WO2023139116A1

WO2023139116A1 - Flow meter

Info

Publication number: WO2023139116A1
Application number: PCT/EP2023/051112
Authority: WO
Inventors: Stefan Menzi
Original assignee: Huba Control Ag
Priority date: 2022-01-19
Filing date: 2023-01-18
Publication date: 2023-07-27

Abstract

A flow meter (1) is described, comprising a housing (11) with a longitudinal axis (L) and defining a flow channel (12) for a fluid flow, a first and a second ultrasonic transducer (15; 16) arranged at the flow channel and each configured to emit and receive ultrasonic signal into and from the flow channel, a first ultrasonic reflecting device (13) arranged at an outer surface (110) of the housing and opposite to the first ultrasonic transducer with respect to the flow channel, a second ultrasonic reflecting device (14) arranged at the outer surface of the housing and opposite to the second ultrasonic transducer with respect to the flow channel, wherein the first and second ultrasonic transducers and the first and second ultrasonic reflecting devices are arranged to guide an ultrasonic signal (USW) emitted by one of the first or second ultrasonic transducer and received by the other of the first or second ultrasonic transducer along a W-shaped path.

Description

FLOW METER

Field of the invention

The present invention relates to a flow meter, in particular, to an ultrasonic flow meter .

Background of the invention

Flow meters such as ultrasonic flow meters are commonly employed to record flow signals in appliances for heating, ventilation and/or air conditioning . A flow meter may, for instance , record flow of a fluid such as water or glycol through a flux calorimeter . A quantity indicative of heat trans fer can then be derived from the recorded flow and from additional measurements of temperature . Ultrasonic flow meters can also be employed to record flow of trans former oil circulating through the ducts of power trans formers . A recorded flow value can then be used to adj ust speeds of oil pumps while the power trans former is in oil directed and air forced cooling mode .

For example , EP 3 199 923 Al describes an ultrasonic flow meter for determining the amount of a fluid flowing through a measuring channel in a metallic hous ing . The flow rate meter comprises two ultrasonic transducers which are arranged at a distance along the measuring channel , the first ultrasonic transducer sending an ultrasonic signal into the measuring channel and the second ultrasonic transducer receiving the emitted ultrasonic signal . Three deflecting mirrors are arranged in the measuring channel and reflect the ultrasonic signal transmitted by the first ultrasonic transducer several times on its way to the second ultrasonic transducer, so that a basically W-shaped path of the ultrasonic signal results . The signal can also run in the opposite direction, i . e . from the second to the first ultrasonic transducer, whereby both transducers can send and receive .

Summary of the invention

When measuring the flow of a fluid using an ultrasonic flow meter, it is desired to improve the measurement signal quality by e . g . reducing or minimi zing interference with the fluid flow so as to provide for improved linearity of the fluid flow .

It is therefore an obj ect of the invention to provide a flow meter which at least partially improves the prior art and avoids at least part of the disadvantages of the prior art .

According to the present invention, this obj ect is particularly achieved by a flow meter comprising a housing with a longitudinal axis and defining a flow channel for a fluid flow, a first and a second ultrasonic transducer arranged at the flow channel and each configured to emit and receive ultrasonic signal into and from the flow channel , a first ultrasonic reflecting device arranged at an outer surface of the housing and opposite to the first ultrasonic transducer with respect to the flow channel , a second ultrasonic reflecting device arranged at the outer surface of the housing and opposite to the second ultrasonic transducer with respect to the flow channel , wherein the first and second ultrasonic transducers and the first and second ultrasonic reflecting devices are arranged to guide an ultrasonic signal emitted by one of the first or second ultrasonic transducer and received by the other of the first or second ultrasonic transducer along a W-shaped path .

Arranging the first ultrasonic reflecting device and the second ultrasonic reflecting device at an outer surface of the housing provides the advantage that spatial interference of the ultrasonic reflecting devices with the fluid flow can be prevented . Linearity of the fluid flow in the vicinity of the ultrasonic reflecting devices can therefore be improved, which improves the signal quality of the flow meter .

Further, accessibility to the first and second ultrasonic reflecting devices can be improved due to the arrangement on the outer surface of the housing . Easier accessibility may for example be advantageous for repairing of replacing of the ultrasonic reflecting devices in case of mal functioning .

