JP5816831B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an ultrasonic flowmeter for measuring a flow rate of gas or the like.

  As shown in FIG. 7, this type of conventional flow rate measuring device comprises a pair of ultrasonic sensors or the like in a measurement flow path 114 in which a fluid supply path 112 is connected upstream and a fluid outflow path 113 is connected downstream. A flow rate detection means (not shown) was arranged.

  Further, the inside of the measurement flow path 114 is divided by a plurality of partition plates 115 so that the fluid becomes a two-dimensional laminar flow.

  Then, the flow velocity of the fluid flowing through the measurement flow path 114 is measured by the flow velocity detection means, and the flow rate is calculated based on the measured flow velocity (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-43015

  However, in the conventional configuration, the flow rate ratio between the layers may be different between the layer at the end of the measurement channel divided by the partition plate and the other layers.

  On the other hand, during flow meter production, the actual flow rate is measured so that the true flow rate value (true value) and the measured flow rate value fall within the specified error range in the measured flow rate range, and the difference from the true value is corrected for instrumental error. Therefore, it is necessary to correct the flow rate so that it can be measured correctly. At this time, it is desirable that the flow coefficient (= true value / measured value) be flat in the measured flow range. That is, if the flow coefficient is flat, the instrumental error correction can be completed only by correcting once with an arbitrary flow rate. Furthermore, it goes without saying that if the flow coefficient is 1 and it is flat, no instrumental error correction is necessary.

  In order to make this flow coefficient flat, it is necessary to make the flow rate ratio of each layer constant regardless of the flow rate, but conventionally, in order to reduce this effect, It is possible to increase the passage pressure loss of the laminar flow path and reduce the flow velocity difference between layers by providing a rectifying member or increasing the number of layers partitioning the flow path and reducing the pitch of one layer, but the structure is There are problems such as increased complexity and cost, or increased passage pressure loss in the flow path and limited measurement flow range.

  The present invention solves the above-mentioned conventional problems, and forms a layered flow path for reducing the height per layer for stabilizing the flow in the measurement flow path, An object of the present invention is to provide an ultrasonic flowmeter that reduces the influence on measurement by reducing the flow velocity difference and has a flat flow coefficient.

In order to solve the above-described conventional problems, an ultrasonic flowmeter of the present invention includes a measurement channel having a rectangular channel cross section through which a fluid to be measured flows, and the measurement channel arranged in the middle of the measurement channel. A plurality of partition plates that are divided into two or more layered flow paths, a pair of ultrasonic sensors that are arranged upstream and downstream on the layered flow path and capable of transmitting and receiving ultrasonic signals, and transmitted from one of the ultrasonic sensors and a flow rate measuring means for detecting the flow rate of the fluid to be measured based on the propagation time until the ultrasonic signal is received propagation to other ultrasonic sensors the fluid to be measured, the layered channel In order to reduce the flow velocity difference between them, the layer height of the layered flow channel at both ends is made smaller than the layer height of the other layered flow channel.

  As a result, the flow rate between the respective layered channels with respect to the flow rate is made uniform, and the flow coefficient can be flattened.

  According to the ultrasonic flowmeter of the present invention, in a wide range of flow rate measurement, the flow rate between the respective layered channels is made uniform, the flow rate coefficient becomes flat, and the flow velocity can be accurately measured.

Sectional drawing of the principal part of the ultrasonic flowmeter in embodiment of this invention Sectional drawing of the principal part of the flow measurement unit of the ultrasonic flowmeter in embodiment of this invention (A) AA principal part sectional drawing in FIG. 2, (b) BB principal part sectional drawing in FIG. Operational explanatory diagram of the ultrasonic flowmeter in the embodiment of the present invention A graph showing the relationship between the measured flow rate and the flow coefficient depending on the layer height of the layered channel FIG. 3 is a conceptual diagram of a cross section of a layered channel in the embodiment of the present invention Configuration diagram of conventional ultrasonic flowmeter

  The first invention is a measurement channel having a rectangular channel cross section through which a fluid to be measured flows, and a plurality of partition plates arranged in the middle of the measurement channel and dividing the measurement channel into three or more layered channels A pair of ultrasonic sensors that are arranged upstream and downstream on the layered flow path and capable of transmitting and receiving ultrasonic signals, and an ultrasonic signal transmitted from one of the ultrasonic sensors propagates through the fluid to be measured. Flow rate measuring means for detecting the flow rate of the fluid to be measured based on the propagation time until the other ultrasonic sensor receives, and the height of the layers of the layered channels at both ends of the layered channel Is made smaller than the height of the layer of the other layered channels, the flow rate difference between the layered channels can be reduced even if the measured flow rate changes, and the flow coefficient can be flattened.

  In the second invention, particularly in the first invention, the height of the layered channel at both ends of the layered channel is 2 to 5% smaller than the height of the layers of the other layered channels. As a result, the flow coefficient can be flattened within the practical range.

