Note: Descriptions are shown in the official language in which they were submitted.
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LOW MASS CORIOLIS MASS FLOWMETER HAVING A LOW
MASS DRIVE SYSTEM
Field of tMe Invention
This invention relates to a Coriolis mass flowmeter and in particular to a
lightweight Coriolis mass flowmeter having a low mass drive system. This
invention
further relates to a lightweight Coriolis mass flowmeter having a small
diameter flow
tube. This invention still further relates to a small, lightweight Coriolis
mass
flowmeter suitable for measuring low volume mass flow rates.
Problem
Coriolis mass flowmeters are available in various sizes and flow capacities to
measure material flow and generate information such as mass flow rates,
density,
etc., pertaining to the material flow. Coriolis mass flowmeters typically have
one or
more flow tubes of straight or irregular configuration which are vibrated
transversely
by an electromagnetic driver. The material flow through the vibrating flow
fiube
induces Coriolis deflections of the flow tube which are detected by one or
more
pick-ofFs. The pick-offs generate output signals that are transmitted to
associated
meter electronics for the generation of material flow information. The
Coriolis
deflections and resultant output signals generated by the pick-offs are
proportional
to the mass of the fluid flowing through the flow tube. The Coriolis
deflections and
resultant output signals generated by the pick-offs are enhanced when the
material-
filled flow tube has a relatively large mass compared to the mass of the
associated
driver and pick-offs.
Typical dual curved-tube Coriolis flowmeters have flow rates ranging from
approximately 100 to 700,000 kg / hour and have flow tubes with inside
diameters
ranging from approximately .3 cm to 11 cm. The desired ratio of the mass of
the
material filled flow tube to the mass of the driver and the pick-offs is
typically in the
range of 10 to 1 or higher. The ratio is achievable in conventional Coriolis
flowmeters due to the relatively large mass of the material filled flow tube
as
compared to the relatively low mass of the associafied drivers and pick-offs.
It is a problem to achieve an acceptable mass ratio in lightweight Coriolis
mass flowmeters using conventional magnets and associated mounting apparatus
affixed to the vibrating flow tube structure. The driver used to vibrate a
material
filled metal flow tube is typically a magnet/coil combination with the magnet
typically
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being affixed to the flow tube and the coil being affixed to a supporting
structure or
to another flow tube. Magnet mass is a problem in the provision of lightweight
flowmeters since the minimum magnet size available is limited by metallurgical
considerations to approximately 5 mg. With associated hardware used to attach
the magnet to the flow tube, the combined mass is approximately 7 mg. This
requires that the mass of the material filled flow tube be at least 70 mg to
achieve
the desired mass ratio of 10 to 1. It is a problem to provide Coriolis mass
flowmeters having a materially filled vibrating flow tube structure with a
mass below
approximately 70 mg for measuring low volume mass flow rates.
S~lution
The above and other problems are solved by the present invention in
accordance of which a Coriolis mass flowmeter is provided that is small,
lightweight, of low mass and ideally suited for the measurement of mass flow
and
density information for a low volume material flow. The flowmeter of the
invention
is small, having flow rates at or below approximately 10 kg / hour and flow
tubes
with inside diameter at or below approximately 2 mm. For instance, the flow
tube
itself may be as small as a human hair with a proportional wall thickness.
In this invention, the flow tubes may be formed of any suitable material
which is then coated with a magnetic material. The magnetic material may be
formed by spraying or deposition on the flow tube. The magnetic material may
alternatively be made integral with the flow tube or the flow tube may be made
of
the magnetic material itself. The invention allows for the elimination of
discrete
magnets avoiding the physical problem of excessive mass as well as the
manufacturing problem of aligning and attaching a magnet to the flow tube.
~5 This invention allows the elimination of both driver and sensor magnets.
Coriolis sensors commonly use a magnet and coil as a phase-sensing "pick-off"
assembly to provide information as to the degree of Coriolis deflection in the
flow
tube. In accordance with this invention, the magnet for the pick-oft assembly
may
be constructed in the same fashion as for the driver. So either the driver, or
the
pick-off magnets, or both may be constructed in the fashion disclosed in this
invention.
