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DESCRIPTION JP2003270012

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DESCRIPTION JP2003270012
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer for transmitting and receiving ultrasonic pulses and an ultrasonic
flowmeter for measuring the flow rate of gas or liquid using the ultrasonic transducer.
[0002]
2. Description of the Related Art An ultrasonic transducer used in a conventional ultrasonic
flowmeter of this type is known, for example, from Japanese Patent Publication No. 6-500389,
and as shown in FIG. The piezoelectric body d which transmits / receives an ultrasonic pulse in
electrode surface b, c is included, and the piezoelectric body d is enclosed by the matching layer
a which consists of an epoxy resin and a micro glass sphere shared as a case.
[0003]
In addition, as shown in FIG. 10, the ultrasonic transducer known in Japanese Patent Application
Laid-Open No. 11-64058 includes a piezoelectric body d enclosed in a metal hollow cylindrical
case e and a top portion of the case e. The piezoelectric body d is adhered and fixed to the inner
surface by an epoxy resin or the like.
Then, a sealed space i is formed by joining the terminal plate h having the terminals f and g and
the case e, and the electrode surface b is electrically connected to the terminal f via the case e
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and the terminal plate h. The face c is electrically connected to the terminal g. The terminals f
and g are electrically isolated by the insulating portion j. Therefore, when the ultrasonic
transducer is attached to the flow path as an ultrasonic flow meter, the pair of electrode surfaces
b and c of the piezoelectric body d are formed of a case from a flammable measured fluid such as
LP gas or natural gas. The structure is shielded by e.
[0004]
However, in the conventional configuration shown in FIG. 9, a case a of an ultrasonic transducer
for transmitting and receiving ultrasonic waves while in contact with a combustible fluid to be
measured is made of an epoxy resin having microporosity. It is conceivable that the flammable
measured fluid penetrates through the case a because it is formed of fine glass spheres.
Therefore, when such an ultrasonic transducer is used as an ultrasonic flow meter, if a discharge
occurs when a high voltage is applied to the piezoelectric body d for some reason, the intrusive
flammable fluid to be measured is There is a problem that there is a risk of fire.
[0005]
Further, in the conventional configuration shown in FIG. 10, since the piezoelectric body d
enclosed in the hollow cylindrical case e is shielded from the flammable measured fluid, it is used
as an ultrasonic flowmeter. There is no problem in safety because there is no risk of ignition even
if discharge occurs in the enclosed space i.
[0006]
However, in the manufacturing process of the ultrasonic transducer, it is very difficult in mass
production processing to make the top portion of the case e uniform and flat in thickness.
In addition, when the thickness of the top portion is uneven and the flatness varies, the
characteristics of the ultrasonic transducer become uneven, and in the case of an ultrasonic flow
meter that performs measurement using such an ultrasonic transducer There is a problem that
the measurement accuracy is lowered. Furthermore, when the piezoelectric body d is adhered to
the case e with an epoxy adhesive in the manufacturing process, the characteristics of the
ultrasonic transducer become nonuniform also due to the variation of the thickness of the
adhesive layer, and this is used It causes the measurement accuracy of the ultrasonic flowmeter
to be reduced.
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[0007]
Therefore, the present invention solves the above-mentioned conventional problems, and an
ultrasonic transducer having uniform characteristics with a simple shield structure, and an
ultrasonic wave capable of performing flow measurement with high accuracy and safety using
this ultrasonic transducer. It aims to provide a flow meter.
[0008]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has a
piezoelectric body for transmitting and receiving ultrasonic pulses on a pair of opposing
electrode surfaces, and in a flow path through which a flammable fluid to be measured flows. In
the ultrasonic transducer to be attached, the outer surface of the piezoelectric body is sealed by a
seal member so that at least one electrode surface is shielded from the combustible fluid to be
measured.
