JPH0447768B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flow rate measuring device for measuring the flow rate of fluid in piping with high accuracy.

An ultrasonic flow meter transmits and receives ultrasonic waves so as to cross the fluid in the forward and reverse directions relative to the flow direction of the fluid, and determines the fluid flow rate from the difference in propagation time of each ultrasonic wave. . 1st
The figure is a principle diagram for explaining the basic principle of an ultrasonic flowmeter. When ultrasonic waves propagate in a fluid, the ultrasonic propagation time in the forward direction with respect to the flow direction and the flow This method utilizes the fact that a propagation time difference occurs between the ultrasound propagation time in the opposite direction and that the propagation time difference is proportional to the fluid flow velocity.

In Fig. 1, 1 is a pipe, d is its inner diameter, and v
is the fluid flow velocity and θ is the angle of incidence of the ultrasonic wave on the fluid. If the sound speed of the ultrasonic wave in the fluid is C, the sound speed of the ultrasonic wave transmitted in the forward direction of the fluid in the pipe 1 in the fluid is sufficiently large compared to the fluid flow velocity, so the incident angle θ changes. Instead, only the sound velocity component of the ultrasonic wave changes, resulting in C+Vcosθ. Further, since the propagation distance of the ultrasonic wave is d/sin θ, the propagation time of the ultrasonic wave propagating in the fluid is d/(C+V cos θ) sin θ.

Therefore, in FIG. 1, the forward ultrasonic propagation time t _L in the fluid is t _L = d/(C+V cos θ) sin θ (I). Similarly, the propagation time t _u of ultrasonic waves propagating in the opposite direction to the flow direction in the fluid is t _u =d/(C-Vcos θ) sin θ (). When determining the fluid flow velocity V from equations (I) and (), it becomes V=tanθ・C ² /2dΔt (). By measuring the propagation time difference Δt in this manner, the fluid flow velocity V can be determined.

By the way, as can be seen from equation (), the fluid flow velocity V determined by the ultrasonic flowmeter is the linear average flow velocity along the ultrasonic propagation path, and in order to determine the fluid flow rate, the fluid flow velocity V at the cross section of the pipe 1 is A surface average flow velocity of is required. The relationship between the linear average flow velocity and the surface average flow velocity is largely dependent on the flow velocity distribution of the fluid in the pipe 1, and even if the flow velocity distribution is sufficiently developed (if a sufficiently long straight pipe section can be obtained from the bent part of the pipe). For example, the relationship between the two can be obtained by the following equation using the well-known Gayville coefficient k.

(Surface average flow velocity) = 1/k (Linear average flow velocity) ... () k = 1 + 0.01√6.24 + 431 ^-0.237 Re; Reynolds number However, when installing an ultrasonic flowmeter in the piping system of an industrial plant, ( ) It is often difficult to obtain the straight pipe length necessary for the formula to hold true, and in reality, it is often necessary to install an ultrasonic flowmeter near a bend in the pipe. Therefore, before installing an ultrasonic flowmeter in a plant,
Previously, it was customary to conduct an actual flow calibration test that simulated the distance from the pipe bend at the installation location.
In order to eliminate this actual flow calibration test, we need an ultrasonic flowmeter that can calculate the surface average flow velocity with high accuracy even when the flow velocity distribution in the pipe is considerably distorted, such as near bends in the pipe. It needs to be realized.

As an example of a conventional ultrasonic flowmeter of this type, the second
I got what is shown in the figure. Figure 2a is a cross-sectional view, and Figure 2b is a side view.In the figure, 2a, 2
b, 2c, and 2d are ultrasonic transceivers provided on one side of the downstream side of the pipe 1; 3a, 3b, 3c, and 3d are ultrasonic transceivers provided on the opposite upstream side;
l ₁ , l ₂ , l ₃ , l ₄ are ultrasonic propagation paths, and A is the fluid flow direction.

Next, the operation will be explained. The ultrasonic transceivers are 2a and 3a, 2b and 3b, 2c and 3c, respectively.
2d and 3d form a pair, and the fluid flow velocity is determined by the above equation () for the propagation paths l ₁ , l ₂ , l ₃ , l ₄ corresponding to each ultrasonic transmitter/receiver pair.

