Abstrict In a vortex flow meter for measuring a varying flow rate of a fluid
through a conduit, an oscillation compensating apparatus is constructed
to remove undesirable externally derived oscillation noise which
is applied to the flow meter. An elongate vortex shedding member
extends into the conduit through part of its wall. The shedding
member forms a shedding portion inside the conduit and a compensating
portion outside the conduit. The shedding portion carries a first
oscillation sensor therewith and the compensating portion, a second
oscillation sensor. The first sensor is sensitive to an oscillation
component caused in the shedding portion by a vortex train shed
in the conduit, and an externally derived oscillation noise component.
The second sensor is sensitive to the noise component only. All
these sensed components are combined to cancel the oscillation noise
so that only the oscillation component in the shedding portion is
picked up.
Claims What is claimed is:
1. In a vortex flow meter for measuring the flow rate of a fluid
which flows through a conduit, an oscillation compensating apparatus
for removing externally derived oscillation noise applied to the
flow meter, comprising:
an elongate vortex shedding member extending into the conduit through
part of a wall of the conduit, said vortex shedding member having
a shedding portion constituted by a portion thereof located inside
the conduit and a compensating portion constituted by a portion
thereof located outside the conduit;
first oscillation sensor means disposed in the shedding portion
for sensing an oscillation component caused in the shedding portion
by a vortex train and the externally derived oscillation noise,
and outputting a first signal having a frequency which corresponds
to the oscillation and noise components; and
second oscillation sensor means disposed in the compensating portion
for sensing only the noise component and outputting a second signal
having a frequency which corresponds to the noise component;
said vortex shedding member being in the form of a cylinder having
a bore thereinside, one end of which is closed;
each of the first and second oscillation sensor means comprising
elongate base electrode means extending in said bore along the axis
of the vortex shedding member.
2. The oscillation compensating apparatus as claimed in claim 1
further comprising circuit means for combining the first and second
signals to remove the noise component and pick up only the oscillation
component in the shedding portion, and outputting a third signal
which corresponds to the oscillation component.
3. The oscillation compensating apparatus as claimed in claim 1
in which the first and second oscillation sensor means are rigidly
confined by an insulating member in the bore at positions which
correspond to the shedding and compensating portions, respectively.
4. The oscillation compensating apparatus as claimed in claim 3
in which the insulating member comprises a glass.
5. The oscillation compensating apparatus as claimed in claim 3
in which the insulating member comprises a preformed glass.
6. The oscillation compensating apparatus as claimed in claim 3
in which the insulating member comprises a resin.
7. The oscillation compensating apparatus as claimed in claim 3
in which the insulating member comprises a ceramic.
8. The oscillation compensating apparatus as claimed in claim 1
in which each of the first and second oscillation sensor means further
comprises a piezoelectric member mounted on an outer periphery of
said base electrode means, and sensor electrode means mounted on
an outer periphery of said piezoelectric member.
9. The oscillation compensating apparatus as claimed in claim 8
in which the base electrode means comprises a flat base plate made
of metal.
10. The oscillation compensating apparatus as claimed in claim
8 in which the base electrode means comprises a cylindrical tube
made of metal.
11. The oscillation compensating apparatus as claimed in claim
8 in which the piezoelectric members of the first and second oscillation
sensor means comprise an integral common piezoelectric element.
12. The oscillation compensating apparatus as claimed in claim
8 in which the piezoelectric members of the first and second oscillation
sensor means are physically separated from each other and located
only in the vicinity of the shedding and compensating portions,
respectively.
13. The oscillation compensating apparatus as claimed in claim
8 in which the sensor electrode means comprises a pair of metal
electrodes which are individually securely mounted on the piezoelectric
member in such a manner as to face each other in a direction perpendicular
to a direction of fluid flow in the conduit.
14. The oscillation compensating apparatus as claimed in claim
13 in which the metal electrodes are deposited by evaporation on
the piezoelectric member.
15. The oscillation compensating apparatus as claimed in claim
13 in which the metal electrodes are deposited by gold paste baking
on the piezoelectric member.
16. The oscillation compensating apparatus as claimed in claim
13 in which each of the first and second oscillation sensor means
comprises a first piezoelectric sensor made up of one of the pair
of metal electrodes and the piezoelectric member, and a second piezoelectric
sensor made up of the other metal electrode and the piezoelectric
member.
