Abstrict An insert for an electromagnetic flow meter is disclosed. The insert
is arranged to be positioned within a flow conduit having a flow
conduit cross-section to define a flow path for fluid, wherein the
insert comprises an inlet, a measuring section with a measuring
cross-section different from the flow conduit cross-section and
having at least two substantially parallel sides over at least part
of its length, and an outlet.
Claims What is claimed is:
1. An insert for an electromagnetic flow meter arranged to be positioned
within a flow conduit having a flow conduit cross-section to define
a flow path for fluid, wherein the insert comprises an inlet, a
measuring section with a measuring cross-section different from
the flow conduit cross-section and having at least two substantially
parallel sides over at least part of its length, and an outlet.
2. The insert according to claim 1 wherein the inlet comprises
an inlet section with a cross-section having a corresponding shape
to that of the flow conduit.
3. The insert according to claim 1 wherein the outlet comprises
an outlet section with a cross-section having a shape corresponding
to that of the flow conduit.
4. The insert according to claim 1 wherein the cross-sectional
shape of at least one of the inlet and the outlet corresponds to
that of the measuring section.
5. The insert according to claim 1 further comprising a transition
section between at least one of the inlet and the outlet and the
measuring section, wherein the cross-sectional shape of the insert
transforms smoothly from the shape of the inlet and/or the outlet
to the shape of the measuring section in the transition section.
6. The insert according to claim 1 wherein at least one of the
inlet and outlet comprises a substantially circular cross-section
or a substantially square or rectangular cross-section over at least
part of its length.
7. The insert according to claim 1 wherein the cross-sectional
area of the measuring section covers less than about 50% of the
cross-sectional area of the flow conduit.
8. The insert according to claim 1 wherein the insert is manufactured
by moulding or extrusion.
9. The insert according to claim 1 wherein the insert is manufactured
substantially from one of a thermoplastic material, ABS (Acrylonitrile
butadiene Styrene), a soft rubber material, a hard rubber material,
PTFE, PVDF, thermoset material, a reinforced thermoset material,
and a reinforced thermoplastics material.
10. The insert according to claim 1 wherein the cross-sectional
size and/or shape of the insert are arranged so that a substantially
uniform magnetic field may be applied over substantially the whole
cross-sectional area of the measuring section of the insert.
11. The insert according to claim 1 wherein the insert is formed
in more than one piece.
12. The insert according to claim 1 further comprising at least
one of electrodes, magnetic field generating means, and an electrostatic
screen provided integrally with the insert or coupled to the insert.
13. The insert according to claim 1 wherein the insert is back-potted
upon insertion into a flow conduit.
14. A method of manufacturing an insert for an electromagnetic
flow meter, comprising forming an insert by moulding, wherein the
insert is formed such that the insert has a conduit therethrough
and comprises an inlet, a measuring section with a cross-section
having at least two substantially parallel sides over at least part
of its length, and an outlet.
15. The method according to claim 14 wherein the inlet comprises
an inlet section with a cross-section having a corresponding shape
to that of the flow conduit.
16. The method according to claim 14 wherein the outlet comprises
an outlet section with a cross-section having a corresponding shape
to that of the flow conduit.
17. The method according to claim 14 wherein the insert is extruded
within a tube having a shape corresponding to that of the formed
insert.
18. The method according to claim 14 wherein the insert is formed
from a shape-memory material.
19. The method according to claim 14 wherein the insert is formed
substantially from one of a thermoplastic material, ABS (Acrylonitrile
butadiene Styrene), PTFE, PVDF, a soft rubber material, a hard rubber
material, a thermoset material, a reinforced thermoset material,
and a reinforced thermoplastics material.
20. An electromagnetic flow meter comprising: a section of a flow
conduit; an insert arranged to be positioned within the flow conduit
having a flow conduit cross-section to define a flow path for fluid,
wherein the insert comprises an inlet, a measuring section with
a measuring cross-section different from the flow conduit cross-section
and having at least two substantially parallel sides over at least
part of its length, and an outlet.
