Abstrict A fluid flow meter comprising a housing having a pair of fluid
ports and defining therebetween a fluid flow path; a flexible membrane
defining a pair of opposing faces and being mounted in the fluid
flow path such that the pair of faces simultaneously define with
the housing fluid impermeable seals at at least two different locations
along the flow path, the membrane being operative to flex so as
to permit passage therepast of discrete quanta of fluid, each having
a known volume; apparatus for generating electrical signals corresponding
to flexure of the membrane; and monitoring apparatus for receiving
the electrical signals and thereby determining a fluid flow rate
along the flow path.
Claims I claim:
1. A fluid flow meter comprising:
a housing having a pair of fluid ports and defining therebetween
a fluid flow path:
a flexible membrane defining a pair of opposing faces and being
mounted in said fluid flow path such that said pair of faces simultaneously
define with said housing fluid impermeable seals at at least two
different locations along said flow path, said membrane being operative
to flex so as to permit passage therepast of discrete quanta of
fluid, each having a known volume varying as a function of flow
rate;
means for generating electrical signals corresponding to flexure
of said membrane; and
monitoring means for receiving the electrical signals over a measured
period of time, determining the rate of said electrical signals,
determining the volume of said quanta based upon said electrical
signal rate, and thereby determining a fluid flow rate along said
flow path.
2. A fluid flow meter according to claim 1 and wherein said membrane
further defines a pair of edges lying in respective planes substantially
parallel to the direction of fluid flow and said fluid flow path
has a uniform cross-sectional configuration along at least part
of its length, said fluid impermeable seals being defined therealong.
3. A fluid meter according to claim 2 and wherein said part of
said flow path length having a uniform cross-sectional configuration
has a rectangular cross-sectional configuration and is defined by
first and second pairs of parallel walls, said membrane being disposed
therebetween such that said respective planes in which said membrane
edges lie are aligned substantially parallel to said first pair
of walls.
4. A fluid flow meter according to claim 3 and wherein said fluid
impermeable seals are defined at at least three locations along
said flow path.
5. A fluid flow meter according to claim 4 and wherein said membrane
edges are spaced from said first pair of walls by substantially
a fluid boundary layer thickness.
6. A fluid flow meter according to claim 5 and wherein said membrane
has a rectangular configuration and is oriented such that its longitudinal
axis lies parallel to the direction of flow.
7. A fluid flow meter according to claim 6 and wherein said membrane
is operative to permit passage of discrete quanta of fluid by flexure
in wavelike fashion, said membrane having first and second ends
mounted in said housing, said flow meter further including at least
one guide member adjacent to at least one of said ends for assisting
the wavelike flexure of said membrane.
8. A fluid flow meter according to claim 7 and wherein said membrane
first and second ends are mounted for partial rotation about respective
first and second axes parallel to said second pair of walls and
passing through said first pair of walls.
9. A fluid flow meter according to claim 8 and wherein said housing
is configured to permit deposition of debris from said fluid at
a location upstream of said membrane but downstream of an adjacent
fluid port.
10. A fluid flow meter according to claim 9 and wherein each of
said walls defines an inward-facing surface having antistatic and
hydrophobic properties.
11. A fluid flow meter according to claim 7 wherein said flow
meter includes a pair of guide block having rounded inner faces
in opposing relationship adjacent at least one of said ends.
12. A fluid flow meter according to claim 7 wherein said at least
one guide member comprises an elongated member.
13. A fluid flow meter according to claim 42 wherein each of said
guide blocks further comprise a fluid permeable extension mounted
to said guide block inner face.
14. A fluid flow meter according to claim 1 and wherein said membrane
comprises a layer of piezoelectric material.
15. A fluid flow meter according to claim 11 and wherein said
membrane also comprises a pair of metallized layers surrounding
said layer of piezoelectric material.
16. A fluid flow meter according to claim 15 and wherein said
piezoelectric material is polyvinylidene fluoride.
17. A fluid flow meter according to claim 15 and wherein said
metallized layer comprises discrete metallized portions provided
at predetermined discrete locations on said membrane.
18. A fluid flow meter according to claim 1 and wherein said means
for generating comprises first and second electrical contacts mounted,
respectively, onto a surface of said membrane and in association
with said monitoring means and such that an electrical signal is
generated upon release of a single quantum of fluid.