[0009]
According to the ultrasonic transducer of the above invention, the piezoelectric member or one
electrode surface of the piezoelectric member is shielded from the flammable fluid to be
measured by the seal member. When a high voltage is applied to the piezoelectric body, etc.,
there is no possibility of ignition even if discharge occurs in the shielded space, and safety can be
ensured.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION An ultrasonic transducer according to a first
aspect of the present invention has a piezoelectric body for transmitting and receiving ultrasonic
pulses on a pair of opposing electrode surfaces, and a flow path through which a flammable fluid
to be measured flows. An ultrasonic transducer attached to the housing, the outer surface of the
piezoelectric body being sealed by a seal member such that at least one of the electrode surfaces
is shielded from the combustible fluid to be measured; Or, since one of the electrode surfaces is
shielded from the flammable fluid to be measured, when this is used as an ultrasonic flow meter,
the shielded space, for example, when a high voltage is applied to the piezoelectric material for
some reason Even if discharge occurs inside, there is no risk of ignition and safety can be
ensured.
[0011]
An ultrasonic transducer according to a second aspect of the present invention is the ultrasonic
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transducer according to the first aspect, including a caseless cylindrical shape, and the seal
member is provided between the inner surface of the case and the outer surface of the
piezoelectric body. Compared to the conventional example in which the piezoelectric body is
enclosed in a hollow cylindrical case and adhered to the inner surface of the upper portion with
an adhesive, the thickness of the upper portion is made uniform or flat as compared with the
conventional example. Since it does not require time and effort, it is suitable for mass production,
and there is no problem that the characteristics become uneven due to variations in flatness and
thickness of the adhesive layer.
[0012]
An ultrasonic transducer according to a third aspect of the present invention is the ultrasonic
transducer according to the second aspect, wherein the electrode surface on the non-sealing side
of the piezoelectric body not sealed by the sealing member is a non-cylindrical case. It is
electrically connected, and can be made excellent in the above-mentioned ultrasonic
characteristics with a simple configuration that can be easily manufactured.
[0013]
An ultrasonic transducer according to a fourth aspect of the present invention is the ultrasonic
transducer according to the first aspect, wherein the ultrasonic transducer is attached to a
transducer attachment hole provided on a side wall of the flow path, and the seal member Is
interposed between the outer surface of the piezoelectric body and the vibrator mounting hole,
and a shield structure without a possibility of ignition can be realized with a simple configuration
in which a case containing the piezoelectric body is unnecessary.
[0014]
In the ultrasonic transducer of the fourth embodiment, when the side wall of the flow path has
conductivity, the electrode surface on the non-sealing side of the piezoelectric body as the
ultrasonic transducer of the fifth embodiment of the present invention Can be electrically
connected to the side wall.
[0015]
An ultrasonic transducer according to a sixth aspect of the present invention is the ultrasonic
transducer according to any one of the first, second and fourth aspects, wherein the electrode
surface on the non-sealing side of the piezoelectric body is sealed with a seal member. It is
extended to the sealing side to be stopped and electrically connected. When used as an ultrasonic
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flowmeter, the shield effect by the seal member can reduce the influence of noise and improve
the accuracy.
Moreover, in the first and second embodiments, the handling is easy without fear of cutting lead
wires in the manufacturing process of the ultrasonic transducer, so that it is suitable for mass
production and the case does not become an external electrode. Therefore, when the ultrasonic
flowmeter is attached to the side wall of the flow path, the risk of discharge can be eliminated to
achieve safety.
[0016]
An ultrasonic transducer according to a seventh aspect of the present invention is the ultrasonic
transducer according to any of the first to sixth aspects, wherein an acoustic matching layer is
provided on the non-sealing side electrode surface of the piezoelectric body. Yes, the sensitivity
of the ultrasonic transducer can be improved.
[0017]
The ultrasonic flowmeter according to the present invention comprises a flow rate measuring
unit for measuring the flow rate of a flammable measured fluid flowing in a flow passage, and a
pair of any one of the first to seventh embodiments provided in the flow rate measuring unit. An
ultrasonic transducer, a measurement circuit for measuring an ultrasonic wave propagation time
between the ultrasonic transducers, and a flow rate calculation circuit for obtaining a flow rate
based on a signal from the measurement circuit are provided.