21. A method of manufacturing a flow meter comprising: inserting
an insert into a flow conduit having a flow conduit cross-section,
wherein the insert comprises an inlet, a measuring section with
a measuring cross-section different from the flow conduit cross-section
and having at least two substantially parallel sides over at least
part of its length, and an outlet; and back-potting the insert to
support the insert within the flow conduit.
22. The method according to claim 21 further comprising providing
at least one of magnetic field generating means, electrodes, and
an electrostatic screen in conjunction with the insert.
23. The method according to claim 21 wherein the flow meter is
a wetted-type or a capacitive-type flow meter.
24. The method according to claim 21 wherein the insert is arranged
within the flow conduit so that a substantially uniform magnetic
field is provided across substantially the whole cross-sectional
area of the measuring section of the insert.
Description BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the field of electromagnetic
flow meters, in particular, to the field of insert to define a fluid
flow path within an electromagnetic flow meter.
[0003] 2. Description of the Related Technology
[0004] Electromagnetic flow meters may be used to determine the
rate of flow of fluid in a conduit. The conduit itself may be used
to define the fluid path within the flow meter or an insert, placed
within the conduit, may define the fluid path within the flow measurement
zone.
[0005] Prior art flow meters, or flow meter inserts, generally
have a substantially circular cross-section, which may be designed
to match the cross-section of the fluid conduit. Circular cross-section
inserts may be manufactured easily and may provide an effective
way to contain the fluid, which may be under pressure. The walls
of the circular fluid conduit may further be used to support the
flow meter insert and, since it is not required to be self-supporting,
the flow meter insert may be manufactured economically as a lightweight
insert.
[0006] A disadvantage of such flow meters or flow meter inserts,
however, is that, due to their generally circular cross-sections,
approximations must be made in determining the flow rate of the
fluid, they require typically 5-10 diameters of upstream pipe work
to ensure an accurate measurement or they are susceptible to the
pipe work conditions in surrounding the installation.
[0007] Flow meters or flow meter inserts with substantially square
or rectangular cross-sections have been designed for specialist
purposes for which a measurement with immunity to flow conditions
is required. Such flow meters may provide improved performance when
compared to the standard circular cross-section flow meters, but
they tend to be bulky to provide the strength required to form a
flow conduit and hence are not suitable as general-purpose flow
meters.
SUMMARY OF CERTAIN INVENTIVE EMBODIMENTS
[0008] A first aspect provides an insert for an electromagnetic
flow meter arranged to be positioned within a flow conduit having
a flow conduit cross-section to define a flow path for fluid, wherein
the insert comprises an inlet, a measuring section with a measuring
cross-section different to the flow conduit cross-section and having
at least two substantially parallel sides over at least part of
its length and an outlet.
[0009] Using flow meter inserts with at least two substantially
parallel sides may also advantageously improve the accuracy of the
flow meter readings since such flow meters may be closer to a theoretically
ideal flow meter, that is a flow meter with a uniform weight function.
This may allow accurate measurements to be obtained even in low
hydraulic performance cases. Having at least two substantially parallel
sides may also increase the available space for the electrodes and
decrease the pressure drops. In addition, the hydraulic performance
of the meter maybe improved so that the meter may be less sensitive
to how it is installed and may provide a higher performance in a
non-optimal installation. Also, for a given geometry, the magnetic
field may be increased by using an insert with at least two substantially
parallel sides. This may allow the coil of the flow meter to be
used more efficiently so that a more economical coil may be used
and/or less power may be used to drive the coils.
[0010] In one embodiment, the inlet comprises an inlet section
with a cross-section having a corresponding shape to that of the
flow conduit. This may allow fluid to flow smoothly into the insert.
[0011] In one embodiment, the outlet comprises an outlet section
with a cross-section having a corresponding shape to that of the
flow conduit. This may further help to smooth the flow of the fluid
through the insert, and particularly through the measuring section
of the insert.
[0012] In one embodiment, the cross-sectional shape of at least
one of the inlet and the outlet corresponds to the cross-sectional
shape of the measuring section.
