a sinusoidal
signal at the resonant frequency of "U" shaped conduit 14.
Since the resonant frequency is determined by the spriny
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 eonduit mass elearly does not change), it will be
appreeiated that any ehange in frequeney is a funetion of
the ehanye in density of the fluid flowing through the
eonduit. Thus, sinee the time period of the oseillation ean
be determined, it is a simple matter to count a fixed fre-
queney oseillator during the time period to determine a
density faetor. Onee generatedl the density faetor can be
eonverted to flu1d density by, for instanee, a ehart or
graph in that the time period is not a linear funetion of
density, but only a determinable funetion thereof. Should a
direet readout he desired, a mieroproeessor ean be readily
programmed to eonvert the density ~aetor direetly to fluid
density.
The nature and funetion of readout eireuit 33 will be
- 30 more readily understood with referenee to the logie eireuit
illustrated in FIGURE 6, and the related timing diagrams of
l ~,
3~
FIGURE 7 and 8. Readout circuit 33 is connected to inlet
side sensor 43 and outlet side sensor 44 ~7hich develop
signals as flags 45 and 46 carried on base leg 19 pass by
the respective sensor at 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 ~hile outlet side sensor 44 is similarly
connected through inverter amplifier 4~ and inverter 50.
Line 52, the output from inverter 50, provides, as a result
of the double inversion, a posltive signal to the set side
of flip-flop 54. Similarly, line 56 provides the output
from inverter 48, ayain 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 provides the output
of inverter amplifier 49 to the reset side of flip-flop 60.
Thus, flip-flop 60 would be set upon the output of a negative
signal from sensor 43, and r~set 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. ~ND 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 ~ND gate 66 to line 69 connected to the upcount side
of updown counter 70.
-13-
l~us, in function, readout circuit 33 provid~s a do~,m-
count signal at ~he frequency of oscillator 67 to updo~
counter 70 for the period during which sensor 44 is activa-
ted prlor 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 readout circuit 33 will be more
readily appreciated with referenee to the timing diagram of
FIGURE 7 and FIGURE 8. In FIGURE 7, wave forms are illu~
strated ~or the condit~on in which "U" shaped conduit 14 is
oscillated in a noflow condition, but in which flags 44 and
46 are not precisely s~atically aligned with plane A-A.
Thus, as shown in the timing diagram, sensor 44 initialLy
switches positive early relative to the ideal time repre~ented
by the vertical lines on the upstroke, and switches negative
late on the down stroke as a result o~ the misalignmen~ o~
flag 46. On the other hand, sensor 43 switches positive
late on the upstroke and switches negative early on the
downstroke. Eowever, wh~n the outputs rom flip-flops 54 and
60 are analysed and considering further than these fllp-
flops provide either downcount or upcount signals respectively
to updown counter 70~ it will be seen that flip10p 54,
operating on the positive or leading edge o the signals of
sensors 43 a~d 44, provid~s an output on the up stroke,
while, in view of the unchanged orientation flags 45 and 46,
; flip-flop 60 provides a similar output on the downstroke.
Accordingly, over a complete cycle, the up down counter 70
is first downcoun~ed a finite number of coun~s by the outp-~
of flip-flop 54, thruugh gate 64J and then upcounted an equal
-14-
l`:
amount by the output of flipflop 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
j 10 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, 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
1ip-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 sid~ 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 oscilla-
tions is directly proportional to mass flow in "U" shaped
conduit 14 during that time period. The number of oscilla-
tions 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 activa'ced a~d, in turn,
activates logic sequencer 74. Logic sequencer 74 is con-
nected to oscillator 67, and at the frequency of oscilla or
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" out-
puts 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 sup-
plied to dlgital integrator 82 which is also connected to
crystal oscillator 84. Thus the counts from updown counter
70 are integrated with re~ard 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 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 84l 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
-16-
98 provides the density factor discussed above. Since the
densit~ 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, in the most pre-
ferred embodiment of flow meter 10 of the present invention,
provides, as desired, instantaneous mass flow rate, cumulative
lQ flow rate over any given period, density information as to
the fluid, and volumetric flow rate if desired, i.e., by
dividiny mass flow rate by density. This is accomplished,
accordin~ to empirical tests, at accuracies of 0.1 ox 0.2
percent and will, for instance, measure gas flow at quite
low rates in an accurate manner. There is no need to regu-
late the amplitude of the frequency of flow meter 10 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, whereat mass flow meter 100, which is similar in many
respects to flow meter device 10, is illustrated. As shown,
flow meter 100 includes a ~ase 102 and "U" shaped conduit
104 extending therefrom in a substantially 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 109, respectively. Legs 108
and 109 are arranged to pivot at points 112 and 11~
along axis W'-W' to permit oscillation of "U" shaped conduit
104 around axis W'-W'. This may be facilita~ed by, for
-17-
..~L~
instance, a thinniny in the walls of "U" shaped conduit 104
at pivots 112 and 114, but such pivot points are continllous
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.
