JP2000304581A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the flow rate of fluid without disordering the flow by smoothing the fitting part for an ultrasonic sensor with the internal surface of a measurement tube. SOLUTION: Ultrasonic sensors 2A and 2B consisting of an ultrasonic vibrator 21, a 1st sound matching layer 31, and a 2nd sound matching layer 32 have their transmission and reception sides arranged opposite vertically at oblique positions of the measurement tube 1, and the 1st sound matching layer 31 has a 1st interface, joined with the ultrasonic vibrator 21, at right angles and a 2nd interface 23, joined with the 2nd sound matching layer 32, at a tilt angle. The material of the 1st sound matching layer 31 is homogeneous in the propagation direction of an ultrasonic wave and has such tilt characteristics that the propagation speed varies in layers or continuously at right angles to the propagation direction; and the length of the 1st sound matching layer 31 in the ultrasonic-wave propagation direction is 1/4 as long as the wavelength of the propagated ultrasonic wave and the 2nd sound matching layer 32 is so made wide that the ultrasonic wave refracted by the 2nd interface 23 can be radiated to measured fluid 1a from a 3rd interface 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter for measuring a fluid flow rate using an ultrasonic technique, and more particularly to an ultrasonic flowmeter for gas.

[0002]

2. Description of the Related Art Referring to FIG. 7, an ultrasonic flowmeter according to the prior art comprises an ultrasonic transducer 4 and an acoustic matching layer 5 which is joined to the ultrasonic transducer 4 and emits sound waves from the other surface. The sensors 4A and 4B are configured such that the transmitting side and the receiving side are arranged so as to be inclined with respect to the measuring pipe 1 in which the measuring fluid 1a is conveyed.

In such a configuration, the ultrasonic flowmeter excites the ultrasonic vibrator 4 of one ultrasonic sensor (for example, 4 A) to match the acoustic impedance with the fluid 1a via the acoustic matching layer 5, and The ultrasonic transducer 4 transmits an ultrasonic signal 4a, and the ultrasonic transducer 4 receives the transmitted ultrasonic signal 4a via the acoustic matching layer 5 of the other ultrasonic sensor (4B). The transmission and reception of the ultrasonic signal 4a are alternately switched to measure the propagation time difference ΔT between the propagation time of the ultrasonic signal 4a to the upstream side and the propagation time to the downstream side. The flow velocity or flow rate of the fluid 1a can be measured.

[0004] The ultrasonic flowmeter shown in FIG.
The transmitting side and the receiving side of the ultrasonic sensors 4A and 4B are disposed so as to be in contact with and in contact with the fluid 1a. At the installation part of the ultrasonic sensors 4A and 4B of this ultrasonic flow meter, the measuring tube 1
The inner surface of the measuring tube 1 has a protruding portion and a concave portion with respect to the inner surface of the measuring tube 1. The inner surface of the measuring tube 1 forms a smooth surface for the fluid 1a flowing through the mounting portion of the ultrasonic sensors 4A and 4B. I haven't. For this reason, the fluid 1a to be measured is disturbed near the mounting portion of the ultrasonic sensors 4A and 4B, and the fluid 1a
Could not be accurately measured.

Although not shown in the figure, the transmitting side and the receiving side of the ultrasonic sensors 4A and 4B are arranged to be inclined to the outside of the measuring pipe 1 so as to face each other. fluid
The flow velocity of 1a can be measured. In this measurement method, when the fluid 1a is a liquid, the acoustic impedance of the fluid 1a is still relatively large, so that the ultrasonic waves can be propagated into the fluid 1a through the measuring tube 1. However, when the fluid 1a is a gas, Is
Since the acoustic impedance of the fluid 1a is small, a reflection phenomenon occurs at the interface between the measurement tube 1 and the gas of the fluid 1a, and it is difficult to propagate the ultrasonic wave into the fluid 1a.

Therefore, the method of disposing the ultrasonic sensor outside the measurement pipe 1 is generally a case where the fluid 1a is composed of a liquid. In this case, the fluid 1a in the measurement pipe 1 is Although there is a feature that the flow is not disturbed, the ultrasonic signals 4a received by the ultrasonic sensors (4A) and 4B on the receiving side which are arranged to be opposed to each other while being propagated through the measuring fluid 1a in the measuring pipe 1 and inclined. In addition, an ultrasonic signal (4c) having a high propagation velocity, which is directly received by the ultrasonic sensors (4A) and 4B on the receiving side, which is directly opposed to the pipe of the measuring pipe 1 and is disposed as a noise component, becomes a noise component. Exists. In a normal flow rate measurement, the ultrasonic signal (4c) directly propagating through the pipe of the measurement pipe 1 and received is removed by masking at the time of reception, but the diameter of the measurement pipe 1 is small. When this mask processing is used, the ultrasonic signal of the noise component
It becomes difficult to remove (4c) stably. Therefore, as described above, a method of directly contacting the ultrasonic sensors 4A and 4B with the measurement fluid 1a is performed.

