JP2000180227A - Ultrasonic vortex flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance S/N ratio in an ultrasonic vortex flowmeter by reducing sneak noises which propagate through a bluff body and a meter body. SOLUTION: A measurement passage 17 is formed inside a bluff body 16 provided across the flow passage 14 of the mater body 15, the measurement passage 17 being communicated with the flow passage 14 by holes 18, 19. Ultrasonic wave transceivers 20, 21 opposite each other across the measurement passage 14 are attached to both ends of the bluff body 16. Circulation of gas in the flow passage 14 generates a Karman vortex causing fluctuation of flow velocity within the measurement passage 17. This flow is detected by means of the ultrasonic transceivers 20, 21 so as to measure the flow rate of the gas. The cylinder parts of the sensor holders 28 of the ultrasonic transceivers 20, 21 are welded together by means of coupling parts 35 into a split structure. Since ultrasonic waves propagating through the cylinder parts of the sensor holders 28 are reflected and attenuated by the boundary faces of the coupling parts 35, sneak noises which propagate through the bluff body 16 and the meter body 15 are reduced whereby S/N ratio is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic vortex flowmeter for measuring the flow rate of gas in a pipeline by detecting the occurrence of Karman vortex using an ultrasonic sensor.

[0002]

2. Description of the Related Art An example of a conventional ultrasonic vortex flowmeter will be described with reference to FIGS. As shown in FIGS. 8 to 10, the ultrasonic vortex flowmeter 1 includes a column-shaped bluff body 4 (a vortex generator) traversing the flow path 2 in a meter main body 3 forming a flow path 2 of a gas to be measured. The measurement passage 5 (internal space) is formed inside the bluff body 4. A pair of holes 6 and 7 communicating with the measurement passage 5 are opened in the bluff body 4 toward the downstream side.
On the bluff body 4, sandwich the measurement passage 5 at both ends,
A pair of ultrasonic transceivers 8 and 9 each having a piezoelectric element (ultrasonic element) are attached.

When the gas flows through the flow path 2 in the meter body 3, a Karman vortex K is generated alternately downstream of the bluff body 4 at a period corresponding to the gas flow rate, and synchronized with the Karman vortex K. The resulting gas flow is introduced into the measurement passage 5 from the holes 6 and 7, and a flow velocity change occurs in the measurement passage 5 at the same cycle as the generation cycle of the Karman vortex K. The ultrasonic wave transmitted from the ultrasonic transmitter 8 and propagated in the gas in the measurement passage 5 is modulated by the gas flow in the measurement passage 5 due to the Karman vortex K and received by the ultrasonic receiver 9. The modulated component is extracted by a phase comparator or the like, and the Karman vortex K is extracted.
The flow rate of the gas in the flow path 2 can be obtained by detecting the generation cycle of the flow.

At this time, a part of the ultrasonic wave transmitted from the ultrasonic transmitter 8 propagates through the bluff body 4 and the meter main body 3 and is received by the ultrasonic receiver 9 as a noise component (the ultrasonic wave goes around). However, since the ultrasonic wave propagates much more easily in the solid such as the bluff body 4 and the meter main body 3 than in the gas to be measured, the ultrasonic wave propagates through the bluff body 4 and the meter main body 3. The wraparound noise increases, the S / N ratio (signal / noise ratio) decreases, and it becomes difficult to detect a stable Karman vortex.

Therefore, conventionally, as shown in FIG. 10, the bluff body 4 is attached to the meter body 3 via an O-ring 10 which is an elastic body, and the ultrasonic transceivers 8 and 9 (since they have the same configuration, By attaching an ultrasonic transmitter 8 (shown only) to the bluff body 4 via an O-ring 11 and a packing 12, which are elastic members, leaked ultrasonic waves propagating to the meter main body 3 and the bluff body 4 are attenuated. Was.

[0006]

However, the conventional ultrasonic vortex flowmeter has the following problems. The meter body, the bluff body, and the ultrasonic transceiver are fastened to each other by bolts or the like, so that leaked ultrasonic waves propagate between the members via these bolts or the like, so that it is not possible to sufficiently shut off sneak noise. . In particular, when the fluid to be measured is at a high pressure, it is necessary to provide a large number of bolts and the like in order to increase the fastening force of each member, and there has been a problem that sneak noise easily propagates.

