Abstrict An electromagnetic flow meter includes an electromagnetic flow
meter body having a connecting end for connecting to a pipe in which
fluid to be metered is conducted, and a grounding device held between
the connecting end of the body and the pipe, the grounding device
having an annular frame of an insulating material having an inner
periphery defining a central opening and an outer periphery and
a grounding wire disposed at least at the inner periphery to be
exposed to the central opening of the annular frame.
Claims What is claimed is:
1. An electromagnetic flow meter for measuring the flow of a liquid
flowing through a pipe, comprising:
an electromagnetic flow meter body having at least one connecting
end for connecting the body to one end of the pipe; and
a grounding device adapted to be fastened between the connecting
end of said body and the end of the pipe, said grounding device
comprising (a) an annular frame of an insulating material having
an inner periphery defining a central opening and an outer periphery
and (b) a grounding wire disposed on said annular frame at least
at said inner periphery to be exposed to said central opening of
said annular frame.
2. An electromagnetic flow meter according to claim 1 wherein
said annular frame has a plurality of holes adjacent to its inner
periphery, and said grounding wire is wound across the surface of
said inner periphery of said annular frame through said holes.
3. An electromagnetic flow meter according to claim 1 wherein
said grounding wire comprises a plurality of grounding wires arranged
at opposite portions of said annular frame.
4. An electromagnetic flow meter according to claim 1 wherein
said annular frame includes a gripping projection having an anchoring
hole therein for anchoring said grounding wire.
5. An electromagnetic flow meter according to claim 1 wherein
said annular frame includes a plurality of grooves along its inner
periphery, and said grounding wire is wound through said grooves.
6. An electromagnetic flow meter according to claim 1 wherein
said annular frame is comprised of material having rubber elasticity
and said grounding wire is sewn through said annular frame at said
inner periphery to be exposed to said central opening.
7. An electromagnetic flow meter according to claim 1 wherein
said grounding wire is attached on the surface of said inner periphery
of said frame by means of an adhesive.
8. An electromagnetic flow meter according to claim 7 wherein
said grounding wire comprises a plurality of ground wires arranged
at a plurality of areas of said inner periphery.
9. An electromagnetic flow meter according to claim 7 wherein
said grounding wire comprises one part disposed along said inner
periphery and another part disposed radially at the side surface
of said annular frame.
10. An electromagnetic flow meter according to claim 1 wherein
the outer end of said grounding wire is anchored at the radially
outer part of said annular frame.
11. An electromagnetic flow meter according to claim 10 wherein
said annular frame includes a hole for anchoring said outer end
of said grounding wire.
12. An electromagnetic flow meter according to claim 1 wherein
said annular frame is comprised of a highly corrosion resistant
plastic.
13. An electromagnetic flow meter according to claim 12 wherein
said plastic is selected from the group consisting of a tetrafluoroethylene
resin, a monochlorotrifluoroethylene resin, and a copolymer of tetrafluoroethylene
and hexafluoroethylene.
14. An electromagnetic flow meter according to claim 1 wherein
said grounding wire is comprised of a highly corrosion resistant
metal.
15. An electromagnetic flow meter according to claim 14 wherein
said metal is selected from the group consisting of platinum and
tantalum.
16. An electromagnetic flow meter according to claim 1 wherein
said annular frame is comprised of a thermoplastic resin and has
a through hole from said inner periphery to said outer periphery
for passage of said grounding wire and wherein said grounding wire
is fixed in said frame by heat shrinkage of said thermoplastic resin.
17. An electromagnetic flow meter according to claim 16 wherein
said thermoplastic resin is selected from the group consisting of
a tetrafluoroethylene resin, polyethylene, and a soft tetrafluoroethylene
polymer.
Description BACKGROUND OF THE INVENTION
1. Technical Field of the Disclosure
The present invention relates to an electromagnetic flow meter,
and more particularly an electromagnetic flow meter having a grounding
means improved and adapted for metering the flow of a highly corrosive
liquid.