The arrangement of the first and second ultrasonic reflecting devices on the outer surface of the housing further provides the advantage that the flexibility of the design of the ultrasonic reflecting devices can be increased as compared to an arrangement of the ultrasonic reflecting devices inside the housing where a modi fication of the design has a direct ef fect on the geometry of the flow channel .

Manufacturing of the flow meter can also be simpli fied as the ultrasonic reflecting devices do not have to be introduced into and positioned in the flow channel , which may be cumbersome and, in particular, lead to inaccuracies in the intended path of the ultrasonic signal i f the ultrasonic reflecting devices are not accurately positioned within the flow channel .

In some embodiments , the first and second ultrasonic reflecting devices are arranged such that the ultrasonic signal guided along the W-shaped path is reflected between reflections at the first and second ultrasonic reflecting devices by an intermediate wall portion of the housing arranged between the first and second ultrasonic transducers and opposite to the first and second ultrasonic reflecting devices with respect to the flow channel .

Using an intermediate wall portion for the reflection of the ultrasonic signal between the reflections from the first and second ultrasonic reflecting devices provides the advantage that a separate ultrasonic reflecting device , such as a mirror, does not have to be introduced into the flow channel .

Preferably, a maj or portion of the ultrasonic signal is reflected at the outer surface of the intermediate wall portion of the housing, i . e . at the interface <housing>/ <air> .

In some embodiments , the housing is made from plastics , preferably in ection-molded plastics , or metal .

The housing may also be made using other manufacturing methods , for example additive manufacturing, such as 3D printing . The plastics may comprise one or more of : an epoxy polymer, polytetrafluoroethylene , polyethylene , polyethylene terephthalate , polyester, etc . The metal may comprise one or more of : steel , austenitic steel , ferritic steel , aluminum, aluminum alloy, brass etc . or an alloy thereof .

Using plastics has the advantage that production of the flow meter can be simpli fied and costs be reduced .

In particular, the ultrasonic reflecting devices can be used for the present flow meter without separate additional reflecting layers , such as for example additional metal plates applied onto a surface of the ultrasonic reflecting devices . Instead, the flow meter can rely on the reflection of the ultrasonic signal at the interface between the ultrasonic reflecting device and air, i . e . at an outer surface of the flow meter . This is particularly advantageous for the housing and the ultrasonic reflecting devices being made from plastics , as the reflection of the ultrasonic signal from the interface <plastics>/<air> is typically signi ficantly stronger than from the interface <flow medium>/<plastics>, wherein the flow medium may include one or more of : water, glycol , oil etc .

In some embodiments , the first and second ultrasonic reflecting devices are integrally formed with the housing .

The housing and the ultrasonic reflecting devices can therefore be produced from the same material and as a one- piece part of the flow meter . The housing and the ultrasonic reflecting device may for example be integrally produced by inj ection molding of plastics .

Integrally forming the first and second ultrasonic reflecting devices with the housing has the further advantage that the number of interfaces can be reduced, as the interface between the housing and the ultrasonic reflecting devices can be eliminated . Reducing the number of interfaces along the path of the ultrasonic signal has the advantage that signal loss can be reduced .

In some embodiments , the first and second ultrasonic reflecting devices are attached on the outer surface of the housing .

The first and second ultrasonic reflecting devices may be made of the same material as the housing, for example plastics . Attaching of the ultrasonic reflecting devices on the outer surface of the housing may enable an improved flexibility in the design of the ultrasonic reflecting devices . For example , restrictions on the design of the ultrasonic reflecting devices imposed when manufacturing the housing and the ultrasonic reflecting devices integrally, such as for example due to cooling in inj ection-molding, may be circumvented by attaching the ultrasonic reflecting devices on the outer surface of the housing .

The ultrasonic reflecting devices may be attached to the housing e . g . by gluing or welding, in particular ultrasonic welding .

In some embodiments , the first and second ultrasonic reflecting devices are monolithically formed and comprise each at least one outer reflecting surface configured to reflect a maj or portion of an ultrasonic signal incident to the respective first or second ultrasonic reflecting device .

