JP2019039805A - Ultrasonic flow meter and ultrasonic flow measurement method - Google Patents

Abstract

To provide an ultrasonic flow meter and an ultrasonic flow measurement method which reduce a noise component due to an ultrasonic wave propagating in an ultrasonic absorber attached on an outer peripheral surface of a pipe.SOLUTION: An ultrasonic absorber 14 for absorbing a pipe propagation wave propagating in a pipe 30 among ultrasonic waves is provided on an outer peripheral surface of the pipe 30. An absorber propagation wave propagating in the ultrasonic absorber 14 among the ultrasonic waves is prevented from propagating to transducers 13A, 13B by propagation suppression parts 24A, 24B provided between the ultrasonic absorber 14 and the transducers 13A, 13B on the outer peripheral surface of the pipe 30.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ultrasonic flow measurement technique for reducing noise components of ultrasonic waves propagating through an ultrasonic absorber attached to an outer peripheral surface of a pipe during flow measurement.

Generally, a clamp-on type ultrasonic flowmeter transmits ultrasonic waves from one transducer attached to the outside of the pipe into the pipe, and the other transducer attached to the outside of the pipe also causes the inside of the pipe to be transmitted. The ultrasonic wave which passed the fluid which flows through is received, and the flow velocity and flow rate of the fluid are measured according to the reception result.
At this time, the reception result obtained by the ultrasonic transmitter includes not only the signal component consisting of the fluid propagation wave that propagates the fluid flowing in the pipe, but also the pipe propagation that propagates in the outer peripheral surface, inner peripheral surface, or wall of the pipe. A noise component consisting of waves is included. For this reason, the measurement accuracy of the flow rate is lowered by the noise component.

Conventionally, as a technique for reducing such noise components, a mat-like ultrasonic absorber is attached to the outer peripheral surface of the pipe to absorb the pipe propagation wave propagating through the outer peripheral surface, inner peripheral surface, or wall of the pipe. Techniques have been proposed (see, for example, Patent Document 1).
This ultrasonic absorber is made of an elastic mat-like elastic body mainly made of rubber or a polymer material, such as uncrosslinked burchi rubber.

  When ultrasonic waves (sound waves) propagate through different media, the transmittance and reflectance at the medium interface change depending on the difference in acoustic impedance between the media. In general, since the difference in acoustic impedance between the pipe and the atmosphere outside the pipe is large, the ratio of the pipe propagation wave propagating through the pipe to the atmosphere is small. On the other hand, since the ultrasonic absorber has a larger acoustic impedance than the atmosphere, the acoustic impedance difference with the pipe is smaller than the acoustic impedance difference between the pipe and the outside atmosphere. Thereby, the noise component which consists of a pipe propagation wave can be reduced by attaching an ultrasonic absorber to the outer peripheral surface of piping.

JP 2014-157129 A

However, in such a conventional technique, although the noise component consisting of the pipe propagation wave propagating through the pipe can be reduced by the ultrasonic absorber attached to the outer peripheral surface of the pipe, the absorber propagation wave propagating through the ultrasonic absorber itself There was a problem that a noise component consisting of
In particular, when the pipe is a small-diameter pipe of 25 A or less, the distance between transducers that transmit and receive ultrasonic waves is short, and the ultrasonic absorber attached between these transducers on the outer peripheral surface of the pipe is also short. For this reason, the noise component which consists of an absorber propagation wave also tends to become large, and the measurement accuracy of flow volume tends to fall.

  This invention is for solving such a problem, and provides the ultrasonic flow measurement technique which can reduce the noise component resulting from the ultrasonic wave which propagates the ultrasonic absorber attached to the outer peripheral surface of piping. It is aimed.

  In order to achieve such an object, an ultrasonic flowmeter according to the present invention is based on ultrasonic waves transmitted and received so as to pass a fluid flowing in the pipe by a transducer provided on the outer peripheral surface of the pipe. An ultrasonic flowmeter for measuring a flow rate, provided on an outer peripheral surface of the pipe, an ultrasonic absorber for absorbing a pipe propagation wave propagating through the pipe among the ultrasonic waves, and an outer peripheral surface of the pipe A propagation suppression unit that is provided between the ultrasonic absorber and the transducer, and suppresses propagation of the absorber propagation wave that has propagated through the ultrasonic absorber among the ultrasonic waves to the transducer. ing.

