Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PIEZOELECTRIC PRESSURE FR~U~ CY SENSO~
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BACKGROUND OF THE INVENTION
This invention relates to a sensor for sensing
the frequency of fluid pressure fluctuations, and more
particularly, to a piezoelectric sensor for a vortex-
shedding flowmeter.
Certain bluff bodies, when placed in fluid
flow paths, shed vortices in a stable vortex formation
known as a von Rarman vortex street. With preferred
bodies, such as in U.S. Patent No. 4,350,047 issued on
September 21, 1982, the spacing of the vortices of the
von Karman vortex street is sufficiently constant over
desirable ranges of fluid velocities that vortex fre-
quency can be considered proportional to fluid velocity.
Vortex frequency can be measured by sensing the frequency
of fluid pressure fluctuation at a fixed point in the
street, since the pressure at the fixed point fluctuates
according to the presence or absence of a vortex at the
point.
Piezoelectric material is a desirable material
as a pressure sensor. The material operates without
external power supply, and responds well to applied
pressure fluctuation, with an electrical signal which
can be amplified for electronic processing. As a result,
piezoelectric material would seem a good choice for the
sensing of fluid pressure fluctuation frequency in a
von Karman vortex street. Recognition of this desir-
ability was evidenced long ago in U.S. Patents 2,809,520;
3,116,639 and 3,218,852.
One particular vortex-shedding flowmeter
pressure sensor that is known to have been offered
commercially does employ piezoelectric material. How-
ever, that sensor utilizes a number of parts and requires
the filling of a chamber with oil. As a result, asse~bly
s~
may be complex. Moreover, the piezoelectric disc em-
ployed in that sensor operates in a flexure mode, i.e.,
the center of the disc moves relative to the disc edges
such that the disc is flexed into varying degrees of
curvature. It is believed that this mode of operation
requires relatively wide deflection of the piezoelectric
disc for signal generation and would also entail wide
deflection of the diaphragms of the sensor, such that
diaphragm fatigue and rupture are a possible concern.
Thus, that particular piezoelectric sensor is not wholly
advantageous. Simplicity and ruggedness remain in the
art as unachieved objectives.
In sum, piezoelectric materials have been long
known to be desirable for vortex-shedding flow meter
sensors, but the art to date has failed to discover a
simplified, rugged piezoelectric sensor suitable for
commercial offering as a fluid pressure fluctuation
frequency sensor. As a result, many commercial
offerings of such sensors continue to be of the hot wire
and other non-piezoelectric types.
SUMMARY OF THE INVENTION
In one aspect of this invention a
piezoelectric pressure sensor suitable for sensing the
frequency of fluid pressure fluctuations in a dynamic
fluid pressure is provided.
In another aspect of this invention a
piezoelectric sensor which is suitable for a vortex-
shedding flowmeter is provided.
Such a piezoelectric sensor suitable for a
vortex-shedding flowmeter is also ingeniously simple.
In yet another aspect of the invention there
is provided an ingeniously simple piezoelectric sensor
for a vortex-shedding flowmeter, which includes a
diaphragm which is able to withstand the high frequency
52
pressure fluctua-tions of a von Karman vortex street (for
example, in specific embodiments of this aspect, 10-120
Hz for liquid, 100-1200 Hz for gas in a 50mm conduit),
without damage from fatigue or rupture, throughout an
extended useful lifeO
In accordance with one aspect of the present
invention, there is provided a sensor adapted to sense a
frequency of pressure fluctuations in a dynamic fluid,
the sensor comprising:
a sensor body having a sensor chamber
including an exterior chamber opening and a solid
interior chamber surface spaced opposite the opening;
a transducer assembly including a
piezoelectric transducer located in the sensor chamber,
seated against the solid interior chamber surface, and
having an end extending from the sensor chamber through
and beyond the chamber opening; and
a diaphragm mounted on the sensor body and
sealing the chamber opening, the diaphragm being pre-
loaded against the transducer assembly to hold the
transducer assembly against the interior chamber surface
in preloaded compression while the diaphragm is held in
preloaded tension by the transducer assembly, and the
diaphragm being formed to conform to the contour of the
end of the transducer assembly and to conform to the
contour of the sensor body adjacent th~ transducer
assembly such that the diaphragm is in physical contact
with the transducer assembly and the sensor body
substantially completely throughout the extent of the
diaphragm and such that pressure fluctuations outside
the chamber against the diaphragm cause compression
fluctuations in the piezoelectric transducer which cause
the piezoelectric transducer to responsively generate an
electrical signal representative of the frequency of the
pressure fluctions.