Therefore , a <flow meter>/<air> or <housing>/<air> ( e . g . <plastics>/<air>) interface can be provided by the at least one outer reflecting surface , at which a maj or portion of the ultrasonic signal can be reflected . Monolithically forming the first and second ultrasonic reflecting devices has the advantage that no separate additional parts such as separate reflecting coatings or plates ( such as mirrors ) are required, and manufacturing of the flow meter can signi ficantly be simpli fied . Further, the number of interfaces can be reduced due to the monolithic design of the ultrasonic reflecting devices .

The at least one outer reflecting surface may comprise a slope with respect to the longitudinal axis of the housing . The slope may include an angle of inclination with the longitudinal axis of the housing of an absolute value between 20 ° and 30 ° , preferably between 23 ° and 27 ° .

In particular, the slope may be configured such that an ultrasonic signal is received by the first and second ultrasonic transducers , respectively, from the flow channel perpendicularly to the longitudinal axis of the housing .

In some embodiments , the first and second ultrasonic reflecting devices each comprise a plurality of subreflectors , wherein each sub-reflector is configured to reflect a portion of an ultrasonic signal incident to the respective first or second ultrasonic reflecting device .

As the sub-reflectors are each configured to reflect a portion of the ultrasonic signal , the plurality of subreflectors can ef fectively function as a single larger ( and unpartitioned, respectively) ultrasonic reflecting device . At the same time , partitioning the first and second ultrasonic reflecting devices into a plurality of sub-reflectors provides the advantage that the si ze of the first and second ultrasonic reflecting devices can be reduced . In particular, the height of the ultrasonic reflecting devices may be reduced by partitioning into a plurality of sub-reflectors .

In some embodiments , the sub-reflectors may exhibit a height between 1 and 5 mm, preferably 2 and 4 mm .

Reducing the si ze of the first and second ultrasonic devices may have , besides improving miniaturi zation of the flow meter, further advantages with regard to manufacturing of the flow meter . For example , detrimental strain ef fects in inj ection-molding manufacturing can be reduced or avoided by reducing the si ze and, in particular, the height of the ultrasonic reflecting devices .

The sub-reflectors may be arranged in a row along the longitudinal axis of the housing . In some embodiments , some sub-reflectors may be arranged in a row transverse to the longitudinal axis of the housing .

The first and second ultrasonic reflecting devices may each comprise two , three or four sub-reflectors .

Preferably, the sub-reflectors are monolithically formed and comprise each at least one outer reflecting surface configured to reflect a maj or portion of an ultrasonic signal incident to the respective sub-reflector .

Preferably, the at least one outer reflecting surface of a sub-reflector of the first ultrasonic reflecting device comprises a slope with a first angle of inclination and the at least one outer reflecting surface of a sub-reflector of the second ultrasonic reflecting device comprises a slope with a second angle of inclination, wherein the first angle of inclination and the second angle of inclination are preferably equal in absolute value .

The outer reflecting surfaces of the sub-reflectors of the first ultrasonic reflecting device may all exhibit a slope with a same first angle of inclination with respect to the longitudinal axis of the housing . The outer reflecting surfaces of the sub-reflectors of the second ultrasonic reflecting device may all exhibit a slope with a same second angle of inclination with respect to the longitudinal axis of the housing . Preferably, the first and second angles of inclination have the same absolute value .

The outer reflecting surfaces of the sub-reflectors of the first ultrasonic reflecting device may be mirror-symmetrical to the outer reflecting surfaces of the sub-reflectors of the second ultrasonic reflecting device with respect a plane perpendicular to the longitudinal axis of the housing .

The absolute value of the first and/or second angle of inclination may be between 20 ° and 30 ° , preferably between 23 ° and 27 ° .

In some embodiments , the outer reflecting surfaces each comprise a concave profile .

By using a concave profile , an improved focusing of the ultrasonic signal may be achieved .

The plurality of sub-reflectors of the first ultrasonic reflecting device may form a first Fresnel reflector and the plurality of sub-reflectors of the second ultrasonic reflecting device may form a second Fresnel reflector . The sub-reflectors of the respective Fresnel reflector may exhibit re flecting outer surfaces with equal angles of inclination, as described above .

