Abstrict An electromagnetic flow meter comprises a detector body interposable
between the flanged ends of upstream and downstream pipes conveying
a fluid whose flow rate is to be measured and an outer casing. The
detector body includes a measuring pipe made of a non-magnetic material
and a pair of electrodes positioned on an imaginary straight line
orthogonal to the axis of the measuring pipe and contacting the
fluid to be measured. The detector body also includes a pair magnetic
flux generating units having magnet cores with coils wound thereon.
The axis of the magnet cores are positioned on an imaginary straight
line that intersects, at right angles, both the imaginary line connecting
the electrodes and the axis of the measuring pipe at a single point
of intersection. The magnetic flux generating units generate magnetic
field lines orthogonal to the imaginary line connecting the electrodes
and the axis of the measuring pipe. The outer casing is split into
two portions and houses the detector body after the detector body
has been assembled. In one embodiment of the invention, the inner
surface of the outer casing includes a plurality of radially inward
pojections that abut against the measuring pipe. In an alternative
embodiment, the measuring pipe includes a plurality of radially
outward projections that abut against the outer casing.
Claims What is claimed is:
1. An electromagnetic flow meter is interposable between the flanged
ends of upstream and downstream pipes conveying a fluid whose flow
rate is to be measured, said flow meter comprising:
a detector body including
a measuring pipe made of a non-magnetic material having longitudinal
end faces contacting said flanged ends of said conveying pipes and
having a pair of diametrally opposed reinforcing portions parallel
to the axis of said measuring pipe, said fluid flowing through said
measuring pipe along said axis of said measuring pipe,
a pair of electrodes mounted in said measuring pipe and positioned
on a first imaginary straight line orthogonal to said axis of said
measuring pipe and passing through said reinforcing portions of
said measuring pipe, said electrodes contacting said fluid flowing
through said measuring pipe, and
a pair of magnetic flux generating units mounted on the outer surface
of said measuring pipe, each of said magnetic flux generating units
including a magnet core having coils wound thereon, each of said
magnet cores having an axis positioned on a second imaginary straight
line that intersects, at right angles, both said first imaginary
line connecting said electrodes and said axis of said measuring
pipe at a common point of intersection, said magnetic flux generating
units generating magnetic field lines orthogonal to said first imaginary
line and said axis of said measuring pipe; and
an outer casing enclosing the radial portion of sid detector body,
said outer casing having longitudinal end faces substantially aligned
with said longitudinal end faces of said measuring pipe.
2. The electromagnetic flow meter of claim 1 wherein said outer
casing is splittable into a plurality of casing portions.
3. The electromagnetic flow meter of claim 1 wherein said outer
casing is split into two portions along a plane that is orthogonal
to said axis of said measuring pipe.
4. The electromagnetic flow meter of claim 1 wherein said outer
casing is split into two portions along a plane that is parallel
with a plane including said axis of said measuring pipe and said
first imaginary line connecting said electrodes.
5. The electromagnetic flow meter of claim 1 wherein said outer
casing is split into two portions along a plane that is parallel
with a plane including said axis of said measuring pipe and said
second imaginary line.
6. The electromagnetic flow meter of claim 1 wherein said outer
casing and said magnetic flux generating units are connected together
by fastening members.
7. The electromagnetic flow meter of claim 1 wherein said magnet
cores are threadably engaged with said outer casing.
8. The electromagnetic flow meter of claim 1 wherein said magnet
cores are secured to said reinforcing portions of said measuring
pipe.
9. The electromagnetic flow meter of claim 8 wherein said magnet
cores are threadably fastened to said reinforcing portions of said
measuring pipe.
