Abstrict An electromagnetic flow meter interposable between ends of upstream
and downstream pipes. The flow meter comprises a measuring pipe
of nonmagnetic material for fluid flow therethrough; two magnetic
flux generating units facing toward and forming gaps with the outer
surface of the measuring pipe; and two casing units of magnetic
material enclosing the magnetic flux generating units and the measuring
pipe, with the magnetic flux generating units being adjustably secured
to the casing units. One of the casing units or the measuring pipe
has projections which make the axes of the casing units and the
measuring pipe coincide.
Claims What is claimed is:
1. An electromagnetic flow meter interposable between ends of upstream
and downstream pipes conveying a fluid whose flow rate is to be
measured, said flow meter comprising:
a measuring pipe made of non-magnetic material, said fluid flowing
through said measuring pipe along the axis of said measuring pipe;
a pair of electrodes for picking up electricity generated depending
on the flow rate of the fluid in said measuring pipe, said electrodes
mounted in said measuring pipe;
first and second magnetic flux generating units for generating
magnetic flux in said measuring pipe, said flux generating units
being arranged facing toward and being separated by gaps from the
outer surface of said measuring pipe;
a first casing unit enclosing said first magnetic flux generating
unit and a first circumferential portion of said measuring pipe,
said first magnetic flux generating unit being adjustably secured
to said first casing unit;
means, including a plurality of spacing members associated with
at least one of said measuring pipe and said first casing unit,
for positioning said first casing unit in spaced relationship with
respect to said measuring pipe; and
a second casing unit enclosing said second magnetic flux generating
unit and a second circumferential portion of said measuring pipe,
said first and second circumferential portions representing the
entire circumference of said measuring pipe, said second magnetic
flux generating unit being adjustably secured to said second casing
unit, and said second casing unit facing toward said measuring pipe
and forming a gap therebetween.
2. A flow meter according to claim 1 wherein said spacing members
are radially inward projections formed on an inner surface or said
first casing unit, said inward projections abutting against said
measuring pipe.
3. A flow meter according to claim 1 wherein said spacing members
are radially outward projections formed on an outer surface of said
measuring pipe, said outward projections abutting against said first
casing unit.
4. A flow meter according to claim 1 wherein said first and second
casing units are fastened to each other at a plane which contains
the axis of said measuring pipe.
5. A flow meter according to claim 1 further comprising screws
for securing said magnetic flux generating unit to said casing units.
6. A flow meter according to claim 1 wherein at least part of
said casing units comprises a magnetic material.
7. A flow meter according to claim 1 wherein:
said electrodes are positioned on a straight line orthogonal to
the axis of said measuring pipe; and
each of said flux generating units has an axis positioned on a
straight line that intersects at right angles to a line connecting
said electrodes and to the axis of said measuring pipe at a common
point of intersection.
8. A flow meter according to claim 1 further comprising an elastic
member for urging said magnetic flux generating units toward said
measuring pipe.
Description BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic flow meter
that can be inserted and clamped between two flanges of piping conveying
a fluid that is to be measured. More particularly, the present invention
pertains to a structure for such an electromagnetic flow meter.
In constructing a conventional electromagnetic flow meter, a measuring
pipe made of a non-magnetic metal is inserted through an opening
in the axial end face of an outer casing made of a magnetic metal,
and the end portions of the measuring pipe are secured to the outer
casing by means of welding. Electrode bosses are inserted through
an opening in the outer casing in a direction perpendicular to the
axis of the measuring pipe and are welded to the measuring pipe.
Insulating spacers then are threaded into the electrode bosses,
and an insulating lining is provided on the inner surface of the
measuring pipe. Then, electrodes are inserted into the insulating
spacers from the inner surface of the measuring pipe and are secured.
Thereafter, a pair of magnet cores provided with exciting coils
are mounted by inserting them from the open ends of upper and lower
magnetic flux generating unit housing portions, which are formed
on the outer casing so as to extend orthogonally to the axis of
the measuring pipe and to the electrodes.
