Abstrict A vortex flow meter includes a vibration sensing element having
a sensor responsive to an external vibration and a sensor responsive
to a vortex train at vertically opposite ends thereof. The sensing
element is fixed to a conduit fulcrumed at an intermediate portion
thereof. A vortex shedding member is integrally and oscillatably
mounted in a lower portion of the sensing element. The flow meter
can be assembled merely by being positioned in the conduit and,
due to an integral structure, it is effectively applicable even
to small diameter conduits through which fluids flow at very small
flow rates. In a path along which leads from a sensor responsive
to pressure variations due to vortex trains are routed to a transducer
box, vibration of the transducer box is prevented from reaching
the sensor via the leads, thereby rendering the flow meter less
susceptive to externally derived vibrations.
Claims What is claimed is:
1. A vortex flow meter, comprising:
a thin-walled cylindrical tube extending throughout a center of
a mounting flange and provided with a pressure receiving plate at
a lower end thereof which is exposed to small pressure variations
of a vortex train shed by a vortex shedder;
sensing elements integrally mounted in said thin-walled cylindrical
tube for converting a small pressure variation acting on said pressure
receiving plate to an electrical signal;
a flexible tubular member rigidly connected to the mounting flange
coaxially with the thin-walled cylindrical tube in such a manner
as to surround the thin-walled cylindrical tube;
a hermetically sealed elastic narrow tube connected at one end
to the tubular member;
a hermetically sealed terminal block connected to the other end
of the elastic narrow tube;
the electrical signal being outputted sequentially via said flexible
tubular member, said elastic narrow tube and said terminal block;
and
a protective tube slidably coupled on an outer periphery of the
terminal block and fixed in place while surrounding the flexible
tubular member, the elastic narrow tube and the mounding flange.
2. A vortex flow meter as claimed in claim 1 wherein the flexible
tubular member has a radially outwardly extending lid portion at
an end thereof, the mounting flange being provided with a recess
around an opening formed therein throughout which the thin-walled
cylindrical tube extends, said recess being formed with a bottom
portion and a stepped portion, said lid portion of the flexible
tubular member and the bottom portion of said recess being held
out of contact with each other.
3. A vortex flow meter as claimed in claim 2 wherein part of the
flexible tubular member comprises a bellows.
4. A vortex flow meter as claimed in claim 3 wherein leads extending
out from the sensing elements inside the flexible tubular element
are connected with the intermediary of an insulating material.
5. A vortex flow meter as claimed in claim 4 wherein the insulating
material comprises a hermetic seal.
6. A vortex flow meter as claimed in claim 5 wherein the elastic
narrow tube comprises a sheath wire.
7. A vortex flow meter as claimed in claim 1 wherein part of the
flexible tubular member comprises a bellows.
8. A vortex flow meter as claimed in claim 7 wherein part of the
flexible tubular member comprises a bellows.
9. A vortex flow meter as claimed in claim 8 wherein the insulating
material comprises a hermetic seal.
10. A vortex flow meter as claimed in claim 9 wherein the elastic
narrow tube comprises a sheath wire.
11. A vortex flow meter as claimed in claim 1 where leads extending
out from the sensing elements inside the flexible tubular element
are connected with the intermediary of an insulating material.
12. A vortex flow meter as claimed in claim 11 wherein the insulating
material comprises a hermetic seal.
13. A vortex flow meter as claimed in claim 12 wherein the elastic
narrow tube comprises a sheath wire.
14. A vortex flow meter as claimed in claim 1 wherein the insulating
material comprises a hermetic seal.
15. A vortex flow meter as claimed in claim 14 wherein the elastic
narrow tube comprises a sheath wire.
16. A vortex flow meter as claimed in claim 1 wherein the elastic
narrow tube comprises a sheath wire.
Description BACKGROUND OF THE INVENTION
The present invention relates to a vortex flow meter for measuring
a flow rate of a fluid based on Karman vortex streets, or vortex
trains.
