DE102017104883A1 - Ultrasonic transducer of an ultrasonic flowmeter and such a flowmeter - Google Patents

Abstract

The invention relates to an ultrasonic transducer of an ultrasonic flowmeter for measuring the flow rate or the volume flow of a flowing through a measuring tube gaseous medium and such an ultrasonic flowmeter, the ultrasonic transducer having an ultrasonic transducer with an end face directed toward the medium and a first region adjacent to the end face , and wherein a widening (31) in a third area is arranged to place a vibration node to a working frequency associated vibration mode in the region of a housing connection.

Description

Ultrasonic transducer of an ultrasonic flowmeter for measuring the flow rate or the volume flow rate of a flowing through a measuring tube gaseous medium and such an ultrasonic flowmeter.

Ultrasonic transducers have been known for a long time and are used in different technical fields. Thus the patent shows US4757227 an ultrasonic transducer specialized for levitation applications that operates continuously at one frequency.

In the technical field of ultrasonic flow measurement, it is advantageous to use ultrasound transducers which emit and receive pulsed ultrasound signals, since a flow measurement or a frequency shift of a spectral range of an ultrasound pulse caused by a flow provides more accurate information than a frequency shift of a continuous ultrasound signal. The patent US3891869 shows an ultrasonic transducer of a flow meter, in which an ultrasonic transducer irradiates ultrasonic signals in a medium by means of a front, which ultrasonic signals are generated by means of a mounted on a rear side of the ultrasonic transducer piezoelectric element and transmitted to the ultrasonic transducer. A disadvantage of the ultrasonic transducer proposed by this document, the housing of the ultrasonic transducer by a housing and by a central radial taper of the ultrasonic transducer, which taper has two annular, opposing surface segments result. The enclosure and the two opposing surface segments provide a strong Resonatoreffekt, which obstructs the free swinging of the front. Furthermore, there is the risk of structure-borne sound transmission between Umhausung and Ultraschallübetragung in the case of condensation, which can greatly change the acoustic properties of the ultrasonic transducer. The ultrasonic transducer with transducer element is further connected to a housing which is in contact with a measuring tube of the ultrasonic flowmeter. Via this contact, sound signals are transmitted between the transducer element and the measuring tube and vice versa, which is responsible for a reduced signal-to-noise ratio.

The object of the invention is therefore to propose an ultrasonic transducer and ultrasonic flowmeter with at least one ultrasonic transducer, in which at least one of the disadvantages mentioned is alleviated.

• Ein Wandlerelement zum Erzeugen und Erfassen von pulsförmigen Ultraschallsignalen;
• Einen Ultraschallübertrager zum Leiten von Ultraschallsignalen zwischen dem Wandlerelement und dem Medium,
• wobei der Ultraschallübertrager eine Längsachse und eine Mantelfläche sowie eine dem Wandlerelement abgewandte Stirnfläche aufweist, welche Stirnfläche die Längsachse schneidet und mediumsberührend ist;
• Ein Gehäuse, welches mit dem Ultraschallübertrager verbunden ist;
• wobei der Ultraschallübertrager auf der der Stirnfläche abgewandten Seite eine Rückseite aufweist, wobei das Wandlerelement und der Ultraschallübertrager akustisch und mechanisch über die Rückseite miteinander gekoppelt sind,
• wobei der Ultraschallwandler auf einer der Stirnfläche abgewandten Seite einen dritten Bereich aufweist, wobei sich der Ultraschallübertrager im dritten Bereich in Richtung der Rückseite zumindest abschnittsweise aufweitet,
• wobei die Aufweitung des Ultraschallübertragers beispielsweise konusförmig ist, wobei der dritte Bereich freistehend und mediumsberührend ist,
• wobei
• der dritte Bereich in einem Bereich maximaler Beabstandung der Mantelfläche von der Längsachse an das Gehäuse angebunden ist,
• wobei die Aufweitung des Ultraschallübertragers im dritten Bereich dazu eingerichtet ist, einen Schwingungsknoten einer zu einer Arbeitsfrequenz des Ultraschallwandlers gehörenden resonanten Schwingungsmode des Ultraschallübertragers in einen Bereich der Gehäuseanbindung zu legen.