10. An electromagnetic flow meter interposable between the flanged
ends of upstream and downstream pipes conveying a fluid whose flow
rate is to be measured, said flow meter comprising:
a detector body including
a measuring pipe made of a non-magnetic material having longitudinal
end faces contacting said flanged ends of said conveying pipes,
said fluid flowing through said measuring pipe along the axis of
said measuring pipe,
a pair of electrodes mounted in said measuring pipe and positioned
on a first imaginary straight line orthogonal to said axis of said
measuring pipe, said electrodes contacting said fluid flowing through
said measuring pipe, and
a pair of magnetic flux generating units mounted on the outer surface
of said measuring pipe, each of said magnetic flux generating units
including a magnet core having coils wound thereon, each of said
magnet cores having an axis positioned on a second imaginary straight
line that intersects, at right angles, both said imaginary line
connecting said electrodes and said axis of said measuring pipe
at a common point of intersection, said magnetic flux generating
units generating magnetic field lines orthogonal to said first imaginary
line and said axis of said measuring pipe; and
an outer casing enclosing the radial portion of said detector body,
said outer casing having longitudinal end faces substantially aligned
with said longitudinal end faces of said measuring pipe and an inner
surface including a plurality of radially inward projections, said
measuring pipe abutting against said projections.
11. An electromagnetic flow meter interposable between the flanged
ends of upstream and downstream pipes conveying a fluid whose flow
rate is to be measured, said flow meter comprising:
a detector body including
a measuring pipe made of a non-magnetic material having longitudinal
end faces contacting said flanged ends of said conveying pipes and
a plurality of radially outward projections, said fluid flowing
through said measuring pipe along the axis of said measuring pipe,
a pair of electrodes mounted in said measuring pipe and positioned
on a first imaginary straight line orthogonal to said axis of said
measuring pipe, said electrodes contacting said fluid flowing through
said measuring pipe, and
a pair of magnetic flux generating units mounted on the outer surface
of said measuring pipe, each of said magnetic flux generating units
including a magnet core having coils wound thereon, each of said
magnet cores having an axis positioned on a second imaginary straight
line that intersects, at right angles, both said first imaginary
line connecting said electrodes and said axis of said measuring
pipe at a common point of intersection, said magnetic flux generating
units generating magnetic field lines orthogonal to said first imaginary
line and said axis of said measuring pipe; and
an outer casing enclosing the radial portion of said detector body,
said outer casing having longitudinal end faces substantially aligned
with said longitudinal end faces of said measuring pipe, and said
outer casing abutting against said radially outward projections
of said measuring pipe.
Description BACKGROUND OF THE INVENTION
1. Field 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.
2. Description of the Prior Art
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, it is possible to confirm whether or not the structural
symmetry required for the electromagnetic flow meter has satisfactorily
been obtained only 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 fluix 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 magnetic 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 housing, which prevents the assembler from checking the
accuracy of the assembly.
It is an object of the present invention to provide an electromagnetic
flow meter which is so constructed that it is easy to obtain the
required degree of assembling accuracy and symmetry among the measuring
pipe, the electrodes, and the magnetic flux generating units.
It is another object of the present invention to provide an electromagnetic
flow meter which is so constructed that it is easy to assemble the
detector body and it is possible to reliably confirm the assembled
condition.
It is still another object of the present invention to provide
an electromagnetic flow meter which is so constructed that it is
possible to reduce the size and weight of the flow meter.
It is a further object of the present invention to provide an electromagnetic
flow meter which is so constructed that there is no need for conducting
the operation of mounting various functional elements in a narrow
space inside the outer casing, and it is therefore possible to remarkably
improve the working efficiency.
Additional objects of the present invention will be set forth in
part in the description that follows and in part will be obvious
from that description or can be learned by practice of the invention.
The objects of the invention can be realized and obtained by the
apparatus particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
The present invention overcomes the problems of the prior art and
achieves the objects listed above by providing an electromagnetic
flow meter having a detector body that can be fully assembled before
being housed within an outer casing.
