JP3328505B2 - Ultrasonic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter which allows a fluid substance such as a gas or a liquid to flow through a measuring tube and measures the flow rate thereof. The present invention relates to an ultrasonic flowmeter capable of performing the following.

[0002]

2. Description of the Related Art An ultrasonic flowmeter is a flowmeter of a flow rate measuring type. The flow rate is obtained by measuring the flow rate of a fluid substance such as a gas or a liquid flowing inside a measuring pipe, and multiplying the measured flow rate by a cross-sectional area of the pipe. Required by The flow velocity measurement by this type of ultrasonic wave includes a pair of electro-acoustic conversion means, and transmits the ultrasonic wave emitted from one of the electro-acoustic conversion means through a fluid substance in a measurement tube and converts the other electric wave into an electric wave. -It is performed by measuring the ultrasonic wave propagation time by receiving the wave by the acoustic conversion means, switching between them, and finding the reciprocal difference of the ultrasonic wave propagation time.

FIG. 5 is a sectional view showing an example of this type of conventional ultrasonic flowmeter. In the example shown in FIG. 5, a pair of electro-acoustic conversion means 1a and 1b are directly opposed to the inner wall portion of the measurement tube 2 at an inclination of about 45 degrees with respect to the axis of the measurement tube 2. Are located.

According to the ultrasonic flowmeter shown in FIG. 5, one electro-acoustic conversion means 1a is connected to the other electro-acoustic conversion means 1b, and a straight line as shown by a solid line in the opposite direction. Ultrasonic wave propagates through a typical propagation path Ta,
By measuring the propagation speed of the ultrasonic wave in the propagation path Ta, the flow rate of the fluid substance flowing through the measurement tube 2 can be calculated.

That is, an ultrasonic beam emitted to the measuring tube 2 from the ultrasonic transducers 1a and 1b as electro-acoustic conversion means provided on the upstream side and the downstream side with respect to the flow direction of the fluid substance. Are switched on both sides, and the forward and backward propagation times t1 and t2 are repeatedly measured.

By calculating the measured time to the reciprocal, the influence of the sound speed C is eliminated and the following equation is obtained.

T1 = L1 / (C + Vcosθ1) Equation 1 t2 = L1 / (C−Vcosθ1) Equation 2

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

Here, L1 is the propagation path length of the ultrasonic wave (L1 =
D / sin θ1) D: Pipe inner diameter C: Sound velocity in fluid material θ1: Angle between ultrasonic wave propagation path and tube axis V: Linear average flow velocity on ultrasonic wave propagation path

The ultrasonic velocimeter having this configuration is an apparatus for measuring an average velocity along an acoustic path. Then, the flow velocity distribution in the measurement tube changes depending on the flow rate. In order to obtain this flow rate, it is necessary to correct a change in the flow velocity distribution. The volume flow rate Q is obtained by measuring the linear average flow velocity V and the cross-sectional area A of the measurement section.
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 a ratio of the measured linear average flow velocity to the average flow velocity of 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 basin 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
It is possible to calculate the flow rate of the fluid substance by performing calculations using theoretical formulas such as Expressions 5 to 5.

Incidentally, in order to improve the measurement accuracy of the flowmeter having the above-described configuration, 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 one and the other electro-acoustic converters 1a and 1b is equal to the one electro-acoustic converter 1a and the other electro-acoustic converter. 1b, which is about 1.4 times the axial distance L2 of the measuring tube, and when the measuring tube 2 is formed small, the propagation distance Ta cannot be large, and the ultrasonic flow rate There are limits to improving the measurement accuracy of the meter.

Therefore, as a means for increasing the propagation distance between the pair of electro-acoustic converters 1a and 1b while making the measuring tube small, a configuration as shown in FIG. 6 can be considered. In the configuration shown in FIG. 6, a pair of electro-acoustic conversion means 1a and 1b is 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 an ultrasonic reflecting surface. By making the propagation path Tb of the ultrasonic wave substantially V-shaped, the propagation distance is increased.

According to the configuration shown in FIG. 6, the electro-acoustic conversion means 1a, 1b with respect to the axis of each measuring tube 2
When the ultrasonic emission angle θ is 45 degrees, the propagation distance can be twice as long as that of 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 ultrasonic wave propagation distance can be doubled as compared with the configuration shown in FIG. Can be expected to be further improved.

However, the output energy of the ultrasonic wave from the pair of electro-acoustic converters 1a and 1b has a relatively wide directional characteristic, and a part of the ultrasonic signal is generated in addition to the output axis of the ultrasonic wave. Radiated.

