A fluid flow monitoring system comprised of a permanent magnet
mounted on a bendable spring blade that provide an output from a
Hall effect transducer as the permanent magnet is deflected toward
or away from the transducer. The permanent magnet can be mounted
to directly approach the Hall effect transducer or can also be mounted
to approach the transducer by a sideways bypass direction. Both
the direct motion and sideways bypass direction allows the use of
a variety of sizes and shapes of magnets that allow the magnetic
field intensity to be modified in any way desired. Various magnet
shapes such as cylinders, rectangles, pyramids, triangles or compound
magnets from these shapes may be used. The output signal of the
transducer is processed through a smoothing filter and circuits
that produce a linear output or a stepped digital output. The system
preferably uses a resistance/capacitance filter to provide a different
time constant for an increasing flow or a decreasing flow. The output
can be used as a flow switching circuit or as a flow meter, or as
a flow quantity totalizer.
What is claimed is:
1. A fluid responsive monitoring system for monitoring the flow
of fluid in a conduit comprising;
a body attached to said conduit;
a support tube mounted on said body, said support tube extending
into said conduit to intercept a fluid flowing in said conduit;
a Hall effect transducer mounted in said support tube;
a flexible arm mounted on said body extending into the path of
a fluid flowing in said conduit;
magnetic means mounted on said flexible arm spaced from said Hall
low flow detecting means for detecting low flow, said low flow
detecting means comprising means for detecting vibration of said
flexible arm caused by vortex shedding;
whereby when a fluid in said conduit deflects said flexible arm
with said attached magnet toward said Hall effect transducer a voltage
output representing the flow rate of fluid in said conduit is produced.
2. The system according to claim 1 in which said flexible arm is
mounted in line with said Hall effect transducer; said permanent
magnet being mounted so that said fluid moves said permanent magnet
in an approach directly towards said Hall effect transducer.
3. The system according to claim 2 in which said permanent magnet
is a cylindrical disc-shaped magnet.
4. The system according to claim 2 in which said magnet is a rectangular
5. The system according to claim 1 including electronic processing
means for processing the output of said Hall effect transducer comprising;
a signal smoothing filter; and output signal conditioning means.
6. The system according to claim 5 in which said signal smoothing
filter is a RC smoothing filter; said RC smoothing filter having
a first time constant for an increasing fluid flow and a second
time constant for a decreasing fluid flow.
7. The system according to claim 5 including a smoothing filter
having the same time constant for both increasing and decreasing
8. The system according to claim 5 in which said signal conditioning
means comprises a comparator for producing a step function digital
9. The system according to claim 5 in which said signal conditioning
means comprises a linear analog output circuit means.
10. The system according to claim 5 in which said output signal
conditioning means comprises a non-linear analog circuit means.
11. The system according to claim 5 in which said signal conditioning
means comprised integrating output circuit means to obtain total
flow quantity over a selected time interval.
12. The system according to claim 5 including means for adding
a small variable electronic hysteresis to prevent sustained electronic
oscillations from occurring in associated electronic systems.
13. The system according to claim 1 including means to enhance
the vortex shedding of said flexible arm.
14. The system according to claim 1 in which said means for enhancing
the vortex shedding comprises appendages on said flexible arm to
15. The system according to claim 14 in which said appendages can
be in any arbitrary shape or size that increases vortex shedding
16. The system according to claim 14 in which said appendages comprise
v-shaped flanges along lateral edges of said flexible arm.
17. The system according to claim 16 including signal conditioning
means for processing both the AC and DC output of said Hall effect
transducer caused by said vortex shedding.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to fluid flow detection switches and flow
meters and more particularly, relates to flow switches and flow
meters that incorporate shaped flexible targets that are deflected
by the fluid flow via a flow sensitive bending beam and, are very
sensitive; include electronic signal processing interfacing to provide
flow switch flow meter and flow totalizer output information via
a Hall Effect transducer.
2. Background Information
This invention is an improvement to existing flow switches and
meters, such as that disclosed and claimed in U.S. Pat. No. 5021619
issued to the same inventor as the device disclosed and described
herein, incorporated herein by reference.
The patent referred to above disclose a cantilevered flat flow
sensing spring blade disposed to extend into the flow of a fluid
through a pipe or conduit. The fluid flow drag forces bends the
spring until the spring comes to rest against a hollow support tube
located downstream of the spring. The support tube holds the spring
steady to protect it from excessive stress and vibration induced
by turbulent fluid flow.
In the prior art, devices known as "bending beam fluid flow
switches and meters," the flow sensing spring activates a reed
switch inside the support tube from the effect of a magnet moving
closer to the support tube. This provides an indication of a certain
level of flow rate.
The switch triggering fluid flow rate is determined by adjusting
the size, shape and stiffness of the spring supporting the magnet.
