DE102008055031A1 - Ultrasonic flow measuring system for determining and/or monitoring flow of measuring medium through measuring tube in e.g. process control engineering field, has projections formed symmetrically to intersection point of three planes - Google Patents

Abstract

The system (1) has an ultrasonic transmitter (2) comprising an electromechanical transducer element (7) that converts electrical signals into acoustic signals. The ultrasonic transmitter comprises a center axis (13), where a measuring tube axis of a measuring tube (5) and the center axis lie in a first plane that is perpendicular to a second plane. A third plane is formed perpendicular to the first and second planes. Projections perpendicular to the second plane of ultrasonic receivers (3, 4) are formed symmetrically to an intersection point (17) of the three planes.

Description

The The present invention relates to an ultrasonic flowmeter for determining and / or monitoring the flow of a measuring medium through a measuring tube, which ultrasonic flow measuring system at least a first ultrasonic transmitter, a first ultrasonic receiver and at least one second ultrasonic receiver.

Ultrasonic flowmeters are widely used in process and automation technology. They allow in a simple way, the volume flow and / or Determine mass flow in a pipeline.

The known ultrasonic flowmeters often work after the Doppler or after the transit time difference principle.

At the Runtime difference principle, the different maturities of ultrasonic pulses relative to the flow direction of Liquid evaluated.

For this Ultrasonic pulses are at a certain angle to the tube axis sent both with and against the flow. Out the transit time difference can be the flow rate and so that with known diameter of the pipe section of the volume flow determine.

At the Doppler principle will be ultrasonic waves with a specific frequency coupled into the liquid and that of the liquid Evaluated reflected ultrasonic waves. From the frequency shift between the coupled and reflected waves also the flow rate of the liquid determine.

reflections in the liquid, however, occur only when air bubbles or impurities are present in this, so this principle mainly with contaminated liquids Use finds.

The ultrasonic waves are generated or received with the help of so-called ultrasonic transducers. For this purpose, ultrasonic transducers are firmly attached to the pipe wall of the relevant pipe section. More recently, clamp-on ultrasonic flow measurement systems have become available. In these systems, the ultrasonic transducers are pressed against the pipe wall only with a tension lock. Such systems are for. B. from the EP 686 255 B1 . US-A 44 84 478 or US-A 45 98 593 known.

Another ultrasonic flowmeter, which operates on the transit time difference principle, is from the US-A 50 52 230 known. The transit time is determined here by means of short ultrasound pulses.

One big advantage of clamp-on ultrasonic flow measuring systems is that they do not touch the measuring medium and on one already existing pipeline are attached.

The Ultrasonic transducers usually consist of a piezoelectric Element, also called piezo for short, and a coupling layer, also coupling wedge or less commonly called Vorlaufkörper. The coupling layer is usually made of plastic, the piezoelectric element exists in industrial process measuring technology usually from a piezoceramic. In the piezoelectric element, the Ultrasonic waves generated and the coupling layer to Passed pipe wall and from there into the liquid directed. Because the speed of sound in liquids and plastics are different, the ultrasonic waves broken in the transition from one medium to another. The angle of refraction is determined in the first approximation according to Snell's law. The angle of refraction is thus dependent on the ratio the propagation speeds in the media.

Between the piezoelectric element and the coupling layer can be another Coupling layer may be arranged, a so-called adaptation layer. The adaptation layer assumes the function of Transmission of the ultrasonic signal and at the same time the reduction a reflection caused by different acoustic impedances at boundary layers between two materials.

The DE10200704936A1 shows an ultrasonic flow measuring system with several measuring paths. The measuring medium is sounded through at various points of the measuring tube, whereby a flow measuring signal can be determined, which is less dependent on the flow profile compared to a single-path measuring device. For the measuring system of the DE10200704936A1 several transmit and receive sensors and reflectors used. This solution is not only very expensive to manufacture and therefore quite expensive, but the flow of the measuring medium is adversely affected by the many measuring tube internals.

The The object of the invention is to provide a multi-path ultrasonic flow measuring system to provide, which is very simple and therefore inexpensive is to produce.