Z
In accordance with another aspect of the
present invention, there is provided a sensor adapted to
sense a frequency oE pressure Eluctuations in a dynamic
fluidf the sensor comprising:
a sensor body defining a sensor cha~ber with a
central axis defining an axial direction along the
central axis, and a transverse direction perpendicular
to the central axis and further defining a transversely
extending exterior chamber opening and a transversely
extending, solid interior chamber surface spaced
opposite the exterior chamber opening along the
transverse direction;
a diaphragm mounted on the body and sealing
the exterior chamber opening; and
a piezoelectric transducer assembly o~ at
least a piezoelectric transducer having a contour sur-
face, the piezoelectric transducer being located in the
sensor chamber between the diaphragm and the solid
interior chambe.r surface, the piezoelectric transducer
being in at least indirect, rigid physical contact with
the diaphragm and the interior chamber surface, the
diaphragm and piezoelectric transducer being preloaded
in the axial direction with the diaphragm being
preloaded to hold the piezoelectric transducer assembly
against the interior chamber surface in preloaded
compression in the axial direc~ion while the diaphragm
is held in preloaded tension by the transducer assembly r
and the diaphragm being formed to the contour of the
piezoelectric transducer assembly and to conform to the
contour of he sensor body adjacent the transducer
assembly such that the diaphragm is in physical contact
with the transducer assembly and the sensor body
...
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- 4a -
substantially completely throughout the extent of the
diaphragm and such that, with the relative rigidities of
the interior chamber surface, piezoelectric transducer
and diaphragm being such that pressure fluctuations
outside the sensor chamber against the diaphragm cause
compression fluctuations in the piezoelectric
transducer, and with the piezoelectric transducer
oriented such that compression fluctuations of the
piezoelectric transducer between the diaphragm and
interior chamber surface cause the piezoelectric
transducer to responsively generate an electrical signal
related to the compression fluctuations, and thereby the
pressure fluctuations.
In the above aspects, the invention is a fluid
pressure fluctuation frequency sensor operating in a
compression mode, involving relatively no deflection of
the diaphragm. Pressure on the diaphragm is directly
transmitted to the transducer substantially without
deflection of the diaphragm. As a result of the struc-
ture, mode of operation and the physical contact,relatively no changing stress, fatigue or rupture of the
diaphragm occurs, as compared with other, prior art,
piezoelectric sensors.
Further, the physical contact of the diaphragm
and transducer and a preferred dry mounting in~olve a
simplicity which is ingenious, especially as compared to
the mentioned commercially-offered sensor. Components
such as the oil fill, oil ports, spacer rings and clamp
rings are absent from the inventive sensor, resulting in
3~ ease of manufacture and economy.
In accordance with still another aspect of the
present invention, there is provided an improvement in a
vortex-shedding flowmeter having a bluff body generating
4~i~
-4b-
a von Karman vortex street of two rows o:E vortices in a
flow of fluid, and a sensor carrying body. The
improvement comprises:
a portion of the sensor-carrying body having
at least a fi.rst side surface and defining a sen~sor
chamber extending in a generally perpendicular direction
to the side surface from the side surface into the
portion, with an exterior chamber opening adjacent the
side surface and an interior chamber surface opposite
the exterior chamber opening r the generally perpendi-
cular direction being an axial direction;
a diaphragm mounted on the body to the side
surface and sealing the exterior chamber opening; and
a piezoelectric transducer assembly of at
least a piezoelectric transducer, the piezoelectric
transducer being located in the sensor chamber between
the diaphragm and the interior chamber surface, the
piezoelectric transducer being in at least indirect,
rigid physical contact with the diaphragm and the
interior chamber surface, the diaphragm and piezo-
electric transducer being preloaded in the axial direc-
tion with the diaphragm being preloaded to hold the
piezoelectric transducer assembly against the interior
chamber surface in preloaded compression in the axial
direction while the diaphragm is held in preloaded
tension by the transducer assembly~ and the diaphragm
being formed to the contour of the piezoelectric
transducer assembly, with the relative rigidities of the
interior chamber surface, the piezoelectric transducer,
3Q and the diaphragm being such that pressure fluctuations
in one of the rows of vortices outside the chamber
again.st the diaphragm cause compression fluctuations in
the piezoelectric transducer, and with the piezoelectric
transducer oriented such that compression fluctuations
~34~i2
-4c-
of the interior chamber surface cause the piezoelectric
transducer to generate a first electrical signal related
to the compression fluctuations, and thereby the
pressure fluctuations, in the one row of vortices.