[0013] In one embodiment, the insert further comprises a transition
section between at least one of the inlet and the outlet and the
measuring section wherein the cross-sectional shape of the insert
transforms smoothly from the shape of the inlet and/or the outlet
to the shape of the measuring section in the transition section.
[0014] Hence a smooth transition between the shapes of the two
sections may be provided. This may minimise the disturbance of the
flow caused by the changing shape of the conduit and may allow a
more accurate flow rate measurement to be obtained.
[0015] In one embodiment, the inlet and/or outlet sections may
comprise a substantially circular cross-section. Hence the inlet
and/or outlet sections may have a cross-sectional shape corresponding
to that of a circular conduit.
[0016] In one embodiment, the cross-sectional area of the measuring
section may cover at least 70% of the cross-sectional area of the
flow conduit. Further, the cross-sectional area of the measuring
section may cover at least 80% of the cross-sectional area of the
flow conduit.
[0017] In an alternative embodiment, the cross-sectional area of
the measuring section may cover less than around 50% of the cross-sectional
area of the flow conduit. This may be useful in a low flow rate
system or to increase the uniformity of the magnetic field in the
measuring section, as discussed in more detail below.
[0018] In one embodiment, the insert is manufactured by moulding
or extrusion, for example by injection moulding, transfer moulding
or rotational moulding. Moulding the flow meter insert, from a material
such as a plastics or rubber material may allow non-circular flow
meter inserts to be provided that are lightweight and economical
but that are strong and robust enough to maintain their integrity
under fluid pressure.
[0019] In one embodiment, the insert may be manufactured substantially
from a thermoplastic material; for example, the insert may be manufactured
from a glass-loaded plastics material.
[0020] In one embodiment, the insert maybe manufactured from ABS
(Acrylonitrilebutadiene Styrene). Alternatively, the insert may
be manufactured from another similar material, such as another polymer
material, another plastics material or natural or synthetic rubber,
such as a soft rubber material or a hard rubber material.
[0021] In an alternative embodiment, the insert maybe manufactured
from a fluorocarbon material such as PTFE (Teflon (RTM)) or ETFE
or the insert may be manufactured from PVDF.
[0022] The insert may also be manufactured as a flexible rubber
insert.
[0023] According to a further embodiment, the insert may be manufactured
substantially from a thermoset material.
[0024] In one embodiment, the insert may be manufactured substantially
from a reinforced thermoset material.
[0025] According to a further preferable embodiment, the insert
may be manufactured substantially from a reinforced thermoplastics
material; for example, the insert may be manufactured from a fibreglass
material.
[0026] The insert may be bonded to backpotting, which may be provided
to give the insert the strength and rigidity required under fluid
pressure. The method of manufacture of the insert is preferably
selected based on the material used for the insert and the most
suitable method for the particular material selected, which may
be a prior art method, may be used.
[0027] In one embodiment, the insert has a substantially square
or rectangular cross-section over at least part of its length. This
may provide the optimal cross-sectional shape to improve the performance
of the flow meter.
[0028] In one embodiment, the cross-sectional size and/or shape
of the insert may be arranged so that a substantially uniform magnetic
field may be applied over substantially the whole cross-sectional
area of the measuring section insert. As discussed in more detail
below, this may advantageously allow a more accurate measurement
of the flow rate to be determined. In some embodiments, this may
be achieved, for example by infilling the corners of a substantially
square insert, by changing the shape of the flow conduit, for example
to a substantially elliptical or rectangular cross-section, so that
the magnetic flux lines preferentially pass directly across the
measuring section, or by providing an insert with a measuring section
having a cross-sectional area much smaller than that of the flow
conduit.
[0029] In one embodiment, the insert may be formed in more than
one piece.
[0030] The flow meter in which the insert may be deployed may be
a wetted-type or a capacitive-type flow meter.
[0031] The electrodes of the flow meter may be provided integrally
with the insert or may be provided as a separate component, for
example they may be coupled to the insert. The electrodes may comprise
metallic or conductive plastics electrodes. A variety of electrode
configurations may be used in conjunction with the insert and the
electrode configuration used may be determined, at least in part,
by the cross-section of the insert.