Alternatively, the sub-reflectors of the respective Fresnel reflector may exhibit reflecting outer surfaces with varying angles of inclination . By using varying angles of inclination of the reflecting outer surfaces , an improved focusing of the ultrasonic signal may be achieved, similar to a concave profile , as described above .

In some embodiments , the sub-reflectors of the first and second ultrasonic reflecting devices are configured that the phase di f ference between portions of an ultrasonic signal reflected from neighboring sub-reflectors is an integer multiple of the wavelength of the ultrasonic signal in the housing .

By adj usting the dimensions and/or arrangements of the subreflectors such that the phase di f ference between portions of an ultrasonic signal reflected from neighboring subreflectors is an integer multiple of the wavelength of the ultrasonic signal in the housing, phase coherence can be maintained . In particular, destructive interference of portions of an ultrasonic signal reflected from neighboring sub-reflectors can be avoided . Adj usting the dimensions and/or arrangements of the sub-reflectors may include adj usting the height of the sub-reflectors and/or the spacing between neighboring sub-reflectors depending on the wavelength of the ultrasonic signal in the housing .

In some embodiments , the housing comprises an inner surface portion in a vicinity of the first and second ultrasonic reflecting devices which is parallel to the longitudinal axis of the housing .

In particular, the inner surface portion in the vicinity of the first and second ultrasonic reflecting devices may therefore form a straight portion of the flow channel along the longitudinal axis of the housing . A straight portion of the flow channel along the longitudinal axis of the housing has the advantage that the fluid may flow linearly and unperturbed . Attaching the ultrasonic reflecting devices on the outer surface of the housing therefore provides the advantage that obstacles in the flow channel along the longitudinal axis of the housing which may adversely af fect linear flow of the fluid can be reduced or eliminated . Further, avoiding obstacles within the flow channel by designing the flow channel to be straight along the longitudinal axis provides the advantage that aggregation of dirt can be reduced or avoided . Further, pressure loss due to obstacles within the flow channel may be reduced or minimi zed .

In some embodiments , the flow channel has along the longitudinal axis in a vicinity of the first and second ultrasonic transducers and the first and second ultrasonic reflecting devices covering the W-shaped path a cross-section with a constant area .

Therefore , the flow channel can be designed to be straight along the longitudinal axis and, in particular, without obstacles in the measurement-relevant region ( i . e . the vicinity covering the W-shaped path) , thereby improving measurement conditions such as linearity, reduction or avoidance of pressure loss , reduction or avoidance of dirt accumulation, etc .

In some embodiments , the first and second ultrasonic transducers each comprise a piezoelectric element attached onto the outer surface of the housing .

Attaching the first and second ultrasonic transducers on the outer surface of the housing provides the advantage that recesses and/or inserts in the housing to introduce the ultrasonic transducers can be avoided . Besides simpli fication in manufacturing, attaching the ultrasonic transducers on the outer surface of the housing provides the advantage that the flow channel can be designed to be straight along the longitudinal axis of the housing in the vicinity of the ultrasonic transducers .

The piezoelectric elements may for example be glued onto the housing .

In particular, an inner surface portion in the vicinity of the first and second ultrasonic transducers may be parallel to the longitudinal axis o f the housing .

Preferably, the first and second ultrasonic transducers are configured to emit the ultrasonic signal into the flow channel perpendicularly to the longitudinal axis of the housing .

For piezoelectric elements attached on the outer surface of the housing, emitting ultrasonic signal perpendicular to the longitudinal axis of the housing has the advantage that total reflection of the ultrasonic signal at the interface <housing>/<f low channel> before entry of the ultrasonic signal into the flow channel can be avoided .

Brief description of the drawings

The present invention will be explained in more detail , by way of exemplary embodiments , with reference to the schematic drawings , in which :

Fig . l shows a perspective view of an embodiment of a flow me ter ;

Fig . 2 shows a side view of the flow meter of Fig . l ;

Fig . 3 shows the flow meter of Fig . 2 in a vertical cut view along the longitudinal axis of the housing;

Fig . 4 shows a close-up of the first ultrasonic reflecting device of the flow meter of Fig . 2 with two exemplary portions of an ultrasonic signal reflected from the first ultrasonic reflecting device .