The present invention has been made in view of the above points, and provides an ultrasonic vortex flowmeter capable of reducing sneaking noise by attenuating leaking ultrasonic waves propagating through a meter body and a bluff body. The purpose is to do.

[0008]

In order to solve the above-mentioned problems, the invention according to claim 1 includes a flow path through which a fluid to be measured flows;
A hole is provided in the peripheral wall portion for generating a Karman vortex on the downstream side and having an internal space provided in the flow path, and for introducing a flow of the fluid to be measured in synchronization with the Karman vortex into the internal space. An ultrasonic vortex flowmeter comprising a vortex generator, and a pair of ultrasonic transceivers arranged with a fluctuation region caused by the flow of the fluid to be measured introduced into the internal space of the vortex generator. At least one of the pair of ultrasonic transceivers has a substantially cylindrical shape with a bottom, and has a holder on the bottom of which an ultrasonic element is mounted. It is characterized in that the above members are joined and formed.

With this configuration, the ultrasonic wave transmitted from the ultrasonic element to the holder is reflected and attenuated by the boundary surface formed by the coupling portion of the holder cylindrical portion.

According to a second aspect of the present invention, in the ultrasonic vortex flowmeter according to the first aspect, at least one coupling portion of the holder is set at a position serving as a node of vibration. And

With this configuration, the bottom of the holder is easily vibrated at the frequency of the ultrasonic wave from the joint of the holder serving as the node.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

A first embodiment of the present invention will be described with reference to FIGS. As shown in FIGS. 1 and 2, the ultrasonic vortex flowmeter 13 is used to flow a gas as a fluid to be measured.
A column-shaped bluff body 16 is pierced through a substantially cylindrical meter main body 15 forming the pipe 14 in a diametrical direction across the flow path 14. A measurement passage 17 (internal space) penetrates the bluff body 16 along its length, and a pair of holes 18, 19 for communicating the flow passage 14 of the meter body 15 with the measurement passage 17 is formed in the side wall. Are open toward the downstream side. At both ends of the bluff body 16, a pair of ultrasonic transceivers 20, 21 facing each other across the measurement passage 17 are attached.

At both ends of the bluff body 16, flange portions 2 are provided.
2 and 23 are formed, and the ultrasonic transceivers 20 and 21 are formed with flange portions 24 and 25, respectively.
The bluff body 16 and the ultrasonic transceivers 20 and 21 are connected to the meter main body 15 by bolts 27 with a packing 26 interposed therebetween and between the flange portions 23 and 25, respectively.

The ultrasonic transmitters / receivers 20, 21 have the same structure (only the ultrasonic transmitter 20 is shown in FIG. 2), and a piezoelectric element 29 (ultrasonic) is provided at the bottom in a substantially bottomed cylindrical sensor holder 28. Sound element) is bonded with an acoustic bonding agent such as a silicone adhesive or an epoxy resin. In addition, the piezoelectric element 29 has P
Lead wire 30 such as TFE wire or urethane wire is connected,
The terminal 31 of the electrode to which the lead wire is connected is joined to the lid member 32 by a hermetic seal.
Is attached to the opening of the sensor holder 28 by adhesion, welding, screwing, or the like, so that the sensor holder 28 is airtightly sealed.

The sensor holder 28 includes a sensor mounting portion 33 having a bottom portion and a bluff body mounting portion having flange portions 24 and 25.
34 has a two-part structure in which two cylindrical parts are combined. The sensor attachment portion 33 and the bluff body attachment portion 34 are connected by welding (TIG welding, laser welding, resistance welding, or the like), brazing, bonding, or the like. The coupling portion 35 formed by this coupling has a different propagation characteristic (acoustic impedance) of the ultrasonic wave from the other portions of the sensor holder 28,
An acoustic boundary surface is formed in the joint 35. Therefore,
Coupling part 35, sensor mounting part 33 and bluff body mounting part 34
Ultrasonic waves transmitted from the piezoelectric element 29 and propagating through the cylindrical portion of the sensor holder 28 are reflected and attenuated at the boundary surface between them. As shown in FIG. 6, the dimensions of each part of the sensor holder 28 are as follows, where λ is the wavelength of the ultrasonic wave to be transmitted and received.
The diameter of the bottom is λ / 2, and the distance from the bottom to the joint 35 is λ
/ 2. By setting these dimensions, when the piezoelectric element 29 vibrates, the coupling portion
The sensor holder 28 vibrates with 35 as a node.