[0032] Similarly, the magnetic field generating means maybe provided
integrally with or maybe coupled to the insert. The magnetic field
generating means may comprise a magnetic circuit. The magnetic field
generating means or magnetic circuit may be provided internally
or externally of the insert.
[0033] In one embodiment, an electrostatic screen may be provided
as part of or in addition to the insert.
[0034] In one embodiment, the insert is back-potted on insertion
into a flow conduit. Back-potting may allow the insert to be supported
and stabilised within the conduit and hence may increase the reliability
of the flow measurements.
[0035] A further aspect provides a method of manufacturing an insert
for an electromagnetic flow meter comprising forming an insert by
extrusion wherein the insert is formed such that the insert has
a conduit therethrough and comprises an inlet, a measuring section
with a cross-section having at least two substantially parallel
sides over at least part of its length and an outlet.
[0036] According to a preferable embodiment, the inlet comprises
an inlet section with a cross-section having a corresponding shape
to that of the flow conduit.
[0037] In one embodiment, the outlet comprises an outlet section
with a cross-section having a corresponding shape to that of the
flow conduit.
[0038] In one embodiment, the insert is extruded within a tube
having a shape corresponding to that of the formed insert.
[0039] Forming the insert using the methods described herein may
allow a robust but lightweight insert to be formed.
[0040] In one embodiment, the insert is formed from a shape-memory
material.
[0041] In one embodiment, the insert is formed substantially from
a thermoplastic material; for example, the insert may be manufactured
from a glass-loaded plastics material.
[0042] In a further preferable embodiment, the insert is formed
substantially from ABS (Acrylonitrile butadiene Styrene)
[0043] In one embodiment, the insert is formed substantially from
a plastics material, such as PTFE or PVDF, or from natural or synthetic
rubber, such as a soft rubber material.
[0044] According to a further embodiment, the insert may be manufactured
substantially from a thermoset material.
[0045] In one embodiment, the insert may be manufactured substantially
from a reinforced thermoset material.
[0046] According to a further preferable embodiment, the insert
maybe manufactured substantially from a reinforced thermoplastics
material; for example, the insert may be manufactured from a fibreglass
material.
[0047] A further aspect provides an electromagnetic flow meter
comprising:
[0048] a section of flow conduit;
[0049] an insert according to the first aspect or any of its preferred
features.
[0050] The insert may allow the electromagnetic flow meter to be
assembled reliably and efficiently.
[0051] A further aspect provides a method of manufacturing a flow
meter comprising:
[0052] inserting an insert into a flow conduit having a flow conduit
cross-section, wherein the insert comprises an inlet, a measuring
section with a measuring cross-section different to the flow conduit
cross-section and having at least two substantially parallel sides
over at least part of its length and an outlet;
[0053] back-potting the insert to support the insert within the
flow conduit.
[0054] In one embodiment, the insert comprises an insert according
to the first aspect or any of its is preferable features.
[0055] In one embodiment, the method further comprises providing
magnetic field generating means and/or electrodes in conjunction
with the insert. The magnetic field generating means and/or the
electrodes may be provided integrally with or separately from the
insert. The magnetic field generating means and the electrodes may
be provided within or outside the flow conduit.
[0056] The method may further comprise providing an electrostatic
screen in conjunction with the insert. The screen may be formed
integrally with the insert or may be coupled to the insert before
the insert is placed within the flow conduit.
[0057] The flow meter may be a wetted-type or a capacitive-type
flow meter.
[0058] In one embodiment, the insert is arranged within the flow
conduit so that a substantially uniform magnetic field is provided
across substantially the whole cross-sectional area of the measuring
section of the insert.
[0059] This feature may be provided, for example, by obscuring
from the fluid regions of the insert where the magnetic field is
not uniform, by providing a flow conduit shaped so that the magnetic
flux lines preferentially pass directly across the measuring section
(for example, using a substantially elliptical or substantially
rectangular flow conduit), or by providing an insert with a substantially
smaller cross-sectional area than the flow conduit.
