JPH09189589A - Flow rate measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately measure a flow rate of a wide range, by providing a plurality of vibrators transmitting/receiving ultrasonic waves and having an equal length to that of either side of a rectangular flow path. SOLUTION: The apparatus is provided with a first vibrator 3 and a second vibrator 4 having an almost equal length to that of either side of a rectangular flow path 1, a measuring member 2 for mounting, at the upstream and downstream sides of the rectangular flow path 1, the first and second vibrators 3, 4 transmitting/receiving ultrasonic waves via the flow path 1, a measuring circuit 6 for measuring an ultrasonic signal propagation time between the vibrators, and a flow rate-operating means 7 for operating a flow rate based on a signal of the measuring circuit 6. A speed distribution in the flow path influences less, a correcting coefficient is changed less and a measuring accuracy is enhanced in a wide range. Moreover, stable measuring results can be obtained against a temperature change of a flow disturbance at the upstream side.

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 channel, the flow velocity is calculated by the arithmetic unit 105 from the difference in the propagation time of the ultrasonic wave, and the flow velocity distribution in the flow channel is calculated from the Reynolds number of the fluid at that time. Was calculated and the correction coefficient was calculated to calculate the flow rate.

[0003]

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 an object thereof is to measure a wide range of flow rates with high accuracy.

[0005]

In the flow rate measuring device of the present invention, an ultrasonic wave is transmitted / received across an upstream side and a downstream side of a rectangular channel, and ultrasonic waves are transmitted to / received from the rectangular channel. A first oscillator and a second oscillator each having a length equal to the length are provided.

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 is reduced, so that the measurement accuracy is improved over a wide range.

[0007]

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.

That is, the rectangular flow path, the first vibrator and the second vibrator having a length substantially equal to the length of one side of the rectangular flow path, and the rectangular flow path on the upstream side and the downstream side of the rectangular flow path. A measuring member for attaching the first and second oscillators that transmit or receive ultrasonic waves across the probe, a measuring circuit for measuring the ultrasonic signal propagation time between the oscillators, and a flow rate based on the signal of the measuring circuit. And a flow rate calculating means for calculating

Further, the first and second oscillators each having a length substantially equal to the shorter side of the rectangular channel are used to transmit and receive across the longer side of the rectangular channel.

The aspect ratio of the rectangular flow path is set to 0.3 or less. The vibrator has a rectangular cross section on the transmitting and receiving side.

Further, the first vibrator and the second vibrator can transmit or receive in the entire area of the cross section facing the flow path.

Further, the first vibrator and the second vibrator have substantially the same transmission sensitivity or reception sensitivity over the entire cross section facing the flow path.

Further, the rectangular flow path, the first vibrator and the second vibrator having a length larger than one of the sides of the rectangular flow path, the shield for blocking a part of the vibrator, and the rectangular flow path. Measuring members for mounting a first vibrator and a second vibrator for transmitting or receiving ultrasonic waves across the rectangular flow path on the upstream side and the downstream side of the path, and a measuring circuit for measuring a signal propagation time between the vibrators. And flow rate calculation means for calculating the flow rate based on the signal from the measurement circuit.

According to the present invention, the flow rate is measured by obtaining the flow velocity from the received signal which is not affected by the flow velocity distribution.

A first embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a rectangular first oscillator 3 and a second oscillator 4 for transmitting and receiving ultrasonic waves are arranged upstream and downstream of a flow in a flow channel member 2 forming a flow channel 1. Since the first vibrator 3 and the second vibrator 4 are arranged obliquely with respect to the flow path, the ultrasonic wave transmitted from the first vibrator 3 passes through the rectangular cross-section flow path 5 as shown in FIG. It propagates so as to traverse, 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 propagation time 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 measuring circuit 6.

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, so that the result of averaging the velocity distributions can be obtained. On the other hand, in the flow velocity distribution on the long side of the flow path shown in FIG. 1, since the ultrasonic waves are operating across the long side,
If the flow velocity distribution does not change between the oscillator 3 and the second oscillator 4, it means that the changes in the propagation velocity due to all the distributions are equally received, 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.