To achieve the objects and in accordance with the purpose of the
invention, as embodied and broadly described herein, the electromagnetic
flow meter of the present invention is interposable between the
flanged ends of upstream and downstream pipes conveying a fluid
whose flow rate is to be measured and comprises a detector body
including a measuring pipe made of non-magnetic material having
longitudinal end faces contacting the flanged edges of the conveying
pipes. The fluid to be measured flows through the measuring pipe
along the axis of the measuring pipe. The detector body also includes
a pair of electrodes mounted in the measuring pipe and positioned
on a first imaginary straight line orthogonal to the axis of the
measuring pipe, the electrodes contacting the fluid flowing through
the measuring pipe. The detector body also includes a pair of magnetic
flux generating units mounted on the outer surface of the measuring
pipe, each of the magnetic flux generating units including a magnet
core having coils wound thereon. Each of the magnet cores has an
axis positioned on a second imaginary straight line that intersects,
at right angles, both the first imaginary line connecting the electrodes
and the axis of the measuring pipe at a common point of intersection.
The magnetic flux generating units generate magnetic fluid lines
orthogonal to the first imaginary line and the axis of the measuring
pipe. The eletromagnetic flow meter also comprises an outer casing
enclosing the radial portion of the detector body, the outer casing
having longitudinal end faces substantially aligned with the longitudinal
end faces of the measuring pipe.
In one embodiment of the invention, the inner surface of the outer
casing includes a plurality of radially inward projections that
abut against the measuring pipe. In an alternative embodiment, the
measuring pipe includes a plurality of radially outward projections
that abut against the outer casing.
Preferably, the outer casing is split into two portions along a
plane that is orthogonal to the axis of the measuring pipe, a plane
that is parallel with a plane including the axis of the measuring
pipe and the first imaginary line connecting the electrodes, or
a plane that is parallel with a plane including the axis of the
measuring pipe and the second imaginary line connecting the axes
of the magnet cores.
The accompanying drawings, which are incorporated in and constitute
a part of this specification, illustrate at least one embodiment
of the invention and, together with the description, explain the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(a) is an exploded perspective view of one embodiment of
the flow meter of the present invention;
FIG. 1(b) is a sectional view of the flow meter of FIG. 1(a) after
assembly, taken along a vertical plane containing the axis of the
measuring pipe;
FIG. 1(c) is a sectional view of the flow meter of FIG. 1(a) after
assembly, taken along a vertical plane perpendicular to the axis
of the measuring pipe;
FIG. 2 is a perspective view of the measuring pipe of the flow
meter shown in FIG. 1(a);
FIG. 3(a) is a sectional view of a second embodiment of the electromagnetic
flow meter of the present invention, taken along a vertical plane
containing the axis of the measuring pipe;
FIG. 3(b) is a sectional view of the second embodiment of the electromagnetic
flow meter of the present invention, taken along a vertical plane
perpendicular to the axis of the measuring pipe;
FIG. 4 is an exploded perspective view of the flow meter shown
in FIGS. 3(a) and 3(b);
FIG. 5(a) is an exploded perspective view of a third embodiment
of the electromagnetic flow meter of the present invention wherein
the way in which the outer casing is split is modified;
FIG. 5(b) is a sectional view of the flow meter of FIG. 5(a), taken
along a vertical plane containing the axis of the measuring pipe;
FIG. 5(c) is a sectional view of the flow meter of FIG. 5(a), taken
along a vertical plane perpendicular to the axis of the measuring
pipe;
FIG. 6(a) is an exploded perspective view of a fourth embodiment
of the electromagnetic flow meter of the present invention, wherein
the way in which the outer casing is split is further modified;
FIG. 6(b) is a sectional view of the flow meter shown in FIG. 6(a),
taken along a vertical plane containing the axis of the measuring
pipe;
FIG. 6(c) is a sectional view of the flow meter of FIG. 6(a), taken
along a vertical plane perpendicular to the axis of the measuring
pipe;
FIG. 7(a) is an exploded perspective view of a fifth embodiment
of the electromagnetic flow meter of the present invention, wherein
the way in which the outer casing is split is further modified;
FIG. 7(b) is a sectional view of the flow meter of FIG. 7(a), taken
along a vertical plane containing the axis of the measuring pipe;
FIG. 7(c) is a sectional view of the flow meter of FIG. 7(a), taken
along a vertical plane perpendicular to the axis of the measuring
pipe;
FIG. 8 is a sectional view of a portion of the electromagnetic
flow meter of FIG. 4 in which the fastening members for securing
together the outer casing and the cores are modified;
FIG. 9 is a perspective view of the electromagnetic flow meter
of FIGS. 1(a) or 4 in which the outer casing portions are modified;
FIG. 10 is a sectional view showing the arrangement for mounting
the measuring pipe in the outer casing portions of FIG. 9;
FIG. 11 is a perspective view of a measuring pipe in accordance
with a still further embodiment;
FIG. 12 is a sectional view showing the arrangement for mounting
the measuring pipe of FIG. 11 in the outer casing portions; and
FIG. 13 is a sectional view of an outer casing portion in accordance
with a still further embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference now will be made in detail to the presently preferred
embodiments of the invention, examples of which are illustrated
in the accompanying drawings.