After assembly, the only way possible to confirm whether or not
the structural symmetry required for the electromagnetic flow meter
has satisfactorily been obtained is by visually checking the outside
of the apparatus. The apparatus, however, is housed in the outer
casing, and it is therefore difficult to effect any accurate confirmation.
For this reason, it is necessary to increase substantially the degree
of machining accuracy to ensure the required symmetry and reduce
the distance between the upper and lower magnetic flux generating
units, which fact inevitably increases the costs. Moreover, it is
difficult to conduct such assembling operations as mounting the
constituent elements and handling the lead wires extending from
the electrodes and the magnetic flux generating units, which must
be carried out in the narrow space within the outer casing. It is
therefore not easy to reduce the time required for assembly.
One example of a prior art electromagnetic flow meter that can
be inserted and clamped between two flanges of piping conveying
fluid to be measured is disclosed in U.S. Pat. No. 4253340. In
this example, a splittable outer casing and the magnet cores are
integral with each other, and coils are mounted on the cores. Accordingly,
although the outer casing comprises two splittable portions, and
these portions are bonded together during assembly, it is still
difficult to confirm the structural symmetry of the flow meter and
reduce the distance between the upper and lower magnetic flux generating
units, because the magnet cores are applied at the same time as
the outer casing, which prevents the assembler from checking the
accuracy of the assembly.
An electromagnetic flow meter representing earlier work of the
present inventor is disclosed in Japanese Patent Disclosure (Kokai)
No. 61-151429. In this example, the splittable outer casing and
the magnetic cores are not in contact with each other. Therefore,
it is difficult to set the outer casing in proper position in relation
to the magnetic cores, the electrodes and the measuring pipe. Since
the outer casing position affects the magnetic field in the measuring
pipe, it is desired that the outer casing position is easily adjustable
and easily confirmed in relation to the measuring pipe. In addition,
if the outer casing is made of magnetic metal, and if the magnetic
cores are in contact with the outer casing, the intensity of the
magnetic field in the measuring pipe increases, which is preferable.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an
improved electromagnetic flow meter. Another object of this invention
is to provide a method for accurately and easily positioning the
casing and the magnetic flux generating units in relation to the
measuring pipe and the electrodes in an electromagnetic flow meter.
Another object of this invention is to provide an electromagnetic
flow meter having an enhanced magnetic field in the measuring pipe.
According to one aspect of the invention there is provided an electromagnetic
flow meter interposable between ends of upstream and downstream
pipes conveying a fluid whose flow rate is to be measured, comprising:
a measuring pipe made of non-magnetic material, the fluid flowing
through the measuring pipe along the axis of the measuring pipe;
a pair of electrodes for picking up electricity generated depending
on the flow rate of the fluid in the measuring pipe, the electrodes
mounted in the measuring pipe; first and second magnetic flux generating
units for generating magnetic flux in the measuring pipe, the flux
generating units being arranged facing toward and being separated
by gaps from the outer surface of the measuring pipe; a first casing
unit enclosing the first magnetic flux generating unit and a first
circumferential portion of the measuring pipe, the first magnetic
flux generating unit being adjustably secured to the first casing
unit; means, including a plurality of spacing members associated
with at least one of the measuring pipe and the first casing unit,
for positioning the first casing unit in spaced relationship with
respect to the measuring pipe; and a second casing unit enclosing
the second magnetic flux generating unit and a second circumferential
portion of the measuring pipe, the first and second circumferential
portions representing the entire circumference of the measuring
pipe, the second magnetic flux generating unit being adjustably
secured to the second casing unit, and the second casing unit facing
toward the measuring pipe and forming a gap therebetween.