A vortex flow meter is well known in the flow measurement art in
which a vortex shedding member is positioned across a passageway
inside a conduit through which a fluid flows. The velocity or flow
rate of the fluid in the conduit is measured by sensing pressure
variations of the fluid caused by vortex trains. In this kind of
flow meter, mechanical and other vibrations attributable to mechanical
vibrations of the conduit, turbulent flows of the fluid itself,
pulsation of a pump, and the like are apt to appear as errors in
an output signal of the flow meter. For the compensation of such
errors in measurement, it has been practiced to use a sensor responsive
to mechanical vibrations and a sensor responsive to vortex trains
and provide a difference between output signals of the two sensors.
The problem with such an approach is that the two sensors are constructed
integrally with each other but separately from the vortex shedding
member and, therefore, have to be assembled independently of the
latter. Especially, where the flow meter is small size, difficulty
is encountered in machining and assembling it, resulting in an inefficient
procedure. Another problem is that since the pressure variation
due to a vortex train is proportional to the square of a flow rate,
the flow meter needs be responsive to a wide range of pressures
and, hence, its sensitivity is very low when flow rate is small.
Such has hitherto been coped with by using a preamplifier having
a gain which is small for large flow rates and large for small flow
rates, i.e. a substantially constant total gain. However, the preamplifier
with such a characteristic is susceptive to externally derived vibrations
of low frequencies which constitute a source of noise. Attempts
have been made to provide a stably operable vortex flow meter by
compensating for the external vibrations or allowing a minimum of
external vibrations to effect the measurement.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
vortex flow meter capable of effectively compensating for errors
in measurements due to external noise.
It is another object of the present invention to provide a vortex
flow meter suitable for measurement of small flow rates.
It is another object of the present invention to provide a vortex
flow meter capable of being installed with ease in a conduit through
which a fluid is flowing.
It is another object of the present invention to provide a vortex
flow meter which is fixed to a conduit fulcrumed at an intermediate
portion of a vibration sensing element, which carries a vortes shedding
member at an end thereof, and provided with a vortex sensor at a
lower portion of the vibration sensing element and an external vibration
sensor in an upper portion of the same, thus having the vortex shedding
member and the vibration sensing element assembled integrally with
each other.
It is another object of the present invention to provide a vortex
flow meter furnished with an improved structure for allowing a minimum
of external vibrations to act thereon.
It is another object of the present invention to provide a generally
improved vortex flow meter.
In one aspect of the present invention, there is provided a vortex
flow meter having a conduit and a vortex sensing body which is detachably
mounted in the conduit through a seal portion. The flow meter comprises
a vortex shedding member, a vortex signal sensor, a fixing flange
and an external vibration sensor which are sequentially and integrally
arranged to constitute the vortex sensing body, the vortex sensing
body being rigidly connected to the conduit at the fixing flange,
the vortex signal sensor and the external vibration sensor being
interconnected in such a manner as to cancel an externally derived
vibration which acts on the vortex sensing body.
In another aspect of the present invention, there is provided a
vortex flow meter comprising a thin-walled cylindrical tube extending
throughout a center of a mounting flange and provided with a pressure
receiving plate at a lower end thereof, sensing elements integrally
mounted in the thin-walled cylindrical tube for converting a small
pressure variation acting on the pressure receiving plate to an
electrical signal, a flexible tubular member rigidly connected to
the mounting flange coaxially with the thin-walled cylindrical tube
in such a manner as to surround the thin-walled cylindrical tube,
a hermetically sealed elastic narrow tube connected at one end to
the flexible tubular member, a hermetically sealed terminal block
connected to the other end of the narrow tube, the electrical signal
being outputted sequentially via the flexible tubular member, the
elastic narrow tube and the terminal block, and a protective tube
slidably coupled on an outer periphery of the terminal block and
fixed in place while surrounding the flexible tubular member, the
elastic narrow tube and the mounting flange.