An inventive ultrasonic transducer of an ultrasonic flowmeter comprises:

• A transducer element for generating and detecting pulsed ultrasonic signals;
• An ultrasonic transducer for conducting ultrasonic signals between the transducer element and the medium,
• wherein the ultrasonic transducer has a longitudinal axis and a lateral surface and an end face facing away from the transducer element, which end face intersects the longitudinal axis and is in contact with the medium;
• A housing which is connected to the ultrasonic transducer;
• wherein the ultrasonic transducer on the side facing away from the end face has a rear side, wherein the transducer element and the ultrasonic transducer are acoustically and mechanically coupled to each other via the back,
• wherein the ultrasound transducer has a third region on a side remote from the end face, wherein the ultrasound transducer expands at least in sections in the third region in the direction of the back side,
• wherein the expansion of the ultrasound transducer is, for example, conical, the third region being free-standing and in contact with the medium,
• in which
• the third region is connected to the housing in a region of maximum spacing of the lateral surface from the longitudinal axis,
• wherein the expansion of the ultrasound transducer in the third region is set up to place a vibration node of a resonant vibration mode belonging to an operating frequency of the ultrasound transducer of the ultrasound transducer in a region of the housing connection.

As a result, the transmission of sound signals between transducer element and measuring tube and vice versa largely suppress, which greatly improves the signal-to-noise ratio and thus the flow measurement.

The transducer element is preferably a piezoelectric element.

In one embodiment, the ultrasound transducer has a first region adjoining the end face and a second region adjoining the first region,
wherein the ultrasonic transducer in the first region at least partially has a transition region, in which transition region is the Ultrasonic transducer tapers in the direction of the second region, wherein the transition region adjacent to the second region, wherein the first region is stimulable with the end face to axial bending vibrations, wherein the bending vibration has an amplitude maximum on the lateral surface.
wherein the first region and the second region are in particular free-standing and medium-contacting.

Exempting the ultrasonic transducer in the first and second regions or avoiding a housing thereof reduces unwanted resonator effects which impair the vibration behavior of the ultrasound transducer, with resonator effects in particular being able to be pronounced in enclosures. Since frequencies of resonance modes of resonance chambers generated by enclosures can have a strong dependence on the medium filling the resonance chamber, as well as its density and temperature, such a resonance chamber would have measurement results with a high degree of uncertainty. In this case, the widening of the ultrasonic transducer in the third region has a further advantage , it prevents a backscatter of ultrasound signals radiated from the first region to the first region and thus a resonator effect, which would disturb the free oscillation of the first region. Exemption of the second region and the third region allows the dispersion of the ultrasonic signals reflected by the expansion into the medium.

In one embodiment of the ultrasonic transducer of the ultrasonic transducer in the first region with the end face can be excited to axial bending vibrations, wherein the bending vibration has an amplitude maximum on the lateral surface.

In an embodiment of the ultrasonic transducer, a function describing the radial distance of the lateral surface to the longitudinal axis is monotonic in the transition region in the direction of the transducer element,
wherein the function is stepwise constant or has stepwise constant, decreasing slope in the direction of the transducer element.

By means of this configuration, a first region can be produced in a manner which is easy to handle in terms of production technology, in which case the bending vibration has an amplitude maximum on the lateral surface.

In one embodiment of the ultrasound transducer, in the transition region in the direction of the transducer element, a function describing the radial distance of the lateral surface to the longitudinal axis in the direction of the transducer element is strictly monotonically decreasing,
the amount of derivative of the function being smaller than 20 in a direction parallel to the longitudinal axis,
The function follows, for example, a linear function, an exponential function, a Bezier curve, a Gaussian function or a hyperbolic function.

