JP6028215B2 - Ultrasonic flow meter - Google Patents

Description

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

  As shown in FIG. 5A, this type of conventional ultrasonic flowmeter has a measurement channel 9 and an opening 10 through which fluid flows in on the upstream side of the measurement channel 9. In addition, a sensor mounting portion 11 adjacent to the measurement flow path 9 is provided, and a pair of ultrasonic sensors 12a and 12b are mounted on the sensor mounting portion 11, and the propagation time measured by the ultrasonic sensors 12a and 12b is provided above the sensor mounting portion 11. A flow rate calculation circuit 13 for calculating the flow rate of the fluid flowing through the measurement flow path 9 is installed.

  FIG. 5B is a cross-sectional view taken along the line CC ′ of FIG. 5A and shows the channel wall surface on the ultrasonic sensor mounting side of the measurement channel 9 for transmission / reception of the ultrasonic sensors 12a and 12b. Are provided with rectangular ultrasonic wave propagation aperture windows 14a and 14b.

  The ultrasonic signal transmitted from one of the pair of ultrasonic sensors is configured to be reflected by the opposing wall surface and received by the other ultrasonic sensor, so-called V-shaped ultrasonic propagation path 15. (For example, refer to Patent Document 1).

  In this way, when the ultrasonic wave propagation path 15 is V-shaped and ultrasonic wave wall reflection is used, the ultrasonic wave propagates twice as long as the case where reflection is not used even with the same flow path width configuration. The flow meter shape can be reduced in size.

  On the other hand, as shown in FIG. 6B, the received waveform is a normal received wave 17 generated by the propagation of the ultrasonic wave through the V-shaped ultrasonic wave propagation path 15, and a superposed wave shown in FIG. An unnecessary received wave 18 that propagates directly through the propagation path 16 due to diffraction between the sound wave propagation aperture windows is generated.

  The received wave 18 is not necessary for measurement. When the arrival time is close to the regular received wave 17, it becomes noise and affects the measurement. For the unnecessary received wave 18 that propagates directly, It is necessary to make a time difference so that it can be separated from the regular received wave 17 in terms of time, or to make it as small as possible.

  Conventionally, the position of the ultrasonic wave propagation aperture window is adjusted so as to have a time difference, and the position of the ultrasonic wave propagation aperture window is devised so as not to affect the regular received wave.

Japanese Patent Laid-Open No. 11-201791

  However, in the conventional configuration, even if it is attempted to avoid the unnecessary received wave, the position and size of the ultrasonic wave propagation aperture window of the measurement channel, or the characteristics of the ultrasonic sensor and the specification of the measurement channel are limited. For example, when it is necessary to lengthen the propagation path, there are problems such as an increase in sensitivity of the ultrasonic sensor and an increase in power consumption of the measurement circuit. In addition, there has been a problem that the measurement channel section is limited in size and optimization as a measurement system.

In addition, if the length of the ultrasonic propagation aperture window in the ultrasonic inlet / outlet is significantly increased in order to solve the above problem, the flow of fluid enters the ultrasonic propagation aperture window and affects the flow velocity distribution. The measurement was unstable.

  The present invention solves the above-mentioned conventional problems, reduces the influence of direct propagation waves (unnecessary received waves) between the ultrasonic propagation aperture windows, simplifies and downsizes the structure, and reduces the cost. An object is to provide an ultrasonic flow meter.

In order to solve the above-described conventional problems, the ultrasonic flowmeter of the present invention relates to an ultrasonic wave propagation opening window at an ultrasonic wave inlet / outlet, and this ultrasonic wave propagation opening window faces 2 parallel to the flow direction of the measurement channel. It is an ultrasonic flowmeter characterized by having an outline shape in which two straight lines and the two straight lines are connected by an arc .

  As a result, the propagation waves directly propagating between the ultrasonic propagation aperture windows are not concentrated in a certain direction, so that they are not propagated at a certain distance and time, and the received unnecessary propagation waves are reduced. The flow rate can be measured accurately.

