JP2006220534A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter which realizes a shoe that reduces multiple reflection wave and has small measurement errors. <P>SOLUTION: In the ultrasonic flowmeter, provided with an ultrasonic transmitter/receiver provide in a measuring tube, the multiplex wave absorber having the same or larger material than an acoustic impedance of a material of the measuring tube, is provided in between the measuring tube and the ultrasonic transmitter/receiver and a position whereto the ultrasonic wave reflected from the boundary between the measuring tube and the measuring fluid reaches the surface of the measuring tube. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic flowmeter with a small measurement error.

Prior art documents related to the ultrasonic flowmeter include the following.
JP-T 2002-535639 Japanese Patent Laid-Open No. 11-287682

  FIG. 8 is an explanatory diagram of a main part configuration of a conventional example that is generally used conventionally, and is an example of a transmission type propagation time difference type ultrasonic flowmeter.

In the figure, reference numeral 1 denotes a measurement tube through which a measurement fluid FL flows.
Reference numeral 2 denotes an ultrasonic transmitter provided in the measurement tube 1.
Reference numeral 3 denotes an ultrasonic receiver provided in the measurement tube 1.
In this case, PZT (lead zirconate titanate) is used for the ultrasonic transceivers 2 and 3.

Reference numeral 4 denotes a shoe made of an acoustic coupling material provided between the measuring tube 1 and the ultrasonic transmitter 2.
Reference numeral 5 denotes a shoe made of an acoustic coupling material provided between the measurement tube 1 and the ultrasonic receiver 3.
In this case, the shoes 4 and 5 are made of PEEK material (polyether ether ketone).

In the above configuration, the ultrasonic wave transmitted from the ultrasonic transmitter 2 propagates to the ultrasonic receiver 3 through the shoe 4 and the measuring tube 1 and through the shoe 5 installed oppositely.
At this time, the transmitted ultrasonic wave is not necessarily a wave that is not ideally spread.
Similarly, some of the transmitted ultrasonic waves are subjected to multiple reflection at the boundary between the measurement tube 1 and the measurement fluid FL due to the acoustic impedance, and the multiple reflected waves also propagate to the shoe 5 in the same manner.

As shown in FIG. 8, when the flow velocity is measured only by the ultrasonic wave a (referred to as a normal wave) refracted by the measurement tube 1 and propagated to the ultrasonic receiver 3, the flow velocity is calculated from an ideal refraction angle. Become.
If the refraction angle at this time is θ ₀ , the ultrasonic path direction component of the flow velocity V is obtained by V × sin θ.

  On the other hand, the incident angle to the liquid when the ultrasonic wave b that has caused the multiple reflection reaches the ultrasonic receiver 3 is smaller than the incident angle of the normal wave, and as a result, as shown in FIG. When the flow velocity is measured by the above, the incident angle θ is smaller than that of the normal wave, so that the flow velocity measured by the multiple reflected waves is estimated to be lower than that of the normal wave.

These received waves are observed as shown in FIG. 10. However, when the flow velocity is obtained from the correlation between both waves using the correlation method, an error (minus error) E of the superposition of the normal wave and the multiple reflected wave occurs. It will be.
Such an error can be achieved by limiting the sampling window to only the normal wave when the normal wave and the multiple wave are completely separable on the time axis, but the normal wave and the multiple wave overlapped. In this case, separation such as detecting only the wave that reaches first on the time axis becomes difficult.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems, and to provide an ultrasonic flowmeter that realizes a shoe that reduces multiple reflected waves and has a small measurement error.

In order to achieve such a problem, in the ultrasonic flowmeter according to claim 1 of the present invention,
In an ultrasonic flowmeter equipped with an ultrasonic transmitter / receiver provided in a measurement tube,
An acoustic impedance of a material of the measurement tube provided between the measurement tube and the ultrasonic transceiver and at a position where an ultrasonic wave reflected from a boundary surface between the measurement tube and the measurement fluid reaches the measurement tube surface; A multiwave absorber having the same or larger material is provided.

In Claim 2 of this invention, in the ultrasonic flowmeter of Claim 1,
The present invention is characterized by comprising correction means for reflecting an ultrasonic wave inside the multiwave absorber and correcting a measured value from a characteristic value of the reflected wave.

According to claim 3 of the present invention, in the ultrasonic flowmeter according to claim 2,
The measurement value is corrected using the arrival time of the reflected wave as the characteristic value of the reflected wave.

According to claim 4 of the present invention, in the ultrasonic flowmeter according to claim 2,
The characteristic value of the reflected wave is corrected using the reflection intensity of the reflected wave.

According to Claim 5 of the present invention, in the ultrasonic flowmeter according to any one of Claims 1 to 4,
A film provided between the multiwave absorber and the measuring tube and having a thickness sufficiently thinner than the ultrasonic wavelength is provided.

According to claim 6 of the present invention, in the ultrasonic flowmeter according to claim 1,
A diffusion attenuating means for diffusing or attenuating ultrasonic waves is provided in the multiwave absorber.