This embodiment makes it possible to produce a first region in which the bending vibration has an amplitude maximum on the lateral surface, wherein the smooth course of the function has a stress-reducing effect, and thus avoids stress fractures occurring due to bending vibrations.

wobei A größer 600 und insbesondere größer als 800 und bevorzugt größer als 1000 ist,
und/oder wobei B kleiner als 2200 und insbesondere kleiner als 2000 und bevorzugt kleiner als 1800 ist,
wobei die Arbeitsfrequenz eine Zentralfrequenz der spektralen Verteilung des Ultraschallsignals ist.In one embodiment of the ultrasound transducer, an axial extent y of the transition region and a maximum radial first distance R1 of the lateral surface relative to the longitudinal axis and a minimum radial second distance R2 of the lateral surface relative to the longitudinal axis and an operating frequency f of the ultrasound transducer have the following relationship: $$\text{A kHz * mm}<\text{f * R1 *}\left(\text{R1}-\text{R2}\right)\text{/ y}<\text{B kHz * mm}\text{.}$$

where A is greater than 600 and in particular greater than 800 and preferably greater than 1000,
and / or wherein B is less than 2200 and in particular less than 2000 and preferably less than 1800,
wherein the operating frequency is a center frequency of the spectral distribution of the ultrasonic signal.

The operating frequency is greater than 20 kHz and in particular greater than 50 kHz and preferably greater than 75 kHz.

The operating frequency is less than 400 kHz and in particular less than 300 kHz and preferably less than 250 kHz.

This makes it possible to set a maximum emission efficiency and / or a maximum reception efficiency of the ultrasonic transducer.

In one embodiment of the ultrasonic transducer, the third region adjoins the second region.

In one embodiment of the ultrasonic transducer, a distance of the lateral surface to the longitudinal axis in the axial direction is at least partially constant in the second region.

In one embodiment of the ultrasonic transducer, the lateral surface is substantially rotationally symmetrical.

In one embodiment of the ultrasonic transducer, the end face is flat.

In one embodiment of the ultrasonic transducer, the transducer element has a backing mass on a side facing away from the back side.

By means of the backing compound, an overall axial length of the transducer element, ultrasonic transducer and backing mass can be set to an odd multiple of half the wavelength of a vibration mode associated with the operating frequency and thus improve the vibration capability of the ultrasonic transducer at the operating frequency.

In one embodiment of the ultrasonic transducer of the ultrasonic transducer is made of a material which material has a longitudinal speed of sound in the range of 5000 m / s to 7000 m / s, the material is in particular a substance from the following list:
Titanium, stainless steel, aluminum, magnesium glass, an alloy comprising nickel and / or molybdenum and / or copper.

In one embodiment of the ultrasound transducer, an axial length of ultrasound transducer and transducer element and, if present, backing element is an odd multiple of half the wavelength of a vibration mode associated with the operating frequency.

In one embodiment, the ultrasound transducer has at least one damping ring, which is arranged at least partially in the first region and the second region and surrounds the ultrasound transducer, wherein the damping ring rests closely against the lateral surface of the ultrasound transducer.

In one embodiment, the ultrasound transmitter has a second widening in the second region, the taper of the ultrasound transducer in the first region and the second widening forming a depression, in which depression the damping ring is arranged.

Dampening rings can be helpful in limiting a time duration of a radiated ultrasonic pulse and restricting a ringing of the ultrasonic transducer upon detection of an ultrasonic pulse. Furthermore, they may also be helpful in avoiding or mitigating the aforementioned resonance effects.

• Ein Messrohr mit einer Messrohrwandung;
• Mindestens einen Ultraschallwandler nach einem der vorigen Ansprüche, wobei der Ultraschallwandler in der Messrohrwandung angeordnet sind;
• Eine Mess-/Betriebsschaltung, welche dazu eingerichtet ist, den Ultraschallwandler zu betreiben und die durch den Ultraschallwandler erfassten Ultraschallsignale auszuwerten.