17. The oscillation compensating apparatus as claimed in claim
13 further comprising a first output terminal connected to the
base electrode means and a second output terminal connected to the
sensor electrodes.
18. The oscillation compensating apparatus as claimed in claim
16 further comprising a first output terminal connected to the
base electrode means and a second output terminal connected to all
the piezoelectric sensors of the first and second oscillation sensor
means.
19. The oscillation compensating apparatus as claimed in claim
18 further comprising a charge amplifier connected to the first
and second output terminals to transform an output of the base electrode
means and an output of the piezoelectric sensor into a voltage variation,
a low-pass filter for cutting off a high frequency component which
is included in an output voltage of the charge amplifier and has
no bearing on the oscillations of the vortex shedding member, and
a Schmitt trigger for transforming an output voltage of the low-pass
filter into a pulse signal having a rectangular waveform.
20. The oscillation compensating apparatus as claimed in claim
16 further comprising a first output terminal connected to the
base electrode means, a second output terminal connected commonly
to the first and second piezoelectric sensors of the first oscillation
sensor means, and a third output terminal connected commonly to
the first and second piezoelectric sensors of the second oscillation
sensor means.
21. The oscillation compensating apparatus as claimed in claim
20 further comprising a first charge amplifier connected to the
first and second output terminals to transform an output of the
base electrode means and outputs of the first and second piezoelectric
sensors of the first oscillation sensor means into a voltage variation,
a second charge amplifier connected to the first and third output
terminals to transform an output of the base electrode means and
outputs of the first and second piezoelectric sensors of the second
oscillation sensor means into a voltage variation, a variable output
level amplifier for making a level of an output voltage of the second
charge amplifier equal to a level of an output voltage of the first
charge amplifier, an adder-subtractor for processing an output voltage
of the first charge amplifier and an output voltage of the variable
output level amplifier, a low-pass filter for cutting off a high
frequency component which is included in an output voltage of the
adder-subtractor and has no bearing on the oscillation of the shedding
portion, and a Schmitt trigger for converting an output of the low-pass
filter into a pulse signal having a rectangular waveform.
22. In a vortex flow meter for measuring a flow rate of a fluid
which flows through a conduit, an oscillation compensating apparatus
for removing externally derived oscillation noise applied to the
flow meter, comprising:
an elongate vortex shedding member extending into the conduit through
part of a wall of the conduit, said vortex shedding member having
a shedding portion constituted by a portion thereof located inside
the conduit and a compensating portion constituted by a portion
thereof located outside the conduit;
first oscillation sensor means disposed in the shedding portion
for sensing an oscillation component caused in the shedding portion
by a vortex train and the externally derived oscillation noise,
and outputting a first signal having a frequency which corresponds
to the oscillation and noise components;
second oscillation sensor means disposed in the compensating portion
for sensing only the noise component and outputting a second signal
having a frequency which corresponds to the noise component; and
adjusting means for varying a characteristic oscillation frequency
of the compensating portion.
23. The oscillation compensating apparatus as claimed in claim
22 in which the adjusting means comprises a balance weight which
is mounted on the compensating portion to be movable along an axis
of the vortex shedding member.
Description BACKGROUND OF THE INVENTION
The present invention relates to an oscillation compensating apparatus
for a vortex flow meter.
One approach to the measurement of a flow rate of a fluid is, as
well known in the art, a vortex flow meter which includes a vortex
shedding member disposed in a fluid passage or conduit. With this
type of flow meter, an instantaneous flow rate of a fluid flowing
through the conduit is measured in terms of frequency of oscillations
of the vortex shedding member which results from the Karman vortex
street, or vortex train, shed in the conduit downstream of the vortex
shedding member.
A problem has existed in the vortex flow meter in that a sensor
thereof sensitive to the oscillations of the vortex shedding member,
or shedder, picks up not only oscillations due to the vortex train
but various kinds of externally derived oscillations, thereby making
accurate flow rate measurement difficult. Sources of the externally
derived oscillations include a pump for compressing the fluid and
a damper which is mechanically opened and closed. Implementations
for solving this problem are disclosed in Japanese Utility Model
Laid-Open Publication Nos. 57-19465/1982 and 57-28370/1982 for example,
which are characterized by the use of two oscillation sensors. The
output of one of the two sensors is employed to automatically control
the triggering level of a Schmitt trigger or, alternatively, the
outputs of both sensors are combined with each other. However, such
implementations are not fully acceptable from the viewpoint of their
applicable flow rate range, because the two sensors located at different
positions which make noise signals picked up thereby different in
waveform or because strict adjustment is required in positioning
the sensors.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an
oscillation compensating apparatus for a vortex flow meter which
effectively eliminates oscillation noise propagating through a conduit
to pick up only expected oscillations of a vortex shedding member
caused by a fluid.
