Abstrict A vortex flow meter includes a bluff body which sheds a vortex
train when a fluid flowing in a conduit moves therepast, the vortex
train developing a delicate pressure variation in proportion to
a flow rate of the fluid. The flow meter detects the flow rate by
sensing the pressure variation and then converting it into an electric
signal by means of a piezoelectric element or the like. A pressure
sensor is detachably mounted in a pressure sensing chamber, which
is defined in an internal space of the bluff body, and comprises
a pressure receiving plate displaceable in response to the pressure
variation, a sensor member such as a piezoelectric element for converting
the displacement into an electric signal. The pressure receiving
plate is arranged such that major part thereof is located in the
conduit, while major part of the sensor member is located in a wall
of the conduit and the outside thereof. The side surfaces of the
pressure receiving plate are oriented parallel to or perpendicular
to a direction of flow of the fluid. A drain port is located below
a pressure induction port which is formed in a bottom portion of
the pressure sensing chamber, so that part of the fluid entering
the pressure sensing chamber is discharged through the drain port.
The bottom wall of the pressure sensing chamber is inclined radially
outwardly or formed with an upright wall. A flange for mounting
the pressure sensor on the outer wall of the conduit and a cylindrical
member for accommodating the sensor member are formed independently
of each other and then welded together by an electron beam or the
like. A support wall for fixing the cylindrical member extends from
the flange. A second sensor member identical in construction with
the first is employed to compensate for externally derived vibrations
which may act on the pressure sensor. Leads extending out from the
pressure sensor have a small rigidity.
Claims What is claimed is:
1. A vortex flow meter for measuring the flow rate of a fluid flowing
through an internal space of a conduit by sensing the pressure variation
which occurs in proportion to the flow rate, said vortex flow meter
comprising, in combination:
(a) a bluff body disposed in the internal space of the conduit
to face the flow of the fluid and having a pressure sensing chamber
defined in an internal space of said bluff body for sensing the
pressure variation due to vortices generated by the flow of the
fluid, said pressure sensing chamber having an upper pressure induction
passageway and a lower pressure induction passageway;
(b) a pressure receiving member disposed in the internal space
of said bluff body to mechanically oscillate or displace in response
to the pressure variation, said pressure receiving member comprising
a flat pressure receiving plate which protrudes into the pressure
sensing chamber to bisect the chamber;
(c) a cylindrical member mounted in and extending through a wall
portion of the conduit and connected to the pressure receiving member
at a lower end of the cylindrical member, said cylindrical member
having an internal space; and
(d) a pressure sensor member disposed in said internal space of
said cylindrical member such as to prevent said pressure sensor
member from being contacted by the fluid flow in said conduit, said
pressure sensor member having imparted thereto the mechanical displacement
of said pressure receiving plate to thereby measure the flow rate
in said conduit, said pressure sensor member comprising a resilient
substrate, a converter element for converting the mechanical displacement
of said pressure receiving plate due to the vortices to an electrical
signal, said converter element being bonded to at least one of opposite
surfaces of said substrate, and an electrically insulative filling
agent for fixing said substrate and converter element in the internal
space of said cylindrical member.
2. A vortex flow meter as claimed in claim 1 in which the pressure
sensing chamber has a drain port in a position lower than the lower
pressure induction passageway and lower than a free end of the pressure
receiving member, whereby part of the fluid tending to deposit on
a bottom wall of the pressure sensing chamber is discharged.
3. A vortex flow meter as claimed in claim 2 in which a wall rises
from a central portion of the bottom wall of the pressure sensing
member to regulate a clearance which is defined between the pressure
receiving member and the bottom wall.
4. A vortex flow meter as claimed in claim 2 in which the bottom
wall of the pressure sensing chamber is inclined from a central
portion thereof toward the drain port.
5. A votex flow meter as claimed in claim 1 in which the pressure
receiving member is oriented parallel to a direction of flow of
the fluid at side surfaces thereof.
