Abstrict In an area flow meter, float 22 made of material larger in specific
gravity than a fluid being measured is movably disposed in vertical
pipe 21. Magnet 23 in the float 22 has its north and south poles
aligned vertically to produce magnetic-force lines 26 symmetrically
with respect to its symmetry axis. Magnetism-gathering tapered element
27 made of a high-permeability material is configured to flare outwardly
from its fixed end to its free end to have their fixed ends mounted
on magnetism-responsive surfaces of magnetic sensors "A"
which are at the same distance from the symmetry axis and disposed
outside the pipe on a plane perpendicular to the axis. The flux
caught by the elements 27 is gathered on the surfaces to boost only
output sensitivity required for detection of the float in position.
Claims What is claimed is:
1. In an area flow meter comprising:
a vertical flow passage pipe through which a fluid being measured
flows upward; and
a float made of a material larger in specific gravity than said
fluid, said float being mounted in said flow passage pipe so as
to be vertically movable in said flow passage pipe, an effective
cross-sectional area of which varies when said float is vertically
moved by said fluid;
the improvement wherein:
the area flow meter further comprises a magnet (23) and a pair
of Hall devices;
said magnet is mounted in said float, and is so magnetized as to
have its north and south poles aligned vertically, whereby said
magnet produces magnetic-force lines symmetrically with respect
to a vertical symmetry axis thereof which is parallel to a direction
in which said float moves; and
each of said pair of Hall devices is provided with a magnetism-responsive
surface, is at the same distance from said symmetry axis of said
magnet, and is disposed outside said flow passage pipe on a plane
perpendicular to said symmetry axis of said magnet so that one of
said Hall devices has said magnetism-responsive surface thereof
arranged horizontally while the other of said Hall devices has said
magnetism-responsive surface thereof arranged vertically.
2. The area flow meter as set forth in claim 1 wherein:
each of said Hall devices is provided with a magnetism-gathering
tapered element in said magnetism-responsive surface thereof, said
magnetism-gathering tapered element being made of a high-permeability
material and so configured as to flare outwardly from a fixed end
thereof to a free end thereof.
3. The area flow meter as set forth in claim 2 wherein:
said magnetism-gathering tapered element is made of Permalloy.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an area flow meter for measuring
a flow rate of a fluid passing through a flow passage pipe on the
basis of a position of a float movably mounted inside the flow passage
pipe.
2. Description of the Prior Art
A so-called area flow meter is widely used, in which a movable
element or float is larger in specific gravity than a fluid being
measured. The float is disposed inside a vertical flow passage pipe
of the flow meter so as to be movable up and down therein. As the
float moves upward, the flow passage pipe has its effective cross-sectional
area gradually increased. A flow rate of a fluid passing through
the flow passage pipe upward is determined on the basis of the position
of the float. Some of the area flow meters have their flow passage
pipes constructed of opaque members. In this opaque type of area
flow meter, some detection means which is disposed outside the flow
passage pipe so as to detect the position or height of the float
outside the pipe is required. It is necessary for such detection
means to convert a value of the position or height of the float
into an electrical signal.
There are various types of the detection means for converting the
value of the height of the float into the electrical signal. As
shown in FIG. 8 (Prior Art), the applicant's company has developed
one of these conventional detection means for determining the height
of the float, in which one: a magnet M is fixedly mounted in a float
F; and, a pair of magnetic sensors such as Hall devices A-1 A-2
are disposed outside the flow passage pipe so that the height of
the float is determined on the basis of output signals issued from
the magnetic sensors such as the Hall devices.