Contrary to the preferred arrangement of flow meter 10,
"U" shaped conduit 104 may advantageously have less resis-
tance to bending around -the Coriolis force distortion axis
than around oscillation axis W'-W' since Coriolis force
10 distortion is nulled. Magnets 118 carried on base leg 116
by supports 119 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 he dispensed with entirely when
base 102 is of substantial mass compared to the mass of "U"
shaped conduit 104 and the fluidized material flowed there~
through. However, in most instances, it is pref~rred 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 m~ter 100 and avoid vibration of base
10~ .
Base leg 116 carries magnets 125 and 126 which depend
down-.7ardly therefrom. Magnet 125 is disposed within sense
coil 128 mounted to base 102, while magnet 126 is similarly
30 disposed within sense coil 129 also mounted on base 102.
Magnet 125 extends within force coil 131 arranged symmetrically
with sense coil 12~, while magnet 126 extends within force
; coil 132 similarly mounted relative to sense coil 129. De-
flection sensing means 133 and 134, which are shown in a
simplified manner in FIGURE 9, but in more de-tail in FIGU~ES
11 through 13, are positioned adjacent the intersection of
inlPt legs 108 and 109 and base leg 116.
Turning now to FIGURE 10 which sets forth the circuit
details not shown in FIGURE ~, it should be noted ~hat
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 'IA" with
an amplitude proportional to the velocity of the "U" shaped
conduit 104. This signal, the magnitude of which is pro-
portional 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
a~plifier 138 is determined by the magnitude of the sinu-
soidal signal. Differential amplifier 138 compares such
input with reference voltage VRl. Thus, if the voltage of
capacitor 137 exceeds VRl, amplifier 138 outpu~s a stronger
signal. The output from AC amplifier 135, which i~ of
cours~ a sinusoidal signal in phase with the oscillation of
'tU" shaped tube 104 and of a magnitude determined by ~he
gain control outputed 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
i9 included in a feedback loop between resistors 140 and
-19 -
142, and the output from the interconnection of resistors
140, 142 and 144 is connected to, for instance, the minus
input of diffexential 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 ~ conventional expedient in servo systems as described in
Feedback Control Systems, Analysis And Synthesis, by D'Azo
and Hopuis, published by McGraw Hill, 1966, forms the feed-
back loop bPtween one input of servo amplifier 150 and the
output therefrom. Signal B, which is a DC signal porpor-
ti~nal 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 am-
plifier 150 is referenced to voltage VR2 and connected
through resistor 148 to LED 147. Thus, as a function of the
magnitude 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 dif-
ferential 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 resis-
tivity, this causes the output of differential amplifier 145
in phase with signal A to increase. The output of differen-
tial amplifier 145 is connected to force coils 131 and 132
which, as described above, are supported on base 102 and
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l.
r;~,
:
connected in series and out o~ phase. Thus, current throug'n
~; force coils 131 and 132 crea~es, with reference to FIGI~ 9,
,.................. a torque by attracting, for instance, magnet 125 and re-
' pelling 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 fro~
: series connected force coils 131 and 132 are also connected
as one input to synchronous demodulator 162, which will be
clescribed in more detail with reference to FIGURE 14. The
output of synchronous demodulator 162 is a DC signal propor-
tional to mass flow rate, and accordingly provides a measure-
ment 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 3 or the DC signal may b directly em-
ployed in, for instance, a control loop to other equipment.
As shown in FIGURE 11, deflection censors 133 and 134
may comprise, or instance, left flag 164 and right flag 165
which depend from conduit 10~. Fixed let 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 svurces 169 and 170 from reaching photosensors
181 and 182, respectivelyO 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
one set of flags may be offset somewhat from the other with
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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. The time difference, and sense, will be
dependent UpOIl, at a fixed oscillating rate of base leg 116,
the Coriolis forces generated and the direction o~ 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. Differentia~ing capaci-
tors 191 and 192 are included in reset input. Similarly,
photosensor 182 is connected to ~he set side of flip-flop
185 and, through inverter 189 to the set sid~ 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 acti-
vates the rese~ side of flip flop 185 and as flags 165 and
167 clo~e, a positive signal is similarly generated by
photosensor 182 to aetîvate the set side of 1ip-flop 185.
Accordingly, flipflop 185 is activated for the period be-
tween 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
~nd 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 from flip-
flop 185 and 186 are provided, through resistors 195 and
196, respectively, to the inputs of differential integrator
198. Integrating capacitor 200 is provided in associatlon
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with resistor 195, while integrating capacitor 201 is pro-
vided in association with resistor 196 at such inputs to
provide integrating capaci~y.
Ou~put signal B from di~ferential 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 differences between the opening
and closing of ~he flags wlll be substantially constant and
the inputs to differential integrator 198 essentially identi-
cal, thereby providing no signal B. On the other hand, inthe event Coriolis forces are generated, base leg 115 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 th~
other set of flags will be late on the firs~ stroke and
early on the other. The activation of flipflops 185 and 186
therefore will not be for equal lengths of ~ime, and differ-
~ntial 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.