The object is achieved by an ultrasonic flow measuring system for determining and / or monitoring the flow of a Measuring medium through a measuring tube, which ultrasonic flow measuring system comprises at least a first ultrasonic transmitter, a first ultrasonic receiver and at least a second ultrasonic receiver, wherein the first ultrasonic transmitter has at least one electromechanical transducer element which converts electrical signals into acoustic signals, and wherein the ultrasonic receiver at least an electromechanical transducer element which converts acoustic signals into electrical signals, the measuring tube having a measuring tube axis, and wherein the ultrasonic transmitter has a central axis which perpendicularly intersects the measuring tube axis, wherein the measuring tube axis and the center axis of the ultrasonic transmitter span a first plane, a second plane is perpendicular to the first plane, wherein the measuring tube axis lies in the second plane, and a third plane is perpendicular to the first plane and the second plane, wherein the central axis of the ultrasound Lsenders lies in the third plane, wherein the projections are perpendicular to the second level of the ultrasonic receiver in the second plane substantially point-symmetrical to the intersection of the three planes.

The electromechanical transducer elements convert acoustic signals, in particular ultrasonic signals, into electrical signals, in particular voltage signals, or the other way around. The electromechanical transducers are preferably so called thickness oscillator, which longitudinal ultrasonic waves generate, in particular by pressure oscillations. Become in fluids only transported longitudinal waves.

The first, second and third levels are imaginary levels. A straight through a likewise imaginary central axis of the ultrasonic transmitter, which cuts the measuring tube axis, and just clamp the measuring tube axis the first imaginary level. The measuring tube axis is also located in the second imaginary plane, which is perpendicular to the first plane. The measuring tube axis is thus the intersection line of these two planes. The third imaginary plane is again perpendicular to the first two Levels. The measuring tube axis intersects the third plane vertically a point, wherein the central axis of the ultrasonic transmitter in the third level lies.

The Ultrasonic flow measuring system is now designed so d. H. The ultrasound receivers are arranged so that the projections the ultrasonic receiver in the second plane now point-symmetrical to the intersection of the measuring tube axis with the central axis of the ultrasonic transmitter lie. Thus, the distance between the ultrasonic transmitter and the same first and second ultrasonic receiver. are arranged several ultrasonic receiver, applies accordingly.

The imaginary projections in the imaginary second level of the ultrasonic receiver done by the ultrasonic receiver perpendicular to second level projected into the second level.

One Another advantage of the invention is that a correction of production-related, geometric asymmetries by means of a control / evaluation unit possible is.

In In a first embodiment, the ultrasonic receivers point symmetric to a point of the central longitudinal axis of the Ultrasonic transmitter arranged. The cutting line of the first and third level corresponds to the center axis of the ultrasonic transmitter.

According to one advantageous development of the invention Measuring system, the measuring system has at least one control / evaluation unit on which control / evaluation unit based on the measurement signals or based of measurement data derived from the measurement signals, the Volume and / or the mass flow of the flowing in the measuring tube Measuring medium determined. The measurement signals are advantageous determined with the transit time difference method. These are going out the electrical signals to control the ultrasonic transmitter and the measured electrical signals of the ultrasonic receiver educated.

The electromechanical transducer elements of the ultrasonic receiver each have at least one sound-receiving surface on. The ultrasonic signals act on these sound-receiving surfaces one. Conversely, sound-emitting surfaces the electromechanical transducer elements of the ultrasonic transmitter, as already described, the ultrasound signals radiated. Mostly located between measuring medium and electromechanical transducer elements still so-called coupling layers. The touching the measuring medium Surfaces of the coupling layers are called accordingly Sound coupling or sound output surfaces. Schalleinkoppelflächen, since the signals can be coupled into the measuring medium via this surface are. Schallauskoppelflächen, because the ultrasonic signals from the measuring medium in the coupling layer can be coupled again. there can the sound receiving surfaces of the Ultrasonic receiver and their sound output surfaces whose coupling layers, have an angle to each other or the both surfaces are parallel. The same applies to the sound-emitting surfaces of the electromechanical Transducer elements of the ultrasonic transmitter and their Schallalleinkoppelflächen.

In a further embodiment of the invention, the electromechanical transducer elements of the ultrasonic receiver each have a sound-receiving surface, which is sound-receiving each surface normal to the respective sound-receiving surface has, which respective surface normal intersects the Messrohrachse. The sound-receiving surfaces of the ultrasonic receiver are thus aligned with the tube center. The surface normals may have an inclination angle to the measuring tube axis in or against the flow of the measuring medium in the measuring tube.