Such magnet operated reed switches have an inherent hysteresis in
their operation as the magnet approaches and recedes from the reed
switch. At some point, the magnet is attracted to the reed switch
by a magnetic force and quickly moves the last bit of distance to
the support flow tube under the influence of the magnetic effect
rather than because of the fluid force on the flow target spring
thus, introducing potential errors into flow measurement.
The reed switch itself also has another mechanical hysteresis effect.
This effect is that once closed, the switch tends to latch in the
closed position; again by nonlinear magnetic attraction. Thus, when
fluid flow declines, the reed switch still stays closed momentarily
until the magnetic force between the magnet and the reed switch
internal members no longer are able to resist their tendency to
return to their normal relaxed position. Therefore, at this instant,
the two magnetic members of the reed switch decouple and snap back
to their normal relaxed positions and the switch opens. However,
the fluid flow rate when the switch opens, will be below the fluid
flow reed rate at which the switch closes. This is the magnetic/mechanical
hysteresis interaction between the magnet and reed switch producing
the related flow differential between the on and off condition,
and is known as the "on-off hysteresis." In some situations,
the hysteresis is a useful phenomenon because it prevents the switch
from chattering on and off due to flow turbulence when the flow
rate happens to be right at the switch triggering point.
In effect, the double magnetic latch, unlatch hysteresis of the
magnet and reed switch internal blades create a fluid flow hysteresis
dead band which reduces flow measuring sensitivity near the flow
switch point. The magnetic hysteresis system and thus, the flow
turbulence hysteresis system is completely determined by local magnetic
fields of the magnetic/reed switch combination, which is a phenomenon
attributed to each particular magnetic/reed switch combination and
cannot be adjusted except by changing one or both members.
It is therefore, one object of the present invention to employ
Hall effect transducer technology to provide no mechanical magnetic
coupling hysteresis since the Hall effect transducer body and internal
components are non-magnetic and thus, totally magnetically transparent.
Yet another object of the present invention is to provide a Hall
effect flow switch and analog flow meter that employs a very small
repeatable and adjustable electronic hysteresis to ensure downstream
electronic systems do not go into electronic oscillation.
It is another object of the present invention to provide a flow
switch and flow meter that provides a flow induced variable magnetic
field applied to a Hall effect transducer, which in turn provides
a variable electronic output signal that precisely represents the
fluid flow field through a pipe or equivalent conduit.
Yet another object of the present invention is to provide a flow
switch and meter that employs Hall effect magnetically sensitive
transducers in a digital mode and flow in a continuous analog output
Yet another object of the present invention is to provide a fluid
flow switch and flow meter that employs a Hall effect transducer
with a variable magnetic field intensity obtained from a variety
of magnet shapes, materials and strengths.
Yet another object of the present invention is to provide a fluid
flow switch and flow meter for measuring the flow of fluids, gases
and vapors impinging upon a flow sensitive bending arm, and employing
a Hall effect transducer to produce a variable output voltage which
is then translated by electronic processing circuitry into flow
Yet another object of the present invention is to provide a flow
switch and flow meter employing a Hall effect transducer, employing
a variety of magnetic shapes, materials and configurations that
include a direct in-line application of a magnet moving toward a
Hall effect device or a sideways offset magnet moving past a Hall
Still another object of the present invention is to provide a flow
switch and flow meter that has improved sensitivity by measuring
the output of the Hall Effect transducer caused by fluid flow vortex
shedding, at and down stream of flow sensitive bending beam.
Yet another object of the present invention is to provide a flow
switch and flow meter that includes appendages on a bending beam
to enhance the vortex shedding to further improve sensitivity.
BRIEF DESCRIPTION OF THE INVENTION
The purpose of the present invention is to provide an improved
fluid flow switch and fluid flow meter employing a Hall effect transducer
and a bending beam that is very sensitive and in which fluid flow
(liquid, gas or vapor) in a container (pipe, duct, etc.) impinge
on a shaped flexible target which is then deflected, resulting in
a modified magnetic field intensity which in turn, modifies the
electronic output via the Hall effect transducer, which directly
relates fluid flow rate to an electronic output voltage. The output
voltage is then subject to electronic signal processing for output
to various electronic instrument and control systems.
The present invention is constructed with a Hall effect transducer,
producing zero magnetic coupling hysteresis, mounted in a support
tube adjacent to a spring bending blade on which a magnet is mounted.
The Hall effect transducer will effectively replace the reed switch
shown in U.S. Pat. No. 5021619 by the same inventor as the invention
disclosed herein, and incorporated herein by reference.
The system employs a Hall effect magnetically sensitive transducer
in a digital mode or in an analog continuous output mode. In the
digital mode, the output voltage signal is zero until a preselected
magnetic field intensity is presented to the transducer, which then
shifts the output from zero to a fixed voltage in a rapid step function
manner. This occurs when the magnet on the bending beam approaches
the Hall effect transducer in the support tube sufficiently close
to cause an output voltage equal to or greater than a preset value
or reference voltage.
