Abstrict An inductive flow meter has a measurement channel body with an
electrically insulating inner wall and defining a flow channel that
extends along a longitudinal axis. A pair of electrodes is exposed
to said flow channel at its inner wall so as to be in contact with
a medium flowing within said channel, and are diametrically opposed
to each other in a transverse plane perpendicular to the longitudinal
axis. A pair of magnetic pole shoes of a magnetic field generating
system is arranged on opposite sides of the measurement channel
body and centered about the transverse plane containing the electrodes,
with the shoes adapted to generate a magnetic field across the flow
channel section, such that lines of the magnetic field extend essentially
perpendicular to both the longitudinal axis and a straight line
between the electrodes. Two associated, electrically conductive
signal lines extend between the electrodes and associated connector
lugs on an outer surface of the measurement channel body. One of
the signal lines extends directly radially between its associated
electrode and connector lug, and the other of the signal lines is
arranged with such symmetry with respect to a point mid-way between
the electrodes that inductive effects in its opposite portions cancel
each other out. In some embodiments, the signal lines and electrodes
arranged symmetrically with respect to the transverse plane containing
the electrodes and about which the pole shoes are centered.
Claims What is claimed is:
1. An inductive flow meter comprising:
a measurement channel body having an electrically insulating inner
wall and defining a flow channel that extends along a longitudinal
axis;
a pair of electrodes exposed to said flow channel at said inner
wall and in contact with a medium flowing within said flow channel,
the electrodes diametrically opposed to each other in a transverse
plane perpendicular to said longitudinal axis;
a pair of magnetic pole shoes arranged on opposite sides of said
measurement channel body and centered about said transverse plane
containing the electrodes, the shoes configured to generate a magnetic
field across the flow channel section, such that lines of the magnetic
field extend essentially perpendicular to both said longitudinal
axis and a straight line between the electrodes;
a pair of associated, electrically conductive signal lines extending
between the electrodes and associated connector lugs on an outer
surface of the measurement channel body;
the signal lines and electrodes arranged symmetrically about said
transverse plane containing the electrodes and about which the pole
shoes are centered; and
wherein at least one of the pole pieces has two sections extending
into corresponding recesses in the measurement channel body on either
side of the transverse plane.
2. The inductive flow meter of claim 1 wherein the signal lines
comprise flat conductor strips oriented to have their broad sides
substantially parallel to the magnetic field lines.
3. The inductive flow meter of claim 1 wherein the signal lines
comprise stamped sections of conductive foil or sheet metal.
4. The inductive flow meter recited in claim 1 wherein one of
the signal lines extends radially between its electrodes and connector
lug, another of the signal lines forming at least two electrically
parallel electrical paths between its associated electrode and connector
lug.
5. The inductive flow meter of claim 4 wherein the two electrically
parallel electrical paths together encircle the flow channel.
6. The inductive flow meter of claim 1 wherein the signal lines
are integrally formed with their associated electrodes of a common
conductive material.
7. The inductive flow meter of claim 1 wherein the signal lines
are permanently embedded within material of the channel body.
8. The inductive flow meter of claim 1 wherein the channel body
comprises two sections joined at said transverse plane, with the
electrodes and signal lines disposed within corresponding recesses
formed in one of the two sections of the channel body.
9. The inductive flow meter of claim 1 wherein the channel body
is an injection-molded part in which the electrodes and signal lines
are insert-molded.
10. The inductive flow meter of claim 9 wherein at least one of
the signal lines is provided with an extension projecting beyond
the outer surface of the channel body for retaining the signal line
as the channel body is molded.
11. The inductive flow meter of claim 1 wherein the connector
lug of said one of the signal lines is U-shaped and extends about
the connector lug of the other of the signal lines.
12. The inductive flow meter of claim 11 wherein one of the signal
lines and its associated connector lug together form a short-circuiting
ring about the other of the signal lines and its associated connector
lug.