19. A fluid flow meter according to claim 1 and wherein said flexible
membrane comprises magnetized material and said means for generating
comprises a magnetic head operative to generate and electrical signal
upon sensing proximity of said membrane thereto.
20. A fluid flow meter according to claim 1 and wherein said monitoring
means includes means for identifying electrical signals generated
by flexure of said membrane upon release therefrom of a single quantum
of fluid.
21. A fluid flow meter according to claim 1 and wherein there
is also provided means for sensing the temperature of said fluid.
22. A fluid flow meter according to claim 21 and wherein said
monitoring means also includes means responsive to said temperature
sensing means for providing an alarm indication when the temperature
of the fluid reaches at least a predetermined temperature.
23. A fluid flow meter according to claim 1 and wherein there
is also provided means for sensing the pressure of the fluid.
24. A fluid flow meter according to claim 23 and wherein said
monitoring means also includes means responsive to said pressure
sensing means for providing an alarm indication when the pressure
of the fluid reaches at least a predetermined pressure.
25. A fluid flow meter according to claim 1 and also including
remote data collection means and wherein said monitoring means also
includes means for providing fluid flow data thereto.
26. A fluid flow meter according to claim 31 wherein said remote
data collection means comprises automatic dialing means operatively
connected to a telephone communications systems.
27. A fluid flow meter comprising:
a housing having a pair of fluid ports and defining therebetween
a fluid flow path;
a flexible membrane having varying thicknesses along at least part
of its length defining a pair of opposing faces and being mounted
in said fluid flow path such that said pair of faces simultaneously
define with said housing fluid impermeable seals at at least two
different locations along said flow path, said membrane being operative
to flex so as to permit passage therepast of discrete quanta of
fluid, each having a known volume;
means for generating electrical signals corresponding to flexure
of said membrane; and
monitoring means for receiving the electrical signals and thereby
determining a fluid flow rate along said flow path.
28. A fluid flow meter comprising:
a housing having a pair of fluid ports and defining therebetween
a fluid flow path;
a flexible membrane defining a pair of opposing faces and being
mounted in said fluid flow path such that said pair of faces simultaneously
define with said housing fluid impermeable seals at at least three
different locations along said flow path, said membrane being operative
to flex so as to permit passage therepast of discrete quanta of
fluid, each having a known volume;
said membrane further defining a pair of edges lying in respective
planes substantially parallel to the direction of fluid flow and
said fluid flow path having a uniform cross-sectional configuration
along at least part of its length, said fluid impermeable seals
being defined therealong;
said part of said flow path length having a uniform cross-sectional
configuration having a rectangular cross-sectional configuration
defined by first and second pairs of parallel walls, said membrane
being disposed therebetween such that said respective planes in
which said membrane edges lie are aligned substantially parallel
to said first pair of walls;
said membrane edges being spaced from said first pair of walls
by substantially a fluid boundary layer thickness; and
said first pair of walls being made from a flexible material;
means for generating electrical signals corresponding to flexure
of said membrane; and
monitoring means for receiving the electrical signals and thereby
determining a fluid flow rate along said flow path.
29. A fluid flow membrane to claim 28 wherein each of said pair
of side walls defines a space adjacent to a portion of said membrane.
30. A fluid flow meter according to claim 28 wherein said flexible
material is a flexible elastomer.
31. A fluid flow meter comprising:
a housing having a pair of fluid ports and defining therebetween
a fluid flow path;
a flexible membrane defining a pair of opposing faces and being
mounted in said fluid flow path such that said pair of faces simultaneously
define with said housing fluid impermeable seals at at least three
different locations along said flow path, said membrane being operative
to flex so as to permit passage therepast of discrete quanta of
fluid, each having a known volume;
said membrane further defining a pair of edges lying in respective
planes substantially parallel to the direction of fluid flow and
said fluid flow path has a uniform cross-sectional configuration
along at least part of its length, said fluid impermeable seals
being defined therealong;
said part of said flow path length having a uniform cross-sectional
configuration having a rectangular cross-sectional configuration
and being defined by first and second pairs of parallel walls, said
membrane being disposed therebetween such that said respective planes
in which said membrane edges lie are aligned substantially parallel
to said first pair of walls;
said membrane edges being spaced from said first pair of walls
by substantially a fluid boundary layer thickness;
each of said first pair of walls comprising a roughened surface;
means for generating electrical signals corresponding to flexure
of said membrane; and
monitoring means for receiving the electrical signals and thereby
determining a fluid flow rate along said flow path.