An alternative implementation for a very lightweight flow tube has the driver
constructed as described and the pick-off signals generated by optical
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measurements. Suitable pick-offs are optical devices having a light emitter
and a
light collector positioned on opposite sides of the flow tube. Flexions of the
flow
tube modulate the transmitted light beam which is received and converted to
output
signals representing the flow tube vibration including Coriolis response.
A fundamental advantage of the Coriolis mass flowmeter of the present
invention is the use of a magnetic plating or a coating on the flow tube. This
plating
can be applied via plating bath, vapor deposition, plasma deposition or any
other
plating system. This is advantageous in that a very thin layer can be
deposited on
the flow tube or made integral therewith. This results in a very low
distributed mass
over a specified length of the tube which is then used in conjunction with a
drive
coil to drive the flow tube at a suitable vibration. The distributed mass of
the plating
as well as the low plating mass helps to reduce the effects of density changes
on
the generated output information. The low plating mass also permits the
Coriolis
mass flowmeter to resonate at an acceptable frequency to permit improved
density
accuracy.
In accordance with one possible exemplary embodiment of the invention, a
magnet coating on the flow tube is used that behaves exactly tike a magnet,
having
an internal North/South field. In accordance with another embodiment of the
invention, a plating bath is used to deposit a soft magnetic material
("ferrous" or
"permeable") on the flow tube. The ferrous material can only be attracted by a
driver coil. A drive system using this material with a single driver coil is
of the
"pull-only" type rather than the standard "push-pull system" of conventional
Coriolis
mass flowmeters. However, opposing drive coils driven by each respective half
of
the drive waveform would enable the flow tube to be alternately pulled in
opposing
~5 directions at the drive frequency. In accordance with another embodiment,
the flow
tube itself may be formed of a magnetic material having an internal
i~orth/South
field.
The plating of the magnetic material can be made continuous on fibs entire
flow tube or only an axial portion with the selective etching being used to
form the
final plating pattern. The ferrous material can also be made from a composite
flow
tube where the ferrous material is co-formed on the outside of the flow tube
and
then selectively etched away.
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In accordance with one embodiment of the invention, the flow tube is straight
and has magnetic material deposited on an axial center portion of the flow
tube.
Another embodiment is a u-shaped flow tube having left and right side legs
together with a center portion connecting the top of the two side legs. The
center
portion of the u-shaped flow tube has a layer of magnetic material deposited
thereon.
Both the straight tube embodiment and the u-shaped flow tube embodiment
embody flowmeters that utilize optical pick-offs for detecting the Coriolis
response
of the flow tube as it is vibrated by a magnetic coil proximate the deposited
layer of
magnetic material. In accordance with another embodiment, the magnetic layer
is
formed of ferrous material and is vibrated in a pull-only mode by a single
drive coil.
Another embodiment is a flow tube having a layer of soft, magnetic ferrous
material is vibrated in a push-pull mode using a pair of coils positioned on
opposite
sides of the flow tube. Another embodiment has magnetic material positioned
only
on an axial center portion of the flow tube. Another embodiment includes a
flow
tube having the entirety of the axial length of the flow tube having a
deposited layer
of magnetic material. Another embodiment has the entirety of the flow tube
formed
of a magnetic material. Another embodiment has the magnetic material applied
to
the entirety of the axial length of the flow tube.
In accordance with another embodiment, the flowmeter has a pair of
u-shaped flow tubes having applied magnetic material on a top center portion,
optical detectors on each leg of the flow tube and a driver magnet positioned
between the flow tubes. In another embodiment the Coriolis mass flowmeter has
a
pair of straight flow tubes having magnetic material deposited thereon
together with
~5 optical detectors and a driver coil positioned intermediate the flow tubes.
In
another embodiment, a pair of straight flow tubes are oriented parallel to
each other
and vibrated by magnets positioned on the outside of the flow tube. In another
embodiment, the Coriolis mass flowmeter has parallel flow tubes formed of a
magnefiic material that is magnetic and has a driver magnet and a pair of pick-
off
magnets positioned between the parallel flow tubes.
