In-flow coriolis effect mass flowmeter

A mass flowmeter has a flow tube inserted within the confines of a conduit containing a material flow. Mass flow information is derived for the material flow within the conduit by generating mass flow information for the material flowing within the smaller flow tube positioned within the conduit and then by adjusting the calculations for the flow tube to represent mass flow information for the conduit. In accordance with a first embodiment of the invention, a pressurized cover is positioned around the flow tube to isolate the exterior surface of the flow tube from the material in the conduit. The space between the exterior of the flow tube and the cover is pressurized to a pressure equal to that of the material in the conduit. Both sides of the flow tube walls are at the same pressure so that a flow tube comprised of thinner and more flexible material may be used. In accordance with a second embodiment of the invention, the cover is not used and the flow tube is inserted directly into the conduit and the exterior walls of the flow tube are in contact with the material within the conduit. This embodiment is advantageous in applications in which the conduit material is of low viscosity. The embodiment with the pressurized cover is ideally suited for use in applications with heavy viscosity material.

FIELD OF THE INVENTION 
The present invention relates to Coriolis effect mass flowmeters. More 
particularly, the invention relates to a method and apparatus for 
generating mass flow information for material flow in a large conduit by 
measuring the material flow in a smaller flow tube inserted into a larger 
conduit. 
STATEMENT OF THE PROBLEM 
Coriolis flowmeters directly measure the rate of mass flow through a 
conduit. As disclosed in the art, such as in U.S. Pat. Nos. 4,491,025 
(issued to J. E. Smith et al on Jan 1, 1985 and hereinafter referred to as 
the U.S. Pat. No. 4,491,025) and Re. 31,450 (issued to J. E. Smith on Feb. 
11, 1982 and hereinafter referred to as the U.S. Pat. No. Re. 31,450), 
these flowmeters have one or more flow tubes of straight or curved 
configuration. Each flow tube configuration in a Coriolis mass flowmeter 
has a set of natural vibration modes, which may be of a simple bending, 
torsional or coupled type. Fluid flows into the flowmeter from an adjacent 
pipeline on the inlet side, is directed to the flow tube or tubes, and 
exits the flowmeter through the outlet side of the flowmeter. The natural 
vibration modes of the vibrating, fluid filled system are defined in part 
by the combined mass of the flow tubes and the fluid within the flow 
tubes. Each flow conduit is driven to oscillate at resonance in one of 
these natural modes. 
When there is no flow through the flowmeter, all points along the flow tube 
oscillate with identical phase. As fluid begins to flow, Coriolis 
accelerations cause each point along the flow tube to have a different 
phase. The phase on the inlet side of the flow tube lags the driver, while 
the phase on the outlet side leads the driver. Sensors can be placed on 
the flow tube to produce sinusoidal signals representative of the motion 
of the flow tube. The phase difference between two sensor signals is 
proportional to the mass flow rate of fluid through the flow tube. A 
complicating factor in this measurement is that the density of typical 
process fluids varies. Changes in density cause the frequencies of the 
natural modes to vary. Since the flowmeter's control system maintains 
resonance, the oscillation frequency varies in response. Mass flow rate in 
this situation is proportional to the ratio of phase difference and 
oscillation frequency. 
U.S. Pat. No. Re. 31,450 discloses a Coriolis flowmeter that avoided the 
need of measuring both phase difference and oscillation frequency. Phase 
difference is determined by measuring the time delay between level 
crossings of the two sinusoidal signals. When this method is used, the 
variations in the oscillation frequency cancel, and mass flow rate is 
proportional to the measured time delay. This measurement method is 
hereinafter referred to as a time delay measurement. 
In the prior art, including Smith, flow tubes must be rigid. The tube walls 
are made thick enough to keep the pressure and bending stresses to an 
allowable level. This requirement is undesirable, since thick walls 
produce Coriolis flowmeters with low sensitivities. The flow tubes must be 
also large enough to carry the entire flow of a supply conduit without 
undue restriction or pressure drop. For flows typical in large pipelines, 
this results in impractical flowmeter dimensions and costs. Similarly, it 
is not practical to use measurement techniques whereby a flow tube is 
operated in a bypass line and not directly in the main conduit. The reason 
is that it is difficult to create conditions wherein the bypass flow 
remains always in the same exact proportions to the main flow, regardless 
of flowrate in the main flow path. These conditions would have to be 
extant in order for the measurement of the bypass flow alone to be used in 
computing the flow in the main conduit. 