In accordance with the present invention, a vortex flow meter includes
a vibration sensing element having a sensor responsive to an external
vibration and a sensor responsive to a vortex train at vertically
opposite ends thereof. The sensing element is fixed to a conduit
fulcrumed at an intermediate portion thereof. A vortex shedding
member is integrally and oscillatably mounted in a lower portion
of the sensing element. The flow meter can be assembled merely by
being positioned in the conduit and, due to an integral structure,
it is effectively applicable even to small diameter conduits through
which fluids flow at very small flow rates. In a path along which
leads from a sensor responsive to pressure variations due to vortex
trains are routed to a transducer box, vibration of the transducer
box is prevented from reaching the sensor via the leads, thereby
rendering the flow meter less susceptive to externally derived vibrations.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a section of a prior art vortex flow meter;
FIG. 2 is a section of a vortex flow meter embodying the present
invention;
FIG. 3 is a fragmentary section of another embodiment of the present
invention; and
FIGS. 4-8 are fragmentary views of modifications to the embodiment
shown in FIG. 3
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 FIG. 1 of the drawings, a conduit 2 has thereinside
a passageway 1 through which a desired fluid flows. The conduit
2 is flanged at opposite ends thereof. The prior art vortex flow
meter comprises a body 3 which is located in an intermediate position
of the conduit 2. A vortex shedding member, or shedder, 5 extends
substantially along a diameter of the passageway 1 and is free at
its lower end 5a and securely connected to the conduit 2 at its
upper end 5b. A vibration sensor assembly, generally 6 carries
sensor elements 7 responsive to a vortex signal at its lower end
portion and sensor elements 8 responsive to external vibrations
other than the vortex signal such as mechanical vibrations imparted
to the passageway 1 at its upper end portion. Specifically, the
sensor elements 7 and 8 are commonly fixed to a flexible support
member 9 by molding. The vortex shedder 5 is formed with a bore
10 in its upper portion. The lower end of the vibration sensor assembly
6 is inserted in the bore 10 to such a degree that the lower sensor
elements 7 are buried in the bore 10 together with a tongue 11
which extends from the bottom of the assembly 6. The assembly 6
is securely yet oscillatably connected to the vortex shedder 5 at
a flange 12 which is located intermediate between the ends of the
assembly 6 to serve as a fulcrum. The portion of the element inside
the bore 10 is spaced a short distance from the wall of the bore
10 while the vortex shedder 5 is provided with openings 14 at opposite
ends thereof where a vortex train will be shed.
In operation, as the vortex shedder 5 sheds a vortex train, a pressure
variation occurs in the fluid flowing through the passageway 1 and
it is communicated to the bore 10 of the vortex shedder 5 through
the openings 14. The resulting change in the condition of the fluid
inside the bore 10 is sensed by the tongue 11 so that the vibration
sensor assembly 6 is caused to swing to the right and left fulcrumed
by the flange 12. The sensor elements 7 sense such oscillation of
the assembly 6 to generate a vortex signal.
Now, mechanical vibrations originating from the turbulence caused
in the passageway 1 or turbulent flows of the fluid itself as well
as pump pulsation are often reflected by errors in a signal derived
from the vortex train, which is shed by the vortex shedder 5. In
the prior art arrangement of FIG. 1 the mechanical vibrations are
sensed by the sensor elements 8 which are disposed on the sensor
assembly 6 and above the flange 12 and, among them, those common
in direction to the movement of the vortex shedder 5 are eliminated
as error signals with special concern. Such allows only a correct
vortex signal to be picked up and, thereby the flow rate to be measured
with accuracy.
Also shown in FIG. 1 are leads 15 led out from the sensor elements
7 and 8 a molding 16 of resin, a protective tube 17 for supporting
a gauge and others at its upper end while covering the sensor assembly
6 and bolts 18 for fastening the flange 12 to the vortex shedder
5.
In the above construction, the sensor elements 8 responsive to
mechanical vibrations and the sensor elements 7 responsive to vortex
trains are built in a physically unitary structure but seprate from
the vortex shedder 5. Hence, the sensor elements 7 and 8 have to
be assembled independently of the vortex shedder 5 at the sacrifice
of efficiency. The inefficiency is particularly pronounced in the
case of a small-size vortex flow meter with a small bore 10.
