Abstrict A fluid flow meter comprising a fluid tight housing including an
inlet and an outlet; a hollow liner mounted within the housing including
at least one slot, the slot for receiving fluid from the inlet and
communicating it to the outlet; a magnetic piston slidably positioned
within the liner for movement in response to the flow of fluid from
the inlet through the slot; and a Hall effect transducer mounted
in the housing in substantially side-by-side relation to the piston
for producing an electrical signal corresponding to the position
of the piston in the cylinder.
Claims What is claimed is:
1. A fluid flow meter comprising:
a fluid tight housing, including an inlet and an outlet;
a hollow liner mounted within said housing including at least one
slot, said slot for receiving fluid from said inlet and communicating
said fluid to said outlet;
a magnetic piston slidably positioned within said liner for movement
in response to the flow of fluid from said inlet through said slot
independent of gravity and spatial orientation; and
transducer means mounted on said housing in substantially side-by-side
relation to said piston for producing an electrical signal corresponding
to the position of said piston in said liner.
2. The flow meter of claim 1 wherein said transducer means comprises
a Hall effect transducer.
3. The flow meter of claim 2 wherein said piston has an upstream
end and a downstream end, and said flow meter includes barrier means
attached to said downstream end of said piston for blocking fluid
flow between said piston and said liner to said outlet.
4. The flow meter of claim 3 wherein said barrier means includes
a flexible tubular shaped bellows attached at one end to said piston
and fixed at the other end to said liner.
5. The flow meter of claim 1 wherein said liner includes a pair
of slots, said slots being symmetrically arranged on opposite sides
of said liner.
6. A fluid flow meter comprising:
a fluid tight housing including an inlet and an outlet, and a pair
of symmetrically arranged longitudinal channels on the inner surface
thereof;
a hollow cylinder mounted within said housing including a pair
of longitudinal slots, one of said slots for alignment with one
end of each of said channels, and a pair of apertures, one of said
apertures being aligned with the other end of each of said channels,
said slots for receiving fluid from said inlet and communicating
it through said channels and said apertures to said outlet;
a magnetic piston slidably positioned within said cylinder for
movement in response to the flow of fluid from said inlet through
said slot; and
transducer means mounted on said housing in substantially side-by-side
relation to said piston for producing an electrical signal corresponding
to the position of said piston in said cylinder.
Description FIELD OF THE INVENTION
This invention relates to flow meters, for measuring the flow of
fluids. More particularly, this invention relates to meters for
accurately measuring fluid flow by measuring the displacement of
a movable piston.
BACKGROUND OF THE INVENTION
In the past, substantial efforts have been devoted to the investigation
and development of more accurate and less complex flow meters for
measuring fluid flow in a variety of circumstances. The accuracy
of a flow meter refers to the extent within which the actual flow
parameters may differ from the meter reading. Repeatability refers
to the ability of a given meter to provide consistent readings over
a large number of repetitions. In many situations, the repeatability
of a flow meter is more important than its accuracy. For example,
in a large industrial process where constant conditions are maintained
to provide maximum efficiency, the repeatability of a flow meter
may be extremely important.
In recent years, it has become increasingly important to provide
a visual readout in conjunction with many types of flow meters.
A readout may be accomplished by means of a mechanical arrangement
in which a dial or gauge is adjusted in response to changes in flow,
or electrical signals may be generated to provide a remote readout
through an electrical display or other suitable means. In many situations,
a readout capability is considered mandatory, while in other situations,
it is generally advantageous.
Despite the advantage provided by a remote readout capability,
the additional instrumentation and electronics necessary to provide
such a capability have made it uneconomical to provide such a capability
for many flow meters used in low cost applications. Such components
as signal preamplifiers, pulse rate converters, pulse rate indicators,
and range extenders and linearizers greatly add to the cost of a
flow meter and often make a visual readout capability economically
unfeasible.
In a prior application, Ser. No. 266622 filed May 22 1981 of
which I am a co-inventor, several varieties of flow meters are described.
The flow meters of that prior application, which application is
specifically incorporated herein by reference, all have the capability
of providing a remote readout. In addition, the flow meters described
and claimed in that prior application are extremely accurate and
provide an increased measure of repeatability in comparison with
prior art flow meters. These advantages are achieved in the invention
of application Ser. No. 266622 by utilizing a magnet or magnetic
field producing element in the flow meter, and a Hall effect transducer
for sensing the position of the magnetic element in the device.
The displacement of the magnet is responsive to the rate of flow
or change in pressure of the fluid being measured. Thus, a change
in the relative position of the magnet with respect to the Hall
effect sensor changes the magnetic flux density sensed by the Hall
effect device. The output voltage of the Hall effect sensor varies
in accordance with the flux density in the vicinity of the Hall
effect sensor. This, the movement of the magnet in response to the
rate of flow of the fluid through the flow meter causes a proportional
change in the output voltage of the Hall effect sensor. The position
of the magnetic element is determined by the difference in pressure
on the upstream and downstream surfaces of the magnetic element.