[0007]

As described above, in the ultrasonic flowmeter according to the prior art, the flow of the fluid is disturbed by the unevenness at the portion where the ultrasonic sensor comes into contact with the fluid, and the reception amplitude of the ultrasonic signal is increased. Fluctuates, which affects the measurement of the propagation time difference, causing a flow measurement error.

[0008] The present invention has been made in view of the above points, and an object of the present invention is to solve the above-mentioned problems and to smooth the mounting portion of the ultrasonic sensor on the inner surface of the measurement pipe, An object of the present invention is to provide an ultrasonic flowmeter for measuring a flow rate without disturbing a flow of a fluid to be measured.

[0009]

According to the present invention, there is provided an ultrasonic transducer, a first acoustic matching layer joined to the ultrasonic transducer at a first interface, and a first acoustic matching layer. And the second
And a second acoustic matching layer that radiates sound waves from a third interface formed in parallel with the first interface and joined at the interface. The first and the second acoustic matching layer of the ultrasonic sensor are disposed vertically at a position where the sides are obliquely opposed to each other.
The first interface to be joined to the ultrasonic vibrator is at a right angle, and the second interface to be joined to the second acoustic matching layer is an oblique angle formed by obliquely cutting a columnar body, and the material constituting the first acoustic matching layer Is homogeneous in the ultrasonic wave propagation direction, and the direction perpendicular to the propagation direction has a slope characteristic that changes laminar or continuously, and the propagation speed in the ultrasonic wave propagation direction changes according to each position in the perpendicular direction. The length of the first acoustic matching layer in the ultrasonic wave propagation direction is set to 1/4 wavelength of the ultrasonic wave propagating at each position, and the second acoustic matching layer of the ultrasonic sensor is joined to the first acoustic matching layer. The second interface is defined as the angle of inclination of the second interface of the first acoustic matching layer, and the dimension of the third interface is such that at least ultrasonic waves refracted at the second interface radiate from the third interface to the measurement fluid. And

With this configuration, the ultrasonic waves generated by the ultrasonic vibrator are incident on the first acoustic matching layer via the first interface, and are transmitted at the sound propagation speed determined for each position of the first acoustic matching layer. 2 Since the light propagates to the second interface with the acoustic matching layer and the length of this ultrasonic wave propagation direction is 1/4 wavelength of the propagating ultrasonic wave, it is refracted at the inclined position formed by the second interface, The reflection phenomenon at the second interface is reduced, and the ultrasonic wave is efficiently transmitted to the second interface.
It can propagate through the acoustic matching layer. In addition, since the third interface, which is the radiation surface from the second acoustic matching layer, is disposed smoothly with the pipe or the measurement fluid on the pipe inner surface, the flow rate must be measured without disturbing the flow of the fluid to be measured. Can be.

The first acoustic matching layer has a constant propagation velocity in the direction of propagation of the ultrasonic wave, and is compounded in a layered manner in a direction perpendicular to the propagation direction, and the product value ρc of the sound velocity c and the density ρ of the material. The sound impedance c is set to a predetermined value, and the distribution of the sound velocity c is configured to be inclined in a stepwise manner.
The acoustic impedance of the acoustic matching layer can be smaller than the acoustic impedance of the first acoustic matching layer.

The first acoustic matching layer has a constant propagation speed in the ultrasonic wave propagation direction and is continuously inclined and mixed in a direction perpendicular to the propagation direction. The product value of the sound velocity c and the density ρ of the material The acoustic impedance composed of ρc is set to a predetermined value, and the distribution of the sound velocity c is continuously inclined. The acoustic impedance of the second acoustic matching layer is smaller than the acoustic impedance of the first acoustic matching layer. Can be.