Another mode that can be useful to improve flow sensitivity by
as much as a factor of two or more, is by measuring an output produced
by vortex shedding. Vortex shedding is a successive variation in
the flow pattern and dynamic drag at and down stream of an object
subjected to fluid flow. A familiar manifestation of the phenomenon
is the fluttering of a flag in the wind. The vortex shedding can
be enhanced by adding appendages to the outer lateral sides of the
flow sensing bending beam.
A continuous mode output is provided by a continuous analog output
signal obtained relative to a variable magnetic field intensity
applied to the Hall effect transducer. The variable magnetic intensity
is obtained by using a variety of magnetic shapes, materials and
strengths. The fluid flowing in a container or conduit impinges
upon a flow sensitive bending beam having a variable shaped magnet
which modifies and controls the magnetic field intensity in and
around the Hall effect transducer mounted in the support tube. This
produces a variable output voltage which completes the translation
of flow input information in a variable analog electrical output
that is processed by down stream electronic circuitry.
The magnets can be small sized disc magnets in relation to the
size of the Hall effect transducer, or disc magnets that are relatively
larger than the Hall effect transducer. Other magnet shapes can
be rectangular, pyramidal, triangular plus variable shaped magnets
as required for special situations. Variations could include a series
of disc magnets that provide an increasing magnetic field or a series
of rectangular magnets providing a variable magnetic field.
There are two methods of approaching the Hall effect transducer
with a magnet. One method is a straight ahead approach in which
a magnet mounted on a flow sensing bending spring blade, moves directly
toward the sensitive surface of the Hall effect transducer. Another
method is to use a sideways bypass approach in which the magnet
is mounted on the flow sensing spring blade and passes by the Hall
effect transducer at a predetermined distance. The shape and composition
of the magnets determines the increase or decrease of the magnetic
field as it approaches the Hall effect transducer.
The invention employs several components, and can be a simple flow
sensing blade having a magnet that approaches the Hall effect transducer
as well as a small system consisting of varying magnet sizes, shapes
and material plus a variety of downstream signal conditioning electronics
that modify the signal received from the Hall effect transducer
to provide a special output pattern such as a linear output. In
one simple method, the flow with turbulence deflects the spring
blade of a bending beam to produce a varying magnetic field. This
in turn, produces a varying electrical output from the Hall effect
transducer. For instance, the output voltage will be a stepped voltage
when the system is configured as a flow switch.
Another more complex system, for using the device as a flow switch
as well as a flow meter, employs variable magnetic fields that produce
a variable non-uniform output voltage from the Hall effect transducer.
In this embodiment, the flow deflects the flow sensing bending beam
having an attached magnet which approaches the Hall effect transducer
and produces an output signal to a signal smoothing filter, which
is then processed by subsequent electronics to provide an analog
flow metering system.
For a digital flow switch system, the electronic circuit includes
a smoothing filter and a comparator comparing the voltage level
with a reference voltage. The signal smoothing filter minimizes
system turbulence effects and maximizes flow measurement sensitivity.
For a flow meter system, the electronic circuit includes a smoothing
filter and microprocessor type circuitry to produce a continuous
The preferable signal smoothing filter used is normally an RC (resistance/capacitance)
signal smoothing filter. The RC smoothing filter receives a signal
from a Hall effect transducer that produces a voltage proportional
to the rate of fluid flow passing the combination of flow sensing
bending beam and Hall effect transducer subsystem. The turbulent
(noisy) voltage from the Hall effect transducer causes a current
to flow through a resistor into a capacitor until it is charged
to the same voltage as that produced by the transducer. The charged
condition of the capacitor remains stable as long as the transducer
voltage remains stable (i.e., the voltage of the capacitor will
follow the transducer voltage exactly except at a new frequency
response determined by the product of the resistor and capacitor,
which is the RC time constant). The values of the resistor and capacitor
can be selected to provide a relatively long time constant of approximately
one second or more, which corresponds to a cut-off frequency of
approximately 0.16 Hz. Lower frequencies pass through the RC filter
and higher frequencies are blocked. The end result is a variable
"low pass filter."
A feedback circuit comprised of a diode in series with a resistor,
provides two different time constants for the RC circuit, one for
increasing fluid flow and the second for decreasing fluid flow,
thus providing additional operational flexibility.
The smooth and amplified output of a suitable processing circuit
can be used to provide a continuous analog output relative to time
to produce a fluid flow rate meter, which can be integrated over
time to provide a fluid quantity totalizer. The smoothed output
voltage can also be fed into a comparator circuit to produce step
function switch actuation, voltages. Thus, the system of the invention
can transform a fluid, gas or vapor flowing past a flow sensing
flexible beam with magnet attached and a Hall effect transducer
into a continuous analog voltage, which is then electronically processed
to provide flow meter, flow totalizer and/or a fluid flow switch
output information in any sequence or combination required.