It is another object of the present invention to provide an oscillation
compensating apparatus for a vortex flow meter which features a
simple construction and high performance.
It is another object of the present invention to provide a generally
improved oscillation compensating apparatus for a vortex flow meter.
In a vortex flow meter for measuring a flow rate of a fluid which
flows through a conduit, an oscillation compensating apparatus for
removing externally derived oscillation noise applied to the flow
meter of the present invention includes an elongate vortex shedding
member extending into the conduit through part of a wall of the
conduit. The vortex shedding member has a shedding portion constituted
by a portion thereof located inside the conduit and a compensating
portion constituted by a portion thereof located outside the conduit.
First oscillation sensor means is disposed in the shedding portion
for sensing an oscillation component caused in the shedding portion
by a vortex train and the externally derived oscillation noise,
and outputs a first signal having a frequency which corresponds
to the oscillation and noise components. Second oscillation sensor
means is disposed in the compensating portion for sensing only the
noise component and outputs a second signal having a frequency which
corresponds to the noise component.
The above and other objects, features and advantages of the present
invention will become apparent from the following detailed description
taken with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a vortex flow meter which employs
an oscillation compensating apparatus embodying the present invention;
FIG. 2 is a block diagram of an exemplary electrical arrangement
of the apparatus shown in FIG. 1;
FIG. 3 is a diagram demonstrating the principle of operation of
the apparatus in accordance with the present invention;
FIG. 4 is a sectional view of an alternative oscillation sensor
construction in accordance with the present invention;
FIG. 5 is a block diagram of an electrical circuit associated with
the sensor construction of FIG. 4; and
FIGS. 6-8 are perspective views of other alternative oscillation
sensor constructions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
While the oscillation compensating apparatus for a vortex flow
meter of the present invention is susceptible of numerous physical
embodiments, depending upon the environment and requirements of
use, substantial numbers of the herein shown and described embodiments
have been made, tested and used, and all have performd in an eminently
satisfactory manner.
Referring to FIG. 1 of the drawings, there is shown a vortex flow
meter furnished with a vibration compensating apparatus 10 embodying
the present invention. An elongate vortex shedding member 12 extends
into a conduit 14 through which a fluid 16 is allowed to flow. The
vortex shedder 12 having a triangular cross-section for example,
is rigidly mounted to the wall of the conduit 14 by means of screws
18 and 20. A bore 12a extends axially through the vortex shedder
12 from the top toward the bottom and accommodates thereinside a
first oscillation sensor 22 inside of the conduit 14 and a second
oscillation sensor 24 outside of the same. The first and second
oscillation sensors 22 and 24 are rigidly confined together in the
bore 12a by a glass envelope 26. A balance weight 28 is coupled
over the vortex shedder 12 adjacent to the outermost end of the
latter. The position of the balance weight 28 relative to the element
12 is controllable as desired by means of an adjusting screw 30.
The first sensor 22 comprises a flat base plate 32 made of metal
and extending substantially along the axis of the bore 12a, a pair
of piezoelectric elements 34 and 36 rigidly mounted on opposite
sides of the base plate 32 and metal electrodes 38 and 40 respectively
deposited on the piezoelectric elements 34 and 36 as by evaporation
or gold paste baking. While sharing the base plate 32 with the first
sensor 22 the second sensor 24 comprises a pair of piezoelectric
elements 42 and 44 individually fixed to opposite sides of the base
plate 32 and metal electrodes 46 and 48 respectively deposited
on the piezoelectric elements 42 and 44. In this construction, a
piezoelectric sensor 22a is formed by the base plate 32 piezoelectric
element 34 and electrode 38 in the first sensor 22. Another piezoelectric
sensor 22b, which faces the sensor 22a, is formed by the base plate
32 piezoelectric element 36 and electrode 40. Likewise, the second
sensor 24 has a piezoelectric sensor 24a formed by the base plate
32 piezoelectric element 42 and electrode 46 and another piezoelectric
sensor 24b formed by the base plate 32 piezoelectric element 44
and electrode 48 the piezoelectric sensors 24a and 24b being located
to face each other.
