Abstrict A piezoelectric vortex flow meter for determining the rate of fluid
flow through piping including a hermetically sealed bluff body having
a vortex generating plate operably associated with a sensing plate.
The vortex generating plate is positioned perpendicular to the fluid
flow for creating a "vortex street". A pair of piezoelectric
sensors are disposed in a pair of recesses formed in the interior
of the sensing plate. Sensing surfaces are formed on each side of
the sensing plate adjacent the piezoelectric sensors. The sensing
surfaces are formed such that the side surfaces of the sensing plate
are free from any discontinuities. The vortices created by the vortex
generating plate exert a force on the sensing surfaces which transmit
a signal proportional to the force exerted, to the piezoelectric
sensors. The piezoelectric sensors transform the mechanical energy
into electrical energy readily readable with an appropriate electrical
circuit.
Claims What is claimed is:
1. An apparatus for use with a vortices generating means for determining
the rate of fluid flow by monitoring the frequency of the vortices
produced via the vortices generating means, said apparatus comprising
(a) a main body;
(b) said main body includes a pair of like members of unitary construction;
(c) each member including upper and lower portions connected by
a vortex generating and sensing portion;
(d) each of said members including an inner planar surface which
surfaces are in contiguous relationship;
(e) the sensing portion of each of member including interior and
exterior surfaces;
(f) said interior surface of each member including interior and
exterior surfaces;
(f) said interior surface of each member being provided with a
circular recess extending transversely from the interior surface
thereof and terminating short of the exterior surface thereof, thereby
forming sensing surfaces on a portion of the exterior surface of
each sensing portion;
(g) a sensing means disposed in the circular recess of each member,
said sensing means being disposed in opposed relation to each other;
(h) an axially extending groove extending from each of said circular
recesses through said members;
(i) and electric wire connected at one end to the sensing means
of each member, said wire being disposed in the axially extending
groove of each of said members;
(j) said vortex generating portion including a plate substantially
planar and perpendicular to the liquid flow, and
(k) means for securing the planar surfaces of said members together.
2. The apparatus of claim 1 wherein
(a) said sensing means is a piezoelectric sensor.
3. The apparatus of claim 2 wherein
(a) said piezoelectric sensor is positioned in the circular recess
of each member in abutting contact with the sensing surface of each
sensing portion.
4. The apparatus of claim 1 wherein
(a) the sensing means of each of said members is of substantially
the same thickness.
5. The apparatus of claim 1 with the addition of:
(a) a tubular housing having an axially extending bore for permitting
fluid to flow therethrough;
(b) said housing being provided with opposed first and second transversely
extending bore of the housing, said first transversely extending
recess extending to the outer periphery of the tubular housing;
(c) said main body upper portion having a configuration substantially
similar to said second transversely extending recess in said housing:
(d) said main body lower portion having a configuration substantially
similar to said first transversely extending recess in said housing,
whereby the lower and upper portions of said main body are seated
in said first and second transversely extending recesses for centering
the main body in the axial bore of said housing; and
(e) a single fastening means operably associated with said first
recess for securing said main body in said housing the enabling
an operator to readily extract said main body from said housing
upon removal of said single fastening means.
6. The apparatus of claim 5 wherein:
(a) said single fastening means includes a threaded plug; and
(b) said second recess includes complemental threaded plug; and
7. An apparatus for use with a vortices generating means for determining
the rate of fluid flow by monitoring the frequency of the vortices
produced via the vortices generating means, said apparatus comprising:
(a) a tubular housing having an axially extending bore for permitting
fluid to flow therethrough;
(b) said housing being provided with opposed first and second transversely
extending recesses in communication with the axially extending bore
of the housing, said first transversely extending recess extending
to the outer periphery of the tubular housing;
(c) a main body having a sensing portion for monitoring the frequency
of vortices impacting the same inserted through said first transversely
extending recess into said housing;
(d) said main body including upper and lower portions
(e) a centering tab extending from said upper portion of the main
body;
(f) said centering tab having a configuration substantially similar
to a portion of said second transversely extending recess in said
housing;
(g) said main body lower portion having a configuration substantially
similar to said first transversely extending recess in said housing,
whereby the lower and upper portions of the main body are seated
in said first and second transversely extending recesses for centering
the main body in the axial bore of said housing; and
(h) a single fastening means operably associated with said first
recess for securing said main body in said housing and enabling
an operator to readily extract said main body from said housing
upon removal of said single fastening means.