13. An inductive flow meter comprising:
a measurement channel body having an electrically insulating inner
wall and defining a flow channel that extends along a longitudinal
axis;
a pair of electrodes exposed to said flow channel at said inner
wall and in contact with a medium flowing within said flow channel,
the electrodes diametrically opposed to each other in a transverse
plane perpendicular to said longitudinal axis;
a pair of magnetic pole shoes arranged on opposite sides of said
measurement channel body and centered about said transverse plane
containing the electrodes, at least one of the pole shoes having
two sections extending into corresponding recesses in the measurement
channel body on either side of the transverse plane, the shoes configured
to generate a magnetic field across the flow channel section, such
that lines of the magnetic field extend essentially perpendicular
to both said longitudinal axis and a straight line between the electrodes;
a pair of associated, electrically conductive signal lines extending
between the electrodes and associated connector lugs on an outer
surface of the measurement channel body, the signal lines comprising
flat conductor strips oriented to have their broad sides substantially
parallel to the magnetic field lines;
the signal lines and electrodes arranged symmetrically about said
transverse plane containing the electrodes and about which the pole
shoes are centered.
Description BACKGROUND OF THE INVENTION
The present invention relates to inductive flow meters.
Practitioners skilled in this art are familiar with the type of
inductive flow meter having a flow channel section that is defined
by an electrically insulating inside wall, with the flow channel
section containing two electrodes that are diametrically opposed
across a cross-section of the flow channel section and exposed to
the flow medium that is under investigation. Insulated measurement
signal lines are connected to the electrodes, and a magnetic field
generating system that is situated outside the flow channel section
is used to generate a magnetic field that passes through the flow
channel section in the vicinity of the cross-section referred to
above, which contains the electrodes. This magnetic field is essentially
perpendicular to a connecting line between the electrodes and is
perpendicular to the longitudinal axis of the flow channel section,
being established between the pole shoes of the magnetic field generating
system that are arranged on opposing sides of the flow channel section.
The field windings of the magnetic field generating system can be
energized either with direct current or with alternating current,
and a measurement signal that is a function of the flow of an electrically
conductive medium within the flow channel section (a DC voltage
signal or an AC signal, depending on the manner in which the exciter
winding of the magnetic field generating system has been energized)
can be tapped off. Inductive flow meters of this general design
and their method of operation are familiar to the practitioner skilled
in the art.
For example, DE-OS 1 773 484 shows a measurement channel body containing
the flow channel section manufactured from plastic, with the electrodes
and the measurement signal lines that lead to them insert-molded.
This results in a defined position of the electrodes and the measurement
signal lines relative to the flow channel and reduces the costs
associated with calibrating and adjusting operations for the production
of large numbers of such a device.
U.S. Pat. No. 4428241 shows measurement signal lines that lead
to the electrodes of a flow meter of the general type in question,
arranged on a circuit board like a printed circuit. The circuit
board is held by special retaining devices in a defined position
relative to the magnetic field generating system of the flow meter,
with the circuit board situated adjacent to a measurement channel
body that contains the flow channel section, and a pole of the magnetic
field generating system passing through an opening in the circuit
board.
Publication DE-OS 3 401 377 shows and describes an inductive flow
meter of the general type described above, in which the electrodes
that are exposed to the flow medium are embedded in the wall of
a flow channel body that contains the flow channel section. Measurement
signal lines are routed from the flow channel body through peripheral
and axial grooves in the pole shoe arrangement of the magnetic field
generating system. However, these measurement signal lines are not
held in a fixed position within narrow limits, either by the measurement
channel body or by the magnetic field generating system.
SUMMARY OF THE INVENTION
It is the task of the present invention to create an inductive
flow meter of the type described in the introduction hereto, which
lends itself to large-scale production, is of comparatively simple
construction that ensures a high level of mechanical strength, and
permits precise mounting of its parts, the construction of which
reduces the expenditures that are associated with equalizing and
adjusting operations performed during serial production.
According to one aspect of the invention, an inductive flow meter
has a measurement channel body that incorporates a flow channel
section with an electrically insulating inner wall, and two electrodes
that are diametrically opposed to each other across a cross-section
of the flow channel and exposed to the medium that is under investigation.