According to this ultrasonic flowmeter, as described above, any electrode surface is shielded from
the flammable measured fluid by the seal member, and the flammable measured fluid is ignited
by the discharge in the shielded space. By using an ultrasonic transducer with no possibility, a
highly safe ultrasonic flowmeter can be obtained.
In addition, even in the case of an ultrasonic transducer having a case, there is no need for
processing of the upper portion and adhesion of the piezoelectric body to the upper portion, so
the ultrasonic transducer does not have variations in flatness or adhesive layer and has
characteristics. By becoming uniform, it is possible to measure the flow rate with high accuracy.
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[0018]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present
invention will now be described with reference to FIGS.
[0019]
FIG. 1 is a schematic block diagram of an ultrasonic flowmeter using an ultrasonic transducer
shown in each embodiment described later of the present invention.
In FIG. 1, 1 is a flow path through which a flammable measurement fluid such as LP gas or
natural gas flows, 2 is a flow rate measuring unit for measuring the flow rate of the fluid flowing
through the flow path 1, 3A and 3B are flow Ultrasonic transducers mounted on the side walls 4,
4 of the passage 1 so as to be opposed to the flow passage 1 in the transducer mounting holes 5,
5 to transmit and receive ultrasonic waves, and 6 is an ultrasonic transducer 3A, A measurement
circuit for measuring the ultrasonic wave propagation time between 3B and 7 is a flow rate
calculation circuit for obtaining a flow rate based on a signal from the measurement circuit 6.
[0020]
The operation of the ultrasonic flowmeter in the flow rate measuring unit 2 configured as
described above will be described.
In the present embodiment, the combustible fluid to be measured is mainly LP gas, and a
household gas meter is assumed as an ultrasonic flow meter, and the material constituting the
flow rate measuring unit 2 is an aluminum alloy die cast.
[0021]
Let L be the distance connecting the centers of the ultrasonic transducers 3A and 3B, and θ be
the angle between this straight line and the longitudinal direction of the flow path 1, which is the
flow direction.
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Further, the velocity of sound in a windless state of the fluid is denoted by C, and the flow
velocity of the fluid in the flow passage 1 is denoted by V.
The ultrasonic wave transmitted from the ultrasonic transducer 3A disposed on the upstream
side of the flow rate measuring unit 2 diagonally crosses the flow path 1 and is received by the
ultrasonic transducer 3B disposed on the downstream side.
The propagation time t1 at this time is
[0022]
It is indicated by.
Next, an ultrasonic wave is transmitted from the ultrasonic transducer 3B and received by the
ultrasonic transducer 3A.
The propagation time t2 at this time is
[0023]
It is indicated by. And when the sound velocity C of the fluid is eliminated from the equations of
t1 and t2,
[0024]
The equation of is obtained. If L and θ are known, the flow velocity V can be obtained by
measuring t1 and t2 in the measuring circuit 6. From the flow velocity V, assuming that the
cross-sectional area of the flow path 1 is S and the correction coefficient is K, the flow rate
calculation circuit 7 can calculate Q = KSV to obtain the flow rate.
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[0025]
The ultrasonic transducer used for the ultrasonic flowmeter which performs flow measurement
according to the above operation principle First, Examples 1 to 4 provided with a caseless
cylindrical tube for containing a piezoelectric body are shown in FIGS. It demonstrates based on
the sectional view shown roughly.
[0026]
Embodiment 1 Embodiment 1 of the present invention will be described with reference to FIG.
In FIG. 2, the ultrasonic transducer 3 (3A and 3B) includes a piezoelectric body 8 having a pair of
opposing electrode surfaces 8a and 8b, and an external electrode terminal 9a electrically
connected to each of the electrode surfaces 8a and 8b. , 9b. The piezoelectric body 8 is airtightly
held on the inner surface of the cylindrical portion of the caseless stainless steel case 10 having
the flange portion 10a via the sealing member 11, and the electrode surface 8a is a sealing
member from LP gas. It has a structure shielded by 11. The seal member 11 is preferably an Oring made of nitrile butyl (NBR) rubber or the like resistant to LP gas.
