JPH05223608A - Ultrasonic flowmeter - Google Patents

Abstract

PURPOSE:To allow application for any kind of fluid with a simple handling along with higher measuring accuracy by a method the section of a measuring tube section is formed between upstream and downstream points of a pipe to be rectangular and a transducer is mounted on the external wall of a parallel surface. CONSTITUTION:A measuring liquid flows into a pipe 1 having a pipe wall 12. The upstream and downstream end parts of the pipe 11 are formed circular in section. A measuring tube section 15 is formed integral between the upstream and downstream end parts and the measuring tube section 15 has a section thereof formed rectangular. Transducers 20 and 21 comprise a piezo-electric vibrator, for instance and mounted on external walls of parallel surfaces 16 and 17 through a resin wedge. The transducers 20 and 21 are arranged in plurality so as to form a plurality of side lines 24. The achieves higher average effect on the surface as a whole thereby improving measuring accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter utilizing ultrasonic waves.

[0002]

2. Description of the Related Art As a conventional ultrasonic flowmeter, for example, there is one as shown in FIGS. 7 and 8
In, 1 is a tube having a tube wall 2 through which a fluid flows,
3 and 4 are plastic wedges, and 5 and 6 are transducers as sensors.

The wave transmitters / receivers 5 and 6 are made of, for example, ceramic vibrators, and fixed to the outer wall of the tube 1 via the wedges 3 and 4 by a fixture. Here, the measurement principle will be briefly described. An ultrasonic wave is transmitted from the upstream / downstream transducer 5, passes through the tube wall 2, propagates obliquely along the flow in the fluid, and further passes through the tube wall 2 to the downstream transducer / receiver 6. The ultrasonic wave propagation time td until reception is

[0004]

[Equation 1]

On the contrary, ultrasonic waves are transmitted from the downstream side wave transmitter / receiver 6, propagated in the opposite direction to the fluid flow and received by the upstream side wave transmitter / receiver 5. The ultrasonic wave propagation time tu until

[0006]

[Equation 2]

It is represented by Here, D is the inner diameter of the pipe, θ is the radiation angle in the fluid, C is the speed of sound, V is the flow velocity of the fluid, and τ is the total time required for the ultrasonic waves to propagate through the pipe wall, etc. It Difference Δt between propagation times tu and td
Is expressed below and is proportional to the flow velocity V of the fluid.

[0008]

[Equation 3]

Usually, when the fluid is water, C = 1500 m /
s, V = -10 m / s, and C >> V. Therefore, the difference Δt between the propagation times tu and td is expressed by the following equation (1).

[0010]

[Equation 4]

(1) Further, the average value to of the propagation times tu and td is

[0012]

[Equation 5]

Therefore, the sound velocity C is expressed by the following equation (2).

[0014]

[Equation 6]

(2) From equations (1) and (2), the flow velocity V expressed by equation (3)
Is obtained.

[0016]

[Equation 7]

(3) The flow rate Q can be obtained by the following equation (4) by multiplying the sectional area by the equation (3).

[0018]

[Equation 8]

(4) However, since the flow velocity V obtained by the equation (3) is an average along the ultrasonic wave propagation path, it must be recalculated to the surface average flow velocity V _A and used correctly. is not. Therefore, the following flow velocity distribution correction coefficient K is obtained by assuming an ideal flow velocity distribution (axisymmetric distribution) in terms of hydrodynamics. K = V _A / V Actually, this coefficient is multiplied to obtain Q by the following equation (5).

[0020]

[Equation 9]

(5) When determining the flow velocity distribution correction coefficient K, for example, an axisymmetric distribution as shown in FIG. 9 is assumed, which is Nikrause.
And so on. On the other hand, as a ratio of the flow velocity V averaged over the diameter and the flow velocity VA averaged over the entire cross-sectional area, Ge I Birgel et al. Propose the following flow velocity distribution correction coefficient K.

[0022]

[Equation 10]

Here, Re is the Reynolds number. This flow velocity distribution correction coefficient K is correct when the pipe wall 2 is smooth and the straight pipe length (the length of the straight pipe portion in the upstream portion from the transducer) is sufficient, but the actual flow is
It is often different from this because the straight pipe length is short. As a method of overcoming such a problem of the flow velocity distribution, there are, for example, the orthogonal two-line method and the parallel multi-line method.

In the orthogonal two-line method, as shown in FIG.
The flow velocity V is measured ultrasonically with respect to two orthogonal measurement lines passing through the center O of the pipe 1, and the flow velocity V1 of the measurement line L1 and the flow velocity V2 of the measurement line L2 are measured.
The flow velocity V is obtained as the average of This is the idea that accuracy can be improved by increasing the number of survey lines and averaging even in a non-axisymmetric distribution, and by this, the effect of the entire surface is sought. In addition, 8 in FIG. 10 shows the contour line of the flow velocity distribution.