The electrodes are enclosed in the measurement channel body in the
same way as insulated measurement signal lines that lead to the
electrodes and the connecting points to the electrodes. A magnetic
field generating system establishes a magnetic field that passes
through the flow channel section in the area of said cross-section,
which is essentially perpendicular to the connecting line between
the electrodes and perpendicular to the longitudinal axis of the
flow channel section. The magnetic field is established between
pole shoes of the magnetic field generating system, said pole shoes
being arranged on opposing sides of the measurement channel body.
The measurement signal lines are stamped out blanks of conductive
foil or conductive sheet metal.
In some embodiments, the measurement signal lines are formed from
electrode material, and the electrodes are connected in one piece
to the measurement signal lines and form part of the stamped out
conductive foil blanks or the conductive sheet metal blanks.
In some cases, the measurement signal lines are formed as conductor
strips that are embedded in the measurement channel body, with their
wide dimension oriented so as to be essentially parallel to the
magnetic field generated by the magnetic field generating system.
In some embodiments, the measurement channel body is divided in
its cross-section plane that contains the electrodes and is formed
from two shaped bodies that can be combined. The electrodes, the
measurement signal lines, and their connection points to the electrodes
are sealed into matching recesses on the parting line.
In some embodiments, the measurement channel body is an injection-molded
part in which the electrodes, the measurement signal lines, and
their collection points to the electrodes are cast, at least in
part.
In some embodiments, the electrodes and/or the measurement signal
lines are provided with extensions that project beyond the outer
surface of the measurement channel body, these extensions being
intended for insertion into the core print of the injection mould
during production of the measurement channel body.
In some embodiments, the measurement signal line that leads to
the electrode on one side of the measurement channel body passes
through the measurement channel body wall directly in a radial direction,
whereas the measurement signal lines that lead to the other electrode
incorporate measurement signal lines sections that are symmetrical
to the magnetic field of the magnetic field generating system and
to the cross section plane that contains the electrodes.
In some embodiments, the measurement signal lines sections within
the measurement channel body incorporate axially routed line sections
that run upstream and downstream between cross section planes from
the cross section area of the measurement channel body that is occupied
by the magnetic field generating system and/or from such cross section
areas to the cross-section area of the measurement channel body
that contains the electrodes.
In some instances, at least one of the axially routed long pieces
of the measurement signal lines sections runs in an axial rail-like
rib of the wall of the measurement channel body.
In some cases, the measurement channel body and/or on pole shoe
elements of the pole shoes of the magnetic field generating system
that lie against this from the outside there are recesses and/or
projections that are of a matching shape for securing the relative
positions of the magnetic field generating system and of the measurement
channel body.
In some embodiments, the measurement channel body incorporates
recesses on its side walls that are adjacent the pole shoes and
opposite each other. The recesses match the shape of the particular
pole shoe and accommodate the pole shoe elements that are near the
flow channel cross-section in such a way that at least in some areas
the pole shoe surfaces that face each other are separated from the
flow channel section wall by measurement channel body material that
is of reduced thickness.
In some cases, the recesses in the side walls of the measurement
channel body incorporate at least one axial, rail-like or radial
curved rib that is of measurement channel body material, this rib
containing a measurement signal line section and being situated
in an appropriately shaped axial or radial recess or break in a
pole shoe element or the pole shoe element receptacle.
The individual structural groups or structural units of the inductive
flow meter proposed herein permit large-scale production and extremely
low production costs. The calibration parameters can be determined
by a random sampling procedure for each manufacturing lot, so that
it is not necessary to calibrate each device individually.
Operation when energizing the exciter windings of the magnetic
field generating system with high frequencies of up to 200 Hz permits
the solution of special control tasks when using an inductive flow
meter of the type described above.
Cost-intensive equalising and adjusting operations can for the
most part be eliminated, and the apparatus will maintain a stable
zero point throughout its complete operating time.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will be described in greater
detail below on the basis of the drawings appended hereto. These
drawings show the following:
FIG. 1 is a diagrammatic perspective view of a measurement channel
body with embedded electrodes and measurement signal lines.
FIG. 2 is a radial cross section through the arrangement shown
in FIG. 1 in a cross-sectional area of the measurement channel
body that contains the electrodes.
FIG. 3 is a perspective, diagrammatic view of a partially cross-sectioned
measurement channel body, showing the electrodes and measurement
signal lines that are embedded in the walls of the measurement channel
body.