In the example of Fig. 2, the ultrasonic transceiver 2
When ultrasonic signals are transmitted from a, 2b, 2c, and 2d to the ultrasonic transceivers 3a, 3b, 3c, and 3d, the direction is opposite to the flow direction, and the ultrasonic transceiver 3
The forward direction with respect to the fluid flow direction is when the ultrasonic signals are transmitted from a, 3b, 3c, and 3d to the ultrasonic transceivers 2a, 2b, 2c, and 2d. This ultrasonic flowmeter is a so-called multi-pair type ultrasonic flowmeter, and ultrasonic transceivers 2a, 2b, 2
A transmission/reception switching method is adopted in which the transmission and reception switching methods are switched at regular intervals between c, 2d and 3a, 3b, 3c, and 3d to measure the propagation time of each ultrasonic wave in the forward or reverse direction with respect to the fluid flow direction. .

Generally, a multi-pair type ultrasonic flowmeter consists of two or more pairs of ultrasonic transmitting and receiving systems to form at least two ultrasonic propagation paths.
The figure shows a device consisting of four pairs of ultrasonic transmitting/receiving systems, and hereinafter, a device having four pairs of ultrasonic transmitting/receiving systems will be described. According to such a multi-pair type ultrasonic flowmeter, even when the cross-sectional flow velocity distribution of the pipe 1 is considerably distorted, the flow rate of the fluid in the pipe 1 can be measured with high accuracy. Regarding this point, according to Figure 3,
explain.

FIG. 3 is a cross-sectional flow velocity distribution diagram in the pipe 1, where v indicates a constant flow velocity line. In such a multi-pair ultrasonic flowmeter, the ultrasonic propagation path l ₁ ,
Corresponding to l ₂ , l ₃ , and l ₄ , fluid flow velocities v ₁ , v ₂ , v ₃ , and v ₄ are determined by the equation () above, respectively. The fluid flow velocities v ₁ , v ₂ , v ₃ , v ₄ are the respective propagation paths l ₁ ,
These are the line average flow velocities corresponding to l ₂ , l ₃ , and l _4. To calculate the surface average flow velocity from these line average flow velocities,
Newton- is an approximate calculation method for numerical integration.
It can be determined using Cotes' formula, Cebysev's formula, or Gauss's formula. That is, the ultrasonic propagation paths l ₁ , l ₂ , l ₃ , l ₄ are determined by the Newton-Cotes method, Cebysev method, or Cebysev method in numerical integration.
If the equinoxes are determined by the Gauss method and the surface average flow velocity is taken as = 1/d ₄ 〓 ⁱ⁼¹ w _i ·v _i ……(V). However, w _i is a weight corresponding to the i-th propagation path, and how to select the propagation path l _i and weight w _i differs depending on which of the above three methods is selected. Using the surface average flow velocity value calculated by equation (V), the flow rate of the fluid in the pipe is calculated by the following equation.

Q=A・...() However, Q is the flow rate and A is the pipe cross-sectional area.

Since the conventional ultrasonic flowmeter is configured as described above, in order to improve the estimation accuracy of the surface average flow velocity of equation (V) and improve the measurement accuracy of the fluid flow rate, it is necessary to The number of ultrasonic propagation paths must be increased. Therefore, in order to measure the flow rate in the pipe 1 with high precision, multiple pairs of ultrasonic transmitting/receiving systems are required, and a device for determining the linear average flow velocity corresponding to each ultrasonic transmitting/receiving system is required. A device for multiplying the linear average flow velocity calculated by these devices by the weight w _i in equation (V) is required, as well as a transmitting device, a receiving device, and a transmitting/receiving switching device for transmitting and receiving ultrasonic waves. As many signal processing systems as there are propagation paths are required,
As a result, it became a very large scale instrument, which caused problems in terms of reliability and economy.

This invention has been made to solve the problems of the conventional ones as described above.
By providing an ultrasonic transmitting/receiving system to form at least two ultrasonic propagation paths parallel to this plane, the number of ultrasonic transmitting/receiving systems can be reduced by almost half, providing an inexpensive and highly accurate ultrasonic flow measuring device. It is intended to.

