JPH11237264A - 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 of the component of ultrasonic waves which are not passed through 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 recieved, and the flow velocity or the flow rate of the fluid is measured on the basis of the time required for their propagation, the amount of a frequency shift or the like. Then, in the ultrasonic flowmeter, an uneven part is formed in at least one point on the inner wall surface of the conduit in a part in which the ultrasonic waves are propagated. Regarding the component of the ultrasonic waves which are propagated so as to be deviated from a shortest propagation route, the point of time of their arrival to the reception-side transducer is delayed due to an increase in the number of times of their reflection on the inner wall surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 ultrasonic wave propagation time.

[0002]

2. Description of the Related Art 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. 3, 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-sectional shape of the flow path is circular, the propagation path of the ultrasonic wave is represented by a straight line between the opposing transducers T1 and T2, as shown by the dotted line in FIG. It is composed of the shortest path to be connected 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 this waveguide having a circular cross section, similarly to the case of a waveguide having a rectangular cross section, the reception waveform is also time-dependent by a reflected wave incident on the receiving-side transducer via a propagation path exemplified by a linear dotted line. There is a problem that it spreads on the axis.

In a flow meter that forms a V-shaped or W-shaped ultrasonic wave propagation path by using the inner wall surface of a pipe as a reflection 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.

[0007]

An ultrasonic flowmeter according to the present invention for solving the above problems radiates ultrasonic waves generated by a transducer into a fluid flowing in a pipeline, receives the ultrasonic waves, and transmits the ultrasonic waves. An ultrasonic flowmeter for measuring the flow velocity or flow rate of a fluid from characteristics such as time and frequency shift amount, wherein at least one of the inner wall surfaces of a pipeline in which ultrasonic waves propagate has irregularities.

[0008]

According to a preferred embodiment of the present invention, the ultrasonic flowmeter is a reflection type ultrasonic wave using a part of the inner wall surface of the pipe having a rectangular cross section as a reflection surface. Constructs a flow meter.

According to another preferred embodiment of the present invention,
Irregularities are formed before and after a reflection expected portion on the inner wall surface used as the reflection surface. According to still another preferred embodiment of the present invention, the unevenness formed on the inner wall surface of the conduit is:
It is composed of a chevron-shaped groove which extends in parallel at substantially equal intervals in the longitudinal direction of the conduit. More preferably, the interval between the mountain-shaped grooves formed on the inner wall surface of the conduit is set to a value that is at least approximately twice the wavelength of the ultrasonic wave propagating in the conduit.

[0010]

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 taken along a plane including a tube axis of a rectangular conduit, and FIG. ) And (C) are cross-sectional views taken along the cutting planes indicated by BB and CC in the vertical cross-sectional view (A).

According to this ultrasonic flow meter, the transducers T1 and T2 are installed on the wall surface above the rectangular pipe forming the fluid flow path. As shown in (A) and (B), on the inner wall surface of the pipeline below the location where the ultrasonic wave propagates, except for the location located between the transducers T1 and T2 along the longitudinal direction of the pipeline. Thus, a mountain-shaped groove extending in the longitudinal direction of the pipeline in parallel with each other while maintaining substantially equal intervals is formed. Further, as shown in (C), on the inner wall surface on the side of the portion of the pipeline where the ultrasonic wave propagates, a mountain-shaped extending in the longitudinal direction of the pipeline parallel to each other while maintaining substantially equal intervals. A groove is formed.