Another problem of currently available Coriolis flow measurement apparatus 
is their limited suitability to gas applications. Gases are less dense 
than liquids and consequently, at the same flow velocities, smaller 
Coriolis forces are generated. This situation requires a higher 
sensitivity flowmeter. Alternatively, a flowmeter with conventional 
sensitivity could be used, if the flow velocity is increased to achieve 
the same Coriolis accelerations. Unfortunately, this alternative leads to 
a flowmeter whose sensitivity is not constant. 
SOLUTION 
The present invention overcomes the above problems and achieves an advance 
in the art by providing an improved method of and apparatus for measuring 
the mass flow of materials through a conduit. In accordance with the 
present invention, mass flow information for flow in a large conduit is 
generated by inserting a relatively small flow tube within the conduit. 
The small flow tube operates as a Coriolis effect mass flowmeter by 
generating Coriolis accelerations due to the flow both internal and 
external to the flow tube. These Coriolis accelerations are additive and 
produce a very sensitive flowmeter. Drivers and sensors are associated 
with the small flow tube to generate the mass flow information for the 
material flow within the flow tube. The ratio of the total flow in the 
conduit to the flow inside the smaller flowtube is constant and defined. 
The output information of the inserted flowmeter is then adjusted in 
accordance with the small portion of the material that flows through the 
flow tube as compared to the portion of the material that flows through 
the conduit to derive accurate mass flow information for the conduit. 
The use of a small flow tube inserted within a larger conduit resolves the 
above-discussed problems associated with prior Coriolis flowmeters. 
Inserting the small flow tube into the material flowing in the larger 
conduit eliminates pressure differential problems since the inside and 
outside surfaces of the inserted flow tube are at the same pressure as the 
material flowing in the conduit. By eliminating this pressure 
differential, the small flow tube may be made of thinner and less rigid 
material than is the case when the outside of the flow tube is at 
atmospheric pressure. A thinner and more flexible flow tube is more 
suitable for the generation of meaningful Coriolis forces. In addition, 
there is no need to interrupt the flow in the conduit to install a 
relatively large and expensive structure to measure flow. The 
insertion-type Coriolis mass flowmeter disclosed herein becomes practical 
for large pipe-dimensions which can not economically served by the 
currently available largest Coriolis mass flowmeter (pipe diameter of 8 
inches or larger). 
As shown on the drawings, the effective cross sectional area of the flow 
tube is small compared to the effective cross sectional area of the 
conduit into which the flow tube is inserted. The exact size of the flow 
tube is not critical. However, it should not be so small that it is 
difficult to manufacture and/or of delicate construction that requires 
special care and handling. The selected size may then be used in any 
application involving a conduit whose effective cross sectional area is 
large relative to the effective cross sectional area of the flow tube. 
The insertion of the small flow tube into the material flow within the 
conduit overcomes the temperature differential problems along the length 
of the tube, as above-discussed, by permitting all portions of the flow 
tube to be at same temperature namely, the temperature of material flow 
within the conduit. As a result, the mass flow measurements for straight 
tube meters using this inserted flow tube are simpler than heretofore. 
The use of thinner and more flexible material for the flow tube walls, as 
above-discussed, results in the provision of a more efficient Coriolis 
effect flowmeter since the more flexible material results in the 
generation of a greater Coriolis effect in the flow tube in response to a 
given drive signal. This increased sensitivity permits the flow tube to be 
better adapted for use in the mass flow measurement of less dense media 
like gases. 
The flow tube can be located anywhere within the conduit for flow 
measurements where Reynolds-numbers indicate that turbulent flow is 
present. However, when the flow within the conduit becomes laminar 
(Reynolds numbers below 4000), the flowtube should be located in the 
geometric center of the large conduit to achieve the best possible 
accuracy. 
