JPH09287990A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter which is compact and gives a high degree of measurement accuracy. SOLUTION: In this ultrasonic flowmeter, a fluid substance is brought to flow in a measurement tube 2, and an ultrasonic wave emitted from either one of electroacoustic converting means 1a or 1b is brought to pass through the fluid substance which flows through the measurement tube 2 and received by the other one of the electroacoustic converting means 1a or 1b. The flow measurement of the fluid substance flowing in the measurement tube 2 is performed by measuring the time of ultrasonic propagation with switching the converting means 1a and 1b. The propagation pass Tc of ultrasonic waves formed by a pair of the electroacoustic converting means 1a and 1b is arranged in shape of letter V that the waves are reflected and received in the measurement tube. A sound insulator 2c is provided at the inside wall of the measurement tube 2 between a pair of the electroacoustic converting means 1a and 1b. This sound insulator 2c enables direct propagation waves which propagate along the surface of the inside wall of the measurement rube, for effective insulation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flow meter which allows a fluid substance such as gas or liquid to flow through the inside of a measuring tube and measures the flow rate thereof, and particularly to improve the measurement accuracy. Ultrasonic flowmeter capable of

[0002]

2. Description of the Related Art An ultrasonic flowmeter is a flowmeter of a flow velocity measuring type. The flow rate is obtained by measuring the flow velocity of a fluid substance such as gas or liquid flowing inside a measuring pipe, and multiplying the measured flow velocity by a pipe cross-sectional area or the like. Required by. Then, the flow velocity measurement by this kind of ultrasonic wave is provided with a pair of electric-acoustic conversion means, and the ultrasonic wave emitted from one electric-acoustic conversion means is transmitted through the fluid substance in the measuring tube to make the other electric It is performed by receiving the waves by the acoustic conversion means, switching between them, measuring the ultrasonic wave propagation time, and obtaining the reciprocal difference of the propagation time of the ultrasonic beam.

FIG. 5 is a sectional view showing an example of a conventional ultrasonic flowmeter of this type. In the example shown in FIG. 5, a pair of electro-acoustic conversion means 1a and 1b are directly opposed to the inner wall portions of the measuring tube 2 which face each other with an inclination of about 45 degrees with respect to the axis of the measuring tube 2. It is arranged.

According to the ultrasonic flowmeter shown in FIG. 5, one electric-acoustic converting means 1a is switched to the other electric-acoustic converting means 1b, and the other direction is a straight line as shown by a solid line in the figure. Ultrasonic wave propagates through the typical propagation path Ta,
By measuring the propagation velocity of the ultrasonic wave in the propagation path Ta, the flow rate of the fluid substance flowing through the measuring pipe 2 can be calculated.

That is, the ultrasonic beam emitted from the ultrasonic wave transmitters / receivers 1a and 1b as electric-acoustic conversion means provided on the upstream side and the downstream side with respect to the flow direction of the fluid substance to the measuring pipe 2. Are switched on both sides to repeatedly measure the forward and backward propagation times t1 and t2.

By calculating the measured time as an inverse number, the influence of the sound velocity C is eliminated and the following equation is obtained.

T1 = L1 / (C + Vcos θ1) Equation 1 t2 = L1 / (C-Vcos θ1) Equation 2

From Equation 1 and Equation 2, V = (L1 / 2cos θ1) × [(1 / t1)-(1 / t1)] Equation 3

Where L1 is the propagation path length of ultrasonic waves (L1 =
D / sin θ1) D: Inner diameter of pipe C: Velocity of sound in fluid substance θ1: Angle between ultrasonic wave propagation path and tube axis V: Average line velocity on ultrasonic wave propagation path

The ultrasonic velocity meter having this structure is a device for measuring the average velocity along the acoustic path. Then, the flow velocity distribution in the measuring pipe changes depending on the flow rate. In order to obtain this flow rate, it is necessary to correct the change in the flow velocity distribution. The volume flow rate Q is the measured linear average flow velocity V and the cross-sectional area A of the measurement part.
And the flow velocity distribution correction coefficient Kn.

That is, it can be expressed by the following equation 4.

Q = A × V × Kn ... Equation 4

The Kn is the ratio of the measured linear average flow velocity to the average flow velocity in the cross section of the pipe, and is a function of the Reynolds number.

Kn = 1 / (1.119−0.011 log Re) Equation 5

Kn in the laminar flow region can be theoretically calculated, and Kn = 0.75 (constant) is obtained. Here, the flow when the Reynolds number is smaller than 2320 is called laminar flow, and its distribution is constant and does not change.