  Further, one configuration example of the ultrasonic flowmeter according to the present invention is formed of a mat-like elastic porous body provided on the outer surface of the ultrasonic absorber, and at the interface between the pipe and the ultrasonic absorber. An ultrasonic buffer that buffers reflection of the pipe propagation wave, a tightening portion that is provided on the outer surface of the ultrasonic buffer, and presses and tightens the ultrasonic buffer in the direction of the pipe. Accordingly, the tightening force of the tightening portion is changed, and the degree of deformation of the ultrasonic buffer due to the pressing is changed to change the acoustic impedance of the ultrasonic buffer, thereby being reflected at the interface. An acoustic matching adjustment unit that adjusts an acoustic matching state related to an acoustic impedance of the pipe, the ultrasonic absorber, and the ultrasonic buffer, which affects the intensity of the pipe propagation wave, and the propagation suppression unit, Piping The ultrasound absorber of the outer circumferential surface, the one in which is provided between the transducer and the ultrasonic cushion, and the fastening portion.

  Moreover, one structural example of the said ultrasonic flowmeter concerning this invention consists of a porous material or air layer in which the said propagation suppression part has many space | gap for containing air.

  The ultrasonic flow rate measuring method according to the present invention is an ultrasonic flow rate measurement method for measuring the flow rate of the fluid based on ultrasonic waves transmitted and received so as to pass the fluid flowing in the pipe by a transducer provided on the outer peripheral surface of the pipe. An ultrasonic flow measurement method used in a meter, wherein an ultrasonic absorber provided on an outer peripheral surface of the pipe absorbs a pipe propagation wave propagating through the pipe among the ultrasonic waves, and an ultrasonic absorption step, Propagation suppression unit provided between the ultrasonic absorber and the transducer in the outer peripheral surface of the pipe is configured to transmit the absorber propagating wave propagating through the ultrasonic absorber of the ultrasonic wave to the transducer. A propagation suppression step for suppressing propagation.

  According to the present invention, it is possible to reduce a noise component composed of a pipe propagation wave propagating through a pipe, and to reduce a noise component composed of an absorber propagation wave propagating through the ultrasonic absorber itself. Therefore, the S / N ratio indicating the ratio of the noise component to the signal component corresponding to the fluid propagation wave propagating through the fluid X can be improved, and as a result, extremely good measurement accuracy can be obtained.

It is an external view of an ultrasonic flowmeter. It is sectional drawing of the ultrasonic flowmeter regarding a pipe radial direction. It is sectional drawing of the ultrasonic flowmeter regarding the longitudinal direction of piping. It is explanatory drawing which shows the principle of acoustic matching. It is a graph which shows an acoustic matching characteristic. It is a signal waveform diagram which shows absorption of a noise component.

Next, an embodiment of the present invention will be described with reference to the drawings.
[Ultrasonic flow meter]
First, an ultrasonic flow meter 1 according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an external view of an ultrasonic flowmeter. FIG. 2 is a cross-sectional view of the ultrasonic flowmeter in the pipe radial direction. FIG. 3 is a cross-sectional view of the ultrasonic flowmeter in the longitudinal direction of the pipe.

  The ultrasonic flow meter 1 is a clamp-on ultrasonic flow meter as a whole, transmits ultrasonic waves from one transducer 13A (13B) attached to the outer peripheral surface 31 of the pipe 30 into the pipe 30, The other transducer 13B (13A) attached to the outer peripheral surface 31 of the pipe 30 receives ultrasonic waves that have passed through the fluid X such as steam flowing in the pipe 30, and measures the flow rate of the fluid X according to the reception result. It has a function to do.