32. A fluid flow meter comprising:
a housing having a pair of fluid ports and defining therebetween
a fluid flow path;
a flexible membrane defining a pair of opposing faces and being
mounted in said fluid flow path such that said pair of faces simultaneously
define with said housing fluid impermeable seals at at least two
different locations along said flow path, said membrane being operative
to flex so as to permit passage therepast of discrete quanta of
fluid, each having a known volume;
means for generating electrical signals corresponding to flexure
of said membrane; and
monitoring means for receiving the electrical signals and thereby
determining a fluid flow rate along said flow path;
said monitoring means including means for identifying electrical
signals generated by flexure of said membrane upon release therefrom
of a single quantum of fluid;
said monitoring means also including means for determining the
rate of fluid flow based upon electrical signals received over a
measured period of time; and
said monitoring means also comprising means for storing a predetermined
value of volume for a single quantum of fluid flow, means for calculating
a fluid flow rate corresponding to a number of electrical signals
received over a measured period of time, means for comparing said
predetermined value for said single quantum with a reference value
of volume based upon the flow delivery characteristics of said meter
at said first rate of flow, means for adjusting said predetermined
value to said reference value of volume based upon the flow delivery
characteristics of said matter, and means for repeatedly adjusting
the predetermined value of volume of a single quantum of fluid so
as to obtain an increasingly more accurate value of flow.
33. A fluid flow meter according to claim 32 and wherein said
monitoring means also includes means for calculating an adjusted
quantum volume according to the sensed temperature of the fluid.
34. A fluid flow meter according to claim 32 and wherein said
monitoring means also includes means for calculating an adjusted
quantum volume according to the sensed pressure of the fluid.
Description FIELD OF THE INVENTION
The present invention relates generally to devices for measuring
volumetric fluid flow and more specifically to a travelling wave
flow meter having a thin flexible membrane whose flexing movement
is operative to permit passage of fluid in travelling waves.
BACKGROUND OF THE INVENTION
There are known various types of flow meter which utilize a member
which vibrates or undulates as fluid flows therepast. Fluid flow
rates can be determined from the frequency of vibration or rate
of undulation, which is generally proportional to the rate of fluid
flow.
An early form of fluid meter having an undulating spring confined
in a fluid flow chamber and a mechanical counter for indicating
the amount of fluid flowing therethrough is described in U.S. Pat.
No 398013 (Welker). A more recent travelling wave flow meter, utilizing
an undulating membrane formed of piezoelectric material which generates
electrical signals as a function of the rate of undulation is described
in U.S. Pat. Nos. 4358954 and 4409830 (both to de Jong).
The flow meter disclosed in the above-referenced U.S. Patents to
de Jong is, however, limited in use to measurement of noncompressible
fluids, such as liquids. If used for compressible fluids, such as
gases, under a relatively high flow rate, the membrane would be
liable to give rise to stretching thereof across a fluid flow path
with which it is associated, so as to block fluid flow therealong.
SUMMARY OF THE INVENTION
It is an aim of the present invention to provide for the measurement
of a wide range of compressible and noncompressible fluid flows,
a positive displacement quantum fluid flow meter which overcomes
disadvantages of the prior art.
There is provided, therefore, in accordance with an embodiment
of the invention, a fluid flow meter comprising a housing having
a pair of fluid ports and defining therebetween a fluid flow path;
a flexible membrane defining a pair of opposing faces and being
mounted in the fluid flow path such that the pair of faces simultaneously
define with the housing fluid impermeable seals at two or more different
locations along the flow path, the membrane being operative to flex
so as to permit passage therepast of discrete quanta of fluid, each
having a known volume; apparatus for generating electrical signals
corresponding to flexure of the membrane; and monitoring apparatus
for receiving the electrical signals and thereby determining a fluid
flow rate along the flow path.