8. The apparatus of claim 7 wherein:
(a) said single fastening means includes a threaded plug, and
(b) said first recess included complemental threads formed therein
for threaded engagement with said threaded plug.
9. The apparatus of claim 7 wherein:
(a) said upper and lower portions of said main body includes outer
and inner surfaces;
(b) said outer surface being substantially planar;
(c) said inner surface being substantially arcuate; and
(d) said inner surfaces having a radius substantially similar to
the radius of said transversely extending bores of said housing.
10. An apparatus for use with a vortices generating means for determining
the rate of fluid flow by monitoring the frequency of the vortices
produced via the vortices generating means, said apparatus comprising:
(a) a tubular housing having an axially extending bore for permitting
fluid to flow therethrough;
(b) said housing being provided with opposed first and second transversely
extending recesses in communication with the axially extending bore
of the housing, said first transversely extending recess extending
to the outer periphery of the tubular housing;
(c) a main body having a sensing portion for monitoring the frequency
of vortices impacting the same inserted through said first transversely
extending recess into said housing;
(d) said main body upper portion having a configuration substantially
similar to said second transversely extending recess in said housing;
(f) said main body lower portion having a configuration substantially
similar to said first transversely extending recess in said housing
whereby the lower and upper portions are seated in said first and
second transversely extending recesses for centering the main body
in the axial bore of said housing; and
(g) a single fastening means operably associated with said first
recess for securing said main body in said housing and enabling
an operator to readily extract said main body from said housing
upon removal of said single fastening means;
(h) said single fastening means including a substantially cylindrical
shaped outer sleeve;
(i) said outer sleeve having an axially extending bore for receiving
said housing therein.
11. The apparatus of claim 10 wherein:
(a) said main body includes a plurality of electrical wires connected
at one end to said sensing portion; and
(f) said outer sleeve includes a first hole extending transversely
therethrough and operably associated with said second recess in
said housing for permitting the other end of said electrical wires
to pass therethrough.
12. The apparatus of claim 11 wherein:
(a) said outer sleeve includes an inner surface in abutting contact
with said housing;
(b) said inner surface including a guide groove extends along said
bore of said outer sleeve and communicates with said first hole.
Description FIELD OF THE INVENTION
This invention pertains generally to devices for measuring the
flow rate of various fluids through piping.
BACKGROUND OF THE INVENTION
This invention relates to the utilization of the Von Karman vortex
principle for determining the flow rate of fluid through piping.
Briefly, the Von Karman principle involves the phenomenon that,
upon insertion of a bluff body in the stream of fluid flow, a vortices
profile is created. The vortices shed alternately at periodic intervals
from opposite sides of the bluff body. This particular vortex profile
is known as the Von Karman "vortex street". The frequency
of the vortices shed by the bluff body is proportional to the velocity
of the fluid, either liquid or gas, flowing through the piping.
By varying the dimensions of the bluff body, the frequency of the
vortex shedding will likewise vary. Each bluff body has a constant
known as the K factor. Thus, one can readily determine the flow
of fluid through piping by monitoring the frequency of the vortex
shedding and having a known K factor for the bluff body.
Numerous devices have been designed for implementing the Von Karman
vortex principle in measuring the flow of a fluid through piping.
One type of vortex flow meter currently known is the thermal sensor
or "hot wire". In this particular vortex flow meter, the
voltage and frequency of the sensor element varies with respect
to changes in cooling rate, resulting in the intermittent passage
of the vortices across the bluff body. The thermal sensor vortex
flow meter has several inherent disadvantages, the first being a
poor signal to noise ratio. Additionally, the thermal sensors are
extremely susceptible to damage by vibrations. Also, the sensors
are easily coated when implemented for measuring the flow rate of
a gas, thereby adversely affecting the meter's accuracy. Further,
the accuracy of the sensor significantly decreases when foreign
articles from a measured liquid build up on the sensor.
An alternative vortex flow meter implements a disc or shuttle-type
sensing element associated with a magnetic pick-up. Pressure pluses
created by the vortices in the "vortex street" vibrate
the shuttle or disc which is monitored by the magnetic pick-up sensor.