In a first possible preferred embodiment, a flow tube positioned within a 
larger conduit is surrounded by a cover that isolates the exterior of the 
flow tube from contact with the material flowing within the conduit. A 
pressure controller supplies sufficient air pressure inside the cover so 
that the exterior surface of the flow tube is at essentially the same 
pressure as that of the material flowing within the flow tube and the 
conduit. Both sides of the flow tube are thereby maintained at the same 
pressure, namely the pressure of the material in the conduit. The walls of 
the flow tube can then be relatively thin, resulting in a mass flowmeter 
of increased sensitivity. 
In accordance with another possible preferred embodiment of the invention, 
a small diameter flow tube is inserted within a larger conduit with the 
flow tube being supported only at its middle portion by a magnetostrictive 
driver. The flow tube is unsupported at its ends which are associated with 
sensors. The sensors detect the movement of the flow tube resulting from 
the Coriolis accelerations generated by the combined effects of the 
transverse movement imparted by the driver and the material flow internal 
and external to the flow tube.

DETAILED DESCRIPTION 
FIGS. 1 and 2 disclose a conduit 101 having a flow tube 104 positioned 
within the conduit with the longitudinal axis of the flow tube being 
parallel to the longitudinal axis of the conduit. Flow tube 104 is 
surrounded by cover 103. Flow tube 104 is affixed at its ends to support 
elements 119 and 120 which are part of support structure 105. A driver 121 
is associated with the center portion of flow tube 104. Driver 121 
comprises a magnet 121A affixed to the center portion of flow tube 104 and 
a drive coil 12lB affixed to support structure 105. Drive coil 121B is 
energized by a drive current from driver circuit 125 over path 117 of 
cable 123 to impart a transverse oscillatory motion to flow tube 104. A 
left sensor comprising magnet 113A and sensing coil 113B and a right 
sensor comprising magnet 112A and a sensing coil 112B are associated with 
flow tube 104 to the left and right, respectively, of driver 121. Magnets 
112A and 113A are affixed to flow tube 104. Sensing coils 112B and 113B 
are affixed to support structure 105. 
Conduit 101 is fitted an its lower surface with a T-shaped branch 
comprising a tube section 122 and a connection flange 106 for receiving 
the flow tube 104 and its associated apparatus including flow tube cover 
103 and its support structure 105. 
The flowmeter support structure 105 includes a flowmeter base flange 107. 
The flow tube 104 ends are attached to support elements 119 and 120 of the 
meter support structure 105 which are of sufficient rigidity to keep the 
ends of flow tube 104 stationary at all times. 
The portion of the flow tube between the support elements 119 and 120 
oscillates transversely in response to the energization of drive coil 
12lB. Coils 113B and 112B sense the velocity of the transverse 
oscillations of the flow tube. If there is no material flowing through the 
flow tube, the output signals of these sensors are identical. When 
material flows through the flow tube while it is oscillating, the output 
of sensor 113B and is identical with 112B except there is now a small 
phase lag in the signal from sensor 113B and a small phase lead in the 
signal from sensor 112B. These phase changes are due to the Coriolis 
accelerations and the total phase difference is proportional to the mass 
flow internal to the flow tube 104. The mass flow external to the flow 
tube 104 is not sensed due to cover 103. 
FIG. 3 illustrates the vibrational pattern of flow tube 104 as it is 
vibrated at its fundamental frequency by driver 121 as well as depictions 
of the vibrational patterns assumed by the flow tube as a result of the 
generated Coriolis forces. Pattern 301 having a top portion 301A and a 
lower portion 301B illustrates the oscillatory movement imparted to flow 
tube 104 by driver 121 for a zero flow condition. Patterns 302 and 303 
illustrate the vibrational patterns generated by the combined effects of 
the driver 121 and the generated Coriolis forces. Pattern 302 has a top 
portion 302A and a lower portion 302B. Pattern 303 has a top portion 303A 
and a lower portion 303B. Coming down from the top maximum deflection, at 
the time when the middle point of the flow tube traverses through the line 
defined by the endpoints of the tube, the flow tube has the oscillatory 
pattern represented by elements 303A. Similarly, 303B is the oscillatory 
pattern during the travel upward from the bottom maximum position of the 
flow tube. These two patterns represent the left-most deviation of the 
amplitude peaks of the flow tube at zero line crossing, assuming the flow 
takes place from left to right. Similarly, the pattern elements 302A and 
302B represent flow tube shapes at the time of centerpoint zero crossing 
during their traverse toward the top or bottom maxima. The generated 
Coriolis forces cause the shape of the tube deflection to change between 
the right-most excursion represented by pattern 303 and the left-most 
excursion represented by pattern 302. The left and right tube halves are 
delayed in time by differing amounts with respect to each other, as a 
function of mass flow rate. Thus, with respect to pattern 302 at no flow 
condition, during flow conditions, the tube left side has a different 
velocity at reference plane crossing than the right side as depicted by 
the different amplitudes of pattern 302A and 302B. Similarly, pattern 
elements 303A and 303B represent the other deviation extreme caused by the 
Coriolis forces. The different velocities cause a delay between the 
velocity signals generated in the sensor coils. The patterns of FIG. 3 are 
shown in exaggerated form to facilitate the understanding thereof. 