FIG. 4 shows another version of the electrodes and the measurement
signal lines, with the surrounding material of the measurement channel
body omitted.
FIG. 5 is a perspective view of yet another configuration of the
electrodes and the measurement signal lines, with the surrounding
material of the measurement channel body omitted.
FIG. 6 is a diagrammatic perspective view, as in FIG. 1 of a second
preferred version of the measurement channel body, and of pole-shoe
elements of a magnetic field generating system that are to be embedded
in recesses in the measurement channel body, to form an inductive
flow meter of the type proposed herein.
FIG. 7 is a view, similar to the one shown in FIG. 6 of a third
version of a measurement channel body with the pole shoe elements
that are to be inserted in recesses in the measurement channel body
to form another inductive flow meter of the type described herein.
DETAILED DESCRIPTION OF EMBODIMENTS
FIG. 1 shows a measurement channel body 1 in the form of a section
of tube that is essentially hollow and cylindrical and which is
formed as an injection-molded plastic part.
The section of tube defines a flow channel 2 through which the
flow of an electrically conductive medium that is under investigation
is directed by way of suitable connections or connectors. On the
electrically insulating inside wall of the flow channel section
2 of the measurement channel body 1 there are diametrically opposed
electrodes 3 and 4 (as shown in FIG. 2), and these electrodes are
exposed to the flow medium. Insulated measurement signal lines 5
and 6 are routed to the electrodes through the material of the measurement
channel body 1 with the measurement signal line 5 only bridging
the short distance between the electrode 3 on the side of the inside
wall of the flow channel section 2 and the measurement channel body
outside wall, whereas the two semicircular sections of the measurement
signal line 6 form the connection of the side of the electrode 4
to the diametrically opposite side of the measurement channel body.
The connections for the measurement signal lines 5 and 6 are in
the form of connector lugs 7 and 8 which protrude from the cylindrical
outside wall of the measurement channel body 1. Connector lug 8
encloses the connector lug 7 in a U-shape and, together with the
associated measurement signal line sections 6 forms a short-circuiting
ring that, as will be understood, permits interference-free signal
transmission between the electrode 4 and the side of the measurement
channel body side on which the electrode 3 is situated.
Mounting sockets 110 are molded onto the upper side and the lower
side of the measurement channel body 1 and these incorporate angled
recesses such that, in diametrically opposed areas of the cylindrical
outside surface of measurement channel body 1 in a direction that
is perpendicular to the connecting line 150 between electrodes 3
and 4 and perpendicular to the longitudinal axis of the flow channel
section 2 as viewed in the radial direction, there are rectangular
guide spaces into which the pole shoe elements 15 and 16 of the
magnetic field generating system are fitted. The pole shoe elements
15 and 16 are thus held in a precise position relative to flow channel
2 of measurement channel body 1 as well as in a precise position
relative to electrodes 3 and 4 and their associated measurement
signal lines 5 and 6 by sockets 110 once the electrodes and the
measurement signal lines have been installed securely in measurement
channel body 1.
This precision of the elements of the magnetic field generating
system, of the measurement channel body, and of the electrodes and
the measurement signal lines results not only from the precise assembly
of the parts relative to each other, but also from the type and
manner of the production of the measurement channel body as an injection-molded
part (or the fact that it is produced from injection molded parts),
and also from the solid inclusion of the electrical conductors therein.
At this point it should be noted that in the embodiment that is
shown in FIGS. 1 and 2 and in the embodiments that are shown and
described subsequently, the measurement channel body 1 is in the
form of a unified injection-molded part into which the electrodes
and the measurement signal lines have been insert-molded. Alternatively,
it is possible to make the measurement channel body 1 in two injection-molded
parts that are divided on a radial plane and which can be joined,
the parting line being provided with recesses 160 in the range of
the wall thickness of the measurement channel body 1 in such a way
that suitably shaped structural units comprising the electrodes
and the measurement signal lines that are connected rigidly thereto
are installed in these recesses, and then the injection-molded parts
are clamped together to form a unit that is easily manipulated and
comprises the measurement channel body, the electrodes, and the
measurement signal lines.