In the conventional detection means, the height of the float is
determined on the basis of the angle of inclination of the magnetic-force
line issued from the magnet mounted in the float. The conventional
detection means requires no movable mechanism with the exception
of the float, and, therefore is excellent in reliability and compact
in construction. However, the conventional detection means is suffering
from the following problems:
(1) Since the magnet is largely spaced apart from the magnetic
sensors, the magnetic force of the magnet damps or weakens in the
vicinities of the magnetic sensors. Consequently, in order to ensure
high-accuracy measurements of the position of the float, it is necessary
for the conventional detection means to have its magnetic sensors
improved in sensitivity or to have its magnet improved in strength
of magnetic force;
(2) In the area flow meter, there is a close relationship between
dimensions/weight of the float and the measuring range of the flow
meter, which limits the magnet mounted in the float in size, and,
therefore in strength of magnetic force;
(3) Of the conventional magnetic sensors, ones excellent in sensitivity
and stable in output are very expensive and not available for reasonable
prices, which makes it difficult to use such expensive sensors in
the conventional area flow meter; and
(4) Some fluid to be measured by the area flow meter is high in
temperature. When such high-temperature fluid is measured in flow
rate, it is necessary to have the flow passage pipe or the float
largely spaced apart from the magnetic sensors so as to permit the
magnetic sensors to be disposed in places having moderate temperatures
which ensure proper operations of the magnetic sensors. However,
this arrangement of the magnetic sensors is not realistic due to
poor sensitivities of the magnetic sensors. Further, there are various
types of magnetic sensors which permit their electrical variables
representing physical quantities to vary in response to the magnetic
flux density of the magnet. Of these types of magnetic sensors,
a typical one is a so-called Hall device.
As shown in FIG. 9 (Prior Art), the Hall device is provided with
four terminals, of which a pair of ones are electric-power supply
terminals. When the Hall device is energized with an electric power
P supplied through the electric-power supply terminals, the other
pair of the terminals of the Hall device produce there between an
output voltage E which corresponds to a magnetic flux density B
of the magnet, which magnetic flux density B is measured in a magnetism-responsive
surface of the Hall device. Consequently, it is possible to determine
the magnetic flux density B of the magnet on the basis of the output
voltage E of the Hall device, the magnetic flux density B appearing
in the magnetism-responsive surface of the Hall device.
In the conventional detection means shown in FIG. 8 described above,
the pair of the Hall devices A-1 A-2 have their magnetism-responsive
surfaces crossed at right angles with each other so that the position
or height of the magnet in the float is determined on the basis
of output voltages issued from the Hall devices A-1 A-2. This conventional
detection means is excellent in principle. However, the detection
means requires the Hall devices to be excellent in output sensitivities
corresponding to the magnetic flux density in order to realize high-accuracy
measurements of the fluid in flow rate. As a means for improving
the Hall device in output sensitivity, there is a known amplifier
means for electrically boosting the output voltage of the Hall device.
However, such amplifier means also boosts any other noises such
as electrical noises of the Hall device itself, external electrical
noises, and other electrical physical quantities forming obstacles
to the measurements of the fluid in flow rate, the obstacles including
the zero drift of the Hall device in the measurements. Consequently,
the amplifier means is not adequate to the needs.
Further, there are various methods for catching the magnetic flux
of the magnet through magnetic-permeability elements excellent in
permeability. However, any of these methods is not good in application
thereof.
The reason why an effective application of any one of the above
methods is not realized in the prior art is that: the magnetic-permeability
element excellent in permeability tends to be magnetically saturated,
which prevents the magnetic flux proportionate to the magnetic flux
density near the element from concentrating in the element.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an area flow
meter, in which a magnetic flux having been caught concentrates
in a magnetism-responsive surface of a magnetic sensor so that only
an output sensitivity required for detection of the position of
a magnet in a float is boosted to determine the flow rate of a fluid
with high accuracy.
According to a first aspect of the present invention, the above
object of the present invention is accomplished by providing:
An area flow meter comprising:
a vertical flow passage pipe through which a fluid being measured
flows upward;
a float made of a material larger in specific gravity than the
fluid, the float being mounted in the flow passage pipe so as to
be vertically movable in the flow passage pipe an effective cross-sectional
area of which varies when the float is vertically moved by the fluid;
a magnet which is mounted in the float and so magnetized as to
have its north and south poles aligned vertically, whereby the magnet
produces its magnetic-force lines symmetrically with respect to
its vertical symmetry axis which is parallel to a direction in which
the float moves; and
a plurality of magnetic sensors provided with magnetism-responsive
surfaces, mounted on each of which surfaces is a fixed end of a
magnetism-gathering tapered element made of a high-permeability
material, the tapered element being so configured as to flare outwardly
from the fixed end to its free end, each of the magnetic sensors
being at the same distance from the symmetry axis of the magnet
and disposed outside the flow passage pipe on a plane perpendicular
to the symmetry axis of the magnet.