The above and other novel features of the invention will be more
fully understood from the following detailed description and the
accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial sectional side elevation of a fluid flow sensing
switch constructed according to the invention.
FIG. 1a is a partial sectional elevation of the fluid flow sensing
switch similar to FIG. 1 with the operation of the bending beam
FIGS. 2(a) through 2(c) are diagrams illustrating the head-on motion
of the embodiment of FIG. 1.
FIG. 3 is a diagram illustrating the operation of the head-on motion
of head-on motion of the embodiment of FIG. 1.
FIG. 4 is a graph of the transducer output relative to separation
FIG. 5 is a graph of the output illustrating the system used as
a digital step function response.
FIG. 6 is a graph illustrating the fluid responsive switch providing
a continuous nonlinear analog function response.
FIGS. 7(a) through 7(d) are diagrams illustrating an optional configuration
of the flow responsive device in a sideways bypass mode.
FIGS. 8(a) through 8(d) are diagrams illustrating another optional
embodiment of the flow responsive device in a sideways bypass mode.
FIGS. 9 and 10 are diagrams illustrating the operation of the sideways
bypass embodiment of the invention.
FIG. 11 is a graph of the transducer output relative to the sideways
offset and separation distance of the embodiments of FIGS. 7 and
FIGS. 12(a) through 12(c) are diagrams that illustrate various
permanent magnet shapes and typical dimensions relative to a typical
Hall effect transducer.
FIGS. 13(a) through 13(i) are illustrations of the various magnetic
shapes that can be used in the fluid responsive switch according
to the invention.
FIGS. 14(a) through 14(d) are diagrams of a flow responsive device
in a sideways bypass mode with an optional magnet configuration.
FIGS. 15(a) through 15(c) are diagrams of a flow responsive device
in a sideways bypass mode having another optional magnet configuration.
FIGS. 16(a) through 16(d) are diagrams of a flow responsive in
a sideways bypass mode having still another optional magnet configuration.
FIGS. 17(a) through 17(d) are diagrams of a flow responsive in
a sideways bypass mode having yet another optional magnet configuration.
FIG. 18 is a schematic block diagram illustrating the signal processing
of the system.
FIG. 19(a) is a schematic block diagram illustrating the system
for providing a digital switched output.
FIG. 19(b) is an informational block diagram describing the schematic
of FIG. 19(a).
FIG. 20(a) is a schematic block diagram of a system for providing
a fluid flow analog output, a digital switched output, and a low
flow output representing vortex shedding.
FIG. 20(b) is an informational block diagram describing the schematic
of FIG. 20(a).
FIG. 21 is a schematic block diagram of a smoothing filter suitable
for use in the systems of FIGS. 6 and 7.
FIGS. 22(a) and 22(b) are graphs of the fluid flow rate before
and after smoothing by the filter of schematic diagram of FIG. 21.
FIG. 23 is a side view of a fluttering flag to illustrate the vortex
FIG. 24 is a top view of the fluttering flag of FIG. 23 illustrating
the path of the flow of air creating vortex shedding.
FIG. 25 illustrates a modification of the bending beam to enhance
FIG. 26 illustrates vortex shedding caused by a flat plate bending
FIG. 27 is a top schematic view of the bending beam according to
the invention, having the specially shaped edges to enhance vortex
FIG. 28 illustrates the voltage output representing the various
stages of flow from no flow to flow producing vortex shedding vibrational
output, to substantial flow producing an enhanced analog output.
DETAILED DESCRIPTION OF THE INVENTION
A Hall effect bending beam fluid flow monitor is illustrated in
FIG. 1 and diagrammatically illustrated in FIGS. 2(a) through 2(c).
This invention is an improvement to the flow responsive switch of
U.S. Pat. No. 5021 619 to the same inventor as the invention disclosed
A fluid responsive switch is generally indicated at 10 having
a housing 12 with threads for attaching the switch to a conduit
or a container to monitor fluid flow in the direction indicated
by the arrows. Flow responsive switch 10 is mounted on a tee-shaped
fitting 14 for intercepting the flow through a conduit or into a
container as indicated by the arrows. Cable 16 provides an electrical
connection to flow responsive switch 10.
Flow responsive switch 10 has leaf spring 18 supporting magnet
20 which is responsive by deflecting according to the flow of fluid
through tee 14 as indicated by the arrows. A transducer 22 is mounted
in a support tube 24 extending into the path of the fluid that is
responsive to the effect of the magnet 20 mounted on leaf spring
18 (i.e., bending beam) as it is deflected by the flow of fluid
through tee 14. Transducer 22 is preferably a Hall effect transducer
that responds to the magnetic effect of magnet 20 on bending beam
The operation of the head-on embodiment of FIG. 1 is illustrated
by the diagram of FIG. 3 and graphs of FIGS. 4 through 6 with only
the magnet 20 and Hall effect 22 shown for clarity. Magnet 20 is
a typical disk or rod shaped magnet and its direction of motion
toward or away from Hall effect transducer is indicated by the arrow
21. A variable output voltage from Hall effect transducer 22 is
produced according to field intensity relative to charges in separation
distance (d) as shown in the graph of FIG. 4.