However, due to the significant amount of energy required to oscillate
the disc or shuttle, the meter cannot be used to satisfactorily
determine the flow rate of a gas or similar fluids whose vortices
do not exert significant pressure on the sensing body.
A number of vortex flow meters implement piezoelectric crystals
or ceramic materials as sensing units. A commonly known piezoelectric
flow meter uses a vortex-generating plate integrally attached to
a sensing plate. The sensing plate includes a liquid-fluid cavity
bounded by a pair of flexible diaphragms welded to the side walls
of the sensing plate. This design has a number of inherent disadvantages,
namely, a marginal low end measurement capability. This inadequacy
of the flow meter is largely a result of a substantial portion of
the vortex signal dampened by the oil contained within the cavity.
Additionally, the process of welding the diaphragms to the side
plates creates discontinuities between the two elements which will
ultimately affect the accuracy of the meter. Also, the welds have
been readily susceptible to fatigue when the flow meter is used
in harsh environments.
To overcome some of the disadvantages of the aforementioned piezoelectric
flow meters, it has been known to position the piezoelectric sensors
in abutting contact with the diaphragms. In this type of meter,
a hole is bored entirely through the sensing plate of the bluff
body. Each piezoelectric sensor is placed on a diaphragm and epoxyed
into the sensing plate. In epoxying the diaphragms to the piezoelectric
sensor and subsequently to the sensing plate, air voids are created
between the piezoelectric sensors and the diaphragms. This will
ultimately dampen the actual vortex signal and thus significantly
reduce the accuracy of the flow meter. Further, with time and in
harsh environments, the epoxy deteriorates, resulting in the diaphragm
loosening or falling off, causing the destruction of the piezoelectric
sensors. Finally, the discontinuities between the diaphragms and
the sensing plate dampen the vortex signals transmitted to the piezoelectric
sensor.
A further type of piezoelectric flow meter currently in use senses
the stress of an element created by the "vortex street".
This requires a tremendous amount of energy to be exerted on the
element before the frequency of the vortices can be detected by
the piezoelectric sensors. This type of flow meter can only be used
with a minimum Reynolds number of 20000.
As is readily seen from the aforementioned discussion, prior to
the present invention the industry has been lacking in a vortex
flow meter capable of detecting low magnitude forces imparted on
a bluff body and determining the flow rate of fluid in harsh environments
for any substantial period of time.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved vortex
flow meter.
Another object of the invention is to provide a vortex flow meter
capable of measuring the flow rate of a wide variety of fluids ranging
from gases to corrosive liquids, and liquids with abrasive solids
such as liquid sulphur.
Yet another object of the invention is to provide a vortex flow
meter having a vortex-generating plate integral with the sensing
plate for minimizing dampening of the vortex signal.
A further object of the invention is to provide a vortex flow meter
with a housing that will enable an operator to readily insert and
extract the bluff body therefrom.
Another object of the invention is to provide a vortex flow meter
capable of measuring the flow rate of harsh fluids such as moltened
sulphur for lengthy periods of time.
Yet another object of the invention is to provide a vortex flow
meter with a bluff body having a centering/aligning tab for centering
the bluff body in a housing without the use of fasteners.
Another object of the invention is to provide a vortex flow meter
with a substantially planar sensing surface free from any discontinuities
thereby significantly reducing the damping effect on the vortex
signal.
A further object of the invention is to provide a vortex flow meter
that is durable, inexpensive to manufacture and extremely accurate.
Another object of the invention is to provide a vortex flow meter
that is able to be inserted in a pipeline while fluid is flowing
therethrough.
An additional object of the invention is to provide a vortex flow
meter free from air gaps between the sensor and the sensing surface.
Another object of the invention is to provide a meter with the
ability to measure vortices produced at a Reynolds number of 10000
or greater.
Yet another object of the invention is to provide a vortex flow
meter with a high vortex signal to noise signal ratio.
Another object of the invention is to provide a vortex flow meter
able to withstand pressures of up to 20000 psi.
An additional object of the invention is to provide a vortex flow
meter with a sensor capable of operating over a frequency range
1.0 Hz. to 3 kHz.
Yet another object of the invention is to provide a vortex flow
meter with a hermetically sealed bluff body, without glued-on or
welded-on diaphragms.