On the other hand, in the parallel multi-line survey method, since a plurality of parallel survey lines 9 are formed as shown in FIG. 11, the averaging effect of the entire surface is remarkably improved. Therefore, accuracy improvement can be expected considerably. In this method, the sound velocity of pipe wall 2 (steel, sound velocity, shear wave 3200 m / s) and water (sound velocity 1500 m / s) are significantly different. As a result, the critical angle is restricted, and the survey line 9 at both ends of FIG. 11 cannot be formed. Therefore, the clamp-on method cannot be adopted in this method, and the wave transmitters / receivers 5 and 6 have a shape in which a hole is formed in the tube wall 2 and contact with water.

[0026]

However, in such a conventional ultrasonic flowmeter, in the orthogonal two-sided line method, as shown in FIG. Considering only the surrounding area, the influence of the surrounding area is small. Therefore, even if the survey line 10 passing through the center O is used many times, an error in the flow velocity distribution occurs, and the accuracy cannot be improved. In particular, when the straight pipe length on the upstream side is short, the error becomes large.

On the other hand, the parallel multi-line method has the following problems. Installation, maintenance and replacement are difficult to handle. Further, a convex portion or a concave portion is formed on the inner surface of the pipe wall, and it is difficult to estimate the flow rate at that portion, which causes an error. Furthermore, since the transducer contacts the liquid, it is difficult to use it for liquids that resist foreign matter, and cannot be applied to drinking water, chemicals, nuclear power, etc.

The present invention has been made in view of the above-mentioned conventional problems, can improve the measurement accuracy, is easy to handle, and can be applied to any kind of fluid. An object is to provide an ultrasonic flowmeter that can be used.

[0029]

In order to achieve the above-mentioned object, the present invention is a super-measuring device for measuring the flow rate of a fluid in a pipe by using a plurality of transducers for transmitting ultrasonic waves and receiving ultrasonic waves. In the sonic flow meter, the measurement pipe portion was formed between the upstream and the downstream of the pipe, the measurement pipe portion was formed to have a rectangular cross section, and the transducer was attached to the outer wall of the parallel surface of the measurement pipe portion. It is a thing.

[0030]

In the present invention, since the measuring tube has a rectangular cross section and a plurality of transducers are attached to its parallel surface, a plurality of parallel measuring lines can be formed, and the average effect of the entire surface is obtained. Therefore, the measurement accuracy can be improved.

Further, the wave transmitter / receiver can be easily attached, maintained and replaced, and can be easily handled. Moreover, since no convex or concave portion is formed on the inner surface of the pipe wall, no error occurs in that portion. Further, since the transducer is not in contact with the liquid, it can be applied to any kind of liquid. Further, if the rectangular cross section of the measuring pipe portion is made smaller than the circular cross sections of the upstream side and the downstream side, a rectifying effect can be expected. S / N
Since the ratio can also be improved, the measurement accuracy can be improved.

[0032]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 are views showing an embodiment of the present invention.
In FIG. 1 and FIG. 2, 11 is a tube having a predetermined tube wall 12, and a measurement liquid, which is a fluid, flows inside the tube 11. Each of the upstream end portion 13 and the downstream end portion 14 of the pipe 11 has a circular cross section. A measuring pipe portion 15 is integrally formed between the upstream end portion 13 and the downstream end portion 14, and the measuring pipe portion 15 has a rectangular cross section. Measuring tube 1
5 is a pair of flat parallel surfaces 16, 17, 18 facing each other,
Has 19.

Reference numerals 20 and 21 denote wave transmitters / receivers as sensors. The wave transmitters / receivers 20, 21 are made of, for example, piezo oscillators, and transmit and receive ultrasonic waves. Transducers 20, 2
1 is attached to the outer wall of the parallel surfaces 16 and 17 via plastic wedges 22 and 23 so as to emit ultrasonic waves at a predetermined radiation angle. A plurality of wave transmitters / receivers 20, 21 are provided so as to form a plurality of parallel survey lines 24.

As shown in FIG. 3, other parallel surfaces 18, 19
The transducers 25 and 26 may be attached to the.
This can increase the average effect of the entire surface.
Further, as shown in FIG. 4, the transducers 20 and 21 may be provided only on one of the parallel surfaces 16 to receive the reflected wave. In FIG. 2, reference numeral 27 denotes a transmission / reception switching device including a switch, and the transmission / reception switching device 27 is connected to the transmission / reception devices 20 and 21, respectively. The transmission / reception switch 27 reverses the ultrasonic wave transmission direction in response to a command from the MPU 28.