  As shown in FIG. 1, the ultrasonic flowmeter 1 according to the present embodiment includes, as main components, a flowmeter main body 10, transducers 13 </ b> A and 13 </ b> B, an ultrasonic absorber 14, an ultrasonic buffer 21, and tightening. A unit 22, an acoustic matching adjustment unit 23, and propagation suppression units 24A and 24B are provided. Among these configurations, the ultrasonic buffer 21, the tightening unit 22, the acoustic matching adjustment unit 23, and the propagation suppressing units 24 </ b> A and 24 </ b> B constitute the ultrasonic buffer device 20.

  The flow meter main body 10 includes a housing that accommodates various circuit units for ultrasonic flow rate measurement, and includes a switching unit 11 and a measurement processing unit 12 as main circuit units.

  The switching unit 11 is a circuit unit that switches and connects the measurement processing unit 12 and the transducers 13 </ b> A and 13 </ b> B in accordance with the switching signal output from the measurement processing unit 12. Thereby, when transmitting an ultrasonic wave from the transducer 13A, an electric transmission signal from the measurement processing unit 12 is output to the transducer 13A, and an electric reception signal from the transducer 13B is output to the measurement processing unit 12, and the transducer When transmitting an ultrasonic wave from 13B, an electrical transmission signal from the measurement processing unit 12 is output to the transducer 13B, and an electrical reception signal from the transducer 13A is output to the measurement processing unit 12.

  The measurement processing unit 12 is composed of a CPU and a signal processing circuit as a whole, and has a function of generating an electrical transmission signal composed of a pulse signal modulated at a constant frequency, and the generated electrical transmission signal is transferred to the transducers 13A and 13B by the switching unit 11. Based on the function of exchanging ultrasonic waves in the upward and downward directions between the transducers 13A and 13B by switching output and the propagation time difference obtained from the upstream electrical reception signal and the downstream electrical reception signal obtained thereby. And the function of calculating the speed and flow rate of the fluid flowing in the pipe 30.

  The transducers 13 </ b> A and 13 </ b> B are composed of an ultrasonic transmitter / receiver as a whole, convert the electric transmission signal output from the flow meter main body 10 into ultrasonic waves, and convert it into the mass X in the pipe 30 via the pipe wall 32 of the pipe 30. And a function of receiving an ultrasonic wave received from the inside of the pipe 30 through the pipe wall 32, converting it into an electric reception signal, and outputting it to the flow meter main body 10. These transducers 13 </ b> A and 13 </ b> B are slanted on the upstream side position and the downstream side position of the fluid X across the reference measurement point P provided at the center position inside the pipe 30, for example, on the outer peripheral surface 31 of the pipe 30. Are arranged opposite to each other.

  In general, when ultrasonic waves are transmitted and received between the transducers 13A and 13B in the upward direction U and the downward direction D with respect to the flow direction F of the fluid X, the fluid that propagates the fluid according to the flow velocity of the fluid X by such an obliquely opposed arrangement. A propagation time difference occurs in the propagation wave. Therefore, the flow rate of the fluid X can be calculated from this propagation time difference and the angle of the ultrasonic wave with respect to the fluid X. In this embodiment, as in the case of Patent Document 1 described above, a case where the flow rate is measured by such a propagation time difference method will be described as an example. However, the present invention is not limited to this, and the present invention is also applied to the case of the Doppler method. The embodiment can be applied in the same manner.

  The ultrasonic absorber 14 is formed of a mat-like elastic body mainly made of rubber or a polymer material such as uncrosslinked buch rubber, and is provided on the outer peripheral surface 31 of the pipe 30, from the transducers 13 </ b> A and 13 </ b> B. Of the transmitted ultrasonic waves, the pipe 30 has a function of absorbing a pipe propagation wave propagating through the pipe 30 itself, such as the outer peripheral surface 31, the inner peripheral surface 32, or the wall 33.

The ultrasonic buffer 21 is made of an open-celled mat-like elastic porous material mainly made of an organic material such as silicone resin, such as a silicone rubber sponge, and is formed on the outer surface of the ultrasonic absorber 14. It is provided and has a function of buffering the reflection of the pipe propagation wave at the interface between the pipe 30 and the ultrasonic absorber 14.
When the fluid X is at a high temperature such as steam, a heat-resistant silicone resin may be used. In addition to this, for example, a sponge made of a polyimide resin can be used to cope with a fluid X having a higher temperature. .

