JP2003270012A - Ultrasonic transducer and ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic transducer made uniform in characteristic with a simple shield structure, and to provide an ultrasonic flowmeter for measuring flow rate with high accuracy and safely by using the ultrasonic transducer. <P>SOLUTION: The ultrasonic flowmeter has a piezoelectric body 8 used to transmit and receive ultrasonic pulses on a pair of mutually opposed electrode faces 8a, 8b, and is constituted by attaching the ultrasonic transducer 3 sealed with a seal member 11 to a flow channel 1 in which a combustible fluid to be measured flows, and so that at least the electrode face 8a on one side is shielded from the combustible fluid to be measured. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[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 As an ultrasonic transducer used in a conventional ultrasonic flowmeter of this type, for example, Japanese Patent Publication No. 6-500389 is known, and as shown in FIG. There is a piezoelectric body d for transmitting and receiving ultrasonic pulses on the electrode surfaces b, c, and the piezoelectric body d is enclosed by a matching layer a made of epoxy resin and micro glass spheres that are commonly used as a case.

An ultrasonic transducer known in Japanese Patent Laid-Open No. 11-64058 has a piezoelectric body d as shown in FIG.
Is enclosed in a metal-made cylindrical case e, and the piezoelectric body d is adhered and fixed to the inner surface of the top of the case e with an epoxy resin or the like. Then, the 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 and the terminal plate h, and the electrode surface c is electrically connected to the terminal g.
The terminals f and g are electrically insulated by the insulating part j. Therefore, the pair of electrode surfaces b and c of the piezoelectric body d are
When this ultrasonic transducer is attached to the flow path as an ultrasonic flow meter, it is structured to be shielded from the combustible fluid to be measured such as LP gas or natural gas by the case e.

[0004]

However, in the conventional configuration shown in FIG. 9, the case a of the ultrasonic transducer that transmits and receives ultrasonic waves while being in contact with the combustible fluid to be measured is made of an epoxy resin having microporosity. It is conceivable that the combustible fluid to be measured may penetrate through the case a because it is formed of fine glass balls. Therefore, when such an ultrasonic transducer is used as an ultrasonic flowmeter, if a discharge occurs when a high voltage is applied to the piezoelectric body d for some reason, the combustible fluid to be measured enters the fluid. There is a problem that it may catch fire.

Further, in the conventional configuration shown in FIG. 10, the piezoelectric body d enclosed in the case e having a cylindrical shape with a ceiling has a structure shielded from the combustible fluid to be measured. When this is used, even if a discharge occurs in the closed space i, there is no danger of ignition, so there is no problem in terms of safety.

However, in the manufacturing process of this ultrasonic transducer, it is very difficult to make the top of the case e uniform and flat in terms of mass production. In addition, when the thickness of the top part is non-uniform and the flatness varies, the characteristics of the ultrasonic transducer become non-uniform, and in an ultrasonic flow meter that uses such an ultrasonic transducer for measurement, However, there is a problem that the measurement accuracy decreases. Furthermore, in the manufacturing process,
When the piezoelectric body d is adhered to the case e with an epoxy adhesive, the thickness of the adhesive layer may cause variations.
This causes the characteristics of the ultrasonic transducer to become non-uniform, which causes a decrease in measurement accuracy of the ultrasonic flowmeter using the ultrasonic transducer.

Therefore, the present invention solves the above conventional problems,
An object of the present invention is to provide an ultrasonic transducer having a simple shield structure and uniform characteristics, and an ultrasonic flowmeter capable of accurately and safely measuring a flow rate using the ultrasonic transducer.

[0008]

In order to achieve the above-mentioned object, the present invention has a piezoelectric body for transmitting and receiving ultrasonic pulses on a pair of opposed electrode surfaces, and a flow path through which a combustible fluid to be measured flows. In the ultrasonic transducer to be attached, the outer surface of the piezoelectric body is sealed with a seal member so that at least one electrode surface is shielded from the combustible fluid to be measured.