According to a second aspect of the present invention, the above
object of the present invention is accomplished by providing:
The area flow meter as set forth in the first aspect of the present
invention, wherein:
each of the magnetic sensors is provided with the magnetism-responsive
surface in each of its opposite sides; and
the magnetism-gathering tapered element is mounted on each of the
magnetism-responsive surfaces of the opposite sides of each of the
magnetic sensors.
According to a third aspect of the present invention, the above
object of the present invention is accomplished by providing:
The area flow meter as set forth in the first or the second aspect
of the present invention, wherein:
each of the magnetic sensors is constructed of a Hall device.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view illustrating the principle of the present invention;
FIG. 2 is a distribution graph of the magnetic flux of the magnet
in the float of an embodiment of the present invention;
FIG. 3 is a view illustrating the relationship between the positions
of the magnet and the tangential angles of the magnetic-force lines
of the magnet in the embodiment of the present invention;
FIG. 4 is an overall schematic view of the embodiment of the present
invention;
FIG. 5(a) is a perspective view of an example of the magnetic sensor
used in the embodiment of the present invention;
FIG. 5(b) is a perspective view of another example of the magnetic
sensor used in the embodiment of the present invention;
FIG. 6 is a perspective view of the embodiment of the present invention,
illustrating its essential construction;
FIG. 7 is a graph illustrating an example of experimantal data
of the magnetic sensors used in the embodiment of the present invention;
FIG. 8 is an overall schematic view of the conventional area flow
meter, illustrating the means for converting a value of the height
of the float into an electrical signal; and
FIG. 9 is a perspective view of an example of the conventional
magnetic sensor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinbelow, the present invention will be described in detail
with reference to the accompanying drawings. FIGS. 1 to 3 show the
principle of the present invention.
As shown in FIG. 1 in an embodiment of an area flow meter of the
present invention, a float 22 is disposed inside a vertical flow
passage pipe 21 so as to be vertically movable therein. A magnet
23 which is so magnetized as to have its north and south poles
aligned in a vertical direction, is fixedly mounted in the float
22. The magnet 22 assumes a symmetrical form having a vertical symmetry
axis L, which results in a symmetrical distribution of the magnetic
flux density of the magnet 22 with respect to the symmetry axis.
Consequently, as shown in FIG. 1 on a circle 25 which consists
of all points at a given distance from its center coinciding with
the symmetry axis L in a horizontal plane 24 perpendicular to the
symmetry axis L: magnetic flux densities B in planes perpendicular
to magnetic-force lines 26 are the same in magnitude at any of the
above-mentioned points; and, tangential angles .phi. (i.e., - .phi..sub.2
- .phi..sub.1 . . . , .phi..sub.3 .phi..sub.4 , , . . . , as
shown in FIG. 2), each of which is an angle formed between each
of the magnetic-force lines 26 and the symmetry axis L, are also
the same in magnitude at any of the above-mentioned points.
Since the magnetic-force lines 26 of the magnet 23 substantially
do not vary in geometry or arrangement thereof even when the magnetic
force of the magnet 23 varies in magnitude to some extent, the tangential
angle .phi. in each of the above-mentioned points on the common
circle 25 shown in FIG. 1 substantially remains constant even when
the magnetic force of the magnet 23 varies in magnitude to some
extent under the influence of its environmental temperature variations.
Consequently, it is possible to determine the tangential angle .phi.
on the basis of a relative height h of the magnet 23 relative to
the plane 24.
In other words, as shown in FIG. 2 which is a side view of the
magnet 23 so magnetized as to have its north and south poles aligned
in a vertical line, when the relative height h of the magnet 23
varies in a condition in which the circle 25 keeps its radius r
constant, the tangential angle .phi. of the magnetic-force line
26 varies in a manner shown in FIG. 3 so as to correspond to the
relative height h of the magnet 23. This phenomenon does not vary
even when the float 22 rotates on its central axis, provided that
the central axis is kept in a position coincident with the symmetry
axis L of the magnet 23.
