U.S. patent application number 09/728021 was filed with the patent office on 2001-06-07 for magneto-inductive flowmeter.
Invention is credited to Willigen, Arnould Leendert van.
Application Number | 20010002553 09/728021 |
Document ID | / |
Family ID | 7931280 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010002553 |
Kind Code |
A1 |
Willigen, Arnould Leendert
van |
June 7, 2001 |
Magneto-inductive flowmeter
Abstract
A magneto-inductive flowmeter for measuring the flow rate of
fluids, incorporates a measuring tube, two magnetic poles
externally contacting the measuring tube, and two interconnected
return plates. Each magnetic pole includes a field coil and a
supporting plate-metal pole shoe. Each pole shoe is connected in
the area of the opening of the field coil supporting the associated
pole shoe with a return plate and features in the area outside the
opening of the field coil supporting the associated pole shoe, and
connecting to the same, sections which butt against the measuring
tube. For obtaining an easily manufacturable magneto-inductive
flowmeter in which the field coils can be precisely and securely
positioned and can be provided with a large number of windings, the
pole shoes are placed in the area of the opening of the field coil
supporting the associated pole shoe at a distance from the
measuring tube in that, in the area of the opening of the field
coil supporting the respective pole shoe, the pole shoes feature
sections which protrude into the opening of the field coil and
extend to the end of the opening, facing away from the measuring
tube, of the field coil supporting the associated pole shoe.
Inventors: |
Willigen, Arnould Leendert van;
(Rotterdam, NL) |
Correspondence
Address: |
John F. McKenna
Cesari and McKenna, LLP
88 Black Falcon Avenue
Boston
MA
02210
US
|
Family ID: |
7931280 |
Appl. No.: |
09/728021 |
Filed: |
December 1, 2000 |
Current U.S.
Class: |
73/861.12 |
Current CPC
Class: |
G01F 1/586 20130101 |
Class at
Publication: |
73/861.12 |
International
Class: |
G01F 001/58 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 1999 |
DE |
199 58 285.8 |
Claims
1. A magneto-inductive flowmeter for measuring the flow rate of
fluids, incorporating a measuring tube (1), two magnetic poles (2)
externally contacting the measuring tube (1), and two
interconnected return plates (3), where each magnetic pole (2)
includes a field coil (4) and a supporting plate-metal pole shoe
(5), each pole shoe (5) is connected in the opening of the
pole-shoe-supporting field coil (4) to a return plate (3) and
includes sections which extend outside the area of the opening of
the field coil (4) supporting the respective pole shoe (5) and are
in contact with the measuring tube (1), characterized in that, in
the area of the opening of the field coil (4) supporting the
associated pole shoe (5), the pole shoes (5) are positioned at a
distance from the measuring tube (1), said pole shoes (5) including
sections in the area of the opening of the field coil (4)
supporting the associated pole shoe (5) which protrude into the
opening of the field coil (4) and extend to the end of the opening
of the pole-shoe-supporting field coil (4) facing away from the
measuring tube (1).
2. The magneto-inductive flowmeter as in claim 1, characterized in
that, outside the area of the opening of the field coil (4), the
sections of the pole shoes (5) contacting the measuring tube (1)
transition into a section that is angled away from the measuring
tube (1).
3. The magneto-inductive flowmeter as in claim 2, characterized in
that the sections of the mutually opposite pole shoes (5) which are
angled away from the measuring tube (1) extend parallel to one
another.
4. The magneto-inductive flowmeter as in one of the claims 1 to 3,
characterized in that, at the end facing away from the measuring
tube (1), of the opening of the field coil (4) supporting the
respective pole shoe, the pole shoes (5) feature a section which
interconnects the sections that protrude into the opening of the
field coil (4) and extend to the end, facing away from the
measuring tube (1), of the area of the opening of the field coil
(4) supporting the associated pole shoe (5).
5. The magneto-inductive flowmeter as in one of the claims 1 to 4,
characterized in that the field coil (4) is saddle-shaped and
particularly adapted to match the curvature of the pole shoe (5)
butting against the measuring tube (1).