Detailed description of exemplary embodiments

Figure 1 shows an embodiment of a flow meter 1 in a perspective view . The flow meter 1 comprises a housing 11 with a longitudinal axis L and defining a flow channel for a fluid flow within the housing 11 . The housing 11 has a cylindrical shape. In other embodiments, the housing may have other shapes, such as for example comprising a rectangular cross section. On the outer surface 110 of the housing 11, there are arranged a first ultrasonic reflecting device 13 and a second ultrasonic reflecting device 14. In the shown embodiment, the first and second ultrasonic reflecting devices 13, 14 are integrally formed with the housing 11. In other embodiments, the first and second ultrasonic reflecting devices may be attached to the outer surface of the housing, for example by gluing or welding.

The first ultrasonic reflecting device 13 comprises a first sub-reflector 13.1 and a second sub-reflector 13.2 which are arranged in a row along the longitudinal axis L. Accordingly, the second ultrasonic reflecting device 14 comprises a first sub-reflector 14.1 and a second sub-reflector 14.2 arranged in a row along the longitudinal axis L. The sub-reflectors 13.1, 13.2 of the first ultrasonic reflecting device 13 and the sub-reflectors 14.1, 14.2 of the second ultrasonic reflecting device 14 are each monolithically formed and exhibit a prism-like shape protruding from the outer surface 110 of the housing 11.

In the shown embodiment, the housing 11 is made from injection-molded plastics. In other embodiments, the housing may be an additively manufactured plastics housing. In other embodiments, the housing may be made of metal.

Figure 2 shows a side view of the flow meter 1 of Figure 1. The first sub-reflector 13.1 of the first ultrasonic reflecting device 13 comprises an outer reflecting surface 13.11. The second sub-reflector 13.2 of the first ultrasonic reflecting device 13 comprises an outer reflecting surface 13.21. Accordingly, the first and second sub-reflectors 14.1, 14.2 of the second ultrasonic reflecting device 14 each comprise an outer reflecting surface 14.11 and 14.21, respectively. The outer surfaces 13.11, 13.21 of the first ultrasonic reflecting device 13 and the outer surfaces 14.11, 14.21 of the second ultrasonic reflecting device 14 are configured to respectively reflect each a portion of an ultrasonic signal incident to the respective ultrasonic reflecting device 13 and 14. Further, the outer surfaces

13.11, 13.21 of the first ultrasonic reflecting device 13 and the outer surfaces 14.11, 14.21 of the second ultrasonic reflecting device 14 are configured to respectively reflect each a major portion of an ultrasonic signal incident to the respective sub-reflector 13.1, 13.2 and 14.1, 14.2.

The outer surfaces 13.11 and 13.21 of the sub-reflectors 13.1 and 13.2 of the first ultrasonic reflecting device 13 exhibit a first angle of inclination

with respect to the longitudinal axis L. The first angle eg is between 20° and 30°. In other embodiments, the first angle eg may be between 23° and 27°. The outer reflecting surfaces 14.11 and 14.21 of the sub-reflectors 14.1 and 14.2 of the second ultrasonic reflecting device 14 exhibit a second angle of inclination eg with respect to the longitudinal axis L, wherein the first and second angles of inclination eg, eg have the same absolute value. The outer reflecting surfaces 13.11 and 13.21 of the sub-reflectors 13.1 and 13.2 of the first ultrasonic reflecting device 13 are mirror-symmetrical to the outer reflecting surfaces 14.11 and 14.21 of the sub-reflectors 14.1 and 14.2 of the second ultrasonic reflecting device 14 with respect to a plane perpendicular to the longitudinal axis L of the housing 11.

The sub-reflectors 13.11 and 13.21 form a first Fresnel reflector with equal angles of inclination eg of the outer reflecting surfaces 13.11 and 13.21. The sub-reflectors 14.1 and 14.21 in turn form a second Fresnel reflector with equal angles of inclination a₂ of the outer reflecting surfaces 14.11 and 14.21.