It is thus seen that the Coriolis mass flowmeter of the present invention
achieves an advance in the art by the provision of a Coriolis mass flowmeter
that is
smaller and of a lower mass by orders of magnitude as compared to the
currently
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available Coriolis mass flowmeters formed of metal. While this invention is
directed
towards small Coriolis mass flow meters, the advantages described by this
solution
is equally applicable to larger sensors.
ASPECTS
An aspect of the invention is a Coriolis flow meter comprising:
flow tube means adapted to receive a material flow;
a driver coil;
meter electronics that applies a drive signal to said driver coil to vibrate
said
flow tube means with material flow;
said flow tube means vibration with material flow generates Coriolis
deflections of said flow tube means; and
pick-off means coupled to said flow tube means for generating pick-off
signals representing said Coriolis deflections of said flow tube means; and
means for applying said pick-off signals to said meter electronics for the
generation of output signals representing said material flow;
characterized in that:
magnetic material embodies at least a part of said flow tube means;
said driver coil is responsive the said application of said drive signal to
generate a magnetic field that interacts with said magnetic material to
vibrate said
material filled flow tube means.
Preferably said magnetic material comprises a layer of ferrous material on at
least a part of the outer surface of said flow tube means.
Preferably said magnetic material is extant on less than all of the axial
length
of said flow tube means.
~5 Preferably said magnetic material is extant on the entirety of the axial
length
of said flow tube means.
Preferably said magnetic material comprises ferrous material integral to at
least an outer radial portion of said flow tube means;
said ferrous material is devoid of an internal magnetic field.
Preferably said magnetic material embodies less than all of the axial length
of said flow tube means.
Preferably said magnetic material embodies the entirety of the axial length of
said flow tube means.
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Preferably said magnetic material comprises hard magnetic material having
self-contained magnetic fields.
Preferably said magnetic material comprises an outer layer extant on less
than all of the axial length of said flow tube means.
Preferably said magnetic material comprise an outer layer extant on the
entirety of the axial length of said flow tube means.
Preferably said magnetic material is integral to at least an outer radial
portion of said flow tube means.
Preferably said magnetic material embodies less than all of the axial length
of said flow tube means.
Preferably said magnetic material embodies the entirety of the axial length of
said flow tube means.
Preferably said flow tube means is straight.
Preferably said filow tube means is of an irregular shape.
Preferably said flow tube means is U-shaped.
Preferably said pick-off means comprises a first and a second optical pick-off
each comprising a light emitter and a light receiver that converts received
light into
electrical signals.
Preferably said driver coil vibrates said flow tube means in a pull-only mode
in which said flow tube means material is magnetically attracted to said
driver coil
when energized with a current flow and in which the inherent elasticity of
said flow
tube means returns said flow tube means to a rest state upon the cessation of
current flow.
Preferably said driver coil defines a first driver coil;
said Coriolis flowmeter furkher comprising a second driver coil;
said first driver coil and said second driver coil are positioned on opposite
sides of said flow tube means;
said meter electronics applies opposing sinusoidal currents to said first
driver
coil and to said second driver coil to generate cyclical changing magnetic
fields that
vibrate said flow tube means cyclically in a push-pull mode between said first
driver
coil and said second driver coil.
Preferably mass flow rate of said material flow is less than 10,000
grams/hour.
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Preferably said flow tube means has an internal diameter of less than 2
millimeters.
Preferably said flow tube means has an internal diameter of less than 2
millimeters and that said mass flow rate of said material flow is less than
10,000
grams per hour.
Preferably mass flow rate of said material flow is less than 10 grams/hour.
Preferably said flow tube means has an internal diameter of less than .2
millimeters.
Preferably said flow tube has an internal diameter of less than .2 millimeters
and that said mass flow rate of said material flow is less than 10 grams per
hour.
Preferably said flow tube means has an internal diameter of less than .9
millimeters.