[0021]

As described above, according to the present invention, the following effects can be obtained.

(1) A rectangular flow path, a first vibrator and a second vibrator having a length substantially equal to one side of the rectangular flow path, and a rectangular flow on the upstream side and the downstream side of the rectangular flow path. Based on the measurement member that attaches the first transducer and the second transducer that transmits or receives ultrasonic waves across the path, the measurement circuit that measures the ultrasonic signal propagation time between the transducers, and the signal of the measurement circuit Since the flow rate calculating means for calculating the flow rate is provided, the influence of the velocity distribution in the flow channel can be reduced, the change of the correction coefficient is small, and the measurement accuracy is wide range. In addition, stable measurement results can be obtained against changes in temperature and turbulence in the upstream flow.

(2) Since the first oscillator and the second oscillator having a length substantially equal to the shorter side of the rectangular channel are transmitted and received across the longer side of the rectangular channel, the flow velocity distribution is obtained. A measurement result that is not affected by is obtained, and there is no need to change the correction coefficient.

(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 vibrator has a rectangular cross section on the transmitting and receiving sides, the shape can be made to match the shape of the flow path, and the accuracy becomes higher.

(5) Since the first oscillator and the second oscillator are capable of transmitting or receiving over 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 first vibrator and the second vibrator are substantially uniform over the entire cross section facing the flow path, an average received signal is obtained and the accuracy is improved. .

(7) A rectangular flow path, a first vibrator and a second vibrator each having a length larger than one of the sides of the rectangular flow path, a shield for blocking a part of the vibrator, and a rectangle. A measuring member for mounting a first oscillator and a second oscillator for transmitting or receiving ultrasonic waves across a rectangular flow path on the upstream side and the downstream side of the flow path, and a measurement circuit for measuring a signal propagation time between the vibrators. Since the flow rate calculating means for calculating the flow rate based on the signal of the measuring circuit is provided, it is possible to cope with various vibrators without being restricted by the shape of the vibrator, and the cost can be reduced.

[Brief description of the 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]

 DESCRIPTION OF SYMBOLS 1 rectangular flow path 2 flow path member 3 1st vibrator 4 2nd vibrator 6 measurement circuit 7 flow rate calculation means 8 rectangular vibrator 11 shield

 ──────────────────────────────────────────────────の Continued from the front page (72) Motoyuki Nawa, Inventor 1006 Odaka, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] 1. A rectangular flow path, and a first vibrator and a second vibrator each having a length substantially equal to a length of one side of the rectangular flow path.
A vibrator, a flow path member to which the first vibrator and the second vibrator that transmit or receive ultrasonic waves across the rectangular flow path are attached to the upstream side and the downstream side of the rectangular flow path, and the vibrator A flow rate measuring device comprising a measuring circuit for measuring a signal propagation time between them, and a flow rate calculating means for calculating a flow rate based on a signal of the measuring circuit. 2. A first oscillator and a second oscillator having a length substantially equal to the shorter side of the rectangular channel, and transmitting / receiving across the longer side of the rectangular channel. Flow meter side device. 3. The flowmeter-side device according to claim 1, wherein the aspect ratio of the rectangular flow path is 0.3 or less. 4. The flow rate measuring device according to claim 1, wherein the vibrator has a rectangular cross section on the transmission / reception side. 5. The flow rate measuring device according to claim 1, wherein the first vibrator and the second vibrator are capable of transmitting or receiving over the entire cross section facing the flow path. 6. The flow rate measuring device according to claim 1, wherein the first oscillator and the second oscillator have substantially the same transmission sensitivity or reception sensitivity over the entire cross section facing the flow path. 7. A rectangular flow path, a first vibrator and a second vibrator each having a length greater than a length of one side of the rectangular flow path, a shield for closing a part of the vibrator, and The signal propagation time between the flow path member between the first and second oscillators that transmits or receives ultrasonic waves across the rectangular flow path on the upstream side and the downstream side of the rectangular flow path and the signal propagation time between the vibrators is set. A flow rate measuring device comprising a measurement circuit for measuring and a flow rate calculating means for calculating a flow rate based on a signal from the measurement circuit.