Electromagnetic flow meter

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.

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.

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.