Preferably said flow tube means has an internal diameter of less than .9
millimeters and that said mass flow rate is less than 10,000 grams per hour.
Preferably said flow tube means comprises a single flow tube.
Preferably said flow tube means comprises a first flow tube and a second
flow tube parallel to said first flow tube;
said driver coil is positioned intermediate said first flow tube and said
second
flow tube to vibrate said first flow tube and said second flow tube in phase
opposition.
Preferably said first flow tube and said second flow tube are U-shaped with
each having a left leg and a right leg connected by a top center element;
said pick-off means comprises first and second optical pick-offs proximate
said flow tubes for generating said pick-off signals representing said
Coriolis
~5 deflections of said flow tubes.
Preferably said driver coil is positioned proximate the axial mid portion of
said top center element.
Preferably said magnetic material comprises hard magnetic material having
internal magnetic fields;
said magnetic material extends along the axial length of said flow tubes so
that the magnetic field of said material is applied to said pick-offs;
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said pick-offs are responsive to the magnetic field of said magnetic material
and to said Coriolis deflections of said U-shaped flow tubes to generate said
pick-
off signals representing said Coriolis deflections.
Preferably said pick-off means comprises first and second optical pick-offs
proximate said flow tubes for generating said output signals representing said
Coriolis deflections of said flow tubes.
Preferably said flow tube is formed of stainless steel.
Preferably said flow tube means is formed of hard magnetic material having
internal North/South magnetic fields;
said pick-offs means are magnetic transducers;
said magnetic material axially extends on said flow tube means proximate
said driver coil and said magnetic transducers; and
said vibration of said material filled flow tube means induces magnetic fields
representing said Coriolis deflections in said magnetic transducers.
Preferably flow tube means comprises dual straight flow tubes;
said driver coil is positioned intermediate said flow tubes and is effective
to
vibrate said dual flow tube in phase opposition.
Preferably flow tube means comprises dual straight parallel flow tubes;
said Coriolis flowmeter further comprises a pair of driver coils positioned on
the outer sides of said flow tubes and being effective to vibrate said dual
flow tubes
in phase opposition.
Preferably said pick-offs are optical pick-offs.
Preferably said pick-offs are magnetic transducers.
Preferably said driver coil is effective to vibrate said flow tube means in
phase opposition in a push-pull mode;
said pick-off means comprises magnetic transducers that interact with the
magnetic fields of said vibrating flow tube means to generate said pick-off
signals.
Preferably said flow tube means comprises a pair of said straight flow tubes;
said driver coil is positioned intermediate said flow tubes proximate the
axial
center portion of said flow tubes to vibrate said flow tubes transversely in
phase
opposition;
said transducers are positioned intermediate said flow tube on opposite
sides of said drive coil.
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Preferably said flow tube means comprises a pair of U-shaped flow tubes;
said driver coil is positioned intermediate said flow tubes proximate a top
axial center portion of said flow tubes;
said transducers are positioned intermediate said flow tubes on opposite
sides of said drive coil.
Brief Description of the Drawings
The above and other advantages and features of the invention are better
understood taken in conjunction with a reading of the following detailed
description
taken in conjunction with the drawings in which:
FIG. 1 discloses the details of one possible exemplary embodiment of a
straight flow tube.
FIG. 2 discloses the details of an exemplary U-shaped flow tube.
FIGS. 3 and 4 disclose the details of a Coriolis mass flowmeter embodying
the straight flow tube of FIG. 1.
FIGS. 5 and 6 disclose the details of a Coriolis mass flowmeter embodying
the U-shaped flow tube of FIG. 2.
FIG. 7 discloses the details of a light emitting diode and a photo detector
comprising the pick-offs of FIGS. 3-6.
FIG. 8 discloses the flow tube of FIG. 1 associated with a single, "pull-only"
driver coil.
FIG. 9 discloses the flow tube of FIG. 1 associated with a "push-pull" type of
d river.
FIGS. 10-13 disclose alternative embodiment of a straight flow tube.
FIG. 14 discloses a dual U-shaped flow tube embodiment of the invention.