Referring to FIG. 2 a vortex flow meter embodying the present
invention is shown. In FIG. 2 the same or similar structural elements
as those shown in FIG. 1 are designated by the same reference numerals
and detailed description thereof will be omitted for simplicity.
In FIG. 2 a vibration sensor assembly 6A carries a vortex shedder
5 rigidly at its lower end and has a flange 12 at its intermediate
portion. The flange 12 is fastened to a cylindrical conduit 2 by
means of bolts 18. The conduit 2 has a passageway 1 thereinside.
The flange 12 is positioned by a stepped wall 20 which is formed
at the top of a through bore 19 while a packing 21 is disposed
in a peripheral portion of the stepped wall 20. The vortex shedder
5 is enlarged in its base portions as at 22 to reduce the spacing
23 between the vortex shedder 5 and the wall of the through bore
19.
In operation, the vortex shedder 5 sheds a vortex flow in a fluid
flowing through the passageway 1 of the conduit 2 and oscillates
in proportion to a flow rate of the fluid. Sensor elements 7 in
a lower portion of the sensor assembly 6A sense the oscillation
of the vortex shedder 5.
Vibrations undesirable for measurement, such as mechanical ones
caused by the flow of the fluid and those derived externally to
act on the passageway 1 are sometimes imparted to the passageway
1 in the same direction as the oscillation of the vortex shedder
5. Such a kind of vibrations obviously appear as an error signal
and, therefore, need be eliminated. This is implemented in the illustrative
embodiment by upper sensor elements 8 on the sensor assembly 6A.
Specifically, the sensor elements 8 constantly sense the undesirable
vibrations so that their output is subtracted as an error from that
of the lower sensor elements 7 i.e. vortex signal. The vortex flow
meter, therefore, succeeds in accurately measuring a flow rate all
the time. Meanwhile, the vortex flow meter can be readily assembled
by fixing the sensor assembly 6A to the conduit 2 with a fulcrum
defined between the upper and lower sensor elements 7 and 8 and
rigidly connecting the vortex shedder 5 to the bottom of the element
6A. In addition, due to the unitary structure, the vortex flow meter
may easily be designed for use with small diameter conduits in which
fluids flow at very small flow rates.
Referring to FIG. 3 another embodiment of the present invention
is shown which is provided with a unique structure for preventing
externally derived vibrations from acting on electrical signals,
which are output from sensor elements and passed through leads,
and reaching a sensor unit to appear as noise in a pressure signal.
In FIG. 3 a sensor is shown as being mounted in a conduit and
in a section as viewed in a direction perpendicular to a direction
in which a pressure variation acts on the sensor. The reference
numeral 31 designates a flange. A cylindrical tube 32 having a relatively
thin wall extends throughout the flange 31 and has a pressure receiving
plate 35 at its bottom. The flange 31 is fastened to a vortex flow
meter 50 by screws 44. A vortex train originating from the flow
of a fluid in the conduit develops a delicately pressure variation
which is imparted to the pressure receiving plate 35 via openings
51 to act on the thin-walled tube 32. The force acting on the tube
32 is transformed by sensor elements 34 such as piezoelectric elements
into a quantity of electricity which is then led out of the tube
32 by leads 37. An insulating material 36 such as resin or glass
fills the space between the tube 32 and the sensor elements 34.