Additionally in accordance with an embodiment of the invention,
the membrane further defines a pair of edges lying in respective
planes substantially parallel to the direction of fluid flow and
the fluid flow path has a uniform cross-sectional configuration
along part of its length, the fluid impermeable seals being defined
therealong.
Further in accordance with an embodiment of the invention, the
part of the flow path length having a uniform cross-sectional configuration
has a rectangular cross-sectional configuration and is defined by
first and second pairs of parallel walls, the membrane being disposed
therebetween such that the respective planes in which the membrane
edges lie are aligned substantially parallel to the first pair of
walls.
Additionally in accordance with an embodiment of the invention,
the fluid impermeable seals are defined at three or more locations
along the flow path.
Further in accordance with an embodiment of the invention, the
membrane edges are spaced from the first pair of walls by substantially
a fluid boundary layer thickness.
Additionally in accordance with an embodiment of the invention,
the membrane has a rectangular configuration and is oriented such
that its longitudinal axis lies parallel to the direction of flow.
Further in accordance with an embodiment of the invention, the
membrane is operative to permit passage of discrete quanta of fluid
by flexure in wavelike fashion, there also being provided apparatus
for assisting the wavelike flexure of the membrane.
Additionally in accordance with an embodiment of the invention,
the housing is configured to permit deposition of debris from the
fluid at a location upstream of the membrane but downstream of an
adjacent fluid port.
Further in accordance with an embodiment of the invention, the
membrane comprises a layer of piezoelectric material.
According to an alternative embodiment of the invention, the apparatus
for generating comprises first and second electrical contacts mounted,
respectively, onto a surface of the membrane and in association
with the monitoring apparatus and such that an electrical signal
is generated upon release of a single quantum of fluid.
According to a further alternative embodiment of the invention,
the flexible membrane comprises magnetized material and the apparatus
for generating comprises a magnetic head operative to generate an
electrical signal upon sensing proximity of the membrane thereto.
Additionally in accordance with an embodiment of the invention,
the monitoring apparatus includes apparatus for identifying electrical
signals generated by flexure of the membrane upon release therefrom
of a single quantum of fluid.
Further in accordance with an embodiment of the invention, the
monitoring apparatus also includes apparatus for determining the
rate of fluid flow based upon electrical signals received over a
measured period of time.
Additionally in accordance with an embodiment of the invention,
the monitoring apparatus also comprises apparatus for storing a
predetermined value of volume for a single quantum of fluid flow,
apparatus for calculating a fluid flow rate corresponding to a number
of electrical signals received over a measured period of time, apparatus
for comparing the predetermined value for the single quantum with
a value of volume corresponding to the flow delivery characteristics
of the meter at the first rate of flow, apparatus for adjusting
the predetermined value to the value of volume corresponding to
the flow delivery characteristics and apparatus for repeatedly adjusting
the predetermined value of volume of a single quantum of fluid so
as to obtain an increasingly more accurate value of flow.
In accordance with an alternative embodiment of the invention,
the fluid flow path has an arched configuration along its length.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and appreciated more fully
from the following detailed description taken in conjunction with
the drawings, in which:
FIG. 1 is a perspective illustration of a quantum fluid invention;
FIG. 2 is a sectional view of the flow meter of FIG. 1 taken along
line 2--2 therein;
FIG. 3 is a cross-section taken along line 3--3 in FIG. 2;
FIG. 4 is a cross-section taken along line 4--4 in FIG. 3;
FIG. 5 shows an enlarged detail of a portion of the cross-section
shown in FIG. 4;
FIG. 6 shows an enlarged detail of a portion of the cross-section
shown in FIG. 4 constructed according to an alternative embodiment
of the invention;
FIG. 7 is a sectional illustration of a portion of a piezoelectric
member useful in the flow meter of FIG. 1;
FIG. 8 is an enlarged cross-sectional view taken along line 8--8
in FIG. 3;
FIG. 9 is a view similar to that of FIG. 8 but showing a construction
according to an alternative embodiment of the invention;
FIG. 10 is a view similar to that of FIG. 8 but showing a construction
according to a further embodiment of the invention;
FIG. 11 shows a piezoelectric member similar to that shown in FIG.