According to claim 7 of the present invention, in the ultrasonic flowmeter according to claim 6,
As the diffusion attenuation means, a quarter wavelength reflector is used.

According to claim 8 of the present invention, in the ultrasonic flowmeter according to claim 6,
The diffusion attenuating means is a rough reflector provided in the multiple wave absorber.

As described above, according to the first aspect of the present invention, the following effects can be obtained.
Since the generation of multiple waves can be reduced, an ultrasonic flowmeter with few errors can be realized.
Moreover, an expensive material such as PEEK (polyetheretherketone) can be reduced, and an ultrasonic flowmeter capable of reducing costs can be obtained.

According to the second, third, and fourth aspects of the present invention, the following effects can be obtained.
Since the correcting means for reflecting the ultrasonic wave inside the multiwave absorber and correcting the measured value from the characteristic value of the reflected wave is provided, an ultrasonic flowmeter with less errors can be obtained.

According to claim 5 of the present invention, there are the following effects.
An ultrasonic flowmeter with good adhesion between the measurement tube and the multi-wave absorber is obtained because it is provided between the multi-wave absorber and the measurement tube and has a coating sufficiently thinner than the ultrasonic wavelength. It is done.

According to claim 6 of the present invention, there are the following effects.
Since the diffusion attenuation means for diffusing or attenuating the ultrasonic waves is provided in the multiwave absorber, the ultrasonic waves reflected and diffused are diffused or attenuated, and an ultrasonic flowmeter with a small measurement error can be obtained.

According to claim 7 of the present invention, there are the following effects.
Since the quarter-wave reflector is used as the diffusion attenuation means, the quarter-wave reflector is commercially available, and an ultrasonic flowmeter can be obtained that can easily obtain the diffusion attenuation means at a low cost.

According to claim 8 of the present invention, there are the following effects.
Since the diffusion attenuation means is a rough reflector provided in the multiwave absorber, the rough surface is easy to make inexpensively, and an inexpensive ultrasonic flowmeter can be obtained.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating the configuration of the main part of one embodiment of the present invention, and FIG. 2 is a diagram illustrating the operation of FIG.
In the figure, the same symbols as those in FIG. 8 represent the same functions.
Only the difference from FIG. 8 will be described below.

  The multiwave absorber 11 is a position where ultrasonic waves reflected from the interface between the measurement tube 1 and the ultrasonic transceivers 2 and 3 and between the measurement tube 1 and the measurement fluid FL reach the surface of the measurement tube 1. And has a material equal to or larger than the acoustic impedance of the material of the measuring tube 1.

That is, the material of the portions of the shoes 4 and 5 is conventionally a plastic material such as PEEK (polyetheretherketone), but this portion 11 is made of the same material as the measuring tube 1.
For example, a stainless steel shoe 11 is used for a stainless steel measuring tube 1.
The length of the shoe 11 is long enough for the multiple reflected waves to return to the shoe 11.
The ultrasonic wave reflected from the measurement tube 1 / fluid interface is further reflected from the surface of the measurement tube 1, but the shoe 11 made of the same material is placed there.

In the above configuration, if the density and sound speed of the material of the measuring tube 1 are ρ1 and C1, and the density and sound speed of the shoe 11 are ρ2 and C2, the transmittance T of the ultrasonic sound pressure from the measuring tube 1 to the shoe 11 is T. Is
T = (2ρ2 × C2) / (ρ2 × C2 + ρ1 × C1)
Therefore, if the shoe 11 is made of a material having substantially the same acoustic impedance ρC as the piping material, the reflected wave on the surface of the measuring tube 1 can be returned to the shoe 11 as it is.
If the ultrasonic wave that enters the shoe 11 is moved in a direction completely different from the propagation direction of the normal wave on the outer surface of the shoe 11, multiple waves can be reduced, and measurement with less error is possible as a result. It becomes.

As a result, since the generation of multiple waves can be reduced, an ultrasonic flowmeter with few errors can be realized.
Moreover, an expensive material such as PEEK (polyetheretherketone) can be reduced, and an ultrasonic flowmeter capable of reducing costs can be obtained.

FIG. 3 is an explanatory view showing the structure of the main part of another embodiment of the present invention.
In the present embodiment, a coating 21 having a thickness sufficiently thinner than the ultrasonic wavelength is provided between the multiwave absorber 11 and the measuring tube 1.
When the shoe 11 made of a metal material comes into contact with the measuring tube 1 made of a metal material, the adhesion may be deteriorated due to a fine scratch or the like.
For this purpose, the shoe 11 is provided with a coating 21 such as Teflon (registered trademark) that is sufficiently thinner than the order of the wavelength of ultrasonic waves.
The reason why the thickness is made thinner than the wavelength of the ultrasonic wave is to prevent multiple reflection in this layer.
An ultrasonic flowmeter with good adhesion between the measuring tube 1 and the shoe 11 can be obtained.