Sensor coils 113B and 112B on FIG. 1 detect the velocity of the flow 
tube--as affected by the Coriolis force when material is flowing--and 
transmit corresponding velocity signals over conductors 116A and 116B and 
cable 123 to detector circuit 124 of meter electronics 108. Cable 123 
extends through conduit box 132 and channel 131 of support structure 105. 
Detector circuit 124 responds to the reception of these signals from cable 
123 and outputs information to signal processing circuit 126 which 
generates mass flow information pertaining to the material flow in the 
conduit. Element 140 is a pressure seal to prevent the leakage of air into 
channel 131 from the pressurized atmosphere within cover 103. 
Conduit box 132 having an access cover 133 is affixed by means of threaded 
connections 131 to the bottom of flowmeter base flange 107 and by threaded 
connection 134 to a conduit containing cable 123 extending to driver 
circuit 125 and detector circuit 124. 
Signals 116A and 116B from the sensors 113B and 112B represent the 
instantaneous velocity of the portions of flow tube 104 associated with 
sensor coils 112B and 113B. As taught in the aforementioned Smith reissue 
patent, the sensors are used to sense the velocity of points on the flow 
tube caused by the displacement of the vibrating flow tube due to the 
combined effect of the Coriolis force and the oscillating movement of 
driver 121 as material flows therethrough. 
Signals 116A and 116B representing the time differential At between the 
movements of corresponding portions of tube 104 with respect to each other 
are applied to detector circuit 124 and then to signal processing circuit 
126 which generates mass flow information for material flowing within 
conduit 101. Detector circuit 104 and signal processing circuit 126 
generate information pertaining to the mass flow rate of the material 
through tube 104. However, since the relationship between that portion of 
the material in conduit 101 and that portion which flows through flow tube 
104 is known, signal processing circuit 126 uses this relationship and 
generates and applies to conductor 127 information representing the mass 
flow information for the total material flowing in conduit 101. 
Cover 103 surrounds flow tube 104 to isolate flow tube 104 from the 
material flowing in conduit 101. This is necessary in applications in 
which the viscosity of the material flowing in tube 101 is such that its 
direct contact with the exterior of flow tube 104 would disadvantageously 
influence the movement imparted to flow tube 104 by the generated Coriolis 
forces- It is desirable that this Coriolis movement be as large as 
possible in order to obtain meaningful measurements and, in addition, that 
it not be influenced by the viscosity of the fluid surrounding it. Such 
would not be the case if the Coriolis movement of the flow tube 104 was 
affected by the viscosity of the material flowing in conduit 101. Cover 
103 isolates flow tube 104 from the material flowing in conduit 101. 
Cover 103 is pressurized by pressure controller 109 whose air output is 
connected via pressure equalization tube 110 to the void comprising the 
space between the exterior of flow tube 104 and the inner surface of cover 
103. Pressure equalization tube 110 extends from the output of pressure 
controller 109 and proceeds upward on FIG. 1 through the support structure 
105 to the airspace surrounding the exterior of flow tube 104. Pressure 
controller 109 is supplied with input information from sensor 111 over 
path 115 regarding the pressure of the material flowing within conduit 
101. Pressure controller 109 receives this pressure information from 
sensor 111 and applies an output pressure via pressure equalization tube 
110 that pressurizes the inner surface of cover 103 so that the base 
surrounding the exterior of flow tube 104 is at the same pressure as is 
the material flowing within conduit 101. Since a portion of the material 
flowing in conduit 101 also flows through flow tube 104 with the same 
pressure, the inside and outside walls of flow tube 104 are at essentially 
the same pressure and therefore, a near zero pressure difference exists 
between inner and outer walls of flow tube 104. 