Fluid moving through tee 14 bends leaf spring 18 to move magnet
20 toward Hall effect transducer in support tube 24. Leaf spring
18 may bend until magnet 20 rests against hollow support tube 24
located just downstream of the bending beam. Adjustment of the size,
shape and stiffness of leaf spring 18 plus Hall effect transducer
characteristics determines the triggering fluid flow rate. The Hall
effect transducer 22 provides a significant improvement because
it provides "zero" magnetic coupling hysteresis since
the body and support tube 24 as well as the internal components
are non-magnetic and thus, are totally magnetically transparent.
A very small and repeatable electronic hysteresis is introduced
in down stream processing circuit to ensure downstream electronic
systems do not go into undamped electronic oscillations, as will
be described in greater detail hereinafter. Thus, flow in conduit
connected to tee 14 introduces a variable magnetic field to Hall
effect transducer 22 which in turn provides a variable electronic
output signal that precisely represents the fluid flow field in
the subcontainer. Thus, this system is more sensitive to fluid flows
and can provide accurate readings of flow through conduit connected
to tee 14.
An optional embodiment, similar to that shown in FIG. 1 is illustrated
in FIG. 1a. This embodiment is just the reverse of the embodiment
shown in FIG. 1. Fluid responsive switch 10' has a leaf spring 18'
supporting magnet 25 responsive by deflecting away from Hall effect
transducer 22' by the flow of fluid as indicated by the arrows.
However, in this embodiment, the output works in the reverse. The
normal rest position of bending beam 18' is with magnet 20 against
tube 24' housing Hall effect transducer 22'. Fluid flowing in the
direction indicated by the arrow, deflects bending beam 18' away
from tube 24' moving magnet 20' away from Hall effect transducer
22'. The result in thus, the opposite of the effect illustrated
in FIG. 1 but in reverse. The output of Hall effect transducer
22' will decrease as magnet 20' is deflected farther and farther
Hall effect transducer 22 employs magnetically sensitive transducers
in two different modes. These modes are illustrated in FIGS. 5 and
6. FIG. 5 illustrates an output that is a step function response
or digital mode, while FIG. 6 illustrates an output that is a non-linear
analog function response. The digital mode provides a continuous
output voltage signal, which remains at zero, until a preselected
magnetic field intensity is presented to Hall effect transducer
22 which then shifts the output from zero to a fixed value in a
rapid step function manner as illustrated in FIG. 5. Hall effect
transducer 22 can also be used in a continuous analog output mode
that varies as magnet 20 on bending beam 18 approaches the transducer
and separation distance "d" becomes smaller.
In a continuous output mode, a continuous non-linear analog function
response or signal, as illustrated in FIG. 6 is obtained relative
to variable magnetic field intensity applied to transducer 22. Thus,
the system disclosed can be used as both a flow switch, and also
as a flow meter to determine the flow rate and total volume of the
The system can employ magnet 20 on bending beam 18 in a straight
head-on approach of the magnet directly to the sensitive surface
of Hall effect transducer 22 as illustrated in FIGS. 1 and 2. However,
the system can also employ a sideways bypass approach illustrated
in the diagrams of FIGS. 7(a) through 7(d) and 8(a) through 8(d).
Referring to FIGS. 7(a) through 7(d), a Hall effect transducer 22'
is placed in support tube 24' facing toward the side rather than
directly toward the magnet as shown in FIG. 1. Leaf spring 18' is
provided with a side extension 19 having a magnet 20'. Thus, the
flow of fluid in tee 14 (FIG. 1) will force leaf spring 18' toward
support tube 24' with extension 19 passing beside Hall effect transducer
A further option would be to have leaf spring 18" as shown
in FIGS. 8(a) through 8(d) with extension 19' extending at right
angle to the bottom of leaf spring 18' so that it will pass beneath
the support tube 24" and Hall effect transducer 22". The
embodiments of FIGS. 7 and 8 have separation distances "d.sub.1
" and "d.sub.2 " between magnets 20 and Hall effect
transducer 22 as shown in the diagram of FIGS. 9 and 10. Separation
distance "d.sub.1 " will vary as magnet 20 moves toward
or away from Hall effect transducer 22 while sideways separation
distance "d.sub.2 " remains constant. Magnet 20 can have
special shapes as will be described in greater detail hereinafter.
The effect is to produce a voltage that has an output curve that
may be a linear straight line of FIG. 11 or could be a non-linear
curve similar to that shown in FIGS. 4 and 6. Non-linear output
curves are made linear with downstream microprocessor electronics,
as will be described in greater detail hereinafter.