Opposite to the first ultrasonic reflecting device 13 with respect to the flow channel, there is arranged a first ultrasonic transducer 15 at the outer surface 110 of the housing 11. Specifically, the first ultrasonic transducer 15 comprises a piezoelectric element 151 glued onto the outer surface 110 of the housing 11. Accordingly, a second ultrasonic transducer 16 is arranged at the outer surface 110 of the housing 11 and opposite to the second ultrasonic reflecting device 14 with respect to the flow channel. The second ultrasonic transducer 16 also comprises a piezoelectric element 161 glued onto the outer surface 110 of the housing 11.

The first and second ultrasonic transducers 15, 16 are configured to emit an ultrasonic signal perpendicular to the longitudinal axis L into the flow channel. Further, the outer reflecting surfaces 13.11, 13.21 and 14.11, 14.21 are sloped with respect to the longitudinal axis L in a fashion that an ultrasonic signal emitted by one of the first or second ultrasonic transducers 15 or 16 is received by the other of the first or second ultrasonic transducers 15 or 16 perpendicular to the longitudinal axis L from the flow channel .

Figure 3 shows the flow meter 1 of Figure 2 in a vertical cut view along the longitudinal axis L of the housing 11 . The housing 11 defines the flow channel 12 for the fluid flow . A (partial ) ultrasonic signal USW emitted by the first ultrasonic transducer 15 propagates across the flow channel 12 and is reflected by the outer reflecting surface 13 . 11 of the first sub-reflector 13 . 1 of the first ultrasonic reflecting device 13 . The so-reflected ultrasonic signal USW propagates back across the flow channel 12 and is reflected by an intermediate wall portion 17 of the housing 11 arranged between the first and second ultrasonic transducers 15 and 16 and opposite to the first and second ultrasonic reflecting devices 13 and 14 with respect to the flow channel 12 . After reflection from the intermediate wall portion 17 , the ultrasonic signal USW propagates across the flow channel 12 and is reflected by the outer reflecting surface 14 . 21 of the second sub-reflector 14 . 2 of the second ultrasonic reflecting device 14 , in order to thereafter propagate across the flow channel 12 to the second ultrasonic transducer 16 which receives the ultrasonic signal USW . The first and second ultrasonic transducers 15 , 16 and the first and second ultrasonic reflecting devices 13 , 14 are therefore arranged to guide the ultrasonic signal USW along a W-shaped path . As a matter of course , the propagating direction of the ultrasonic signal USW may also be reversed, such that the second ultrasonic transducer 16 emits the ultrasonic signal USW which is received by the first ultrasonic transducer 15 after being guided along the W-shaped path.

The ultrasonic signal USW may be a partial ultrasonic signal of a total ultrasonic signal emitted by one of the first or second ultrasonic transducers 15 or 16 and received by the other of the first or second ultrasonic transducers 15 or 16, wherein the sub-reflectors 13.1, 13.2 and 14.1, 14.2 are respectively each configured to reflect a portion of the total ultrasonic signal, as illustrated in Figure 3. The subreflectors 13.1, 13.2 forming the first ultrasonic reflecting device 13 therefore exhibit a functionality of a single, large ultrasonic reflecting device. Accordingly, the subreflectors 14.1, 14.2 forming the second ultrasonic reflecting device 14 exhibit a functionality of another single, large ultrasonic reflecting device.

As illustrated in Figure 3, a major portion of the ultrasonic signal USW is reflected at the interface <first sub-reflector 13.1>/<air> (or <housing ll>/<air>, respectively, as the first sub-reflector 13.1 is integrally formed with the housing 11) . A minor (and negligible) portion of the ultrasonic signal USW reflected from the interface <housing ll>/<flow medium> is not shown in Figure 3 for the purpose of clearer illustration. Accordingly, a major portion of the ultrasonic signal USW reflected from the intermediate wall portion 17 is reflected at the interface <housing ll>/<air> and only a minor (negligible) portion of the ultrasonic signal USW is reflected at the interface <housing ll>/<flow medium> at the intermediate wall portion 17. Again, the reflection of a minor portion of the ultrasonic signal USW at the interface <housing ll>/<flow medium> at the intermediate wall portion 17 is not shown in Figure 3. Further, deviations from an exact W-shaped path due to refraction at interfaces <flow medium>/<housing> are not shown in Figure 3. In the context of the present disclosure, "W-shaped path" shall be understood to comprise, in particular, an essentially W- shaped path including deviations due to such refraction effects of the ultrasonic signal and/or due to imperfections of the housing and/or due to other perturbations due to e.g. dirt or inhomogeneities of the flow medium, etc.