An inventive ultrasonic flowmeter for measuring the flow rate or the volume flow rate of a flowing through a measuring tube gaseous medium according to the transit time difference principle or Doppler principle comprising:

• A measuring tube with a measuring tube wall;
• At least one ultrasonic transducer according to one of the preceding claims, wherein the ultrasonic transducers are arranged in the measuring tube wall;
• A measurement / operating circuit which is adapted to operate the ultrasonic transducer and to evaluate the detected by the ultrasonic transducer ultrasonic signals.

• 1 zeigt einen skizzenhaften Querschnitt durch einen beispielhaften Ultraschallwandler.
• 2 zeigt einen skizzenhaften Querschnitt durch einen weiteren beispielhaften Ultraschallwandler mit einem Dämpfungsring.
• 3 zeigt einen skizzenhaften Querschnitt durch einen weiteren beispielhaften Ultraschallwandler mit einem Dämpfungsring.
• 4.1 bis 4.4 zeigen Konturen einer Frontseite eines beispielhaften Ultraschallübertragers des Ultraschallwandlers.
• 5 zeigt einen schematischen beispielhaften Aufbau eines erfindungsgemäßen Ultraschall-Durchflussmessgeräts.

In the following the invention will be described by means of exemplary embodiments.

• 1 shows a sketchy cross section through an exemplary ultrasonic transducer.
• 2 shows a sketchy cross-section through another exemplary ultrasonic transducer with a damping ring.
• 3 shows a sketchy cross-section through another exemplary ultrasonic transducer with a damping ring.
• 4 FIGS. 1 to 4.4 show contours of a front side of an exemplary ultrasound transducer of the ultrasound transducer.
• 5 shows a schematic exemplary structure of an ultrasonic flowmeter according to the invention.

wobei A größer 600 und insbesondere größer als 800 und bevorzugt größer als 1000 ist, und/oder wobei B kleiner als 2200 und insbesondere kleiner als 2000 und bevorzugt kleiner als 1800 ist und beispielsweise zwischen 1400 und 1500 sein kann. Die Arbeitsfrequenz des Ultraschallwandlers ist dabei in einem Bereich zwischen 50 kHz und 300 kHz. Dadurch wird einerseits die Steifigkeit des Ultraschallübertragers im ersten Bereich 10 gegenüber einem Ultraschallübertrager mit einer schwingfähigen Platte ohne Übergangsbereich erhöht, wodurch die Arbeitsfrequenz erhöht wird. Bei einem Ultraschallübertrager mit einer schwingfähigen Platte ohne Übergangsbereich müsste diesbezüglich eine in axialer Richtung dickere Platte angewandt werden, womit die axiale Schwingfähigkeit der Platte reduziert wird und somit die Sende- und Empfangsleistung des Ultraschallwandlers reduziert wird. Andererseits wird durch die vorgegebene Randbedingung sichergestellt, dass ein sehr langsamer Übergang zwischen einer Zone umfassend R1 und einer Zone umfassend R2 vermieden wird, weil ein solcher sehr langsamer Übergang eine axiale Schwingung des Ultraschallübertragers im ersten Bereich 10 komplett unterbindet. 1 shows a sketchy cross section through an ultrasonic transducer according to the invention 1 , wherein the ultrasonic transducer 1 an ultrasonic transducer U with a face S , a lateral surface M and a back R ; and a (piezo) transducer element 50 for generating and detecting pulsed ultrasonic signals; a baking mass 60 ; and a via a housing connection 41 connected housing 40 having. The ultrasonic transmitter U is set up to receive ultrasonic signals between the one on the back R of the ultrasonic transducer attached transducer element 50 and one of the back R facing away from the first area 10 of the ultrasonic transducer and vice versa. The first area 10 In this case, it adjoins an end face facing a medium and has a transition region 11 in which a radial distance of the lateral surface decreases to a longitudinal axis of the ultrasonic transducer in the direction of the transducer element, wherein a second region 20 of the ultrasonic transducer connects to the first region. An excitation of the ultrasonic transducer U by means of a pulse-shaped, from the transducer element 50 outgoing or via a medium over the end face or the first area 10 incoming ultrasonic signal creates an axial bending vibration of the ultrasonic transducer in the first region 10 with the face S parallel to the longitudinal axis L the ultrasonic transducer, wherein the bending vibration of a maximum amplitude on the Has lateral surface. As a result, ultrasonic signals become very efficient between ultrasonic transducers U and the medium and vice versa. The excitation of the ultrasonic transducer comprises the formation of a longitudinal vibration mode along the longitudinal axis L Ultrasonic transducer. In order to ensure a maximum transmission and reception power of the ultrasonic transducer, a desired operating frequency of the ultrasonic transducer must fit the longitudinal vibration mode, wherein the working frequency is a central frequency of a spectral range of the ultrasonic signal. It may therefore be advantageous to have a backing mass 60 to one of the back R opposite side of the transducer element 50 attach so that the vibration mode across the ultrasonic transducer U as well as via the transducer element 50 and the backing mass 60 extends. The axial extent of the vibration mode via the ultrasonic transducer and transducer element and if present backing mass is an odd multiple of half the wavelength of the vibration mode, wherein the vibration mode in the first region 10 has a vibration abdomen. The vibration capability of the ultrasonic transducer in the first region 10 with the amplitude maximum on the lateral surface is achieved by an adaptation of geometric properties of the ultrasonic transducer in the first region, wherein an axial extent y of the ultrasonic transducer and a maximum radial first distance R1 of the ultrasonic transducer in the transition region to the longitudinal axis L and a minimum radial second distance R2 of the ultrasonic transducer in the transition region 11 to the longitudinal axis and the operating frequency f of the ultrasonic transducer following boundary condition: $$\text{A kHz * mm}<\text{f * R1 *}\left(\text{R1}-\text{R2}\right)\text{/ y}<\text{B kHz * mm}\text{.}$$