It is, however, preferred that the electrodes and the measurement
signal lines be cast into the measurement channel body 1 that is
in the form of an injection-molded part, since during production,
the measurement signal lines and the electrodes that are rigidly
connected thereto are inserted into the core point of the injection
mold in an exact position relative to the mold space and are kept
in this position once the measurement channel body has been removed
from the mold. Extensions of the conductors, such as the unattached
ends of the electrodes 3 and 4 the connectors 7 and 8 and additional
extensions (such as 112 in FIG. 2) can be used as core point support.
In another embodiment not shown in the drawings, tubular inserts
(of, for instance, ceramic or a reinforcing material) are molded
or cast in measurement channel body 1.
The routing of the measurement signal lines does not necessarily
have to be confined to a radial plane that contains electrodes 3
and 4 particularly if measurement channel body 1 is a uniform injection-molded
part. The diagrammatic perspective view shown in FIG. 3 indicates
one possible routing. The short measurement signal line section
5 runs from the connector 7 directly through the wall of the measurement
channel body 1 to the electrode 3. Immediately adjacent to this,
a measurement signal line section 6 runs from the connector 8 as
far as the middle of the wall of the measurement channel body 1
where it turns in the axial direction and proceeds along an axial
section that is longer than the axial extent of the pole shoe element
(not shown in FIG. 3) in this same direction, and then turns into
a 90.degree. curved section that ends at about the uppermost point
of the measurement channel body 1 where it joins a longitudinal
portion of line section 6 that extends in the opposite axial direction
relative to the axial section adjacent to the connector. The axial
length of this longitudinal portion of line section 6 is greater
than the total axial extent of the pole shoe elements of the magnetic
field generating system. Finally, there is another arc shaped section
that extends downwards through 90.degree.. This is followed by an
axial line section and finally by a line section of the measurement
signal line section 6 that is directed radially inwards to electrode
4. The routing of the measurement signal lines for electrode 4
as shown in FIG. 3 provides a specific symmetry to the radial plane
that contains electrodes 3 and 4 and to the magnetic field that
passes through flow channel section 2 with only the longitudinal
conductor section that connects the 90.degree. curved sections being
affected by the magnetic field lines. The signal line passes through
two identical parts of the magnetic field with opposite orientation,
so that inductive effects in the two parts cancel each other out.
FIG. 4 shows a further development of the arrangement of conductors
that is associated with electrodes 3 and 4. In addition to signal
line section 6 (as shown in FIG. 3) there is an additional signal
line section 152 forming a mirror image of line section 6 associated
with electrode 4 as the practitioner skilled in the art can recognize
in FIG. 4. As viewed in an axial direction, the four quarter-circle
curved sections of the measurement signal line section 6 combine
to form a short-circuiting ring 6 associated with electrode 4 and
completed by the U-shaped connector 8 that encloses connector 7.
FIG. 5 illustrates another arrangement of measurement signal line
sections 6 forming a short-circuiting ring associated with electrode
4 in conjunction with U-shaped connector 8. The short circuiting
ring formed from the measurement signal line sections 6 of FIG.
5 encloses the magnetic field oriented perpendicular to both connecting
line 150 between electrodes 3 and 4 and the longitudinal axis 154
of flow channel section 2.
The following should be noted with respect to the configuration
of the structural elements that are cast, in particular injection-molded,
into the measurement channel body, namely, the electrodes 3 and
4 the measurement signal lines 5 and 6 and the connectors 7 and
8:
In some cases, it may be useful to manufacture electrodes 3 and
4 from a special electrode material, if necessary one that is matched
to the flow medium under investigation, and then connect these electrodes
to the associated measurement signal lines by welding, soldering,
or the like.
According to a preferred embodiment, however, the measurement signal
lines and the associated connectors are of one and the same material
as the electrodes 3 and 4 namely an electrode material, and are
connected to their respective electrodes 3 and 4 at one piece. In
this case, it is possible to configure the electrodes, the measurement
signal lines, and the connectors as stamped sheet metal conductors
or stamped foil conductors that are shaped, for example, as shown
in FIG. 2 or else can be bent to form the shapes that are shown
in FIGS. 3 and 5 so that the conductor system can be inserted into
an injection mold and then the measurement channel body material
molded around them. The production of the electrodes, the measurement
signal lines that are connected to them in one piece, and the connectors
that lead out of the measurement channel body, as stamped foil parts
or sheet metal parts results in properties of the associated electrical
system that remain constant over a large series of devices that
are to be manufactured, in particular from the electrical standpoint
and in conjunction with the magnetic field generating system.
