JP3488003B2 - Flow measurement device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring device for measuring the flow rate of gas or the like using ultrasonic waves.

[0002]

2. Description of the Related Art A conventional flow rate measuring device of this type is known, for example, from Japanese Patent Application Laid-Open No. 4-140214.
As shown in, the ultrasonic transducers 103 and 104 are provided in a part of the duct body 102 forming the flow path 101 at an angle in the flow direction so that the ultrasonic waves traverse the flow upstream and downstream. Is provided.

In this way, the ultrasonic wave is made to scan across the cross section of the flow path, the flow velocity is calculated by the arithmetic unit 105 from the difference in the propagation time of the ultrasonic wave, and the inside of the flow path is calculated from the Reynolds number of the fluid at that time. The flow rate distribution was calculated by analogy, the correction coefficient was calculated, and the flow rate was calculated.

[0004]

However, in the above-mentioned conventional flow rate measuring device, not only the flow rate correction coefficient must be changed in accordance with the change in Reynolds number, but also the environmental condition such as the kind of fluid or temperature or the upstream condition. The relationship of the flow velocity distribution to the Reynolds number changed depending on the flow condition of the, and the measurement value had an error. It is also possible to measure with two or more pairs of transducers in order to reduce the influence of the flow velocity distribution, but it has the drawback of being complicated and expensive.
It has been a new problem to obtain a structure that can measure the flow rate with high accuracy by a simple structure.

The present invention is intended to solve the above-mentioned problems and has an object to measure a wide range of flow rates with high accuracy.

[0006]

In the flow rate measuring device of the present invention, a rectangular channel having a rectangular cross section through which a fluid flows, and a short side of the rectangular channel are disposed so as to traverse the rectangular channel. a pair of transducers that transmit or receive sound waves, the signal propagation time between said transducers is measured, and and a flow rate calculation means for calculating the flow rate of the fluid based on the measurement result, before
The pair of transducers transmits ultrasonic waves over the entire cross section of the flow path.
Alternatively, the lengths of the sending and receiving surfaces are quadrature so that they can be received.
The length is set to be substantially equal to the length of the opposing short sides of the shaped channel .

According to the present invention, the influence of the velocity distribution in the flow path can be reduced and the correction coefficient can be changed little, so that the measurement accuracy is improved over a wide range.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In order to achieve the above object, a flow rate measuring device of the present invention has the following configuration.

A rectangular channel having a rectangular cross section through which a fluid flows, a pair of transducers arranged on the short side of the rectangular channel and transmitting or receiving ultrasonic waves across the rectangular channel, and the vibration. And a flow rate calculating means for calculating the flow rate of the fluid based on the measurement result of the signal propagation time between the children.
The pair of transducers transmits ultrasonic waves over the entire cross section of the flow path.
The length of their sending and receiving surfaces to receive or receive
The length of the opposite short sides of the rectangular channel is set to be almost equal.
Of.

The aspect ratio of the above rectangular flow path should be 0.3 or less.
In addition, the pair of transducers mentioned above are
Has a rectangular cross section.

Further , the transmission feeling is felt over the entire cross section facing the flow path.
The degree of reception or the reception sensitivity is made substantially uniform.

According to the present invention, the flow rate is obtained by measuring the flow rate from the received signal which is not influenced by the flow rate distribution.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a rectangular first vibrator 3 for transmitting and receiving ultrasonic waves to the flow path member 2 forming the flow path 1 and a second
The oscillators 4 are arranged upstream and downstream of the flow.

Since the first oscillator 3 and the second oscillator 4 are arranged obliquely with respect to the flow path, the ultrasonic waves transmitted from the first oscillator 3 flow in a rectangular cross section as shown in FIG. It propagates so as to traverse the path 5, reaches the second oscillator 4, and conversely, when transmitted from the second oscillator 4, reaches the first oscillator 3 as described above. The propagation time of each ultrasonic wave changes due to the existence of a flow in the flow path 1. This propagation time is measured by the measuring circuit 6 and converted into a flow rate value by the flow rate calculating means 7.

Next, the operation will be described. As for the propagation time, when the sound in the stationary fluid is c and the velocity of the fluid flow is v, the propagation velocity of the ultrasonic wave in the forward direction of the flow is (c + v). Assuming that the distance between the transducers 3 and 4 is L and the angle between the ultrasonic wave propagation axis and the central axis of the conduit is φ, the time t1 for the ultrasonic wave to propagate from upstream to downstream is t1 = L / (c + vCOSφ ) (1) and the time to propagate from the downstream to the upstream is t2 = L / (c-vCOSφ) (2), and if L and φ are known, the flow velocity v can be obtained by measuring t1 and t2 with the measurement circuit 6. To be

From the flow velocity, the flow rate Q is obtained by calculating Q = KSv (3) in the flow rate calculation circuit 7 where S is the passage area of the flow path and K is the correction coefficient.

The flow velocity in the flow path 1 generally has a flow velocity distribution as shown in FIG. 1, and the distribution changes depending on the Reynolds number and the turbulence of the upstream flow. This flow velocity distribution is two-dimensionally generated, and also occurs on one long side (long side) of the rectangular cross section as shown in FIG. 1 and on one short side (short side) of the rectangular cross section as shown in FIG. . If the ratio of the long side to the short side (aspect ratio) is preferably set to 0.3 or less, the flow velocity distribution is further stabilized. When there is such a flow velocity distribution, its propagation time is the integral of the change in velocity received by the minute portion.

FIG. 4 shows a second embodiment, which is a rectangular vibrator 8
The transmission / reception surface 8'has a rectangular shape, and one side thereof has substantially the same length as the short side of the rectangular flow path, so that ultrasonic waves in the entire short side flow path can be received.

