ULTRASONIC TRANSDUCER, ULTRASONIC FLOW METER AND METHOD

Description

[0001] The invention relates to an ultrasonic transducer for an ultrasonic flow meter, comprising a transducer housing and a transducer element, wherein the transducer housing has an ultrasonic window and wherein the transducer element is arranged in the transducer housing and is configured to transmit ultrasonic signals to a signal path and to receive ultrasonic signals from the signal path, and comprising a control and evaluation unit for controlling the transducer element and evaluating the ultrasonic signals. The invention further relates to an ultrasonic flow meter and a method for operating an ultrasonic flow meter.

[0002] Ultrasonic flow meters are known in large numbers from the prior art and are used to determine the flow rate of a flowing medium through a measuring tube. For this purpose, ultrasonic flow meters generally have at least two ultrasonic transducers, which are designed as ultrasonic transmitters and / or ultrasonic receivers and are arranged spaced apart from each other in the direction of flow (axially with respect to the measuring tube axis). To determine the flow rate, an ultrasonic signal is emitted along a signal path between the ultrasonic transducers, once in the direction of flow of the medium and once against the direction of flow. The transit time of the ultrasonic signal(s), which differ from each other due to the medium's entrainment effect, is then determined.The flow velocity of the medium can be determined from the difference in transit time, and the volumetric flow rate of the medium can be calculated from the flow velocity and the cross-sectional area of ​​the measuring tube.

[0003] The ultrasonic signals are generated and received by a transducer element located within the transducer housing of the ultrasonic transducer. In practice, these transducer elements are usually electromechanical, operating on the piezoelectric effect. The ultrasonic signals are then transmitted into the measuring tube via the ultrasonic window of the transducer housing and received via the ultrasonic window of the transducer housing.

[0004] Ultrasound is transmitted well in liquids, which exhibit low attenuation of ultrasound. In air, however, ultrasound signals are strongly attenuated. If there is no medium in the measuring tube, the transmission of ultrasound from one transducer to another is extremely attenuated, so that little or no ultrasound signal can be received. In practice, however, the case of an empty measuring tube is not easily distinguishable from the case of a defective transducer element. In both cases, the receiving transducer receives no or only a very weak ultrasound signal.

[0005] From DE 10 2007 062 913 A1, an ultrasonic transducer is known which, in addition to a transducer element, also has a buffer element. The buffer element serves to guide ultrasonic waves generated by the transducer element through the buffer element to the measuring tube wall or into the medium. Furthermore, the ultrasonic signal emitted by the transducer element is reflected at an interface of the buffer element. The reflected ultrasonic signal is received again by the transducer element and used for self-analysis of the ultrasonic transducer. A disadvantage of the ultrasonic transducers and ultrasonic flowmeters known from the prior art is that it is not readily possible to distinguish between an empty tube condition and a fault condition of the ultrasonic transducer.

[0006] The invention is therefore based on the objective of providing an ultrasonic transducer and an ultrasonic flow meter that exhibit enhanced fault detection capabilities. Furthermore, the invention is based on the objective of providing a method for operating the ultrasonic transducer and the ultrasonic flow meter.

[0007] In the ultrasonic transducer in question, a buffer element is arranged in or on the transducer housing within the signal path. This buffer element forms at least a partially reflective boundary layer within the signal path. During operation, the transducer emits an ultrasonic signal, which is at least partially reflected at the boundary layer of the buffer element. The reflected signal component is then received back by the transducer element. The transmitted signal component is emitted through the ultrasonic window.

[0008] When it is stated that the buffer element is arranged in the converter housing, this means that the buffer element is arranged inside the converter housing. When it is stated that the buffer element is arranged on the converter housing, this means that the buffer element is connected to the converter housing, at least indirectly (which is not within the scope of protection of the claim), preferably directly.

[0009] This does not mean that the buffer element is positioned outside the converter housing, spaced away from it and not connected to it.

