JPH11237263A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-accuracy ultrasonic flowmeter in which the point of time of a reception in a reception-side transducer can be decided with high accuracy by reducing the influence on the reception-side transducer of the component of ultrasonic waves propagated so as to be deviated from a shortest propagation route between a transmitting transducer and the receiving transducer. SOLUTION: In an ultrasonic flowmeter, ultrasonic waves which are generated by a transducer T1 and a transducer T2 are radiated into a fluid which flows inside a conduit, the ultrasonic waves are received, and the flow velocity or the flow rate of the fluid is measured on the basis of a characteristic such as the time required for their propagation, the amount of a frequency sift or the like. Then, in the ultrasonic flowmeter, the cross-sectional shape of the conduit in which the ultrasonic waves are propagated is formed to be nearly rectangular, and the inner wall surface which is nearly parallel to the propagation route of the ultarsonic waves has a gentle inclination. As a result, the number of times of their reflection on the inner wall surface is increased with reference to the component of the ultrasonic waves which are propagated so as to be deviated from a shortest route, and the point of time of their arrival to the reception-side transducer is delayed.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter for measuring a flow rate and a flow velocity of a fluid from a difference in propagation time of ultrasonic waves. [0002] Ultrasonic waves are propagated in a fluid to be measured,
Ultrasonic flowmeters that measure the flow rate and flow velocity from the difference in propagation time in the downstream and upstream directions are widely used. In an ultrasonic flow meter having the simplest configuration, a pair of transducers (electric / acoustic transducers or ultrasonic transducers) are installed so as to face the upstream side and the downstream side in the fluid. However, usually, in many cases, the transducer is installed outside the fluid flow path in order to avoid problems such as disturbance of the flow velocity caused by installing the transducer in the flow path. In such an ultrasonic flowmeter in which a transducer is installed outside a flow path, as shown in FIG.
A pair of transducers T1 and T2 are installed outside the flow path so as to be oblique and opposed to each other with respect to the pipeline, and the ultrasonic straight line indicated by a dotted line inclined at a predetermined angle with respect to the flow indicated by the arrow A propagation path is formed. As shown in FIG. 4, in order to install a pair of transducers T1 and T2 on one wall surface of the pipeline, the inner wall surface of the pipeline opposite to the surface on which each transducer is installed is used as a reflection surface. There is also known a method of forming a V-shaped ultrasonic wave propagation path indicated by. Further, a method of forming a W-shaped ultrasonic wave propagation path by causing three reflections on upper and lower inner wall surfaces is also known. [0004] When the cross section of the flow path is circular, the propagation path of the ultrasonic wave is, as shown by a dotted line in FIG. 5A, between the opposing transducers T1 and T2. , And a number of curved paths appearing around the shortest path. The ultrasonic wave that has propagated on the curved outer propagation path is received later than the ultrasonic wave that has passed through the shortest straight path. As a result, the reception waveform of the ultrasonic wave spreads on the time axis, and at the time of reception,
Therefore, it becomes difficult to determine the required propagation time. Also, in the waveguide having the circular cross section, similarly to the case of the rectangular cross section, the reception waveform spreads on the time axis due to the reflected wave incident on the transducer on the reception side via the propagation path exemplified by the straight line. There's a problem. In a flowmeter which forms a V-shaped or W-shaped ultrasonic wave propagation path by using the inner wall surface of a pipe as a reflecting surface, a transducer is installed as shown in FIG. In order to secure a flat reflecting surface on the inner wall surface facing the tube wall surface, a rectangular cross-sectional shape channel is used. In such a duct having a rectangular cross section, of the ultrasonic waves radiated from one of the transducers T1 and T2, a component radiated obliquely to the side wall is reflected by the one side wall, the lower reflecting surface, and the other side wall. Therefore, since the light is incident on the other transducer, it is incident on the receiving-side transducer later than the component radiated parallel to the side wall, making it difficult to determine the reception time point defined as a zero-cross point or the like. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an ultrasonic flowmeter capable of determining a reception time with high accuracy by reducing the influence of an ultrasonic component which does not pass through the shortest propagation path. An ultrasonic flowmeter according to the present invention for solving the above problems radiates ultrasonic waves generated by a transducer into a fluid flowing through a pipeline, and receives the ultrasonic waves. An ultrasonic flowmeter that measures the flow velocity or flow rate of a fluid based on characteristics such as the time required for propagation and the amount of frequency shift. The cross-sectional shape of the conduit through which the ultrasonic waves propagate has a substantially rectangular shape, and the ultrasonic waves propagate. The inner wall substantially parallel to the path has a gentle slope. According to the ultrasonic flowmeter of the preferred embodiment of the present invention, the inner wall surface substantially parallel to the ultrasonic wave propagation path has a shape bulging outward. According to the ultrasonic flowmeter of another preferred embodiment of the present invention, the cross-sectional shape of the conduit through which ultrasonic waves propagate is as follows:
It is a polygon circumscribing a rectangle. According to an ultrasonic flowmeter of still another preferred embodiment of the present invention, a V-shaped propagation path is formed by using a part of the inner wall surface of a rectangular cross-section pipe as a reflection surface. The front and rear of a part of the inner wall surface used as the reflection surface has a gentle inclination. FIG. 1 is a sectional view showing the structure of an ultrasonic flowmeter according to an embodiment of the present invention. FIG. 1A is a longitudinal sectional view cut along a plane including a tube axis of a rectangular conduit. , (B) and (C) are cross-sectional views cut along the cut surfaces indicated by BB and CC in the vertical cross-sectional view (A). According to this ultrasonic flow meter, a pair of transducers T1 and T2 are installed on the wall surface above a substantially rectangular pipe forming a fluid flow path. In the portion of the conduit where the ultrasonic wave propagation path is formed between the transducers T1 and T2, the central portions of the left and right inner wall surfaces that are substantially parallel to the ultrasonic wave propagation direction are slightly bulged outward and become slow. It has an inclined surface. Further, as shown in (B), at the intermediate position between the transducers T1 and T2, the lower inner wall surface has a flat shape, but before and after this flat portion, as shown in (C), the lower inner wall surface has a flat shape. The central portion of the wall surface slightly swells outward to exhibit a gentle slope. Among the ultrasonic waves radiated from one of the transducers T1 and T2, as shown by S0 in the figure, a component radiated in parallel to the left and right side walls and propagated on the shortest propagation path is a side component. Of the transducers T1 and T
The light is reflected at a portion where the inclined surface located between the two is not formed, and enters the other transducer. That is, a V-shaped propagation path is formed between the transducers T1 and T2. On the other hand, transducers T1 and T
2, the components propagating on the shortest path S0 and the propagation path inclined with respect to the side wall, as shown by S1 to S6 in the drawing, The light is incident on a gentle inclined surface formed on the inner wall surface, and is reflected in a direction depending on the angle of incidence on the inclined surface. Most of the ultrasonic components reflected on these inclined surfaces repeat multiple reflections at various points on the inner wall surface of the pipeline, so that the components passing through the shortest path S0 reach the transducer on the receiving side. Thereafter, the transducer does not reach the receiving transducer until a considerable time has elapsed. Alternatively, even when the signal reaches the transducer on the receiving side, the amplitude is greatly attenuated due to repeated multiple reflections. As a result, the identification of the ultrasonic reception point defined by the zero-cross point (the point at which the received voltage waveform crosses the 0 volt line) is performed mainly on the ultrasonic component that has passed through the shortest propagation path, and the measurement accuracy is low. improves. FIG. 2 is a sectional view showing a shape of a conduit in a modification of the above embodiment. 2 (B) and 2 (C) show, on the contrary to FIGS. 1 (B) and 1 (C), a gentle slope on the inner wall surface due to the central portion of the inner wall surface slightly expanding inward. Are formed. Also in this embodiment, as in the case of FIG. 1, the ultrasonic wave incident on the inclined surface is not superimposed on the ultrasonic wave having passed through the shortest propagation path by repeating multiple reflections, and the ultrasonic wave determined by the zero-cross point and the like. The receiving point becomes clear. The configuration in which the reflecting surface is provided in the middle to form a V-shaped propagation path is described above. However, FIG.
As shown in the above, the present invention can be applied to a configuration in which a pair of transducers is installed on both sides of the wall of a pipeline and ultrasonic waves are directly transmitted and received between the transducers. In this case, a gentle slope is formed on both side surfaces and the bottom surface. In addition, the present invention can be applied to a case where a W-shaped ultrasonic wave propagation path is formed by causing reflection three times. Further, the present invention has been described with respect to an apparatus for measuring a flow rate from a difference in propagation time of ultrasonic waves. However,
The present invention can also be applied to a flow meter of a type that measures the flow velocity or the flow rate from the Doppler shift amount of ultrasonic waves. As described above in detail, since the ultrasonic flowmeter of the present invention has a configuration in which a gentle slope is formed on the inner wall surface parallel to the ultrasonic waves, it deviates from the shortest propagation path. The component of the ultrasonic wave incident on the inner wall surface is subjected to multiple reflections on such an inclined surface, and the propagation time is prolonged and the attenuation increases. As a result, the reception time is determined by the component of the ultrasonic wave that has passed through the shortest propagation path, and the effect of improving the measurement accuracy is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a configuration of an ultrasonic flowmeter according to one embodiment of the present invention. FIG. 2 is a sectional view showing the shape of the inner wall surface of a conduit in an ultrasonic flowmeter according to another embodiment of the present invention. FIG. 3 is a cross-sectional view showing an example of the configuration of a conventional typical ultrasonic flowmeter. FIG. 4 is a cross-sectional view showing another example of the configuration of a conventional typical ultrasonic flowmeter. FIG. 5 is a cross-sectional view for explaining a problem to be solved by the present invention. [Description of Signs] T1, T2 Transducer S0 Shortest ultrasonic propagation path between transducers S1 to S10 Ultrasonic propagation path incident on inner wall surface with gentle slope

Claims (1)

Claims: 1. An ultrasonic wave generated by a transducer is radiated into a fluid flowing through a pipeline, the ultrasonic wave is received, and a flow velocity of the fluid is determined based on characteristics such as a propagation time and a frequency shift amount. Alternatively, in an ultrasonic flowmeter for measuring a flow rate, the cross-sectional shape of a conduit through which the ultrasonic waves propagate has a substantially rectangular shape, and the inner wall surface substantially parallel to the ultrasonic wave propagation path has a gentle slope. And ultrasonic flow meter. 2. The ultrasonic flowmeter according to claim 1, wherein an inner wall surface substantially parallel to the ultrasonic wave propagation path has a shape bulging outward. 2. The ultrasonic flowmeter according to claim 1, wherein a cross-sectional shape of the conduit through which the ultrasonic wave propagates is a polygon circumscribing a rectangle. 4. The reflection type ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter forms a V-shaped propagation path by using a part of an inner wall surface of a pipe having a rectangular cross section as a reflection surface. An ultrasonic flowmeter, which is an ultrasonic flowmeter. 5. The ultrasonic flowmeter according to claim 4, wherein the ultrasonic flowmeter has a gentle slope before and after a part of an inner wall surface used as the reflection surface.