2. Description of the Prior Art
In the field of electromagnetic flow meters, it is known to measure
the flow of an electrically conductive or semi-conductive liquid
in a pipeline by utilizing the phenomenon that an electric conductor
moving in a magnetic field induces an electromotive force, the value
of which is proportional to the movement of the conductor. In known
devices based on this principle, the liquid flows through a pipeline
placed in a uniform magnetic field, so that its axis is at right
angles to the lines of force of the field. Arranged diametrically
opposite to one another in the wall of the pipeline are two electrodes,
so that the connecting pipeline is about at right angles to the
lines of force. Due to the flow of the liquid, a voltage is induced
between the electrodes, which is substantially proportional to the
flow of the liquid and which is measured.
In the electromagnetic flow meter, a grounding means is indispensable
from the standpoint of improving the electrical characteristics.
Effective grounding of the electromagnetic flow meter is necessary
for maximum accuracy. If the connecting pipelines are provided with
corrosion-resistant internal coats or linings, or are completely
of plastic, the connection to the counterflanges fails to achieve
reliable grounding. A grounding means or grounding ring must be
mounted on the inlet or outlet side of the electromagnetic flow
meter body. The grounding ring, that is, the ring-shaped liquid-contacting
electrode, comprises a grounding plate and a liquid-contacting electrode
and is frequently sandwiched between the electromagnetic flow meter
body and a mating pipe section of some plant pipeline.
Now, the grounding ring may be made of SUS 304 or 316 stainless
steel, which is relatively inexpensive, in the case where the fluid
to be metered is water or a slightly corrosive liquid. In case the
fluid to be metered is a highly corrosive liquid such as potassium
hydroxide (KOH), sodium hydroxide (NaOH), sulfuric acid (H.sub.2
SO.sub.4) or hydrochloric acid (HCl), however, it is difficult to
use the SUS 316 stainless steel, as will be explained in the following
Table, so that an extremely expensive material such as platinum-iridium,
platinum or tantalum, which is highly corrosion resistant, is frequently
used:
______________________________________ Name of Concen- Material
Chemical tration Temperature Pt--Ir Ir Ta SUS316 ______________________________________
HCl 10% Room A A A C 20% Temp. 35% Boiling Point C A A C H.sub.2
SO.sub.4 10% Room A A A A 60% Temp. 80% 5% Boiling A A A C 95% Point
HNO.sub.3 10% Room A A A A 30% Temp. 60% 10% Boiling A A A C 30%
Point 60% Aqua HCl:3 Room C C A C Regia HNO.sub.3 :1 Temp. Caustic
20% Room Temp. A A B B Soda 20% Boiling Point A A C B 40% Room Temp.
Boiling Point A A C -- ______________________________________
In the above Table, letters A, B and C designate "completely
corrosion resistant", "usable" and "corroded",
respectively. The platinum-iridium is a mixture containing 80 wt.
% of platinum and 20 wt. % of iridium.
According to the prior art, the grounding ring has to be made of
an expensive material from the standpoint of corrosion resistance.
Accordingly, the propriety of the material has to be taken into
consideration in view of the amount of the material used and the
construction of the grounding ring. In short, the ring-shaped, liquid-contacting
electrode according to the prior art cannot avoid an increase in
its production cost and is not proper for industrial application
because it requires a large amount of expensive material. In one
of the liquid-contacting electrodes according to the prior art,
on the other hand, screw-shaped electrodes made of an expensive
material are used together with a ring of an insulating material.