A very advantageous development of the invention Measuring system can be seen in that the electromechanical transducer elements the ultrasonic receiver each a sound-receiving Have surface, which sound receiving surface a surface normal to the sound-receiving surface which surface normal intersects the measuring tube axis perpendicularly. The surface normal is again an imaginary surface normal.

A advantageous development of the invention Measuring system suggests that the electromechanical transducer element the ultrasonic transmitter has a sound-emitting surface, which sound-emitting surface is a surface normal has perpendicular to the sound-emitting surface, which Surface normal intersects the measuring axis perpendicularly. Also Here, the surface normal is an imaginary one Surface normal. The sound-emitting surface the transducer element of the ultrasonic transmitter is thus parallel to Measuring tube axis. In one embodiment, the sound-emitting Surface of the transducer element of the ultrasonic transmitter in parallel aligned to the second imaginary level and the pipe center.

In Another variant is the surface normals of sound-receiving surfaces of the electromechanical Transducer elements of the ultrasonic receiver perpendicular to at least one sound-emitting surface at least an electromechanical transducer element of the at least one ultrasonic transmitter. Does the electromechanical transducer element a curved Shape, such. B. the shape of a hemisphere, to, several Receiving surfaces simultaneously parallel to a radiant surface or their surface normal fall together.

A Further development of the invention proposes that an ultrasonic transmitter a first electromechanical transducer element and at least one second electromechanical transducer element, which first Transducer element, a first sound-emitting surface and a first surface normal perpendicular to the first sound-emitting one Surface, which second transducer element has a second sound-emitting surface and a second surface normal perpendicular to the second sound-emitting surface, wherein a first ultrasonic receiver is a first electromechanical transducer element having a first sound receiving surface and wherein a second ultrasonic receiver is a second Electromechanical transducer element with a second sound-receiving Surface, wherein the first surface normal is perpendicular to the first sound-receiving surface and wherein the second surface normal is perpendicular to the second sound-receiving surface stands.

A further possibility of the position of the sound-receiving Surfaces of the electromechanical transducer elements of Ultrasound receiver is so that the sound-receiving Surfaces of the electromechanical transducer elements of Ultrasonic receiver substantially parallel to them each opposite sound-emitting surfaces arranged the electromechanical transducer elements of the ultrasonic transmitter are.

According to one advantageous development of the invention it is proposed that the ultrasonic transmitter at least one Schallalleinkoppelfläche has over which Schalleinkoppelfläche the acoustic signals from the ultrasonic transmitter into the measuring medium are einkoppelbar and that the ultrasound receiver respectively have at least one sound output surface over which sound output surfaces the acoustic signals the measuring medium in the respective ultrasonic receiver auskoppelbar are, wherein the sound output surfaces of the ultrasonic receiver in each case a surface normal to the respective sound output surface of the Have ultrasound receiver, which surface normal is perpendicular to the Schallalleinkoppelfläche. Under decoupling is the decoupling of the measuring signals from the measuring medium in a coupling element understood, therefore, the coupling could also be used as a coupling the measurement signals are understood in the coupling element. The surface normals perpendicular to the sound output surfaces are vertical on at least one Schallalleinkoppelfläche, z. B. one Spherical curved Schallalleinkoppelfläche.

are several Schallalleinkoppelflächen can z. B. every surface normal perpendicular to only one Schallalleinkoppelfläche stand, with each sound output surface on a parallel opposite Schalleinkoppelfläche would be aligned. A three- or four-sided pyramid as a coupling element, or as a first part of a two-part coupling element for beam splitting on the receiving sensors, with an electromechanical Transducer element on the base of the pyramid would represent an embodiment.

Now are many combinations of positions of radiating and receiving Surfaces of the transducer elements and the coupling and uncoupling Surfaces of the coupling elements conceivable. An exemplary Embodiment will be briefly mentioned here. Thus, a coupling element is designed so that it is a pyramid-like Recess has, on which individual transducer elements acoustically can be coupled, which in turn together to form a transmitting unit are switchable.