  The tightening portion 22 is provided on the outer surface of the ultrasonic buffer 21 and has a function of pressing the ultrasonic buffer 21 in the direction of the pipe 30 and tightening, and includes a pressing plate 22A and a tightening band 22B. It is composed of

The holding plate 22A is made of, for example, a metal plate such as stainless steel, and is provided on the outer surface of the ultrasonic buffer 21 and has a function of dispersing the fastening force of the fastening band 22B.
The fastening band 22B is made of, for example, a metal plate such as stainless steel, and is provided so as to go around the outer surface of the pressing plate 22A. By tightening the pressing plate 22A, the ultrasonic buffer 21 is further interposed via the pressing plate 22A. Has a function of pressing the entire ultrasonic absorber 14 evenly against the outer surface of the pipe 30.

  The acoustic matching adjustment unit 23 changes the degree of deformation of the ultrasonic buffer 21 by pressing by changing the tightening force of the tightening band 22B of the tightening unit 22 by the operator's tightening operation. Which influences the acoustic matching situation regarding the acoustic impedance of the pipe 30, the ultrasonic absorber 14, and the ultrasonic buffer 21, which influences the intensity of the pipe propagation wave reflected at the interface between the ultrasonic absorber 14 and the ultrasonic absorber 14. It has a function of adjusting the acoustic impedance of the buffer body 21.

  The propagation suppressing unit 24A is disposed between the ultrasonic absorber 14 and the transducer 13A on the outer peripheral surface 31 of the pipe 30, and between the ultrasonic buffer 21 and the tightening unit 22 (pressing plate 22A) and the transducer 13A. And has a function of suppressing the propagation of the absorber-propagating wave that has propagated through the ultrasonic absorber 14 among the ultrasonic waves transmitted from the transducer 13B to the transducer 13A.

  The propagation suppressing unit 24B is located between the ultrasonic absorber 14 and the transducer 13A in the outer peripheral surface 31 of the pipe 30, and between the ultrasonic buffer 21 and the tightening unit 22 (pressing plate 22A) and the transducer 13A. And the function of suppressing the propagation of the absorber propagating wave propagating through the ultrasonic absorber 14 among the ultrasonic waves transmitted from the transducer 13A to the transducer 13B.

  The propagation suppressing portions 24A and 24B are made of an open cell porous material having a large number of voids for containing air. When the fluid X is at a high temperature such as steam, a heat-resistant silicone resin may be used. In addition to this, for example, a sponge made of a polyimide resin can be used to cope with a fluid X having a higher temperature. . Furthermore, as the propagation suppressing portions 24A and 24B, inorganic fibers such as glass wool, rock wool, and urethane foam, which are open-cell porous materials, may be used. In addition, these propagation suppression parts 24A and 24B may be comprised from an air layer other than such a porous material, and can implement | achieve propagation suppression parts 24A and 24B with a simple structure.

[Attaching method of ultrasonic buffer]
Next, with reference to FIGS. 1-3, the attachment method of the ultrasonic buffer 21 with respect to the ultrasonic flowmeter 1 is demonstrated.
Here, as described in Patent Document 1, the case where the ultrasonic shock absorber 20 is attached later to the ultrasonic flowmeter 1 in which the ultrasonic absorber 14 is already provided in the pipe 30 will be described as an example. .

  First, after the ultrasonic buffer 21 is attached to the outer surface of the ultrasonic absorber 14 by a process such as winding or bonding, the ultrasonic wave is applied by the fastening portion 22 provided on the outer surface of the ultrasonic buffer 21. The buffer body 21 is pressed in the direction of the pipe 30 and tightened. At this time, with respect to the tightening portion 22, after the pressing plate 22 </ b> A is wound around the outer surface of the ultrasonic buffer 21, the tightening band 22 </ b> B is rotated around the outer surface of the pressing plate 22 </ b> A.