Using the apparatus shown in FIG. 5, the above equation 1 is used.
It is possible to calculate the flow rate of the fluid substance by calculating with a theoretical formula such as Formula 5.

By the way, in order to improve the measurement accuracy of the flow meter having the above-mentioned structure, it is necessary to accurately measure the propagation time of the ultrasonic beam. In this case, it is possible to accurately measure the propagation time of the ultrasonic beam by increasing the propagation distance of the ultrasonic beam,
Therefore, the measurement accuracy of the flow rate can be improved.

However, in the configuration shown in FIG. 5, the propagation distance Ta between the one and the other electro-acoustic converting means 1a and 1b is determined by the one electro-acoustic converting means 1a and the other electro-acoustic converting means. 1b is about 1.4 times the axial distance L2 of the measuring tube from 1b, and when the measuring tube 2 is formed in a small size, the propagation distance Ta cannot be made large and the ultrasonic flow rate There is a limit to improving the measurement accuracy of the meter.

Therefore, as a means for increasing the propagation distance between the pair of electro-acoustic converting means 1a and 1b while forming the measuring tube in a small size, a configuration as shown in FIG. 6 can be considered. In the configuration shown in FIG. 6, a pair of electro-acoustic converting means 1a and 1b are arranged on one inner wall 2a of the measuring tube 2, and the other inner wall 2b of the measuring tube 2 is used as a reflection surface of ultrasonic waves. By making the ultrasonic wave propagation path Tb substantially V-shaped, the propagation distance can be increased.

According to the configuration shown in FIG. 6, the electro-acoustic conversion means 1a and 1b with respect to the axis of each measuring tube 2 are arranged.
When the ultrasonic wave emission angle θ is 45 degrees, the propagation distance can be doubled as compared with the example shown in FIG. Therefore, the measurement accuracy of the ultrasonic flowmeter can be further improved.

[0021]

As described above, according to the configuration shown in FIG. 6, the propagation distance of ultrasonic waves can be doubled as compared with the configuration shown in FIG. 5, and therefore, the measurement accuracy of the ultrasonic flowmeter can be improved. Can be expected to improve.

However, the output energy of ultrasonic waves from the pair of electro-acoustic conversion means 1a and 1b has a relatively wide range of directional characteristics, and a part of the ultrasonic signal other than the ultrasonic output axis is present. Is emitted.

For this purpose, as shown in FIG. 6, one electric-acoustic conversion means 1a is transmitted from the one electric-acoustic conversion means 1a along the surface path of one inner wall 2a of the measuring tube 2 in which a pair of electric-acoustic conversion means 1a, 1b are arranged. A phenomenon occurs in which a part of the ultrasonic signal directly propagates (directly propagated wave) in the other electro-acoustic converting means 1b and in the opposite direction, as indicated by a broken line Ts in the figure.

The direct propagating wave Ts as shown in FIG.
Appears immediately before the arrival of the original wave, or at the same time,
A measurement error is generated by causing waveform distortion etc. to the original received wave. This degree includes a problem that the measurement error increases as the flow rate in the measuring tube 2 increases, that is, as the flow rate increases.

The present invention has been made in view of the above-mentioned problems of the conventional one, and in particular, the ultrasonic wave emitted from one electro-acoustic conversion means is reflected in the measuring tube to make the other electro-acoustic. In an ultrasonic flowmeter having a V-shaped ultrasonic wave propagation path that is received by a conversion means, it is possible to reduce the factors that receive an interfering wave other than the original received wave and improve the measurement accuracy. It is intended to provide.

[0026]

The ultrasonic flowmeter according to the present invention, which has been made in order to achieve the above-mentioned object, is arranged so that ultrasonic waves emitted from one of the electro-acoustic conversion means are contained in a fluid substance in a measuring tube. An ultrasonic flowmeter which transmits the other electric-acoustic conversion means to receive, and switches the both to measure the ultrasonic propagation time to measure the flow rate of the fluid substance flowing inside the measuring tube, A V-shaped ultrasonic wave propagation path is formed in which the ultrasonic wave emitted from the one electric-acoustic conversion means is reflected in the measuring tube and is received by the other electric-acoustic conversion means, and the one electric-acoustic conversion is performed. The sound insulating material is arranged on the inner wall surface of the measuring pipe connecting the means and the other electro-acoustic converting means. The sound insulating material is preferably arranged such that the same material forming the measuring tube is integrally projected with respect to the inner surface of the measuring tube. Further, the sound insulation material may be composed of a sound insulation material attached inside the measuring tube. In this case, the sound insulation material is preferably glass wool. Further, the measuring tube has a rectangular cross-sectional shape perpendicular to the axial direction of the measuring tube.