In accordance with yet another aspect of the
present invention, there is provided an improvement in a
vortex-shedding flowmeter having a bluff body generating
a von Karman vortex street of two rows oE vor-tices in a
flow of fluid, and a sensor carrying body, the
improvement comprising:
a portion of the sensor-carrying body having
at least a first side surface and having a sensor cham-
ber in the first side surface including an exterior
chamber opening and an interior chamber surface spaced
opposite the opening;
a piezoelectric transducer assembly including
a piezoelectric transducer located in the sensor
chamber, seated against the interior chamber surface,
and having an end extending from the sensor chamber
through and beyond the exterior chamber opening; and
a diaphragm mounted on the sensor body to the
first side surface and sealing the exterior chamber
opening/ the diaphragm being preloaded against the
piezoelectric transducer assembly to hold the piezo-
electric transducer assembly against the interior
chamber surface in preloaded compression while the
diaphragm is held in preloaded tension by the piezo-
electric transducer assembly, and the diaphragm being
formed to conform to the end of the plezoelectric
transducer assembly such that pressure fluctuations in
one of the rows of vortices outside the chamber against
~3~5i~2
-4~-
the diaphragm cause compression fluctuations in the
piezoelectric transducer which cause the piezoelectric
transducer to responsively generate a first electrical
signal representative of the frequency of the pressure
fluctuations in the one row of vortices.
The above and other objects, aspects and
advantages of the inven-tion are further detailed in the
description which follows~
BRIEF DESCRIPTION OF THE DRAWINGS
_
The preferred embodiments of the invention
are described in relation to the accompanying drawing.
The drawing consists of eleven figures, wherein:
Figure 1 is a perspective view of a vortex-
shedding flowmeter, cut away to reveal the location of
the first preferred embodiments of the invention;
Figure 2 is a broken, cross-section and
schematic view of the first preferred embodiment, taken
along line 2-2 in Figure l;
Figure 3 is a perspective view of the first
preferred eTnbodiment, with some elements cross-sectioned
as in Figure 2 and others shown in full, for clarity;
Figure 4 is a cut-away, perspective view of a
second preferred embodiment of the invention;
Figure 5 is a broken cross-section view of the
second preferred embodiment, taken along line 5-5 in
Figure 4;
Figure 6 is an exploded, perspective view of
the second preferred embodiment;
Figure 7 is a perspective view similar to
Figure 3 of a third preferred embodiment of the inven-
tion;
~a
5~
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Figure 8 is a perspective view similar to
Figure 1 of the flow meter cut away to reveal a fourth
preferred embodiment of the invention;
Figure 9 is a broken, side ele~ation view of
the fourth preferred embodiment;
Eigure 10 is a broken, cross section view of
the flowmeter of Figure 1, similar to Figure 2, during
a step of assembly;
Figure 11 is another broken, cross-section
view of the flowmeter of Figure 1, similar to Figure 2,
during another step of assembly; and
Figure 12 is a detail, cross section view
taken along line 12-12 of Figure 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the accompanying drawing, the
first preferred embodiment of the invention is a fluid
pressure fluctuation frequency sensor generally desig-
nated 10. Referring to Figures 1-3, the sensor 10 is
located within and as part of a vortex-shedding flow-
meter generally designated 12. The purpose of the meter
12 is to measure the velocity of a fluid flowing within
a pipe (not shown). The meter 12 includes pipe sections
16 and 17 to be fitted to the pipe, and velocity report-
ing or recording instruments such as electronic signal
conditioning and enhancing circuitry associated with a
gauge 18.
The meter 12 operates by creating a von Karman
vortex street in the pipe section 16, and measuring the
frequency of fluid pressure fluctuations at a fixed
point in the street. In the embodiment illustrated, a
bluff body 14 is adapted to cause the street within the
pipe section 16. Fluid flows past the body 14 in the
direction of the arrow 8. A sensor-carrying body 20
(also a bluff body) is located downstream of the
,,
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separation point of the bluff body 14, within the wake
thereof, with two (one is shown in Figure 1) side sur-
faces 22a, 22b parallel to and directly inside the rows
of the street. The vortices of one row pass directly
beside one side surface 22a; the vortices of the other
row pass directly beside the other side surface 22b.