In summary the present invention provides a vortex flow meter having
a hermetically sealed bluff body including a vortex-generating plate
integral with a sensing plate. The sensing plate includes two side
surfaces which are substantially planar and free from any discontinuities.
The bluff body further includes a centering/aligning tab for centering
the bluff body in the vortex flow meter housing. The vortex flow
meter formed in accordance with the present invention is susceptible
to a significantly wider range of uses, and is substantially more
durable and accurate than the previously known vortex flow meters.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded view of the vortex flow meter formed in accordance
with the present invention.
FIG. 1A is an alternative embodiment of the bluff body of the vortex
flow meter depicted in FIG. 1.
FIG. 2 is a cross-section of FIG. 1 with all of the elements of
the vortex flow meter assembled in the housing.
FIG. 3 is a perspective view of the bluff body;
FIG. 4 is a cross-sectional view of the bluff body.
FIG. 5 is an exploded view of the second embodiment of the vortex
flow meter formed in accordance with the present invention.
FIG. 6 is a cross-sectional view of the second embodiment of the
present invention with all of the vortex flow meter elements assembled
in the housing.
FIGS. 7A-E depict the process for manufacture of the bluff body.
FIGS. 8A-B depict an alternative process for manufacturing the
bluff body.
DESCRIPTION OF THE DRAWINGS
FIGS. 1-4
Referring to FIG. 1 the piezoelectric vortex flow member A includes
a housing 2 a seal 4 a bluff body 6 and a threaded plug 8. Vortex
flow meter housing 2 includes an axially extending bore 10 for permitting
fluid to flow therethrough. Housing 2 further includes transversely
extending recesses 12 and 14. Recess 12 includes first and second
portions 16 and 18. First portion 16 extends through the outer periphery
of housing 2. Second portion 18 communicates with first portion
16 as well as axial bore 10. Seal 4 rests in second portion 18
as best seen in FIG. 2. Recess 14 extends through the outer periphery
of housing 2 opposite recess 12 and communicates with axial bore
10.
Bluff body 6 includes left and right body members 20 and 22 as
viewed in FIGS. 1-4. Left and right body members 20 and 22 are each
of one-piece construction and include an upper portion 24 a lower
portion 26 a vortex generating portion 28 connecting the upper
and lower portions, and a sensing portion 30.
Referring to FIG. 2 the upper portions 24 of left and right body
members 20 and 22 each include outer and inner surfaces 32 and 34
respectively. Outer surfaces 32 are substantially planar and abut
seal 4. Inner surfaces 34 are arcuate in shape and conform with
the radius of axial bore 10. This particular configuration of inner
surfaces 34 prevents extraneous elements of bluff body 6 from encountering
the fluid flow path thus minimizing turbulence. This feature significantly
enhances the accuracy of the vortex flow meter. Lower portions 26
of left and right body members 20 and 22 respectively include outer
and inner surfaces 36 and 38. Outer surfaces 38 are substantially
planar and positioned in abutting contact with threaded plug 8.
Similar to inner surfaces 34 inner surfaces 36 have an arcuate
configuration identical to the radius of axial bore
Referring to FIGS. 2-4 sensing portions 30 of left and right body
members 20 and 22 include interior and exterior surfaces 40 and
42. Circular recesses 44 extend transversely from interior surfaces
40 and terminate short of exterior surfaces 42 thereby forming
sensing surfaces 46 on a portion of the exterior surfaces 42 of
sensing portions 30 of left and right body members 20 and 22. A
pair of axially extending grooves 48 are formed in left and right
body members 20 and 22 for receiving one of a pair of wires 50 (note
only one groove 48 is shown).
A piezoelectric sensor 52 is positioned in each of the circular
recesses 44 formed in sensing portions 30. Wires 50 are connected
at one end to piezoelectric sensors 52 and at the other end to an
amplifier not shown. An insulating pad/layer 54 is interposed between
the piezoelectric sensor 52 and wire 50 operably associated with
left body member 20 and the piezoelectric sensor 52 and wire 50
operably associated with right body member 22. Insulating pad 54
prevents contact between the piezoelectric sensors 52 and wires
50 and thus prevents the sensing system from shorting out. Insulating
pad 54 can be formed from an epoxy or like substance.