6. The magneto-inductive flowmeter as in one of the claims 1 to 5,
characterized in that the pole shoes (5) and the return plates (3)
consist of mutually different magnetizable materials.
7. The magneto-inductive flowmeter as in one of the claims 1 to 6,
characterized in that the return plates (3) peripherally surround
the magnetic poles (2) and the measuring tube (1).
Description
[0001] This invention relates to a magneto-inductive flowmeter for
measuring the flow of fluids, incorporating a measuring tube, two
magnetic poles externally contacting the measuring tube, and two
interconnected return plates, where each magnetic pole is provided
with a field coil supporting a sheet-metal pole shoe, each pole
shoe connects to a return plate at the open end of the field coil
supporting the respective pole shoe and each is provided on the
outside of, and extending from, the open end of the respective
field coil supporting the associated pole shoe with sections which
are in contact with the measuring tube. A flowmeter of this type
has been described earlier, for instance in the German patent
document DE 35 01 768 C2.
[0002] The underlying concept of a magneto-inductive flowmeter for
measuring the flow of a fluid, or medium, goes all the way back to
Faraday who in 1832 proposed to employ the principle of
electrodynamic induction for measuring flow rates. According to
Faraday's law of induction, a moving fluid that contains charge
carriers and flows through a magnetic field generates an electrical
field intensity perpendicular to the flow direction and
perpendicular to the magnetic field. A magneto-inductive flowmeter
employs this phenomenon by means of a magnet which, typically
consisting of two magnetic poles each associated with a field coil,
generates a magnetic field perpendicular to the direction of the
flow in the measuring tube. Within this magnetic field, each volume
element of the flowing medium that travels through the magnetic
field and contains a certain number of charge carriers,
contributes, by virtue of the field intensity generated in the
volume element concerned, to a measuring voltage that can be
collected by way of test electrodes. In prior-art magneto-inductive
flowmeters, the test electrodes are so designed as to be either
electrically or capacitively coupled to the flowing medium. Of
particular significance in magneto-inductive flowmeters is the
proportionality between the measuring voltage and the flow rate of
the medium as averaged over the cross section of the tube, i.e.
between the measuring voltage and the volume flow.
[0003] In the prior-art magneto-inductive flowmeter described
above, two mutually opposite pole shoes are in essentially full
contact with the measuring tube. Each of these pole shoes supports
a saddle-shaped field coil into the opening of which protrudes a
core section which extends all the way to, and rests against, the
pole shoe. These core sections are constituted of sheet-metal
segments integrally connected to the return plates which enclose
the entire assembly consisting of measuring tube, pole shoes and
field coils. The result is a compact magneto-inductive flowmeter
capable of producing a constant magnetic field sufficiently strong
for magneto-inductive flow-rate measurements, given that there are
virtually no air gaps between the pole shoe and the circumference
of the tube or in the area of the the core sections which gaps
might interfere with the magnetic flux.
[0004] However, that prior-art design has a number of drawbacks.
For example, producing such conventional magneto-inductive
flowmeters is a complex process insofar as it is necessary during
the assembly of the individual components of the magneto-inductive
flowmeter to mount the field coils on the pole shoes which
completely hug the measuring tube, leaving no possibility for the
localized attachment of the field coil. Moreover, the core sections
which form an integral part of the return plates are mounted on the
pole shoe in a recess provided in the return plates, meaning that
the opening of the respective field coil which determines the size
of the recess must be of a diameter large enough to allow access to
the bottom of the recess for a mounting tool, for instance a spot
welder or a riveter. This also severely limits the number of
windings of the field coil, given that in view of these mounting
requirements, the field coil cannot be of as small a diameter as
might be desirable.
[0005] It is the objective of this invention to introduce a
magneto-inductive flowmeter which is easy to manufacture and which
can accommodate a large field coil with many windings.
[0006] The magneto-inductive flowmeter according to this invention,
designed to solve the above-mentioned problem, is characterized in
that the pole shoes, located in the open-end area of the field coil
supporting the pole shoe concerned, are positioned at a distance
from the measuring tube in such fashion that, in the area of the
opening of the field coil supporting the individual pole shoes, the
pole shoes are provided with sections which protrude into the field
coil and extend to the far end of the opening of the
pole-shoe-supporting field coil away from the measuring tube. This
invention thus makes it possible to attach a radially configured
return plate to the pole shoe outside the field coil, providing
sufficient accessibility for practically any type of mounting tool.