An electromagnetic flow meter in accordance with one embodiment
of the present invention is shown in FIGS. 1(a), 1(b), 1(c) and
2. The electromagnetic flow meter comprises a detector body 20 housed
in an outer casing 30. The detector body 20 includes a measuring
pipe 21 made of a non-magnetic metal, for example, stainless steel.
As seen best in FIG. 2 the measuring pipe 21 is so shaped that
each of its end portions has a relatively large wall thickness so
that the measuring pipe has a collar-like configuration. A pair
of reinforcing portions 21a having the same wall thickness as that
of the collar-like end portions are provided in symmetry with each
other with respect to the axis of the pipe 21 on diametrally opposed
sides of the pipe 21. This structure enables the measuring pipe
21 to endure the internal pressure of fluids flowing through it
and the compressive force applied it from the upstream and downstream
flanges of the piping that conveys the fluid to be measured when
the measuring pipe 21 is mounted in the piping. A threaded bore
21b is provided in each of the pair of reinforcing portions 21a
for the purpose of mounting insulating spacers 24 which insulate
electrodes 23 held within the spacers 24 from the measuring pipe
21. Each threaded bore 21b extends concentrically along the diameter
passing through the longitudinal center of the measuring pipe 21
and the lateral center of the corresponding reinforcing portion
21 a. Further, as seen in FIG. 2 each reinforcing portion 21a is
provided in both sides surfaces thereof with screw receiving holes
21c for mounting a magnetic flux generating unit.
As shown in FIGS. 1(b) and 1(c), an insulating lining 22 is provided
over the entire inner surface of the measuring pipe 21. Both ends
of the lining 22 are flared to overlap the end faces of the measuring
pipe 21. A pair of electrodes 23 are mounted through the insulating
spacers 24 which are screwed into the threaded bores 21b of the
measuring pipe 21 so that the head of each electrode 23 is exposed
where it meets the surface of the lining 22. A pair of magnetic
flux generating units 25 are mounted on the exterior surface of
the measuring pipe 21 in such a manner that the respective axes
of their magnet cores 27 having coils 26 wound thereon are positioned
on an imaginary straight line that intersects, at right angles,
both the imaginary line that connects the pair of electrodes 23
and the axis of the measuring pipe 21 at a single point of intersection.
The radially inward end of each magnet core 27 is brought into close
contact with the outer surface of the measuring pipe 21. The pair
of magnetic flux generating units 25 generate magnetic field lines
that extend orthogonally to both the imaginary line connecting the
pair of electrodes 23 and the axis of the measuring pipe 21.