According to another aspect of the invention there is provided
a method for constructing an electromagnetic flow meter interposable
between ends of upstream and downstream pipes conveying fluid whose
flow rate is to be measured, comprising the steps of: mounting a
pair of magnetic flux generating units temporarily with flexible
fastening means on the outer surface of the measuring pipe; subsequently,
mounting a plurality of casing units enveloping the side of the
measuring pipe with the magnetic flux generating units; and subsequently,
securing the magnetic flux generating units to the casing units.
Further objects, features and advantages of the present invention
will become apparent from the detailed description of the preferred
embodiments that follows, when considered with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute
a part of this specification, illustrate preferred embodiments of
the invention and, together with the description, serve to explain
the principles of the invention. In the drawings:
FIG. 1 is a cross-sectional view of an embodiment of the flow meter
of the present invention, taken along a vertical plane containing
the axis of the measuring pipe;
FIG. 2 is a cross-sectional view taken along line II--II of FIG.
1;
FIG. 3 is an exploded perspective view of the embodiment shown
in FIG. 1;
FIG. 4 is a detailed perspective view of the lower casing unit
according to the invention;
FIG. 5 is an elevational view of the measuring pipe and the magnetic
flux generating units combined with the elastic belts under construction;
and
FIG. 6 is a cross-sectional view of another embodiment of the flow
meter of the present invention, taken similarly as in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
One embodiment of an electromagnetic flow meter of the present
invention is shown in FIGS. 1 2 and 3.
A measuring pipe (10 ) is made of a non-magnetic metal, for example,
stainless steel. The measuring pipe (10) has a pair of recesses
(12) on the outer side at the axially central part. The two recesses
(12) are symmetrically located across the axis of the pipe (10),
and the bottom surfaces of the recesses (12) are in a single cylindrical
surface coaxial with the pipe (10). A flange (14) is formed at each
axial end of the pipe (10).
A pair of electrodes (16 ) are positioned across the pipe (10)
on a straight line at right angles to the axis of the pipe (10)
and to the line connecting the centers of the two recesses (12).
The electrodes (16) are electrically insulated from the pipe (10).
An insulating lining (18) is provided over the entire inner surface
of the measuring pipe (10) except at the tips of the electrodes
(16). Both ends of the lining (18) are flared to overlap the end
faces of the pipe (10).
Upper casing unit (20) and lower casing unit (22) are made of magnetic
material and are semi-cylindrically shaped to cover the side of
the measuring pipe (10). The casing units (20) and (22) meet together
at a horizontal plane that includes the axis of the pipe (10), and
they are welded to each other at horizontal side lines (23). The
casing units (20) and (22) have hollow extensions (24), in which
magnetic flux generating units (28) are contained.
Each of the magnetic flux generating units (28) consists of a magnet
core (32) and a coil (36) wound around the core (32). The magnet
cores (32) are secured to the inner surfaces of the hollow extensions
(24) of the casing units (20) and (22), with bolts (40). Coil supporting
plates (41) of magnetic material are inserted between the coils
(36) and the hollow extensions (24). The magnet cores (32) are arranged
in a straight line across the pipe (10) at right angles to the axis
of the pipe (10) and to the line connecting the electrodes (16).
And the magnet cores (32) are provided with flanges (42) which face
toward the recesses (12) of the measuring pipe (10) and form small
gaps (44) between themselves and the bottom surfaces of the recesses
(12).
The bolts (40) penetrate holes (46) in the hollow extensions (24)
of the casing units (20) and (22), and they are screwed in threaded
blind holes (48) in the magnet cores (32). The holes (46) in the
hollow extensions (24) are large enough so that the location of
the magnetic cores (32) in relation to the casing units (20) and
(22) is adjustable.
The lower casing unit (22) has two projections (50) near each end
in the semi-cylindrical inner surface abutting against the measuring
pipe (10), as better shown in FIG. 4. The four projections (50)
have equal heights and are arranged symmetrically. The inner surfaces
(52) of the projections (50) are curved to fit with the outer surface
of the pipe (10). The inner surfaces (52) of the projections (50)
are finished mechanically so that the axis of the casing units (20)
and (22) and the axis of the pipe (10) are aligned. Therefore, the
gap (54) between the upper casing unit (20) and the pipe (10), and
the gap (56) between the lower casing unit (22) and the pipe (10)
are equal.