FIGS. 15-1 ~ disclose dual straight flow tube embodiments of the invention.
~~tailc~ ~~scrip~:i~c~
~escri~ation of FIG. 1
FIG. 1 discloses the details of a straight flow tube 101 comprising a hollow
tube 102 having an axial portion surrounded by magnetic element 103 which can
comprise either a hard magnetic material or a soft ferrous magnetic material.
Hollow tube 102 has a left end 104L and a right end 1048. Magnetic element 103
may be a plating applied to the surface of straight tube 102. The plating is a
thin
layer having a thickness of approximately .0013 cm. The plated element 103 may
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be applied over the axial length of flow tube 102 as shown in FIG. 11 or may
be
concentrated in the middle axial portion of flow tube 102 as shown on FIGS. 1
and
10. In one possible exemplary embodiment, element 103 may be a magnetic
coating that behaves exactly like a magnet. This material can be deposited
with
plasma deposition systems. The use of such material permits the element 103 to
behave exactly as a magnet having a North or South magnetic field. This, in
turn,
permits the flow tube 101 to be vibrated by single driver coil in a "push-
pull"
operation.
In accordance with a second possible exemplary embodiment, element 103
may comprise a soft, ferrous magnetic material that does not have its own
North/South field, but which may be operated in association with a single coil
which
can only attract element 103 to the coil. A drive system of this type is
referred to as
a "pull-only" system since the driver coil has the capability of only
attracting the
ferrous mafierial 103. The ferrous material 103 is atfiracted to the energized
coil
regardless of the current direction through the coil. The flow tube 101 is
vibrated
when in use by energizing an associated driver coil to attract ferrous element
103
towards the coil. The inherent elasticity of flow tube 101 is utilized to bend
the flow
tube back to its rest state away when current through the driver coil ceases.
A flow
tube and associated coil of this type is shown on FIG. 8.
Alternatively, the flow tube 101 may be operated with the use of two driver
coils as shown on FIG. 9 to vibrate flow tube 102 and its element 103 as coils
D1
and D2 are alternately energized by current flow.
Description of FIG. 2
FIG. 2 discloses a U-shaped flow tube 201 that is similar to flow tube 101.
U-shaped flow tube 201 comprises a tube element 202 having a left side 202L
and
a right side 2020 together with a magnetic element 203 coupled to the top
center
portion 2020 of tube 202. U-shaped tube 202 has a bottom left terminus 20~L
and
bottom right terminus 204F~. then in use, flow tube 202 is vibrated by fibs
magnetic infieraction between magnetic element 203 and a associated driver
coil as
shown on FIGS. 5 and 6.
Description of FIGS. 3 and 4
FIGS. 3 and 4 disclose flow tube 101 embodied in a Coriolis mass flowmeter
300. Coriolis mass flowmeter 300 includes flow tube assembly 101, that
includes
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flow tube 102, magnetic material 103, driver coil D, left pick-off LPO, right
pick-off
RPO, a left flange or process connection 105 and a right flange or process
connection 106. Coriolis mass flowmeter 300 further includes meter electronics
321 whose conductors 306 and 307 controllably energize driver coil D to
vibrate
flow tube 101 in a pull-only mode in which the current through the energized
coil D
deflects flow tube 101 towards the driver coil with the natural elasticity of
flow tube
101 being used to restore flow tube 101 to its rest state upon the cessation
of
current through driver coil D.
The material flow to be processed is received by process connection 105
from a material source not shown. It then flows to the right through flow tube
102
towards process connection 106 from which it exits the Coriolis mass
flowmeter.
The vibration of flow tube 102 by driver coil D together with the material
flow
induces Coriolis deflections in flow tube 102. These deflections are detected
by
pick-offs LPO and RPO and converfied to electric signals. The elecfirical
signals and
applied over pafihs 304, 305, 308 and 309 to meter electronics 321 which
processes the signals and generates information pertaining to the material
flow.
This information is applied over output path 322 to a utilization circuit not
shown.