According to the ultrasonic vibrator of the above invention, the piezoelectric member or one of its electrode surfaces is shielded from the combustible fluid to be measured by the seal member. Therefore, when this is used as an ultrasonic flowmeter, When a high voltage is applied to the piezoelectric body for some reason, there is no risk 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 embodiment of the present invention has a flow path through which a combustible fluid to be measured has a piezoelectric body that transmits and receives ultrasonic pulses on a pair of opposing electrode surfaces. In the ultrasonic transducer mounted on the outer surface of the piezoelectric body,
At least one of the electrode surfaces is sealed by a seal member so as to be shielded from the combustible fluid to be measured, and the piezoelectric member or one of the electrode surfaces is shielded from the combustible fluid to be measured by the sealing member. Therefore, when this is used as an ultrasonic flow meter, if a high voltage is applied to the piezoelectric body for some reason, there is no risk of ignition even if discharge occurs in a shielded space, and safety is ensured. Can be secured.

An ultrasonic oscillator according to a second aspect of the present invention is the ultrasonic oscillator according to the first aspect, which includes a case having a non-topped cylindrical shape, and the seal member includes an inner surface of the case and an outer surface of the piezoelectric body. And the piezoelectric body is enclosed in a cylindrical case with a ceiling and is adhered to the inner surface of the ceiling with an adhesive, compared with the conventional example in which the thickness of the ceiling is made uniform or flat. It is suitable for mass production because there is no need for processing, and there is no problem of uneven characteristics due to variations in flatness and adhesive layer thickness.

An ultrasonic oscillator according to a third aspect of the present invention is the ultrasonic oscillator according to the second aspect, wherein the electrode surface on the non-sealing side of the piezoelectric body which is not sealed by the sealing member is shaped like a ceiling-free cylinder. It is electrically connected to the case of (1), and can have excellent ultrasonic characteristics as described above with a simple structure that can be easily manufactured.

An ultrasonic oscillator according to a fourth aspect of the present invention is the ultrasonic oscillator according to the first aspect, which is attached to an oscillator mounting hole provided in a side wall of the flow path. The seal member is interposed between the outer surface of the piezoelectric body and the vibrator mounting hole, and a simple structure that does not require a case for enclosing the piezoelectric body can realize a shield structure without fear of ignition. .

In the ultrasonic transducer of the fourth aspect,
When the side wall of the flow path has conductivity, the electrode surface on the non-sealing side of the piezoelectric body can be electrically connected to the side wall as the ultrasonic transducer of the fifth aspect of the present invention. Is.

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. It is extended to the sealing side where it is sealed by a member and electrically connected, and when used as an ultrasonic flow meter, the effect of noise can be reduced and the accuracy can be improved due to the shielding effect of the sealing member. . Further, the first and second embodiments are suitable for mass production because they can be handled easily without worrying about cutting of lead wires in the manufacturing process of the ultrasonic vibrator, and the case does not serve as an external electrode. Therefore, when attached to the side wall of the flow path as an ultrasonic flow meter, there is no fear of electric discharge, and safety can be achieved.

An ultrasonic oscillator according to a seventh aspect of the present invention is the ultrasonic oscillator according to any one of the first to sixth aspects, wherein:
Since the acoustic matching layer is provided on the electrode surface of the piezoelectric body on the non-sealing side, the sensitivity of the ultrasonic transducer can be improved.