A further advantageous embodiment of the invention Measuring system provides that the electromechanical transducer element at least the first ultrasonic transmitter and the electromechanical Transducer elements of the first ultrasonic receiver and at least of the second ultrasonic receiver from different Consist of materials. The materials of the ultrasonic receiver are preferably preformed substantially the same. in one embodiment the invention consists of the electromechanical transducer element at least the first ultrasonic transmitter of a first piezoceramic and the electromechanical transducer elements of the first ultrasound receiver and at least the second ultrasonic receiver consist of a second piezoceramic, wherein the material of the first piezoceramic does not correspond to the material of the second piezoceramic. here we can also two different technologies are used. So are z. B. the active ultrasonic transmitter made of piezoceramics or speaker materials and the passive ultrasonic receivers respond z. B. with Resistance changes and / or capacity changes on pressure waves or pressure fluctuations.

at a very advantageous development of the invention is the respective Noise coupling surface of the ultrasonic receiver small in comparison to the sound output surface of the ultrasonic transmitter.

A advantageous development of the invention Solution is that at least the first sound-emitting Surface of the electromechanical transducer element of Ultrasound receiver is great compared to the sound-receiving surfaces of the electromechanical Transducer element of the ultrasonic receiver.

The sound-emitting surface of the electromechanical transducer element The ultrasound transmitter is in one embodiment in a size ratio from about 100: 1 to the sound-receiving surface the electromechanical transducer element of an ultrasonic receiver. In another embodiment, the sound-emitting surface Approximately 50 times as large as the sound-receiving Surface, in particular, it is about 20 times so big, or even 10 times as big, according to one Design only 5 times as large. The proportions of the sender to the receivers depend among other things also on the used wavelength of the ultrasonic signals from. In addition, the technology used is transforming the ultrasonic signals in electrical signals a role. For Passive ultrasonic receivers are recommended for. B. resistive Sensors and for the active ultrasonic transmitter are z. B. capacitive sensors used instead of piezoceramics. So the receivers can become very small, such as B. a needle hydrophone with a diameter of one mm or less. Depending on the frequency, ultrasonic transmitters, which are made of piezoceramic, move are manufactured in orders of z. B. 5 mm to 20 mm diameter. But there are also z. B. 50 mm at lower Frequencies and larger pipes conceivable.

The electromechanical transducer elements of the ultrasonic transmitter in one Measuring system according to the invention can be very be powerful. By contrast, the transducer elements are preferred very sensitive, compared to the transducer elements of the ultrasonic transmitter. This has the advantage that the ultrasonic sensors, in particular The ultrasound receiver is very small compared to the stand the technology can be built. This will make very small holes in the tube wall of the measuring tube for the placement of the sensors, in particular the receiver is needed. These in turn influence the flow of the measuring medium less. Another advantage results from creating a relative to the sensor size large mounting hole, both the ultrasonic transmitter as also with the ultrasonic receivers. This is the measuring system sterilizable.

According to a further advantageous development of the measuring system according to the invention, it is proposed that the ultrasonic transmitter essentially generates ultrasonic spherical waves. This is particularly advantageous in one, having a substantially circular cross-section, measuring tube, since then the orientation of the ultrasonic receiver on the tube inner wall is vornehmbar very streamlined. The ultrasonic receivers are almost flush with the measuring tube inner wall in the measuring tube wall to sink. But even a small offset is only slightly flow-influencing. This embodiment can also be advantageous in all other conceivable measuring tubes. By spherical waves ultrasonic signals are understood, which they propagate substantially uniformly from a source in all spatial directions in strictly concentric wavefronts. If z. B. a half-shell or hemispherical electromechanical transducer element used, the ultrasonic waves are emitted perpendicular to the, then sound-emitting surface of the electromechanical transducer element. The point from which the wavefronts would propagate out would be the center of the ge curved electromechanical transducer element. Similarly, a spherical wave is to be generated by a flat electromechanical transducer element and a correspondingly shaped coupling layer, such. B. a coupling lens.

A Further development of the invention provides that each ultrasonic receiver exactly one control / evaluation unit is assigned. This can, for example simultaneously a transit time difference and / or a phase difference between the individual signal paths from the transmitter to the different ones Receivers are measured.

In a variant of a measuring system according to the invention are the functions of the ultrasonic transmitter and ultrasonic receiver reversed, d. H. formerly acting as recipients Ultrasonic receivers now send an ultrasonic signal and the former ultrasonic transmitter receives these ultrasonic signals. The evaluation of the measuring signals and / or the derived therefrom Measurement data is sequential or parallel on different Frequencies.