  In particular, in the first or second invention, the third aspect of the invention is to stabilize the flow of the measurement flow path by setting the height of one layer of the layered flow path to 2 mm or less. The change in the flow rate ratio can be reduced, and the flow coefficient can be made more stable and flat.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the pair of ultrasonic sensors are arranged on the same surface side of the layered flow path, and are transmitted from one of the ultrasonic sensors. The signal is reflected on the inner wall of the measurement channel facing the ultrasonic sensor and received by the other ultrasonic sensor, and the measurement flow is configured so that the flow rate difference between the layers is small. By using the path, it is possible to increase the propagation distance of the ultrasonic wave using reflection and improve the measurement accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
In FIG. 1, the fluid supply path 3 has a shut-off valve 5 that is opened and closed by a valve body 9 that is linked to a drive unit 4 that is an electromagnetic device such as a stepping motor. When the shutoff valve 5 is open, the fluid to be measured flows out from the fluid supply path 3 into the meter housing 2. The flow channel of the measurement flow channel 1 is a rectangle having a rectangular cross section, and the fluid to be measured filled in the meter housing 2 flows into the measurement flow channel 1 from the measurement flow channel inlet 1a side, and further on the downstream side thereof. It flows out of the meter housing 2 through the fluid outlet 6 connected to the measurement channel outlet 1b.

  The shutoff valve 5 is closed when there is an abnormality in the fluid flow or when an earthquake occurs.

  FIG. 2 shows a cross section of the flow rate measurement unit according to the present embodiment. As shown in the figure, a pair of ultrasonic sensors 7 and 8 constituting the flow velocity detecting means are arranged obliquely inward with respect to the sensor mounting member 12. In such a state, they are assembled so as to be positioned on the same surface of the measurement channel 1. The flow rate measurement means 10 is connected to the pair of ultrasonic sensors 7 and 8 by lead wires 10a and 10b, and is fixed to the measurement flow path 1, and is integrated as a flow rate measurement unit. The flow rate measuring means 10 measures the propagation time until the ultrasonic signal transmitted from one ultrasonic sensor is reflected by the opposing wall 1c of the measurement flow path 1 and transmitted / received by the other ultrasonic sensor, The flow rate of the fluid to be measured flowing through the path 1 is calculated.

  In this configuration, since the fluid to be measured is once filled in the meter housing 2 and then flows into the measurement flow path 1, the meter housing 2 becomes a chamber and is directly measured by a pipe bent from the inflow portion of the fluid to be measured. Compared with the method of connecting to the flow path, the flow that flows into the measurement flow path is less likely to occur, and the measurement reliability is improved.

  3A is a cross-sectional view of the main part AA in FIG. 2, and FIG. 3B is a cross-sectional view of the main part BB in FIG. 2. The flow path of the measurement flow path 1 is a rectangular cross section as described above. As shown in FIG. 3A, the short side of the flow path is divided by three partition plates 11a, 11b, and 11c to form four layered flow paths 13a to 13d.

  That is, the flow of the fluid to be measured becomes two-dimensional by partitioning the flow path narrowly with the partition plates 11a to 11c, and the flow in the height direction of the flow path is dispersed by the layered flow path. Compared to a single-layer flow path, the flow velocity distribution is made uniform, and measurement by ultrasonic waves is stabilized.

  The pair of ultrasonic sensors 7 and 8 are both arranged so as to be able to transmit and receive ultrasonic signals within the range C in the flow direction of the layered flow paths 13a to 13d, and transmitted from one ultrasonic sensor. The ultrasonic signals dispersed and propagated in the respective layered flow paths 13a to 13d are reflected on the opposing wall 1c and received by the other ultrasonic sensor.

  Note that although four layers are used in this embodiment, a configuration other than four layers is also possible. However, increasing the number of layers not only increases costs, but also increases pressure loss due to increased passage resistance in the fluid flow path, and attenuation due to reflection of ultrasonic waves on the partition plate. However, there are many issues that must be limited.

  In addition, a certain cross-sectional area of the flow path is required due to pressure loss, but in the case of three layers, it is necessary to increase the interlayer pitch and the height per layer increases, so the measured flow rate range as a layered flow path There are few merits of multi-layered flow paths, such as difficulty in two-dimensional flow, and the effect of the configuration of the embodiment of the present invention cannot be expected.

Next, the flow measurement operation using ultrasonic waves will be described with reference to FIG. As shown in FIGS. 1-3, in this Embodiment, a pair of ultrasonic sensor 7 and 8 and a measurement flow path are unitized, and the ultrasonic sensors 7 and 8 are on the same surface of the rectangular cross section of a measurement flow path. Therefore, the propagation path for transmitting and receiving the ultrasonic signal is a V-shaped propagation path reflected by the opposing wall of the ultrasonic sensor, and the ultrasonic sensor 7 disposed upstream and the ultrasonic wave disposed downstream. An ultrasonic signal is transmitted and received between the sensors 8.

  In this configuration, the propagation time T <b> 1 until the ultrasonic signal emitted from the upstream ultrasonic sensor 7 is received by the downstream ultrasonic sensor 8 is measured. On the other hand, the propagation time T <b> 2 until the ultrasonic signal emitted from the downstream ultrasonic sensor 8 is received by the upstream ultrasonic sensor 7 is measured.

  Based on the propagation times T1 and T2 measured in this way, the flow rate is calculated by the calculation means by the following calculation formula.