The sub-reflectors 13.1, 13.2 and 14.1, 14.2 of the first and second ultrasonic reflecting devices 13 and 14 are dimensioned such that the phase difference between partial ultrasonic signals USW of a total ultrasonic signal reflected from neighboring sub-reflectors 13.1, 13.2 and 14.1, 14.2 is an integer multiple of the ultrasonic wavelength in the housing 11. For example, the height of the sub-reflectors 13.1, 13.2 and 14.1, 14.2 protruding from the outer surface 110 or the distance between neighboring sub-reflectors 13.1, 13.2 and 14.1, 14.2 may be adjusted such that the phase difference between partial ultrasonic signals USW of a total ultrasonic signal reflected from neighboring sub-reflectors 13.1, 13.2 and 14.1, 14.2 is an integer multiple of the ultrasonic wavelength in the housing 11.

The flow channel 12 has along the longitudinal axis L in a vicinity V (symbolized by the dotted-dashed double arrow) of the first and second ultrasonic transducers 15, 16 and the first and second ultrasonic reflecting devices 13, 14 covering the W-shaped path of the ultrasonic signal USW a cross-section with a constant area . In particular, an inner surface portion 111 in the vicinity V of the first and second ultrasonic reflecting devices 13 , 14 covering the lower hal f of the circumference of the flow channel 12 is parallel to the longitudinal axis L of the housing 11 . Further, an inner surface portion 112 in the vicinity V of the first and second ultrasonic transducers 15 , 16 covering the upper hal f of the circumference of the flow channel 12 is parallel to the longitudinal axis L of the housing 11 . Thus , a straight flow channel 12 without obstacles in the measurement-relevant region can be obtained owing to the arrangement of the first and second ultrasonic reflecting devices 13 , 14 at the outer surface 110 of the housing 11 and of the first and second ultrasonic transducers 15 , 16 at the outer surface 110 of the housing 11 .

Figure 4 shows a close-up of the first ultrasonic reflecting device 13 of the flow meter of Fig . 2 with two exemplary portions USW₂, USW₂ of an ultrasonic signal USW reflected from the first ultrasonic reflecting device 13 . The portion USW₂ of the ultrasonic signal USW is reflected from the first sub-reflector 13 . 1 , whereas the portion USW₂ of the ultrasonic signal USW is reflected from the second subreflector 13 . 2 . The sub-reflectors 13 . 1 , 13 . 2 are configured that the phase di f ference between the portions USW₂ and USW₂ is an integer multiple of the wavelength X of the ultrasonic signal USW in the housing, such that d=n *X, where n is an integer .

Claims

1. A flow meter (1) comprising a housing (11) with a longitudinal axis (L) and defining a flow channel (12) for a fluid flow, a first and a second ultrasonic transducer (15; 16) arranged at the flow channel and each configured to emit and receive ultrasonic signal into and from the flow channel, a first ultrasonic reflecting device (13) arranged at an outer surface (110) of the housing and opposite to the first ultrasonic transducer with respect to the flow channel, a second ultrasonic reflecting device (14) arranged at the outer surface of the housing and opposite to the second ultrasonic transducer with respect to the flow channel, wherein the first and second ultrasonic transducers and the first and second ultrasonic reflecting devices are arranged to guide an ultrasonic signal (USW) emitted by one of the first or second ultrasonic transducer and received by the other of the first or second ultrasonic transducer along a W-shaped path .