Therefore, even if there is a flow velocity distribution on the short side as shown in FIG. 3, a signal obtained by integrating all the ultrasonic waves is received, and the result of averaging the velocity distributions can be obtained.

On the other hand, the flow velocity distribution on the long side of the flow path shown in FIG.
Since the ultrasonic wave is operating across the long side, if the flow velocity distribution does not change between the first vibrator 3 and the second vibrator 4,
This means that the changes in the propagation velocity due to all distributions are received equally, and the influence of the flow velocity distribution can be eliminated. Therefore, it is not necessary to change the above-mentioned correction coefficient K.

The transmission / reception surface 8'of the rectangular vibrator 8 is formed of only a piezoelectric element, and transmission / reception can be performed on the entire surface. The transmission / reception sensitivity is almost the same in all parts as shown in FIG. In FIG. 6, the periphery of the piezoelectric element is reinforced by the casing 7 to increase the mechanical strength, but the transmitting / receiving surface 9'has a length equal to the short side of the rectangular flow path.

FIG. 7 shows a third embodiment. The vibrator 10 has a circular cross-sectional shape, a part of which is covered with a shield 11 and the transmitting / receiving surface 10 'corresponds to a rectangular flow path. Ultrasonic waves can be transmitted and received only where they are.

As described above, according to the present embodiment, (1) a rectangular channel having a rectangular cross section through which a fluid flows, and a rectangular channel which is arranged so as to face the rectangular channel and which transmits ultrasonic waves across the rectangular channel or A pair of transducers to be received, and a flow rate calculation means for measuring a signal propagation time between the transducers and calculating a flow rate of the fluid based on the measurement result, are provided for the rectangular flow path of the transducers. Since the sending and receiving are set so as to be performed over the entire opposite sides of the rectangular flow path, the influence of the velocity distribution in the flow path can be reduced, the correction coefficient can be changed little, and the measurement accuracy can be increased over a wide range. In addition, stable measurement results can be obtained against changes in temperature and turbulence in the upstream flow.

(2) Since the sending and receiving surfaces of the pair of transducers are set to be substantially equal to the length of the short side of the rectangular flow path, the measurement result not affected by the flow velocity distribution can be obtained, and the correction coefficient needs to be changed. Disappear.

(3) Since the ratio of the length and width of the rectangular flow path is set to 0.3 or less, the flow velocity distribution is reduced and the measurement accuracy is further improved.

(4) Since the cross section of the vibrator on the transmitting and receiving side is rectangular, it can be made to match the shape of the flow path, and the accuracy becomes higher.

(5) Since the pair of transducers can transmit or receive in the entire area of the cross section facing the flow path, an ultrasonic signal of the entire flow path can be obtained and the accuracy is improved.

(6) Since the transmission sensitivity or the reception sensitivity of the pair of transducers is substantially uniform over the entire cross section facing the flow path, an average reception signal is obtained and the accuracy is improved.

(7) Since the sending and receiving surfaces of the pair of vibrators are made larger than the length of the short side of the rectangular flow path, and the part of the length of the short side or more is closed by the shield, It can be applied to various vibrators without being restricted by its shape and can be constructed at low cost.

[0031]

As described above, according to the present invention, the influence of the velocity distribution in the flow path can be reduced, and the change of the correction coefficient can be reduced.
The measurement accuracy is also high over a wide range. In addition, stable measurement results can be obtained against changes in temperature and turbulence in the upstream flow.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a flow rate measuring device according to a first embodiment of the present invention.

FIG. 2 is a side view of the flow channel structure of the device.

FIG. 3 is a cross-sectional view of the flow path configuration of the device.

FIG. 4 is a perspective view of a vibrator of a flow rate measuring device according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing reception sensitivity of the device.

FIG. 6 is a perspective view showing an embodiment of a vibrator of the same device.

FIG. 7 is a perspective view of a vibrator of a flow rate measuring device according to a third embodiment of the present invention.

FIG. 8 is a block diagram of a conventional flow rate measuring device.

[Explanation of symbols]

1 rectangular flow path 2 flow path members 3 First transducer 4 second oscillator 6 measuring circuit 7 Flow rate calculation means 8 Rectangular vibrator 11 Shield

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yuji Nakabayashi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Motoyuki Nawa, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Incorporated (56) References JP-A-5-223608 (JP, A) JP-A-5-506092 (JP, A) International Publication 91/09282 (WO, A1) (58) Fields investigated (Int.Cl . ⁷ , DB name) G01F 1/66

Claims (4)

(57) [Claims] 1. A rectangular channel having a rectangular cross section, in which a fluid flows,
The signal propagation time between a pair of transducers arranged on the short side of the rectangular channel and transmitting or receiving ultrasonic waves across the rectangular channel and the transducers is measured. Flow rate calculating means for calculating the flow rate of the fluid based on the ultrasonic wave in the entire cross section of the flow path.
The length of their sending and receiving surfaces to send or receive
Set the length to be approximately equal to the length of the opposite short sides of the rectangular flow path.
Flow rate measuring device. 2. The flow rate measuring device according to claim 1, wherein the ratio of the length and width of the rectangular flow path is 0.3 or less. 3. A pair of transducers are cross-sections of their transmitting and receiving surfaces.
The flow measuring device according to claim 1 , wherein is a rectangle . 4. A pair of transducers comprises an entire cross section facing the flow path.
The flow rate measuring device according to claim 1 , wherein the transmission sensitivity or the reception sensitivity is substantially uniform in the range .