wherein A is greater than 600 and in particular greater than 800 and preferably greater than 1000, and / or wherein B is less than 2200 and in particular less than 2000 and preferably less than 1800 and may for example be between 1400 and 1500. The operating frequency of the ultrasonic transducer is in a range between 50 kHz and 300 kHz. As a result, on the one hand, the rigidity of the ultrasonic transducer in the first region 10 increased compared to an ultrasonic transducer with a vibratory plate without transition region, whereby the operating frequency is increased. In an ultrasonic transducer with a vibratory plate without transition region in this regard, a thicker in the axial direction plate should be applied, whereby the axial vibration capacity of the plate is reduced and thus the transmission and reception power of the ultrasonic transducer is reduced. On the other hand, it is ensured by the predetermined boundary condition that a very slow transition between a zone comprising R1 and a zone comprising R2 is avoided, because such a very slow transition axial oscillation of the ultrasonic transducer in the first region 10 completely stopped.

To the transition area 11 of the first area 10 closes the second area 20 at, wherein the distance of the lateral surface to the longitudinal axis as in 1 shown following the transition area 11 can be constant. For example, the distance may be following the transition area 11 along the longitudinal axis but also increase first and then be constant. Instead of a section-wise constant distance, the distance of the lateral surface can only partially increase or decrease in sections, wherein a slight change in the longitudinal axis with respect to the absolute value of a maximum slope of 0.1. To the second area 20 closes a third area 30 on, wherein the ultrasonic transducer in the third area 30 an expansion 31 at which widening of the distance of the lateral surface to the longitudinal axis in the direction of the transducer element 50 increases, with a slope of the expansion amount is at least 0.3. In the area of the maximum radial expansion of the expansion 31 is a housing 40 via a housing connection 41 tethered, wherein the connection is preferably a welded joint. The expansion 31 is adapted to the ultrasonic transducer U to stiffen, so that the vibration mode at the working frequency of the ultrasonic transducer, a node in the expansion zone 31 having. This has the advantage that a transmission of structure-borne noise between a measuring tube, in which the ultrasonic transducer is arranged, and the transducer element and vice versa is strongly suppressed. This improves the signal-to-noise ratio, allowing for better flow measurement. The expansion may be, for example, conical, but also take forms, as in the 4 .1 to 4.4 are discussed. Preferably, the ultrasonic transducer is in the second region 20 as well as in the third area 30 like the first area 10 freestanding. This results in a further advantage of the expansion 31 , wherein by the bending vibration of the ultrasonic transducer in the first region 10 radiated ultrasound signals not to the first area 10 be reflected back, but scattered into the medium. As a result, the bending vibration is not disturbed, so the transmission and reception capability of the ultrasonic transducer can be further improved.