The ultrasonic flowmeter of the present invention has a flow rate measuring section for measuring the flow rate of the combustible fluid to be measured flowing through the flow path, and any one of the first to seventh aspects provided in the flow rate measuring section. 1
It is provided with a pair of ultrasonic transducers, a measurement circuit for measuring the ultrasonic wave propagation time between the ultrasonic transducers, and a flow rate calculation circuit for obtaining a flow rate based on a signal from this measurement circuit. According to this ultrasonic flowmeter, as described above, one of the electrode surfaces is shielded from the combustible fluid to be measured by the sealing member, and the flammable fluid to be measured is ignited by the discharge in the shielded space. By using an ultrasonic transducer that eliminates the possibility, it is possible to obtain an ultrasonic flowmeter with high safety. Further, even in the case of an ultrasonic transducer provided with a case, it is not necessary to process the top portion or to bond the piezoelectric body to the top portion, so that the ultrasonic transducer has no flatness or variation in the adhesive layer and has a characteristic. By making it uniform, the flow rate can be measured with high accuracy.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic configuration diagram of an ultrasonic flowmeter using an ultrasonic transducer shown in each embodiment of the present invention described later.
In FIG. 1, 1 is a flow path through which a combustible fluid to be measured such as LP gas or natural gas flows, 2 is a flow rate measurement unit for measuring the flow rate of the fluid flowing through this flow path 1, and 3A and 3B are flow rates. Transducer mounting holes 5 and 5 provided in the side walls 4 and 4 of the passage 1.
Is an ultrasonic transducer that is attached to face the flow path 1 to transmit and receive ultrasonic waves, 6 is a measuring circuit that measures the ultrasonic wave propagation time between the ultrasonic transducers 3A and 3B, and 7 is a measuring circuit 6 It is a flow rate calculation circuit for obtaining a flow rate based on a signal from.

The operation of the ultrasonic flow meter in the flow rate measuring unit 2 constructed as above will be described. In this embodiment, it is assumed that the combustible fluid to be measured is LP gas and the ultrasonic flow meter is a household gas meter, and the material forming the flow rate measuring unit 2 is aluminum alloy die casting.

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 direction of flow. Also, let C be the sound velocity of the fluid in a no-air state, and V be the flow velocity of the fluid in the flow path 1. The ultrasonic wave transmitted from the ultrasonic transducer 3A arranged on the upstream side of the flow rate measuring unit 2 obliquely traverses the flow path 1 and is received by the ultrasonic transducer 3B arranged on the downstream side. Propagation time t at this time
1 is

[0022]

[Equation 1] Indicated by. Next, ultrasonic waves are transmitted from the ultrasonic vibrator 3B and received by the ultrasonic vibrator 3A. Propagation time t at this time
2 is

[0023]

[Equation 2] Indicated by. Then, when the sound velocity C of the fluid is deleted from the equations of t1 and t2,

[0024]

[Equation 3] Is obtained. If L and θ are known, t is measured by the measurement circuit 6.
The flow velocity V can be determined by measuring 1 and t2. This flow velocity V
From the flow rate Q, if 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.

Regarding the ultrasonic transducer used in the ultrasonic flowmeter for measuring the flow rate based on the above-described operation principle, first, Examples 1 to 4 provided with a caseless cylindrical case for accommodating a piezoelectric body are shown in FIGS. Description will be given based on the cross-sectional view schematically shown in FIG.

(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) are provided with a piezoelectric body 8 having a pair of opposing electrode surfaces 8a, 8b and a terminal plate 9 having external electrode terminals 9a, 9b electrically connected to the respective electrode surfaces 8a, 8b. There is. The piezoelectric body 8 is hermetically held on the inner surface of the tubular portion of the caseless stainless steel case 10 having the flange portion 10a via the seal member 11, and the electrode surface 8a.
Has a structure in which it is shielded from the LP gas by the seal member 11. The seal member 11 is preferably an O-ring such as nitrile butyl (NBR) rubber having resistance to LP gas.

The electrode surface 8b on the non-sealing side which is 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. This acoustic matching layer 1
Reference numeral 7 is a disk-shaped member made of epoxy resin and micro glass spheres, which is acoustically matched and efficiently transmits and receives ultrasonic waves. With this structure, even if the fluid to be measured is LP gas having a small acoustic impedance, the ultrasonic transducer 3 that can transmit and receive ultrasonic waves with high sensitivity can be configured, and the reliability becomes high when used as an ultrasonic flowmeter. .

The electrode surface 8b is attached to the case 10 by the lead wire 12
Are electrically connected to each other, and the outer peripheral portion 9c of the terminal plate 9 is electrically welded to the flange portion 10a of the case 10, so that the terminal is provided through the case 10 also serving as an external electrode and the outer peripheral portion 9c of the terminal plate 9. It is electrically connected to 9b. The other electrode surface 8a is electrically joined to the terminal 9a by the lead wire 13, and the insulating portion 1 made of glass is formed between the electrode surface 8a and the terminal 9b.
4 is provided to electrically insulate the terminals 9a and 9b from each other. Closed space 1 formed by case 10 and terminal board 9
5 is evacuated and replaced with an inert gas such as nitrogen gas.