FIG. 4 is a side view showing a part of the piping in an actual plant, and FIG. 5 is a flow velocity distribution diagram at the BB cross section. In general, many of the factors that distort the flow velocity distribution within the pipe 1 are the presence of the bent portion 4 of the pipe 1. However, in actual plant piping, a plurality of bent portions 4 of the piping 1 are often provided within the same plane, as shown in FIG. In an actual plant, it is easy to install an ultrasonic flowmeter at such a location. The flow velocity distribution in the pipe 1 at the BB cross section in FIG. 4 is as shown in FIG. It is symmetrical with respect to plane C. Therefore, by determining the linear flow velocity for one side of the plane C, the overall surface average flow velocity can be determined. The present invention utilizes the symmetry of such flow velocity distribution to reduce the number of ultrasonic transmitting/receiving systems.

An embodiment of the present invention will be described below with reference to the drawings. Figure 6a is its cross-sectional view, b is its side view, and Figure 7
The figure is a flow velocity distribution diagram, and in the figure, the same reference numerals as in FIGS. 1 to 5 indicate the same or corresponding parts.
The ultrasonic transceivers 2a, 2b, 3a, and 3b are provided on the downstream and upstream sides of one side of the plane C including the bent portion 4 of the pipe 1, and the ultrasonic transceivers 2c and 2d on the opposite side of the plane C , 3c, and 3d are omitted. These downstream and upstream ultrasonic transmitter/receivers 2a and 3a, 2b and 3b are arranged in pairs and parallel to a plane C formed by the central axis of the pipe at the bend 4 of the pipe 1. , plane C
at least two ultrasound propagation paths parallel to l ₁ , l ₂
is formed.

In the ultrasonic flowmeter configured as described above, ultrasonic signals are transmitted and received in each pair of ultrasonic transceivers 2a and 3a and 2b and 3b,
For the propagation paths l ₁ and l ₂ corresponding to each pair of ultrasonic transmitting/receiving systems, the difference in propagation time between the two is determined from the propagation times of the ultrasonic waves in the forward direction and in the reverse direction with respect to the flow direction. Then, the fluid flow velocities v ₁ and v ₂ are determined by the equation () above, corresponding to the respective propagation paths l ₁ and l ₂ . These fluid flow rates
v ₁ and v ₂ are line average flow velocities corresponding to the propagation paths l ₁ and l ₂ , respectively.

In order to determine the surface average flow velocity from the linear average flow velocity obtained in this way, the three numerical integration methods described above, namely the Newton-Cotes formula, Cebysev formula, and Gauss formula, can be used. In this case, the ultrasonic propagation paths l ₁ , l ₂ , l ₃ , and l ₄ form nodal points determined by the Newton-Cotes method, Cebysev method, or Gauss method in numerical integration, and the surface average flow velocity is the flow velocity in pipe 1. It is calculated by utilizing the property that the distribution is symmetrical with respect to the plane C formed by the pipe central axis at the bend 4 of the pipe 1. first,
If the ultrasonic propagation path that passes through the center of the pipe cross section is not included, it is calculated using the following formula.

=2/d ₂ 〓 ^di=1 w _i・v _i ...() Here, w _i is the weight corresponding to the i-th propagation path, and how to select the propagation path l _i and weight w _i is
Newton-Cotes formula, Cebysev formula and
It depends on which Gauss formula you choose.

In addition, when an ultrasonic propagation path passing through the center of the tube cross section is included, the ultrasonic propagation path passing through the center of the tube cross section is i=1. That is, if the line average flow velocity along this ultrasonic propagation path is v ₁ and the weight is w ₁ , then =2/d{w ₁ /2・v ₁ + _o 〓 ⁱ⁼² w _i・v _i } ...() The surface average flow velocity can be determined by Using the surface average flow velocity value obtained in this manner, the fluid flow rate Q in the pipe is calculated as the pipe cross-sectional area A by the following equation.

Q=A・ ...() In this way, the ultrasonic flowmeter of the present invention utilizes the symmetry of the distortion of the flow velocity distribution in the pipe, so the ultrasonic propagation path is n when the conventional one is n. /2 may be sufficient, and even if an ultrasonic propagation path passing through the center of the tube cross section is included, 2/2+1 may be sufficient. In this way, the ultrasonic propagation path and the equipment required for it can be reduced by approximately half. Furthermore, since the constant flow velocity lines v are more uniformly distributed in the direction perpendicular to the plane C than in the direction parallel to the plane C, it is better to form the ultrasonic propagation path l parallel to the plane C with higher precision than in the conventional method. Flow rate measurements can be made with

In the above embodiment, the case where there are two ultrasonic propagation paths on one side of the plane C is explained, but there is no limit to the number as long as there are two or more, and all the ultrasonic propagation paths are on one side of the plane C. It is not necessary to arrange it on the opposite side of the plane C, and a part of it may be arranged on the opposite side of the plane C. Furthermore, although the above description has focused on the propagation time difference of ultrasonic waves, it goes without saying that equivalent values, such as frequency differences, may be used.