  The ultrasonic flowmeter of the present invention can perform accurate flow velocity measurement by reducing unnecessary propagation waves that propagate directly between the ultrasonic propagation aperture windows.

(A) Cross-sectional view of the ultrasonic flowmeter in Embodiment 1 of the present invention, (b) Side view of the ultrasonic flowmeter Operational explanatory diagram of the ultrasonic flowmeter in Embodiment 1 of the present invention (A) The figure which shows the outline shape of the ultrasonic propagation opening window of the A-A 'arrow cross section in FIG. 1, (b) The figure which shows the other outline shape of the same ultrasonic propagation opening window (A) The figure which shows the waveform type part between the ultrasonic propagation aperture windows of the ultrasonic flowmeter in Embodiment 2 of this invention, (b) B-B 'arrow sectional drawing of Fig.4 (a) (A) The block diagram of the conventional ultrasonic flowmeter, (b) C-C 'arrow line view of Fig.5 (a) (A) The figure which shows the ultrasonic propagation path of the conventional ultrasonic flowmeter, (b) The figure which shows the ultrasonic received wave of the conventional ultrasonic flowmeter

A first invention is a pair of a measurement channel having a rectangular cross-section and a pair of ultrasonic channels that are installed on the same wall surface side of the measurement channel and that use reflection on the opposite wall surface. Flow rate based on ultrasonic sensor, two ultrasonic wave propagation opening windows for ultrasonic signals provided on the wall surface on the installation side of the ultrasonic sensor, and ultrasonic wave propagation time by transmission / reception of the ultrasonic sensor The two ultrasonic wave propagation aperture windows have a contour shape in which two straight lines parallel to the flow direction of the measurement flow path and the two straight lines are connected by an arc . This feature prevents diffracted propagation waves from the ultrasonic propagation aperture window from propagating to other ultrasonic propagation aperture windows at a fixed distance, reducing unnecessary propagation waves and accurately measuring the flow velocity. can do.

According to a second aspect of the invention, in particular, in the first aspect of the invention, the interval between the two straight lines forming the ultrasonic wave propagation aperture window is the same as the channel width on the ultrasonic sensor installation side. In addition to the suppression, the ultrasonic wave propagation path measures the entire area in the short side direction in the fluid measurement unit, so that accurate measurement is possible without correction of the measurement value.

According to a third aspect of the invention, in particular, in the first or second aspect of the invention, the wall surface of the measurement flow path between the ultrasonic wave propagation aperture windows is formed in a corrugated cross-sectional shape perpendicular to the direction in which the fluid flows. A time difference occurs in the diffracted wave generated in the ultrasonic wave propagation aperture window due to the difference in the height of the wall surface, and the reception level of the diffracted wave can be further lowered.

In a fourth aspect of the invention, particularly in the third aspect of the invention, the cross-sectional area of the measurement flow path between the ultrasonic wave propagation aperture windows and the cross-sectional area of the measurement flow path other than between the ultrasonic wave propagation aperture windows coincide with each other. As a result, since the cross-sectional area of the measurement channel does not change in the propagation path of the ultrasonic wave, even if it has a corrugated wall surface, the influence on the measurement performance can be minimized.

  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)
FIG. 1 is a sectional view of an ultrasonic flowmeter according to the first embodiment of the present invention.

  FIG. 1A is a side sectional view, and FIG. 1B is a side view as seen from the fluid inflow side. In the figure, the ultrasonic flowmeter 1 includes a measurement channel 2 and a fluid upstream of the measurement channel 2. It has the opening part 3 comprised by the inflow path 1a which flows in. In addition, a sensor mounting portion 4 adjacent to the measurement flow path 2 is provided, and a pair of ultrasonic sensors 5a and 5b is mounted on the sensor mounting portion 4, and the flow rate is calculated from the propagation time obtained by the ultrasonic sensor above the sensor mounting portion 4. A flow rate calculation circuit 6 is installed as a flow rate calculation means.

  Further, as shown in FIG. 2B, the cross section of the flow path through which the fluid of the measurement flow path 2 flows is formed in a rectangular shape.

  The flow rate calculation circuit 6 may be configured not to be adjacent to the measurement flow path and the sensor mounting portion.