  Thereafter, the acoustic matching adjustment unit 23 is operated to change the tightening force of the tightening band 22B of the tightening unit 22. As a result, the degree of deformation of the ultrasonic buffer 21 due to the pressing of the tightening portion 22 changes, and the acoustic impedance of the ultrasonic buffer 21 changes. For this reason, the acoustic matching status regarding the acoustic impedance of the pipe 30, the ultrasonic absorber 14, and the ultrasonic buffer 21 is adjusted, and the intensity of the pipe propagation wave reflected at the interface between the pipe 30 and the ultrasonic absorber 14. Is reduced.

In this embodiment, the case where the pressing plate 22A is used has been described as an example. However, if the ultrasonic buffer 21 is not partially deformed by the tightening band 22B, the pressing plate 22A is omitted and tightening is performed. The ultrasonic buffer 21 may be directly clamped by the band 22B.
In this embodiment, the case where the tightening band 22B is used has been described as an example. However, the pressing plate 22A may be directly tightened by the acoustic matching adjustment unit 23.

[Operation of this embodiment]
Next, as an operation of the ultrasonic flowmeter 1 according to the present embodiment, an absorption action of a pipe propagation wave propagating through the pipe 30 will be described with reference to FIG. FIG. 4 is an explanatory diagram showing the principle of acoustic matching.

  When ultrasonic waves propagate through an arbitrary medium, the speed at which the medium particles vibrate with a constant sound pressure varies depending on the medium. In general, the ease (or difficulty) of such vibration of the medium particles is called acoustic impedance, and the acoustic impedance Z is the product of the density ρ of the medium and the speed of sound c at which the ultrasonic wave propagates in the medium, Z = It is represented by ρ · c.

When ultrasonic waves propagate between different media, the transmittance and reflectance of the ultrasonic waves at the medium interface change according to the acoustic impedance difference of each medium, and the reflectance increases as the acoustic impedance difference increases.
When propagating between media having such a large acoustic impedance difference, there is a method of matching the acoustic impedance by inserting a third medium called an acoustic matching layer between the two media.

As shown in FIG. 4, if between the medium M ₁ and the medium M ₂ of the acoustic impedance Z ₂ of the acoustic impedance Z _1, was inserted medium M ₃ in the acoustic impedance Z ₃ in the width L, the medium M _1, M ₃ and the acoustic matching condition in which the acoustic impedance is matched in the whole M ₂ is expressed by the following equations (1) and (2).
_{L = λ 3/4 ... (} 1)
Z ₃ = √Z ₁ Z ₂ (2)
Note that lambda ₃ is the characteristic wavelength of the medium M _3, if the density of the medium M ₃ and the speed of sound in the medium M ₃ and C ₃ has a [rho _3, obtained by _{λ 3 = C 3 / ρ 3} .

When such an acoustic matching condition is satisfied, the acoustic matching state becomes a matching state, the reflectivity at each of the medium interfaces R ₁₃ and R ₂₃ becomes zero, and the intensity I of the reflected wave with respect to the ultrasonic wave incident on the medium M _{1 3} becomes cello. Thereby, the reflection loss becomes zero, and the intensity I _{1 of the} ultrasonic wave incident on the medium M ₁ is equal to the intensity I _{2 of the} ultrasonic wave emitted from the medium M2.

In the present invention, even when the acoustic impedances Z ₁ , Z ₃ , and Z _{2 of the three} media M ₁ , M ₃ , and M ₂ are different from each other, it is possible to improve the propagation of ultrasonic waves by improving the acoustic matching situation. Focusing on the fact that the characteristics are obtained, these media M ₁ and M ₃ are regarded as the wall 33 of the pipe 30 and the ultrasonic absorber 14, and the ultrasonic buffer 21 corresponding to the medium M ₂ is used as the ultrasonic absorber 14. It is provided on the outer surface of the pipe so as to efficiently absorb the pipe propagation wave propagating through the pipe 30.

  In addition, an elastic porous body such as a silicone rubber sponge is focused on the fact that the volume of bubbles is reduced and the density is changed and the acoustic impedance is also changed by the pressure deformation. The tightening portion 22 is provided on the outer surface of the pipe 30 and the tightening force, that is, the pressing force with respect to the ultrasonic buffer 21 is adjusted by the acoustic matching adjusting section 23, so that the pipe 30 can be adjusted according to the acoustic impedance of the pipe 30 depending on the pipe material. The acoustic impedance of the ultrasonic buffer 21 that affects the acoustic matching state of the ultrasonic absorber 14 and the ultrasonic buffer 21 is adjusted.

