Ultrasonic flowmeter

An ultrasonic flowmeter is provided with at least one measuring tube having at least one recess. Disposed in the recess are at least a first ultrasonic transducer and a second ultrasonic transducer, wherein the first ultrasonic transducer is designed as an ultrasonic transmitter and/or as an ultrasonic receiver and the second ultrasonic transducer is designed as an ultrasonic transmitter and/or as an ultrasonic receiver. Further disposed in the recess is at least one reflection surface. The first and second ultrasonic transducers are arranged on the measuring tube such that the measuring path between the first and the second ultrasonic transducers comprises at least one reflection at the reflecting surface. The provision of the reflection surface in the recess provides an ultrasonic flowmeter with which the flow profile can be easily measured, especially in the edge region.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to an ultrasonic flowmeter with at least one measuring tube, wherein the measuring tube has at least one recess, with at least a first ultrasonic transducer and a second ultrasonic transducer, wherein the first ultrasonic transducer is designed as an ultrasonic transmitter and/or as an ultrasonic receiver and wherein the second ultrasonic transducer is designed as an ultrasonic transmitter and/or as an ultrasonic receiver having at least one reflection surface, wherein the first and the second ultrasonic transducer are arranged on the measuring tube, such that the measuring path between the first and the second ultrasonic transducer comprises at least one reflection at the reflection surface.

The measurement of the flow of a medium flowing through a measuring tube using an ultrasonic flowmeter is known in the prior art. Ultrasonic flowmeters generally have a measuring tube and at least two ultrasonic transmitters designed as ultrasonic transmitters and/or ultrasonic receivers, which are arranged at a distance from one another on the measuring tube in the flow direction (axially along the measuring tube axis). To measure the flow, an ultrasonic signal is emitted along the measuring path between the ultrasonic transducers both in the direction of flow and opposite to the direction of flow. The duration or transit time of signals that move along a measuring path with the flow is different from the transit time of signals moving against the flow due to an entrainment effect. The flow velocity is determined from the transit time difference, as well as the volume flow rate when the measuring tube cross section is taken into account.

In determining flow speed, the flow profile of the flowing medium is also to be considered. Basically, laminar and turbulent flow profiles should be distinguished. The formation of a turbulent or laminar flow is particularly dependent on the Reynolds number.

In order to ensure the lowest possible error in the determination of the speed of flow, it is known to measure the flow profile both in the region of the measuring tube axis at r=0 R1and in the edge regions at a radius r>0.5 R1, where R1is the inner measuring tube radius.

Description of Related Art

EP 0 639 776 B1 corresponding to U.S. Pat. No. 5,546,812 discloses an ultrasonic flowmeter in which the ultrasonic signal passes through acoustic paths which have different degrees of sensitivity with respect to swirling of the medium. In this case, the signals emitted by the ultrasonic transmitter are received by the ultrasonic receiver after at least two reflections against the inner wall of the measuring tube. The ultrasonic signals pass through a large part of the measuring tube cross-section and thus provide a reliable picture of the flow.

DE 10 2012 013 916 A1 corresponding to U.S. Pat. No. 9,528,866 B2 discloses an ultrasonic flowmeter with two ultrasonic transducers arranged on a measuring tube, wherein the ultrasonic transducers are arranged in such a way that the measuring path has a plurality of reflection surfaces between the ultrasonic transducers. The measuring path has at least three straight subsections between the ultrasonic transducers. The minimum distances of the three sections to the measuring tube axis are between 0.4 and 0.8 R1, where R1is the measuring tube radius. Also shown is an embodiment in which the ultrasonic signal reaches the ultrasonic receiver via five reflection surfaces.

In contrast to the aforementioned prior art, it is the object of the present invention to provide an ultrasonic flowmeter with which the flow profile can be particularly easily measured, especially in the edge region.

SUMMARY OF THE INVENTION

According to the invention, this object is achieved by arranging the reflection surface in a recess in the inner wall of the tube. In such a case, the reflection surface is set back in relation to the inner measuring tube wall. In the context of the present invention, a recess is understood as meaning both a local reduction of the material thickness and a material recess, that is to say a blind hole in the material.

Due to the rearrangement of the reflection surface in a recess in the inner wall of the tube, the measuring path between the ultrasonic transducers can be shifted into the edge region of the flow profile due to the changed emission angle. Advantageously, the edge region of the flow profile can thus be measured particularly easily.

According to an advantageous embodiment, the ultrasonic flowmeter has at least a first and at least a second reflection surface and at least a first and a second recess, wherein the first reflection surface is arranged in the first recess and the second reflection surface is arranged in the second recess and wherein the first and the second ultrasonic transducers are arranged in the measuring tube such that the measuring path between the ultrasonic transducers comprises at least one reflection at the first reflection surface and at least one reflection at the second reflection surface.