With such a configuration, the ultrasonic wave propagation path formed by the pair of electro-acoustic conversion means forms a so-called V-shape that reflects the inside of the measuring tube and receives the wave.
In this case, since the sound insulation material is arranged on the inner wall surface of the measuring pipe that connects the pair of electric-acoustic converting means, it is affected by the direct propagating wave Ts propagating on the inner wall surface of the measuring pipe unlike the conventional one. There is no.

Therefore, it is possible to solve the problem that a measurement error is generated by causing waveform distortion in the original received wave.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION An ultrasonic flowmeter according to the present invention will be described below with reference to FIG. In the embodiments described below, components having the same configurations and functions as those of the conventional device are designated by the same reference numerals.

The measuring tube 2 has flange-like connecting portions 3a, 3 at both ends as shown in a sectional view in FIG. 1 (a).
b to the pipes 4a and 4b, respectively. As shown in FIG. 1B, the measuring tube 2 has a rectangular cross-sectional shape perpendicular to the axial direction of the measuring tube 2, and its opening has a lateral width W and a height h. It constitutes a duct. The aspect ratio (W to h) of the opening of the measuring tube 2 in the embodiment shown in FIG. 1 is 1: 5. The aspect ratio of this opening is generally 1:
It is selected in the range of 3 to 1: 7.

A pair of electro-acoustic conversion means 1a,
1b are respectively arranged on one inner wall 2a of the measuring tube 2, and the other inner wall 2b opposite from the one electro-acoustic converting means 1a to the other electro-acoustic converting means 1b and vice versa. The V-shaped ultrasonic signal propagation path Tc is configured with the reflection surface as a reflection surface.

Then, as shown in FIG. 2, one electric-acoustic converting means 1a and the other electric-acoustic converting means 1b.
Are arranged so as to be emitted at an intersecting angle θ with respect to the axis of the measuring tube 2.

Further, the one electro-acoustic conversion means 1a is provided.
And a measuring tube 2 connecting the other electro-acoustic conversion means 1b.
A sound insulating material 2c is disposed on the inner wall 2a of the. The sound insulation material 2c is arranged so as to be integrally formed of the same material forming the measuring tube, for example, synthetic resin.

The sound insulating material 2c is formed on the other inner wall 2b facing the one inner wall 2a on which the sound insulating material 2c is formed.
The concave portion 2d is formed to correspond to the protruding form of c,
Due to the presence of the recess 2d, the flow velocity of the fluid substance flowing in the measuring pipe 2 is devised so as to be constant.

The pair of electro-acoustic conversion means 1a,
Reference numeral 1b denotes an ultrasonic wave transmitter / receiver composed of, for example, a piezoceramic element, and the ultrasonic wave transmitters / receivers 1a and 1b intermittently and alternately emit ultrasonic waves of about 200 KHz, and the propagation time of the ultrasonic beam is increased. Based on the measuring tube 2
It is adapted to measure the flow rate of a fluid substance flowing therethrough.

In this way, the ultrasonic transducers 1a and 1b
Ultrasonic beams are alternately emitted from the ultrasonic wave transmitters and the ultrasonic wave transmitters / receivers 1a and 1b alternately receive the ultrasonic beams to measure the flow rate of the fluid substance flowing into the measuring tube 2. The calculation processing in this case is the same as that of the conventional example shown in FIG. 5, and the detailed description thereof will be omitted.

In this case, the pair of electro-acoustic conversion means 1
The sound insulation material 2c is provided on the inner wall 2a of the measuring pipe 2 connecting between a and 1b.
Is arranged so as to project, it is possible to block the direct propagation wave Ts propagating along the surface of the inner wall 2a of the measuring tube 2 connecting the electro-acoustic converting means 1a and 1b.

Therefore, the pair of electro-acoustic conversion means 1
It is possible to eliminate the possibility that a and 1b receive the direct propagating waves Ts with each other as shown in FIG. 6 and cause waveform distortion or the like with respect to the original received waves.

FIG. 2 shows another embodiment of the ultrasonic flowmeter according to the present invention in a sectional state. In the example shown in FIG. 2, a separate sound insulating material 5 is prepared as the sound insulating material 2c, and the sound insulating material 5 is attached to the inner wall 2a of the measuring tube 2 connecting between the pair of electro-acoustic converting means 1a and 1b. It is the one. Examples of the sound insulating material 5 include glass wool, rubber, plastic, metal, and the like, but other substances that generally act as the sound insulating material can also be adopted.