While the flow meters described and claimed in application Ser.
No. 266622 solve many of the problems of the prior art, there are
still certain drawbacks to the use of the meters shown as specific
embodiments in that application. One of the primary disadvantages
is a requirement that the output of the Hall effect sensor must
be linearized in order to more correctly represent fluid flow. Linearity
refers to a straight line function, while a non-linear relationship
may be exponential or logarithmic. Obviously, the closer the function
is to being linear, the more accurate will be the representation
of the desired function. Although non-linear signals can be linearized
electronically or pneumatically, this greatly adds to the cost of
producing the device, and may adversely affect accuracy.
In addition to the non-linear nature of the output of the devices
described in application Ser. No. 266622 it has been found that
the arrangement of the "slot" on one side of the housing
in the specific embodiments described therein produces an unequal
distribution of forces on the magnetic element in the flow meter.
As a result of this unequal distribution, the magnetic element may
encounter frictional and other forces which can reduce the accuracy
of measurement of the device. In addition, the relatively large
clearance between the magnetic element and the cylinder in which
it moves allows fluid to flow between the magnetic element and the
cylinder thereby bypassing the slot, and not being measured.
Accordingly, it is a primary object of this invention to improve
the accuracy and repeatability of flow meters utilizing a Hall effect
sensor.
It is a further object of this invention to economically provide
a linearized output from a flow meter which is a direct function
of the rate of flow of the fluid through the meter.
Yet another object of the invention is to balance the forces on
a magnetic element in a flow meter for more accurate measurement
by an accompanying Hall effect device.
A still further object of the invention is to prevent leakage around
the magnetic element of a flow meter having a Hall effect device,
thereby increasing the accuracy of measurement of the device.
SUMMARY OF THE INVENTION
To achieve the foregoing objects and in accordance with the purpose
of the invention, as embodied and broadly described herein, the
flow meter of the present invention comprises a housing, including
an inlet and an outlet; a hollow liner mounted within the housing,
including at least one slot, the slot for receiving fluid from the
inlet and communicating the fluid to the outlet; a magnetic piston
slidably positioned within the liner for movement in response to
the flow of fluid from the inlet through the slot; and transducer
means mounted on the housing in substantially side-by-side relation
to the piston for producing an electrical signal corresponding to
the position of the piston in the cylinder. Preferably, the transducer
means comprises a Hall effect transducer. It is also preferred that
the liner be cylindrical in shape.
Preferably, the piston has an upstream end and a downstream end,
and the flow meter includes barrier means attached to the downstream
end of the piston for blocking fluid flow between the piston and
the liner to the outlet.
Preferably, the liner includes a pair of opposed elongated slots.
The barrier means preferably includes a flexible tubular shaped
bellows attached at one end to the piston and fixed at the other
end to the liner.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings which are incorporated and constitute
a part of this specification illustrate several embodiments of the
invention and, together with the description, serve to explain the
principles of the invention.
OF THE DRAWINGS
FIG. 1 is an elevational diagrammatic view, partly in section,
showing a flow meter in accordance with the invention;
FIG. 2 is a cross-sectional view of the flow meter of FIG. 1;
FIG. 3 is a longitudinal view, partly in cross section, of a further
embodiment of the invention;
FIG. 4 is a cross section of still a further embodiment of a flow
meter in accordance with the invention;
FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG.
4;
FIG. 6 is an isolated view of the piston and bellows arrangement
of the embodiment of FIG. 4;
FIG. 7 is a cross section of the embodiment of FIG. 4 showing the
slots, bypass passages and apertures in alignment;
FIG. 8 is a cross-sectional view taken along the line 8--8 of FIG.
7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the present preferred embodiments
of the invention, examples of which are illustrated in the accompanying
drawings.
In accordance with the invention, the fluid flow meter of the present
invention comprises a fluid tight housing including an inlet and
an outlet; a hollow liner mounted within the housing, including
at least one slot, the slot for receiving fluid from the inlet and
communicating it to the outlet; a magnetic piston slidably positioned
within the liner for movement in response to the flow of fluid from
the inlet through the slot; and transducer means mounted on the
housing in substantially side-by-side relation to the piston for
producing an electrical signal corresponding to the position of
the piston in the cylinder.
As here embodied, the transducer means comprises a Hall effect
transducer. As shown in FIG. 1 which is similar to the embodiment
shown in FIG. 5 of co-pending application Ser. No. 266622 the
flow meter comprises a fluid tight housing 12 formed of any suitable
material, such as plastic or metal. The housing has an inlet 14
and an outlet 16 at the respective ends thereof. Located within
the housing 12 is a hollow liner 18 which is affixed to a bottom
wall 13 of housing 12. Liner 18 may also be formed of any suitable
material such as metal or plastic.