Among the ultrasonic waves radiated from one of the transducers T1 and T2, as shown by S0 in the figure, the component radiated parallel to the side wall and propagated on the shortest propagation path is the side of the pipe. Without being incident on the uneven surface formed on one inner wall surface, the light is reflected on a portion of the lower inner wall surface where the uneven surface located between the transducers T1 and T2 is not formed, and is incident on 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
Of the ultrasonic waves radiated from one of the two, the components propagating on the propagation path oblique to the side wall as shown by S1 to S6 in the figure were all formed on the inner wall surface of the pipeline. The light is incident on the mountain-shaped groove, and is reflected in various directions depending on the angle of incidence on the incident surface. Most of the ultrasonic components reflected on the uneven surface repeat multiple reflections at various points on the inner wall surface of the pipeline, so the component that has passed the shortest path reaches the transducer on the receiving side. Until the time elapses, the signal does not reach the receiving-side transducer, or if it does, the amplitude is greatly attenuated due to multiple reflection. For this reason, the time point at which the received voltage waveform crosses the 0 volt line, that is, the time point of reception defined by the zero-cross point or the like, is identified mainly by the ultrasonic component that has passed through the shortest propagation path, and the measurement accuracy is improved.

When the height or pitch of the mountain-shaped groove is extremely small as compared with the wavelength of the ultrasonic wave, the function of reflecting the incident wave in various directions is lost. Therefore, the height or pitch of the mountain-shaped groove is set to a value that is at least twice the wavelength of the ultrasonic wave. For example, if the fluid whose flow rate is to be measured is a gas, the propagation speed of the ultrasonic wave propagating inside the gas is 340 m / sec, so if the frequency of the ultrasonic wave is 680 kHz, the ultrasonic wave propagating inside the gas The wavelength of the sound wave is 0.5 mm. In this case, a mountain-shaped groove having a height and a pitch of about 1 mm or more, which is about twice the wavelength, is formed on the inner wall surface. When an ultrasonic wave having a shorter wavelength is used, an irregular rough surface can be formed by sandblasting the inner wall surface of the pipeline.

The configuration in which the reflecting surface is provided in the middle to form a V-shaped propagation path has been 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, uneven surfaces are formed on both side surfaces.

Further, the present invention has been described by taking as an example the case where the cross-sectional shape of the conduit is rectangular. However, the present invention can be applied to the case of a cross section having another appropriate shape such as a circle. In this case, an uneven surface is formed on the inner wall surface or the like of the side wall.

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.

[0018]

As described above in detail, the ultrasonic flowmeter of the present invention has a configuration in which at least one of the inner wall surfaces of the pipe where the ultrasonic wave propagates has irregularities. The component of the ultrasonic wave deviating from the propagation path and entering the inner wall surface undergoes multiple reflections on such an uneven surface, so that 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 cross-sectional view showing an example of a configuration of a conventional typical ultrasonic flowmeter.

FIG. 3 is a cross-sectional view showing another example of the configuration of a conventional typical ultrasonic flow meter.

FIG. 4 is a cross-sectional view for explaining a problem to be solved by the present invention.

[Explanation of symbols]

T1, T2 Transducer S0 Propagation path of the shortest ultrasonic wave between transducers S1 to S6 Propagation path of ultrasonic wave incident on inner wall surface with uneven surface

Claims (5)

[Claims] An ultrasonic wave generated by a transducer is radiated into a fluid flowing in a pipe, and the ultrasonic wave is received, and the flow rate or flow rate of the fluid is measured based on characteristics such as a propagation time and a frequency shift amount. An ultrasonic flowmeter according to claim 1, wherein at least one of the inner wall surfaces of the conduit in which the ultrasonic wave propagates has irregularities. 2. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter is a reflection type ultrasonic flowmeter that uses a part of an inner wall surface of a pipe having a rectangular cross section as a reflection surface. Flowmeter. 3. The ultrasonic flowmeter according to claim 2, wherein the unevenness is formed before and after a portion to be reflected on an inner wall surface of the conduit used as the reflecting surface. 4. The ultrasonic flowmeter according to claim 1, wherein the unevenness is a mountain-shaped groove extending in parallel at substantially equal intervals in a longitudinal direction of the conduit. 5. The method according to claim 4, wherein the interval between the chevron-shaped grooves is approximately two wavelengths of the emitted ultrasonic wave.
An ultrasonic flowmeter characterized by being set to a value that is twice or more.