This design has the advantage that the flow profile can be measured particularly accurately in the edge region at a radius r>0.5 R1with only two ultrasonic transducers. The measuring path between the ultrasonic transducers forms an equilateral triangle in axial plan view. Using the geometric relationships of an equilateral triangle, the depth of the recess can be determined using the formula: R2=2·x1·R1, where R2is the distance of the reflection point to the measuring tube axis, where x1is between 0 and 1, in particular between 0.5 and 1, and where R1is the inner measuring tube radius.

According to a further design, the reflection surface is configured flat or concave or in the form of a circular arc. Particularly advantageously, the reflection surface is designed as a circular arc of a circle with a radius of curvature R2.

It is also advantageous when the sidewalls of the recess are designed obliquely and, in particular, include an obtuse angle to the reflection surface. This design has the advantage that the ultrasonic signal can enter the recess and leave the recess at a larger angle and, that the flowing medium is less disturbed by the slanted sides.

The at least one recess can be an axially extending recess which is introduced into the measuring tube, for example by means of machining, in particular with a broaching tool.

In a further advantageous design, a reflection element with a reflection surface is arranged in the at least one recess. Due to the reflection element being introduced as a separate component in the recess, it can be particularly flexibly designed, in particular adapted to the flow of fluid. The recess can, in particular, be designed as a hole in which the reflection element is arranged in a sealing manner. This design has the advantage that the disruption of the flow of fluid caused by the recess can be minimized.

If the flow entering the recess is at an angle, with respect to a perpendicular direction to the reflection surface that is greater than the critical angle according to Snell's law of refraction, then in addition to the reflection of the ultrasonic signal, surface waves are also excited. These surface waves are guided to the ultrasonic receiver both via the medium and via the measuring tube itself. These waves interfere with the signal to be measured and are therefore undesirable.

According to a further advantageous design, the reflection recess may have a special geometry for suppressing or minimizing this interference signal, wherein the interference signal is guided away from the ultrasonic receiver due to the geometric configuration of the reflection recess.

According to a particularly advantageous design, the reflection recess is designed such that the inner surface facing the medium has the shape of the top surface of a truncated cone. In the context of the present invention, a cover surface is understood to be the outer surface of a truncated cone. Preferably, the edge of the truncated cone has the shape of a section of the truncated cone foot with a part of a cylinder. Particularly preferably, the cylinder has a circular or oval base. According to a further design, the edge of the truncated cone foot has the shape of a section of the truncated cone with a half cylinder or with a part of a cylinder whose outer surface comprises a circular arc that is smaller than a semicircle.

In this case, the reflection surface is preferably designed such that the largest possible part of the ultrasonic signal is reflected. For example, the reflection surface is designed in a circle with a diameter D, where D essentially corresponds to the cross section of the ultrasonic signal. If further surface waves are excited, which, inter alia, emit interference signals in the medium, these interference signals are not emitted in the direction of the receiver due to the oblique side surfaces of the truncated cone. The disturbance of the flow or the containment of the medium can be minimized due to the oblique side surfaces of the truncated cone.

In a further design, the reflection element consists at least partially of synthetic material or metal, in particular bronze, brass, steel, aluminum or titanium.

The use of these materials ensures minimization of the previously-described interference or Rayleigh effect.

According to a further design, at least one further recess is provided, wherein the first and/or the second ultrasonic transducer is or are arranged in the at least one further recess. According to this design, the ultrasonic transducers are arranged in the measuring tube such that they do not influence the flow. Preferably, the ultrasonic transducers are also set back, whereby the measuring path is located between the ultrasonic transducers in the edge region of the flow profile at a radius r>0.5 R1.

Particularly preferably, the ultrasonic transducers are arranged at least partially in the lower half of the measuring tube. This design has the advantage that if the medium has air or gas bubbles, these do not accumulate in the region of the ultrasonic transducers, and in particular not in the recesses in which the ultrasonic transducers are arranged, thus causing a measurement error.

According to a further preferred design, at least a third and a fourth ultrasonic transducer are provided, each of which is designed as an ultrasonic transmitter and/or as an ultrasonic receiver, wherein the third and fourth ultrasonic transducers are arranged offset in the flow direction on the measuring tube such that the measuring path crosses the measuring tube axis between the third and the fourth ultrasonic transducer at r=0 R1.

In detail, there are a plurality of possibilities for designing and further developing the ultrasonic flowmeter according to the invention. Reference is made to both the claims subordinate to the independent claim and to the following description of preferred embodiments in conjunction with the drawings described below.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a schematic sectional illustration of a measuring tube2according to a first embodiment of an ultrasonic flowmeter1with the measuring path3through which the ultrasonic signal passes. A first ultrasonic transducer4and a second ultrasonic transducer5are arranged offset from one another in the flow direction. The signal emitted from the ultrasonic transducer4,5designed as an ultrasonic transmitter reaches the ultrasonic transducer4,5designed as an ultrasonic receiver after reflection at a first reflection surface6and after reflection at a second reflection surface7. The resulting measuring path3has the shape of an equilateral triangle in an axial plan view.