The present invention is applicable not only to plant piping but also to measurement of flow rates in any piping.

As described above, according to the present invention, ultrasonic waves are transmitted so that at least two ultrasonic propagation paths are formed on one side of the plane formed by the central axis of the pipe at the bent portion of the pipe in parallel with this plane. Since it is configured to include a transmitting/receiving system, the number of ultrasonic transmitting/receiving systems can be reduced by almost half, making it possible to simplify the device and providing an inexpensive and highly accurate ultrasonic flow rate measuring device.

[Brief explanation of the drawing]

Figure 1 is a diagram of the principle of an ultrasonic flowmeter, Figure 2a is a cross-sectional view of a conventional ultrasonic flowmeter, b is a side view thereof, Figure 3 is a diagram of the flow velocity distribution in a conventional pipe, and Figure 4 6 is a side view showing a part of the piping of the plant, FIG. 5 is a flow velocity distribution diagram in the BB cross section, FIG. 6 a is a cross-sectional view showing an ultrasonic flowmeter according to an embodiment of the present invention, Its side view, FIG. 7, is a flow velocity distribution diagram in the pipe. In the figure, 1 is a pipe, 2a, 2b, 2c, 2
d, 3a, 3b, 3c, and 3d are ultrasonic transceivers. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An ultrasonic flowmeter that calculates the flow rate of a fluid in a pipe from the difference in propagation time of ultrasonic waves crossing the fluid in the forward and reverse directions with respect to the flow direction of the fluid in the pipe, or from a numerical value equivalent thereto. In an ultrasonic flow measurement device installed in a pipe, the pipe has a plurality of bends in the same plane, and the ultrasonic flowmeter is arranged in a plane formed by a central axis of the pipe at the bend of the pipe. 1. An ultrasonic flow rate measuring device comprising, on one side of the plane, an ultrasonic transceiver that forms at least two ultrasonic propagation paths parallel to the plane. 2 Ultrasonic propagation path is Newtonian in numerical integration
- The above Newton-
2. The ultrasonic flow rate measuring device according to claim 1, wherein the surface average flow velocity of a pipe cross section is determined by a numerical integration method using Cotes method, Cebysev method, or Gauss method. 3. The ultrasonic flow rate measuring device according to claim 1 or 2, wherein the ultrasonic propagation path does not include a path passing through the center of the tube cross section, and the flow rate in the tube is determined by the following formula. =2/d _o 〓 ⁱ⁼¹ w _i・v _i Q=A・ However, w _i is the weight for the ultrasonic propagation path as the i-th node determined by the Newton-Cotes method, Cebysev method, or Gauss method. , v _i is the linear average flow velocity along the i-th ultrasonic propagation path, n is the number of ultrasonic propagation paths, d is the inner diameter of the pipe, is the surface average flow velocity of the pipe cross section, A is the pipe cross-sectional area, and Q is the inner flow velocity of the pipe. is the flow rate of the fluid. 4. Claim 1 or 2, characterized in that the ultrasonic propagation path includes a path passing through the center of the pipe cross section, and the flow rate in the pipe is determined by the following formula with i=1. The ultrasonic flow measuring device described. =2/d{w ₁ /2・v ₁ + _o 〓 ⁱ⁼² w _i・v _i } Q=A・ However, w _i is the i-th The weight for the ultrasonic propagation path as a nodal point, v _i is the linear average flow velocity along the i-th ultrasonic propagation path, n is the number of ultrasonic propagation paths, d is the inner diameter of the pipe, and is the surface average flow velocity of the pipe cross section. , A is the pipe cross-sectional area, and Q is the flow rate of the fluid in the pipe. 5. The ultrasonic flow measuring device according to any one of claims 1 to 4, wherein a part of the ultrasonic propagation path is arranged on the opposite side of the plane including the pipe bending part. .