[0010] Furthermore, the control and evaluation unit is designed to monitor the reception of the reflected signal component during the operation of the ultrasonic transducer. If no reflected signal component is received, the control and evaluation unit detects a fault in the ultrasonic transducer.

[0011] The design of the ultrasonic transducer allows for easy detection of whether the transducer element has generated and emitted an ultrasonic signal. If this is not the case, no signal component is reflected at the boundary layer of the buffer element and consequently is not received again by the transducer element. The absence of reception of the reflected signal component is detected by the control and evaluation unit. This allows a user to easily determine whether a fault condition of the ultrasonic transducer exists. In a preferred embodiment, the control and evaluation unit is further designed to signal a detected fault condition with an error signal. This signaling can be carried out in various ways, for example, by outputting a visual or audible warning signal. Alternatively, an error code can be generated and output.

[0012] In an alternative embodiment of the ultrasonic transducer, a buffer element is also arranged in the signal path and forms at least a partially reflective boundary layer (10) within the signal path. In contrast to the embodiment described above, a second transducer element is arranged in the transducer housing. During operation, the transducer element emits an ultrasonic signal that is at least partially reflected at the boundary layer of the buffer element. The second transducer element is arranged in the transducer housing such that the reflected signal component is received by the second transducer element. It is particularly preferred that the second transducer element is designed solely for receiving ultrasonic signals.In the alternative design, the control and evaluation unit is configured in such a way that, in the operating state of the ultrasound transducer, it monitors the reception of the reflected signal component and detects a fault condition of the ultrasound transducer if no reflected signal component is received.

[0013] This alternative design is particularly advantageous when the emitted ultrasonic signal does not strike the partially reflective boundary layer perpendicularly and is thus reflected at an angle of reflection equal to the angle of incidence. This situation occurs particularly with ultrasonic transducers in clamp-on ultrasonic flowmeters. Clamp-on ultrasonic flowmeters are clamped externally onto the measuring tube through which the medium to be measured flows. Such flowmeters usually have two ultrasonic transducers. The ultrasonic transducers, or rather the transducer elements of the ultrasonic transducers, are then oriented at an oblique angle to the surface of the measuring tube, so that the ultrasonic signals are emitted into the measuring tube at an oblique angle. This is ensured by the geometry of the buffer element. For this purpose, the buffer element has, for example, a triangular cross-section.

[0014] The buffer element is implemented in different ways in various embodiments of the ultrasound transducer according to the invention.

[0015] Preferably, the boundary layer is formed on the side of the buffer element facing away from the transducer element. The emitted ultrasound signal then preferably travels the entire length of the buffer element along the signal path before being partially reflected on the side of the buffer element facing away from the transducer element. The reflected signal component travels through the buffer element again along the signal path before being received again by the transducer element. The buffer element thus ensures a time interval between the transmission of the ultrasound signal and the reception of the partially reflected signal component.

[0016] According to the invention, the buffer element is formed by the ultrasonic window. The ultrasonic window has an increased thickness, the thickness being defined as the extent of the ultrasonic window along the signal path of the ultrasonic signal.

[0017] In one variant, the buffer element formed by the ultrasonic window protrudes into the transducer housing. In an alternative embodiment, the buffer element formed by the ultrasonic window protrudes out of the transducer housing.

[0018] In principle, the ultrasonic window can be formed integrally with the transducer housing, whereby "integral" means that the transducer housing and ultrasonic window are manufactured as a single component and are not joined together. Alternatively, the ultrasonic window can be implemented as a separate component that is directly connected to the transducer housing. In particular, a medium-tight connection between the ultrasonic window and the transducer housing is necessary to prevent the medium from entering the interior of the transducer housing. The ultrasonic window can, for example, be welded to the transducer housing.

[0019] In an example of an ultrasonic transducer that is not covered by the scope of protection of the claim, the buffer element is designed as a separate component. This design has the advantage that the buffer element can be replaced if necessary.