The liner 18 has an entrance 20 in fluid communication with the
inlet 14 of the housing 12. A slot 22 is provided in the wall 23
of the liner 18. The slot 22 is longitudinally shaped, but may be
non-linear, varying in width along its length or linear along its
length.
As here embodied, the piston comprises a slidable moving magnet
24 located within the hollow liner 18. The magnet 24 is preferably
polarized along its length, for example, from north (N) to south
(S) as shown in FIG. 1. At the other end of liner PG,8 18 is an
opening 31 which communicates between the chamber 25 formed by the
housing 12 and chamber 21 formed by liner 18. A relief valve 28
is provided at the end of a bore 27 passing through the length of
the magnet 24. The operation of the relief valve 28 is described
in more detail below.
It is preferred that the magnet 24 be biased toward the inlet 14
by a spring 29 which typically has a biasing force sufficient only
to prevent the magnet 24 from moving when the flow meter is tilted
from a vertical orientation, as shown.
As embodied herein, a Hall effect transducer 30 is mounted on the
outside of the housing 12 in substantially side-by-side relation
to the magnet 24. The Hall effect transducer 30 may be mounted by
any suitable means, for example, an epoxy adhesive or other bonding
agent. The transducer 30 is shown as having three leads, one lead
being a voltage input, one a voltage output, and the third which
provides a reference potential for the voltage input and the voltage
output. A suitable Hall effect transducer which is commercially
available is a type 9SS series linear output Hall effect transducer
(LOHET) marketed by the Microswitch Division of Honeywell, Inc.
When the Hall effect transducer 30 is mounted as shown in FIGS.
1 and 2 in substantially side-by-side relation with the magnet
24 movement of the magnet 24 relative to the Hall effect transducer
30 produces an output voltage from the transducer which is linearly
related to the movement of the magnet 24. This arrangement is also
referred to herein as "slide-by-sensing". In slide by
sensing, a tightly controlled gap is maintained between the magnet
and the Hall effect transducer. As the magnet 24 moves back and
forth at the fixed gap, the magnetic field seen by the transducer
30 has one orientation as the sensor approaches the north pole and
the opposite orientation as the sensor approaches the south pole.
This type of position arrangement results in mechanical simplicity,
and can detect position over a relatively long magnet travel. The
output characteristic is very close to linear over nearly the entire
range of movement of the magnet.
By contrast, the arrangement shown in FIG. 4 of application Ser.
No. 266622 also called unipolar-head-on-sensing, results in a
non-linear output from the Hall effect transducer. When the magnet
is farthest away from the transducer, the magnetic field at the
sensing face is near zero. As the south pole of the magnet approaches
the sensor, the magnetic field at the sensing surface becomes stronger
and stronger. The output as a function of distance is non-linear,
and must be linearized by a suitable electronic circuit such as
an operational amplifier.
In operation, as shown in FIGS. 1 and 2 the fluid enters the inlet
14 and passes into the liner 18. The magnet 24 moves against the
bias of the spring 29 in response to the pressure exerted by the
fluid. Movement of the magnet 24 uncovers the slot 22 to provide
an outlet for the major portion of the fluid. The fluid flows through
the slot 22 into the chamber 25 in the housing 12 through opening
31 into the chamber 21 in liner 18 and exits through the outlet
16. The differential pressure between the upstream and downstream
sides of magnet 24 caused by flow of the fluid through the slot
controls the movement of the magnet 24. The bore 27 through the
magnet 24 operates as a relief mechanism in the event that the fluid
flow overpressurizes within the liner 18. In that event, fluid escapes
through bore 27 and check valve 28.
Thus, the invention of the above described embodiment eliminates
the need for any additional electronic circuitry to linearize the
output voltage of the Hall effect transducer, thereby making the
device much more economical to produce, and more simple to operate.
Referring now to FIGS. 3-8 a further embodiment of the invention
is illustrated. In this embodiment, the flow meter, generally referred
to as 38 is essentially formed from a single tube or liner of material
with an outer housing which covers the flow passage. As shown FIG.
3 a tubular member 40 formed of any suitable non-magnetic material
such as metal, plastic, or the like, has an inlet end 42 and an
outlet end 44. A piston 48 similar to the magnet 24 of FIGS. 1 and
2 is slidably mounted within the tubular member 40.
Preferably, barrier means are attached to the downstream end of
the piston for blocking fluid flow between the piston and the tubular
member to the outlet. As here embodied, the barrier means includes
a bellows 85 attached to the downstream end 86 of the piston 48.
