JP4178346B2 - Ultrasonic vortex flowmeter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic vortex flowmeter that measures the flow rate of gas in a pipe line by detecting the generation of Karman vortices using an ultrasonic sensor.
[0002]
[Prior art]
An example of a conventional ultrasonic vortex flowmeter will be described with reference to FIGS. As shown in FIGS. 8 to 10, an ultrasonic vortex flowmeter 1 includes a columnar bluff body 4 (vortex generation) that crosses a flow path 2 in a meter body 3 that forms a flow path 2 of a gas to be measured. Body) and a measurement passage 5 (internal space) is formed inside the bluff body 4. The bluff body 4 has a pair of holes 6 and 7 that communicate with the measurement passage 5 toward the downstream side. A pair of ultrasonic transmitters / receivers 8 and 9 having piezoelectric elements (ultrasonic elements) are attached to the bluff body 4 at both ends across the measurement passage 5.
[0003]
When gas flows through the flow path 2 in the meter body 3, Karman vortices K are alternately generated at a period corresponding to the gas flow velocity downstream of the bluff body 4, and the gas generated in synchronization with the Karman vortices K is generated. Is introduced into the measurement passage 5 from the holes 6 and 7, and the flow velocity changes in the measurement passage 5 at the same cycle as the generation cycle of the Karman vortex K. Since the ultrasonic wave transmitted from the ultrasonic transmitter 8 and propagating in the gas in the measurement passage 5 is modulated by the gas flow in the measurement passage 5 by the Karman vortex K and received by the ultrasonic receiver 9. By extracting this modulation component with a phase comparator or the like and detecting the generation period of the Karman vortex K, the flow rate of the gas in the flow path 2 can be obtained.
[0004]
At this time, a part of the ultrasonic wave transmitted from the ultrasonic transmitter 8 propagates through the bluff body 4 and the meter body 3 and is received as a noise component by the ultrasonic receiver 9 (the ultrasonic wave wraps around). However, since ultrasonic waves are much easier to propagate in solids such as the bluff body 4 and the meter body 3 than in the gas that is the fluid to be measured, wraparound noise that propagates through the bluff body 4 and the meter body 3 is generated. The S / N ratio (signal / noise ratio) decreases and stable Karman vortex detection becomes difficult.
[0005]
Therefore, conventionally, as shown in FIG. 10, the bluff body 4 is attached to the meter main body 3 via an O-ring 10 which is an elastic body, and the ultrasonic transmitters and receivers 8 and 9 (because they have the same configuration, Only the vessel 8 is shown) is attached to the bluff body 4 via an O-ring 11 and a packing 12 which are elastic bodies, thereby attenuating leaking ultrasonic waves propagating to the meter body 3 and the bluff body 4.
[0006]
[Problems to be solved by the invention]
However, the conventional ultrasonic vortex flowmeter has the following problems. Since the meter body, the bluff body, and the ultrasonic transmitter / receiver are fastened to each other by bolts or the like, leakage ultrasonic waves propagate between the members via these bolts or the like, so that the wraparound noise cannot be sufficiently blocked. . In particular, when the fluid to be measured is at a high pressure, it is necessary to provide a large number of bolts or the like in order to increase the fastening force of each member.
[0007]
This invention is made in view of said point, and provides the ultrasonic vortex flowmeter which can reduce a wraparound noise by attenuating the leaking ultrasonic wave which propagates a meter main body and a bluff body. Objective.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the invention of claim 1 includes a flow path through which a fluid to be measured flows,
A hole is provided in the flow path to generate a Karman vortex on the downstream side and to have an internal space, and a hole for introducing a flow of a fluid to be measured synchronized with the Karman vortex is provided in the internal wall. The generated vortex generator,
An ultrasonic vortex flowmeter comprising a pair of ultrasonic transmitters / receivers arranged across a fluctuation region due to 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 transmitters / receivers has a substantially bottomed cylindrical shape, and has a holder to which an ultrasonic element is attached at the bottom,
The holder is formed by coupling two or more members in a cylindrical portion, and at least one coupling portion is arranged at a position that becomes a vibration node .
