Abstrict An electromagnetic flow meter consists of a metering tube made
of an electrically non-conductive material and having a thick outer
wall. The tube has at least two measuring electrodes and at least
two magnetic poles, each of which is disposed in a blind bore of
the tube. The poles are linked to one another by a yoke fitted with
a magnetic coil. To achieve greater measuring precision both the
yoke and the magnetic coils are mounted in a recess inside the outer
surface of the metering tube. The recesses are in the form of through
holes and grooves. When fully assembled all magnet components are
disposed inside the outer surface of the metering tube.
Claims What is claimed is:
1. An electromagnetic flow meter comprising a metering tube having
an axially extending flow-through bore and a relatively thick wall
surrounding the bore terminating at and defining an exterior surface
of the tube, the tube including first and second blind openings
extending from the exterior surface into the tube and terminating
proximate the flow-through bore, a passage way generally parallel
to and spaced from the blind openings, extending through the tube
and terminating at the exterior surface, and open grooves formed
in the exterior surface of the tube and in communication with ends
of the blind openings and ends of the passage way, the blind openings,
the passage way and the open grooves being prefabricated from an
electrically non-conductive material, first and second magnetic
pole pieces disposed in the blink openings, a yoke interconnecting
the pole pieces and disposed in the passage way and the open grooves,
a magnetic coil operatively connected with the yoke an disposed
in at least one of the passage way and the grooves, and at least
two measuring electrodes operatively positioned in the metering
tube relative to the flow-through bore.
2. A flowmeter according to claim 1 wherein the yoke includes
a midsection which carries the magnetic coil (10) and the passage
way comprises a through hole (5) which extends parallel to the blind
openings (4) for the magnetic pole pieces (7), the yoke including
intermediate sections (9) which connect the midsection with the
magnetic pole pieces (7), the intermediate sections being disposed
in the open grooves (6).
3. A flowmeter according to claim 1 wherein the metering tube
(1) has a plurality of passage ways which are parallel to the blind
openings (4) that receive the magnetic pole pieces (7).
4. A flowmeter according to claim 1 wherein the yoke includes
a midsection (12) which carries the magnetic coil (10) and wherein
the passage way is a semicircularly-shaped open trough in the exterior
surface of the tube which includes the open grooves and connects
with the blind openings (4).
5. A flowmeter according to claim 1 including parallel arcuate
yokes (14) which connect the magnetic pole pieces (7).
6. A flowmeter according to claim 1 wherein the tube includes
a plurality of successive passage ways and open grooves, the yoke
is shaped to extend along the successive passage ways and grooves,
and including a plurality of electromagnetic coils operatively coupled
with the yoke.
7. A flowmeter according to claim 1 wherein the yoke is constructed
of at least two segments which can be placed into the blind openings,
the passage way and the grooves (611) and which can be interconnected.
8. A flow meter according to claim 1 wherein the passage way defines
an open trough in the exterior surface of the tube.
9. A flow meter according to claim 1 wherein the passage way defines
an elongated, open ended hole.
Description BACKGROUND OF THE INVENTION
The invention relates to an electromagnetic flow meter, comprising
a metering tube having a thick outer wall made of an electrically
non-conducting material. It has at least two measuring electrodes
and at least two magnetic poles, each of which is disposed in a
blind bore of the metering tube. They are linked to one another
by a yoke and have at least one magnetic coil.
In a known magnetic-inductive flow meter, as described for example
in German patent publication DE-OS 15 73 066 the yoke linking the
magnetic poles is disposed outside the periphery or outer surface
of the metering tube. Such an arrangement requires an inordinate
amount of space for the yoke and, for small diameters, results in
significant losses of magnetic flux and a reduced sensitivity. These
drawbacks are also encountered with arrangements in which the cores
of the magnetic coils are mounted on a ferromagnetic housing for
the magnetic reflux (cf. EP 0047342 B1; U.S. Pat. No. 4089113;
German Patent DE 35 11 033).
SUMMARY OF THE INVENTION
To overcome these drawbacks the present invention places the yoke
and the magnetic coils into a recess inside the outer wall of the
metering tube.
Positioning the yoke and the excitation coil inside the tube renders
the magnetic circuit significantly more stable and increases the
measurement accuracy. Moreover, the magnet components require no
additional space. Thus, such instruments are significantly more
compact.