The advantage of the sideways bypass devices of FIGS. 7 and 8 is
that they permit three principle methods to be employed to modify
the magnetic field intensity in the volume of space in and around
Hall effect transducers 22' and 22". One of these methods is
to employ a variety of magnet shapes as illustrated in FIGS. 12(a)
through 12(c) and 13(a) through 13(i). FIGS. 12(a) through 12(c)
illustrate varying the size of disk magnet 20 relative to Hall effect
transducer 22. In FIG. 12(a) a magnet is shown that could be smaller
or the same size as Hall effect transducer 22 while in FIG. 12(c)
a much larger disk shaped transducer is shown. FIG. 13(a) shows
a conventional cylindrical disk-shaped permanent magnet 20 that
is illustrated in FIG. 1. Permanent magnet 20b could also be rectangular,
as shown in FIG. 13(b); a pyramid shaped magnet 20c, as illustrated
in FIG. 13(c) or a triangular magnet 20d as illustrated in FIG.
13(d). Other optional shapes are a compound permanent magnet 20e,
comprised of a plurality of cylindrical disk-shaped magnets as shown
in FIG. 13(c), or a compound permanent magnet 20f, comprised of
a plurality of rectangular magnets as shown in FIG. 13(f). FIGS.
13(g) and 13(i) illustrate the various shapes and combinations of
magnets that can be used in the system.
The various magnetic shapes, materials and strengths illustrated
in FIGS. 13(a) through 13(i) provide a variety of magnetic field
intensities. The varying magnetic field intensities can be used
to activate both digital and linear Hall effect transducers. The
device disclosed herein is principally concerned with fluids, gases
and vapors impinging upon flow sensitive leaf spring 18 which modifies
and controls a magnetic field intensity level in and around Hall
effect transducer 22 which then produces a variable output voltage
which completes the translation of flow input information into a
variable electrical output.
The operation of the system is generally indicated in the block
diagram of FIG. 18. A fluid flows through a conduit or tee 14 (FIG.
1) and produces a flow with turbulence 26 which provides a uniform
or variable deflection 30 of bending beam 28. Bending beam leaf
spring 28 with permanent magnet 20 produces a magnetic field strength
which directly effects a Hall effect transducer 32 producing a
uniform or variable output voltage 34 that is then processed by
an output signal processing circuit 36. The circuit can be designed
to produce a digital step output as illustrated in FIG. 5 for an
on/off function, or an analog magnetic output as shown in FIG. 6.
The permanent magnets as previously described, can provide a variety
of magnetic field intensities according to the shape and composition
of the magnet, but also by the size of the magnet as shown in FIGS.
12(a) through 12(c). A small size disc magnet 20 (FIG. 12(a)), in
relation to the size of Hall effect transducer 22 will produce a
lower voltage output. A slightly larger size magnet 20 (FIG. 12(c)),
relative to typical Hall effect transducer 22 will produce a different
output function. Also, whether or not magnet 20 approaches Hall
effect transducer 22 directly, or by the sideways bypass of FIGS.
7 and 8 will effect the shape of output function.
A Hall effect system, used as a digital flow switch system, is
illustrated in the schematic block diagram of FIGS. 19(a) and 19(b).
FIG. 19(b) is an informational block diagram describing schematic
block diagram of FIG. 19(a) with like reference numbers indicating
like functions. Bending beam 38 having magnet 40 is deflected
toward a Hall effect transducer 42 with a linear or digital output
43 as illustrated in FIG. 1. The system illustrated in the schematic
block diagram of FIG. 19(a) can be the direct approach permanent
magnet of FIG. 1 or the sideways bypass permanent magnets 20' or
20" of FIGS. 7 and 8. The voltage output of Hall effect transducer
42 is then fed to a signal smoothing filter 44. Signal smoothing
filter 44 is an important element in the system. Because the system
shown in FIGS. 1 7 and 8 substantially minimize or eliminate the
system hysteresis of the system illustrated in prior U.S. Pat. No.
5021619 the flow measurement sensitivity is maximized, which
is a desirable operational parameter. However, this also increases
the sensitivity of the system to flow turbulent noise. The low signal-to-noise
ratio condition, presented by the sensitivity to flow turbulence
is corrected by including a signal smoothing filter 44 as a part
of the signal processing electronics. The output of smoothing filter
44 is then fed to a voltage level comparator 45 which also receives
a variable hysteresis signal 46. Variable hysteresis 46 is a very
small and repeatable electronic hysteresis introduced to ensure
downstream electronic systems do not go into undamped electronic
Voltage level comparator 45 compares the output from signal smoothing
filter 44 with a reference voltage and produces digital output 47
when the signal reaches or exceeds the reference level. The output
may be amplified by downstream amplifier 48 and then fed to output
signal processor (not shown) for additional processing and delivery
to a suitable control system input function. Interface 49 indicates
that downstream operations such as amplification 48 and other processing,
are operations that may be provided by the customer. Voltage level
comparator 45 can be an LM393 or equivalent. An LM393 is specifically
designed as a comparator, however, voltage level comparator 45 could
also be an operational amplifier without a feedback resistor due
to its very high open-loop gain. Further, more sophisticated electronic
filtering can be employed; such as digital notch filters, band pass
filters, etc. to suppress acoustic, mechanical and electrical noise
introduced into the system from outside sources.