With such a configuration, the acoustic impedance of the second acoustic matching layer is kept matched with the measuring fluid or the measuring fluid on the inner surface of the measuring pipeline, or particularly when the fluid is gas, the acoustic impedance of the measuring fluid is reduced. The acoustic impedance of the second acoustic matching layer is reduced as much as possible, and the acoustic impedance is inclined and mixed with the ultrasonic wave propagation direction, so that the ultrasonic wave from the ultrasonic sensor can be efficiently inclined to the measurement fluid at an angle. Can be propagated.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a main part of an ultrasonic flowmeter according to one embodiment of the present invention, and FIG. 2 is an explanatory diagram of a first acoustic matching layer and a second acoustic matching layer according to one embodiment. 3 is an explanatory view of a first acoustic matching layer that is inclinedly blended stepwise, FIG. 4 is an explanatory view of a first acoustic matching layer that is continuously inclinedly blended, FIG. 5 is an explanatory view of a balloon, and FIG. FIG. 9 is an explanatory view of a first acoustic matching layer which is continuously inclined and mixed by the method, and the same members corresponding to FIGS. 7 and 8 are denoted by the same reference numerals.

In FIG. 1, an ultrasonic flowmeter according to the present invention includes an ultrasonic oscillator 21 and a first interface with the ultrasonic oscillator 21.
A first acoustic matching layer 31 (3a, 3b, 3c,...) Joined at 22;
This first acoustic matching layer 31 and the second interface 23 are joined at the first interface
The ultrasonic waves 2a, 2b, 2c
The ultrasonic sensors 2A and 2B, which are composed of the second acoustic matching layer 32 emitting 2 m, and the transmitting side and the receiving side are obliquely opposed to the measuring pipe 1 in which the fluid 1a is conveyed. It is configured to be deployed vertically.

The first acoustic matching layer of the ultrasonic sensors 2A, 2B
Reference numeral 31 denotes a layered structure of acoustic matching layers (3a, 3b, 3c,...) In the illustrated example, and a propagation direction (vertical direction in the illustrated example) of ultrasonic waves (2a, 2b, 2c,. The first interface 22 joined to the ultrasonic vibrator 21 has a right angle, and the second interface 23 joined to the second acoustic matching layer 32 has an inclination angle formed by cutting a columnar body obliquely. 31 (3a, 3b, 3c, ...) is homogeneous in the direction of propagation of the ultrasonic wave, and the direction perpendicular to this direction of propagation has a layered or continuously changing inclination characteristic. Position ((i = a, b, c ...) or
(x) In the following, the position in the perpendicular direction is i for stepwise, x for continuous
), Or the propagation velocity (ci = ca, cb, cc,...) Or (cx) in the propagation direction of the ultrasonic wave (2a, 2b, 2c...) This ultrasonic (2a, 2b, 2c ・
The length of the first acoustic matching layer 31 (3a, 3b, 3c...) In the propagation direction of the ultrasonic waves (2a, 2b, 2c) propagating at each position (i or x)
..) or (cx) 1/4 wavelength.

The second acoustic matching layer 32 of the ultrasonic sensors 2A and 2B has a second interface 23 joined to the first acoustic matching layer 31 with the same inclination angle as the second interface 23 of the first acoustic matching layer 31. And the third
The dimensions of the interface 24 are such that at least the ultrasonic waves 2a, 2b, 2c,... 2m refracted at the second interface 23
It is configured to have a spread that can radiate to 1a.

With this configuration, the ultrasonic waves generated by the ultrasonic transducer 21 are transmitted through the first interface 22 to the first acoustic matching layer 31 (3
a, 3b, 3c, ..), and the first acoustic matching layer 31 (3a, 3c).
b, 3c, ...)) sound wave propagation velocity (ca, c
b, cc,...) and propagates to the second interface 23 with the second acoustic matching layer 32, and the length of this ultrasonic wave propagation direction is 1/4 wavelength of the propagating ultrasonic wave. The light is refracted at an angle determined by a ratio between the inclination angle formed by the second interface 23 and the sound wave propagation speed between the first acoustic matching layer 31 and the second acoustic matching layer 32. This second interface 23
The ultrasonic wave can efficiently propagate through the second acoustic matching layer 32. Also, the second acoustic matching layer 32
Since the third interface 24, which is a radiation surface from, is disposed smoothly with the pipe 1 or the measurement fluid 1a on the inner surface of the pipe 1, the flow rate can be measured without disturbing the flow of the fluid 1a to be measured. .