Placing the yoke and the magnetic coil inside the metering tube
makes it easier to conform the instrument to special design requirements
and facilitates its manufacture. In a simple embodiment of the invention,
a midportion of the yoke which supports the magnetic coil is disposed
inside a through hole which extends parallel to the blind bores
for the magnetic poles. An intermediate section of the yoke, which
connects the midportion to the magnetic poles, is disposed in grooves
in the exterior surface of the metering tube. In a more developed
embodiment of the invention, multiple through holes in the metering
tube extend parallel to the blind bores for the magnet poles. In
this manner, one or more yokes can optionally be inserted into or
extended through the holes as desired.
In another simple embodiment of the invention, the midportion of
the yoke mounting the magnetic coils is placed inside a semi-circular
groove which extends between the blind bores. This permits insertion
of the yoke and the magnetic coils into the groove from the outside.
The magnetic coils may be constructed as required by the surroundings
and operational considerations. For example, the magnetic poles
may be connected with two arcuate yokes which are parallel to one
another. To enhance the magnetic flux, the yoke can be extended
through multiple, successive bores and provided with multiple coil
windings.
To facilitate the installation of the magnet components in the
bore or grooves, the yoke is preferably constructed of two or more
sections that can be inserted into and assembled in the holes and/or
grooves.
BRIEF DESCRIPTION OF THE DRAWINGS
Multiple embodiments of the present invention are shown in the
below, in which,
FIG. 1 is a side elevational view of a metering tube,
FIG. 2 is a cross-section taken at a midportion of the tube of
FIG. 1 and shows the magnetic poles and a yoke,
FIG. 3 is a plan view of the tube of FIG. 1
FIG. 4 is a second embodiment of a metering tube,
FIG. 5 is a cross-section taken at a midportion of the tube of
FIG. 4 and shows the magnetic poles and a yoke,
FIG. 6 is a cross-section of a third embodiment of the present
invention and shows the magnetic poles and a yoke, and
FIG. 7 is a perspective view of a yoke provided with three magnetic
coils.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A metering tube 1 for a magnetically inductive flow meter as shown
in FIG. 1-3 is constructed of an electrically non-conductive material
such as plastic, ceramic or the like. It has a cylindrical shape
and an axial flow-through bore 2. The metering tube has an especially
thick outer wall, that is, the diameter of the outer wall is several
times greater than the diameter of flow bore 2. Two measuring electrodes
3 are mounted inside metering tube 1 perpendicular to flow bore
2 at diametrically opposite locations in an air and water impervious
manner. The electrode heads extend to flow bore 2 to bring them
into contact with the fluid being metered.
Metering tube 1 further includes two, diametrically opposite blind
bores 4 which are displaced 90.degree. relative to measuring electrodes
3 and receive two magnetic poles 7 constructed of a ferromagnetic
material. A through hole 5 within metering tube 1 extends parallel
to blind bores 4 on one side of the flow bore 2 and receives a yoke
8 that connects magnetic poles 7 to each other. Each of the outer
ends of through hole 5 is linked to the adjacent blind bores by
a groove 6 which receives an intermediate section 9 of the yoke
that is connected to the adjacent magnetic pole. Both yoke 8 and
the intermediate section 9 are also made of a ferromagnetic material.
The magnetic components of the instrument, formed by two magnetic
poles 7 intermediate section 9 and yoke 8 which includes a magnetic
coil 10 are of a modular construction to facilitate their installation
in blind bore 4 and in the recess defined by through bore 5 and
grooves 6. The components must be in mutual contact to assure magnetic
reflux. When installed, all components of the magnets are located
inside the exterior surface of metering tube 1.
In an alternative embodiment, shown in FIGS. 4 and 5 a groove
11 for receiving the midportion 12 of yoke 8 extends along the periphery
of the outer surface of the metering tube and links the blind bores
4. The magnet components of this embodiment are also of a modular
construction to permit their installation and assembly within the
metering tube.
FIG. 6 shows an embodiment of a metering tube 1 which has two diametrically
opposite through holes 5 that are connected by grooves 6. The magnetic
poles 7 are connected by two parallel arcuate yokes 14. Each of
these arcuate yokes has a magnetic coil 15 through which parallel
currents flow in like directions. This embodiment exhibits an increased
magnetic flux.
To further intensify the magnetic flux it is possible, as shown
for example in FIG. 7 to pass the yoke that connects the magnetic
poles sequentially through multiple bores and to provide it with
multiple magnetic coils 23 to 25. FIG. 7 shows only the magnet components
and a schematic of flow bore 2. This embodiment has 3 elbows 16
to 18 and associated through holes (not shown) suitably arranged
within the metering tube. Further, the metering tube includes grooves
(also not shown) in the exterior surface of the metering tube which
link the blind bores 4 which house the magnetic poles 7 with the
through holes and receive intermediate sections 19 to 22. |