The screw-shaped electrodes are made of platinum-irridium, tantalum
or the like. The reason why the platinum-iridium is used in place
of platinum is that the corrosion resistance of platinum is superior
to the platinum-iridium, but pure platinum is too soft to be used
in the screw-type electrode. Here, the platinum-iridium has its
hardness augmented by mixing platinum with about 20 wt. % of iridium,
but it suffers several defects, namely, that it is inferior in its
corrosion resistance to platinum and that it is far more expensive
than platinum. For example, in case of using the screw-type platinum-iridium,
the amount of the material is about 32 g for 8 electrodes.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide
a novel and improved electromagnetic flow meter which can allow
its grounding means to sufficiently perform the function by using
a small amount of an expensive material having excellent corrosion
resistance.
It is another object of the invention to provide a novel electromagnetic
flow meter in which there can be mounted a grounding means without
requiring a high degree of hardness of the conductor.
It is a further object of the invention to provide a novel electromagnetic
flow meter which has a grounding means having a wire-shaped electrode
made of a less expensive platinum-containing material, without increased
hardness.
It is a still further object of the invention to provide a novel
electromagnetic flow meter which has a grounding means adaptable
for metering the flow of a highly corrosive fluid without failure
over a long time period.
It is also an object of the invention to provide an electromagnetic
flow meter wherein the conductive area of the grounding means can
be easily adjusted in accordance with the conductivity of the fluid
having its flow measured.
In accomplishing the foregoing objects, there has been provided
according to the invention an electromagnetic flow meter comprising
a flow meter body having at least one connecting end for connecting
to one end of a pipe in which the flow of a fluid is to be metered,
and grounding means held between the connecting end of the body
and the pipe, the grounding means comprising an annular frame of
an insulating material having an inner periphery defining a central
opening and an outer periphery, and a grounding wire disposed at
least at the inner periphery to be exposed to the central opening
of the annular frame.
Other objects, features and attendant advantages of the invention
will become readily apparent as the method and the apparatus become
better understood by reference to the following detailed description
of preferred embodiments, when considered in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, forming a part hereof, in which like reference
characters denote like parts in the various views,
FIG. 1 is a side view, partly broken away, of an electromagnetic
flow meter connected between pipe sections of a pipeline according
to a preferred embodiment of the invention;
FIGS. 2 and 3 are enlarged side views, partly in section, showing
the first and second constructions of connecting to the pipe according
to preferred embodiments of the invention;
FIG. 4 is a front view of grounding means according to a preferred
embodiment of the invention;
FIG. 5 is an enlarged sectional side view of the grounding means
of FIG. 4;
FIG. 6 is an enlarged front view of the grounding means of FIG.
4;
FIGS. 7 8 9 and 10 are front views of grounding means according
to other embodiments of the invention;
FIGS. 11A to 11F are enlarged sectional views of grounding ring
frames for explaining means for enhancing the air-tightness of the
end portion of a grounding wire; and
FIG. 12 is an enlarged front view of grounding means according
to a further embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention will now be described in connection with
the embodiments thereof with reference to the accompanying drawings.
In FIG. 1 a flow meter is installed between mating pipe sections
10 and 12 extending to the right and left as part of a plant pipeline.
The electromagnetic flow meter body 14 is equipped with a grounding
means and will be described in detail hereinafter. An area A appearing
in FIG. 1 is shown in an enlarged scale in FIGS. 2 and 3. The construction
and operation of the flow meter body 14 is conventional and will
not be explained in detail. Reference is made to the prior art,
e.g., Japanese Utility Model No. 38-22047 the disclosure of which
is hereby incorporated by reference.
Referring first to FIG. 2 the body 14 has flanges 16 and 18 at
both ends to enable it to be connected with flanges 20 and 22 of
the mating pipe sections 10 and 12. The body 14 is provided with
a lining 24 on its inner surface. The grounding means or grounding
ring 26 is sandwiched between the mating pipe section 12 and the
electromagnetic flow meter body 14 with intermediate packings 28.
The flange 18 of the body 14 and the flange 22 of the pipe section
12 are coupled together by fastening bolts 30. A grounding connector
32 from the grounding ring 26 is anchored on the flange 16 of the
electromagnetic flow meter body 14 by a fastening bolt 34.