[0009]
With this configuration, the ultrasonic wave propagated 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. In addition, the bottom portion of the holder is likely to vibrate at an ultrasonic frequency from the joint portion of the holder that is a node.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. As shown in FIGS. 1 and 2, the ultrasonic vortex flowmeter 13 is arranged in a diametrical direction so as to cross a flow path 14 in a substantially cylindrical meter body 15 that forms a flow path 14 of a gas to be measured. A columnar bluff body 16 is penetrated along. A measurement passage 17 (internal space) is passed through the bluff body 16 along the length thereof, and a pair of holes 18 and 19 for communicating the flow passage 14 of the meter body 15 and the measurement passage 17 on its side wall. Is opened toward the downstream side. A pair of ultrasonic transmitters / receivers 20 and 21 that are opposed to each other across the measurement passage 17 are attached to both ends of the bluff body 16.
[0014]
Flange portions 22 and 23 are formed at both ends of the bluff body 16, and flange portions 24 and 25 are formed in the ultrasonic transceivers 20 and 21, respectively, and between the flange portions 22 and 24 and between the flange portions 23 and 25. The bluff body 16 and the ultrasonic transmitters / receivers 20 and 21 are coupled to the meter body 15 by bolts 27 with packings 26 interposed therebetween.
[0015]
The ultrasonic transmitters / receivers 20 and 21 have the same structure (only the ultrasonic transmitter 20 is shown in FIG. 2), and a piezoelectric element 29 (ultrasonic element) is provided at the bottom of a substantially bottomed cylindrical sensor holder 28. Are bonded by an acoustic bonding agent such as a silicon adhesive or an epoxy resin. In addition, a lead wire 30 such as a PTFE wire or a urethane wire is connected to the piezoelectric element 29, and an electrode terminal 31 to which the lead wire is connected is joined to a 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 hermetically sealed.
[0016]
The sensor holder 28 has a two-part structure in which two cylindrical portions of a sensor attachment portion 33 having a bottom portion and a bluff body attachment portion 34 having flange portions 24 and 25 are coupled. The sensor attachment portion 33 and the bluff body attachment portion 34 are coupled by welding (TIG welding, laser welding, resistance welding, etc.), brazing, adhesion, or the like. Since the coupling portion 35 formed by this coupling is different in ultrasonic propagation characteristics (acoustic impedance) from other portions of the sensor holder 28, an acoustic boundary surface is formed in the coupling portion 35. Therefore, the ultrasonic wave transmitted from the piezoelectric element 29 and propagating through the cylindrical portion of the sensor holder 28 is reflected and attenuated at the boundary surface between the coupling portion 35 and the sensor attachment portion 33 and the bluff body attachment portion 34. As shown in FIG. 6, the dimension of each part of the sensor holder 28 is such that the wavelength of the ultrasonic wave to be transmitted and received is λ, the diameter of the bottom is λ / 2, and the distance from the bottom to the coupling portion 35 is λ / 2 is set. By setting such dimensions, when the piezoelectric element 29 vibrates, the sensor holder 28 vibrates with the coupling portion 35 as a node.
[0017]
Next, the operation of the present embodiment configured as described above will be described.
[0018]
An ultrasonic signal transmitted from the bottom of the sensor holder 28 by vibrating the piezoelectric element 29 of the ultrasonic transmitter 20 by an electrical signal from a sensor drive circuit (not shown) and propagated in the measurement passage 17 of the bluff body 16 A sound wave is received by the piezoelectric element 29 of the ultrasonic receiver 21 and converted into an electric signal. When the gas that is the fluid to be measured flows through the flow path 14 of the meter body 15, Karman vortices are alternately generated 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 this change in flow velocity, the ultrasonic wave propagating in the measurement passage 17 is modulated in accordance with the generation period of the Karman vortex, so by extracting the ultrasonic modulation component by 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.
[0019]
At this time, the sensor holder 28 is connected to the ultrasonic wave propagating through the cylindrical portion of the sensor holder 28 because the sensor mounting portion 33 and the bluff body mounting portion 34 are coupled by the coupling portion 35 having different tissues (acoustic impedance). In addition, the sensor mounting portion 33 and the interface between the bluff body mounting portion 34 and the coupling portion 35 become an acoustic obstacle, and sound waves are attenuated (reflected and scattered) and leaked to the bluff body 16 and the meter body 15 Ultrasound is reduced. Further, since the coupling portion 35 is set to be a node of vibration by the piezoelectric element 29, the sensor holder 28 vibrates as indicated by a broken line in FIG.
[0020]
When the fluid to be measured is a gas, since the sound velocity and density are smaller than those of solid and liquid, the acoustic impedance is small and the transmittance of ultrasonic waves is low. Therefore, a large sound pressure is required. In addition, in order to prevent the flow rate from being detected because the phase difference generated while the ultrasonic wave transmitted from the ultrasonic wave transmission 20 is received by the ultrasonic wave receiver 21 exceeds ± 2π due to the low sound velocity. It is necessary to use a low frequency. For this reason, the piezoelectric element 29 is a unimorph element that causes large radial vibrations at a low frequency (primary mode frequency).