FIG. 5 is a graph showing the acoustic matching characteristics, in which the horizontal axis represents the pipe acoustic impedance Z ₁ and the vertical axis represents the ultrasonic buffer acoustic impedance Z ₂ . In FIG. 5, the acoustic matching characteristic Q is the pipe acoustic impedance Z ₁ that satisfies the acoustic matching self-requirement when the acoustic impedance Z ₃ of the ultrasonic absorber 14 is fixed at 1.9e + 06 [Pa · s / m]. It shows the relationship between the ultrasonic cushion acoustic impedance Z _2.

For example, when the pipe 30 is made of an aluminum pipe (AL), the acoustic impedance Z ₁ is about 17e + 06 [Pa · s / m]. Therefore, it can be seen from the acoustic matching characteristic Q that the ultrasonic buffer acoustic impedance Z _{2 that} provides good acoustic matching with the pipe 30 is about 0.22e + 06 [Pa · s / m].
On the other hand, when the pipe 30 is made of stainless steel pipe (SUS), the pipe acoustic impedance Z ₁ is about 45 to 46e + 06 [Pa · s / m]. When the pipe 30 is made of SGP pipe (SGP), the pipe acoustic impedance Z ₁ is It is about 46e + 06 [Pa · s / m]. Therefore, it can be seen from the acoustic matching characteristic Q that the ultrasonic buffer acoustic impedance Z _{2 that} provides good acoustic matching with these pipes 30 is about 0.08e + 06 [Pa · s / m].

On the other hand, the ultrasonic buffer acoustic impedance Z ₂ of the silicone rubber (SG) itself without bubbles is about 0.2e + 06 [Pa · s / m]. By using rubber as the ultrasonic buffer 21, a good acoustic matching state can be obtained.
On the other hand, since the ultrasonic buffer acoustic impedance of air is about 0.0004e + 06 [Pa · s / m], a good acoustic matching condition can be obtained by using a silicone rubber sponge as the ultrasonic buffer 21. Will be.

Therefore, by using a silicone rubber sponge as the ultrasonic buffer 21 and pressing and deforming it, an ultrasonic buffer acoustic impedance that can obtain good acoustic matching with various pipes from aluminum pipes to stainless steel pipes and SGP pipes. Z ₂ can be obtained.
Thereby, the acoustic matching status of the pipe 30, the ultrasonic absorber 14, and the ultrasonic buffer 21 can be improved by an extremely simple operation of changing the tightening force of the tightening portion 22 by the tightening operation. It is possible to efficiently absorb the pipe propagation wave propagating through the pipe 30, that is, the noise component.

Further, in the present invention, propagation suppression units 24A and 24B are provided between the ultrasonic absorber 14 and the transducers 13A and 13B in the outer peripheral surface 31 of the pipe 30 so that the absorber propagation propagates through the ultrasonic absorber 14. Wave propagation to the transducers 13A and 13B is suppressed.
At this time, the propagation from the ultrasonic absorber 14 to the propagation suppression units 24A and 24B and the propagation from the propagation suppression units 24A and 24B to the transducers 13A and 13B are determined by the acoustic impedance of these media through which the ultrasonic wave passes. Is done.

In general, when the acoustic impedances of the _two media M ₁ and M ₂ are Z ₁ and Z ₂ , the reflectance r at the boundary between both M ₁ and M ₂ is obtained by the following equation (3).
r = {(Z ₂ −Z ₁ ) / (Z ₂ + Z ₁ )} ² (3)
Therefore, the reflectance r tends to increase as the difference between Z ₁ and Z ₂ increases.

For example, as described above, the acoustic impedance Z ₁ of the stainless steel pipe (SUS) or the SGP pipe (SGP) is about 46e + 06 [Pa · s / m], and the acoustic impedance Z _{2 of the} air is about 0.0004e + 06 [Pa · s / m], according to the above-described formula (3), the reflectance r between the two is about 99.9%, and the propagation of ultrasonic waves is substantially suppressed.