The operation of the embodiment constructed as above will be described below.

The piezoelectric element 29 of the ultrasonic transmitter 20 is vibrated by an electric signal from a sensor drive circuit (not shown) to transmit ultrasonic waves from the bottom of the sensor holder 28, and the ultrasonic wave is transmitted through the measurement passage 17 of the bluff body 16. The transmitted ultrasonic wave is transmitted to the ultrasonic receiver 21
Received by the piezoelectric element 29 and converted into an electric signal. When the gas to be measured flows through the flow path 14 of the meter main body 15, Karman vortices are generated alternately downstream of the bluff body 16 at a period corresponding to the flow velocity. The gas flow synchronized with the Karman vortex is introduced into the measurement passage 17 from the holes 18 and 19, and the flow velocity changes in the measurement passage 17 at the same cycle as the Karman vortex generation cycle. Due to the change in the flow velocity, the ultrasonic wave propagating in the measurement passage 17 undergoes modulation according to the generation cycle of the Karman vortex. Therefore, by extracting the modulation amount of the ultrasonic wave by using a phase comparator or the like (not shown), The generation period of the Karman vortex can be detected based on this modulation, and the gas flow rate can be obtained.

At this time, in the sensor holder 28, the sensor mounting portion 33 and the bluff body mounting portion 34 are connected by the connecting portions 35 having different tissues (acoustic impedance).
For ultrasonic waves propagating through the cylindrical portion of the sensor holder 28, the interface between the sensor mounting portion 33 and the bluff body mounting portion 34 and the coupling portion 35 becomes an acoustic obstacle, and attenuation (reflection and scattering) of sound waves occurs. The leakage ultrasonic wave transmitted to the bluff body 16 and the meter main body 15 is reduced. In addition, the joint 35
Is set to be a node of the vibration by the piezoelectric element 29, so that the sensor holder 28 vibrates as shown by a broken line in FIG.

When the fluid to be measured is a gas, a solid,
Since sound velocity and density are lower than liquid, acoustic impedance is small and ultrasonic wave transmittance is low, so a large sound pressure is required. Also, due to the low sound speed, ultrasonic transmission
It is necessary to use a low frequency in order to prevent that the phase difference generated while the ultrasonic wave transmitted from the ultrasonic receiver 21 is received by the ultrasonic wave receiver 21 exceeds ± 2π and the flow rate cannot be detected. Therefore, the piezoelectric element 29 has a low frequency (1
A unimorph-type element that causes large radial vibration at the next mode frequency) is used.

When this unimorph type piezoelectric element 29 is attached to the bottom of the sensor holder 28 and vibrated in the radial direction (FIG. 7).
7 (a)), the bottom of the sensor holder 28 is deformed in the height direction of the sensor holder 28 as shown in FIG. 7 (b) (when contracted) and FIG. 7 (c) (when extended) due to the expansion and contraction. Due to this deformation, the ultrasonic vibration can be directly transmitted to the gas, so that an ultrasonic wave having a large sound pressure at a low frequency can be transmitted and received.

If the dimensions of the sensor holder from the connecting portion 35 to the bottom are set to the dimensions shown in FIG. 6, the sensor holder 28 vibrates (deforms) from the connecting portion 35 to the bottom using the connecting portion 35 as a node. ), And a vibration with a large sound pressure can be obtained with a small voltage. It should be noted that the diameter of the bottom and the distance from the bottom to the coupling portion 35 do not necessarily have to be λ / 2, but may be an integral multiple of this. Further, depending on other conditions, each of the diameter of the bottom of the sensor holder 28 and the distance from the bottom to the coupling portion 35 is not necessarily λ / 2.
It is not necessary to be an integral multiple of, and it is sufficient that the joint is set so that a node of vibration comes.