[0060] A skilled person will appreciate that variations of detail
may be provided and features of one aspect may be applied to other
aspects within the scope of the invention as set out in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] Embodiments of the flow meter insert will now be described
with reference to the drawings in which:
[0062] FIG. 1 illustrates one embodiment of a flow meter insert;
[0063] FIG. 2 illustrates a further embodiment of an insert;
[0064] FIG. 3 is a schematic diagram of an insert according to
one embodiment inserted into a flow conduit;
[0065] FIG. 4 is a schematic cross-sectional diagram of a substantially
square section insert according to one embodiment;
[0066] FIG. 5 is a schematic cross-sectional diagram of a substantially
square section insert with infilled corner sections according to
a further embodiment;
[0067] FIG. 6a is a schematic cross-sectional diagram of an insert
positioned within a flow conduit of substantially elliptical cross-section
according to a further embodiment;
[0068] FIG. 6b is a schematic cross-sectional diagram of an insert
positioned within a flow conduit of substantially rectangular cross-section
according to a further embodiment;
[0069] FIG. 7 is a schematic cross-sectional diagram of an insert
according to a further embodiment.
DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS
[0070] The flow meter insert illustrated in FIG. 1 comprises an
inlet section 110 and an outlet section 112 of substantially circular
cross-section and a central measuring section 114 of substantially
square cross-section. The inlet 110 and outlet 112 sections of the
present embodiment are of a similar cross-sectional shape to that
of the flow conduit into which the insert is to be inserted, in
this case they are circular. The dimensions of the inlet 110 and
outlet 112 sections are such that these sections of the insert just
fit within the flow conduit. Ribs 122 124 maybe provided on the
outer surface of one or both of the inlet 110 and outlet 112 sections.
The ribs may provide rigidity to the insert and may enable the insert
to be fixed more securely to the fluid conduit.
[0071] The insert may further be provided with one or more flanges.
The insert of FIG. 1 comprises a flange 126 at one end of the insert.
In this embodiment, the flange 126 is formed integrally with the
insert, but, in an alternative embodiment, the flange may be coupled
to the insert. The flange may allow the insert to be anchored securely
to the flow conduit.
[0072] The measuring section 114 of the embodiment illustrated
in FIG. 1 has a generally square cross-section. However, the corners
of the square are rounded. This may allow the fluid to flow more
smoothly through the measuring section 114. In alternative embodiments,
the measuring section 114 may have a cross-section of a different
shape, for example the measuring section 114 may have a rectangular,
hexagonal or octagonal cross-section. The measuring section 114
may have any number of sides and may include curved portions, but
it is preferred if the section has at least two generally or substantially
parallel sides.
[0073] In the insert of FIG. 1 a transition region 120 is provided
between the inlet section 110 and the measuring section 114 and
between the measuring section 114 and the outlet section 112 so
that a smooth transition may be provided between the cross-sectional
shapes of the different sections. This may allow the fluid to flow
smoothly through the measuring section 114. In an alternative embodiment,
the transition region 120 may be provided only between the inlet
section 110 and the measuring section 114.
[0074] Connecting portions 116 118 may further be provided to
allow electrodes and/or magnetic-field-producing means to be provided
and operated to obtain a measurement of the fluid flow within the
flow meter insert measuring section 118.
[0075] FIG. 2 illustrates a further embodiment of a flow meter
insert in which magnetic field generating means 210 212 in this
case in the form of coils, are provided on the surface of the insert.
In alternative embodiments, the magnetic field generating means
may be provided on the inside of the insert or on the outside of
the flow conduit.
[0076] Electrodes, or connectors for electrodes 214 216 which
may be positioned within or outside the insert, are further provided
in the present embodiment. Positive and/or negative electrodes maybe
provided and a ground electrode may further be provided.
[0077] A further flange 218 is provided in the embodiment of FIG.
2. This flange 218 is detachable from the insert to allow the insert
to be placed within the flow conduit, as discussed in more detail
with reference to FIG. 3.