The above assembly comprises the detector body 20 which is housed
within an outer casing 30 made of a magnetic metal and having a
configuration that enables the whole of the detector body 20 to
be accomodated therein with a slight gap left therebetween. In the
embodiment shown in FIGS. 1(a), 1(b), and 1(c), the outer casing
30 is split into two portions, a first outer casing portion 28 and
a second outer casing portion 29 along a plane that includes the
axis of the measuring pipe 21 and the imaginary line connecting
the pair of electrodes 23. Each of the portions 28 and 29 is provided
with engagement portions 31 against which the end portions of the
measuring pipe 21 abut. The detector body 20 is assembled in such
a manner that the detector body 20 is fitted into the first casing
portion 28 and the second casing portion 29 is then fitted onto
the other side of the pipe 21. Then, the end portions of the pipe
21 and the corresponding engagement portions 31 are connected by,
for example, welding, and the respective joint ends of the portions
28 and 29 are similarly connected together. Portions 28 and 29 of
casing 30 are provided, respectively, with joint ends 30a and 30
b, which form lap joints at the connection between portions 28 and
29. Joint ends 30a are on the interior side of casing portion 28
and joint ends 30b are on the exterior side of casing portion 29.
The thus-arranged electromagnetic flow meter in accordance with
the first embodiment of the present invention 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 of the piping outside the outer casing
30. At this time, the compressive force from the flanges is applied
to the measuring pipe 21 alone, and no external force is applied
to the outer casing 30. When the coils 26 are supplied with an exciting
current, the magnetic flux generating units 25 generate magnetic
field lines that extend orthogonally to both the imaginary line
connecting the pair of electrodes 23 and the axis of the measuring
pipe 21. 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 lead wires (not shown) to a converter
(not shown) where it is converted into a flow rate measurement.
Thus, the electromagnetic flow meter in accordance with the first
embodiment of the present invention is arranged such that the whole
assembly is completed by housing the detector body 20 within the
two-part splittable outer casing 30 after the assembly of the detector
body 20 has been completed by mounting the insulating spacers 24
and the electrodes 23 on the measuring pipe 21 forming the insulating
lining 22 on the interior the measuring pipe 21 mounting the magnetic
flux generating units 25 on the measuring pipe 21 and connecting
lead wires extending from the electrodes 23 and the magnetic flux
generating units 25 to a converter.
Accordingly, it is easy to assemble the detector body 20 whereas
the conventional flow meter of this type requires various elements
to be handled inside the outer casing as the detector body and casing
are assembled together. Further, it is possible to confirm easily
and reliably the assembled condition and the symmetry of the pair
of upper and lower magnetic flux generating units 25 with respect
to the measuring pipe 21. Because the magnetic flux generating units
25 have a structure that brings the radially inward end of each
core 27 into close contact with the outer surface of the measuring
pipe 21 it is possible to reduce the distance between the upper
and lower magnetic flux generating units 25. Furthermore, since
each magnetic flux generating unit 25 is secured to the measuring
pipe 21 by screws extending through screw receiving holes 21c, the
gap between each of the mounting screws and the hole for the screw
can be utilized as an allowance for correction when positional adjustment
is effected, which facilitates obtaining the required symmetry of
the magnetic flux generating units. Additionally, it is possible
to check the assembled detector body 20 before it is housed within
the outer casing 30.
Because the compressive forces applied from the piping flanges
are borne by the measuring pipe 21 the outer casing 30 is only
required to satifactorily house the detector body 20 magnetically
shield the magnetic flux generating units 25 and protect the detector
body 20 from external disturbances such as, for example, moisture
or other substances falling onto the flow meter. For this reason,
it is not necessary to have an especially rigid outer casing, and
the strength of the outer casing is not required to be as high as
in the case of a conventional flow meter. Furthermore, because it
is not necessary to provide the outer casing with a special internal
space for the assembly of the various functional elements, the outer
casing 30 can be arranged to be compact, and the weight thereof
can be reduced correspondingly. In addition, the flow meter of the
present invention can meet any of the standards (Japanese Industrial
Standards, American National Standards and Deutshes Institut fur
Normung) for the piping flanges between which the flow meter is
to be clamped, because the outer casing 30 can be accomodated in
the space within the diameter of the bolt circle formed by the mounting
bolts that connect the flanges.