7 but wherein the ends thereof are thickened;
FIG. 12 is a cross-sectional partial view of spring mounts for
guide blocks shown in FIG. 8 to 10;
FIG. 13 is an elevational view of an end portion of the piezoelectric
member shown in FIG. 3 and showing mounting details thereof;
FIG. 14 is a cut away illustration of a portion of a side wall
of the housing of the flow meter shown in FIG. 1;
FIGS. 15A, 15B and 15C show three successive stages in the transport
of discrete fluid quanta across the flow meter of FIG. 1;
FIG. 16 is a schematic illustration of a fluid flow meter similar
to that shown in FIG. 1 but having arched walls;
FIG. 17 is a block diagram illustration of electronic apparatus
associated with a fluid flow meter of the present invention;
FIG. 18 is a block diagram illustration showing a telemetering
system, useful in conjunction with a fluid flow meter of the present
invention;
FIG. 19 is a block diagram illustration showing an alternative
telemetering system, useful in conjunction with a fluid flow meter
of the present invention;
FIG. 20 is a block diagram illustration showing a further alternative
telemetering system, useful in conjunction with a fluid flow meter
of the present invention;
FIG. 21 shows a multiplexed telemetering system, useful in conjunction
with a fluid flow meter of the present invention;
FIG. 22 shows a partial side-section of a fluid flow meter, constructed
and operative with an alternative embodiment of the invention;
FIG. 23 shows a partial side-section of a fluid flow meter, constructed
and operative with a further alternative embodiment of the invention;
and
FIG. 24 is a top view of a piezoelectric member, constructed and
operative in accordance with an alternative embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1 2 and 3 there is shown a positive displacement
fluid flow meter, referenced generally 10 having a housing 12 defining
a fluid flow chamber 14 (FIG. 2) and first and second ends 16 and
20 having respective first and second fluid ports 18 and 22.
Although in the shown embodiment, fluid ports 18 and 22 function
respectively as an inlet and outlet, it will be appreciated from
the ensuing description that the internal arrangement of flow meter
10 is such that fluid flow may take place in any chosen direction
and with the flow meter at any preferred orientation.
According to a preferred embodiment of the invention, flow meter
10 is used for metering the flow of compressible fluids, such as
gas. As, however, as the flow meter of the present invention may
also be used for the metering of noncompressible fluids such as
oil or water, the flow of `fluid` is described herein throughout
except where not applicable.
According to the shown embodiment, housing 12 includes a first
end receiving chamber 26 for receiving fluid flow from inlet 18
prior to the fluid passing through flow chamber 14. Chamber 26 permits
any debris and, in the case of gas flow, moisture, to be deposited
therein prior to flow through flow chamber 14. There is also provided
a second end chamber 27 similar to first end chamber 26 for receiving
therein any deposition of debris and moisture in a case of flow
in a direction opposite to that indicated.
According to the present invention, discrete quanta of fluid, each
having a known volume, are permitted to pass across a membrane 35
and volumetric flow may be determined according to the number of
such quanta passing across the membrane. This is described in greater
detail below. Although membrane 35 is positioned such that in a
non-flow situation edges 33 thereof are very close to sidewalls
29 typically in the order of magnitude of several scores of microns,
such that leakage of any fluid therepast is prevented, it is preferable
in a flow situation, that the gap between the membrane edges and
the sidewalls be reduced.
With reference additionally to FIGS. 4 and 5 flow chamber 14 is,
therefore, provided with a pair of preferably rigid first sidewalls
30 and a pair of non-rigid second sidewalls 29 fabricated of a flexible
elastomer, such as rubber. As fluid passes across membrane 35 pressure
inside flow chamber 14 drops and the flexible, second sidewalls
29 tend, therefore, to move slightly inwards so as to reduce the
gap between edges 33 of the membrane and sidewalls 29 to a fluid
boundary layer thickness. Due to the high resistance to flow along
the gap, leakage is, therefore, substantially prevented. The inward
movement of sidewalls 29 is further facilitated by spaces 31 provided
adjacent to edges 33 of membrane 35.
Referring briefly to FIG. 6 it has been found that when second
sidewalls are not made from a flexible material. fluid leakage may
be substantially prevented by providing them with a roughened surface
32 (also shown in FIG. 3).
