Abstrict A radial field electromagnetic flow meter includes a radial magnetic
flux generator, a magnetic device surrounded by a fluid passage
for fluid to be measured and electrically insulated magnetic poles
separately positioned on a center line of the fluid passage, a tubular
part surrounding a range including the mutually opposite magnetic
poles of the magnet device through the fluid passage, and ribs radially
crossing portions of the fluid passage between one end of the magnet
device and a portion of the tubular part surrounding the one end
of the magnet device, respective surfaces of the tubular portions
and the ribs which come into contact with the fluid to be measured
being electrically insulated, whereby the magnetic reluctance of
the magnetic circuit of the magnet device can be reduced and the
sensitivity of the electromagnetic flow meter can be improved.
Claims I claim:
1. A radial field electromagnetic flow meter comprising:
a tubular outer member (1) made of a ferromagnetic material having
an inner electrically insulated wall;
a radial magnetic field generating device disposed inside said
outer member (1), having an outer electrically insulated wall;
said radial magnetic field generating device including:
an electromagnet having a core (3) made of a ferromagnetic material
and a coil (4) wound thereon, an inner cylindrical ferromagnetic
member (5) receiving one end of said core (3), and a connecting
ferromagnetic member (2) for receiving an opposite end of said core
(3), and interconnecting said magnetic field generating device with
said outer member (1), said inner magnetic member (5) and said connecting
member (2) being coaxial with said core;
an annular passage for a flow of the fluid to be measured formed
between said inner wall of said outer member and said outer wall
of said field generating device;
means for energizing said coil to produce said radial magnetic
field;
means for measuring said fluid flow by detecting the voltage induced
by said radial magnetic field passing through said fluid in said
annular passage between said inner and outer members.
2. A flow meter according to claim 1 wherein said connecting ferromagnetic
member comprises:
an inner cylindrical part (2c) for receiving said one end of said
core (3);
an outer tubular part (2a) coaxially extending at one end of said
outer member (1); and
a plurality of ribs (26) passing through said fluid passage for
connecting said inner and outer parts (2a, 2c), said ribs having
surfaces contacting said fluid electrically insulated.
Description BACKGROUND OF THE INVENTION
The present invention relates to a radial field electromagnetic
flow meter. The "radial field electromagnetic flow meter"
is defined herein as an electromagnetic flow meter which comprises:
a linear fluid passage for allowing an electrically conductive fluid
to flow therethrough, having an annular cross-section and being
surrounded by electrically insulating surfaces; a radial field generator
for generating magnetic flux over the entire circumference in a
space including a cross-section of the fluid passage in radial directions
with respect to the center line of the space; a separating plate
made of non-magnetic material, extended along at least a part of
the radial magnetic flux, and projected into the fluid passage in
parallel with the center line, the surfaces of both sides of the
separating plate being electrically insulated from each other; and
a pair of electrodes disposed in the foregoing space of the radial
magnetic flux respectively, at portions close to mutually opposite
ends of an angular range not including the separating plate; whereby
a signal voltage proportional to the flow rate of the fluid to be
measured is generated on the basis of an electromotive force induced
across the pair of electrodes due to the movement of the electrically
conductive fluid across the radial magnetic flux.
As prior art of such a radial field electromagnetic flow meter,
there are those disclosed in Japanese Pat. Publication No. 56-54565
and U.S. Pat. No. 3911742. The magnetic circuit of the radial
field generator used in these radial field electromagnetic flow
meters is arranged so that none of its parts are made of ferromagnetic
material with the exception of a magnet device having north and
south magnetic poles arranged along the center line of the fluid
passage.
In the conventional radial field electromagnetic flow meter described
above, the magnetic circuit of the radial magnetic flux generator
does not have any parts made of ferromagnetic material with the
exception of the magnet device, so a disadvantage has existed in
prior devices that the magnetic reluctance is a large amount and
large energy is required to obtain the sufficient magnetic flux
density required by the radial magnetic field.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to eliminate
the disadvantage of the prior art as described above.