The following is a description of another embodiment of the present
invention, which differs from the first embodiment in the method
of securing the detector body to the outer casing, with reference
to FIGS. 3(a), 3(b), and 4. The portions of this embodiment that
are common to the embodiment shown in FIGS. 1(a) through 2 are denoted
by the same reference numerals, and detailed description thereof
is omitted.
The electromagnetic flow meter embodied in FIGS. 3(a), 3(b), and
4 comprises a detector body 42 housed within an outer casing 33.
Detector body 42 includes a measuring pipe 21 having a pair of reinforcing
portions 21a including threaded bores 21b for mounting insulating
spacers 24 each of which holds an electrode 23 and insulates the
corresponding electrode 23 from the measuring pipe 21. The threaded
bores 21b are positioned at the longitudinal center of the measuring
pipe 21 and extend coaxially with each other along an imaginary
line coinciding with the diameter of the pipe 21 that passes through
the lateral center of each reinforcing portion 21a. An insulating
lining 22 is provided over the entire inner surface of the measuring
pipe 21. The electrodes 23 are mounted in the respective insulating
spacers 24 which are screwed into the measuring pipe 21 so that
the head of each electrode 23 is exposed where it meets the surface
of the lining 22. A pair of magnetic flux generating units 41 are
secured to the respective side surfaces of the reinforcing portions
21a of the measuring pipe 21 in such a manner that the axis of each
magnet core 40 having a coil 26 wound thereon is positioned on an
imaginary straight line that intersects, at right angles, both the
imaginary line connecting the pair of electrodes 23 and the axis
of the pipe 21 at a single point of intersection. The radially inward
end of the core 40 is brought into close contact with the outer
surface of the measuring pipe 21. The pair of magnetic flux generating
units 41 generate magnetic field lines that extend orthogonally
to both the imaginary line connecting the pair of electrodes 23
and the axis of the measuring pipe 21. Further, a threaded hole
34 is provided at the free end of each magnet core 40.
The above assembly comprises the detector body 42 which is housed
within an outer casing 33. The casing 33 has the general shape of
a cylinder into which are fitted the outer peripheral surfaces of
the collar-like thick-walled portions formed at both ends of the
measuring pipe 21. The casing 33 further includes a pair of magnetic
flux generating unit housing portions 34a, 34b in its longitudinally
central portion. The housing portions 34a, 34b extend coaxially
on an imaginary straight line orthogonal to a plane including the
axis of the cylindrical outer casing 33 and each housing portion
has the shape of a tube for housing one of the magnetic flux generating
units 41. The radially inward end of each portion 34a, 34b is fitted
into a bore 33a in the wall of the casing 33 and its radially outward
end is closed by a cover 34c. Further, the casing 33 is constituted
by two splittable portions, outer casing portions 35 and 36 which
are divided along a plane including the axis of the casing 33 and
intersecting the respective axes of the housing portions 34a, 34b
at right angles. The casing portions 35 and 36 are made of a magnetic
metal. A bore 38 for receiving the threaded portion of a fastening
member 37 is formed in the cover 34c of each of the magnetic fluix
generating unit housing portions 34a and 34b. The reference numeral
39 shown in FIGS. 3(a), 3(b) and 4 denotes coil retainers that are
interposed between the radially outward portions of the magnetic
flux generating units 41 and the inner surfaces of the top portions
of the housing portions 34a, 34b when the casing portions 35 and
36 are assembled together. Preferably, O-rings (not shown) are provided
between the heads of fastening members 37 and covers 34c to seal
the casing 33 around the bores 38.
The thus-arranged electromagnetic flow meter in accordance with
the second embodiment of the present invention is assembled as follows.
First, the measuring pipe 21 is provided with the insulating lining
22. Then, the insulating spacers 24 the electrodes 23 and the
magnetic flux generating units 41 are mounted on the pipe 21 and
the lead wires (not shown) extending from the electrodes 23 and
the units 41 are properly arranged, thus completing the assembly
of the detector body 42. The thus-assembled detector body 42 is
covered with the outer casing portions 35 and 36 and the magnet
cores 40 and the covers 34c of the magnetic flux generating unit
housing portions 34a and 34b of the casing portions 35 and 36 are
respectively fastened together by the fastening members 37 so that
the corresponding portions are properly aligned with each other.