Thus, the frequency of the pressure fluctuations in the
street can be measured at the side surfaces 22a, 22b.
The frequency is measured by the sensor 10,
which is located on and within the body 20. The sensor
includes the portion 24 of the body 20 adjacent the
vortex rows, and two diaphragms 26a, 26b. One diaphragm
26a is located on the one side surface 22a, and other
diaphragm 26b is located on the other side surface 22b.
~he sensor further includes two sensor cham-
bers 28a, 28b; two piezoelectric discs 30a, 30b; two
pairs 32a, 34a and 32b, 34b of electrical leads; and two
electrical insulators 35a, 35b. The sensor chambers 28a,
28b extend generally perpendicular to the body side sur-
faces 22a, 22b in an axial direction. The piezoelectric
discs 30a, 30b are located within the chambers 28a, 28b
and the leads 32a, 32b, 34a, 34b extend from within the
chambers through a passage 36 in the body 20 toward the
gauge 18. The leads are electrically connected to the
signal conditioning and enhancing circuitry.
The pairs of sensor chambers 28a, 28b; discs
30a, 30b; leads 32a, 34a, 32b, 34b; and insulators 35a,
35b are substantially identical to each other. The
chamber 28a, disc 30a, and leads 32a, 34a are mirror
images of the chamber 28b, disc 30b, and leads 32b, 34b,
respectively. For clarity of drawing and description,
only chamber 28a, disc 30a, leads 32a, 34a and insulator
35a are now described.
'B '~'~ '~ A ~/ ~
-7- 21 56-5524A
Chamber 28a is a substantially cylindrical
bore defined by an inner sidewall 38a which extends
axially inward from a chamber opening defined by a
transversely extending ledge 42a of a counterbore in the
body side surface 22a. The chamber sidewall 38a has a
substantially uniform diameter, from the chamber opening
at ledge 42a to a substantially circular, transversely
extending inner or interior chamber surface 44a. The
surface 44a meets the sidewall 38a to form the "bottom"
of the chamber 28a. The surface 44a i9 substantially
planar, substantially circular, and parallels the side
surface 22a and ledge 42a.
The ledge 42a supports the periphery of the
diaphragm 26a, which is a thin, circular member, across
the chamber opening. The diameters of an axially
extending outer sidewall portion 4Oa and the diaphragm
26a are sized to provide a snug fit between the dia-
phragm 26a and the sidewall portion 40a of the counter-
bore. The width of the sidewall portion 40a is sized
to provide for support of the diaphragm 26a by the ledge
42a with the outer surface of the periphery of the dia-
phragm 26a being substantially coplanar with the body
side surface 22a.
The diaphragm 26a is secured to the ledge 42a.
A laser weld may, for example, seal the diaphragm 26a
about its periphery to the ledge. The seal provided by
the laser weld isolates the interior of the chamber 28a
from the fluid in the flowmeter 12, to provide a benign
environment for the disc 30a, leads 32a, 34a and insula-
tor 35a. The laser weld is especially desirable for 'heseal, to eliminate disc damage from overheating during
the sealing.
The disc 30a is fitted within the chamber 28a
between the two leads 32a, 34a, and the insulator 35a.
The disc 30a is in direct physical contact with the
leads and insulator, and thereby in indirect physical
ii2
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contact with the diaphragm 26a, the inner chamber surface
44a and the sidewall 38a. More specifically, the disc
30a is sandwiched between a thin, planar and circular
portion 46a of the lead 32a and a substantially identi-
cal portion 48a of the lead 34a. The lead portion 46a
is parallel to, and abuts, the diaphragm 26a over its
surface, whil~ the lead portion 48a is parallel to, and
abuts, the chamber inner surface 44a over its surface.
The insulator 35a extends around the edge of the disc
30a along the chamber sidewall 38a, from one side of the
narrow strip 50a of conductor 32a to the other side
thereof.