With particular reference to FIGS. 2 and 14 sidewalls 30 are preferably
coated with a thin layer 34 of an antistatic and hydrophobic material
such as carbonated polyethylene. Layer 34 prevents the build-up
of static electricity in the flow chamber and condensation of moisture
on the sidewalls which might otherwise interfere with the flexing
of membrane 35. As will be appreciated from the description below,
the unimpeded flexing action of membrane 35 is important to maintain.
According to an alternative embodiment of the invention, the sidewalls
may be made entirely from an antistatic and hydrophobic material.
With particular reference to FIG. 7 there is shown a cross-section
of a portion of membrane 35. According to the shown embodiment,
membrane 35 is piezoelectric and comprises a thin layer 36 of piezoelectric
material, such as polyvinylidene fluoride and metallized surrounding
layers, referenced 38 and 42.
According to the embodiment shown in FIG. 24 membrane 35 is piezoelectric
but, as distinct from the embodiment shown in FIG. 7 the layer
36 of piezoelectric material is overlaid, on either or both faces
thereof, by discrete metallized strips 44 each having electrical
connections 45 to a pulse detector unit 66 (FIG. 17). As the membrane
flexes, as shown and described below in conjunction with FIGS. 15A
to 15C, it is thus possible to determine the speed of wave propagation
along the flow chamber which can be used by microcontroller 70 (FIG.
17) to further `correct` the calculated volume of each quanta of
fluid.
According to a preferred embodiment of the invention, membrane
35 has a substantially vertical position within flow chamber 14.
This avoids possible unsymmetrical functioning of the membrane due
to the effects of gravity.
As shown in FIG. 2 membrane 35 is preferably longer than the length
of flow chamber 14 in which it is positioned. This ensures that
membrane 35 takes up a wavelike position and that flat sides 42
of the membrane are in constant engagement with sidewalls 30 of
the flow chamber, preferably, at at least three locations.
Referring now to FIGS. 2 and 13 it is seen that membrane 35 is,
according to a preferred embodiment, secured at ends 51 thereof
about rods 52. Each rod 52 is in turn secured to a fixed rod 54
by means of a spring 53 contained within a housing 56. This type
of mounting, it will be appreciated, permits limited longitudinal
movement of the membrane within flow chamber 14.
Referring now to FIGS. 2 and 8 rounded guide blocks 48 are provided
so as to induce instability of membrane 35 it being noted that
as each quantum of fluid passes thereacross, a very rapid change
of position by flexure of membrane 35 is required. Provision of
the guide blocks is an important feature as they assist in switching
of the membrane from one position to another under a very low input
of kinetic energy, such as occurs in gas flows. The range of positions
taken up by membrane 35 upon flexure are described below in detail
with reference to FIGS. 15A to 15C.
Referring briefly to FIG. 9 there is shown an alternative embodiment
of guide blocks 48 in which each of the guide blocks also has an
additional layer of rubber.
With reference to FIG. 10 there are provided fluid permeable guide
extensions 60 that are attached to guide blocks 48 and constitute
extensions of curved surfaces 49 thereof. Referring additionally
to FIGS. 15A to 15C, it is seen that although membrane 35 generally
does not move along the length of the flow chamber, as the discrete
quanta of fluid pass through the flow meter, causing the membrane
to undulate, points of contact between the membrane and the flow
chamber walls `travel` in the direction of fluid flow, the membrane
moving by flexure from a first position just prior to release of
a quantum of fluid, to a second position just after release of the
quantum.
Guide extensions are made, for example, from wire mesh. While not
interfering, therefore, with the fluid flow, they have configurations
similar to the membrane in either of its two respective positions
taken up just before and after release of a quantum of fluid. As
the points of contact between the membrane and the chamber walls,
which are coincident with the maximum points of curvature of the
membrane, move along the flow chamber towards an end thereof, they
leave side walls 30 and mount guide extensions 60. Extensions 60
induce a degree of instability that causes, under a relatively low
kinetic energy input, a relatively fast change of position of the
membrane between the positions taken up thereby just before and
after release of a quantum of fluid.
Although, as stated, membrane 35 generally does not move along
flow chamber 14 a certain amount of relative motion does occur
between the membrane and sidewalls 30 of the flow chamber. It is,
therefore, important that inward-facing surfaces 37 of sidewalls
30 are very smooth.