Preferably, the ultrasonic transducer is rotationally symmetrical, since it can then be finished in a simple and inexpensive way.

2 shows a sketchy cross-section through an ultrasonic transducer 1 according to the in 1 shown ultrasonic transducer, wherein the Ultrasonic transducer has a damping ring D, which surrounds the ultrasonic transducer and at least partially in the first region 10 , in the second area 20 as well as in the third area 30 is arranged. The damping ring can also be arranged only in the first and second areas. The damping ring lies close to the lateral surface M of the ultrasonic transducer and attenuates axial bending oscillations of the ultrasonic transducer in the first region with the end face S , whereby a temporal duration of emitted ultrasonic pulses can be limited, which can advantageously affect a measuring rate of an ultrasonic flowmeter.

3 shows a sketchy cross-section through another ultrasonic transducer with a damping ring, wherein the ultrasonic transducer in the second region 20 a second expansion 21 which second expansion with the taper of the ultrasonic transducer in the transition region 11 a trough 22 forms, in which trough 22 of the damping ring is arranged. The damping ring lies close to the lateral surface M of the ultrasonic transducer and attenuates axial bending oscillations of the ultrasonic transducer in the first region with the end face S , whereby a temporal duration of emitted ultrasonic pulses can be limited, which has an advantageous effect on a measuring rate of an ultrasonic flowmeter.

The in the 1 to 3 Sketched taper of the ultrasonic transducer in the first area is optional. An inventive ultrasound transducer can also be characterized only by the features of the third region, so that the transducer is substantially cylindrical from the end face to the third region.

The in the 2 and 3 shown damping rings are optional. An inventive ultrasonic transducer may also have a plurality of damping rings arranged axially one behind the other.

4 .1 to 4.4 sketch sections of an ultrasonic transducer U with exemplary contours of the transition region according to the invention 11 , where at 4 .1 the cutout a cone-shaped transition area 11 as in 1 shown shows.

4 .2 sketches a section with a transition area 11 which has two cone-shaped segments, wherein a slope of the respective segments with respect to the longitudinal axis L with increasing distance of the segments to the face S decreases in amount. It can also be set up with decreasing slope more than two segments.

4 .3 outlines a section with a transition area 11 , which several segments each with a constant radial distance of the lateral surface M to the longitudinal axis L having. The number of segments can also be, for example, not equal to three, for example also two or four or even more than five or more. The extent of individual segments in the direction of the longitudinal axis can be constant, increasing or decreasing.

In the 4 .2 and 4 . 3 shown contours have the advantage that they are easy to implement manufacturing technology. The dimensions of the individual gradations are much smaller than the wavelength of the generated or detected ultrasonic signal in the medium.

4 .4 outlines a section with a transition area 11 , in which the distance of the lateral surface to the longitudinal axis decreases continuously with increasing distance to the end face. A function describing the radial distance of the lateral surface from the longitudinal axis follows, for example, an exponential function, a Bezier curve, a Gaussian function or a hyperbolic function. A course of an exponential function results in a uniform stress distribution in a flexural vibration, but the amplitude of the flexural vibration is rather low. A hyperbolic curve allows a greater amplitude of the bending vibration. A Bezierkurwenförmiges or Gaussian shape also allow larger amplitudes, while uniform stress distribution, but in these forms geometric optimal boundary conditions must be determined by simulations.

A like in 4 .1 shown conical shape of the transition region can be easily finished, but has a small relatively low amplitude of the bending vibration. In the 4 The stepped shape shown in FIG. 3 is also easy to fabricate and allows for large amplitudes, but may be susceptible to fractures at high transmission powers, particularly at step edges.