When left and right body members 20 and 22 are assembled, vortex
generating portions 28 together form vortex generating plate generally
designated 56. Vortex generating plate 56 is substantially planar
and is perpendicular to the flow of fluid through axial bore 10
of housing 2. Further, sensing portions 30 form sensing plate 58
as best seen in FIG. 3. Sensing plate 58 is substantially perpendicular
to and integral with vortex generating plate 56. Additionally, sensing
plate 58 is positioned in vortex flow meter housing 2 substantially
parallel to the fluid flow therethrough.
The sensing plate 58 includes leading and trailing edges 60 and
62 respectively, as best seen in FIG. 3. Sensing plate 58 is tapered
slightly inwardly from leading edge 60 to trailing edge 62. Referring
to FIG. 1 vortex generating plate 56 includes side edges 64 and
66. Side edges 64 and 66 of vortex generating plate 56 are positioned
outwardly from the sensing portions 30 of sensing plate 58. Thus,
sensing surfaces 46 are positioned inwardly from the sides 64 and
66 of vortex generating plate 56. This particular configuration
ensures that the vortices will shed cleanly at vortex generating
plate 56 resulting in the meter accurately determining the flow
rate of fluid through housing 2.
Upper portions 24 of left and right body members 20 and 22 form
a substantially cylindrical upper alignment element 68 as best seen
in FIG. 3. The upper alignment element 68 has a centering/aligning
tab 70 extending upwardly therefrom. Upper alignment element 68
is positioned in second portion 18 of recess 12 while centering/aligning
tab 70 is positioned in first portion 16 of recess 12. Lower portions
26 of left and right body members 20 and 22 form a substantially
cylindrical lower alignment element 72. Lower alignment element
72 is positioned within recess 14. The upper alignment element 68
centering/aligning tab 70 and lower alignment element 72 ensure
proper alignment of the bluff body 6 within the housing 2 without
the use of fasteners.
Threaded plug 8 is inserted in recess 14 of housing 2. Threaded
plug 8 includes a recess 74 for receiving a tool for removing the
same from recess 14 of housing 2. Recess 74 can be configured to
receive a screwdriver, allen wrench or similar tool, thereby enabling
an operator to readily remove bluff body 6 from housing 2.
Referring to FIG. 1A, bluff body 6' is a modified form of bluff
body 6 and is designed to be directly inserted into the fluid flow
line. Bluff body 6' eliminates the lower alignment element 72 of
bluff body 6. Further, the lower end 57' of the bluff body 6' is
arcuate in configuration to conform with the axial bore extending
through the fluid flow line. It will be readily perceived that the
bluff body 6' can be adapted to fit any size line by merely varying
the length of the vortex generating plate 56' and the sensing plate
58'.
ALTERNATIVE EMBODIMENT
FIGS. 5 and 6
An alternative form of the present invention will be described
with reference to FIGS. 5 and 6. Referring to FIG. 5 the piezoelectric
vortex flow meter B includes a housing 76 a bluff body 78 and
an outer sleeve 80. Housing 76 includes an axially extending bore
82 for permitting fluid flow therethrough. Housing 76 further includes
recesses 84 and 86 positioned directly opposite each other and extending
through the outer periphery of housing 76 for communicating with
axially extending bore 82.
Outer sleeve 80 includes an axially extending bore 90 for receiving
housing 76 therein. Outer sleeve 80 further includes a groove 92
extending axially along bore 90. A hole 94 communicates with groove
92 for permitting wires 96 of bluff body 78 to pass therethrough.
Additionally, outer sleeve 80 includes beveled grooves 93 formed
along the inner circumference of each end.
Bluff body 78 includes left and right body members 98 and 100
and vortex generating plate 102. Vortex generating plate 102 is
secured to left and right body members 98 and 100 by any suitable
means such as welding or the like.
Left and right body members 98 and 100 each include an upper portion
104 a lower portion 106 and a sensing portion 108. Upper portions
104 include inner and outer surfaces 110 and 112 as best seen in
FIG. 6. Outer surface 110 is substantially planar while inner surface
112 is arcuate in shape. The radius of inner surface 112 is identical
to the radius of bore 82 of housing 76. Similarly, lower portions
106 include inner and outer surfaces 114 and 116. Outer surfaces
116 are substantially planar while inner surfaces 114 are arcuate
in shape to conform with bore 82. Sensing portions 108 include circular
recesses 118 for receiving a pair of piezoelectric sensors (not
shown). The piezoelectric sensors, in the preferred form, are substantially
continuous with recesses 118. Electrical wires 96 connect the piezoelectric
sensors positioned in recesses 118 to an amplifier (not shown).