The first and second sensors 22 and 24 having the above construction
are installed in the axial bore 12a of the vortex shedder 12 such
that the electrodes 38 and 40 and the electrodes 46 and 48 face
each other each in a direction perpendicular to the flow direction
of the fluid 16 in the conduit 14. Stated another way, as shown
in FIG. 1 the electrodes 38 and 40 are located face-to-face in
symmetrically with respect to the base plate 32 and so are the electrodes
46 and 48 as viewed from the upstream or downstream side with respect
to the fluid flow.
The glass envelope 26 retaining the sensors 22 and 24 inside the
bore 12a functions in three ways: completely insulating the sensors
from the surrounding elements, causing the sensors to oscillate
in a unitary structure with the vortex shedder 12 and enhancing
the resistivity of the sensors to heat. Therefore, so long as these
functions are satisfied, the envelope 26 may be made of resin, ceramic
or the like, instead of glass.
Referring to FIG. 2 there are shown electrical connections of
the sensor made up of the piezoelectric sensors 22a and 22b and
the sensor made up of the piezoelectric sensors 24a and 24b, and
a circuit arrangement for processing outputs of the two sensors
to remove noise components therefrom. As shown, the output signals
of the first and second sensors 22 and 24 are sequentially processed
by a charge amplifier 50 a low-pass active filter 52 and a Schmitt
trigger 54. A pulse signal appears at an output terminal 56.
In operation, when the fluid 16 flows through the conduit 14 a
vortex train is shed in a known manner in a position downstream
of that part of the vortex shedder 12 located inside of the conduit
14 (this part will be referred to as the "shedding portion"
hereinafter). The vortex train causes the shedding portion of the
vortex shedder 12 to oscillate substantially perpendicular to the
flow of the fluid through the conduit 14 that is, in the lateral
direction as seen in FIG. 1. The piezoelectric sensors 22a and 22b
of the first sensor 22 which is integral with the vortex shedder
12 as mentioned earlier, sense the oscillations to deliver a signal
proportional to the oscillation frequency. Here, due to the common
interconnection of the piezoelectric sensors 22a and 22b, their
output levels are added to each other. However, the problem is that
the output signal of the first sensor 22 is entraining noise due
to external oscillations which propagate through the conduit 14
in addition to the expected oscillations due to the vortex train.
In detail, because the piezoelectric sensors 22a and 22b of the
first sensor 22 face each other in the direction perpendicular to
the fluid flow, they are hardly sensitive to oscillations parallel
to the fluid flow and, if sensitive, the resulting outputs would
cancel each other to not constitute any noise due to the differential
interconnection of the electrodes. However, when it comes to externally
derived oscillations of the conduit 14 perpendicular to the fluid
flow and vortex shedder 12 they are allowed to reach the shedding
portion of the shedder 12 to be detected together with the oscillations
caused by the vortex train.
Meanwhile, the second sensor 24 is adapted to sense only the external
oscillations which are transferred through the conduit 14. As previously
mentioned, the vortex shedder 12 is firmly fastened to the conduit
14 by means of the screws 18 and 20 so that the oscillation of the
shedding portion of the shedder 12 is prevented from propagating
outwardly beyond the fastened position to the remaining outer portion
of the shedder 12 (this portion will be referred to as the "compensating
portion" hereinafter). The second sensor 24 therefore, is
immune to oscillation except for those which are introduced into
conduit 14 from the outside. It will be noted that the second sensor
24 is common to the first 22 in sensing only the oscillations in
the direction perpendicular to the fluid flow and shedder 12.
Now, consideration will be given to oscillations of the vortex
shedder 12 originating from external oscillations which propagate
through the conduit 14 with particular reference to FIG. 3. In
response to a leftward oscillation indicated by a dotted arrow A,
both the shedding and compensating portions of the shedder 12 bend
themselves to the right in the drawing as indicated by dotted arrows
B, each fulcrumed by the interconnected portion of the shedder 12
and conduit 14. The resulting position of the shedder 12 is indicated
by a dash-and-dot line 12b in the drawing. In response to a righward
oscillation indicated by a solid arrow C, on the other hand, both
the shedding and compensating portions of the shedder 12 bend to
the left to a position indicated by a dash-and-dots line 12c. Therefore,
the first and second sensors 22 and 24 translate an external oscillation
into a same waveform. Concerning the second sensor 24 however,
it senses the composite oscillations of oscillations due to external
oscillations and oscillations due to the vortex train.