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

The directly propagating wave Ts as shown in FIG.
Appears just before or at the same time that the original wave arrives,
A measurement error is generated by causing waveform distortion or the like with respect to the original received wave. This degree includes a problem that the measurement error increases as the flow rate in the measurement 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 prior art. In particular, the present invention reflects an ultrasonic wave emitted from one electro-acoustic conversion means in a measurement tube and converts the other electro-acoustic sound into another. An ultrasonic flowmeter having a V-type ultrasonic wave propagation path for receiving a wave by a conversion means, which is capable of reducing a factor receiving an interfering wave other than the original wave and improving the measurement accuracy. The purpose is to provide.

[0026]

In order to achieve the above-mentioned object, an ultrasonic flowmeter according to the present invention is characterized in that an ultrasonic wave emitted from one of the electro-acoustic converting means is used for measuring the ultrasonic wave in a fluid substance in a measuring tube. An ultrasonic flowmeter that transmits the light and receives it with the other electro-acoustic conversion means, switches between them, measures the ultrasonic propagation time, and measures the flow rate of the fluid substance flowing inside the measurement tube, The ultrasonic wave emitted from the one electro-acoustic converter is reflected in the measurement tube to form a V-type ultrasonic wave propagation path for receiving the wave by the other electro-acoustic converter, and the one electro-acoustic converter is formed. The sound insulation material is arranged on the inner wall surface of the measurement tube connecting the means and the other electro-acoustic conversion means. The sound insulating material is preferably arranged such that the same material forming the measuring tube is integrally protruded from the inner surface of the measuring tube. Further, the sound insulating material may be constituted by a sound insulating material adhered in a measuring tube. In this case, the sound insulating material is desirably glass wool. The measuring tube has a rectangular cross section perpendicular to the axial direction of the measuring tube.

With such a configuration, the propagation path of the ultrasonic wave formed by the pair of electro-acoustic converters forms a so-called V-shape that reflects the inside of the measuring tube and receives the wave.
In this case, since the sound insulating material is arranged on the inner wall surface of the measurement tube connecting the pair of electro-acoustic conversion means, the sound insulation material is affected by the direct propagation wave Ts transmitted through the inner wall surface of the measurement tube as in the related art. There is no.

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

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An ultrasonic flow meter according to the present invention will be described below with reference to FIG. In the following embodiments, those having the same configuration and function as those of the conventional device are denoted by the same reference numerals.

As shown in a sectional view in FIG. 1A, the measuring tube 2 has flange-like connecting portions 3a, 3 at both ends.
b are connected to the pipes 4a and 4b, respectively. As shown in FIG. 1 (b), the measuring tube 2 has a rectangular cross section perpendicular to the axial direction of the measuring tube 2, and has a square width W and a height h. Constructs 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 from about 3 to 1: 7.

Then, a pair of electro-acoustic conversion means 1a,
1b are arranged on one inner wall 2a of the measuring tube 2, respectively, and the other inner wall 2b facing from one electro-acoustic converting means 1a to the other electro-acoustic converting means 1b and in the opposite direction. Is used as a reflection surface to form a V-shaped ultrasonic signal propagation path Tc.

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

Further, the one electro-acoustic conversion means 1a
Tube 2 connecting between the other and the electro-acoustic conversion means 1b
A sound insulating substance 2c is disposed on the inner wall 2a of the first embodiment. The sound insulating substance 2c is disposed so as to be integrally formed of the same material constituting the measuring tube, for example, a synthetic resin.

The sound insulating material 2c is provided on the other inner wall 2b opposite to the one inner wall 2a on which the sound insulating material 2c is formed.
A concave portion 2d is formed corresponding to the projection form of c.
Due to the presence of the recess 2d, the flow rate of the fluid substance flowing in the measurement tube 2 is designed to be constant.

The pair of electro-acoustic conversion means 1a,
Reference numeral 1b denotes an ultrasonic transducer formed of, for example, a piezoceramic element. The ultrasonic transducers 1a and 1b emit ultrasonic waves of about 200 KHz alternately and intermittently, and the propagation time of the ultrasonic beams Measuring tube 2 based on
It is adapted to measure the flow rate of a fluid substance flowing through the inside.