Electric leads (not shown) connected to the electrodes (16) and
the coils (36) penetrate a hole (not shown) in the hollow extension
(24) in the upper casing unit (20).
The process for constructing the electromagnetic flow meter is
described below:
The two magnetic flux generating units (28) are abutted to the
recesses ( 12) in the measuring pipe (10) with the electrodes (16),
and they are temporarily bound with two elastic belts (58) set on
the flanges (42) of the magnet cores (32), as shown in FIG. 5. Since
the belts (58) are elastic, the flux generating units (28) are easily
adjusted to sit at the right positions.
Subsequently , the measuring pipe (10 ) provided with the electrodes
(16) and the flux generating units (28) is put on the lower casing
unit (22), and then the upper casing unit (20) is put on them. Since
the projections (50) on the lower casing unit (22) are accurately
finished, the axes of the pipe (10) and the casings (20) and (22)
coincide.
The electric leads connected to the electrodes (16) and the coils
(36) are drawn out through a hole in the upper casing unit (20).
Then the bolts (40) are screwed through the holes (46) in the hollow
extensions (24) of the casing units (20) and (22) into the threaded
holes (48) in the magnet cores (32). Since the belts (58) are elastic,
the magnetic cores (32) are drawn off the pipe (10) toward the casing
units (20) and (22) as the bolts (40) are screwed in. The belt (40)
on the lower casing unit (22) should be screwed in before the bolt
(40) on the upper casing unit (20) is screwed in, so that the measuring
pipe (10 ) will not be suspended on the belts (58). The holes (46)
in the hollow extensions (2)) are large enough so that the magnet
cores (32) are positioned at the right place regardless of inaccuracy
in the positions of the centers of the holes (46).
Then the upper and lower casing units (20) and (22) at the horizontal
side lines (23), and the ends of the casing units (20) and (22)
and flanges (14 ) of the measuring pipe (10) are, respectively,
welded.
The electromagnetic flow meter described above is mounted between
respective flanges of upstream and downstream portions of piping
(not shown) that conveys the fluid to be measured. The flow meter
is tightly clamped by tightening mounting bolts (not shown) that
connect together the flanges (not shown) of the piping outside the
hollow extensions (24) of the casing units (20) and (22). When the
coils (36) are supplied with an exciting current, the magnetic flux
generating units (28) generate magnetic field lines that extend
orthogonally to both the imaginary line connecting the pair of electrodes
(16) and the axis of the measuring pipe (10). An electromotive force
is produced when the fluid conveyed by the piping flows through
the flow meter and cuts the magnetic field lines. The electromotive
force, which is proportional to the flow velocity, is delivered
by the electrodes (16 ) and lead wires (not shown) to a converter
(not shown) where it is converted into a flow rate measurement.
In the embodiment described above, it is easy to make the axes
of the measuring pipe (10) and the casing units (20) and (22) coincide,
and it is easy It is also easy to draw the electric leads connected
positions to the electrodes (16) and the coils (36) out of the casing
units (20) and (22). Furthermore, the magnetic field generated in
the measuring pipe (10) is stronger, since the magnet cores (32)
are in direct contact with the casing units (20) and (22) of magnetic
metal.
In another embodiment shown in FIG. 6 a measuring pipe (10) has
projections (150) on its outer surface abutting against the inner
surface of a lower casing unit (122). The lower casing unit (122)
does not have projections abutting against the measuring pipe (110
). The other features are the same as in the first embodiment, and
the same advantages can be obtained.
The foregoing description has been set forth merely to illustrate
preferred embodiments of the invention and is not intended to be
limiting. Since modification of the described embodiments incorporating
the spirit and substance of the invention may occur to persons skilled
in the art, the scope of the invention should be limited solely
with respect to the appended claims and equivalents. |