Meter electronics 321 is shown only on FIG. 3 in order to minimize the
complexity
of the drawings.
Driver coil D, when energized intermittently by conductors 306 and 307,
vibrates flow tube 102 in a "pull-only" mode in which the energized coil D
intermittently attracts tube 102. Flow tube 102 returns to its rest state due
to its
inherent elasticity upon each cessation of current through coil D. Driver coil
D
vibrates the flow tube up and down as shown on FIG. 4. The vibration of tube
102
as portrayed on FIG. 3 is inward and outward with respect to the plane of the
paper
of FIG. 3. Pick-offs LPO and RPO are advantageously optical pick-offs
embodying
light emitting diode 701 and photo detector 702 as shown on FIG. 7. Flow tube
102 vibrates under the influence of driver coil D. In so doing, it interrupts
and
modulates the light beam 703 transmitted from LED 701 towards photo detector
702. Photo detector 702 translates the received light wave pattern into output
signals which are transmitted over paths 304, 305, 308 and 309 to meter
electronics 321.
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Description of FIGS. 5 and 6
FIGS. 5 and 6, respectively, show a front side and a perspective view of flow
tube 201 of FIG. 2 embodied into a Coriolis mass flowmeter 500. Legs 202L and
2028 of U-shaped flow tube 202 are affixed to manifold 503 which receives
material flow at its process connection 501, extends the received flow through
leg
202L and further extends it through the center portion 202C and right leg 2028
from which the material flow is received by the output end of manifold 503 and
applied to right side process connection 502. Driver coil D vibrates flow tube
2020
in a "pull-only" mode in a manner similar to that described with respect to
Coriolis
mass flowmeter 300 FIGS. 3 and 4. The vibration of flow tube 202 together with
the material flow induces Coriolis deflections of flow tube 202 which are
detected
by pick-offs LPO and RPO and applied over conductors 304, 305, 308 and 309 to
meter electronics 321 which process fihe signals and generates output
information
pertaining to the material flow. This output information is extended over path
322 to
a utilization circuit not shown.
The Coriolis mass flowmeter of Figures 5 and 6 have been produced and
found to meet the 10 to 1 ratio of the mass of the material filled flow tube
to the
mass of the driver and pick-offs. One such embodiment included a flow tube
having an internal diameter of .2 mm and a flow rate of 10 grams / hour. A
second
embodiment included a flow tube having an internal diameter of .9 mm and a
flow
rate of 10,000 grams / hour.
Description of FIGS. 8 and 9
Flow tubes 102 are operated in a "pull-only" mode of vibration using a single
driver coil D associated with the flow tube as shown on FIG. 8. In this mode,
current through the driver coil D attracfis the flow tube 102 from its natural
rest
position. Cessation of the flow permits the natural elasticity of the flow
tube 102 to
restore it to its rest position. Alternatively, flow tube 102 may be vibrated
in a
"push-pull" mode using a pair of driver coils D1 and D2 as shown on FIG. 9. In
this
mode, current through coil D1 deflects element 103 and flow tube 102 upwards.
The cessation of current through driver coil D1 and together with current
through
driver coil D2 deflects element 103 and flow tube 102 downwards. This
alternate
energization and de-energization of driver coils D1 and D2 creates alternate
magnetic fields which vibrates flow tube 102 transversely as shown on FIG. 9.
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The embodiment of FIG. 3 may be used in applications in which the natural
elasticity of the flow tube 102 structure is adequate to restore flow tube 102
to its
rest state when driver coil D is not energized. The embodiment of the "push-
pull"
embodiment of FIG. 9 may be used in applications in which it is desired that
flow
tube 102 be vibrated under the influence of magnetic fields in each direction
transverse to the longitudinal access to the flow tube. U-shaped flow tube 202
may
similarly be operated in either a "pull-only" or a "push-pull" mode.
Conductors
306A and 307A of FIG. 9 are connected to meter electronics 321.
Description of FIGS. 10-13
FIGS. 10-13 illustrate different alternative structures that may be used to
embody flow tubes 101 and 202. FIG. 10 illustrates a flow tube in which the
magnetic material is integral to aacial center portion 1002 of flow tube 1000.