Then, the end portions of the measuring pipe 21 are secured to the
end portions of the casing portions 35 and 36 by, for example, welding.
Further, the respective joint ends of the casing portions 35 and
36 are similarly secured together by, for example, welding, thus
completing the assembly of the second embodiment of the electromagnetic
flow meter of this invention.
The electromagnetic flow meter in accordance with the second embodiment
of this invention is so constructed that the assembly of the whole
of the apparatus is completed by completely assembling the detector
body 42 and then covering this detector body with the two-part splittable
outer casing 33. In consequence, the lining is provided on the inner
surface of the measuring pipe before the electrodes, magnetic flux
generating units, and housing portions are applied and, therefore,
it is easy to provide the lining. Because it is possible to mount
the electrodes and the pair of magnetic flux generating units on
the measuring pipe before the casing is applied, the assembling
operation is facilitated, and it is possible to confirm the assembled
condition, the symmetry of the magnetic flux generating units, and
so forth by visual inspection and measurement. Thus, it is possible
to increase the degree of accuracy in assembly. Because the end
of the magnet core 40 of each magnetic flux generating unit 41 is
secured to the side surface of the corresponding reinforcing portion
21a of the measuring pipe 21 by means of screws, it is possible
for the pair of the magnetic flux generating units 41 to be disposed
close to each other. It is also possible to effect adjustment while
visually checking the symmetry by utilizing the clearance between
the screw receiving holes 21c and the corresponding screws (not
shown). Further, it is easy to handle the lead wires extending from
the electrodes 23 and the magnetic flux generating units 25 since
this operation is conducted before the outer casing 33 is assembled
so as to cover the detector body 42 and it is also possible to
accurately and reliably effect wiring and connect the lead wires
to predetermined positions.
When the outer casing 33 is mounted on the assembled detector body
42 the two splittable casing portions 35 and 36 are placed on the
detector body 42 and the portions 35 and 36 and the magnet cores
40 of the magnetic flux generating units 41 are respectively fastened
by means of the fastening members 37. In this state, the corresponding
portions can be aligned with each other. It is therefore unnecessary
to employ any complicated and expensive jig or tool for fastening
the casing portions 35 and 36 which fact leads to an increase in
productivity.
Further, the fastening members 37 also serve as auxiliary magnetic
poles that fill the gap between the outer casing 33 and the magnet
cores 40 of the magnetic flux generating units 41. It is therefore
possible to reduce the number of turns of the coils 26 in the magnetic
flux generating units 41 the applied current required, and so forth.
Furthermore, the measuring pipe 21 is provided with a strength high
enough to withstand the compression applied in the direction of
the axis of the pipe 21. The pipe 21 bears the entire compressive
force applied from the flanges of the piping between which the flow
meter is clamped. For this reason, it is necessary for the outer
casing 33 to serve only as a magnetic shield against the magnetic
flux generating units 41 as a feedback magnetic path, and to protect
the detector body 42 from external disturbances, such as moisture
or other substances falling onto the flow meter. Accordingly, the
weight of the casing 33 can be reduced. As a whole, these advantageous
effects make it possible to reduce the size and weight of the electromagnetic
flow meter. To comply with any of the standards (Japanese Industrial
Standards, American National Standards and Deutshes Institut fur
Normung) for the piping flanges between which the flow meter is
to be clamped, the outer casing 33 can be accomodated in a space
within the diameter of the bolt circle formed by the fastening bolts
connecting the flanges. Thus, the flow meter according to the present
invention is applicable to any of these standards. Since the magnet
cores 40 and the outer casing 33 are connected together by means
of the fastening members 37 in the embodiment shown in FIGS. 3(a),
3(b), and 4 the efficiency with which magnetic path is formed is
higher than that in the case of the embodiment shown in FIGS. 1(a)
through 1(c).
