Abstrict Electrodes for an electromagnetic flow meter are mounted through
a pipe wall using pairs of concentric electrodes electrically insulated
from each other and from the mounting pipeline while electrically
contacting a fluid in the pipeline being measured for flow rate.
The electrode pairs are held on the pipeline wall on a line intersecting
the fluid flow at a right angle and are electrically connected to
supply signals induced by the fluid flow to a measuring circuit.
The concentric electrode structure provides two electrode pairs
at each electrode site on the pipeline wall.
Claims The embodiments of the invention in which an exclusive property
or privilege is claimed are defined as follows:
1. An electrode structure comprising
a center electrode,
an electrically insulating tube surrounding a portion of said center
electrode,
an outer electrode surrounding a portion of said tube and
clamping means for compressing said center electrode and outer
electrodes against said insulating tube wherein said center electrode
includes a first radially outwardly extending collar, said outer
electrode includes a second radially outwardly extending collar
and said tube includes a third radially outwardly extending collar
located between said first and second collars and said clamping
means is arranged to urge said first and second collars against
said third collar.
2. An electrode structure as set forth in claim 1 and further including
means for mounting said electrode structure through a pipeline wall
whereby said center and outer electrodes are in electrical contact
with a fluid carried by said pipeline and electrically insulated
from the pipeline wall.
3. An electrode structure as set forth in claim 2 and further
including first electrical connection means for providing an electrical
connection to said center electrode and second electrical connection
means for providing an electrical connection to said outer electrode.
4. An electrode structure as set forth in claim 1 and further including
means for mounting said electrode structure through a pipeline wall
whereby said center and outer electrodes are in electrical contact
with a fluid carried by said pipeline and electrically insulated
from the pipeline wall, said mounting means including spring means
to further urge said second collar against an electrically insulated
pipeline wall.
5. An electrode structure as set forth in claim 1 and further including
first electrical connection means for providing an electrical connection
to said center electrode and second electrical connection means
for providing an electrical connection to said outer electrode.
6. In an electromagnetic flow meter including a pipe for guiding
fluid, a magnetic field generator for generating a magnetic field
which intersects the fluid flow direction at a right angle and fluid
contacting electrodes facing each other across the pipe in such
a manner that a center line combining them intersects the flow direction
and the magnetic field at a right angle, characterized in that at
least one of the fluid contacting electrodes is an electrode assembly
having a plurality of coaxial electrodes and electrically insulating
means electrically isolating said plurality of electrodes from each
other, said electrode assembly including
a center electrode,
an electrically insulating tube surrounding a portion of said center
electrode,
an outer electrode surrounding a portion of said tube and
clamping means for compressing said center and outer electrodes
against said insulating tube,
wherein said center electrode includes a first radially outwardly
extending collar, said outer electrode includes a second radially
outwardly extending collar and said tube includes a third radially
outwardly entending collar clamped between said first and second
collars and said clamping means is arranged to urge said first and
second collars against said third collar.
7. In an electromagnetic flow meter as set forth in claim 6 and
further including means for mounting said electrode structure through
a pipeline wall whereby said center and outer electrodes are in
electrical contact with a fluid carried by said pipeline and electrically
insulated from the pipeline wall.
8. In an electromagnetic flow meter as set forth in claim 6 and
further including first electrical connection means for providing
an electrical connection to said center electrode and second electrical
connection means for providing an electrical connection to said
outer electrode.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electromagnetic flow meters. More
specifically, the present invention is directed to electrodes for
electromagnetic flow meters.
2. Description of the Prior Art
The well-known electromagnetic flow meter is an instrument in which
there is provided a magnetic field at a right angle through a fluid
flow in a pipeline and also there are provided electrodes contacting
the pipeline fluid for detecting flow quantity. The electrodes are
located facing each other across the flow passing through said magnetic
field and are intersecting the flow direction and the magnetic field
at a right angle. The flow quantity can be determined by measuring
an electromotive force that is generated between the electrodes
in proportion to the average flow quantity. In the electromagnetic
flow meter of this kind, the following prior art structure has been
used in order to increase the level of the detected electromotive
force between said electrodes without increasing the intensity of
the magnetic field. Namely, according to the prior art structure,
there are provided a plurality of pairs of rod type electrodes which
are arranged along the wall of a fluid flow carrying pipe so as
to make a straight line along the axis of said pipe. Further, the
electromotive forces generated between respective electrode pairs
are summed to increase the total level of the electromotive force.