FIG. 4 is an explanatory view showing the configuration of the main part of another embodiment of the present invention.
In this embodiment, the ultrasonic wave absorbed by the shoe 11 may be further reflected by the shoe 11 and guided to the ultrasonic transmitter 2 that is used for transmission, for example, made of a piezoelectric element.
In that case, by measuring the time, it can be used for thickness measurement, temperature measurement, and temperature correction of the measuring tube 1.
As a result, an ultrasonic flowmeter with a smaller measurement error can be obtained.

FIG. 5 is an explanatory view showing the structure of the main part of another embodiment of the present invention.
In the present embodiment, a multiwave absorber 31 having a triangular cross section is provided on the surface of the measuring tube 1, and a PZT material, for example, is provided on the surface of the multiwave absorber 31 via an acoustic coupling body 32 such as a PEEK material. This is an example in which an ultrasonic transmitter 2 is provided.

  As a result, an ultrasonic flowmeter capable of sending the multiple reflected waves b of ultrasonic waves to a place completely different from a certain position of the ultrasonic transmitter 2 is obtained.

FIG. 6 is an explanatory view showing the configuration of the main part of another embodiment of the present invention.
In the present embodiment, the ultrasonic transmitter 2 is provided via the acoustic coupling body 41 provided on the surface of the measurement tube 1, and the ultrasonic wave that has caused multiple reflections in the measurement tube 1 is the outer surface of the measurement tube 1. This is an embodiment in which the multiwave absorber 42 is separately arranged at the position where the light exits from the center.
As a result, the amount of the multiwave absorber 42 can be reduced, and an inexpensive ultrasonic flowmeter can be obtained.

FIG. 7 is an explanatory view showing the configuration of the main part of another embodiment of the present invention.
In the present embodiment, the diffusion attenuation means 51 diffuses or attenuates the ultrasonic waves provided in the multiwave absorber 52 and subjected to multiple reflections.
In this case, a ¼ wavelength reflector is used as the diffusion attenuation means 51.
As a result, an ultrasonic flowmeter having a small measurement error is obtained by diffusing or attenuating multiple reflected ultrasonic waves.
Since the quarter-wave reflector is used for the diffusion attenuating means 51, the quarter-wave reflector is commercially available, and an ultrasonic flowmeter can be obtained that can easily obtain the diffusion attenuator.

  The diffusion attenuation means 51 may be a rough reflecting plate 51 provided on the multiwave absorber. A rough surface can be easily produced at low cost, and an ultrasonic flowmeter from which the diffusion attenuation means 51 can be obtained at low cost is obtained.

The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention.
Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

It is principal part structure explanatory drawing of one Example of this invention. It is operation | movement explanatory drawing of FIG. It is principal part structure explanatory drawing of the other Example of this invention. It is principal part structure explanatory drawing of the other Example of this invention. It is principal part structure explanatory drawing of the other Example of this invention. It is principal part structure explanatory drawing of the other Example of this invention. It is principal part structure explanatory drawing of the other Example of this invention. It is principal part structure explanatory drawing of the prior art example generally used conventionally. It is operation | movement explanatory drawing of FIG. It is operation | movement explanatory drawing of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measuring tube 2 Ultrasonic transmitter 3 Ultrasonic receiver 4 Shoe 5 Shoe a Ultrasonic b Ultrasonic wave which caused multiple reflection 11 Multiwave absorber 21 Coating 31 Multiwave absorber 32 Acoustic coupling body 41 Acoustic coupling body 42 Multiwave Absorber 51 Diffusion Attenuating Means 51 1 / 4λ Reflector 52 Multiwave Absorber FL Measuring Fluid

Claims (8)

In an ultrasonic flowmeter equipped with an ultrasonic transmitter / receiver provided in a measurement tube,
An acoustic impedance of a material of the measurement tube provided between the measurement tube and the ultrasonic transceiver and at a position where an ultrasonic wave reflected from a boundary surface between the measurement tube and the measurement fluid reaches the measurement tube surface; An ultrasonic flowmeter comprising a multiple wave absorber having the same or larger material. 2. The ultrasonic flowmeter according to claim 1, further comprising correction means for reflecting an ultrasonic wave inside the multiwave absorber and correcting a measured value from a characteristic value of the reflected wave. The ultrasonic flowmeter according to claim 2, wherein the measurement value is corrected using the arrival time of the reflected wave as the characteristic value of the reflected wave. The ultrasonic flowmeter according to claim 2, wherein the measured value is corrected using the reflection intensity of the reflected wave as the characteristic value of the reflected wave. The ultrasonic wave according to any one of claims 1 to 4, further comprising a coating provided between the multiwave absorber and the measurement tube and having a thickness sufficiently thinner than the ultrasonic wavelength. Flowmeter. The ultrasonic flowmeter according to claim 1, further comprising diffusion attenuation means provided on the multiwave absorber for diffusing or attenuating ultrasonic waves. The ultrasonic flowmeter according to claim 6, wherein a ¼ wavelength reflector is used as the diffusion attenuation means. The ultrasonic flowmeter according to claim 6, wherein the diffusion attenuation means is a rough reflector provided in the multiwave absorber.

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