6. A vortex flow meter as claimed in claim 1 in which the pressure
receiving member is oriented perpendicular to a direction of flow
of the fluid at side surfaces thereof.
7. A vortex flow meter as claimed in claim 1 further comprising
a flange for mounting the cylindrical member on an outer wall of
the conduit.
8. A vortex flow meter as claimed in claim 7 in which the cylindrical
member and the flange are formed integrally with each other by welding
by means of at least one of an electron beam and a laser.
9. A vortex flow meter as claimed in claim 8 in which the flange
has an annular support wall at at least one of opposite sides thereof
for fixing the cylindrical member in place.
10. A vortex flow meter as claimed in claim 1 in which said converter
element comprises a piezoelectric element.
11. A vortex flow meter as claimed in claim 10 in which the piezoelectric
element bonded to be substrate is covered with a ceramic material.
12. A vortex flow meter as claimed in claim 1 in which the filling
agent comprises glass.
13. A vortex flow meter as claimed in claim 1 further comprising
leads for picking out the electrical signal from the sensor member,
said leads being individually made of a conductor having a small
regidity.
14. A vortex flow meter as claimed in claim 13 further comprising
a cylindrical tube for supporting the leads by means of a shield
member.
15. A vortex flow meter as claimed in claim 1 in which the cylindrical
member accommodates a second pressure sensor member in the internal
space thereof.
16. A vortex flow meter as claimed in claim 15 in which the two
sensor members are electrically connected to compensate for an externally
derived vibration.
17. A vortex flow meter for measuring a flow rate of a fluid flowing
through an internal space of a conduit by sensing a pressure variation
which occurs in proportion to the flow rate, said vortex flow meter
comprising:
(a) a bluff body disposed in the internal space of the conduit
to face the flow of the fluid and having a pressure sensing chamber
defined in an internal space thereof, said pressure sensing chamber
having an upper pressure induction passageway and a lower pressure
induction passageway;
(b) a pressure receiving member disposed in the internal space
of said bluff body to be displaceable in response to the variation;
(c) a drain port in the pressure sensing chamber in a position
lower than the lower pressure induction passageway and lower than
a free end of the pressure receiving member, whereby part of the
fluid tending to deposit on a bottom wall of the pressure sensing
chamber is discharged;
(d) a wall rising from a central portion of the bottom wall of
the pressure sensing chamber to regulate a clearance which is defined
between the pressure receiving member and the bottom wall;
(e) a sensor member arranged to be positioned in a wall portion
of the conduit and outwardly thereof; and
(f) a cylindrical member mounted in the wall portion of the conduit
and connected to the pressure receiving member at a lower end thereof,
said cylindrical member accommodating the sensor member fixed in
place in an internal space thereof.
18. A vortex flow meter for measuring a flow rate of a fluid flowing
through an internal space of a conduit by sensing a pressure variation
which occurs in proportion to the flow rate, said vortex flow meter
comprising:
(a) a bluff body disposed in the internal space of the conduit
to face the flow of the fluid and having a pressure sensing chamber
defined in an internal space thereof, said pressure sensing chamber
having an upper pressure induction passageway and a lower pressure
induction passageway;
(b) a pressure receiving member disposed in the internal space
of said bluff body to be displaceable in response to the pressure
variation;
(c) a drain port in the pressure sensing chamber in a position
lower than the lower pressure induction passageway and lower than
a free end of the pressure receiving member, the bottom wall of
the pressure sensing chamber being inclined from a central portion
thereof toward the drain port, whereby part of the fluid tending
to deposit on a bottom wall of the pressure sensing chamber is discharged;
(d) a sensor member arranged to be positioned in a wall portion
of the conduit and outwardly thereof, and
(e) a cylindrical member mounted in the wall portion of the conduit
and connected to the pressure receiving member at a lower end thereof,
said cylindrical member accommodating the sensor member fixed in
place in an internal space thereof.