It is another object of the present invention to provide a radial
field electromagnetic flow meter, with improved sensitivity through
reduced reluctance of the magnetic circuit.
The electromagnetic flow meter according to the present invention
is a radial field electromagnetic flow meter that comprises, as
a main part of a radial field generator, a single magnet device
surrounded by a fluid passage for fluid to be measured and electrically
insulated from the fluid passage, north and south poles thereof
being separately positioned on center line of the fluid passage.
The radial field generator also comprises a tubular part surrounding
the fluid passage surrounding the magnet device in a range including
north and south magnetic poles, and ribs radially crossing a portion
of the fluid passage between one end of the magnet device and a
portion of the tubular part surrounding the one end of the magnet
device, the tubular part and the ribs both being made of ferromagnetic
material and the surface thereof which contacts the fluid to be
measured, being electrically insulated from the fluid.
The magnetic flux of the magnet device (4 5 3 2c, and 6) due
to excitation in one direction, radially passes through the fluid
passage (8) having an annular cross-section from the one end (5)
(inner yoke) of the magnet device opposite to the other end (2),
enters the main portion (1) (outer yoke) of the tubular part, and
comes back to the one end (2c) of the magnet device through one
end (2a) of the tubular part and the ribs (2b), as shown in FIG.
4. In case of reverse excitation, the direction of the magnetic
flux is of course reversed. In each case, the magnetic flux portion
in the fluid passage (8) is in the radial direction of the fluid
passage (8) (as shown by arrows in FIG. 3), and the induced voltage
is maintained in one circumferential direction over the entire fluid
passage portion while the magnetic flux is maintained in one direction.
Accordingly, by proper selection of the respective positions of
the electrodes (10a) and (10b) on mutually opposite sides of the
separating plate (9), an induced voltage, integrated substantially
over the entire circumference 2 .pi.r, can be derived as a signal
voltage. Since the fluid passage (8) surrounding the magnet device
(4 5 3 2c, and 6) is surrounded by the tubular part which is
made of magnetic material and the end (2c) of the magnet device
is magnetically connected to the end (2a) of the tubular portion
through the ribs (2b), no leakage of the magnetic flux occurs to
the outside.
The above and other objects and features of the invention will
appear more fully hereinafter from consideration of the following
description taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an embodiment according to the present invention and
is a longitudinal cross-section taken on line I--I in FIG. 2 extending
in parallel with the flowing direction of the fluid;
FIG. 2 is a side view taken on line II--II of FIG. 1;
FIG. 3 is a cross-section taken on line III--III of FIG. 1; and
FIG. 4 is a reduced schematic diagram of FIG. 1 showing the path
of the magnetic flux.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In an embodiment shown in FIGS. 1 and 2 an additional electronic
circuit is provided for processing a signal voltage induced across
the electrodes and a housing for containing the electronic circuit,
(not shown) cylindrical outer yoke 1 made of a soft ferromagnetic
material, is fitted at one end of a connecting yoke 2 which serves
as a mouth piece. The connecting yoke 2 is made of a soft ferromagnetic
material and integrally constituted by a cylindrical short tubular
portion 2a having substantially the same inner diameter as that
of the outer yoke 1 four radial ribs 2b crossing a fluid passage,
and a cylindrical portion 2c are disposed at the center of the fluid
passage coaxially with the outer yoke 1. The right end of the cylindrical
portion 2c in FIG. 1 is shaped in a substantially semispherical
streamline, so as not to disturb the flow of the fluid. The ribs
2b act to mechanically and magnetically connect the short tubular
portion 2a and the cylindrical portion 2c with each other. A male
thread 2d is formed on the outer periphery of the short tubular
portion 2a. The short tubular portion 2a of the connecting yoke
2 is fitted on the right end of the outer yoke 1 with a watertight
O-shaped ring interposed therebetween.
A mouth piece 2' made of non-magnetic material is fitted on the
other end, of the outer yoke 1 and integrally constituted by a
cylindrical mouth piece portion 2a' having substantially the same
inner diameter as that of the outer yoke 1 four ribs 2b', and a
cylindrical portion 2c' shaped in substantially semispherical streamline.