  Next, a flow measurement operation using ultrasonic waves will be described. As shown in FIG. 2, in the present invention, a pair of ultrasonic sensors 5a and 5b are arranged on the same plane of the rectangular cross section of the measurement channel 2 (in FIG. 1, the short side of the rectangular cross section) The ultrasonic wave transmission / reception propagation path is a V-shaped propagation path reflected by the opposing wall surface, and ultrasonic waves are transmitted and received between the upstream and downstream ultrasonic sensors.

  In this configuration, the propagation time T1 until the ultrasonic wave emitted from the upstream ultrasonic sensor 5a is received by the downstream ultrasonic sensor 5b is measured. On the other hand, the propagation time T2 until the ultrasonic wave emitted from the downstream ultrasonic sensor 5b is received by the upstream ultrasonic sensor 5a is measured.

  Based on the propagation times T1 and T2 thus measured, the flow rate calculation circuit 6 calculates the flow velocity by the following calculation formula.

  If the angle between the flow velocity V of the fluid to be measured in the flow direction of the measurement channel and the ultrasonic propagation path is θ, the distance between the ultrasonic sensors is 2 × L, and the sound velocity of the fluid to be measured 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)
The speed of sound C is eliminated from the equation for subtracting the reciprocal of T2 from the reciprocal of T1. Equation (3) V = (2 × L / 2 cos θ) ((1 / T1) − (1 / T2))
Since θ and L are known, the flow velocity V can be calculated from the values of the propagation times 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, and instantaneous measurement is possible.

  FIG. 3 is a diagram showing the shape of an ultrasonic wave propagation aperture window that is an ultrasonic wave entrance / exit, which is a feature of the present invention, and is a view taken along the line AA ′ of the wall surface of the measurement flow channel of FIG. 7a and 7b are ultrasonic propagation aperture windows for ultrasonic transmission / reception of the ultrasonic sensors 5a and 5b in FIG.

  As described above in the conventional example, in the flow path of the V-shaped propagation path, the ultrasonic wave transmitted from one ultrasonic sensor is reflected by the wall surface facing the sensor mounting portion and received by the other ultrasonic sensor. However, a part of the ultrasonic wave is diffracted between the two ultrasonic wave propagation aperture windows, and a signal from the ultrasonic sensor directly propagates to the other ultrasonic sensor. If this directly propagated received wave is close in time to a received wave that has passed through a regular propagation path (that is, a V-shaped propagation path), measurement logic malfunctions and the received wave becomes noise, which adversely affects measurement performance. There is a possibility to bring.

  In the present embodiment, as shown in FIG. 3 (a), the outer shape of the short channel side that causes diffraction in the two ultrasonic wave propagation aperture windows 7a and 7b is configured by a curve, and thus the conventional example (FIG. 5). 6), the propagation wave caused by diffraction is not diffracted in a certain direction, and the propagation path is dispersed by diffusing in a normal line with respect to the curve, so that the other ultrasonic sensor does not need to receive it. The level of the received wave is greatly reduced.

  As a result, in the conventional ultrasonic wave propagation aperture shape, the directly propagated received wave is close in time to the received wave that has passed through the normal propagation path due to the position and size of the V-shaped propagation path and the ultrasonic propagation aperture window. In order to avoid this, it was necessary to reduce the specifications of the flow measurement unit, but the level of direct propagation waves due to diffraction can be reduced and the design freedom of the flow meter is increased. It is possible to reduce the measurement performance to the optimum specifications for the flow path design according to the purpose.

  In addition, since the diffracted waves that adversely affect the measurement are generated on the sides close to each other of the ultrasonic propagation aperture windows, as shown in FIG. 3B, in the contour shapes of the ultrasonic propagation aperture windows 7a ′ and 7b ′, The arc may be formed only on the side closer to each other, and the same effect can be obtained even if the other is a straight line as in the prior art.