The radius r of the circle 25 is so determined as to dispose the
circle 25 outside the flow passage pipe 21. A pair of magnetic sensors
A-1 A-2 having the same properties are disposed on the circle 25.
Each of the magnetic sensors A-1 A-2 is provided with magnetism-responsive
surfaces, and issues an electrical signal corresponding to the magnetic
flux density detected in the magnetism-responsive surfaces. Typical
ones of the magnetic sensors A-1 A-2 are Hall devices and like
magnetism-responsive devices. In the embodiment of the area flow
meter of the present invention, the Hall devices are used as the
magnetic sensors A-1 A-2.
Of the magnetic sensors or Hall devices A-1 A-2 one A-1 has its
magnetism-responsive surfaces disposed perpendicularly to the symmetry
axis L of the magnet 23 while the other A-2 has its magnetism-responsive
surfaces disposed parallel to the symmetry axis L. The Hall devices
A-1 and A-2 are provided with signal-converter circuits to issue
with the same gain K their output signals E.sub.1 and E.sub.2 respectively.
These output signals E.sub.1 E.sub.2 correspond to the magnetic
flux densities detected in the magnetism-responsive surfaces of
the Hall devices A-1 A-2. In other words, the output signals E.sub.1
E.sub.2 can be represented by the following equations:
where: B.sub.1 is the magnetic flux density detected in the magnetism-responsive
surfaces of the Hall device A-1; and, B.sub.2 is the magnetic flux
density detected in the magnetism-responsive surfaces of the Hall
device A-2.
As already described above, since the tangential angle .phi., which
is formed between the magnetic-force line and the symmetry axis
at each of all the points on the circle 25 and, the magnetic flux
density B in each of the planes perpendicular to the magnetic-force
lines are constant in magnitude at any of the points on the circle
25 each of the output signals E.sub.1 E.sub.2 is determined on
the basis of an angle formed between each of the magnetism-responsive
surfaces of the Hall devices and each of the magnetic-force lines.
Consequently, the output signals E.sub.1 E.sub.2 can be represented
by the following equations:
where: K is a constant.
Combining these equations and eliminating both the magnetic flux
density B and the constant K gives the following equations (1) and
(2):
The equation (2) clarifies that the tangential angle .phi. of the
magnetic-force lines is derived from only the output signals E.sub.1
E.sub.2 of the two sensors A-1 A-2 without using the magnetic flux
density B, and, therefore clarifies that the relative position h
of the magnet 23 relative to the plane 24 in which the sensors A-1
A-2 are provided is determined on the basis of the output signals
E.sub.1 E.sub.2 of the two sensors A-1 A-2 without using the magnetic
flux density B.
As is clear from FIG. 2 in operation, the relative position h
of the magnet 23 varies over several centimeters in the embodiment
of the area flowmeter of the present invention. Consequently, the
magnetic flux density B in positions in which the sensors A-1 A-2
are disposed varies appreciably as the relative position or height
h of the magnet 23 varies. However, according to the present invention,
it is possible to determine the tangential angles .phi. of the magnetic-force
lines with high accuracy as is clear from the above equation (2),
which makes the present invention applicable to the area flow meter.
Incidentally, the relationships between the tangential angles .phi.
of the magnetic-force lines 26 (i.e., tan .phi.) and the relative
positions h of the magnet 23 can be previously determined on the
basis of the specifications of the magnet 23 and the installation
positions of the sensors A-1 A-2 on the circle 25 (the radius of
which is r) through calculations and experiments, and, therefore
are known.
Consequently, in the area flow meter of the embodiment of the present
invention, it is possible to determine the tangential angles .phi.
by the use of the output signals E.sub.1 E.sub.2 issued from the
sensors A-1 A-2 through the calculations of the equations (1),
(2), and, therefore to determine the relative position or height
h of the magnet 23 relative to the plane 24.