Description BACKGROUND OF THE INVENTION
The present invention relates to an improved vortex flow meter
for measuring the velocity and flow rate of a fluid flowing through
a conduit by sensing a delicate pressure variation caused by a vortex
train, which a buffle body disposed in the conduit sheds on the
movement of the fluid past the buffle body, and converting the sensed
pressure variation into an electric signal by means of a piezoelectric
element or the like.
An example of vortex flow meters of the type described is disclosed
in Japanese Utility Model Publication No. 46-21501/1971. This prior
art vortex flow meter includes a strain gauge or like displacement
sensor mounted on a membrane such as a diaphragm, so that a displacement
sensed by the sensor is transformed into an electric signal. Such
a flow meter construction, however, suffers from various drawbacks
as enumerated below due to the inherent location of the sensor inside
a narrow space formed in a bluff body.
(1) The flow meter cannot be manufactured, machined or assembled
with ease due to the intricacy of construction.
(2) A large displacement cannot be sensed on account of the limited
space available for the displacement of the sensor, whereby the
sensitivity attainable with the flow meter is poor.
(3) The sensor is arranged to remain in direct contact with the
fluid flowing through the conduit and, therefore, it is apt to be
damaged to shorten the service life thereof.
(4) Any externally derived vibration is imparted to the sensor
by way of the conduit or leads which are connected to the sensor.
The external vibration is introduced as noise into a pressure variation
component resulted from the vortex train, thereby noticeably lowering
the sensing accuracy.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
vortex flow meter which is easy to manufacture, machine and assemble.
It is another object of the present invention to provide a vortex
flow meter which features excellent sensitivity.
It is another object of the present invention to provide a vortex
flow meter which desirably functions over a long time.
It is another object of the present invention to provide a vortex
flow meter which is capable of measuring pressure variations with
accuracy without being effected by external vibrations.
It is another object of the present invention to provide a generally
improved vortex flow meter.
A vortex flow meter for measuring a flow rate of a fluid flowing
through an internal space of a conduit by sensing a pressure variation
which occurs in proportion to the flow rate of the present invention
comprises a bluff body disposed in the internal space of the conduit
to face the flow of the fluid and having a pressure sensing chamber
defined in an internal space thereof, the pressure sensing chamber
having an upper pressure induction passageway and a lower pressure
induction passageway, a pressure receiving member disposed in the
internal space of the bluff body to be displaceable in response
to the pressure variation, a sensor member arranged to be positioned
in a wall portion of the conduit and outwardly thereof, and a cylindrical
member mounted in the wall portion of the conduit and connected
to the pressure receiving member at a lower end thereof, the cylindrical
member accommodating the sensor member fixed in place in an internal
space thereof.
In accordance with the present invention, a vortex flow meter includes
a bluff body which sheds a vortex train when a fluid flowing in
a conduit moves therepast, the vortex train developing a delicate
pressure variation in proportion to a flow rate of the fluid. The
flow meter detects the flow rate by sensing the pressure variation
and then converting it into an electric signal by means of a piezoelectric
element or the like. A pressure sensor is detachably mounted in
a pressure sensing chamber, which is defined in an internal space
of the bluff body, and comprises a pressure receiving plate displaceable
in response to the pressure variation, a sensor member such as a
piezoelectric element for converting the displacement into an electric
signal. The pressure receiving plate is arranged such that major
part thereof is located in the conduit, while major part of the
sensor member is located in a wall of the conduit and the outside
thereof. The side surfaces of the pressure receiving plate are oriented
parallel to or perpendicular to a direction of flow of the fluid.
A drain port is located below a pressure induction port which is
formed in a bottom portion of the pressure sensing chamber, so that
part of the fluid entering the pressure sensing chamber is discharged
through the drain port. The bottom wall of the pressure sensing
chamber is inclined radially outwardly or formed with an upright
wall. A flange for mounting the pressure sensor on the outer wall
of the conduit and a cylindrical member for accommodating the sensor
member are formed independently of each other and then welded together
by an electron beam or the like. A support wall for fixing the cylindrical
member extends from the flange. A second sensor member identical
in construction with the first is employed to compensate for an
externally derived vibrations which may act on the pressure sensor.