Cover 103 is of such shape and dimension so as to allow flow tube 104 to 
oscillate transversely without interference and without being affected by 
the viscosity of the material flowing in tube 101. Since a zero pressure 
difference exists between the inner and outer walls of flow tube 104, the 
flow tube may be made of relatively thin material to provide for increased 
measurement sensitivity. 
A particle filtration screen 102, if desired may be positioned in the 
conduit upstream from the flowmeter so as to remove potentially damaging 
particles from the flow material. 
Meter electronics 108 is not shown in detail since such details are not a 
part of the invention. If desired, meter electronics 108 may comprise the 
mass flow rate electronics element 20 shown in detail on FIGS. 1, 2, and 3 
of U.S. Pat. No. 4,879,911 of Nov. 14, 1989, to Michael J. Zolock and 
assigned to the assignee of the present invention. The temperature 
information of Zolock is provided by temperature sensor 140 over path 195 
which extends to detector circuit 124 of FIG. 1. 
FIGS. 4 and 5 
FIGS. 4 and 5 depict an alternative exemplary preferred embodiment of the 
invention that is suited to applications involving mass flow measurements 
of low density and low viscosity materials such as gases and the like. It 
is similar to the exemplary embodiment of FIG. 1 with a few exceptions. 
The embodiment of FIGS. 4 and 5 is depicted as a section of conduit 401 
with a mass flowmeter 400 inserted inside the interior of conduit 401. 
This conduit section may be mated to appropriate sections of a supply 
conduit (not shown). As in FIG. 1, a flow tube 404 is positioned within 
material flowing through the conduit 401. Flow tube 404 is supported at 
its center by a magnetostrictive driver 418 which is mounted on support 
414 of flowmeter support structure 405. Magnetostrictive driver 418, in 
addition to supporting flow tube 404, oscillates flow tube 404 at its 
natural resonant frequency, transversely at its midpoint. The ends of the 
flow tube are free to vibrate up and down due to the vibrations induced by 
the drive force. 
A magnet 112A and 113A is affixed to each end of flow tube 404. Under each 
magnet, mounted on the flowmeter support structure 419 and 420, are sensor 
coils 113B and 112B. The ends of flow tube 404 oscillate up and down due 
to the forces imparted by the magnetostrictive driver 414. Sensor coils 
113B and 112B sense the velocity of the magnets 112A and 113 A as their 
velocity it varies due to the vibrational and Coriolis forces and generate 
voltage signals proportional to this velocity. The normal (zero flow) 
oscillation of the flow tube due to the force imparted by only the 
magnetostrictive driver 418 is similar to a beam deflecting under load. 
With material flowing in the flow tube, the generated Coriolis forces 
alter the timing relationship between the deflections in proportion to the 
mass flow rate within the vibrating flow tube. This is shown in 
exaggerated form in FIG. 8. Essentially similar to FIG. 3, the depicted 
shapes show the tube shapes at the time of reference plane crossing, 
during their upward and downward movement, without and with flow through 
flowtube 404. 
In the exemplary embodiment of FIG. 4, because of the lower viscosity 
material (gas or liquid) flowing in conduit 401 the need for the cover 103 
of FIG. 1 and the related pressure equalization apparatus is eliminated. 
The low viscosity material does not significantly affect the flow tube 
oscillations and therefore no flow tube cover is required. The pressures 
on the inside and outside walls of the flow tube are inherently equal. 
This permits the use of a flow tube 404 having thinner walls and the need 
for a lower drive force. 
Driver circuit 425 , detector circuit 424, and processing circuit 426 
operate in a manner similar to their counterparts of FIG. 1 to drive flow 
tube 404 and measure its Coriolis movement to generate information about 
mass flow rate in conduit 401. Element 440 is a pressure seal to prevent 
the flow of pressurized material from conduit 401 to channel 441. 
