Abstrict 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
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.
Claims What is claimed:
1. A fluid responsive monitoring system for monitoring the flow
of fluid in a conduit comprising;
a support body attached to said conduit;
a support tube mounted on said support 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 support body extending into the
path of a fluid flowing in said conduit, said flexible arm having
an extension at right angles to the plane of said flexible arm;
magnetic means mounted on said flexible arm spaced from said Hall
effect transducer;
said magnetic means being mounted on said right angle extension
so that said fluid moves said magnet means in a sideways bypass
approach to said Hall effect transducer;
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 magnetic means
mounted on said flexible arm comprises a permanent magnet.
3. The system according to claim 2 in which said flexible arm is
mounted proximate said Hall effect transducer; said permanent magnet
being mounted so that said fluid moves said permanent magnet toward
to said Hall effect transducer.
4. The system according to claim 3 in which said permanent magnet
has a shape that increases the magnet's intensity as it passes toward,
or by said Hall effect transducer.
5. The system according to claim 3 in which said permanent magnet
is a cylindrical disc-shaped magnet.
6. The system according to claim 3 in which said magnet is a rectangular
magnet.
7. The system according to claim 2 in which said permanent magnet
is a cylindrical magnet.
8. The system according to claim 2 in which said permanent magnet
is a rectangular magnet.
9. The system according to claim 2 in which said permanent magnet
has a pyramidal shape.
10. The system according to claim 9 in which said permanent magnet
is a triangular cross-sectional shape.
11. The system according to claim 2 in which said permanent magnet
has a triangular cross-sectional shape.
12. The system according to claim 2 in which said permanent magnet
is a series of increasingly larger permanent magnets.
13. The system according to claim 12 in which said series of increasingly
larger permanent magnets is a series of increasingly larger cylindrical
disc-shaped magnets.
14. The system according to claim 13 in which said series of increasingly
larger permanent magnets is an increasingly larger rectangular magnets.
15. 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.
16. The system according to claim 15 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.
17. The system according to claim 15 in which said signal conditioning
means comprises a comparator for producing a step function digital
output mode.
18. The system according to claim 15 in which said signal conditioning
means comprises a linear analog output circuit means.
19. The system according to claim 15 in which said output signal
conditioning means comprises a non-linear analog circuit means.
20. The system according to claim 15 in which said signal conditioning
means comprised integrating output circuit means to obtain total
flow quantity over a selected time interval.
Description 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, 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 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 accept 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 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 in a continuous analog output
mode.
Yet another object of the present invention is to provide a fluid
flow switch and 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 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
output information.
Yet another object of the present invention is to provide a flow
switch and 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 pass moving past a Hall effect device.
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, is 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.
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 minimum
of a simple flow sensing blade having a magnet that approaches the
Hall effect transducer to 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
analog output.
The preferable signal smoothing filter used is normally an RC (resistance/capacitance)
signal smoothing filter. The RC smoothing filter receives a signal
from an 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.
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 the embodiment of FIG. 1.
FIG. 4 is a graph of the transducer output relative to separation
distance.
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
8.
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
both a fluid flow analog output and a digital switched output.
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.
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. 5021619 to the same inventor as the invention disclosed
herein.
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
18.
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 support body or housing 12 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.
Hall effect transducer 22 employs magnetically sensitive transducers
in two different modes. These modes are illustrated in FIGS. 5 and
6. 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 flow.
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
22'.
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 nonlinear
curve similar to that shown in FIGS. 4 and 6. Nonlinear 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
oscillations.
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 system can also be used as a combined 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 two circuits. One is a flow analog output circuit 52
while the second is a voltage level comparator 54. Flow linear analog
output circuitry 48 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.
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 R1. 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. |