According to the electrode arrangement like that, however, there
occur the disadvantages that more pipeline sites are needed for
installing the electrodes, that more pipeline area is required for
installing the electrodes, that the size of the flow meter becomes
larger, that the number of parts of the flow meter is increased,
and so forth. Accordingly, it is desirable to provide an electrode
structure for providing an increase in the detected flow signal
while avoiding the aforesaid disadvantages of the prior art.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved electrode
structure for an electromagnetic flow meter.
In accomplishing these and other objects, there has been provided
in accordance with the present invention, an electrode structure
for an electromagnetic flow meter having a pair of coaxial electrodes,
insulating means electrically isolating the pair of electrodes from
each other and clamping means for clamping the coaxial electrodes
and the insulating means together. The electrode structure further
includes mounting means for mounting the electrode structure through
a pipeline wall in electrical contact with a fluid carried by the
pipeline.
BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the present invention may be had when
the following detailed description is read in connection with the
accompanying drawings, in which:
FIG. 1 is a diagrammatical representation of the electromagnetic
flow meter embodying this invention,
FIG. 2 a magnified cross-sectional view of a part of an outside
mounting type electrode assembly according to this invention;
FIG. 3 a cross-sectional view of a part of an inside mounting type
electrode assembly according to this invention, and
FIG. 4 illustrates another example of an electromagnetic flow meter
according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a cross-sectional view of an electromagnetic flow meter
according to this device. In FIG. 1 a reference numeral 1 designates
a wall of a pipe for guiding fluid to be measured which is made
to a non-magnetic material like a suitable type of stainless steel.
Reference numeral 2 designates an excitation coil for generating
a magnetic field which is arranged to intersect the longitudinal
axis of the pipe 1 i.e., the flow direction of the pipe fluid,
at a right angle. Reference numeral 3 designates a lining coated
on the inside wall of the pipe 1 for the purpose of electrical insulation.
An electrode assembly 4 according to the present invention includes
an inner electrode 5 an insulation spacer 6 and an outer electrode
7. These inner and outer electrodes 5 and 7 are held in a coaxial
relation via the insulating spacer 6. A similar complex electrode
assembly 4' located on the opposite side of the pipe 2 from the
electrode assembly 4 comprises an inner electrode 5', an insulating
spacer 6' and an outer electrode 7', and these three constituents
are also held in coaxial relation. Inner electrodes 5 and 5', and
outer electrodes 7 and 7' constitute opposing electrode pairs, respectively,
and are connected to output terminals 8 and 9 respectively. Electromotive
forces generated between these electrode pairs are, thus, applied
to the terminals 8 and 9 in proportion to the average flow quantity
in the pipe 2.
FIG. 2 is a magnified cross-sectional view of one of the electrode
assemblies 4 4' to show the details thereof. In FIG. 2 an insulating
lining 3 applied to the inner surface of the pipe wall 1 extends
along the inner surface of a hole 41 in the pipe wall 1. The hole
41 is formed in the pipe wall 1 so as to receive tightly the assembly
4 and extends from the inside surface to the outside surface of
the pipe wall 1. A hollow cylindrical outer electrode 7 is tightly
inserted into the hole 41 in contact with the line 3. One end of
this outer electrode 7 is preferably flush with the lining 3 while
being exposed to the inside of the pipe. The other end of the same
has a radially outwardly extending collar 71 from which a connecting
electrically conductive rod 72 having an insulating coating on its
outer surface periphery is extended outwardly from the pipe wall
1 upwardly. The connecting rod 72 has an electrical connection terminal
73 at its free end.
The insulating spacer 6 in the form of a hollow cylinder or tube
is inserted into the hollow center portion of the outer electrode
7 with an inner end also flush with the insulating lining 3. Similarly,
the cylindrical center or inner electrode 5 is inserted into the
hollow center portion of the insulating tube 6 with one end flush
with the lining 3. This inner electrode 5 has a radially outwardly
extending collar 51 at its center portion. An upper or outward portion
of the electrode 5 extending past the collar 51 has an insulating
coating 52 formed around its outer periphery while the electrode
5 extends further to an electrical connection terminal 53. A radially
outwardly extending collar 61 is formed at the outer end of the
insulating tube 6 to insulate the collar 71 of the outer electrode
7 from the collar 51 of the inner electrode 5. The insulating coating
52 covering the upper or outward portion of said inner electrode
5 is extended to also cover the outer surface of the collar 51.
The electrode group or assembly as arranged above is fluid-tight
installed on the pipe 1 by means of a lower or inner plate 10 an
upper or outer plate 11 a spring 12 disposed therebetween and threaded
bolts 13 for fastening those together. Specifically, the lower and
upper plates 10 11 are similar elements each having a center hole
for allowing the center electrode 5 and the insulating coating 52
to extend therethrough. A radially displaced hole in each of the
plates 10 and 11 allows the rod 72 and its insulating coating to
extend therethrough when the radially displaced holes are aligned.
