Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
1998-09-03
2001-05-29
Noori, Max (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
Reexamination Certificate
active
06237425
ABSTRACT:
BACKGOURD OF THE INVENTION
1. Field of the Invention
The present invention relates to a Kármán vortex flowmeter for measuring the flow rate of fluid such as water.
2. Description of the Prior Art
Generally, a Kármán vortex occurs in the downstream in fluid flowing at a uniform speed. By detecting the frequency of the Kármán vortex, the flow velocity of the fluid can be measured. An example of the device for measuring the flow velocity or flow rate of the fluid using such a technique is disclosed in Japanese Patent Publn. 56-9654.
An example of previously known Kármán vortex flowmeters is shown in
FIGS. 7 and 8
. A Kármán vortex flowmeter, generally F′, includes a flowmeter body
1
, vortex generator
2
, vortex detector
4
, elastic sheath
15
, piezoelectric element
16
, etc.
A flow passage
1
a
having a circular sectional passage is formed to pass through the interior of the body
1
, and fluid passes along the flow passage
1
a
in a direction of X. A flat region
1
b
is formed at a part of the outer wall of the flowmeter body
1
. In the flat area
1
b
, a first hole
1
b
1
and a second hole
1
b
2
which communicate with the flow passage
1
a
are formed. The first hole
1
b
1
is located upstream.
The vortex generator
2
has an outer shape of a square pole and includes a shaft portion
2
a
and a head portion
2
b
fitting in the first hole
1
b
1
and engaged with the flat region
1
b
. The shaft portion
2
a
is inserted in the flow passage
1
a
from the first hole
1
b
1
. A temperature-sensitive element
3
, which is embedded in the shaft portion
2
a
of the vortex generator
2
, serves to detect the fluid flowing through the flow passage
1
a
. The temperature signal detected by the temperature-sensitive element
3
is derived through a lead wire
3
a.
The vortex detector
4
includes an insulating elastic sheath
15
and a piezoelectric element
16
. A pressure-receiving wing piece
15
a
of the elastic sheath
15
is inserted in the flow passage
1
a
from the second hole
1
b
2
.
The elastic sheath
15
is formed of elastic synthetic resin, and includes the pressure receiving wing piece
15
a
and a head portion
15
b
. The pressure receiving wing piece
15
a
hangs over upstream and downstream from the flow passage
1
a
. The head portion
15
b
is fit into the second hole
1
b
2
and engaged with the flat region
1
b
. Such an elastic sheath
15
is shown in FIG.
9
. The pressure receiving wing piece
15
a
is integrally formed with a piezoelectric element accommodating portion
15
c
which is also integrally formed with the head portion
15
b
which is a circular cylinder. The lower end
15
c
1
of the piezoelectric element accommodating portion
15
c
is flush with the lower end
15
a
1
of the pressure receiving wing piece
15
a.
As shown in
FIGS. 7 and 8
, the piezoelectric element
16
is a bimorph type element which is embedded in the piezoelectric element accommodating portion
15
c
of the elastic sheath
15
with a thermosetting insulating elastic epoxy resin
7
. A detected signal is externally derived through a lead wire
16
a.
A cover
8
is attached to the flat region
1
b
by means of a thread locker. The cover
8
includes a first thread hole
8
a
1
corresponding to the first hole
1
b
1
and a second thread hole
8
a
2
corresponding to the second hole
1
b
2
.
A first ring body
9
A is threaded with the first thread hole
8
a
1
to bring the head portion
2
b
of the vortex generator body
2
into intimate contact with the flat region
1
b
through packing
10
A, thus preventing fluid leakage. A second ring body
9
B is threaded with the first thread hole
8
a
2
to bring the head portion
15
b
of the elastic sheath
15
into intimate contact with the flat region
1
b
through packing
10
B, thus preventing fluid leakage.
An explanation will be given of the operation of the flowmeter F′ having the above configuration.
The vortex generator
2
generates the Kármán vortex in the fluid flowing in the direction of X through the flow passage
1
a
of the flowmeter body
1
. The Kármán vortex thus generated moves toward the vortex detector
4
, and alternately passes both sides of the pressure wing piece
15
a
of the elastic sheath
15
. Thus, every time the Kármán vortex passes, electric charges are generated in the piezoelectric element
16
owing to distortion force.
Therefore, the flow rate of the fluid can be measured in such a manner that the electric charges generated in the piezoelectric element
16
are derived through the lead wire
16
a
as a detected signal, the detected signal is converted into a square wave signal corresponding to a vortex frequency by a wave shaping circuit, for example, and the square wave signal is converted into a flow rate indicating output signal by a coefficient circuit or a control signal to a flow rate control device.
The temperature signal detected by the temperature-sensitive element
3
embedded in the vortex generator
2
can be used as a signal for recognizing the fluid density or fluid viscosity. Further, the temperature signal as well as the flow rate indicating output is supplied to an arithmetic unit to provide a thermal flow rate output signal.
However, the conventional vortex flowmeter having the above configuration, the detector itself generates vortexes. Since the vortexes thus generated interfere with the vortexes to be detected, the detector cannot stably detect vortexes, thus deteriorating measurement accuracy.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the problem involved with the above Kármán vortex flowmeter, and intends to provide a Kármán vortex flowmeter with high measurement accuracy capable of reducing the vortex to be generated by the detector itself to detect a vortex stably.
The invention defined in claim
1
is a Kármán vortex flowmeter comprising a vortex generator provided in a tube-like flow passage, a vortex detector having a piezoelectric element embedded in an elastic sheath having a pressure receiving wing piece, spaced apart by a prescribed distance from the vortex generator, downstream of the flow passage, wherein the vortex detector includes the pressure receiving wing piece of a square plate, and a piezoelectric element accommodating portion of a circular cylinder having a larger outer diameter than the pressure receiving wing piece, the pressure receiving wing piece protruding from an end face of the piezoelectric element accommodating portion.
The invention defined in claim
2
is characterized in that a rate of a protruding length of the pressure receiving wing piece to a total of a length of the piezoelectric element accommodating portion in an axial direction and a protruding length of the pressure receiving wing piece is 0.05-0.6.
In accordance with the invention defined in claims
1
and
2
, the vortex detector of the Kármán vortex flowmeter includes the pressure receiving wing piece of a square plate, and a piezoelectric element accommodating portion of a circular cylinder having a larger outer diameter than the pressure receiving wing piece, the pressure receiving wing piece protruding from an end face of the piezoelectric element accommodating portion.
Therefore, the Kármán vortex flowmeter according to the present invention can reduce the number of vortexes and detect vortexes stably.
REFERENCES:
patent: 4285247 (1981-08-01), Klobe
patent: 4627295 (1986-12-01), Matsubara et al.
patent: 4706503 (1987-11-01), Kamenster
patent: 4776222 (1988-10-01), Lew
patent: 4862750 (1989-09-01), Nice
patent: 56-9654 (1981-03-01), None
Kabushiki Kaisha Saginomiya Seisakusho
McDermott & Will & Emery
Noori Max
Patel Jagdish
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