A male thread 2d' is formed in the outer periphery of the mouth
piece portion 2a'. The mouth piece 2' is fitted on the left end
of the outer yoke 1 with an O-shaped ring interposed therebetween.
A core 3 made of a ferromagnetic material and a coil 4 would thereon
constitute an electromagnet. A cylindrical inner yoke 5 made of
a soft magnetic material, the core 3 of the electromagnet, and the
cylindrical portion 2c of the connecting yoke 2 are arranged coaxially.
A magnet cover 6 has a cylindrical external shape and is made of
an electrically isnulating and nonmagnetic material. As shown in
FIG. 1 a relatively shallow cylindrical hole formed in the magnet
cover 6 at the left end thereof is fitted on the right end of the
cylindrical portion 2c' of the mouth piece 2'. In a relatively deep
cylindrical hole formed at the right end of the magnetic cover 6
the inner yoke 5 the core 3 and the coil 4 constituting the electromagnet
are adjoiningly received in the order as described above from the
exterior, and the left end of the cylindrical portion 2c of the
connecting yoke 2 is fitted to the same cylindrical hole with an
O-shaped ring 7 interposed therebetween. As shown in FIG. 1 the
opposing ends of the electromagnet core 3 are coaxially fitted in
the inner yoke 5 and the cylindrical portion 2c of the connecting
yoke 2 respectively. Thus, a fluid passage 8 having an annular cross-section
is formed between the cylindrical outer yoke 1 and the magnet cover
6 so that a fluid to be measured flows in the fluid passage 8. Each
of the inner surface of the outer yoke 1 and the outer surface of
the magnet cover 6 is convered with an electrically insulating coating.
A separating plate 9 formed integrally with the magnet cover 6
and projected so as to abut on the inner surface of the outer yoke
1 is provided along the center line of and in a radial direction
of the fluid passage 8 upper portion. The outer surface of the separating
plate 9 is also covered with an insulating coating. Electrodes 10a
and 10b are provided respectively on the mutually opposite surfaces
of the separating plate, and a signal voltage across the electrodes
is derived through insulated lead wires passed through the outer
yoke 1 to the outside.
Lead wires 11 of the electromagnet coil 4 are water-tight and are
radially led out through a hole which penetrates through one of
the ribs 2b of the connecting yoke 2. FIG. 3 illustrates the shape
in cross-section of the magnetic circuit and the fluid passage.
In FIG. 3 the distance between the electrodes 10a and 10b in the
direction of potential is determined on the basis of the average
radius r of the fluid passage 8 to be approximately 2 .pi.r. While
the exciting current is kept constant, the magnetic flux in the
fluid passage 8 is limited to a single direction from the inner
yoke 5 to the outer yoke 1 (or, alternatively, from the outer yoke
to the inner yoke), so that the length of gap in the magnetic circuit
is limited to a path from the outer peripheral surface of the inner
yoke 5 to the inner peripheral surface of the outer yoke 1. Although
an electromagnet is employed in the foregoing embodiment, a permanent
magnet may be used to generate radial magnetic flux.
According to the present invention, all parts of the magnetic path
except the gap are made of ferromagnetic material, so that magnetic
reluctance due to the gap in the magnetic circuit is small and the
sensitivity in measuring the flow rate is improved. Further, the
excitation power can be reduced when the induced voltage is about
the same degree as in the conventional case, so that in case batteries
are used for performing excitation, the batteries may have reduced
capacity. Thus, the required number of batteries may be reduced
to half or less in comparison with the case where a non-magnetic
tube is used instead of the outer yoke 1. Moreover, since the whole
of the magnetic circuit is housed within the outer yoke which is
used as a pipe for example, the magnetic circuit can be of smaller
size and the magnetic flux is prevented from leaking to the outside.
The magnetic circuit is not affected by any ferromagnetic body even
if the latter closely approaches the former to thereby obtain stable
accuracy. Moreover, since the mechanical strength is assigned to
the pipe for example, the structure can be made simple. |