Although in the first and second embodiments the outer casing is
split along a path including the axis of the measuring pipe 21 and
the electrodes 23 it is to be noted that it is not always necessary
to split the outer casing in this way. For example, the outer casing
may be split in a manner such as that shown in FIGS. 5(a), 5(b),
and 5(c) in which an outer casing 50 is split into outer casing
portions 51 and 52. As shown, the outer casing may be split at a
right-hand portion (as viewed in FIGS. 5(a) and 5(b) by a plane
orthogonal to the axis of the measuring pipe 21.
Further, the arrangement of the outer casing may be such that,
as shown in FIGS. 6(a), 6(b), and 6(c), an outer casing 60 is split
into two portions 61 and 62. As shown, the outer casing may be split
along a plane that is orthogonal to the axis of the measuring pipe
21 and includes the imaginary line connecting the electrodes 23.
FIGS. 7(a), 7(b), and 7(c) show a further embodiment including
an outer casing 70 which is split into outer casing portions 71
and 72 along a plane that is orthogonal to the imaginary line connecting
the electrodes 23 and includes the axis of the measuring pipe 21.
Moreover, in each of the above embodiments, the outer casing may
be made of a synthetic resin, for example, fiber reinforced plastic,
in place of a magnetic metal. In such a case, the inner surface
of the outer casing is coated with a magnetic metal, so that the
outer casing provides a magnetic shielding function. Furthermore,
the magnetic flux generating unit and the measuring pipe may be
secured together by welding or other means of bonding in place of
threaded fasteners.
The measuring pipe also may be made of a ceramic material in addition
to non-magnetic metals. In such a case, it is not necessary to provide
any insulating lining on the inner surface of the pipe.
Although the embodiment shown in FIGS. 3(a), 3(b), and 4 employs
O-rings for sealing the gaps between the fastening members 37 and
the covers 34c of the magnetic flux generating unit housing portions
34a, 34b of the outer casing 33 the gaps may be sealed by means
of welding or bonding (using, for example, a resin adhesive or a
brazing material) after tightening the fastening members 37 in
place of the O-rings. In addition, it is not always necessary to
employ the coil retainers 39.
Further, each of the fastening members 37 shown in FIGS. 3(a) and
3(b) may be replaced by a fastening member 37A having an internally-threaded
hole 37B which does not extend completely through the fastening
member, as shown in FIG. 8. In such a case, the end portion of each
magnet core 40 has an extended portion 40A provided with an external
thread so that this threaded end portion threadably engages the
internally threaded hole of the fastening member 37A.
FIG. 9 shows an embodiment in which an outer casing portion 90
is provided with projections 91 that abut against the measuring
pipe 21. In this case, it is possible for the respective axes of
the outer casing and the measuring pipe to be aligned with each
other without the need for any special jig or tool for effecting
alignment, as shown in FIG. 10.
FIGS. 11 and 12 show an arrangement in which projections 101 are
provided on the exterior surface of the measuring pipe 21 to abut
against the inner surface of the outer casing.
Because the projections that enable the respective axes of the
outer casing and the measuring pipe to be easily aligned with each
other are provided on either the outer casing or the measuring pipe,
the symmetry required for an electromagnetic flow meter is accurately
maintained, and the assembling efficiency is improved. Thus, it
is possible to readily produce a highly accurate and inexpensive
electromagnetic flow meter.
FIG. 13 shows another structure of an outer casing portion. With
this structure, it is possible to employ one type of casing portion
that can be used, for example, as both first portion 28 and second
portion 29 of the flow meter of FIG. 1(a). The outer casing portion
of FIG. 13 includes both an interior joint end 30a and an exterior
joint end 30b.
It will be apparent to those skilled in the art that other modifications
and variations can be made in the electromagnetic flow meter of
this invention. The invention in its broader aspects, therefore,
is not limited to the specific details and illustrated examples
shown and described. Accordingly, departure can be made from such
details without departing from the spirit of applicant's general
inventive concept. |