The noise reduction due to the attenuation of the leaked ultrasonic wave due to the acoustic boundary formed at the joint 35 and the increase in the signal due to the improvement of the efficiency of the vibration at the joint 35 increase the S / N ratio. Improved and stable detection of Karman vortices can be performed, and flow measurement accuracy can be increased.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. Note that the second embodiment has substantially the same structure as the first embodiment except that the structure of the sensor holder of the ultrasonic transceiver is different. Therefore, the first embodiment shown in FIGS. 1 and 2 will be described below. The same parts as those of the embodiment are denoted by the same reference numerals, and only different parts will be described in detail.

As shown in FIGS. 3 and 4, in the ultrasonic eddy flow meter 36 of the second embodiment, the sensor holders of the ultrasonic transceivers 37 and 38 (only the ultrasonic transmitter 37 is shown in FIG. 3). 39
Has a three-part structure in which a cylindrical sensor adapter 40 is connected between the sensor mounting part 33 and the bluff body mounting part 34. The sensor mounting portion 33, the bluff body mounting portion 34, and the sensor adapter 40 are connected in the same manner as in the first embodiment, and connecting portions 41, 42 having different ultrasonic wave propagation characteristics (acoustic impedance) are formed therebetween. Have been.

Then, as much as the sensor adapter 40 is connected,
The height of the sensor holder 39 in the height direction is increased, and the tip of the sensor holder 39 is moved to the measurement passage of the bluff body 16.
17, the distance L ₁ between the ultrasonic transceivers 37 and 38 and the holes 18 and 19 with respect to the diameter D of the flow path 14 of the meter body 15.
The distance L ₂ between are reduced.

With this configuration, two coupling portions 41 and 42 serving as an acoustic obstacle layer are formed in the sensor holder 39, and the ultrasonic waves leaking to the bluff body 16 and the meter main body 15 are transmitted to the first holder. It can be further reduced than that of the embodiment.

Sensor mounting part 33 and bluff body mounting part
34 is common to that of the first embodiment, and sensor holders 39 having various axial dimensions can be manufactured by combining with sensor adapters 40 having different axial dimensions. Cost can be reduced. Here, the processing accuracy of the mounting surface of the piezoelectric element 29 at the bottom of the sensor holder 39 greatly affects the transmission / reception characteristics of ultrasonic waves. However, in the case of a conventional integrated sensor holder, when the axial dimension is increased, the processing accuracy is reduced. Since the surface becomes deep, it was difficult to obtain sufficient processing accuracy. However, in the present invention, the sensor holder 39 is divided into a separate structure and the sensor mounting portion 33 is formed separately, so that the bottom of the sensor mounting portion 33 is formed. Processing of the mounting surface of the piezoelectric element 29 is facilitated, and processing accuracy can be improved.

Since the dimension of the sensor holder 39 in the height direction can be increased, as shown in FIG.
Even if the diameter D of the 14 large, the distance L ₁ between the ultrasonic transceivers 37 and 38 regardless of the diameter D of the channel can be freely selected.

Generally, in a flow meter using ultrasonic waves,
When the distance between the ultrasonic transmitter and the receiver increases, the modulation amount of the ultrasonic wave increases, the attenuation of the ultrasonic wave, the flow noise, the influence of the change in the propagation speed of the ultrasonic wave due to the temperature fluctuation of the fluid to be measured, and the like, increase the accuracy. Flow meter rules become difficult. In other words, when the distance between the ultrasonic transmitters and receivers is increased, the attenuation of the sound wave in the gas to be measured is extremely large, and the reception level is significantly reduced, while the sound propagates through the bluff body and the meter body. Since the attenuation of the wraparound noise is relatively small, the S / N ratio is reduced, and stable detection of Karman vortex cannot be performed, and the flow rate measurement accuracy decreases. Also,
Conventionally, the distance between the ultrasonic transmitter and receiver may be limited due to the limit of the allowable range of the phase difference of the phase comparator.When increasing the diameter of the flow path, the transmission frequency is changed by changing the piezoelectric element and the sensor holder. I needed to change it.

On the other hand, according to the present invention, the axial dimension of the sensor holder 39 can be increased by increasing the axial dimension of the sensor adapter 40. Therefore, regardless of the diameter D of the flow path 14, The distance between the ultrasonic transmitters / receivers 37 and 38 can be freely selected, and the above-mentioned problems can be solved to achieve a stable and high-precision flow meter rule.