  Normally, the wedge resin used when the transducers 13A and 13B are fixed obliquely with respect to the outer peripheral surface 31 of the pipe 30 is often based on polyimide, and its acoustic impedance is 3e + 06 [Pa · s / m]. Therefore, as described above, when an elastic body having an acoustic impedance of 1.9e + 06 [Pa · s / m] is used as the ultrasonic absorber 14, the acoustic impedance between the transducers 13A and 13B and the ultrasonic absorber 14 is low. Get closer. In this case, according to the above-described equation (3), the reflectance r between the two is about 0.08%, and the ultrasonic wave is easily propagated.

Therefore, the propagation suppressing units 24A and 24B are preferably made of a material that differs from these acoustic impedances to a certain extent. If an air layer is used as the propagation suppressing units 24A and 24B, according to the above-described equation (3), the reflectance r between the elastic body of the ultrasonic absorber 14 and air is about 99.9%. Propagation of sound waves will be substantially suppressed.
In general, the porous material becomes closer to the air layer as the porosity (ratio of gap volume per unit volume) increases, and the acoustic impedance also decreases. Therefore, a porous material having a higher porosity than the ultrasonic absorber 14 and close to the acoustic impedance of air, for example, a porous material such as glass wool, rock wool, or urethane foam, may be used as the propagation suppressing portions 24A and 24B. I understand.

  FIG. 6 is a signal waveform diagram showing the absorption of noise components. FIG. 6A shows a received ultrasonic waveform (electric reception waveform) without the propagation suppressing units 24A and 24B, and FIG. A reception ultrasonic waveform (electric reception waveform) in the case where there are propagation suppression units 24A and 24B is shown. At this time, the fluid X was steam that flowed through the pipe 30 at a flow rate of 12 m / s at a pressure of 0.9 MPaG, the pipe 30 was a 25 A SGP pipe, and the ultrasonic frequency was 1 MHz.

In FIG. 6, the signal component corresponds to a fluid propagation wave propagated through the fluid X, and the noise component corresponds to a pipe propagation wave propagated through the pipe 30 itself.
Comparing these FIG. 6 (a) and FIG. 6 (b), the amplitude of the absorber propagation wave, that is, the noise component is greatly attenuated by providing the ultrasonic buffer 21 and adjusting the acoustic impedance. It can be seen that the propagation suppression units 24A and 24B are effectively suppressed.

[Effects of the present embodiment]
As described above, in the present embodiment, the ultrasonic absorber 14 that absorbs the pipe propagation wave propagating through the pipe 30 among the ultrasonic waves is provided on the outer peripheral face 31 of the pipe 30. In the propagation suppressing units 24A and 24B provided between the sound absorber 14 and the transducers 13A and 13B, the propagation of the absorber propagating wave propagating through the ultrasonic absorber 14 out of the ultrasonic waves to the transducers 13A and 13B is suppressed. It is what you do.

  Thereby, while being able to reduce the noise component which consists of a pipe propagation wave which propagates the piping 30, the noise component resulting from the absorber propagation wave which propagates the ultrasonic absorber 14 itself can also be reduced. Therefore, the S / N ratio indicating the ratio of the noise component to the signal component corresponding to the fluid propagation wave propagating through the fluid X can be improved, and as a result, extremely good measurement accuracy can be obtained.

  Moreover, in this Embodiment, it consists of the mat-like elastic porous body provided in the outer surface 31 of the ultrasonic absorber 14, and the piping 30 resulting from the difference of the acoustic impedance of the piping 30 and the ultrasonic absorber 14 and An ultrasonic buffer 21 for buffering the reflection of the pipe propagation wave at the interface with the ultrasonic absorber 14 is provided, and the acoustic matching adjustment unit 23 is used to tighten the tightening unit 22 provided on the outer surface of the ultrasonic buffer 21. By changing the applied force according to the tightening operation and changing the degree of deformation of the ultrasonic buffer 21 by pressing, the acoustic matching status of the pipe 30, the ultrasonic absorber 14, and the ultrasonic buffer 21 is changed left and right. The acoustic impedance of the ultrasonic buffer 21 is adjusted, and the propagation suppressing portions 24A and 24B are connected to the ultrasonic absorber 14, the ultrasonic buffer 21, the tightening portion 22 and the transducer on the outer peripheral surface of the pipe 30. P o 13A, may be provided between the 13B.