[0021]
When the unimorph type piezoelectric element 29 is attached to the bottom of the sensor holder 28 and vibrated in the radial direction (see FIG. 7A), the expansion and contraction of the unimorph type piezoelectric element 29 causes the bottom of the sensor holder 28 to be as shown in FIG. As shown in FIG. 7C (when extended), the sensor holder 28 is deformed in the height direction. Due to this deformation, it is possible to transmit the vibration of the ultrasonic wave directly to the gas, so that it is possible to transmit / receive an ultrasonic wave having a large sound pressure at a low frequency.
[0022]
Here, if each dimension from the coupling part 35 to the bottom part of the sensor holder is set to the dimension of FIG. 6, the sensor holder 28 is likely to vibrate (deform) from the coupling part 35 to the bottom part with the coupling part 35 as a node. Thus, vibration with a large sound pressure can be obtained with a small voltage. The diameter of the bottom part and the distance from the bottom part to the coupling part 35 are not necessarily λ / 2, and may be an integer multiple of this. Further, depending on other conditions, the diameter of the bottom of the sensor holder 28 and the distance from the bottom to the coupling portion 35 do not necessarily have to be integral multiples of λ / 2, so that a vibration node comes to the coupling portion. It only has to be set.
[0023]
The S / N ratio is improved due to the reduction of noise due to attenuation of leaked ultrasonic waves by the acoustic boundary surface formed in the coupling portion 35 and the increase of the signal due to the improvement of vibration efficiency with the coupling portion 35 as a node. Stable Karman vortices can be detected and flow measurement accuracy can be improved.
[0024]
Next, a second embodiment of the present invention will be described with reference to FIGS. The second embodiment is generally similar to the first embodiment except that the structure of the sensor holder of the ultrasonic transmitter / receiver is different. Therefore, the first embodiment shown in FIGS. 1 and 2 will be described below. The same parts as those in the embodiment are given the same reference numerals, and only different parts will be described in detail.
[0025]
As shown in FIGS. 3 and 4, in the ultrasonic vortex flow meter 36 of the second embodiment, the sensor holder 39 of the ultrasonic transmitters / receivers 37 and 38 (only the ultrasonic transmitter 37 is shown in FIG. 3) A three-part structure in which a cylindrical sensor adapter 40 is coupled between the sensor mounting portion 33 and the bluff body mounting portion 34 is employed. The sensor mounting portion 33 and the bluff body mounting portion 34 and the sensor adapter 40 are coupled in the same manner as in the first embodiment, and coupling portions 41 and 42 having different ultrasonic propagation characteristics (acoustic impedance) are formed therebetween. Has been.
[0026]
Then, the height in the height direction of the sensor holder 39 is increased as much as the sensor adapter 40 is coupled, and the tip of the sensor holder 39 is protruded into the measurement passage 17 of the bluff body 16 by that amount, The distance L ₁ between the ultrasonic transceivers 37 and 38 and the distance L ₂ between the holes 18 and 19 are made smaller than the diameter D of the flow path 14.
[0027]
With this configuration, the two coupling portions 41 and 42 serving as an acoustic obstacle layer are formed in the sensor holder 39. Therefore, leakage ultrasonic waves to the bluff body 16 and the meter main body 15 are detected in the first embodiment. It can be further reduced than that.
[0028]
A sensor holder 39 having various axial dimensions can be manufactured by combining the sensor mounting part 33 and the bluff body mounting part 34 with those of the first embodiment and combining with the sensor adapter 40 having different axial dimensions. Therefore, the manufacturing cost can be reduced by sharing the parts. 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 conventional integrated sensor holder, if the axial dimension is increased, the processing accuracy Since the surface becomes deeper, it has been difficult to obtain sufficient processing accuracy, but in the present invention, the sensor holder 39 is divided and the sensor mounting portion 33 is separated, so that the bottom of the sensor mounting portion 33 is The mounting surface of the piezoelectric element 29 can be easily processed, and the processing accuracy can be improved.
[0029]
Since the height dimension of the sensor holder 39 can be increased, even if the diameter D of the flow channel 14 of the meter body 15 is large as shown in FIG. the distance L ₁ between can be chosen freely.