[0019]

2 and 3 show the structure of the first acoustic matching layer 31 in which the distribution of the sound velocity of the ultrasonic sensor of the present invention is graded in a stepwise manner, and FIGS. 4 to 6 show that the distribution of the sound velocity is continuous. The following description focuses on an example of the configuration of the first acoustic matching layer 31 that is inclinedly mixed. (Embodiment 1) In FIG.
Is that the material properties composed in the propagation direction of the ultrasonic waves (2a, 2b, 2c ...) are constant, and the material properties composed in the direction perpendicular to the propagation direction of the ultrasonic waves (2a, 2b, 2c ...) Is mixed in a gradient, and the acoustic impedance (ρi ci, ρx cx) represented by the product value ρc of the sound velocity c (ci, cx) and the density ρ (ρi, ρx) of this material
Is constant, and the distribution of the sound speed c is inclined and mixed stepwise.

The first acoustic matching layer 31 has, for example, a sound velocity c (Ci) and a density ρ (ρi) different from each other as shown in FIG.
In addition, materials (3a, 3b, 3c ·) having the same product value ρc (ρi ci)
・) Are laminated in layers. This bonding is the sound speed c
Are arranged in the relation shown in the equation (1) according to the magnitude relation of

[0021]

C a <c b <c c <· <c i <(1) The first acoustic matching layer 31 forms the first interface 22 on the bonding surface side with the ultrasonic transducer 2 at a right angle, Materials (3a, 3b, 3c ・
In each layer, the length Li of the layer is set to a quarter wavelength (1 / 4λi) represented by the equation (2), and the thickness of the layer is set to the length Li (La, Lb, Lc) of each layer.
・ ・) Is selected so that the line connecting the central part of this layer is a straight line.

[0022]

Li = (1/4) λi = ci / 4f (2) where ci is the sound speed ca, cb, cc,..., F is the frequency of the ultrasonic wave. The second interface 23 bonded to the first acoustic matching layer 31 has the same inclination angle as the second interface 23 of the first acoustic matching layer 31, and the third interface formed parallel to the first interface 22
24 is at least the ultrasonic wave refracted at the second interface 23
... 2m are provided such that they can be radiated from the third interface 24 to the measurement fluid 1a without being reflected on the side surface of the second acoustic matching layer 32.

FIG. 2A shows the length Li (La, Lb, Lc.
・) Is made slightly longer than the dimension of formula (2), and the second interface 23
Can be formed by smooth polishing, or the first acoustic matching layer 31 described above can be configured to be long, and cut and polished to form a plurality of first acoustic matching layers 31. FIG.
(B) shows that the length Li (La, Lb, Lc.
It can be constituted by laminating in a layered manner with the dimensions of the formula. (Embodiment 2) The first acoustic matching layer 31 shown in FIG. 4 is another embodiment, in which the material characteristics in the ultrasonic wave propagation direction are uniform, and the material characteristics in the direction perpendicular to the ultrasonic wave propagation direction are inclined. The acoustic impedance composed of the product value ρx cx of the sound velocity cx and the density ρx of the material is selected to a predetermined value, and the distribution of the sound velocity cx is continuously (or stepwise) inclined and blended. Things.

The first acoustic matching layer 31 having such a configuration can be configured as follows. In FIG. 4 (A), plastic or glass balloons (hereinafter, abbreviated as balloons) having different densities ρ1 and ρ2 shown by white circles and black circles are mixed with uncured low-viscosity resin for a certain period of time. put. Then, by the action of gravity, the density ρ
As shown in FIG. 4 (B), the distribution of balloons having different ρ1 takes a position x in the vertical direction, and a dark balloon having a density ρ1 indicated by a black circle in a low-viscosity resin moves downward. Many balloons are distributed, and thin white circle balloons of density ρ2, which are illustrated by white circles, are distributed upward, and the distribution of black and white circle balloons is distributed at a substantially uniform concentration in the horizontal direction. A distribution can be created.

By curing the resin in this state,
The first acoustic matching layer 31 having a different sound speed cx and a different density ρx can be manufactured. In manufacturing the first acoustic matching layer 31, any balloon such as a plastic sphere or a glass sphere can be used as long as the value of the density ρ can be controlled.

FIG. 5 shows a plastic balloon or a glass balloon, which can be composed of a hollow plastic sphere or a hollow glass sphere, respectively. (Embodiment 3) In FIG. 6 (A), uncured low-viscosity resin was mixed with charged plastic spheres or metal powders having different densities ρ3, ρ4 as shown by white circles and black circles to form an electric field. Alternatively, it is inserted in a magnetic field. The charged plastic sphere or metal powder body is subjected to the action of an electric field or a magnetic field, as shown in FIG. 6B, takes a position x in the lateral direction in the illustrated example, and electrophoreses (or magnetizes). In the resin, many balloons of density ρ3 shown in black circles are distributed to the left, and many white circle balloons of density ρ4 shown in white circles are distributed to the right. As a result of the distribution, a step-like or continuous density distribution can be generated. By curing the resin in this state, the first acoustic matching layer 31 having a different sound velocity cx and a different density ρx can be manufactured.