[0078] FIG. 3 illustrates an insert according to one embodiment
positioned within a flow conduit 310. In the present embodiment,
the insert is slid into the conduit and a flange 218 is coupled
to the insert to retain the insert in place within the conduit.
The flange 218 may also ensure that all of the fluid in the flow
conduit passes within the insert.
[0079] In the embodiment of FIG. 3 the flow conduit 310 further
comprises an outlet 312 which may be used to provide power to the
magnetic field generating means and to the electrodes within the
flow conduit 310 and may be used to allow readings to be obtained
from the equipment within the conduit.
[0080] On insertion into the flow conduit, the insert is preferably
back-potted to support the insert and stabilise it within the flow
conduit. Any suitable potting compound may be used, for example
epoxy resin or polyurethane.
[0081] The flow meter insert may be manufactured by injection moulding.
The insert may be manufactured from a plastics material, such as
ABS, from natural or synthetic rubber, or from another similar material.
[0082] An insert manufactured from materials that are less affected
by elevated temperatures or corrosive fluids (such as PTFE, PFA,
i.e. `Teflon` family) maybe manufactured from methods already used
by these industries (including machining, sintering, Transfer moulding,
rotational moulding etc). The methods of manufacture for these materials
is slightly different to `normal` plastics due to the viscoelastic
properties of these materials at their processing temperatures.
Other more conventional plastics that could be used for less demanding
specialist applications such as HDPE or PVDF could be manufactured
from more conventional techniques such as injection moulding.
[0083] A further, optional development of the embodiment of the
insert described above may be to arrange the insert so that a perfectly
uniform magnetic field is provided throughout the measuring section.
With reference to FIG. 4 the insert 414 of the embodiment described
above may be inserted into a cylindrical pipe or fluid flow conduit
412 with the magnetic return circuit being made with the pipe or
with a layer of silicon steel wrapped inside the pipe. As illustrated
in FIG. 4 at 410 the magnetic field within the insert may not be
uniform throughout the insert, in fact, in some embodiments, the
magnetic flux lines 416 may be facing in the wrong direction in
the corners of the measuring section 410. This is due to two factors:
firstly, the proximity of the return circuit 412 (the flow conduit
in FIG. 4) to the edge of the pole piece plate and secondly the
amount of room for the magnetic pole piece 418 and coil 420.
[0084] Having a non-uniform magnetic field throughout the insert
may have an adverse affect on the performance of the sensor or flow
meter. A number of developments may optionally be implemented to
improve this design problem.
[0085] As illustrated schematically in FIG. 5 the corners of the
insert 510 may be filled with material to make a flow measuring
section almost in the shape of a `Maltese cross`. This embodiment
may alleviate non-uniform field problem by ensuring that the fluid
only passes through the uniform field sections.
[0086] In an alternative embodiment, the shape of the pressure
containment vessel, for example the flow conduit, may be changed
so that the magnetic flux lines/field preferentially passes across
the measuring region rather than back to the return circuit. For
example, as shown in FIG. 6a, the vessel 610 may be implemented
in a substantially elliptical form or, as shown in FIG. 6b, the
vessel 612 may be implemented in a substantially rectangular or
square form.
[0087] In a further alternative embodiment, an example of which
is illustrated in FIG. 7 the diameter of the pressure containment
vessel 710 may be increased or the size of the measuring section
712 may be reduced so that the measuring section only falls within
the uniform field.
[0088] Alternative configurations of the insert and the pressure
containment vessel maybe implemented to keep the magnetic field
substantially uniform within the measuring section and such configurations
would be obvious to one skilled in the art.
[0089] The description above is provided by way of illustration
only and further modifications and variations of detail would be
possible to one skilled in the art. Each feature disclosed in this
specification (which term includes the claims) and/or shown in the
drawings may optionally be incorporated in the invention independently
of other disclosed and/or illustrated features. Statements in this
specification of the "objects of the invention" relate
to certain embodiments of the invention, but not necessarily to
all embodiments of the invention falling within the claims. |