5 outlines an ultrasonic flowmeter 100 with a measuring tube 70 , two ultrasonic transducers according to the invention 1 which are provided in ultrasound transducer receptacles 72 provided in a measuring tube wall 71 are incorporated and an electronic measuring / operating circuit 80 which is adapted to the ultrasonic transducers 1 to operate. To maintain clarity, electrical connections between the electronic measuring / operating circuit 80 and the ultrasonic transducers 1 not sketched. In a transit time difference method, ultrasonic signals are alternately emitted in and against a flow direction of the medium in the measuring tube and their Travel times measured, wherein a signal emitted by a first ultrasonic transducer ultrasonic signal is detected by a second ultrasonic transducer. In order to alternately emit ultrasonic signals in and against the flow direction, each ultrasonic transducer is used alternately as a transmitting and receiving transducer. From a determined transit time difference, the flow velocity of the medium can be determined. The alternation between transmitting and receiving operation need not take place after every single emission of an ultrasonic signal, but may also take place only after a series of ultrasonic signals in one direction.

Alternatively, the flow velocity can also be determined by means of a frequency shift of the spectral range of an ultrasound signal, which is transmitted to particles in the medium to the ultrasound transducer 1 is backscattered. Since this method is based on the Doppler effect, this method is called Doppler method. In this case, an ultrasonic flowmeter 100 also only an ultrasonic transducer according to the invention 1 exhibit.

Instead of the in 5 indicated direct path of an ultrasonic signal between two ultrasonic transducers, a path of an ultrasonic signal and one or more reflections on the Meßrohrwandung 71 or have reflectors designed for it.

LIST OF REFERENCE NUMBERS

1

ultrasound transducer

10

first area

11

Transition area

20

second area

21

second expansion

30

third area

31

widening

41

housing connection

40

casing

50

transducer element

60

Backing mass

70

measuring tube

71

Messrohrwandung

80

electronic measuring / operating circuit

100

Ultrasonic flowmeter

S

face

M

lateral surface

U

Ultrasound transducer

R

back

L

longitudinal axis

R1

first distance R1

R2

second distance R2

y

axial extent

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4757227 [0002]
• US 3891869 [0003]

Claims (14)

An ultrasonic transducer (1) of an ultrasonic flowmeter (100) for measuring the flow rate or volume flow of a gaseous medium flowing through a measuring tube, comprising: a transducer element (50) for generating and detecting pulsed ultrasonic signals; An ultrasonic transducer (U) for conducting ultrasonic signals between the transducer element (50) and the medium, the ultrasonic transducer (U) has a longitudinal axis (L) and a lateral surface (M) and an end face facing away from the transducer element (S), which end face the Longitudinal axis (L) intersects and mediumsberührend, wherein the end face is preferably flat; A housing (40) connected to the ultrasonic transducer (U); wherein the ultrasonic transducer on the side facing away from the end face has a rear side (R), wherein the transducer element (50) and the ultrasonic transducer acoustically and mechanically coupled to each other via the back, the ultrasonic transducer on a side facing away from the end face a third region (30) wherein the ultrasonic transducer expands at least in sections in the third region in the direction of the rear side (R), wherein the widening (31) is, for example, cone-shaped, the third region being freestanding and in contact with the medium, characterized in that the ultrasonic transducer is in the third region (30 ) is connected to the housing in a region of maximum spacing of the lateral surface from the longitudinal axis, wherein the widening (31) of the ultrasound transducer in the third region is adapted to a vibration node of a resonant oscillation belonging to an operating frequency of the ultrasonic transducer Mode of ultrasonic transducer in an area of the housing connection (41) to lay. Ultrasonic transducer after Claim 1 wherein the ultrasonic transducer has a first region (10) adjoining the end face (S) and a second region (20) adjoining the first region, the first region (10) having at least sections a transition region (11) in which transition region (11) the ultrasonic transducer (U) tapers in the direction of the second region (20), wherein the transition region adjoins the second region, wherein the first region can be excited with the end face to axial bending oscillations, wherein the bending vibration has an amplitude maximum on the lateral surface (20). M). wherein the ultrasonic transducer in the first region is free-standing and medium-contacting. Ultrasonic transducer after Claim 1 or 2 wherein the ultrasonic transducer in the first region (10) with the end face (S) can be excited to axial bending vibrations, wherein the bending vibration has an amplitude maximum on the lateral surface (M). Ultrasonic transducer after Claim 2 or 3 , wherein in the transition region (11) in the direction of the transducer element (50) a function describing the radial distance of the lateral surface to the longitudinal axis is monotonous, wherein the function is stepwise constant or has stepwise constant, decreasing in the direction of the transducer element slope. Ultrasonic transducer after Claim 2 or 3 wherein in the transition region (11) in the direction of the transducer element (50) a function describing the radial distance of the lateral surface to the longitudinal axis in the direction of the transducer element is strictly monotonically decreasing, wherein the amount of a derivative of the function according to a direction parallel to the longitudinal axis is less than 20, The function follows, for example, a linear function, an exponential function, a Bezier curve, a Gaussian function or a hyperbolic function. Ultrasonic transducer according to one of Claims 2 to 5 , wherein in the transition region (11) have an axial extent y of the ultrasonic transducer and a maximum radial first distance R1 of the lateral surface to the longitudinal axis and a minimum radial second distance R2 of the lateral surface to the longitudinal axis and an operating frequency f of the ultrasonic transducer following relationship: $$\text{A kHz * mm}<\text{f * R1 *}\left(\text{R1}-\text{R2}\right)\text{/ y}<\text{B kHz * mm}\text{.}$$