The disc 30a, leads 32a, 34a, and insulator
35a are snugly dry-mounted in the chamber 28a with
allowance for disc dimensional changes on the order of
less than 0.1 micrometer. They are not attached to
each other in the chamber 28a, or to the diaphragm 26a
or body 20. No fluid or adhesive is present in the cham-
ber 28a. Fluids, adhesive and other resilient materials
are considered to be detrimental.
As shown in Figures 10 and 11, the disc 30a,
leads 32a, 34a, insulator 35a and diaphragm 26a are
assembled in the chamber 28a. The disc 30a, leads 32a,
34a and insulator 35a form a transducer assembly 51.
The thickness of the assembly 51 is the sum of the
thicknesses of the disc 30a, and leads 32a, 34a. All
thicknesses are defined in the axial direction defined
by the centerline 52 of the chamber 28a. The assembly
thickness exceeds the depth of the chamber 28a between
the ledge 42a and the surface 44a. As a result, the
assembly 50 has an end extending through and beyond the
chamber opening at ledge 42a.
During the assembly of the sensor 10, a fix-
ture 54 holds the diaphragm 2~a against the ledge 42a
rCd
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and the transducer assembly 51 and axially preloads the
diaphragm 26a against the transducer assembly 51 which
is seated against interior chamber surface 44a, as in
Figure 10. The laser weld 56 is made, while the fixture
5 54 holds the diaphragm 26a and the assembly 51, also as
in Figure 10. The weld 56 if formed on the ledge 42a
and outer sidewall 40a away from the inner sidewall 38a.
After completion of the weld 56, the fixture
54 is removed and the diaphragm 26a is hydroformed under
a pressure of approximately 2,000 psi, or approximately
13,730 kilopascals (kPa), to conform around and to the
surface of the protruding end of the assembly 51, as in
Figure 11. Within the periphery 58, a central, exposed
fluid pressure receiving surface portion 59 is defined
in the diaphragm 26a. The surface portion 59 is raised
from the periphery 58. The surface portion 59 is in
direct physical contact with the circular portion 46a
of the electrical lead 32a over its whole area. As
stated above, the circular lead portion 46a is in direct
physical contact with the disc 30a over its whole area.
Because of the relationship of the thickness of the
transducer assembly 51 to the inner chamber wall depth,
the diaphragm 26a remains preloaded in both radial and
axial tension, while the disc 30a remains preloaded in
compression.
The disc 30a is a piezoelectric transducer,
and more specifically, a cylindrical disc of ceramic or
crystalline material having piezoelectric properties.
One such disc is made by the Vernitron Corporation of
Bedford, Ohio. Compression across the opposite, planar
surfaces of the disc causes the disc to generate posi-
tive and negative charges at the opposite surfaces.
These charges are related to the amount of compression
across the disc.
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The generated charges are carried by the leads
32a, 34a to the gauge 18. Electrical contact with the
charged surfaces of the disc 30a is provided by the
clrcular portions 46a, 48a of the leads.~ The leads are
formed by copper deposit on a polyimide film, etching to
remove undesired deposit, application of a second film,
and stamping to separate completed leads. ~s in Figures
10 and 11, the copper deposits of the circular portions
46a, 48a of the leads 32a, 34a, such as deposit 90, are
exposed to the disc 30a. The deposits are insulated
from the sensor body and diaphragm by the polyimide film
thereof, such as film 91. As in Figure 12, in the
remainder of the leads, the copper deposits 93 are
sealed within the films 94.
The insulator 35a is also formed of an insula-
tlon (e.g., polyimide) coated copper or other stiff
and springly material. The polyimide film completely
envelopes the copper. The insulator is initially
formed as a flat strip, with the copper providing the
support and flexibility required for shaping of the
insulator 35a.
The disc 30a is thus held within the chamber
28a, between the diaphragm 26a and chamber surface 44a.
The rigidities of the chamber surface 44a, disc 30a and
diaphragm 26a are related such that pressure fluctuations
applied against the diaphragm 26a cause compression
fluctuations in the disc 30a, but do not vibrate the
diaphragm 26a. The diaphragm is essentially or sub-
stantially static, flexing only to the extent of com-
pression in the transducer assembly 51. As a result ofthis minimal flexing, the diaphragm is substantially
free of fatigue, while the disc 30a responds sufficient-
ly to pressure fluctuations to function as a sensor of
the frequency of fluid pressure fluctuations.