End
portions 1001 and 1003 do not contain the magnetic material. The embodiment of
FIG. 11 differs from that of FIG. 10 in that entirety of the flow tube1100 is
darkened
to indicate that the magnetic material is integral to the entire length of the
flow tube.
The magnetic material of flow tube 1100 of FIG. 11 may be either of the soft
or
hard type. Also, the flow tube 1100 may be formed in its entirety of a
material such
as steel or stainless steel 400 having its own internal North/South field.
FIG. 12
illustrates an embodiment in which the magnetic material is applied as a film
to the
surface of the flow tube. In FIG. 12, the magnetic material 1202 is applied to
the
center of 1202 of the flow tube while the end portions 1201 and 1203 do not
have
the magnetic material. The embodiment of FIG. 13 differs from that of FIG. 12
in
that the flow tube 1300 has magnetic material 1301 applied to its surface for
the
entirety of its length. The magnetic material of the flow tubes of FIGS. 10-13
may
be either of the soft or hard type.
FIGS. 10-13 show alternative embodiments for the straight tube 101 of FIG.
1. The U-shaped tube 203 may have correspondingly similar embodiments within
that the magnetic material may be integral to all or less than all of the flow
tube.
Alternatively, the magnetic material may be deposited on the surface of all or
less
than all of the length of the U-shaped flow tube 203 of FIG. 2. Alternatively,
the
U-shaped flow tube of FIG. 2 may be formed of a material such as steel or
stainless
steel 400 having its own internal North/South field.
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The term "magnetic material" as used herein applies to "soft" ferrous
material which does not have its own magnetic North/South field. It also
applies to
hard magnetic material which can have a permanent North/South field.
Description of FIG. 14
FIG. 14 discloses a dual U-shaped flow tube Coriolis mass flowmeter 1400
embodying the invention. The Coriolis mass flowmeter 1400 is analogous to the
single U-shaped flow tube Coriolis mass flowmeter of FIG. 6 except that the
Coriolis
mass flowmeter of FIG. 14 has a pair of U-shaped flow tubes 1402-1 and 1402-2.
A driver coil D is positioned intermediate the two flow tubes. The magnetic
material
on the axial mid-portion of the top element of the flow tubes are designated
1403-1
and 1403-2. The magnetic material may be either of the hard or soft type. If
it is of
the soft type, the driver coil D vibrates the two flow tubes in phase
opposition with
the flow tubes being atfiracted to the driver coil D when energised with
current flow
and is returned to fiheir normal rest position due to their inherent
elasticity when
current flow ceases. If the magnetic material is of the hard type having its
internal
North/South fields, driver coil D can vibrate the two flow tubes bi-
directionally in
phase opposition. The pick-offs LPO and RPO comprise a light emitter and a
photo
detector. These operate in a well known manner to generate an output signal
representing vibrations of the two flow tubes. The output signals are
modulated by
the amount of light received by the photo detector in response to the
vibratory
positions of the flow tubes. The output conductors 304, 305, 308, 309, 306 and
307 extending to meter electronics 321 are designated in the same manner as
described for FIG. 6. These functions include the control of driver D so that
it
vibrates the two flow tubes at their resonant frequency of the flow tubes with
material flow. These functions further include the extension of the pick-off
output
signals to meter electronics 321 so that it can generate information
pertaining to the
material flow and extend this information over path 322 to a utilisation
circuit not
shown. iUianifold 503 operates in the same manner as described in connection
with
FIG. 6. The left legs of the U-shaped flow tubes are designated 1402L1 and
1402L2. The right legs are designated 140281 and 140282. The top element of
the flow tubes are designated are 1402C1 and 1402C2.
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Description of FIGS. 15 and 16
FIGS. 15 and 16 disclose dual straight tube Coriolis mass flowmeters 1500
and 1600. The embodiment of FIG. 15 uses the single driver coil D positioned
intermediate the two flow tubes to vibrate the flow tubes in phase opposition.