Reference numeral 29 is a transceiver including a transceiver, and the transceiver 29 transmits a signal to the transmission / reception switch 27 and receives a signal from the transmission / reception switch 29. Reference numeral 30 is a counter connected to the transmitter / receiver 29, and the counter 3
In 0, the number of pulses is measured to obtain ultrasonic wave propagation times td and tu. The output of the counter 30 is given to the MPU 28, and the MPU 28 calculates the flow rate Q (equation (5), reference) based on the ultrasonic wave propagation times td and tu. The calculated flow rate Q is displayed by the MPU 28 on the printer 31 or the display 32.
Is output to.

Since a plurality of parallel survey lines 24 can be formed in this way, the averaging effect of the entire surface can be improved and the measurement accuracy can be improved. Since the transducers 20 and 21 are mounted on the plane parallel surfaces 16 and 17 by the clamp-on method, mounting, maintenance and replacement are easy. Further, since the convex portion or the concave portion is not formed on the inner surface of the tube wall 12, no error occurs in that portion.

Further, since the transducers 20 and 21 do not come into contact with the measuring liquid, the measuring liquid can be applied to any kind of measuring liquid. In this way, the advantages of both methods can be combined. Further, if the rectangular cross section of the measuring pipe portion 15 is made smaller than the internal cross sections of the upstream end portion 13 and the downstream end portion 14, the rectifying effect can be expected.

That is, the upstream flow velocity distribution as shown in FIG. 5 is narrowed in the measuring pipe portion 15 and rectified as shown in FIG. 6, and the flow velocity distribution becomes uniform. Therefore, the nonuniformity of the flow velocity distribution near the inner wall of the pipe is reduced, and improvement in measurement accuracy can be expected. Furthermore, since the flow is restricted in the measuring pipe portion 15, the flow velocity is high. Therefore, Δt, which is the original signal of the flow velocity, becomes large. This can be understood by modifying the equation (5) as follows.

[0039]

[Equation 11]

That is, both upstream and in the measuring pipe section 15,
Although Q does not change, it is considered that the inner diameter D has decreased. On the other hand, the propagation time t also becomes smaller as D becomes smaller, but the numerator has an effect of square, while the denominator has an effect of cube. Therefore, Δt becomes large. Since the increase in Δt also improves the S / N ratio, the improvement of the measurement accuracy can be expected in this respect as well.

[0041]

As described above, according to the present invention, the measurement accuracy can be improved, the handling is simple, and the present invention can be applied to any kind of measurement liquid.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is another sectional view.

FIG. 3 is a diagram showing an example of adding a transceiver.

FIG. 4 is a diagram showing another example of mounting the wave transmitter / receiver.

FIG. 5 is a diagram showing an upstream flow velocity distribution.

FIG. Diagram showing the flow velocity distribution in the measuring pipe section

FIG. 7 is a sectional view showing a conventional example.

FIG. 8 is another cross-sectional view of the conventional example.

FIG. 9 is a diagram showing an axisymmetric distribution of flow velocity.

FIG. 10 is an explanatory diagram of the orthogonal two-sided line method.

FIG. 11 is an explanatory diagram of the parallel multi-line method.

FIG. 12 is an explanatory diagram of problems

[Explanation of symbols]

 11: Pipe 12: Pipe wall 13: Upstream end 14: Downstream end 15: Measuring pipe 16-19: Parallel planes 20, 21, 25, 26: Transducer 22, 23: Wedge 24: Measurement line 27: Transmission / reception Switching device 28: MPU 29: Transmitter / receiver 30: Counter 31: Printer 32: Display device

Claims (4)

[Claims] 1. An ultrasonic flowmeter for measuring the flow rate of a fluid in a pipe using a plurality of transducers for transmitting ultrasonic waves and receiving ultrasonic waves, comprising: a measuring pipe between an upstream side and a downstream side of the pipe. The ultrasonic flowmeter is characterized in that the measuring tube portion is formed as a section so as to have a rectangular cross section, and the transducer is attached to the outer wall of the parallel surface of the measuring tube portion. 2. The rectangular cross section of the measuring pipe section is made smaller than the circular cross section upstream of the pipe.
Ultrasonic flow meter. 3. The ultrasonic flowmeter according to claim 1, wherein the transducer is attached in a horizontal direction and a vertical direction to the outer wall of the parallel surface of the measuring tube portion. 4. The ultrasonic flowmeter according to claim 1, wherein the transducer is attached only to an outer wall of one parallel surface of the measuring tube portion.