Turning to FIG. 3 a protector ring 36 is juxtaposed through the
packing 28 in the grounding ring 26 on its one side, i.e., on the
side of the mating pipe section 12 to thereby protect the grounding
ring 26 from a mechanical impact. The protector ring 36 is prepared
by applying a lining 38 to the outer surface of the inner side of
a protector frame 40. The protector ring 36 is fastened to the flange
18 of the body 14 by bolts 42 one of which is shown.
Next, FIGS. 4 to 12 are various embodiments of the grounding ring
26 of FIGS. 2 and 3. As shown in FIGS. 4 5 and 6 an annular frame
44 having a ring shape has an inner periphery 46 defining a central
opening 47 and an outer periphery 48 and is constructed by forming
through holes 49 which are equidistantly arranged along the inner
peripheral edge 46 thereof. A grounding wire 50 is then threaded
through holes 49 in order, each time passing over the side surface
of the frame 44 through one of the holes 49 around the back of
the frame 44 and through the central opening 47 until it is wound
on the inner peripheral edge 46 of the frame 44.
Grounding means 26 has the grounding electrode or the grounding
wire 50 wound along the inner periphery including the part of the
grounding wire 50 which passes across the inner edge surface 46
of the frame 44 and the adjacent portions of the side surfaces of
the frame 44 which functions as an actual grounding electrode.
As shown in FIGS. 5 and 6 the grounding wire 50 has its one end
52 fixedly secured at one end of the through holes 49 and its other
end 54 fixed to an attachment means 56 which is formed by a special
through hole 58 positioned near the outer peripheral edge portion
48 of the frame 44. From there it is led out to the outside through
the grounding connector 32. The grounding connector 32 is connected
with the end portion 54 of the grounding wire 50 by means of winding
and welding.
The annular frame 44 thus constructed is made of a highly corrosion
resistant plastic, such as a tetrafluoroethylene resin, a monochlorotrifluoroethylene
resin, or a copolymer of tetrafluoroethylene and hexafluoroethylene,
and the annular frame 44 functions as an insulation bobbin for the
grounding wire 50.
On the other hand, since the grounding wire 50 is prepared by the
process of winding a thin wire, it does not require a high hardness
and there can be used platinum wire of 0.3 mm diameter, for example,
having excellent corrosion resistance. Moreover, as shown in FIG.
4 since the grounding wire 50 provides the electrode of the grounding
means 26 the area of the liquid-contacting portion can be increased
if the grounding wire 50 is wound in a different shape, e.g., a
zigzag shape. The area of the liquid-contacting portion can be varied
depending upon the value of the electrical conductivity of the fluid
to be metered, and the liquid-contacting area of the grounding means
26 must be widened for a liquid having a lower electrical conductivity.
It is possible to provide an electromagnetic flow meter which can
have the area of its liquid-contacting portion freely varied and
which can thereby enlarge its applicable range.
Except for the grounding wire 50 disposed in the grounding wire
leadout hole 78 most of the grounding wire can be used as the grounding
electrode, and the grounding wire itself is made so thin that it
can be made of a small amount of platinum or the like. The amount
of platinum for use as the grounding electrode having a diameter
of 0.03 mm and a length of 600 mm is about 0.015 g.
Accordingly, the sealing between the packings 28 and the grounding
means 26 can be accomplished by means of merely tightening the bolt
30.
FIG. 7 shows a construction in which the grounding wire 50 is divided
into two halves which are wound on opposite sides of the inner peripheral
edge 46 of the frame 44. Specifically, the grounding ring 26 is
prepared by forming the through holes 49 which are equidistantly
arranged within a predetermined range on the area adjoining the
inner peripheral edge 46 of the annular frame 44 and by winding
the divided grounding wires 60a and 60b in a manner similar to that
of FIG. 4 until their ends are fixedly wound upon the grounding
wire attachment means 62a and 62b.