When
flow tube elements 1503-1 and 1503-2 comprise soft magnetic material, driver
coil
D is effective to vibrate the flow tubes in phase opposition using a pull-only
mode.
In this mode, the flow tubes are attracted to driver coil D only when
energized.
Upon the cessation of current flow, the flow tubes return to their rest state
due to
their inherent elasticity. When the magnetic material is of the hard type
having its
internal North/South magnetic fields, driver coil D is effective to vibrate
the flow
tubes in a "push-pull" mode. The pick-offs LPO top and LPO bottom as well as
the
pick-offs RPO top and RPO bottom may be of the optical type as shown and
described in FIG. 1~ to generate pick-off signals representing the vibratory
positions of the flow tubes. The pick-off signals are transmitted to meter
electronics
321 in the same manner as described for FIG. 14.
The embodiment of FIGS. 15 and 16 includes a left input manifold 1505
which receives the material flow at its opening 1503. The embodiment of FIGS.
10
and 15 further includes output manifold1506 connected to the right side of the
flow
tubes and having an output 1509 from which material is discharged by the
Coriolis
mass flowmeter.
FIG. 16 differs from the embodiment of FIG. 15 only it its provision of a pair
of driver coils designated D1 and D2. These driver coils D1 and D2 function
under
control of meter electronics 321 to vibrate the two flow tubes in phase
opposition.
The "pull-only" mode is used if the magnetic material is of the soft type. The
"push-pull" mode is used if the magnetic material is of the hard type.
Description of FIG. 17
FIG. 17 discloses a dual straight tube Coriolis mass flowmeter in which the
filow tube is made of magnetic steel having its own internal i~orth/South
magnetic
fields. Steels of this type may be stainless steel 400 or conventional steel
having
the capability of having its own internal magnetic field. With the use of such
steels,
a separate magnetic coating or material either internal or external is not
required.
Instead, the internal magnetic fields of the flow tubes made out of such
steels can
be used. As shown on FIG. 17, the single driver coil D is controlled by the
meter
CA 02513419 2005-07-14
WO 2004/072591 PCT/US2003/003335
electronics 321 to vibrate two flow tubes 1713-1 and 1703-2 in phase
opposition.
The vibratory position of the two flow tubes is detected by magnetic pick-offs
LPO
and RPO which transmit signals to the meter electronics 321 representing the
flow
tube vibrations including the Coriolis deflection generated by the vibrating
flow
tubes with the material flow. The advantage of the Coriolis mass flowmeter of
FIG.
17 is that the deposition of an external magnetic coating or the use of
special
manufacturing techniques to add magnetic material to the flow tubes is not
required
since the flow tubes are formed of material, having its own magnetic field. A
Coriolis mass flowmeter having U-shaped flow tubes as shown on FIGS. 5, 6, and
14 may be provided using magnetic steel to form the flow tube/tubes instead of
hard or soft magnetic coatings. As shown in FIG. 17, the dual U-tube
embodiment
uses a driver coil to vibrate the flow tube/tubes in the "push-pull" mode
using
magnetic transducers as pick-offs to detect the flow tube deflections
including
Coriolis deflections from material flow.
It is expressly undersfiood 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. The term
"soft
magnetic material" or "ferrous material" shall be understood as characterizing
material that is attracted by a magnetic field, but does not have its own
internal
North/South magnetic field.
Both the "soft" or the "hard magnetic material" may be applied as a coating,
film, or outer layer to an already formed flow tube, or may be combined with a
flow
tube when fabricated to form an integrated structure that functions as the
soft or
hard magnetic material used in its fabrication.
The terms "fluid" and "fluid flow" used therein shall be understood as
encompassing fluids such as liquids and the like as well as any material that
flows
such as flurries, plasma, gases, etc. Also, while the disclosed invention is
particularly advantageous for use with small Coriolis mass flowmeters having
small
flow tubes and small flow rates, it shall be understood thafi the principles
of the
present invention are also advantageous and applicable to flowmeters of any
size
and formed of any material.
16