According to one embodiment of the invention, as stated, membrane
35 is made from piezoelectric material. According to an alternative
embodiment, however, as shown in FIG. 10 membrane 35 is not made
from a piezoelectric material but instead has mounted on it a pair
of electrical contacts 61 each which is alternately brought into
contact with a corresponding one of a pair of electrical contacts
63 mounted onto guide extensions 60.
It will be appreciated that as each quantum of fluid passes through
flow chamber 14 and as membrane 35 switches from one position to
the other, an electrical pulse is generated by contact of one of
contacts 61 with a corresponding contact 63.
This embodiment has a particular advantage over a piezoelectric
membrane as a discrete pulse is generated each time membrane 35
moves so as to release a quantum of fluid. When a piezoelectric
membrane is used, however, every movement thereof generates electrical
signals, a change in position of the membrane being indicated simply
by an increase in intensity of the signals.
According to an alternative embodiment of the invention only a
single one of each of electrical contacts 61 and 63 is provided,
a single pulse thus being generated as every alternate quantum of
fluid is passed. It will also be appreciated that contacts 61 and
63 may be incorporated into other embodiments of the invention,
such as those illustrated in FIGS. 8 and 9. In yet a further alternative
embodiment of the invention, electrical contacts 63 may be provided
independently of guide blocks 48.
Referring now to FIG. 22 there is shown an alternative embodiment
of the invention in which membrane 35 comprises a magnetic tape.
Incorporated into sidewalls 30 are, preferably, a pair of magnetic
heads 39. As the points of contact between the membrane and sidewalls
30 travel along the flow chamber, typically just as a quantum of
fluid is released, a point of contact of membrane 35 with one of
the sidewalls moves across an adjacent head 39 thereby generating
an electrical pulse. According to the shown embodiment a signal
is generated as every quantum of fluid is released while, according
to an alternative embodiment, a single magnetic head may be provided
so as to indicate release of alternate quanta of fluid.
Referring now to FIG. 23 in the shown embodiment, as with the
embodiment of FIG. 22 membrane 35 comprises a magnetic tape. According
to the shown embodiment, however, magnetic head 39 is embedded into
second sidewall 30 of the flow chamber, and is operative to engage
a face 41 of membrane 35 as it passes in contact therewith.
According to the shown embodiment, the membrane includes a plurality
of magnetic bands provided thereon at a known frequency, such as
5 KHz. As face 41 passes in contact with head 39 processing apparatus
43 associated therewith is operative to sense not only passage of
a portion of the membrane across the head, but it is also operative
to sense the frequency at which the magnetic bands pass, and thus
to determine the speed at which the fluid is passing.
Referring to FIG. 11 membrane 35 is shown with thickened ends
46 which may also include additional layers 65 of piezoelectric
material. The thickened end and the additional layers of material
serve to reduce the possibility of failure of the membrane due to
fatigue stresses. According to an alternative embodiment, membrane
35 may have different cross-sectional thickness along the entire
length thereof or along selected portions thereof.
As shown in FIGS. 12 and 13 guide blocks 48 are not rigidly positioned
but are preferably secured by springs 58 to sidewalls 30 of the
flow chamber.
Reference is now made to FIGS. 15A to 15C, in which there are shown
successive stages of fluid flow through the flow meter of the invention.
Initially, a first quantum of fluid passes into the flow chamber
and exerts a force on the membrane until it is forced to change
position. At this stage, the first quantum, referenced 62a, becomes
entrapped between the wall of the flow chamber, the membrane and
two points of contact, referenced 67 between the membrane and the
flow chamber wall.
As the point of contact nearest an inlet 69 is being established,
a second quantum of fluid, referenced 62b, enters the chamber and
also exerts a force on the membrane, travelling downstream until
eventually it too becomes entrapped.
A third quantum of fluid, referenced 62c, enters the flow chamber
and also exerts a force on the membrane. The points of contact continue
to travel downstream until the membrane moves by flexure from one
position to another, thereby releasing the first quantum of fluid
and generating an electrical pulse.
It has been found that when the membrane is in touching engagement
with the flow chamber walls at at least three locations, possible
distortion of the membrane and consequent blockage of the flow chamber,
such as might otherwise result from a high rate of flow, is prevented.