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 the piezoelectric body 8 is charged with electric charges. Consider the case of accumulation. When a high voltage is applied between the electrode surface 8a and the electrode surface 8b of the piezoelectric body 8 or when a very large amount of electric charge is accumulated, it is between the electrode surface 8a and the electrode surface 8b or between the electrode surface 8a and the case 10.
Discharge may occur between. However, even if a discharge occurs, the electrode surface 8a is shielded in the sealed space 15 by the joining of the seal member 11 and the case 10 and the case 10 and the terminal plate 9, and LP gas cannot enter the sealed space 15. The gas never ignites.

When the case 10 is used to mount the ultrasonic transducer, which also serves as an external electrode, in the vicinity of the flow-rate side wall having conductivity, an insulator is interposed at the mounting site, It is preferable that the case and the side wall have the same potential.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. Example 2 is similar to Example 1,
The ultrasonic transducer 3 has a piezoelectric body 8 having a pair of opposing electrode surfaces 8a and 8b, and a terminal plate 9 having external electrode terminals 9a and 9b electrically connected to the respective electrode surfaces 8a and 8b.
And an acoustic matching layer 17 adhered to the upper surface of the electrode surface 8b. The piezoelectric body 8 is hermetically held on the inner surface of the tubular portion of a stainless steel case 10 having a flange and having a ceiling and a sealing member 11, and the electrode surface 8a is LP.
The seal member 11 shields gas from the gas.

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 and is directly connected to the terminal 9b by the lead wire 16. It is in the point of being electrically connected. In FIG. 3, the electrode surface 8b extends to the side surface of the piezoelectric body 8, and in FIG. 4, the electrode surface 8b extends around the electrode surface 8a. In this way, the electrode surface 8 extended in the closed space 15
Since b and the other electrode surface 8a are shielded,
When used as an ultrasonic flow meter, the influence of noise can be reduced and accuracy can be improved. Further, since it is easy to handle without worrying about cutting of the lead wire in the manufacturing process of the ultrasonic transducer, it is suitable for mass production, and since the case 10 does not serve as an external electrode, it is used as an ultrasonic flow meter on the side wall of the flow path. It is possible to eliminate the risk of electric discharge when attached and to ensure safety. 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 is formed. An insulating portion 14 made of glass is provided between the terminals 9 and 9 to electrically insulate the terminals 9a and 9b from each other.

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 caused by lightning, or a very large amount of charge is accumulated, so that the electrode surface 8a and the electrode surface When a discharge occurs between the surfaces 8b or between the electrode surface 8a and the case 10, the extended electrode surface 8b as well as the electrode surface 8a is in the closed space 15 where LP gas cannot enter, so that the discharge is generated. The risk of ignition can be reduced.

(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 combustible fluid to be measured. In the case of a liquid having a high fluid density, the reception efficiency of ultrasonic waves is good, so the acoustic matching layer shown in Examples 1 and 2 may not be provided. Since the ultrasonic transducer 3 is not provided with the acoustic matching layer, it is possible to improve the measurement accuracy when it is used as an ultrasonic flow meter because there is no influence due to its variation.

In each of the embodiments shown in FIGS. 2 to 5, the caseless cylindrical case 10 is used. It is suitable for mass production because it does not require the work of making the thickness of the part uniform or making it flat, and there is no problem that the characteristics become uneven due to variations in flatness and thickness of the adhesive layer.

(Fourth Embodiment) A fourth embodiment 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 has the sealing member 11
Vibrator mounting hole 5 provided on the side wall 4 of the flow path 1 through
Mounted on. In FIG. 6, a cross-sectional view of the flow rate measuring unit 2 as shown in FIG. 1 is shown.