[0027]
The non-sealed electrode surface 8b not sealed by the sealing member 11 is in contact with the
LP gas, and the acoustic matching layer 17 is adhered to the upper surface thereof. The acoustic
matching layer 17 is in the form of a disc made of an epoxy resin and fine glass spheres, and
efficiently transmits and receives ultrasonic waves in acoustic matching. With this structure, even
if the fluid to be measured is LP gas having a small acoustic impedance, the ultrasonic transducer
3 capable of transmitting and receiving ultrasonic waves with high sensitivity can be configured,
and reliability is enhanced when used as an ultrasonic flow meter .
[0028]
The electrode surface 8b is electrically connected to the case 10 by the lead wire 12, and the
outer peripheral portion 9c of the terminal plate 9 is electrically welded to the flange portion 10a
of the case 10, thereby the case 10 serving as an external electrode and the terminal The
terminal 9 b is electrically connected to the outer peripheral portion 9 c of the plate 9. The other
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electrode surface 8a is electrically joined to the terminal 9a by the lead wire 13, and an
insulating portion 14 made of glass is provided between the electrode surface 8a and the
terminal 9b to electrically insulate between the two terminals 9a and 9b. ing. The sealed space
15 formed by the case 10 and the terminal plate 9 is evacuated and replaced with an inert gas
such as nitrogen gas.
[0029]
Here, for some reason, for example, a high voltage generated by lightning is applied to the
piezoelectric body 8 through a lead wire (not shown) connecting the terminals 9a and 9b and the
measuring circuit 6, or charge is accumulated in the piezoelectric body 8 Think about the case.
When a high voltage is applied between the electrode surface 8a and the electrode surface 8b of
the piezoelectric body 8 or a very large amount of charge is accumulated, between the electrode
surface 8a and the electrode surface 8b or between the electrode surface 8a and the case 10
Discharge may occur. However, even if discharge occurs, the electrode surface 8a is shielded in
the sealed space 15 by joining the seal member 11, the case 10 and the case 10, and the terminal
plate 9, and LP gas can not penetrate into the sealed space 15. There is no fire on the gas.
[0030]
In the case where the ultrasonic transducer in which the case 10 doubles as the external
electrode is attached close to the conductive flow side wall as in the first embodiment, an
insulator may be interposed in the attachment portion, or the case and the side wall It is
preferable to set the same potential.
[0031]
(Embodiment 2) Embodiment 2 of the present invention will be described with reference to FIGS.
In the second embodiment, as in the first embodiment, the piezoelectric vibrator 8 having the
pair of electrode surfaces 8a and 8b facing each other and the external electrodes electrically
connected to the electrode surfaces 8a and 8b, respectively, as in the first embodiment. A
terminal plate 9 having terminals 9a and 9b and an acoustic matching layer 17 bonded to the
upper surface of the electrode surface 8b are provided. The piezoelectric body 8 is airtightly held
on the inner surface of the cylindrical portion of the caseless stainless steel case 10 having a
flange via the seal member 11, and the electrode surface 8 a is made of the LP gas by the seal
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member 11. It has a shielded structure.
[0032]
The second embodiment differs from the first embodiment in that the electrode surface 8b on the
non-sealing side (the side in contact with the LP gas) is extended to the sealing side to electrically
connect the lead 9 directly to the terminal 9b. It is in the connected point. In the case shown in
FIG. 3, the electrode surface 8b is extended to the side surface of the piezoelectric body 8, and in
the case shown in FIG. 4, the electrode surface 8b is extended around the electrode surface 8a.