Wires 96 are received in axially extending grooves 120 formed in
each of left and right body members 98 and 100. An insulating plate
element 121 is positioned intermediate the sensor and wire 96 operably
associated with left body member 98 and the sensor and wire 96 operably
associated with right body member 100 for preventing a short in
the electrical system.
Upper portions 104 form a rectangularly-shaped upper alignment
element 122. Lower portions 106 form a rectangularly-shaped lower
aligning element 124. Sensing portions 108 form sensing plate 126.
Lower alignment element 124 passes through recess 84 and is positioned
in recess 86. As is readily seen from FIG. 5 recesses 84 and 86
each include first and second portions 128 and 130. Lower alignment
element 124 is positioned within second portion 130 of recess 86
while the lower end of vortex generating plate 102 is received in
first portion 128 of recess 86. Similarly, upper alignment element
122 is received in second portion 130 of recess 84 while the upper
end vortex generating plate 102 is received in first portion 128
of recess 84. Upon insertion of the bluff body 78 into housing 76
housing 76 is inserted in axial bore 90 of outer sleeve 80. Outer
sleeve 80 is welded to housing 76 along grooves 93. The weld at
each end of the vortex flow meter B provides the necessary seal
between outer sleeve 80 and housing 76. Unlike vortex flow meter
A, the bluff body 78 is not readily removable. The housing 76 and
outer sleeve 80 enable vortex flow meter B to be used in high pressure
environments.
The vortices generating plate 102 has a width greater than the
width of sensing plate 126. Sensing plate 126 includes a leading
edge 132 adjacent vortex generating plate 102 and a trailing edge
134. The sensing plate 126 is slightly tapered inwardly in the direction
of trailing edge 134. This configuration ensures a clean detachment
of the vortices from vortices generating plate 126 and thus enhances
the accuracy of the flow meter B.
In environments where the vortex flow meter B is not exposed to
high pressures, the housing 80 can be eliminated. The bluff body
is then directly inserted and sealed in the housing 76. Further,
threads or flanges can be formed on the ends of housing 76 for facilitating
insertion of the same in the pipeline.
Bluff body 78 can be adapted in a similar manner as bluff body
6 for direct insertion into the fluid flow line.
METHOD OF MANUFACTURING THE BLUFF BODY
FIGS. 7A-E
The method of manufacturing bluff body 6 will now be described
with reference to FIGS. 7A-E. The method of manufacturing bluff
body 78 is substantially similar and will not be discussed in detail.
However, any differences in the method of manufacturing bluff body
78 will be fully explained.
Left and right body members 20 and 22 are formed substantially
identical to each other as seen in FIG. 7A. Transversely extending
recesses 44 are formed in each of the body members 20 and 22. Recesses
44 extend from the inner surfaces 40 through only a portion of corresponding
body members 20 and 22. Axially extending grooves 48 are formed
in left and right body members 20 and 22 and communicate with the
corresponding recesses 44. The outer periphery of left and right
body members 20 and 22 are beveled as best seen in FIG. 7B. Subsequently,
piezoelectric sensors 52 are positioned in recesses 44 and wires
50 associated therewith are received in grooves 48. An epoxy or
like adhesive material is applied to the inner face of the piezoelectric
sensors 52 and an area of the inner surfaces 40 adjacent recesses
44. This process is referred to as "back filling". The
epoxy is further applied along grooves 48 to prevent contact between
wires 50.
Subsequently, left and right body members are positioned in abutting
contact with each other as best seen in FIG. 7B. The beveled outer
peripheries of body members 20 and 22 form a groove 136 extending
along the outer periphery of bluff body 6. The left and right body
members 20 and 22 are welded along groove 136. It is a phenomenon
of welding that welded members draw towards the weld. Therefore,
body members 20 and 22 will draw inwardly forming a hermetically
sealed bluff body. The bluff body is subsequently machined to a
desired configuration. As will be readily appreciated from the above
discussion, the process of welding the body members at a point intermediate
recesses 44 will cause sensing surfaces 46 formed adjacent thereto
to draw inwardly towards piezoelectric sensors 52 positioned in
recesses 44 thereby eliminating any air pockets therebetween. As
previously noted, any air pockets between the piezoelectric sensors
and the sensing surface will dampen the actual vortex signal, and
ultimately adversely effect the accuracy of the vortex flow meter.