The reflection surfaces6,7are arranged in respective recesses8,9and the ultrasonic transducers4,5are arranged in a recess10of the measuring tube2. As a result of both the reflecting surfaces6,7and the ultrasonic transducers4,5being set back from the inner wall of the tube2, the flow profile within the measuring tube2can advantageously be measured in the edge region at a measuring range r>0.5 R1, wherein R1is the measuring tube radius. Any error in determining the speed of the medium due to a turbulent or laminar design of the flow profile is particularly small due to the measurement in the edge region. In this respect, the flow profile in the edge region can be measured particularly accurately with only two ultrasonic transducers4,5using the embodiment shown inFIG. 1.

With the help of the geometric relationships of an equilateral triangle, the depth of the recess and the distance R2of the reflection point to the measuring tube axis at a known measuring tube radius R1can be easily calculated as follows: R2=2·X1·R1. If, for example, the inner measuring tube radius is R1=10 mm and the range is measured at r=0.7 R1or at r>0.7 R1, then the distance to the reflection point is R2=14 mm.

In the illustrated embodiment, the reflection surfaces6,7are configured as a circular arc of a circle with the radius R2.

FIG. 2shows a second illustration of the measuring tube2according to the first embodiment of a flowmeter1, wherein the measuring tube2has recesses8,9and10. The recesses8,9and10are axial recesses, which are introduced in the measuring tube2by machining.

FIGS. 3ato 3cshow possible embodiments of the recesses8,9, and10. According to the embodiment shown inFIG. 3a, each reflection surface6,7is configured as a circular arc of a circle with the radius R2and the side walls are configured substantially perpendicular to the circular arc. According to the embodiment shown inFIG. 3b, the reflection surface6,7is made flat and the side walls11are configured substantially perpendicular to the reflection surface6,7. According to the embodiment shown inFIG. 3c, the reflection surface6,7is made flat and the side walls11form an obtuse angle with the reflection surface6,7.

FIG. 4shows a sectional representation of a second embodiment of the flowmeter1, with a measuring tube2, with two ultrasonic transducers4,5, which are designed each as ultrasonic transmitter and ultrasonic receiver. Only one ultrasonic transducer4is shown in the sectional view and the measuring tube2has four recesses8,9, and10, of which three recesses8,9, and10are shown. The ultrasonic transducer4is arranged in a recess10. Reflection elements12and13with reflection surfaces6and7are arranged in each of the two remaining recesses8and9.

In the illustrated embodiment, the recesses8,9, and10are configured as blind holes, in which the ultrasonic transducers4,5or the reflection elements12,13are inserted in a sealing manner. The reflection surfaces6,7, are made flat. The measuring path3of the ultrasonic signal corresponds overall to an equilateral triangle in an axial plan view.

FIG. 5shows a third embodiment of the flow meter1, wherein in addition to the two ultrasonic transducers4,5for measuring the flow profile in the edge region, two further ultrasonic transducers14,15are provided. Transducers14,15are arranged on the measuring tube2such that they measure the flow profile in the area of the measuring tube axis by means of a V-shaped measuring path. According to this embodiment, the flow profile can be measured particularly precisely both in the region of the measuring tube axis and particularly precisely in the edge region and with only four ultrasonic transducers4,5,14,15. The error in determining the speed of the medium and the determination of the volume flow is thus particularly small.

FIG. 6shows a fourth embodiment of the flowmeter1with two ultrasonic transducers4,5and two reflection elements12,13, which are arranged in recesses8,9, in a sectional view, wherein only one ultrasonic transducer4is shown, as above. The reflection elements12,13are configured in their design such that, on the one hand, the largest possible part of the ultrasonic signal is reflected and, on the other hand, any excited surface waves are guided away from the measuring path3and away from the ultrasonic receiver4,5, so they do not influence measurement as interference signals.

FIG. 7shows an enlarged illustration of a reflection element12,13arranged inFIG. 6in a recess8,9. The reflection element12,13has a flat reflection surface6,7and oblique side walls11. The diameter of the reflection surface6,7is dimensioned such that a large part of the ultrasonic signal is reflected. If the incident ultrasonic signal has an angle exceeding the critical angle according to Snell's law of refraction, surface waves are formed. The reflection element12,13then emits a further acoustic signal16into the medium. In this case, the reflection element12,13is designed such that the radiation of the interference signal16does not occur in the propagation direction of the ultrasonic signal of interest due to the oblique side surfaces.

FIGS. 8ato 8dshow different views of the reflection element12,13shown inFIGS. 6 and 7. The reflection surface6,7is configured in a circle with a diameter D, wherein D essentially corresponds to the diameter of the reflected ultrasonic signal. The side walls11form an acute angle β with the vertical line to the reflecting surface6,7. Overall, the surface facing the medium has the shape of a top surface of a truncated cone, wherein the edge of the truncated cone has the shape of a section of the truncated cone foot with a part of a circular cylinder and wherein the base of the cylinder has a radius R1.