Referring to FIG. 16 there is shown a flow chamber constructed
in accordance with an alternative embodiment of the invention. The
flow chamber, referenced 55 comprises a pair of curved walls 64a
and 64b. The curvature of chamber 55 results in instability in the
positions taken up by the membrane, which, as described above, is
desirable. Although quanta of fluid flowing alongside the outer
wall 64a will be larger than those flowing alongside inner wall
64b, the quantity of flow can be determined by taking an average
of the two different-sized quanta.
Referring now to FIGS. 3 and 17 there is shown an electrical connection
47 to a metallized layer of piezoelectric membrane 35 for carrying
to a pulse detector unit 66 (FIG. 17) electrical signals generated
by movement of the membrane. According to an embodiment of the invention
wherein membrane 35 is not piezoelectric but electrical contacts
are used instead, electrical connection 47 is connected to the electrical
contacts.
When a piezoelectric membrane is used, the pulse detector unit
preferably includes signal processing electronic circuitry that
is operative to recognize a particular shape of a pulse or an electrical
signal corresponding to flexure of the membrane at the time of release
of a quantum of fluid from outlet 22 of the fluid flow meter. It
will be appreciated that it is important to be able to distinguish
such pulses from background signals that are constantly being generated
by the membrane.
A value for the volume of each quantum of fluid is either preset
or predetermined and stored in a memory 68 of a microprocessor 70
such that each signal received represents the flow of a reference
volume of fluid through the flow meter. The microprocessor preferably
also has a display 72 and a serial communication port 74.
According to a preferred embodiment of the invention, by using
the preset value for each quantum and according to electrical signals
received, the microprocessor is operative to calculate the flow
rate. By using flow delivery data, as are typically contained in
a look-up table and by comparing the preset quantum value with a
quantum value in the table corresponding the calculated flow rate,
the microprocessor is operative to alter the preset quantum value
to a different value. By repeating these steps of calculating and
comparing, in iterative fashion, the microprocessor is operative
to reach a "true" quantum value and, hence, a true flow
value.
Also, according to a preferred embodiment of the invention, pressure
and temperature sensors, respectively referenced 108 and 110 (FIG.
17), are mounted in the flow chamber and are effective to continuously
provide to the microprocessor pressure and temperature readings.
The microprocessor also calculates any necessary adjustment of the
preset value for the volume of each quantity of fluid, according
to the pressure and temperature data received.
The pressure and temperature readings may also be used by microcontroller
70 to provide an alarm indication when the temperature rises to
a dangerously high level, which may indicate fire or where the pressure
drops below a predetermined threshold value, which may serve as
an indication of leakage in the system.
According to an alternative embodiment of the invention, multiple
flow meters may be provided to accommodate a very large fluid flow,
with the flow pulse signals being directed to a central microcontroller
for determination of the overall fluid flow rate.
Reference is now made to FIG. 18 wherein there is shown, in block
diagram form, centralized data collection apparatus utilizing the
flow meter of the present invention. In accordance with a preferred
embodiment of the invention, a dialer 78 which permits communication
between the flow meter and a domestic telephone line 8-, is operative
to automatically dial a data center 106 and to send thereto information
pertaining to fluid flow as measured by the meter.
A timer 76 may also be provided to trigger dialer 78 at a given
interval, such as once a month and preferably at a time when the
telephone line is unlikely to be in use. The dialer is also preferably
operative to continue dialing from the time it is triggered by timer
76 until it manages to get through to data center 106 and pass
the required information. In the event that the connection is broken
while the information is being passed, dialer 78 is operative to
redial, if necessary repeatedly, until the information is successfully
passed.
Referring now to FIG. 19 communication between the flow meter
and a mini-terminal 86 may be provided by means of a first receiver-transmitter
82 linked to the flow meter and a second receiver-transmitter 84
associated with the mini-terminal. The mini-terminal may also be
equipped with a memory bank 88 and a display panel 90. Local networks
of an optically-isolated unit 92 may be provided through a connector
94 to a mini-terminal 96 as shown in FIG. 20.
Referring to FIG. 21 fluid meters 10 which, according to a preferred
embodiment are gas flow meters, may be connected with a remote data
center 106 by means of a modem 104. This permits not only regular
sending of flow information from the gas meters to the data center,
but it also permits data center initiated scanning of the gas meters.
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