In FIG. 6, a pair of ultrasonic transducers 3A and 3B face each other in a state where the transducer mounting hole 5 is inclined with respect to the side wall 4 of the flow path 1 through which the LP gas as the combustible fluid to be measured flows. Is provided. Also in the fourth embodiment, the sealing member 11 seals the one electrode surface 8a so as to be shielded from the LP gas, thereby eliminating the possibility of ignition due to electric discharge. With a simple structure that does not require a case to enclose, it is possible to realize a shield structure without the risk of ignition.

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 is electrically connected to the conductive side wall 4 by the lead wire 18, and is sealed. The side electrode surface 8a is electrically connected by a lead wire 19. As shown in FIGS. 3 and 4,
It is also possible to extend the electrode surface 8b to the sealing side by the sealing member 11 and electrically connect it.

FIG. 7 shows a modification of the fourth embodiment, in which the piezoelectric body 8 is used.
The side surface of the is coated with a soft elastic material 20 such as an epoxy resin. Piezoelectric body 8 made of ceramic material
Since the side surface of is sealed and the roughened surface is coated with the soft elastic material 20, the sealing function of the seal member 11 can be ensured, which is preferable.

(Fifth Embodiment) A fifth embodiment of the present invention will be described with reference to FIG. Similarly to the fourth embodiment, the fifth embodiment does not include a case for holding the piezoelectric body 8. Also,
The piezoelectric body 8 is attached to the vibrator mounting hole 5 that is provided obliquely on the side wall 4 of the flow path 1, and also serves as a sealing member for shielding the piezoelectric body 8 from LP gas.
The slope formed by utilizing a part of the
I am trying. The piezoelectric body 8 is attached to the sealing member 21 to be attached to the vibrator attachment hole 5. In the fifth embodiment, the acoustic matching layer 17 is provided on the fluid side of the seal member 21.

In the fifth embodiment, the piezoelectric member 8 is sealed by the sealing member 21 so as to be shielded from the LP gas, thereby eliminating the possibility of ignition due to discharge. Further, the electrode surface 8b facing the flow path 1 via the seal member 21 is
It is electrically connected by a lead wire 23 via the side wall 4 having conductivity, and the one electrode surface 8a is connected to the lead wire 22.
Are electrically connected by.

The present invention can be configured in various modes other than that shown in the above embodiment. For example, as long as one electrode surface of the piezoelectric body is shielded from the combustible fluid to be measured by the seal member, the seal is maintained. The structure and shape are not limited to those shown in the above embodiment.

[0043]

As is apparent from the above description, according to the ultrasonic vibrator of the present invention, the piezoelectric member or one of its electrode surfaces is shielded from the combustible fluid to be measured by the seal member. When used as an ultrasonic flow meter, there is no danger of ignition even if discharge occurs in a shielded space when a high voltage is applied to the piezoelectric body for some reason,
The safety can be secured.

If the above ultrasonic transducer is a case in which a piezoelectric member is held by a seal member in a caseless cylindrical case, it is suitable for mass production because it does not require the work of making the thickness of the top uniform or making it flat. In addition, the characteristics can be made uniform without causing problems due to variations in flatness and thickness of the adhesive layer. Further, if the electrode surface on the non-sealing side of this ultrasonic vibrator is electrically connected to the caseless cylindrical case, it can be easily manufactured.

If the ultrasonic vibrator is to be mounted in the vibrator mounting hole provided in the side wall of the flow path, the piezoelectric member can be held by the sealing member in the vibrator mounting hole, and the piezoelectric member is included. With a simple structure that does not require a case, it is possible to realize a shield structure without the risk of ignition.

In the above ultrasonic oscillator, an ultrasonic flow meter is used if 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, the effect of noise can be reduced by the shielding effect of the seal member and accuracy can be improved, and with the case equipped, it can be handled without worrying about cutting of lead wires in the manufacturing process of the ultrasonic transducer. Since it is easy and suitable for mass production, the case does not serve as an external electrode. Therefore, when the case is attached to the side wall of the flow path as an ultrasonic flow meter, there is no fear of electric discharge and safety can be achieved.

In the above ultrasonic oscillator, if the acoustic matching layer is provided on the electrode surface of the piezoelectric body on the non-sealing side, the sensitivity of the ultrasonic oscillator can be improved.