In producing the first acoustic matching layer 31, the first acoustic matching layer 31 is formed by increasing or decreasing the amount of the plastic sphere or metal powder for each charge amount without changing the density of the plastic sphere or metal powder. Acoustic matching layer
31 tilt characteristics can be controlled.

[0028]

As described above, in the ultrasonic flowmeter according to the present invention, the angle between the ultrasonic radiation surface of the acoustic matching layer and the vibration surface of the ultrasonic transducer is controlled by the mounting angle of the ultrasonic sensor. Thus, the portion where the ultrasonic sensor is attached to the inner surface of the measurement tube of the ultrasonic flowmeter can be smoothed, and the flow rate can be measured without disturbing the flow of the fluid to be measured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of an ultrasonic flowmeter as one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a first acoustic matching layer and a second acoustic matching layer according to one embodiment.

FIG. 3 is an explanatory view of a first acoustic matching layer that is graded and mixed stepwise.

FIG. 4 is an explanatory view of a first acoustic matching layer that is continuously compounded with a gradient.

FIG. 5 is an explanatory view of a balloon.

FIG. 6 is an explanatory view of a first acoustic matching layer which is continuously graded by another method.

FIG. 7 is a configuration diagram of a main part of an ultrasonic flowmeter according to the related art.

FIG. 8 is an explanatory diagram of an acoustic matching layer according to the related art.

[Explanation of symbols]

 1 Measuring tube 1a Measuring fluid 21, 4 Ultrasonic transducer 22 First interface 23 Second interface 24 Third interface 2A, 2B, 4A, 4B Ultrasonic sensor 2a, 2b, 2c ... 4a, 4c Ultrasonic signal 31, 3a, 3b, 3c ··· 5 first acoustic matching layer 32 second acoustic matching layer 35 balloon 36 hollow ρ, ρi, ρx density c, ci, cx sound velocity i, x position

Claims (3)

[Claims] 1. An ultrasonic vibrator and a first ultrasonic vibrator
A first acoustic matching layer joined at the interface, and a second acoustic matching layer joined at the first acoustic matching layer and the second interface and emitting a sound wave from a third interface formed in parallel with the first interface. The ultrasonic sensor is disposed vertically at a position where the transmitting side and the receiving side are obliquely opposed to the measurement pipe in which the fluid is conveyed, and the first acoustic matching layer of the ultrasonic sensor The first interface to be joined to the ultrasonic transducer is perpendicular to the direction,
The second interface to be joined to the acoustic matching layer has a slant angle formed by cutting the columnar body obliquely, and the material constituting the first acoustic matching layer is homogeneous in the ultrasonic wave propagation direction and perpendicular to the propagation direction. The direction has a layered or continuously changing inclination characteristic, and the propagation speed in the ultrasonic wave propagation direction changes according to each position in the perpendicular direction. The length of the first acoustic matching layer in the ultrasonic wave propagation direction is: The second acoustic matching layer of the ultrasonic sensor has a second interface bonded to the first acoustic matching layer and a slope of the second interface of the first acoustic matching layer. An ultrasonic flowmeter, wherein the angle is an angle, and the dimension of the third interface has at least an extent that an ultrasonic wave refracted at the second interface radiates from the third interface to the measurement fluid. 2. The ultrasonic flowmeter according to claim 1, wherein the first acoustic matching layer has a constant propagation speed in the ultrasonic wave propagation direction, and the direction perpendicular to the propagation direction is inclined and mixed in a layered manner.
The acoustic impedance consisting of the product value ρc of the sound velocity c and the density ρ of this material is set to a predetermined value, and the distribution of the sound velocity c is graded in a stepwise manner, and the acoustic impedance of the second acoustic matching layer is (1) An ultrasonic flowmeter, which is smaller than an acoustic impedance of an acoustic matching layer. 3. The ultrasonic flowmeter according to claim 1, wherein the first acoustic matching layer has a constant propagation speed in an ultrasonic propagation direction, and a direction perpendicular to the propagation direction is continuously inclined and mixed. The acoustic impedance consisting of the product value ρc of the sound velocity c and the density ρ of this material is set to a predetermined value, and the distribution of the sound velocity c is continuously inclined and compounded. The acoustic impedance of the second acoustic matching layer is (1) An ultrasonic flowmeter, which is smaller than an acoustic impedance of an acoustic matching layer.