The bluff body 78 includes the additional step of securing the
vortex-generating plate 102 to upper and lower alignment elements
122 and 124. Vortex generating portions 28 and the corresponding
sensing portions 30 are formed from a single piece and thus alleviate
the need for this additional step. This specific arrangement of
vortex generating portions 28 and the corresponding sensing portions
30 eliminate any chance of misalignment which may occur in welding
a separate vortex generating plate.
An alternative method of manufacturing bluff body 6 will now be
described with reference to FIGS. 8A and B. Left body member 20'
is provided with a raised substantially rectangular surface 23'.
Further, a plurality of holes 25' are formed along the outer circumference
of raised surface 23'. Holes 25' extend through left body member
20'.
Right body member 22' is provided with a substantially rectangular
surface 27' that is inwardly offset to receive raised surface 23'
of left body member 20'. A plurality of holes 29' are formed in
the outer circumference of inwardly offset surface 27' and correspond
with one of holes 25' formed in left body member 20'. Holes 25'
and 27' receive bolts therein for securing the left and right body
members 20' and 22' together. Subsequently, the bluff body is machined
to the desired configuration.
OPERATION
The operation of the piezoelectric vortex flow meter of the present
invention will be described with reference to the first embodiment
depicted in FIGS. 1 through 4. The operation of the second embodiment
of the piezoelectric vortex flow meter disclosed in FIGS. 5 and
6 will be readily understood from the explanation of the operation
of the first embodiment.
The housing 2 is positioned in an appropriate location in the pipeline
for which the fluid flow is to be measured. Fluid passes through
axial bore 10 and impacts vortex generating plate 56 of bluff body
6. As a result of the fluid striking vortex generating plate 56
the Von Karman "vortex street" is produced. The vortices
alternately exert a force on sensing surfaces 46 which in turn transmit
a vortex signal to the piezoelectric sensors 52 positioned within
recesses 44. The piezoelectric sensors 52 convert the mechanical
energy imparted by the vortices on the sensing surface 46 into electrical
energy. The piezoelectric sensors 52 are electrically connected
by wires 50 to an amplifier which will provide the operator with
a signal indicating the flow rate of the fluid therethrough. The
process of forming recesses 44 from the interior surfaces 40 outwardly
provides sensing plate 58 with a pair of continuous sensing portions
30.
The continuous sensing portions 30 of sensing plate 58 eliminate
any dampening of the vortex signal transmitted to the piezoelectric
sensors that would result from discontinuities formed thereon. Thus,
a high ratio of vortex to noise signal is produced. Further, sensing
surfaces 46 being continuous with sensing portions 30 provide a
significantly more durable sensing plate 58. Therefore, the bluff
body 6 can be used to measure the fluid flow of harsh fluids such
as molten sulphur without resulting in fatal deterioration thereof.
The vortex flow meters disclosed herein have been described as
employing a pair of piezoelectric sensors. However, any suitable
sensing element may be used in conjunction with the vortex flow
meters of the present invention. Further, a plurality of piezoelectric
sensors may be positioned in each body member 20 and 22 to obtain
an average flow profile.
In inserting piezoelectric vortex flow meters A and B of the present
invention, the fluid flowing through the pipeline must be temporarily
cut off in order to insert the respective housings to the pipeline.
The bluff bodies 6 and 78 of the present invention can be readily
adapted to be inserted in the pipeline while fluid is still flowing
therethrough. This process is commonly known as "hot tapping".
This process enables the bluff bodies to be readily inserted or
extracted from the pipeline without causing any down time in the
conduit system.
The present invention provides a vortex flow meter capable of detecting
low magnitude forces, producing a high signal to noise ratio and
determining the flow rate of fluid in harsh environments for substantial
intervals of time.
While this invention has been described as having preferred embodiment,
it is understood that it is capable of further modification, uses
and/or adaptions of the invention following generally the principle
of the invention and including such departures from the present
invention and including such departures from the present disclosure
as come within the known or customary practice in the art to which
the invention pertains and as may be applied to central features
set forth and fall within the scope of the invention and of the
limits of the appended claims.
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