2. The flow meter (1) according to claim 1, wherein the first and second ultrasonic reflecting devices (13; 14) are arranged such that the ultrasonic signal (USW) guided along the W-shaped path is reflected between reflections at the first and second ultrasonic reflecting devices by an intermediate wall portion (17) of the housing (11) arranged between the first and second ultrasonic transducers (15; 16) and opposite to the first and second ultrasonic reflecting devices with respect to the flow channel (12) . The flow meter (1) according to claim 1 or 2, wherein the housing (11) is made from plastics, preferably injection-molded plastics, or metal or is made by additive manufacturing. The flow meter (1) according to claim 3, wherein the first and second ultrasonic reflecting devices (13; 14) are integrally formed with the housing (11) . The flow meter according to claim 3, wherein the first and second ultrasonic reflecting devices are attached on the outer surface of the housing. The flow meter (1) according to one of the preceding claims, wherein the first and second ultrasonic reflecting devices (13; 14) are monolithically formed and comprise each at least one outer reflecting surface (13.11, 13.21; 14.11, 14.21) configured to reflect a major portion of an ultrasonic signal (USW) incident to the respective first or second ultrasonic reflecting device . The flow meter (1) according to claim 6, wherein the at least one outer reflecting surface (13.11, 13.21; 14.11, 14.21) comprises a slope with respect to the longitudinal axis (L) of the housing (11) , wherein the slope preferably includes an angle of inclination (eg; eg) with the longitudinal axis (L) of the housing (11) of an absolute value between 20° and 30°, particularly preferably between 23° and 27°. The flow meter (1) according to one of the preceding claims, wherein the first and second ultrasonic reflecting devices (13; 14) each comprise a plurality of sub-reflectors (13.1, 13.2; 14.1, 14.2) , wherein each sub-reflector is configured to reflect a portion of an ultrasonic signal (USW) incident to the respective first or second ultrasonic reflecting device. The flow meter (1) according to claim 8, wherein the first and second ultrasonic reflecting devices (13; 14) each comprise two, three or four sub-reflectors (13.1, 13.2; 14.1, 14.2) . The flow meter (1) according to claim 8 or 9, wherein the sub-reflectors (13.1, 13.2; 14.1, 14.2) are monolithically formed and comprise each at least one outer reflecting surface (13.11, 13.21; 14.11, 14.21) configured to reflect a major portion of an ultrasonic signal (USW) incident to the respective sub-reflector. The flow meter (1) according to claim 10, wherein the at least one outer reflecting surface (13.11, 13.21) of a sub-reflector (13.1, 13.2) of the first ultrasonic reflecting device (13) comprises a slope with a first angle of inclination

and the at least one outer reflecting surface (14.11, 14.21) of a sub-reflector

(14.1, 14.2) of the second ultrasonic reflecting device (14) comprises a slope with a second angle of inclination (a₂) , wherein the first angle of inclination and («i) the second angle of inclination (a₂) are preferably equal in absolute value. The flow meter according to claim 10, wherein the outer reflecting surfaces each comprise a concave profile. The flow meter (1) according to one of the claims 8 to

12, wherein the sub-reflectors (13.1, 13.2; 14.1, 14.2) of the first and second ultrasonic reflecting devices (13; 14) are configured that the phase difference between portions (USWi, USW₂) of an ultrasonic signal (USW) reflected from neighboring sub-reflectors is an integer multiple of the ultrasonic wavelength (X) in the housing (11) . The flow meter (1) according to one of the preceding claims, wherein the housing (11) comprises an inner surface portion (111) in a vicinity (V) of the first and second ultrasonic reflecting devices (13; 14) which is parallel to the longitudinal axis (L) of the housing (11) • The flow meter (1) according to one of the preceding claims, wherein the flow channel (12) has along the longitudinal axis (L) in a vicinity (V) of the first and second ultrasonic transducers (15; 16) and the first and second ultrasonic reflecting devices (13; 14) covering the W-shaped path a cross-section with a constant area. The flow meter (1) according to one of the preceding claims, wherein the first and second ultrasonic transducers (15; 16) each comprise a piezoelectric element (151; 161) attached onto the outer surface (110) of the housing (11) . The flow meter (1) according to one of the preceding claims, wherein the first and second ultrasonic transducers (15; 16) are configured to emit the ultrasonic signal (USW) into the flow channel (12) perpendicularly to the longitudinal axis (L) of the housing (11) . The flow meter (1) according to claim 6 and one of the preceding claims, wherein the at least one outer reflecting surface (13.11, 13.21; 14.11, 14.21) comprises a slope with respect to the longitudinal axis

(L) of the housing (11) , wherein the slope is configured such that the ultrasonic signal (USW) is received by the first and second ultrasonic transducers (15; 16) from the flow channel (12) perpendicularly to the longitudinal axis of the housing.