[0030]
In general, in flowmeters using ultrasonic waves, the greater the distance between the ultrasonic transmitters and receivers, the greater the amount of ultrasonic modulation, and the propagation of ultrasonic waves due to ultrasonic attenuation, flow noise, and temperature fluctuations of the fluid being measured. The influence of speed change and the like becomes large, and an accurate flow meter rule becomes difficult. In other words, when the distance between the ultrasonic transmitter / receiver increases, the attenuation of the sound wave in the gas to be measured is very large, so that the reception level is significantly reduced, whereas it propagates through the bluff body and the meter body. Since the attenuation of the sneak noise is relatively small, the S / N ratio is lowered and stable Karman vortex detection cannot be performed, and the flow rate measurement accuracy is lowered. Conventionally, the distance between ultrasonic transmitters / receivers may be limited due to the limit of the phase difference allowable range of the phase comparator. When the diameter of the flow path is increased, the piezoelectric element and the sensor holder are changed for transmission. It was necessary to change the frequency.
[0031]
In contrast, in the present invention, since the axial dimension of the sensor holder 39 can be increased by increasing the axial dimension of the sensor adapter 40, ultrasonic transmission / reception is performed regardless of the diameter D of the flow path 14. The distance between the devices 37 and 38 can be freely selected, and the above problem can be solved and a stable and highly accurate flow meter rule can be realized.
[0032]
In the first and second embodiments, the case where the sensor holder has a two-divided and three-divided structure has been described. However, the present invention is not limited to this, and a divided structure of four or more divided parts can also be used. is there. In the above-described embodiment, the ultrasonic wave is modulated by a flow velocity change that occurs in the measurement passage 17 (inner space of the bluff body 16) when a gas flow synchronized with the Karman vortex is introduced from the holes 18 and 19. However, the present invention is not limited to this. For example, the ultrasonic wave may be modulated by a change in gas density in the internal space caused by introducing a gas flow synchronized with the Karman vortex into the internal space of the bluff body 16. Good.
[0033]
【The invention's effect】
As described in detail above, according to the ultrasonic vortex flowmeter of the first aspect of the present invention, the cylindrical portion having two or more members having a substantially bottomed cylindrical holder for placing the ultrasonic element of the ultrasonic transceiver is provided. Since the ultrasonic waves propagated from the piezoelectric element to the cylindrical portion of the holder are reflected and attenuated by the boundary surface of the combined portion formed in the cylindrical portion of the holder, the S / N is formed. The ratio can be improved and stable Karman vortices can be detected, and flow measurement accuracy can be improved.
[0034]
In addition, by arranging at least one coupling portion of the holder at a position to be a vibration node, it is difficult for sound waves from the coupling portion to propagate, and it is easy to cause vibration from the coupling portion of the holder to the bottom portion, It is possible to efficiently transmit and receive ultrasonic waves.
[Brief description of the drawings]
FIG. 1 is a longitudinal 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 the main part of an ultrasonic vortex flowmeter according to a second embodiment of the present invention.
FIG. 4 is a longitudinal sectional view across a flow path of an ultrasonic vortex flowmeter according to a second embodiment of the present invention.
5 is a longitudinal sectional view across the flow path of an ultrasonic vortex flowmeter having a flow path having a smaller diameter than that of FIG. 4. FIG.
FIG. 6 is a diagram showing dimensions and vibration states of each part of the 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 an ultrasonic flowmeter according to an embodiment of the present invention.
FIG. 8 is a longitudinal sectional view crossing a flow path of a conventional ultrasonic vortex flowmeter.
9 is a transverse cross-sectional view along the flow path of the ultrasonic vortex flowmeter of FIG. 8. FIG.
10 is an enlarged view of an ultrasonic transmitter mounting portion of the ultrasonic vortex flowmeter of FIG. 8. FIG.
[Explanation of symbols]
13,36 Ultrasonic vortex flowmeter
14 Flow path
16 Bluff body
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

Claims (1)

A flow path through which the fluid to be measured flows;
A hole is provided in the flow path to generate a Karman vortex on the downstream side and to have an internal space, and a hole for introducing a flow of a fluid to be measured synchronized with the Karman vortex is provided in the internal wall. The generated vortex generator,
An ultrasonic vortex flowmeter comprising a pair of ultrasonic transmitters / receivers arranged across a fluctuation region due to 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 transmitters / receivers has a substantially bottomed cylindrical shape, and has a holder to which an ultrasonic element is attached at the bottom,
The ultrasonic vortex flowmeter is characterized in that the holder is formed by coupling two or more members in a cylindrical portion, and at least one coupling portion is arranged at a position that becomes a node of vibration .

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