Next, FIG. 8 shows a construction, in which four divided grounding
wires 64a, 64b, 64c and 64d are attached to the inner peripheral
surface portions of the annular frame 44 such that they can contact
with the liquid. In this embodiment, one end 66a, 66b, 66c or 66d
of each grounding wire is attached radially to the side surface
of the annular frame 44 whereas the other end 68a, 68b, 68c or
68d is attached radially at a distance from the first end, but also
to the side surface of the frame 44 and then is fixed to the grounding
wire attachment means or hole 70a, 70b, 70c or 70d. The attachment
of the grounding wires 64a, 64b, 64c and 64d to the frame 44 is
effected by the use of a suitable adhesive, such as, for example,
a silicone adhesive. Both ends of grounding wire 64a, 64b, 64c and
64d may penetrate radially through the annular frame 44.
On the other hand, FIG. 9 shows an example in which an annular
frame 44 having a grip portion 72 is used for facilitating assembly
and connection of the grounding connector 32 whereas FIG. 10 shows
an example in which an annular frame 44 having bolt holes 74 is
used for fitting a pipe (not shown) having bolt holes in order to
connect to the pipeline.
Normally the lead portion of the grounding wire 50 which leads
to the outside of the frame 44 is embedded in an adhesive, such
as the silicone adhesive, from the standpoint of air-tightness;
however, it is also possible to resort to other means, such as those
shown in FIGS. 11A to 11F, for example.
Specifically, as shown in FIGS. 11A to 11D, a needle or a needle-shaped
drill 76 is forced from the outside to the inside of the annular
frame 44 thereby forming a grounding wire lead-out hole 78. Subsequently,
the end portion 54 of the grounding wire 50 as shown in FIG. 11E
is inserted into the grounding wire lead-out hole 78. The annular
frame 44 is heated to cause shrinking of the plastic material in
the step depicted by FIG. 11F until it is restored to its initial
state, to thereby enhance the air-tightness. Finally, the end portion
54 is fixed to the grounding attachment means 56 or hole 58 as
shown in FIGS. 5 and 6. Generally speaking, because the tetrafluoroethylene
resin has typical plastic characteristics, if it is used to make
the annular frame 44 it experiences cold flow when extended or contracted
in a cold condition by an amount exceeding its elastic limit, until
it cannot be restored to its initial state without difficulty when
heated. A material having such characteristics is exemplified not
only by tetrafluoroethylene but also by polyethylene, soft chloroethylene
polymers and so on. Incidentally, materials having so-called "rubber
elasticity", such as chloroprene rubber require no heating
step. In this case, it is sufficient to sew the thin platinum wire
50 for example, of 0.03 mm, by the use of a hard needle connected
to the wire 50 at its end portion (not shown). In either case, the
air-tightness can be maintained if a grounding wire 50 thicker than
the lead-out hole 78 is forced into the grounding wire lead-out
hole 78. In case the grounding wire lead-out hole 78 is bigger than
the grounding wire 50 the air-tightness can be ensured by fastening
the wire between flanges.
As shown in FIG. 12 in another embodiment grooves 80 are equidistantly
formed in and along the inner peripheral edge of the grounding annular
frame 44 and are used to wind the grounding wire 50 through the
grooves 80. The grounding wire 50 is exposed to the central opening
47 of the frame 44 through the grooves 80.
The present invention should not be limited to the embodiments
thus far described. For example, the grounding wire 50 60 and 64
may be made not only of platinum but also of another material such
as tantalum or silver. Moreover, it is possible to form the grounding
wire lead-out hole 78 by preparing a mold with a needle inserted
in advance, so that the needle will be embedded when the grounding
annular frame 44 is molded, and by subsequently extracting the needle.
Moreover, the invention can be put into practice in a variety of
modifications without departing from the scope of the invention. |