In the case shown in FIG. 2, the direct propagating wave Ts as shown in FIG. 6 propagating along the surface of the inner wall 2a of the measuring tube 2 connecting the electro-acoustic converting means 1a and 1b is used as the sound insulating material. 5 can be absorbed.

Therefore, also in the example shown in FIG. 2, it is possible to eliminate the possibility that the pair of electro-acoustic converting means 1a and 1b directly receive the propagating wave Ts and cause a waveform distortion or the like to the originally received wave. can do.

FIG. 3 shows the results regarding the measurement accuracy of the ultrasonic flowmeter according to the present invention shown in FIG. 2, in which the vertical axis shows the signal level and the horizontal axis shows the passage of time. The measurement condition is that air is used as the fluid substance and the flow rate is 5 m ³ / H.
It was carried out in an environment of 20 ° C. The waveform shown on the lower side of FIG. 3 is the waveform signal that has passed through the fluid substance (air) in the measuring tube, and the peak-shaped signal shown on the upper side of the figure shows the received signal generated by this. ing.

As shown in FIG. 3, in the first half, it is not affected by the noise component due to the direct propagating wave Ts and the like, and therefore the waveform is not distorted with respect to the original received wave. It can be seen that the recognized peaked signal occurs at the correct location.

On the other hand, FIG. 4 shows a measurement of the conventional example shown in FIG. 6 under the same conditions. As shown in FIG. 4, the influence of noise components due to the direct propagating wave Ts and the like in the first half thereof is shown. Therefore, the waveform is distorted with respect to the original received wave, and a peak-shaped signal recognized as a received signal occurs earlier in time than the case shown in FIG. It can be seen that an error has occurred.

[0045]

As is clear from the above description, according to the ultrasonic flowmeter of the present invention, the ultrasonic wave propagation path formed by the pair of electro-acoustic converting means is received by reflecting inside the measuring tube. Since the sound-insulating substance is arranged on the inner wall of the measuring tube connecting between the pair of electric-acoustic converting means, the measuring tube connecting between the electric-acoustic converting means is constructed. Directly propagating wave T propagating along the inner wall surface
s can be effectively blocked. Therefore, it is possible to eliminate the possibility that the pair of electro-acoustic conversion means directly receive the propagating wave Ts and cause a waveform distortion or the like to the original received wave, unlike the conventional one, and it is possible to eliminate the possibility of high measurement accuracy. A sonic flow meter can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view showing a basic configuration of a first embodiment of an ultrasonic flowmeter according to the present invention.

FIG. 2 is a sectional view showing a basic configuration of a second embodiment of the ultrasonic flowmeter according to the present invention.

FIG. 3 is a waveform diagram showing characteristics in the ultrasonic flowmeter shown in FIG.

FIG. 4 is a waveform diagram showing the characteristics of a conventional ultrasonic flowmeter.

FIG. 5 is a sectional view showing a basic configuration of a conventional ultrasonic flowmeter.

FIG. 6 is a cross-sectional view showing a basic configuration of another conventional ultrasonic flowmeter.

[Explanation of symbols]

 1a Ultrasonic transducer (electric-acoustic conversion means) 1b Ultrasonic transducer (electric-acoustic conversion means) 2 Measuring pipe 2c Sound insulation material 2d Recess 3a Connection part 3b Connection part 4a Piping 4b Piping 5 Sound insulation material Tc Propagation path

Claims (5)

[Claims] 1. An ultrasonic wave emitted from one electro-acoustic conversion means is transmitted through a fluid substance in a measuring tube and is received by the other electro-acoustic conversion means, and these are switched to propagate ultrasonic waves. An ultrasonic flowmeter for measuring a flow rate of a fluid substance flowing inside a measuring tube by measuring time, wherein ultrasonic waves emitted from one of the electro-acoustic conversion means are reflected in the measuring tube and the other electric- A substantially V-shaped ultrasonic wave propagation path that is received by the acoustic converting means is formed, and a sound insulating material is arranged on the inner wall surface of the measuring pipe that connects between the one electric-acoustic converting means and the other electric-acoustic converting means. An ultrasonic flowmeter characterized in that 2. The ultrasonic flowmeter according to claim 1, wherein the sound insulation material is arranged such that the same material forming the measuring tube is integrally projected with respect to the inner surface of the measuring tube. 3. The ultrasonic flowmeter according to claim 1, wherein the sound insulation material is a sound insulation material attached inside a measuring tube. 4. The ultrasonic flowmeter according to claim 3, wherein the sound insulation material is glass wool. 5. The ultrasonic flowmeter according to claim 1, wherein the measurement tube has a rectangular cross-section that is perpendicular to the axial direction of the measurement tube.