  Thereby, the acoustic matching status of the pipe 30, the ultrasonic absorber 14, and the ultrasonic buffer 21 can be improved by an extremely simple operation of changing the tightening force of the tightening portion 22 by the tightening operation. The ultrasonic wave absorber 14 can be efficiently absorbed by the same ultrasonic wave absorber 14 without replacing the ultrasonic wave absorber 14, i.e., the noise component, and the ultrasonic wave absorber 14 and the ultrasonic wave buffer. 21 and the propagation of the ultrasonic wave propagating through the tightening portion 22 to the transducers 13A and 13B can be suppressed, and extremely good measurement accuracy can be obtained.

[Extended embodiment]
The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Ultrasonic flowmeter, 10 ... Flowmeter main body, 11 ... Switching part, 12 ... Measurement processing part, 13A, 13B ... Transducer, 14 ... Ultrasonic absorber, 20 ... Ultrasonic buffer, 21 ... Ultrasonic buffer , 22 ... clamping part, 22A ... pressing plate, 22B ... clamping band, 23 ... acoustic matching adjustment part, 24A, 24B ... propagation suppression part, 30 ... piping, 31 ... outer peripheral surface, 32 ... inner peripheral surface, 33 ... Wall.

Claims (4)

An ultrasonic flowmeter that measures the flow rate of the fluid based on ultrasonic waves transmitted and received so as to pass the fluid flowing in the pipe by a transducer provided on the outer peripheral surface of the pipe,
An ultrasonic absorber that is provided on an outer peripheral surface of the pipe and absorbs a pipe propagation wave propagating through the pipe among the ultrasonic waves;
Of the outer peripheral surface of the pipe, provided between the ultrasonic absorber and the transducer, suppresses propagation of the absorber propagating wave propagating through the ultrasonic absorber of the ultrasonic wave to the transducer. An ultrasonic flowmeter comprising: a propagation suppression unit. The ultrasonic flowmeter according to claim 1,
An ultrasonic buffer that is made of a mat-like elastic porous body provided on the outer surface of the ultrasonic absorber, and buffers reflection of the pipe propagation wave at the interface between the pipe and the ultrasonic absorber;
A tightening portion that is provided on an outer surface of the ultrasonic buffer, and presses and tightens the ultrasonic buffer in the direction of the pipe;
Reflecting at the interface by changing the tightening force of the tightening portion according to the operation and changing the degree of deformation of the ultrasonic buffer due to the pressing to change the acoustic impedance of the ultrasonic buffer. Further comprising an acoustic matching adjustment unit that adjusts an acoustic matching state related to an acoustic impedance of the pipe, the ultrasonic absorber, and the ultrasonic buffer, which influences the intensity of the pipe propagating wave.
The ultrasonic wave flowmeter characterized in that the propagation suppressing part is provided between the ultrasonic absorber, the ultrasonic buffer, and the tightening part and the transducer in the outer peripheral surface of the pipe. . The ultrasonic flowmeter according to claim 1 or 2,
The ultrasonic flowmeter, wherein the propagation suppressing unit is made of a porous material or an air layer having a large number of voids for containing air. An ultrasonic flow measurement method used in an ultrasonic flowmeter that measures the flow rate of the fluid based on ultrasonic waves transmitted and received so as to pass through the fluid flowing in the pipe by a transducer provided on the outer peripheral surface of the pipe,
The ultrasonic absorber provided on the outer peripheral surface of the pipe absorbs a pipe propagation wave propagating through the pipe among the ultrasonic waves, and an ultrasonic absorption step,
Propagation suppression unit provided between the ultrasonic absorber and the transducer in the outer peripheral surface of the pipe is configured to transmit the absorber propagating wave propagating through the ultrasonic absorber of the ultrasonic wave to the transducer. An ultrasonic flow rate measurement method comprising: a propagation suppression step for suppressing propagation.

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