As illustrated in FIG. 3 the other end of the bellows 85 is sealingly
attached to a ring 87 which prevents fluid from leaking past the
piston 48 to the outlet 44.
The tubular member 40 has two symmetrically arranged longitudinal
slots 50 adjacent the inlet end 42 of the tubular member 40 on opposite
sides of the member 40. The slots 50 have a length generally corresponding
to the distance of travel of the piston 48 and may be formed in
any suitable shape, depending upon the flow response to be measured.
A pair of bypass passages 51 are symmetrically arranged in fluid
communication with the slots 50 on the outer surface of the wall
of the tubular member 40. A pair of symmetrically arranged apertures
52 are provided in the tubular member 40 adjacent the outlet end
44.
Fluid entering through the inlet 42 displaces the piston 48 thereby
uncovering the slots 50. The fluid then passes through the bypass
passages 51 and the apertures 52 exiting at the outlet end 44. The
differential pressure between the upstream side of the piston 48
and the downstream side 86 thereof controls the movement of the
piston 48 as a function of flow. The differential is a result of
the constriction of the flow through the slots 50 and passages 51.
The bypass passages 51 are formed within a housing 58 which may
be plastic or other similar material, and is fastened over the tubular
member 40. As shown in FIG. 3 the housing 58 extends over the slots
50 and the apertures 52. The ends of housing 58 are fastened in
a fluid tight manner, for example, by O-rings, epoxy, or any other
suitable material.
In FIG. 3 the Hall effect transducer 30 is shown as being mounted
in slide-by-sensing relation with the piston 48. The transducer
30 may be mounted in an opening on the housing 58 in any suitable
manner. A typical arrangement is shown in more detail in FIG. 4.
As described with respect to the embodiment of FIGS. 1 and 2 the
cooperation between the piston 48 and the Hall effect transducer
30 is such that the movement of the piston 48 provides a linear
output voltage from the Hall effect transducer 30. Accordingly,
the flow rate of the fluid is linearly related to the meter reading
from the Hall effect transducer 30.
Referring now to FIGS. 4-8 a further embodiment is illustrated.
This embodiment is similar to that illustrated in FIG. 3 with additional
modifications.
As shown in FIG. 4 tubular member 40 is arranged within a housing
58 in a fluid-tight relation. Inlet 42 and outlet 44 are attached
to the tubular member 40 with suitable O-rings 60 therebetween.
A magnetic piston 48 is slidably mounted within the tubular member
40 near the inlet end 42.
As best shown in FIG. 5 a pair of symmetrically arranged slots
50 are arranged in the walls of the tubular member 40. Each of the
slots 50 communicates with a bypass passage 51 running longitudinally
along the outer surface of the tubular member 40 within the housing
58. A pair of symmetrically arranged apertures 52 in the walls of
the tubular member 40 are located at the other end of the passages
51.
As shown in FIG. 6 the magnetic piston 48 has a bellows member
85 attached to the downstream side thereof. The bellows member 85
is further connected to a cylindrical seal 95 which is fixed within
the tubular member 40. A pair of apertures 75 in the cylindrical
seal 95 are symmetrically arranged for alignment with the apertures
52 in the tubular member 40 as shown in FIG. 7. Thus, the fluid
entering the inlet end 42 of the tubular member 40 causes the piston
48 to be displaced. Movement of the piston 48 uncovers the slots
50 allowing the fluid to pass through the bypass passages 51 the
apertures 52 and the apertures 75 to exit through the outlet opening
44. The cylindrical seal 95 prevents leakage of fluid past the piston
48 to the outlet 44. The fluid from aperture 75 also passes through
the cylindrical seal 95 and bellows 85 to act on the downstream
side of the piston 48. Thus, the differential pressure caused by
the constricted flow controls the position of the piston 48 as
discussed previously.
As shown in FIGS. 4 and 5 the Hall effect transducer 30 may be
mounted in an opening 62 in the housing 58. A recess 64 may be formed
in the tubular member 40 for receiving the Hall effect transducer
30.
As shown in FIG. 8 the bypass passages 51 the apertures 52 the
apertures 75 and the outlet of 44 are in direct alignment to form
an unimpeded channel from passageway 51 through the outlet 44.
The present invention also includes an improved method of measuring
the rate of flow of a fluid. In accordance with the invention, the
method of measuring the rate of flow of a fluid comprises the steps
of passing the fluid through a confined area; producing a varying
magnetic flux at a transducer as a function of the flow of the fluid
through the confined area; transducing the flux into an electrical
signal from a point substantially parallel to the path of flow of
the fluid; and gauging the electrical signal. The method may be
practiced by the apparatus described above, or any other suitable
apparatus.
It will be apparent to those skilled in the art that various modifications
and variations could be made in the structure and method of the
invention without departing from the scope and spirit of the invention.
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