wherein A is greater than 600 and in particular greater than 800 and preferably greater than 1000, and / or wherein B is less than 2200 and in particular less than 2000 and preferably less than 1800, wherein the operating frequency is a central frequency of the spectral distribution of the ultrasonic signal. Ultrasonic transducer after one of the previous ones Claims 2 to 6 wherein the third region (30) adjoins the second region (20). Ultrasonic transducer according to one of Claims 2 to 7 , wherein in the second region (20) a distance of the lateral surface (M) to the longitudinal axis (L) in the axial direction is at least partially constant. Ultrasonic transducer according to one of the preceding claims, wherein the transducer element (50) on a The rear side facing away from a backing mass (60). Ultrasonic transducer according to one of the preceding claims, wherein the ultrasonic transducer (U) is made of a material which material has a longitudinal speed of sound in the range of 5000 m / s to 7000 m / s, wherein the material is in particular a substance from the following list: Titanium, stainless steel, aluminum, magnesium glass, an alloy comprising nickel and / or molybdenum and / or copper. Ultrasonic transducer according to one of the preceding claims, wherein an axial length of the ultrasonic transducer (U) and transducer element (50) and if present backing element (60) is an odd multiple of half the wavelength of a frequency belonging to the vibration mode. Ultrasonic transducer according to one of the preceding claims, wherein the ultrasonic transducer (1) has at least one damping ring (D), which is arranged at least partially in the first region (10) and second region (20) and surrounds the ultrasonic transducer (U), wherein the damping ring (D) on the lateral surface (M) of the ultrasonic transducer (U) is applied. Ultrasonic transducer after Claim 12 wherein the ultrasonic transducer in the second region (20) has a second widening (21), wherein the taper of the ultrasonic transducer in the first region and the second widening (21) form a trough (22), in which trough the damping ring is arranged. Ultrasonic flow meter (100) for measuring the flow rate or the volume flow rate of a gaseous medium flowing through a measuring tube according to the transit time difference principle or Doppler principle comprising: A measuring tube (70) having a measuring tube wall (71); At least one ultrasonic transducer (1) according to one of the preceding claims, wherein the ultrasonic transducer are arranged in the measuring tube wall (71); An electronic measuring / operating circuit (80) which is adapted to operate the ultrasonic transducer (1) and to evaluate the ultrasonic signals detected by the ultrasonic transducer (1).

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