Thus, since the electrode surface 8b extended in the enclosed space 15 and the other electrode
surface 8a are shielded, when used as an ultrasonic flowmeter, the influence of noise can be
reduced and the accuracy can be improved. it can. Moreover, since it becomes easy to handle
without fear of cutting lead wires in the manufacturing process of the ultrasonic transducer, it is
suitable for mass production, and since the case 10 does not become an external electrode, it can
be used on the side wall of the flow path as an ultrasonic flowmeter. When attached, the
possibility of discharge can be eliminated and safety can be achieved. Also in any of the second
embodiment, the other electrode surface 8a is electrically joined to the terminal 9a by the lead
wire 13, and the terminal 9b And an insulating portion 14 made of glass is provided to
electrically insulate between the two terminals 9a and 9b.
[0033]
Also in the second embodiment, a high voltage is applied between the electrode surface 8a and
the electrode surface 8b of the piezoelectric body 8 generated by lightning or the like, or a very
large amount of charge is accumulated, and the electrode surface 8a and the electrode surface 8b
When a discharge occurs between the electrode surface 8a and the case 10, the electrode surface
8a as well as the extended electrode surface 8b is in the sealed space 15 to which the LP gas can
not enter, so there is a risk of ignition due to the discharge. Can be reduced.
[0034]
Third Embodiment A third embodiment of the present invention will be described with reference
to FIG.
In the third embodiment, a liquid such as kerosene is assumed as the flammable measured fluid.
In the case of a liquid having a large fluid density, the acoustic matching layer shown in the first
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and second embodiments may not be provided because the ultrasonic wave reception efficiency
is good. Since the ultrasonic matching element 3 is not provided with the acoustic matching
layer, the measurement accuracy can be improved when used as an ultrasonic flow meter, since
there is no influence by the variation.
[0035]
Further, in each of the embodiments shown in FIGS. 2 to 5 above, since the caseless cylinder 10
is used, the thickness of the top portion is larger than that in the case where the piezoelectric
body is adhered to the conventional hollow cylinder case. This method is suitable for mass
production because it does not require time-consuming processing to make the surface uniform
or flat, and there is no problem that the characteristics become uneven due to the variation of the
flatness and the thickness of the adhesive layer.
[0036]
Embodiment 4 Embodiment 4 of the present invention will be described with reference to FIG.
In the fourth embodiment, a case for holding the piezoelectric body 8 is not provided, and the
piezoelectric body 8 is attached to the vibrator attachment hole 5 provided in the side wall 4 of
the flow path 1 via the seal member 11. In FIG. 6, it has shown with sectional drawing of the flow
volume measurement part 2 as shown in FIG.
[0037]
In FIG. 6, the transducer attachment hole 5 is provided such that the pair of ultrasonic
transducers 3A and 3B are opposed to each other in the side wall 4 of the flow passage 1
through which the LP gas, which is a flammable fluid to be measured, flows. It is done. Also in the
fourth embodiment, the sealing member 11 seals the one electrode surface 8a from the LP gas so
as to shield it from the LP gas, and the possibility of ignition due to the discharge is eliminated.
With a simple configuration that does not require a case to be enclosed, a shield structure
without the risk of ignition can be realized.
[0038]
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11
The electrode surface 8b on the non-sealing side (the side in contact with the LP gas) is provided
with the acoustic matching layer 17 and electrically connected to the conductive side wall 4 by
the lead wire 18, and the electrode on the sealing side The surface 8 a is electrically connected
by the lead wire 19. Incidentally, as shown in FIG. 3 and FIG. 4, the electrode surface 8 b can be
extended to the sealing side by the seal member 11 to be electrically connected.