Signal processing of the output signals E.sub.1 E.sub.2 and the
calculations of the equations (1), (2) can be easily performed by
the use of analog/digital converters and microprocessors which may
easily perform linearization processings of the output signals E.sub.1
E.sub.2 of the sensors A-1 A-2 to eliminate the necessity of having
these output signals E.sub.1 E.sub.2 be proportional to the magnetic
flux densities B.
Further, in the area flow meter of the present invention, the relationship
between the relative position or height h of the magnet 23 in the
float 22 and the flow rates of the fluid being measured is generally
non-linear, and varies according to the specifications of the fluid
being measured, which requires complex calculations to determine
the flow rate of the fluid on the basis of the relative position
of height h of the magnet 23 of the float 22. However, these complex
calculations may be performed by the above-mentioned microprocessors,
which may considerably reduce the manufacturing cost of the area
flow meter of the present invention.
FIG. 4 shows the embodiment of the area flow meter using the magnetic
sensors or Hall devices A-1 A-2 of the present invention.
In the embodiment of the present invention, as shown in FIG. 4
each of the magnetic sensors such as the Hall devices A-1 A-2 is
provided with magnetism-responsive surfaces in its opposite sides.
Fixedly mounted on each of the magnetism-responsive surfaces of
the Hall devices A-1 A-2 is a fixed end of a magnetism-gathering
tapered element 27 made of high-permeability material such as permalloys
and the like. As shown in FIGS. 5(a) and 5(b), the tapered element
27 is flared outwardly from the fixed end thereof to its free end.
In the Hall devices A-1 A-2 of the embodiment of the present invention,
the magnetic flux of the magnet 23 in the float 22 is gathered by
the magnetism-gathering tapered elements 27 and condensed in the
fixed ends of the elements 27 to increase in density.
Consequently, the magnetic flux thus condensed in density in the
magnetism-responsive surfaces of the Hall devices A-1 A-2 increases
the output signals of the Hall devices A-1 A-2 in magnitude so
that the apparent output sensitivities of the Hall devices A-1
A-2 increase.
In each of the Hall devices A-1 A-2 since the magnetic flux density
detected by each of the Hall devices A-1 A-2 itself is amplified,
there is no fear that other electrical physical quantities such
as noises and like obstacles are amplified, which makes it possible
to obtain the intense electrical signals E.sub.1 E.sub.2 substantially
free from any noises or electrical physical obstacles.
As described above, the present invention has succeeded in increasing
the apparent output sensitivities of the Hall devices A-1 A-2 by
gathering the magnetic flux of the magnet 23 in the magnetism-responsive
surfaces of the Hall devices A-1 A-2 by the use of the magnetism-gathering
tapered elements 27 being substantially equal to each other in magnetism-gathering
capacity:
(1) each of which tapered elements 27 flares outwardly from its
fixed end to its free end;
(2) a pair of which elements 27 have their fixed end fixedly mounted
on the magnetism-responsive surfaces of each of the Hall devices
A-1 A-2 so that the pair of the elements 27 are symmetrical with
respect to each of the Hall devices A-1 A-2; and
(3) each of which magnetism-gathering tapered elements 27 is made
of high-permeability material such as permalloys and the like.
FIG. 7 shows a graph of the experimental data of the the embodiment
of the present invention, illustrating the effects of the embodiment
of the present invention. In the graph shown in FIG. 7 the relationship
between: the output voltages of a pair of the Hall devices A-1
A-2 used in the area flow meter shown in FIG. 4; and, the vertical
displacement of the float 22 is illustrated to compare the case
of using the magnetism-gathering elements 27 with the case of not
using these elements 27. The graph shown in FIG. 7 clarifies that
the apparent output sensitivities of the Hall devices A-1 A-2 with
the magnetism-gathering elements 27 are approximately 2.5 times
as much as those of the Hall devices A-1 A-2 without these elements
27.
In the above embodiment of the present invention, the Hall devices
are used as the magnetic sensors. However, it is also possible to
use any other magnetic sensors such as magnetic-resistance devices
and like devices in the present invention, and obtain the same effects
by using these sensors or devices. |