Leads extending out from the pressure sensor have a small rigidity.
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. 1a is a vertical section of a vortex flow meter embodying
the present invention;
FIG. 1b is a section along line 1b--1b of FIG. 1a;
FIGS. 1c and 1d are fragmentary views of the vortex flow meter
shown in FIG. 1a representing electric connection of a pressure
sensor installed therein;
FIG. 1e is a bottom plan view of the pressure sensor shown in FIG.
1c;
FIG. 2a is a vertical section of a modification to the embodiment
shown in FIG. 1a;
FIG. 2b is a section along line 2b--2b of FIG. 2a;
FIGS. 2c and 2d are fragmentary views of the modified flow meter
shown in FIG. 2a representing electric connection of a pressure
sensor installed therein;
FIG. 2e is a bottom plan view of the pressure sensor shown in FIG.
2c;
FIGS. 3a and 3b are vertical sections showing other modifications
to the embodiment of FIG. 1a;
FIGS. 4a and 4b are vertical sections of a modification to the
pressure sensor included in the embodiment of FIG. 1a; and
FIGS. 5a and 5b are vertical sections of another embodiment of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
While the 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 performed in an eminently satisfactory manner.
Referring to FIGS. 1a-1e of the drawings, a vortex flow meter embodying
the present invention is shown as being disposed in a conduit 10.
As shown, the conduit 10 has a space 12 defined therein for the
passage of liquid, gas or like fluid whose flow rate is to be measured.
An opening 14 extends throughout the conduit 10 to communicate the
space 12 to the outside. The outer wall of the conduit 10 is machined
in a portion thereof where the opening 14 is located, the machined
portion defining a flat surface 16 as illustrated.
The vortex flow meter includes a bluff body or vortex shedder generally
designated by the reference numeral 18. The bluff body 18 is disposed
in the space 12 of the conduit 10 to face the flow of the fluid
and may have a triangular cross-section as illustrated in FIG. 1b
by way of example. A central portion of the bluff body 18 is bored
to have a relatively wide space which is substantially common in
inside diameter to the through opening 14 in the conduit 10 and
intercommunicated to the opening 14. This space in the bluff body
18 is adapted to sense pressure variations due to a vortex train
as will be described. Pressure induction passageways 22 and 24 extend
throughout the bluff body 18 in upper and lower portions of the
space or pressure sensing chamber 20 respectively. As shown in FIG.
1b, each of the pressure induction passageways 22 and 24 is located
to oppose both sides of a flat pressure receiving plate 36 which
will be described.
A pressure sensor, generally 26 is detachably mounted in the intercommunicated
opening 14 and pressure sensing chamber 20 in order to convert a
pressure variation due to a vortex train into an electric signal.
As best shown in FIGS. 1c--1e, the pressure sensor 26 comprises
a flange 28 rigidly connected to the flat surface 16 of the conduit
10 by suitable connecting means, a relatively thin-walled hollow
cylindrical member 30 which is substantially bisected by the flange
28 into an upper portion 30a and a lower portion 30b intercommunicated
with the upper cylinder 30a, and a sensor member 34 rigidly mounted
in the bore of the hollow cylindrical member 30 by means of an electrically
insulative filling agent 32. The flat pressure receiving plate 36
extends downwardly from one end of the cylindrical member 30 i.e.,
lower end of the lower cylindrical portion 30b, to protrude into
the pressure sensing chamber 20 in the bluff body 18 in such a manner
as to bisect it.
The sensor member 34 is made up of a resilient substrate 38 extending
substantially along the axis of the cylinder 30 and a pair of piezoelectric
elements 40a and 40b which are bonded to opposite surfaces of the
substrate 38. These structural elements of the sensor 34 are fixed
in place together by the filling agent 32 inside the cylinder 30.