[0039]
FIG. 7 shows a modification of the fourth embodiment, in which the side surface of the
piezoelectric body 8 is coated with a soft elastic material 20 such as an epoxy resin. The side
surface of the piezoelectric body 8 formed of a material such as ceramic is polished, and the
roughened surface is coated with the soft elastic material 20 to ensure the sealing function of the
sealing member 11. Is preferable because it can
[0040]
Fifth Embodiment A fifth embodiment of the present invention will be described with reference
to FIG. Also in the fifth embodiment, as in the fourth embodiment, the case for holding the
piezoelectric body 8 is not provided. Further, in the fifth embodiment, the piezoelectric body 8 is
attached to the vibrator mounting hole 5 provided to be inclined to the side wall 4 of the flow
path 1 and the sealing body for shielding the piezoelectric body 8 from LP gas. An inclined
surface formed by utilizing a part of or the like is used as the seal member 21. The piezoelectric
body 8 is attached to the vibrator attachment hole 5 by adhering to the seal member 21. In the
fifth embodiment, the acoustic matching layer 17 is provided on the fluid side of the seal
member 21.
[0041]
In the fifth embodiment, the piezoelectric member 8 is sealed by the seal member 21 so as to
shield the LP gas from the LP gas, thereby eliminating the possibility of ignition due to discharge.
Further, the electrode surface 8 b facing the flow path 1 through the seal member 21 is
electrically connected by the lead wire 23 through the conductive side wall 4, and one electrode
surface 8 a is formed by the lead wire 22. It is electrically connected.
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[0042]
The present invention can be configured in various modes other than those shown in the above
embodiment. For example, as long as one electrode surface of the piezoelectric body is shielded
from the flammable fluid to be measured by the seal member, its seal structure or shape Are not
limited to those shown in the above embodiment.
[0043]
As is apparent from the above description, according to the ultrasonic transducer of the present
invention, the piezoelectric member or one of the electrode surfaces thereof is shielded from the
flammable fluid to be measured by the seal member. When using as an ultrasonic flowmeter,
there is no possibility of ignition even if discharge occurs in a shielded space when high voltage
is applied to the piezoelectric material for some reason, etc., and safety can be ensured.
[0044]
If the above-mentioned ultrasonic transducer is made by holding the piezoelectric body by the
seal member in a caseless cylindrical case, processing time for making the thickness of the top
part uniform or flat is not required, which is suitable for mass production, The characteristics can
be made uniform without the problems caused by the flatness and the variation of the thickness
of the adhesive layer.
In addition, the electrode surface on the non-sealing side of the ultrasonic transducer can be
easily manufactured by electrically connecting it to a caseless cylindrical case.
[0045]
If the above-mentioned ultrasonic transducer is attached to the transducer attachment hole
provided on the side wall of the flow path, the piezoelectric attachment can be held by the seal
member in the transducer attachment hole, and the case containing the piezoelectric is
unnecessary. Can be realized with a simple structure that does not have the risk of fire.
[0046]
In the above ultrasonic vibrator, when the electrode surface on the non-sealing side of the
piezoelectric body is extended to the sealing side sealed by the sealing member and electrically
connected, when used as an ultrasonic flowmeter In addition, the effect of noise can be reduced
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by the shield effect by the seal member, and the accuracy can be enhanced, and in the case
equipped with the case, the handling becomes easy without the concern of cutting lead wires in
the manufacturing process of the ultrasonic transducer. Therefore, it is suitable for mass
production, and the case does not serve as an external electrode. Therefore, when the ultrasonic
flowmeter is attached to the side wall of the flow path, the possibility of discharge can be
eliminated and safety can be achieved.
[0047]
In the above ultrasonic transducer, when the acoustic matching layer is provided on the nonsealed electrode surface of the piezoelectric body, the sensitivity of the ultrasonic transducer can
be improved.
[0048]
If an ultrasonic flowmeter is configured using the above-described pair of ultrasonic transducers,
the possibility of ignition to the combustible fluid to be measured due to the discharge in the
space shielded by the seal member is eliminated, and the ultrasonic flow rate is eliminated. It is
possible to improve the safety of the
In addition, in the case of the ultrasonic transducer provided with the case, it is not necessary to
process the upper part and the adhesion of the piezoelectric body to the upper part, so that the
ultrasonic transducer does not have flatness and variation of the adhesive layer and the
characteristics become uniform. By this, it is possible to measure the flow rate with high
accuracy.
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