(Embodiment 2)
FIG. 4 is a view showing a second embodiment of the present invention, FIG. 4 (a) is an arrow view of the flow path wall in the AA ′ direction of FIG. 1, and FIG. 4 (b) is FIG. ) Shows a cross-sectional view of the measurement flow path (F) in the BB ′ direction. As shown in FIG. 4, the cross section perpendicular to the fluid flow on the wall surface 8 between the two ultrasonic wave propagation aperture windows is formed into the wave shape 8a, so that the position where diffraction occurs in the ultrasonic wave propagation aperture window is corrugated. Since the propagation distance changes and dispersion is further promoted because of the change in height, the influence of the direct propagation wave becomes smaller.

  In this embodiment, as shown in FIG. 4 (b), the wave shape is a triangular shape. However, it is not particularly reduced if it is uneven, and the interval between the unevenness is uniform. A configuration is possible without it.

Further, in the present embodiment, the corrugated height h1 is set to a flow path (upstream side of the ultrasonic wave propagation aperture window 7a (
The channel cross-sectional area of E) and the channel cross-sectional area of the measurement channel (F) having a corrugated shape are made the same. Needless to say, the channel cross-sectional area of the measurement channel (G) on the downstream side of the ultrasonic wave propagation window 7b is the same.

  For example, in the present embodiment, the waveform is a triangular wave, and the average h2 of the peak and valley positions is the same as the flow path height h3 on the upstream side (E) of the ultrasonic wave propagation aperture window 7a. The flow cross-sectional areas are the same.

  The wall surface on the ultrasonic sensor mounting side may have a full-surface wave shape.

  As described above, the ultrasonic flowmeter according to the present invention is configured on the same wall surface side of the measurement flow channel and the measurement flow channel and constitutes an ultrasonic propagation path using reflection on the opposite measurement flow channel wall surface. A pair of ultrasonic sensors arranged in such a manner, and a flow rate calculation circuit for detecting a flow rate based on the propagation time of ultrasonic waves transmitted and received by the ultrasonic sensors. The shape of the ultrasonic wave propagation aperture window in the short side direction is a shape that does not have a straight portion perpendicular to the flow direction of the measurement flow path, and the diffracted wave from the ultrasonic wave propagation aperture window is constant. Since it does not propagate to the other ultrasonic wave propagation aperture window at a distance, unnecessary propagation waves can be reduced, the flow velocity can be measured accurately, the measurement accuracy is improved, and the degree of freedom in design increases. Since it is small and low in cost, it can be used for gas meters. It is applicable deployed as various flowmeter.

DESCRIPTION OF SYMBOLS 1 Ultrasonic flowmeter 2 Measurement flow path 5a, 5b Ultrasonic sensor 6 Flow rate calculation circuit (flow rate calculation means)
7a, 7b, 7a ', 7b' Ultrasonic wave propagation aperture window

Claims (4)

A measurement channel having a rectangular cross-section;
A pair of ultrasonic sensors installed on the same wall surface side of the measurement flow channel and arranged to constitute an ultrasonic wave propagation path utilizing reflection on the opposite wall surface;
Two ultrasonic wave propagation aperture windows for entering and exiting an ultrasonic signal provided on the wall surface on the installation side of the ultrasonic sensor;
Flow rate calculation means for detecting a flow rate based on the propagation time of ultrasonic waves by transmission and reception of the ultrasonic sensor,
The ultrasonic flowmeter according to claim 2, wherein the two ultrasonic wave propagation aperture windows have a contour shape in which two opposing straight lines parallel to the flow direction of the measurement flow path and the two straight lines are connected by an arc . The distance between the two straight lines forming the ultrasonic wave propagation opening windows, ultrasonic flow meter according to claim 1 which is the same as the channel width of the ultrasonic sensor installation side. The ultrasonic flowmeter according to claim 1 or 2 , wherein the wall surface of the measurement flow path between the ultrasonic propagation aperture windows has a corrugated cross-sectional shape perpendicular to the direction in which the fluid flows. The ultrasonic flowmeter according to claim 3 , wherein a cross-sectional area of the measurement flow path between the ultrasonic propagation aperture windows matches a cross-sectional area of the measurement flow path other than between the ultrasonic propagation aperture windows.