With the above principles in mind, if the first and second sensors
22 and 24 are held in differential interconnection, the output of
the second sensor 24 will cancel a noise component in the output
of the first sensor 22 thereby leaving only the signal resulted
from the vortex train. Because the sensors 22 and 24 are high impedance
elements, their outputs are transformed into voltage variations
by the charge amplifier 50. The low-pass active filter 52 removes
from the voltage variations high frequency components which have
no bearing on the oscillations of the vortex shedder 12. The Schmitt
trigger 54 processes an output of the filter 52 into a rectangular
pulse signal which accurately reflects an oscillation frequency
provided by the vortex train only. Counting the output pulses of
the Schmitt trigger 54 provides any instantaneous flow rate of the
fluid 16.
The unique construction described, in which two sensors 22 and
24 are commonly installed in the shedder 12 affords the following
advantage. Where one of the sensors is located inside the conduit
14 and the other outside the same, they receive exactly the same
external oscillations and thereby pick up noise signals from the
conduit 14 as exactly the same waveforms regardless of the direction
or the like of the oscillations. As a result, a noise component
will be completely cancelled when outputs of the sensors 22 and
24 are combined with each other. Where the fluid 16 is a liquid
and, therefore, the shedding portion of the shedder 12 is in the
liquid and the compensating portion in air, the oscillation modes
of the shedding and compensating portions will differ from each
other. Another factor that brings about a difference between their
oscillation modes is derived externally, e.g., a difference in mass
and/or shape between them. Any such difference in oscillation mode
between the two portions can be readily eliminated by shifting the
balance weight 28 to a desired position on the element 12.
Referring to FIG. 4 a modification to the sensor assembly of FIG.
1 is illustrated. In FIG. 4 the same reference numerals as those
of FIG. 1 designate the same structural elements. While in FIG.
1 the piezoelectric elements 34 and 36 of the first sensor 22 are
physically independent of their adjacent counterparts 42 and 44
of the second sensor 24 in FIG. 4 the adjacent piezoelectric elements
are replaced by a pair of common piezoelectric elements 56 and 58.
A terminal 60 is led out from the metal base plate 32; a terminal
62 is led out from the electrodes 38 and 40 which are respectively
associated with the elements 56 and 58 of opposite polarities; and
a terminal 64 is led out from the electrodes 46 and 48 which are
respectively associated with the elements 56 and 58 of opposite
polarities.
A circuit for processing outputs of the sensors 22 and 24 of FIG.
4 is shown in FIG. 5 in which the same reference numerals as those
of FIG. 2 designate the same structural elements. In FIG. 5 the
circuit includes a charge amplifier 50a connected to the output
terminals 60 and 62 of the first sensor 22 a second charge amplifier
50b connected to the output terminals 60 and 64 of the second oscillation
sensor 24 a variable amplifier 66 and an adder or subtractor 69.
For the reason which will follow, the circuit of FIG. 5 will prove
effective when the output level of the first sensor 22 differs from
that of the second 24. Although the waveform of noise included in
the output of the first sensor 22 is in principle the same as the
waveform of the output of the second sensor 24 as already discussed,
a difference sometimes develops between the two output levels due
to a difference in amplitude or the like between the inner and outer
portions of the shedder 12. To eliminate this, the circuit of FIG.
5 allows the output of the amplifier 66 and thereby that of the
second sensor 24 to be adjusted such that the second sensor output
reaches a same level as the first sensor output, which is provided
through the charge amplifier 50a. Then, the first and second sensor
outputs will be combined by the adder or subtractor 69 to remove
the noise component.
It should be noted in FIG. 5 that the low-pass active filter 52
and Schmitt trigger 54 individually function in the same manner
as those described with reference to FIG. 2.