Finally, each of the plates 10 and 11 have peripheral holes extending
therethrough to allow the shanks of the bolts 13 to extend therethrough.
The threaded bolts are arranged to thread into threaded holes 15
in the pipe wall 1. Thus, the assembled layered structure having
the plates 10 and 11 and the spring 12 therebetween is held on the
pipe wall 1 by the bolts 13. The spring 12 is arranged to be concentric
with the center electrode 5 whereby it is effective to transmit
a pressure from the outer plate 11 produced by the bolt heads of
the bolts 13 bearing on the outer plate 11 to the inner plate 10.
The inner plate 10 in turn, exerts a pressure on the collars 51
61 and 71 through the insulating coating 52 to hold the electrode
assembly against the insulating lining 3 on the pipe wall 1 to assure
a fluid-tight connection. Concurrently, the electrodes 5 and 7 are
electrically insulated from each other and the pipe wall 1.
The electrode assembly as shown in FIG. 2 is a so-called outside
mounting type electrode which is installed on the outside of the
pipe wall 1. However, the present invention is not limited to this
type but is also applicable to a so-called inside mounting type.
FIG. 3 is a magnified cross-sectional view of an inside mounting
type electrode structure according to the present invention. In
FIG. 3 a hollow cylindrical outer electrode 7A without an outwardly
extending collar is inserted from the inside of the pipe wall 1
into the hole 41 having an insulating lining 3 on its inside wall.
A tubular electrically insulating member 6A is inserted into the
hollow center of the electrode 7A and extends into the inner end
of the electrode 7A to a point past the outer end of the electrode
7A. Then an inner electrode 5A is inserted through the hollow portion
of the insulating member 6A. An insulating washer 14 is mounted
on a wedge ring 74 which has a ridge contact with the upper or outer
end of the outer electrode 7A. The outer end of the center electrode
5A is threaded to accept a flattened nut 16. An concentric spring
17 is positioned around the electrode 5A between the nut 16 and
the washer 14 while being electrically insulated from the electrode
5A by the tube 6A and from the wedge ring 74 by the electrically
insulating washer 14. The head of the electrode 5A is tapered to
urge the adjacent ends of the tube 6A and the electrode 7A against
the insulating lining 3 when the electrode 5A is pulled into the
hole 41 by spring 17 and nut 16. The resulting layered combination
may form a substantially smooth transition surface across the hole
41 although the flush surface state with the lining 3 exhibited
by the outer electrode assembly of FIG. 2 may not be achieved. However,
when the spring 17 sandwiched between the washer 14 and nut 16 is
compressed by tightening the nut 16 the electrode assembly of FIG.
3 can thus be mounted fluid-tight on the wall of the pipe 1. Electrical
connections 18 19 may be made by any convenient technique to the
electrodes 5A and 7A, respectively, to provide electrical signal
paths thereto.
In examples of the present invention explained hereunto, the electrode
assembly comprises the outer and inner electrodes, e.g., electrodes
5 and 7. However, the present invention is not limited to the case
of a two electrodes structure but is also capable of being extended
to a greater number of electrodes, e.g., a coaxial three electrodes
structure, when it is needed.
The foregoing explanation has also been made in connection with
the case wherein the coaxial electrode assemblies include two similar
electrode assemblies located in the pipe wall 1 opposite each other
and having a substantially identical structure to each other. However,
it should be noted that the present invention is not limited thereto.
That is, as shown in FIG. 4 it is possible to constitute a pair
of electrodes by means of the electrode assembly 4 located in pipe
wall 1 and including the inner electrode 5 and the outer electrode
7 in coaxial relation to form one of the pair of electrodes and
a single conventional electrode 40 located in the pipe wall 1 and
having a large area as the other of the pair of electrodes.
As discussed above, according to the present invention, at least
one of opposing electrodes are constituted with the coaxially arranged
electrode assembly. Therefore, it is possible to establish a small
electromagnetic flow meter wherein the number of parts is decreased
and a larger electromotive force can be obtained without increasing
the number of electrode sites and the area for electrode installation.
Further, according to the present invention, a plurality of electrode
pairs are arranged coaxially in the small area, so that respective
electrodes can measure the flow quantity under a uniform magnetic
field whereby errors among the electrodes are minimized.
Accordingly, it may be seen that there has been provided, in accordance
with the present invention, an improved electrode assembly for an
electromagnetic flow meter. |