The The invention will be explained in more detail with reference to the following figures. There are many combinations of possible characteristics of the invention, so that only a small selection is shown in the figures can be.

1 shows a measuring system according to the invention in cross-section through the measuring tube,

2 shows the same measuring system in a first longitudinal section,

3 shows the same measuring system in a second longitudinal section,

4 shows a further inventive measuring system in longitudinal section with an ultrasonic transmitter and four ultrasonic receivers,

5 shows in perspective a measuring tube with three imaginary spatial planes,

6 shows a longitudinal section of a further measuring system according to the invention,

7 shows a longitudinal section of another measuring system according to the invention.

In 1 is an inventive measuring system 1 with an ultrasonic transmitter 2 and two ultrasound receivers 3 . 4 represented, which in one, a measuring medium 6 leading measuring tube 5 are arranged according to the invention. The section across the measuring tube corresponds to a section parallel to the imaginary third spatial plane. The imaginary measuring tube axis 10 is thus perpendicular to the plane of the drawing. An imaginary central axis 13 of the ultrasonic transmitter 2 runs centrally through the here rotationally symmetrical ultrasonic transmitter 2 , It is perpendicular to the measuring tube axis 10 , The detailed illustrations reveal the structural design of the ultrasonic transmitter 2 and one of the two identical ultrasonic receiver 3 . 4 ,

Both the ultrasonic transducer 2 as well as the ultrasound receivers 3 . 4 each have an electromechanical transducer element 7 . 8th , preferably from a piezoceramic, and one each the measuring medium 6 Touching and acoustically coupling surface 20 . 21 on. Because the sound-emitting surface 11 the electromechanical transducer element 7 of the ultrasonic transmitter 2 parallel to the Schallalleinkoppelfläche 21 of the ultrasonic transmitter 2 and because the sound-receiving surfaces 12 the electromechanical transducer elements 8th the ultrasound receiver 3 . 4 are also parallel to their respective Schallauskoppelflächen 21 , are the surface normals 18 to the sound-emitting surface 11 the electromechanical transducer element 7 of the ultrasonic transmitter 2 and the surface normals 23 to the Schallalleinkoppelfläche 20 same, and the surface normals 19 to the sound-receiving surfaces 12 the electromechanical transducer elements 8th the ultrasound receiver 3 . 4 fall along with the surface normals 24 to the sound decoupling surfaces 21 , At the same time, both the surface normals correspond 18 to the sound-emitting surface 11 the electromechanical transducer element 7 of the ultrasonic transmitter 2 , as well as the surface normals 23 to the Schallalleinkoppelfläche 20 of the ultrasonic transmitter 2 here the central axis 13 of the ultrasonic transmitter 2 , Therefore, in the following only from the surface normal 18 to the sound-emitting surface 11 the electromechanical transducer element 7 of the ultrasonic transmitter 2 and from the surface normals 19 to the sound-receiving surfaces 12 the electromechanical transducer elements 8th the ultrasound receiver 3 . 4 spoken.

All illustrated ultrasonic sensors 2 . 3 . 4 are aligned towards the center of the pipe, ie the surface normal 18 to the sound-emitting surface 11 the electromechanical transducer element 7 of the ultrasonic transmitter 2 and the surface normals 19 to the sound-receiving surfaces 12 the electromechanical transducer elements 8th the ultrasound receiver 3 . 4 stand perpendicular to the measuring tube axis 10 , as well as 2 and 3 clarify. As in 2 and 3 but to see clearly, only the surface normal cuts 18 to the sound-emitting surface 11 the electromechanical transducer element 7 of the ultrasonic transmitter 2 the point of intersection 17 the three spatial levels 14 . 15 . 16 ,

By means of this sensor arrangement, it is possible Lich, a transit time difference between a first ultrasonic signal between transmitter 2 and the first receiver on the one hand and a second ultrasonic signal between the transmitter and the second receiver on the other hand to determine and therefrom by means of the control / evaluation unit, not shown here for clarity, to determine the flow, since one of the two ultrasonic signal paths 22 in the flow direction of the measuring medium 6 in the measuring tube 5 shows, the other opposite, or one, having a direction component in the flow direction and the other, a direction component opposite to the flow direction.