Referring to FIG. 6 a cylindrical sensor assembly is shown as
an alternative to the configuration of FIG. 1 or 4. In FIG. 6 the
same reference numerals as those of FIG. 1 or 4 designate the same
structural elements. The first sensor 22 shown in FIG. 6 comprises
a cylindrical metal tube 70 an annular piezoelectric element 72
mounted on the tube 70 and a pair of metal electrodes 74 and 76
which are individually deposited on the piezoelectric element 72
as by evaporation or gold paste baking in such a manner as to oppose
each other. The second sensor 24 shares the metal tube 70 with the
first sensor 22 and has, in addition thereto, an annular piezoelectric
element 78 fit around the tube 70 and a pair of metal electrodes
80 and 82 deposited on the element 78 in the same manner as the
electrodes 74 and 76. The tube 70 piezoelectric element 72 and
electrode 74 constitute one piezoelectric sensor 22a in combination,
while the tube 70 piezoelectric element 72 and electrode 76 constitute
another piezoelectric sensor 22b which faces the piezoelectric sensor
22a. Further, the tube 70 cooperates with the piezoelectric element
78 and electrode 80 to form one piezoelectric sensor 24a, while
cooperating with the piezoelectric element 78 and electrode 82 to
form another piezoelectric sensor 24b, which faces the piezoelectric
sensor 24a. Again, the orientation of the sensor assembly inside
the element 12 is such that the electrodes 74 and 76 and the electrodes
80 and 82 face each other each in a direction perpendicular to the
flow direction of the fluid 12 in the conduit 14. Stated another
way, as in the case of FIG. 1 the electrodes 74 and 76 located
face-to-face in the lateral direction and so are the electrodes
80 and 82 as seen from the upstream or downstream side with respect
to the fluid flow.
Shown in FIG. 7 is a modification to the sensor assembly of FIG.
6. In FIG. 7 a piezoelectric element 84 covers the whole outer
periphery of the metal tube 70 in contrast to the spaced piezoelectric
elements 72 and 78 of FIG. 6. The electrodes 74 and 76 constituting
the first sensor 22 are carried on one axial end of the piezoelectric
element 84 while the metal electrodes 80 and 82 constituting the
second sensor 24 are carried on the other axial end of the same.
Still another modification to the cylindrical sensor configuration,
particularly to that of FIG. 6 is shown in FIG. 8. A pair of spaced
piezoelectric elements 72a and 72b are mounted on one end of the
metal tube 70 and a pair of spaced piezoelectric elements 78a and
78b on the other end. That is, the piezoelectric element pair 72a-72b
is a divided version of the piezoelectric element 72 of FIG. 6 and
the piezoelectric element pair 78a-78b, that of the piezoelectric
element 78.
The circuits shown in FIGS. 2 and 5 are selectively usable for
processing output signals of the cylindrical oscillation sensor
assemblies shown in FIGS. 6-8 just as they are used for the others.
Now, an oscillation sensor using a piezoelectric element or the
like has to have its electrode portions perfectly insulated from
the surrounding members by means of glass or the like. This has
heretofore been implemented by a method which fills the space concerned
with glass powder and then heats the glass to melt and harden it,
or a method which fills the space with a preformed glass. The problem
encountered with the use of glass powder is that the filling and
heating procedure has to be repeated several times because the volume
of glass is smaller in the hardened state after heating than in
the initial powdery state. The method using a preformed glass invites
an increase in cost due to the intricate structure required therefor.
In contrast, any one of the cylindrical sensor configurations shown
in FIGS. 6-8 will facilitate the procedure for fixing the sensors
within the vortex shedding member 12. That is, it is possible to
insert, melt and harden a cylindrical glass tube or preformed glass
in the annular space between the wall of the bore 12a in the shedder
12 and the outer periphery of the sensors. This enveloping procedure
does not need to be repeated inasmuch as the volume of the glass
tube or preformed glass is free from reduction after hardening.
Even the use of a preformed glass is cost-effective due to the simply
cylindrical sensor configuration.
In summary, it will be seen that the present invention provides
an oscillation compensating apparatus for a vortex flow meter which
offers an excellent signal-to-noise ratio despite its simple and
easy-to-produce structure.
Various modifications will become possible for those skilled in
the art after receiving the teachings of the present disclosure
without departing from the scope thereof. For example, various other
designs are applicable concerning the shape of the vortex shedding
member 12 fixing means therefor, means for fixing the sensors inside
the shedder 12 configurations of the piezoelectric elements and
electrodes of the sensors, circuit arrangement for combining the
outputs of the sensors, etc. The sensors 22 and 24 may comprise
physically separate members which are individually nested in the
shedder 12 instead of the integral structure on a single base plate
or a tube shown and described. |