Obviating the need for recess mounting eliminates the minimum size
restrictions for the diameter of the field coil so that even field
coils with a very small diameter can be employed. By the same
token, a field coil with a smaller inner diameter can accommodate a
larger number of windings which permit the generation of a larger
magnetic field. Moreover, the pole-shoe sections positioned at a
distance from the measuring tube and protruding into the field-coil
opening allow for a simple and secure placement of the field coil
during the assembly of the individual components of the
magneto-inductive flowmeter according to this invention.
[0007] In a preferred design enhancement of the magneto-inductive
flowmeter according to this invention, the sections of each pole
shoe located outside the opening of the field coil and contacting
the measuring tube connect to a section angled away from the
measuring tube. This pole-shoe configuration offers a number of
advantages: The sections angled away from the measuring tube add
support and stabilization to the field coils which substantially
facilitates the positioning of the field coils during the assembly
process of the magneto-inductive flowmeter. Also, the sections
angled away from the measuring tube define the direction of the
magnetic field in the area near the electrodes. Indeed, if in a
further, preferred design enhancement of this invention, the
sections of the mutually opposite pole shoes, angled away from the
measuring tube, are lined up parallel to one another, it is
possible to obtain particularly good homogeneity of the magnetic
field generated by the field coils over a very wide range and
essentially throughout the cross section of the measuring tube.
Finally, the sections angled away from the measuring tube
electrically shield the electrodes, and thus the measuring voltage
collected from the electrodes, from the coil signal. This, in turn,
further improves the signal-to-noise ratio of the measuring voltage
collected in the magneto-inductive flowmeter according to the
invention.
[0008] In another, preferred design enhancement of the
magneto-inductive flowmeter according to this invention, the pole
shoes are provided, at the end of the opening of the pole-shoe
supporting field coil away from the measuring tube, with a
pole-shoe section which interconnects the pole-shoe sections that
protrude into the field-coil opening and extend to the end of the
opening, facing away from the measuring tube, of the field coil
supporting the respective pole shoe. This allows the pole shoe to
be produced as a single unit which substantially improves its
stability. It also permits planar contact between the return plate
and the pole-shoe section which, in turn, simplifies the connection
of the return plates with the pole shoe.
[0009] In another preferred design enhancement according to this
invention, the field coil is saddle-shaped. This allows the field
coil to match the curvature of the pole shoe contacting the
measuring tube.
[0010] In a preferred design enhancement according to this
invention, the magneto-inductive flowmeter can be provided with
certain application-specific properties by producing the pole shoes
and the return plates from mutually different magnetizable
materials.
[0011] Finally, in a preferred design enhancement of the
magneto-inductive flowmeter according to this invention, the return
plates surround the magnetic poles and the measuring tube in
peripheral fashion.
[0012] There are numerous ways in which the magneto-inductive
flowmeter according to this invention can be configured and further
enhanced. In this context, reference is made to the dependent
patent claims and to the following detailed description of
preferred embodiments of this invention with the aid of the
drawings in which:
[0013] FIG. 1 is a schematic, cross-sectional view of a
magneto-inductive flowmeter according to a first invention
embodiment;
[0014] FIG. 2 is a schematic, cross-sectional view of a
magneto-inductive flowmeter according to a second invention
embodiment; and
[0015] FIG. 3 is a schematic, cross-sectional view of a
magneto-inductive flowmeter according to a third invention
embodiment.
[0016] A magneto-inductive flowmeter according to a first invention
embodiment is illustrated in FIG. 1. In this case, two mutually
opposite magnetic poles 2 are in external contact with the
measuring tube 1 through which flows the medium whose flow rate is
to be measured. This assembly of measuring tube 1 and magnetic
poles 2 is surrounded and fully enclosed by two return plates 3,
each slipped over the assembly on the side of a corresponding
magnetic pole 2, and both laterally overlapping and mutually
connected. For connecting the two return plates 3, simple clamping
may suffice; preferably, however, the return plates 3 are welded
together--ideally spot-welded--or riveted together. The thickness
of the return plates is typically about 1 mm.