As the 2 and 3 show, the ultrasonic receiver 3 . 4 a distance in the longitudinal direction of the measuring tube 5 as well as a distance across to each other. This results in the plotted angles α, β, γ and better coverage of the tube cross-section, compared to an ultrasonic signal parallel to the first spatial plane. In this case, the ultrasonic receiver 3 . 4 the respective same angle α, β, γ to the central axis 13 of the ultrasonic transmitter 2 and to the measuring tube axis 10 on. Your vertical projections into the second room level 15 are thus point-symmetrical to the point of intersection 17 the three spatial levels 14 . 15 . 16 ,

Due to the specialization of the sensors for transmission and reception, these have to be designed specifically. The recipients 3 . 4 may be much smaller than the transmitter 2 , The measuring tube 5 can z. B. for sterilization purposes a free space 25 around the ultrasonic sensors 2 . 3 . 4 exhibit.

4 discloses a measuring system according to the invention 1 with four ultrasonic receivers 3 . 4 . 26 . 27 , Also these four ultrasonic receivers 3 . 4 . 26 . 27 are point symmetrical to a point of the central axis 13 of the ultrasonic transmitter 2 arranged. There are a total of four different, virtually lossless, because direct, ie without reflection, measuring paths possible, with only one transmitter.

In 5 is a measuring tube 5 of a measuring system according to the invention illustrated. In addition, the three imaginary spatial levels 14 . 15 . 16 outlined. The ultrasound transmitter 2 lies in the third room level.

6 describes a longitudinal section through a measuring tube 5 a measuring system according to the invention. The ultrasound transmitter 2 In this case, a coupling element with a sound coupling surface, via which sound coupling surface the acoustic signals from the ultrasonic transmitter are coupled into the measuring medium, on which sound coupling surface is configured shell-shaped. The respective surface normals of the sound output surfaces of the ultrasonic receivers 3 and 4 each stand perpendicular to the Schallalleinkoppelfläche. In this embodiment, the ultrasonic receiver is capable of transmitting ultrasonic signals in the form of spherical waves in the region of the measuring tube into the measuring medium, which is the signal paths 22 suggest.

In 7 is the measuring system with an ultrasonic transmitter with two piezoelectric elements, ie two electromechanical transducer elements 7a and 7b drawn. They are with their respective sound-emitting surfaces or the respective surface normal to the sound-emitting surfaces, which here the signal paths 22 correspond to the ultrasound receiver 3 . 4 aligned.

1

Ultrasonic flow measuring system

2

ultrasonic transmitter

3

first ultrasonic receiver

4

second ultrasonic receiver

5

measuring tube

6

measuring medium

7

electromechanical Transducer element of the ultrasonic transmitter

8th

electromechanical Transducer element of an ultrasonic receiver

9

Control / evaluation unit

10

Measuring tube axis

11

Sound emission Dende Surface of an electromechanical transducer element of a ultrasonic transmitter

12

Sound receiving end Surface of an electromechanical transducer element of a ultrasonic receiver

13

central axis of the ultrasonic transmitter

14

First room level

15

Second room level

16

third room level

17

intersection the three spatial levels

18

surface normal to the sound-emitting surface of the electromechanical Transducer element of the ultrasonic transmitter

19

surface normal to the sound receiving surface of an electromechanical Transducer element of an ultrasonic receiver

20

Schalleinkoppelfläche

21

sound out

22

Ultrasonic signal path

23

surface normal to the Schallalleinkoppelfläche

24

surface normal to the sound output surface

25

recess

26

third ultrasonic receiver

27

fourth ultrasonic receiver

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 686255 B1 [0008]
• - US 4484478 A [0008]
• - US 4598593 A [0008]
• - US 5052230 A [0009]
• - DE 10200704936 A1 [0013, 0013]

Claims (9)