The substrate 38 and the piezoelectric elements 40a and 40b are
electrically connected to terminals 42 and 44 on the upper cylinder
portion 30a respectively. Leads 46 and 48 respectively extend from
the terminals 42 and 44 to an electric measuring circuit (not shown).
Preferably, the piezoelectric elements 40a and 40b bonded to the
surfaces of the substrate 38 are covered with a ceramic material
and then fixed in place by glass or like filling agent.
In operation, when the fluid passes the bluff body 18 while flowing
through the internal space 12 of the conduit 10 the bluff body
18 sheds a vortex train at both sides thereof in a well known manner
in accordance with a velocity of the fluid. The vortex train is
introduced as a pressure variation into the pressure sensing chamber
20 via the upper and lower pressure induction passageways 22 and
24 thereby developing a delicate fluctuation in the pressure inside
the chamber 20. In response to the pressure variation, the pressure
receiving plate 36 associated with the cylinder 30 oscillates as
indicated by an arrow A in FIG. 1a and this oscillation is imparted
to the substrate 38 and piezoelectric elements 40a and 40b. Such
a displacement is transformed by the piezoelectric elements 40a
and 40b into an electric signal which is then applied via the leads
46 and 48 to the electric measuring circuit. Thus, the instantaneous
flow velocity and flow rate of the fluid in the conduit 10 are determined.
Noteworthy features of the vortex flow meter described above are
as follows.
(1) The pressure receiving plate 36 integral with the cylinder
34 of the pressure sensor 26 extends vertically through the pressure
sensing chamber 20 which is formed vertically in the bluff body
18 over a substantial cross-sectional area. The plate 36 therefore,
allows a pressure variation due to a vortex train to be sensed as
a substantial displacement and, thereby, contributes a great deal
to the improvement in sensitivity.
(2) The pressure receiving plate 36 and the sensor member 34 of
the pressure sensor 26 are arranged at entirely different positions:
the plate 36 within the bluff body 18 and the sensor member 34 within
the cylinder 30 and above the bluff body 18. This prevents the sensor
member 34 from directly contacting the fluid flowing in the conduit
10 that is, the sensor member 34 withstands a long time of use
with hardly any damage caused thereto.
In the particular embodiment discussed above, opposite surfaces
of the plate 36 in the chamber 20 are so oriented as to be parallel
to the direction of the fluid flow in the conduit 10 as shown in
FIG. 1a, while the pressure induction passageways 22 and 24 are
positioned to individually face both sides of the plate 36 in the
chamber 20 as shown in FIG. 1b. This is not restrictive, however,
and may be replaced by an arrangement shown in FIGS. 2a-2e in which
both sides of the plate 36 extend perpendicularly to the direction
of fluid flow while, as shown in FIG. 2b, the pressure induction
passageways 22 and 24 individually open into the chamber 20 in such
a manner as to face both surfaces of the plate 36. The alternative
arrangement shown in FIGS. 2a-2e is successful to suppress the influence
of mechanical vibrations of the conduitwork on the accuracy of measurement.
Where the vortex flow meter is applied to a specific kind of fluid
such as steam which contains mist, part of the fluid admitted into
the pressure sensing chamber 20 via the pressure induction passageways
22 and 24 flows down along the opposite surfaces of the pressure
receiving plate 36 to collect itself on the bottom 20a of the chamber
20. As a result, a clearance 50 defined between the chamber bottom
20a and the plate end 36a tends to become stopped up by the collected
fluid. This would prevent the plate 36 from moving in response to
a pressure variation due to a vortex train and, thereby, make the
velocity or flow rate measurement inaccurate. Such a problem is
solved by a modification to the first embodiment shown in FIGS.
3a or 3b.
Referring to FIGS. 3a and 3b, the bluff body 18 is formed with
drain ports 52 at a level lower than the lower pressure induction
passageway 24 and even lower than the lower end 36a of the pressure
receiving plate 36. In this construction, part of the fluid flowing
down along the plate 36 to reach the bottom 20a of the chamber 20
is effectively discharged to the outside via the drain ports 52.