Another arrange~ent to provide the same result is shown
i~ FIGUP~ 12. As shown, strain gages 204 and 205 are moun~ed
adjacent the intersection of inlet leg 108 and base leg 116,
and ouklet leg 109 and base leg 116, respectively. Strain
gages 204 and 205, which may be viewed as variable resistors
dependent upon the distor~ion of the adjacent portion of "U"
shaped condui~s 104, are connected with resis~ors 207 and
208 to form a bridge circuit communicating with a voltage
sour~e as indicated, and connected to AC differential ampli-
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i,:
fi r 210. In the case of simple oscilla~ion of "U" shaped
~ conduit 104, the resistivfity of strain gages 204 and 205
;~ vary equally thereby providlng essentially identical inputs
to AC differential amplifier 210. However, in the event of
distortion due to Coriolis forces, one of strain gages 204
and 205 will increase in resistivity while the other de-
.:
creases thereby providing different inputs to AC differen-
tial amplifier 210 and providing an output in the form of an
AC signal proportional in magnitude and sense to the dif-
10 ferent strains imposed upon strain gages 204 and 205.
The output from AC differential amplifier 210 is pro-
vided to synchronous demodulator 211, which, in conjunction
with signal A, provides a DC output propor~ional in mag-
nitude 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 wi~h reference to
;~ FIGURE 14.
: A somewhat similar arrangemen~ for generating signal B
is illustrated in FIGURE 13. In this instance, however,
pivot member 215 is mounted centrally on base leg 116 and
carries inertia bar 217 which is free ~o rotate around pivot
~! member 215 and balanced thereon. Crystals 219 and 220 are
connected between inertia bar 217 and ba~e leg 116. Thus,
if base leg 116 undergoes simple oscillation, inertia bar
217 merely follows the o~cillation without a tendency to
rotate around pivot member 215. How~ver, in the event of
distortion of "U" shaped conduit 104 as a resul~ of Coriolis
forces, base leg 116 tends to rotate relative to inertia bar
217, thereby imposing forces in opposite directions upon
; crystal 219 and 220 and thus generating, as a result of
-2~-
piezoelectric effect, signals from crystals 219 and 220.
The outputs from erystals 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 eonduit 104. It is to be
understood, of eourse, that a voltage source and strain
gages eould be eonveniently employed in place of crystals
219 and 220.
Synehronous demodulator 162, deseribed above with
reference to FIGURE 10, and accordingly, similar to synchronous
demodulators 211 and 224, is deseribed in more detail at
FIGURE 14. As shown, input signal in the form of an AC sig-
nal is provided at input line 225 to the primary winding 227
of a transformer. Seeondary windings 228, having a common
ground, are, as indieated by the polarity, wound in opposi~e
directions. Thus, the output from the opposed ends of
seeondary windings 228 will be out of phase by 180. Switeh-
ing meansr in the form of FET transistors 230 and 2.31 are
provided in the outputs from seeondary windings 228. Compara-
tor 233, whieh is eonneeted to signal A, outputs positive or
negative signals depending upon the relationship of signal A
to referenee voltage VR3. ~he output of eomparator 233 thus
is a square wave signal of positiv~ or negative sense, and
is provided to inverter 235 whieh inverts the signal. Thus,
one portion of the square wave signal turns on switehing
means 230 while switehing means 231 is turned off, and the
other portion turns on switehing means 231 while switehing
means 230 is of. Aeeordingly, the portion of input signal
225 whieh is in phase with signal A is provided to RC eireuit
237 formed of resistor 238 and eapaeitor 239 whieh outputs
L~
,:
a DC signal which is propvrtional to the root mean square of
, the input to filter 237. This DC output consti~utes the
-readout as described above, i.e., 2 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, incipien~ 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
10 signal, signal B, ls in essence a feedback 3ignal 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 10~ through the drive
circuit described above3 also provides signal ~, a signal in
phase with the Coriolis forces thus providing for proper
modulation o~ force coils 131 and 132, proper synchroniz~tion
of the output of AC amplifier 135 to drive "U" shaped conduit
s 20 104 and proper de~odulation of the synchronous signal of
force coil9 131 and 132 to produce a DC output proportional
to mas s f low rate .
Though the two generally preferred means for measuring
the Coriolis forces are described in detail above, i.e.,
allowing resilient deflection o~ the conduit and measuring
the de1ection, or nulling the force to preclude deflection
and measuring the nulling force, numerous other generally
less desirable means exist. In any event, by uslng a solidly
mounted "Ui' shaped conduit essentlally free of pressure
30 sensitive joints or pivot means, oscillation and deflection
may be readily accomplished and mass flow determined over
wide pressure ranges.
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Although only limited preferred embodiments of the
invention have been illustrated and described, it is anti-
cipated 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 inven-
tion as defined by the following claims.
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