[0017] Each magnetic pole includes a field coil 4 and a pole shoe
5. The pole shoes 5 are also made from plate metal, typically 1 mm
thick and they include sections which firmly butt against the
measuring tube 1 and match the outer curvature of the latter.
However, in the area of the opening of the field coil 4, the pole
shoes 5 are positioned at a distance from the measuring tube 1. As
can be seen in FIG. 1, sections of the pole shoes 5 protrude into
the openings of the field coils 4, extending all the way to the end
of the opening of the field coil 4 facing away from the measuring
tube 1, and transitioning into a pole-shoe section which
interconnects these through-sections. In the first preferred
embodiment, this interconnecting pole-shoe section which extends
more or less tangentially relative to the measuring tube 1 is used
for attaching the pole shoe 5 to its associated return plate 3.
[0018] As can also be seen in FIG. 1, the area in which the return
plate 3 is to be connected to the pole shoe 5 is fully accessible,
with no restrictions relative to the size or shape of a mounting
tool such as a riveter or spot welder. In this first preferred
embodiment of the invention, the electrodes 6 are capacitively
coupled to the flowing medium. In the direction of the electrodes
6, the sections of the pole shoes 5 contacting the measuring tube 1
transition into sections which are angled away from the measuring
tube 1. FIG. 1 clearly shows that by virtue of the sections of the
pole shoes 5 protruding into the opening of the field coil 4 and,
respectively, the sections angled away from the measuring tube 1,
it is possible to precisely position and align the field coils 4,
which significantly facilitates the assembly process of the various
components of the magneto-inductive flowmeter according to the
first preferred embodiment of this invention.
[0019] The sections of the mutually opposite pole shoes 5 which are
angled away from the measuring tube 1 extend parallel to one
another. As a result, there is particularly good homogeneity of the
magnetic field generated by the two mutually opposite magnetic
poles 2 even in the fringe area and thus throughout the cross
section of the measuring tube 1. In addition, the sections that are
angled away from the measuring tube 1 provide for an electrical
shielding of the coil signal from the measuring voltage collected
from the electrodes 6 which results in an improved signal-to-noise
ratio.
[0020] FIG. 2 is a schematic, cross-sectional illustration of a
magneto-inductive flowmeter according to a second preferred
embodiment of this invention. In contrast to the first preferred
embodiment depicted in FIG. 1, the magneto-inductive flowmeter in
the second preferred embodiment of this invention does not include
a pole-shoe section that interconnects the sections of a pole shoe
5 that protrude into the opening of the field coil 4. Instead, it
is provided with a block-shaped spacer 7 consisting of a
non-magnetizable material. In this case, the pole shoe 5 is
attached to the return plate 3 by spot welding since there is not
enough room for riveting.
[0021] FIG. 2 also shows that, in contrast to the first preferred
embodiment of this invention as illustrated in FIG. 1, where the
sections of the pole shoe 5 which protrude into the opening of the
field coil 4 are located at a distance from the field coil 4, the
field coil 4 itself can extend directly to the sections which
protrude into the opening of the field coil 4. This fully utilizes
the space available for the field coil 4 which allows for a maximum
number of windings. FIG. 2 further indicates schematically that it
is possible to use electrodes 8 which are electrically coupled to
the medium flowing through the measuring tube 1, in lieu of the
electrodes 6 which are capacitively coupled to the flowing
medium.
[0022] Finally, FIG. 3 is a schematic, cross-sectional illustration
of a magneto-inductive flowmeter according to a third preferred
embodiment of this invention. As one particular feature of this
embodiment, the return plates 3 are not slipped over the assembly
on the sides corresponding to the two mutually opposite magnetic
poles 2 but are instead offset by 90.degree. relative to the
former. The ends of the return plates 3 thus meet the sections of
the pole shoe 5 protruding into the opening of the field coil 4, at
which point they are spot-welded to the pole shoes 5. This
configuration of the return plates 3 may be more advantageous for
certain installation layouts.
* * * * *