In the first and second embodiments, the case where the sensor holder is divided into two parts and three parts is described. However, the present invention is not limited to this. Is also possible. In the above embodiment, the gas flow synchronized with the Karman vortex is introduced from the holes 18 and 19, and the ultrasonic wave is modulated by the flow velocity change occurring in the measurement passage 17 (the internal space of the bluff body 16). However, the present invention is not limited to this.For example, even if the ultrasonic wave is modulated by a gas density change in the internal space caused by introduction of a gas flow synchronized with the Karman vortex into the internal space of the bluff body 16, Good.

[0033]

As described above in detail, according to the ultrasonic vortex flowmeter of the first aspect of the present invention, the substantially bottomed cylindrical holder on which the ultrasonic element of the ultrasonic transceiver is mounted is formed by the cylindrical portion. Since the two or more members are formed by being combined, the ultrasonic wave propagated from the piezoelectric element to the cylindrical portion of the holder is reflected and attenuated by the boundary surface of the connected portion formed on the cylindrical portion of the holder. Therefore, the S / N ratio is improved, and stable Karman vortex detection can be performed, and the flow rate measurement accuracy can be improved.

According to the ultrasonic vortex flowmeter of the second aspect of the present invention, in the configuration of the first aspect, at least one coupling portion of the holder is set at a position serving as a node of vibration. As a result, it becomes difficult for the sound waves to propagate, and it is easy for vibration to occur from the joint portion of the holder to the bottom portion, so that transmission and reception of ultrasonic waves through the measurement passage can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view across a flow path of an ultrasonic vortex flowmeter according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is an enlarged view of a longitudinal section across a flow path showing a main part of an ultrasonic vortex flowmeter according to a second embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of the ultrasonic vortex flowmeter according to a second embodiment of the present invention, which crosses the flow path.

FIG. 5 is a longitudinal sectional view of the ultrasonic vortex flow meter having a smaller diameter channel than that of FIG.

FIG. 6 is a diagram showing dimensions and vibration states of respective parts of a holder of the ultrasonic vortex flowmeter according to one embodiment of the present invention.

FIG. 7 is a diagram showing a state of vibration of an ultrasonic transceiver using a unimorph type piezoelectric element of the ultrasonic flowmeter according to one embodiment of the present invention.

FIG. 8 is a vertical cross-sectional view of the conventional ultrasonic vortex flowmeter, which crosses the flow path.

FIG. 9 is a cross-sectional view along a flow path of the ultrasonic vortex flow meter of FIG.

FIG. 10 is an enlarged view of an ultrasonic transmitter mounting portion of the ultrasonic vortex flowmeter of FIG. 8;

[Explanation of symbols]

 13,36 Ultrasonic vortex flowmeter 14 Flow path 16 Bluff body (vortex generator) 17 Measurement passage (internal space) 20,37 Ultrasonic transmitter 21,38 Ultrasonic receiver 29 Piezoelectric element (ultrasonic element) 28, 39 Sensor holder (holder) 35,41,42 Joint

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsuro Sen, 4-1-2, Hirano-cho, Chuo-ku, Osaka City Inside Osaka Gas Co., Ltd. No. Tokiko Corporation (72) Inventor Kaname Ueno 1-6-3 Fujimi, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside Tokiko Corporation (72) Inventor Tatsuo Sugata 1-6-3, Fujimi, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Tokiko Inside the corporation

Claims (2)

[Claims] 1. A flow path through which a fluid to be measured flows, and a fluid to be measured which is provided in the flow path, generates a Karman vortex on the downstream side and has an internal space, and which is synchronized with the Karman vortex in the internal space. A vortex generator in which a hole for introducing the flow of the fluid is provided in the peripheral wall portion, and a pair of super-conductors arranged with a fluctuation region caused by the flow of the fluid to be measured introduced into the internal space of the vortex generator An ultrasonic vortex flowmeter comprising: an ultrasonic transceiver, at least one of the pair of ultrasonic transceivers,
An ultrasonic wave having a substantially cylindrical shape with a bottom, and having a holder on which an ultrasonic element is placed, the holder being formed by joining two or more members at a cylindrical portion. Vortex flow meter. 2. The ultrasonic vortex flowmeter according to claim 1, wherein at least one coupling portion of the holder is set at a position that serves as a node of vibration.