The electrical signal generated as stated above is coupled to insulated
thin lines 38 and, therefrom, to an input terminal of an amplifier
(not shown) inside a transducer box 70 via terminals 41 of external
leads. These leads are connected to the sensor elements 34 within
the flexible tube 33 and to the terminals 41 of the external leads
within a hermetically sealed terminal block 40. A thin-walled elastic
narrow tube 39 made of stainless steel or the like is hermetically
sealed and rigidly connected at one end to the tube 33 and at the
other end to the terminal block 40 by welding, for example. In this
particular embodiment, the elastic narrow tube 39 comprises a sheath
wire. The other end of the hollow tube 33 is fixed to the flange
31. Inside the terminal block 40 as inside the tube 32 an insulating
material such as resin or glass sealingly retains the leads. The
outer periphery of the terminal block 40 is slidably and sealingly
retained by a protective tube 60 with the intermediary of an elastic
sealing member 42. The other end of the protective tube 60 is rigidly
connected to the vortex flow meter 50 while embracing the flange
31. The transducer box 70 is fastened to the protective tube 60
by screws 43 while covering the outer periphery of an upper portion
of the latter. Therefor, the displacement of the transducer box
70 caused by an external vibration is absorbed at the box side and
the sensor elements 34 are not affected by the external vibration.
While the sensor elements 34 in the illustrated embodiment have
been described as transforming a delicate pressure variation acting
on the plate 35 into a quantity of electricity, it may additionally
feature a function of compensating an external vibration other than
the delicate pressure variation.
Referring to FIGS. 4-7 various modifications to the embodiment
shown in FIG. 3 are shown. In these modifications, it is to be noted
that the thin tube 32 extends throughout the flange 31 in a fashion
similar to that shown in FIG. 3 though FIGS. 4 to 7 illustrates
these elements in such a manner as to be constructed integrally
with each other. In FIG. 4 the flexible tube 33 is provided with
a radially outwardly extending lid portion 47 at its lower end for
the purpose of farther reducing the bending strength of the tube
33. The flange 31 on the other hand, is provided with a recess
45 around an opening formed therein throughout the cylindrical tube
32 extends. The process 45 comprises a bottom portion 45a and a
stepped portion 45b. The lid portion 47 of the tube 33 is rigidly
connected to the stepped portion 45b of the flange 31 by an electron
beam or like fusing means while being prevented from contacting
the bottom portion 45a of the recess 45 of the flange 31. With such
a structure the tube 33 attains a decrease in bending strength due
to a longer arm of bending moment.
In FIG. 5 the smaller bending strength described above with reference
to FIG. 4 is implemented by a bellows 48 which forms part of the
flexible tube 33. Although the bellows 48 is shown in an intermediate
position of the tube 33 It may be positioned adjacent to the upper
or lower end of the tube 33 in which case the bending strength will
become even smaller than one attainable with the FIG. 4 structure.
In FIG. 6 a hermetic seal 80 is disposed in the flexible tube
33 in order to retain the thin lines 38 so that the latter may be
prevented from toughing the inner wall of the tube 33 to detriment
the insulation. The thin lines 38 extending from the sensor elements
34 are connected to the elastic narrow tube 39 by leads 81 which
are insulated from each other by an insulator 82.
The modification shown in FIG. 7 is a combined version of the modifications
described above with reference to FIGS. 4-6.
Constructed as discussed above, the second embodiment of the present
invention is hardly effected by externally derived vibrations and,
therefore, operable with stability in sensing vortex trains. This
is because, although the moment developed by the protective tube
60 and transducer box 70 is transformed into a moment which is imparted
through the elastic narrow tube 39 that moment acts on the flexible
tubular member 33 and only the force transmitted through the leads
38 is allowed to act on the sensor elements 34.
Still another modification to the embodiment of FIG. 3 is shown
in FIG. 8. As shown, the protective tube 60 is fastened at its lower
end to the flow meter 50 by means of screws 91 and 92 while being
spaced from the latter as at 93 and 94. The spaces 93 and 94 are
effective to damp mechanical vibrations. The vortex shedder in accordance
with this particular modification is provided with openings 95 for
removing bubbles and openings 96 for removing impurities such as
dust, in addition to the pressure variation inlet openings 51. The
reference numeral 97 in FIG. 8 designates a packing or an O-ring.
The O-ring 97 is fitted in an annular recess 98 which is formed
in the flow meter 50. The flange 31 is provided with an annular
projection 31a which is engaged in the recess 98 to positively position
the flange 31 relative to the flow meter 50. |