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Since the disc 30a responds to compression
fluctuations with an electrical signal related to the
compression fluctuations of the disc, and since the
compression fluctuations are representative of the
pressure fluctuations, the signal of the disc 30a is
representative of the pressure fluctuations. Thus, the
frequency of pressure fluctuations adjacent the one body
side surface 22a can be determined from the frequency of
the signal of the disc 30a.
It should be understood that each disc 30a,
30b generates an electrical signal. The signals have
the same fre~uency, since the vortex rows have the same
frequency. As a result, the signals may be electroni-
cally processed together or separately, as desired, to
record or report the frequency of fluid pressure fluc-
tuations in the street, and thereby the velocity of the
fluid. One desired processing alternative is the sub-
traction of signals from the sensor pair to achieve a
high signal-to-noise ratio.
Referring now to Figures 4-6, the second pre-
ferred emodiment is a fluid pressure fluctuation fre-
quency sensor generally designated 600 The sensor 60
includes a portion 64 of a body 62, and two diaphragms
66a, 66b (now shown in Figures 4 and 6, for clarity).
One diaphragm 66a is located on one side surface 68a of
the body 64, and the other diaphragm 66b is located on
the opposite side surface 68b of the body 64.
The sensor 60 further includes a sensor
chamber 70; two piezoelectric plates 72a, 72b; two pairs
74a, 76a and 74b, 76b of electrical leads; and an elec-
trical insulator body 78. The sensor chamber 70 extends
generally perpendicular to the body side surfaces 68a,
68b through the body portion 64. In planes parallel to
the body side surfaces 68a, 68b, the sensor chamber 70
is oblate in shape, as are the diaphragms 66a, 66b.
39~
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The insulator 78 occupies the chamber 70. The
insulator 78 is externally shaped to match the chamber
70. A passage 80 in the insulator 78 is aligned with a
passage 82 in the body portion 64, and opens into two
plate chambers 84a, 84b in the insulator 78. The
piezoelectric plates 72a, 72b and the leads 74a, 76a,
74b, 76b are located within the chambers 84a, 84b,
respectively. The leads extend from within the chambers
84a, 84b through the passages 80, 82.
In further detail, the sensor 60 is similar
to the sensor 10. For example, the plates 72a, 72b are
sandwiched between their respective leads 74a, 76a, 74b,
76b in indirect physical contact with the respective
diaphragms 66a, 66b and inner chamber surfaces 86a, 86b.
Referring to Figure 7, the third preferred
embodiment is a sensor 100. The sensor 100 is substan-
tially identical to the sensor 10. The exception is
that the piezoelectric elements 102a, 102b are oblate
and the sensor chambers, leads and diaphragms are shaped
to match. Physical interrelationships are retained, and
function is enhanced, as with sensor 50, by the increas-
~ ed dimension of the piezoelectric elements in a direc-
tion transverse to the street.
Referring to Figures 8 and 9, the fourth
preferred embodiment is a sensor 110 having the enhanced
function of the sensors 60, 100 achieved by pairing
piezoelectric discs 30a, 30b and the associated struc-
ture of the sensor 10 with two further, spaced discs
30a, 30b and structure (30b discs not shown), for a
total of four discs. In structure, the sensor 10 is
equivalent to two sensors 10, with the leads of the
30a discs connected and the leads of the 30b discs
connected.
The preferred embodiments of the invention
have now been described in detail, with the non-sensor
9L5~
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aspects of the illustrated flowmeter only generally
described, for clarity. Further information about the
vortex-shedding flowmeter as generally described can be
obtained from U.S. Patent No. 4,350,047 issued September
21, 1982 to C. Forbes Dewey, Jr. and David E. Wiklund.
However, it should be understood that while the
invention is described in the context of a specific type
of vortex-shedding flowmeter for which it is especially
adapted, the invention is not restricted to such an
application. Vortex-shedding flowmeters of various
types may include the invention, as may non-vortex-
shedding flowmeters. For example, a vortex-shedding
flowmeter with a single bluff body may include the
invention. As another example, a vortex-shedding
flowmeter may include the invention positioned on a wall
of the meter. Moreover, the invention may be applied to
diverse flow measurement apparatus, such as may be used
in ducts/ open channels and wherever the sensing of -the
frequency of dynamic fluid pressure fluctuations is
desired.
Thus, while preferred embodiments of the
present invention have been described and illustrated in
specific applications, the invention should not be
limited thereto, but may be otherwise embodied within
the scope of the following claims.