By constructing an ultrasonic flowmeter using the above-mentioned pair of ultrasonic transducers, the possibility of ignition of the combustible fluid to be measured due to discharge in the space shielded by the seal member is eliminated. The safety of the ultrasonic flow meter can be improved.
In addition, since the ultrasonic vibrator with a case does not require the processing of the top part or the bonding of the piezoelectric body to the top part, the ultrasonic vibrator has uniform flatness and adhesive layer characteristics. Thus, it is possible to measure the flow rate with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an ultrasonic flowmeter using the ultrasonic transducer shown in Examples 1 to 5 of the present invention.

FIG. 2 is a sectional view schematically showing an ultrasonic transducer according to the first embodiment of the present invention.

FIG. 3 is a sectional view schematically showing an ultrasonic transducer according to a second embodiment of the present invention.

FIG. 4 is a sectional view schematically showing an ultrasonic transducer according to a modified example of the second embodiment of the present invention.

FIG. 5 is a sectional view schematically showing an ultrasonic transducer according to a third embodiment of the present invention.

FIG. 6 is a cross-sectional view schematically showing a state in which an ultrasonic transducer according to a fourth embodiment of the present invention is attached to a side wall as an ultrasonic flow meter.

FIG. 7 is a cross-sectional view schematically showing a modification of the ultrasonic transducer according to the fourth embodiment.

FIG. 8 is a sectional view schematically showing a state in which an ultrasonic transducer according to a fifth embodiment of the present invention is attached to a side wall as an ultrasonic flow meter.

FIG. 9 is a sectional view showing a conventional ultrasonic transducer.

FIG. 10 is a cross-sectional view showing another conventional ultrasonic transducer.

[Explanation of symbols]

1 flow path 2 Flow rate measurement unit 3, 3A, 3B ultrasonic transducer 4 side walls 5 Transducer mounting hole 6 measuring circuit 7 Flow rate calculation circuit 8a, 8b electrode surface 8 Piezoelectric body 10 cases 11, 21 Seal member 17 Acoustic matching layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yukinori Ozaki             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Masato Sato             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Masahiko Ito             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 2F035 AA06 DA05 DA19                 5D019 BB01 BB12 FF01 GG01

Claims (8)

[Claims] 1. An ultrasonic transducer having a piezoelectric body for transmitting and receiving ultrasonic pulses on a pair of opposing electrode surfaces, the ultrasonic transducer being attached to a flow path through which a combustible fluid to be measured flows, the outer surface of the piezoelectric body being An ultrasonic transducer, wherein at least one electrode surface is sealed by a seal member so as to be shielded from the flammable fluid to be measured. 2. The ultrasonic transducer according to claim 1, further comprising a caseless cylindrical case, wherein the seal member is interposed between the inner surface of the case and the outer surface of the piezoelectric body. 3. The ultrasonic transducer according to claim 2, wherein the electrode surface on the non-sealing side of the piezoelectric body which is not sealed by the sealing member is electrically connected to the case having a cylindrical shape. 4. An ultrasonic vibrator mounted in a vibrator mounting hole provided on a side wall of a flow path, wherein a sealing member is interposed between an outer surface of a piezoelectric body and the vibrator mounting hole. The ultrasonic transducer according to claim 1. 5. The ultrasonic transducer according to claim 4, wherein the side wall of the flow path is electrically conductive, and the electrode surface on the non-sealing side of the piezoelectric body is electrically connected to the side wall. 6. The electrode surface on the non-sealing side of the piezoelectric body is extended to and electrically connected to the sealing side sealed by a sealing member. The ultrasonic transducer according to the item. 7. The ultrasonic transducer according to claim 1, wherein an acoustic matching layer is provided on the electrode surface of the piezoelectric body on the non-sealing side. 8. A flow rate measuring section for measuring a flow rate of a combustible fluid to be measured flowing through a flow path, and a pair of ultrasonic waves according to claim 1, which is provided in the flow rate measuring section. An ultrasonic flowmeter comprising a vibrator, a measuring circuit for measuring an ultrasonic wave propagation time between the ultrasonic vibrators, and a flow rate calculating circuit for obtaining a flow rate based on a signal from the measuring circuit.