  Now, the angle between the flow velocity V in the flow direction of the fluid to be measured in the measurement channel 1 and the propagation path D of the ultrasonic signal is θ, the distance between the ultrasonic sensors 7 and 8 is 2 × L, and the fluid to be measured When the speed of sound is C, the flow velocity V is calculated by the following equation.

Formula (1) T1 = 2 × L / (C + V cos θ)
Formula (2) T2 = 2 × L / (C−V cos θ)
From equations (1) and (2), the sound speed C is eliminated by subtracting the reciprocal of T1 from the reciprocal of T1, and equation (3) V = (2 × L / 2 cos θ) ((1 / T1) − (1 / T2 ))
It becomes.

  Since θ and L are known, the flow velocity V can be calculated from the values of T1 and T2. Assuming that the air flow rate is measured, assuming that the angle θ = 45 degrees, the distance L = 35 mm, the sound velocity C = 340 m / s, and the flow velocity V = 8 m / s, T1 = 2.0 × 10−4 seconds, T2 = 2.1 × 10 −4 seconds. Thus, by measuring the propagation time of the ultrasonic signal between the ultrasonic sensors, the flow velocity V of the fluid to be measured can be instantaneously measured.

  FIG. 5 shows a graph based on experimental data obtained by actually measuring the flow rate and the flow rate coefficient K when the height of each layer is changed in a measurement flow channel having a four-layered flow channel.

  In FIG. 5, (a) shows a case in which all four layers have the same layer height, and the flow rate coefficient K decreases to the right when the layered channels are formed with the layer heights being equally spaced. Inclined shape.

  This means that the flow rate distribution ratio in each layer changes depending on the measured flow rate.

  In addition, h1 to h4 mean the layer height of each layered channel as shown in FIG.

  Also, (b) and (c) show the case where the layer height of the layered channel located at both ends of the four layers is made smaller than the layer height of the other layered channels. Regardless of the height, the flow coefficient converges to 1 on the high flow rate side. When the heights of the layers are equal, the flow coefficient is large on the low flow rate side, and converges to the same value on the large flow rate side regardless of the layer height.

  Therefore, in the present embodiment, as shown in FIG. 6, the layer height of the layered channels 13a and 13d in which one channel wall is the wall of the measurement channel 1 is set to the inner layered channels 13b and 13d. On the other hand, it is small. Specifically, the layer heights h1 and h4 of the layered flow channels at both ends are set to 1.95 mm, and the other layer heights h2 and h3 are set to 2.00 mm. With this configuration, FIG. The following characteristics are obtained.

  Further, at the measurement channel inlet 1 a of the measurement channel 1, the tips of the partition plates 11 a to 11 c are located at positions separated from the tip of the measurement channel 1 by a distance m on the downstream side.

  And by this structure, it has implement | achieved making a flow coefficient substantially 1 over the measurement flow velocity range.

  In the present embodiment, the layered channels 13a and 13d in the vicinity of the wall surface 1d are reduced by 0.05 mm to 1.95 mm with respect to the layer height of 2.00 mm of the layered channels 13b and 13c. The appropriate range is 2 to 5% of the height of the reference layer (the layer excluding the layered channels at both ends).

  As described above, the ultrasonic flowmeter according to the present invention can make the flow rate ratio of each layered flow path constant even if the measured flow rate changes in the measurement flow path composed of a plurality of layered flow paths. Since the flow coefficient can be flattened, the instrumental error correction at the time of production can be facilitated, and the size and cost can be reduced, so that it can be applied to various flow meters including gas meters.

DESCRIPTION OF SYMBOLS 1 Measurement flow path 2 Meter housing 5 Shut-off valve 7, 8 Ultrasonic sensor 10 Flow measurement means 11a-11c Partition plates 13a-13d Layered flow path

Claims (4)

A measurement channel having a rectangular channel cross-section through which the fluid to be measured flows, and
A plurality of partition plates arranged in the middle of the measurement channel and dividing the measurement channel into three or more layered channels;
A pair of ultrasonic sensors arranged upstream and downstream on the laminar flow path and capable of transmitting and receiving ultrasonic signals;
Flow rate measuring means for detecting a flow rate of the fluid to be measured based on a propagation time until an ultrasonic signal transmitted from one of the ultrasonic sensors propagates through the fluid to be measured and is received by the other ultrasonic sensor; With
The ultrasonic flowmeter which made the height of the layer of the layered flow path of both ends smaller than the height of the layer of other layered flow paths so that the flow velocity difference between the layered flow paths might be small.   The ultrasonic flowmeter according to claim 1, wherein the height of the layered channel at both ends of the layered channel is 2 to 5% smaller than the height of the layers of the other layered channels.   The ultrasonic flowmeter according to claim 1 or 2, wherein the height of one layer of the layered flow path is 2 mm or less. The pair of ultrasonic sensors are arranged on the same surface side of the layered flow path, and an ultrasonic signal transmitted from one of the ultrasonic sensors is reflected on the inner wall of the measurement flow path facing the ultrasonic sensor, The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter is configured to be received by the other ultrasonic sensor.

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