FIG. 8 
FIG. 8 illustrates, in exaggerated form, a vibrational pattern of flow tube 
404 driven at its fundamental resonant frequency by driver 414 as well as 
the vibrational patterns assumed by the flow tube as a result of the 
generated Coriolis forces. Pattern 802 has a top portion 802A and a lower 
portion 802B. Pattern 803 has a top portion 803A and a lower portion 803B. 
At the time when the center of the tube is at the center of its movement, 
during its travel downward from the top, the flow tube has the oscillatory 
pattern represented by 803A. 803B is the oscillatory pattern during the 
travel upward from the bottom position of the flow tube. This represents 
the right-most deviation of the amplitude peaks of the flow tube, assuming 
the flow takes place from left to right. Similarly, the pattern elements 
802A and 802B represent flow tube shapes during their traverse toward top 
or bottom maxima. The combination of the driven vibration and the 
generated Coriolis forces cause the shape of the tube deflection in a 
given point in time to change between the right-most excursion represented 
by pattern 803 and the left-most excursion represented by pattern 802. As 
shown by these patterns, the left and right tube ends are delayed in time 
by differing amounts with respect to each other from the reference plane 
804, due to the Coriolis forces. Thus, as opposed to pattern 802 showing a 
no-flow condition, during flow conditions the tube left end velocity is 
different from the velocity of the right end, as shown by the shapes of 
pattern 802A and 802B. Pattern elements 803A and 803B represent the other 
deviation extreme caused by the Coriolis forces during the other half 
vibratory cycle. The Coriolis forces create this time delay between the 
velocities of the flow tube ends, as shown by patterns 802A and B, and 
803A and B. The velocity difference is represented by the time delay 
between the output signals of coils 112B and 113 B. The signals are 
forwarded to detector circuit 424 in a manner similar to the one depicted 
in FIG. 1. 
FIG. 6 discloses an embodiment of the invention wherein conduit 601 has a 
mid-portion of increased diameter with respect to the remainder of the 
conduit. The sides of this mid-portion are semi-circular and match the 
semi-circular cover 603 which surrounds flow tube 604 positioned within 
the conduit 601. Conduit 601, flow tube cover 603, and flow tube 604 are 
similar in most respects to conduit 101, cover 103 and flow tube 104, 
respectively. The top and bottom surfaces of cover 603 are semi-circular 
in configuration. The mid-portion of conduit 601 is of slightly greater 
diameter than the remainder of the conduit and is configured to be 
semi-circular to match the semi-circular configuration of the flow tube 
cover 603. This widened portion of conduit 601 facilitates material flow 
through the conduit 601 and around flow tube cover 603. This portion of 
greater diameter provides a flow path of less impedance around flow tube 
cover 603 than would be the case if conduit were of a fixed diameter. The 
area of increased diameter compensates for the material flow impedance 
provided by cover 603. This permits the fluid flow within conduit 601 to 
be laminar around the portions of the flow tube where the material flow is 
diverted around flow tube cover 603. 
FIG. 7 shows a flow tube 704 having a funnel-shaped opening 701 on its left 
end. Flow tube 704 maybe positioned within a flow conduit such as conduit 
101 in FIG. 1. The purpose of the funnel shaped end 701 is to increase the 
amount of material flow, and hence the velocity of flow, through the tube 
704 when it is positioned in the larger conduit such as conduit 101 or 
601. The dashed lines to the right of the funnel section 701 represent a 
cover membrane such as membrane 603 of FIG. 6. If desired, the flow tube 
704 may be positioned within a conduit such as 601 having a center portion 
of increased diameter in order to maintain laminar material flow around 
the sides of flow tube 704. The increased flow velocity provided by end 
701 increases the sensitivity of flow tube 704 to Coriolis forces. 
It is expressly understood that the claimed invention is not to be limited 
to the description of the preferred embodiment but encompasses other 
modifications and alterations within the scope and spirit of the inventive 
concept. Thus the detectors 112, 113 may be of any suitable type including 
optical, position, acceleration or velocity. The driver 121 may be of any 
suitable electromagnetic type.