The Hall effect flow meter and flow switch described above is a
new device developed in a continuing quest for increase fluid flow
sensitivity based on the integrated combination of a bending beam/shaped
flow target described in U.S. Pat. No. 5021619 dated Jun. 4 1991
to the same inventor as the invention shown herein. The flow sensitivity
of the extremely narrow Hall effect hysteresis dead band (approximately
0.035 inches) can be further increased by a factor of approximately
two (2) or more by the use of bending beam flow target fitted with
a vortex shedding enhancing configuration, plus operating the flow
transducer in a flow meter mode.
Vortex shedding is best illustrated in the classic "flag flutter
phenomenon" illustrated in FIGS. 23 and 24. Flag 60 on flag
pole 62 flutters according to the flow of fluid or air over its
surface, as shown in FIG. 24 (Fluid Dynamic Drag, Dr. S. F. Hoerner,
1965 PP. 3-25 Library of Congress Catalog No. 64-19666). Vortex
shedding, indicated by swirling arrows 64 in FIG. 24 is caused
by the flow of air over the surface of flag pole 62 and flag 60.
This vortex shedding can be put to use in the flow meter of the
FIGS. 25 through 28 illustrate the general features of a modification
to flow sensitive bending beam transducer system to enhance and
use vortex shedding to increase flow sensitivity and measure low
flows. The flow sensitive switch of FIG. 25 is shown upside down
from the system of FIG. 1 to better illustrate vortex shedding.
In the embodiment of FIGS. 25 through 28 bending beam 68 has magnet
70 and appendages 72 in the form of flanges having a v-shaped cross
section along the lateral of lengthwise edge of bending beam 68.
Appendages 72 enhance the flow of fluid over the surface of bending
beam 68 creating vortex shedding 74 along either side of bending
The turbulence caused by appendages 72 increases the vortex shedding
from the normal turbulence caused by bending beam of the embodiment
of FIG. 1 as shown in FIGS. 26 and 27. In FIG. 26 bending beam
18 without any enhancing appendages, will vibrate slightly, causing
some vortex shedding 76. In FIG. 27 lateral flanges or appendages
72 on bending beam 68 enhance vortex shedding 78 which can be detected
and used to increase the sensitivity and measure low flow. Bending
beam 68 will vibrate or oscillate as indicated by the dotted line,
providing vortex shedding 78 that will provide an output as illustrated
in FIG. 28 before it begins a steady state bend.
Alternating series of vortexes 78 produce alternating pressures
on either side of bending beam 68 which in turn, induce alternating
changes in the drag coefficient of the bending beam which finally
appears as a fluid flow induced longitudinal oscillation of the
bending beam along the axis of the primary fluid flow vector, as
illustrated by the dotted lines. As discussed above and illustrated
in FIGS. 26 through 28 the configuration of bending beam 68 modulates
the magnetic field surrounding the Hall effect transducer which
in turn, oscillates the electrical voltage output of the flow transducer
system. The amplitude of vibrating bending beam 68 is rather small,
however, it produces a measurable alternating electrical output
signal which can be amplified to any reasonable level (e.g., 500MV
AC or more). The AC output signal will be zero (0) for a no flow
initial condition indicated at 80 for a zero (0) flow input bias
voltage. Very low initial fluid flow cause vortex shedding 78 from
appendages 72 to vibrate bending beam 68 which will produce a small
low frequency output indicated by the minimum detectable vortex
shedding AC output (F.sub.2) at 82 (e.g., less than about a 10 Hz
AC output signal which can be amplified as required).
The result of the configuration shown in FIG. 27 is to detect a
very low flow of fluid, the order of about 0.1 foot/second past
bending beam target 68 by looking for induced minute beam oscillations
rather than steady state bending of the beam. This approach is equivalent
to the human ear detecting minute acoustic sound pressure vibrations
rather than steady state pressure variations. The transition of
the output (V.sub.out) from transducer 22 from a fixed zero (0)
flow (F.sub.1) initial condition to a very low flow condition (e.g.
equal to about 0.1 Ft/Sec) small vortex shedding induced vibrations
of bending beam 68 which produce small variations in the magnetic
field penetrating the Hall effect transducer, which finally produces
a variable electrical AC output signal. As fluid flow input increases
past (F.sub.2) to higher flow rates at (F.sub.3) a measurable transducer
DC component is added to the AC shedding voltage indicated at 84.