The plate 36 therefore, is capable of responding to pressure variations
with accuracy.
To promote more effective discharge of the fluid from the bottom
20a of the chamber 20 via the drain ports 52 a wall 54 facing the
lower end 36a of the plate 36 may be formed upright in a central
area of the chamber bottom 20a, as illustrated in FIG. 3a. The wall
54 defines the clearance 50 at a level higher than the drain ports
52. Another possible implementation for effective discharge of the
fluid is shown in FIG. 3b in which the chamber bottom 20a is inclined
downwardly toward the drain ports 52.
While the flange 28 and the thin cylinder 30 of the pressure sensor
26 have been shown and described as being in an integral structure
they may be formed as separate members as shown in FIGS. 4a and
4b. In these drawings, the flange 28 has a through bore 56 the inside
diameter of which is somewhat larger than the outside diameter of
the cylinder 30. Annular support walls 58a and 58b extend away from
each other from opposite ends of the flange 28 while defining extensions
of the through bore 56 thereinside. When the cylinder 30 is coupled
in the through bore 56 of the flange 28 the support walls 58a and
58b extend along the axis of the cylinder 30. After the cylinder
30 is suitably positioned relative to the flange 28 they are welded
together by the application of an electron beam, a laser or the
like from the outside. Welding with an electron beam, a laser or
like means realizes accurate machining eliminating various drawbacks
experienced with conventional welding techniques such as thermal
distortion due to the large heat capacity.
It will be noted that provision of the two flanges 58a and 58b
is not essential and either one of them may be omitted depending
upon the operating conditions as well as others.
The plate 36 and cylinder 30 may be formed separately from each
other and joined together using an electron beam or a laser, instead
of forming them integrally as in the first embodiment.
Now, when various externally derived vibrations are imparted to
the pressure sensor 26 by way of the conduit 10 leads 46 and 48
and the like, they would be added to a pressure variation due to
a vortex train and thereby introduced into a sensor output as noise,
lowering the S/N ratio to a critical extent. Reference will be made
to FIGS. 5a and 5b for describing a second embodiment of the present
invention which is an approach to overcome such a problematic situation.
Referring to FIG. 5a, the vortex flow meter includes a second sensor
member 60 in addition to the sensor member 34 of the first embodiment.
The sensor members 34 and 60 are substantially identical in construction
and positioned substantially symmetrically to each other with respect
to the flange 28. The sensor member 60 shares the resilient substrate
38 with the sensor member 34 and has piezoelectric elements 62a
and 62b individually bonded to opposite surfaces thereof. When some
external vibration is applied to the pressure sensor 26 via the
conduit 10 it acts on both the sensor members 34 and 60. Therefore,
if the sensor members 34 and 60 are electrically connected such
that vibrations acting thereon cancel each other, only the desired
pressure variation component will be converted into an electric
signal to set up an excellent S/N ratio in the sensor output.
In FIG. 5b, on the other hand, a lead support tube 64 having a
relatively thin wall is rigidly mounted at one end 64a thereof on
the flange 28 of the pressure sensor while surrounding the entire
cylinder 30. The other end 64b of the lead support tube 64 is hermetically
closed by a seal member 66. In this particular embodiment, the leads
46 and 48 extending from the pressure sensor 26 via the terminals
42 and 44 are individually made of a conductor having a relatively
small rigidity. The leads 46 and 48 are respectively connected to
terminals 70 and 72 which are fixed to the seal member 66 by a molding
68. The terminals 70 and 72 are individually connected to an electric
measuring circuit 74. In this construction, if an externally derived
vibration is imparted to the pressure sensor 26 propagation thereof
will be effectively interrupted by the nonrigid leads 46 and 48
before applied to the piezoelectric elements as noise. If desired,
the lead support tube 64 may comprise a bellows.
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. |