Ultrasonic flow measuring system ( 1 ) for determining and / or monitoring the flow of a measuring medium ( 6 ) through a measuring tube ( 5 ), which ultrasonic flow measuring system ( 1 ) at least one first ultrasonic transmitter ( 2 ), a first ultrasonic receiver ( 3 ) and at least one second ultrasonic receiver ( 4 ), wherein the first ultrasonic transmitter ( 2 ) at least one electromechanical transducer element ( 7 ), which converts electrical signals into acoustic signals, and wherein the ultrasonic receivers ( 3 . 4 ) at least one electromechanical transducer element ( 8th ), which convert acoustic signals into electrical signals, wherein the measuring tube ( 5 ) a measuring tube axis ( 10 ), and wherein the ultrasonic transmitter ( 2 ) a central axis ( 13 ), which the measuring tube axis ( 10 ) perpendicularly intersects, the measuring tube axis ( 10 ) and the central axis ( 13 ) of the ultrasonic transmitter ( 2 ) a first level ( 14 ), a second level ( 15 ) perpendicular to the first plane ( 14 ), the measuring tube axis ( 10 ) in the second level ( 15 ) And a third level ( 16 ) perpendicular to the first plane ( 13 ) and the second level ( 14 ), wherein the central axis ( 13 ) of the ultrasonic transmitter ( 2 ) in the third level ( 16 ), the projections being perpendicular to the second plane ( 14 ) the ultrasonic receiver ( 3 . 4 ) to the second level ( 14 ) substantially point-symmetrical to the point of intersection ( 17 ) of the three levels ( 14 . 15 . 16 ) lie. Measuring system ( 1 ) according to claim 1, characterized in that the measuring system at least one control / evaluation unit ( 9 ), which control / evaluation unit ( 9 ) based on the measurement signals or on the basis of measurement data, which are derived from the measurement signals, the volume and / or the mass flow of the in the measuring tube ( 5 ) flowing measuring medium ( 6 ). Measuring system ( 1 ) according to claim 1 or 2, characterized in that the electromechanical transducer elements ( 8th ) the ultrasonic receiver ( 3 . 4 ) each have a sound-receiving surface ( 12 ), which sound-receiving surface ( 12 ) a surface normal ( 19 ) perpendicular to the sound-receiving surface ( 12 ), which surface normals ( 19 ) the measuring tube axis ( 10 ) cuts vertically. Measuring system ( 1 ) according to one of claims 1 to 3, characterized in that the electromechanical transducer element ( 7 ) of the ultrasonic transmitter ( 2 ) a sound emitting surface ( 11 ), which sound-emitting surface ( 11 ) a surface normal ( 18 ) perpendicular to the sound-emitting surface ( 11 ), which surface normals ( 18 ) the measuring tube axis ( 10 ) cuts vertically. Measuring system ( 1 ) according to one of claims 1 to 4, characterized in that the ultrasonic transmitter ( 2 ) at least one sound coupling surface ( 20 ), via which sound coupling surface ( 20 ) the acoustic signals from the ultrasonic transmitter ( 2 ) into the measuring medium ( 6 ) and that the ultrasonic receivers ( 3 . 4 ) at least one sound output surface ( 21 ), via which sound output surfaces ( 21 ) the acoustic signals from the measuring medium ( 6 ) in the respective ultrasonic receiver ( 3 . 4 ) can be decoupled, wherein the sound output surfaces ( 21 ) the ultrasonic receiver ( 3 . 4 ) each have a surface normal ( 24 ) perpendicular to the respective sound output surface ( 21 ) the ultrasonic receiver ( 3 . 4 ), which surface normals ( 24 ) perpendicular to the Schallalleinkoppelfläche ( 20 ) stands. Measuring system ( 1 ) according to one of claims 1 to 5, characterized in that the electromechanical transducer element ( 7 ) at least the first ultrasonic transmitter ( 2 ) and the electromechanical transducer elements ( 8th ) of the first ultrasound receiver ( 3 ) and at least the second ultrasonic receiver ( 4 ) consist of different piezoceramics. Measuring system ( 1 ) according to one of claims 1 to 6, characterized in that the respective sound output surface ( 21 ) the ultrasonic receiver ( 3 . 4 ) small compared to the sound input surface ( 20 ) of the ultrasonic transmitter ( 2 ). Measuring system ( 1 ) according to one of claims 1 to 7, characterized in that the ultrasonic transmitter ( 2 ) generates substantially ultrasonic spherical waves. Measuring system ( 1 ) according to one of claims 1 to 8, characterized in that each ultrasonic receiver ( 3 . 4 ) exactly one control / evaluation unit ( 9 ) assigned.