FIG. 6 shows another special configuration in which measurement
channel body 1 is fixed relative to the magnetic field generation
generating system, the pole shoes 15 and 16 of which being shown
in an exploded view in FIG. 6 radially separated from measurement
channel body 1. On the side of measurement channel body 1 there
is a symmetrically shaped recess 9 in the shape of a hollow cylindrical
sector, and on the underside of the measurement channel there is
a corresponding, diametrically opposed and similar cylindrical recess
10. The cylindrical recesses 9 and 10 each consist of two axial
sections. In other words, at their axial mid-points, each recess
9 and 10 contains an annular rib 11 12. The importance of this
rib will be discussed in greater detail below. The depth of the
recesses 9 and 10 is so selected that the bottoms of the recesses
remain separated from the flow channel section of the measurement
channel body 2 by wall sections, of sufficient strength, of the
measurement channel body material.
Elements of the pole shoes 15 or 16 of the magnetic field generating
system of the flow meter are inserted into recesses 9 and 10 in
a radial direction towards the longitudinal axis of the flow channel
section. In the embodiment shown in FIG. 6 the pole shoes 15 and
16 the cores that are connected also no piece with them and wound
about by the field windings of the magnetic field generating system,
and the yoke elements that are connected to these to complete the
magnetic closing circuit, consist of three axially adjacent groups
of transformer plates, namely two groups forming the pole shoe elements
that extend when assembled into the axial sections of recesses 9
and 10 and an interposed group of plates that are cut back more
towards the outside, in the radial direction, such that between
the outermost groups of metal plates of pole shoes 15 and 16 there
are corresponding annular grooves that accommodate annular ribs
11 and 12.
The recesses 9 and 10 and the elements of pole shoes 15 and 16
that fit into them result in precise positioning of the magnetic
field generating system and of the measurement channel body 1 when
assembled, such that no equalising and adjustment operations are
needed with respect to these structural units. In addition, when
assembled, the pole shoe surfaces are pressed against the thin bases
of the recesses 9 and 10 and thus support these thin-walled areas
against any increased internal pressure within flow channel section
2. The thin-walled sections permit closer spacing between the pole
shoe surfaces and thus an increase of the overall efficiency of
the device. The energy consumption for energizing the magnetic field
generating system can be reduced to the extent that ensures compliance
with safety regulations regarding explosions.
Measurement signal line sections 6 are embedded in annular ribs
11 and 12 of measurement channel body 1 which is formed as a plastic
injection-molded element.
In a modified embodiment of the inductive flow meter shown in FIG.
6 as shown in FIG. 7 the upper cylindrical recess 9 of measurement
channel body 1 incorporates an axial rail-like rib 20 and the surface
of pole shoe 15 that fits into recess 9 incorporates a corresponding
axial groove 21 that accommodates rib 20 when the pole shoe 15 is
displaced radially towards the longitudinal axis of flow channel
section 2 and the pole shoe elements fit into recess 9. On the
opposite side, there is a recess 10 in the wall of measurement channel
body 1 that is not divided by a rib, and thus there is no groove
in the pole shoe 16 that is to be slid into recess 10.
Also, in the embodiment of FIG. 7 the pole shoes, the cores that
are connected in one piece with them and wound about by the excitement
winding, and, the yoke elements that are connected to them to complete
the magnetic return flow, consist of groups of transformer plates.
The electrode 3 that is located on the inside of measurement channel
body 1 is connected directly to connector 7 by an insulated measurement
signal line, extending through the wall of the measurement channel
body. In contrast to this, the connection between electrode 4 and
connector 8 that ensures the symmetrical positions of the signal
lines sections relative to the magnetic field of the magnetic field
generating system is routed as described in connection with FIG.
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