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

In this case, the pair of electro-acoustic conversion means 1
a sound insulating material 2c on the inner wall 2a of the measuring tube 2 connecting between
Are arranged so as to protrude, so that the direct propagation wave Ts propagating along the surface of the inner wall 2a of the measuring tube 2 connecting between the electro-acoustic conversion means 1a and 1b can be cut off.

Therefore, the pair of electro-acoustic conversion means 1
As shown in FIG. 6, it is possible to eliminate the possibility that a and 1b receive the directly propagated wave Ts and cause a waveform distortion or the like to the original received wave.

FIG. 2 is a sectional view showing another embodiment of the ultrasonic flowmeter according to the present invention. In the example shown in FIG. 2, a separate sound insulating material 5 is prepared as the sound insulating substance 2c, and the sound insulating material 5 is attached to the inner wall 2a of the measuring tube 2 connecting the pair of electro-acoustic conversion means 1a and 1b. It was made. As the sound insulating material 5, for example, glass wool, rubber, plastic, metal and the like can be cited, but other materials generally acting as a sound insulating material can also be employed.

In the case shown in FIG. 2, a direct propagation wave Ts as shown in FIG. 6 propagating along the surface of the inner wall 2a of the measuring tube 2 connecting between the electro-acoustic conversion means 1a and 1b is applied to 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 converters 1a and 1b receive the directly propagating wave Ts and cause waveform distortion or the like with respect to the original received wave. can do.

FIG. 3 shows the results related to 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 time passage. The measurement conditions were as follows: air was used as the fluid substance, and the flow rate was 5 m ³ / H
, In a 20 ° C. environment. The waveform drawn on the lower side in FIG. 3 is a waveform signal that has passed through the fluid substance (air) in the measurement tube, and the peak-like signal drawn on the upper side in the figure indicates a received signal generated thereby. ing.

As shown in FIG. 3, the first half is not affected by the noise component due to the directly propagating wave Ts and the like, so that the original received wave is not affected by the waveform distortion, etc. It can be seen that the recognized peak signal occurs at the correct position.

On the other hand, FIG. 4 shows the result obtained by measuring the conventional example shown in FIG. 6 under the same conditions. As shown in FIG. Therefore, the original received wave is subjected to waveform distortion, etc., and a peak signal recognized as a received signal is generated earlier in time than the case shown in FIG. It can be seen that an error has occurred.

[0045]

As is apparent 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 conversion means is received by reflecting the inside of the measurement tube. The sound-insulating material is arranged on the inner wall of the measuring tube connecting between the pair of electro-acoustic converting means, so that the measuring tube is connected to the pair of electro-acoustic converting means. Directly propagating wave T propagating along the inner wall surface
s can be effectively blocked. Therefore, it is possible to eliminate the possibility that a pair of electro-acoustic conversion means receive the directly propagating wave Ts from each other and cause waveform distortion or the like with respect to the original received wave, as in the conventional case, and it is possible to eliminate the possibility of high accuracy of measurement. An acoustic flow meter can be provided.

[Brief description of the 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 of the ultrasonic flowmeter shown in FIG.

FIG. 4 is a waveform diagram showing 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 substance 2d Depression 3a Connection 3b Connection 4a Pipe 4b Pipe 5 Sound insulation Tc Propagation path

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/00-9/02

Claims (5)

(57) [Claims] 1. An ultrasonic wave emitted from one electro-acoustic converter is transmitted through a fluid substance in a measuring tube and received by the other electro-acoustic converter, and these are switched by both to transmit ultrasonic waves. An ultrasonic flowmeter for measuring the flow rate of a fluid substance flowing inside a measurement tube by measuring time, wherein the ultrasonic wave emitted from one of the electro-acoustic conversion means is reflected inside the measurement tube and the other electric- A substantially V-shaped ultrasonic wave propagation path for receiving waves by the acoustic conversion means is formed, and a sound insulating material is arranged on an inner wall surface of a measuring tube connecting between the one electro-acoustic conversion means and the other electro-acoustic conversion means. An ultrasonic flowmeter characterized in that: 2. The ultrasonic flowmeter according to claim 1, wherein the sound insulating material is arranged such that the same material constituting the measuring tube is integrally protruded from the inner surface of the measuring tube. 3. The ultrasonic flowmeter according to claim 1, wherein the sound insulating material is a sound insulating material adhered in a measuring tube. 4. The ultrasonic flowmeter according to claim 3, wherein said sound insulating material is glass wool. 5. The ultrasonic flowmeter according to claim 1, wherein the measuring tube has a rectangular cross section perpendicular to the axial direction of the measuring tube.