Subsequent electronic processing provides two useful flow transducer
outputs: 1) An AC vortex shedding induced voltage with a positive
proportional frequency related to the fluid flow rate; and 2) A
DC voltage proportional to the bending of flow detecting bending
beam 68. Either flow detecting mode, or both modes, can be used
simultaneously as required in each particular flow measurement.
At the low flow region, between F.sub.2 and F.sub.3 the AC vibrating
mode will predominate as an initial on/off flow switch detection,
but may not provide useful flow meter output until the flow rate
at F.sub.3 is obtained. The minimum detectable Hall effect analog
output, just after the flow rate reaches F.sub.3 indicated at 84
at this point will be an AC voltage with a DC component indicated
by the dotted line.
The system can also be used as a combined low flow meter, flow
totalizer and flow switch with signal processing illustrated in
the schematic block diagram of FIGS. 20(a) and 20(b). FIG. 20(b)
is an informational diagram of FIG. 20(a) of system 10' as before.
In this system, fluid flow deflects beam 38 having magnet 40 toward
Hall effect transducer 42 as before. The output of Hall effect transducer
42 is then smoothed by signal smoothing filter 44 for output to
amplifier 50 that provides outputs to three circuits. One is a flow
analog output circuit 52 a second is a voltage level comparator
54 and a third is vortex shedding AC signal conditioning 52 comprised
of suitable electronic filtering to provide an AC vortex shedding
induced voltage with a positive proportional frequency related to
the fluid flow rate. Flow linear analog output circuitry 52 transforms
the input signal into a continuous analog voltage which is then
electronically linearized to provide a typical flow meter output
signal. This output can then be integrated over time to provide
a flow quantity totalizer output signal. The second output from
amplifier 50 is fed to a voltage level comparator 54 which changes
states when the output goes above or below a reference voltage thereby,
providing a typical flow switch step function output signal.
Vortex shedding AC signal conditioner 55 detects the AC component
of the flow between F.sub.2 and F.sub.3 output representing very
low flow. This mode can be used alone or with the flow above F.sub.3
as required for each particular flow measurement. In the low flow
condition below F.sub.2 and F.sub.3 vortex shedding AC signal conditioning
output 55 will predominate as an initial on/off flow detection,
but may not necessarily provide a useful flow meter output until
flow beyond F.sub.3 is obtained.
One form of a signal smoothing filter is illustrated in FIGS. 21
22(a) and 22(b). FIG. 22(a) shows the output turbulence while FIG.
22(b) shows the output smoothed by the filter of FIG. 21. Bending
beam 18 is deflected by the flow of fluid in a tee 14 (FIG. 1) to
move permanent magnet 20 toward Hall effect transducer 22 providing
a sensor 56 output Hall effect transducer 58 to RC filter 60. The
output of Hall effect transducer 58 produces a voltage proportional
to the rate of fluid flow passing past flow sensing leaf spring
18 and permanent magnet 20. This voltage causes a current to flow
from Hall effect transducer 58 through resistor R3 into capacitor
C1 until it is charged to the same voltage as that produced by Hall
effect transducer 58. The charge condition of capacitor C1 will
remain stable as long as the output voltage of Hall effect transducer
58 remains stable (i.e., the voltage of capacitor C1 will follow
transducer 58 voltage exactly except at a new frequency response
determined by the product of resistor R3 and capacitor C1 (known
as the RC time constant)). For instance, resistor R3 and capacitor
C1 can be selected to provide a relatively long time constant of
approximately one second which corresponds to a cutoff frequency
of approximately 0.16 Hz (FIG. 21). Lower frequencies will pass
through the RC filter and higher frequencies will be blocked.
When the flow of fluid decreases, the voltage output of Hall effect
transducer decreases and capacitor C1 discharges to ground through
parallel resistors R2 and R3 in series with resistor Rl. Diode D.sub.1
thus, provides two different time constants, one for increasing
fluid flow and a second for decreasing fluid flow thus, providing
additional operation and flexibility. Feedback circuit of resistor
R2 and diode D1 can be eliminated if desired, which would produce
a different time constant dependent on the values of resistors R1
R3 and C1.
Thus, there has been disclosed a fluid responsive monitoring system
utilizing a Hall effect transducer that transform a fluid, gas or
vapor flowing past a bending beam having a permanent magnet into
a continuous analog voltage which is then electronically processed
to provide a flow meter, a flow totalizer and/or a fluid flow switch
output information in any sequence or combination as required. The
system employs a bending beam magnet that is mounted to directly
approach a Hall effect transducer or by a sideways bypass system
to produce a voltage output from the transducer.
This invention is not to be limited by the embodiment shown in
the drawings and described in the description which is given by
way of example and not of limitation, but only in accordance with
the scope of the appended claims.