[0020] The buffer element is preferably arranged between the transducer element and the ultrasonic window inside the transducer housing. It is further preferred that the transducer element is arranged directly adjacent to the buffer element.

[0021] In a further particularly preferred embodiment of the ultrasound transducer according to the invention, the buffer element forms a first boundary layer and at least one second boundary layer in the signal path of the ultrasound signal. The ultrasound signal is at least partially reflected at the first boundary layer, with the reflected signal component being reflected from the first boundary layer to the second boundary layer. Particularly preferably, the reflected signal component strikes the second boundary layer perpendicularly. The reflected signal component is reflected back from the second boundary layer to the first boundary layer and from there back to the transducer element, by which it is received again.

[0022] Such a design is particularly advantageous when the ultrasonic transducer is used in a clamp-on ultrasonic flowmeter.

[0023] To further increase the partial reflection of the ultrasound signal at the interface, a particularly preferred embodiment of the ultrasound transducer according to the invention provides for the application of a coating that enhances partial reflection to the interface formed by the buffer element. Such a configuration is particularly advantageous when measuring a medium that has similar acoustic properties to the transducer element or the ultrasound window of the transducer element, such that – without an additional coating – no or hardly any partial reflection occurs.

[0024] A particularly preferred ultrasonic transducer according to the invention is characterized in that the control and evaluation unit is designed such that, during the operating state of the ultrasonic transducer, it determines a quantity describing the reflected signal component and compares it with a reference value for this quantity. In a preferred embodiment, such a quantity is the intensity of the reflected signal component. The reference value is the value of the quantity when the ultrasonic transducer is functioning correctly. If the determined quantity deviates from the reference value beyond a predetermined tolerance range, the control and evaluation unit outputs an error signal. Such a design of the ultrasonic transducer enables enhanced fault diagnostics of the ultrasonic transducer.Monitoring the partially reflected signal component allows not only for the functionality of the transducer element in the ultrasonic transducer to be determined, but also for the quantity describing the reflected signal component to be detected. Furthermore, monitoring this quantity can reveal whether the transducer element has changed its position within the transducer, for example, by becoming detached and shifting, or whether other defects exist that do not, however, lead to a total failure of the transducer element. All such circumstances would have an impact on the quantity describing the reflected signal component.

[0025] In addition to the ultrasonic transducer, the invention also relates to an ultrasonic flow meter for determining the flow rate of a flowing medium. The ultrasonic flow meter comprises a first ultrasonic transducer and a second ultrasonic transducer and also includes a control and evaluation unit. The ultrasonic transducers are configured to transmit an ultrasonic signal to a signal path and / or to receive an ultrasonic signal from the signal path and are operatively interconnected via the ultrasonic signal path.

[0026] When it is said that the ultrasound transducers are interconnected via the signal path, this means that at least one of the ultrasound transducers receives the ultrasound signal sent by the other ultrasound transducer via the signal path.

[0027] In the ultrasonic flowmeter in question, the problem is solved primarily and essentially by the fact that at least one ultrasonic transducer configured for transmission has a buffer element, that the buffer element is arranged in or on the transducer housing within the ultrasonic signal path, and that the buffer element forms at least a partially reflective boundary layer within the signal path. According to the invention, the buffer element is formed by the ultrasonic window. The ultrasonic window has an increased thickness, the thickness being defined as the extent of the ultrasonic window along the ultrasonic signal path. The buffer element formed by the ultrasonic window projects into or out of the transducer housing.

[0028] In the operating state of the ultrasonic flow meter, the transducer element of the transmitting ultrasonic transducer emits an ultrasonic signal, whereby the ultrasonic signal is at least partially reflected and partially transmitted at the boundary layer of the buffer element.

[0029] In a first embodiment of the ultrasonic flowmeter according to the invention, the reflected signal component is received by the transducer element of the transmitting ultrasonic transducer. In an alternative embodiment of the ultrasonic flowmeter according to the invention, a second transducer element is arranged in the transducer housing of the transmitting ultrasonic transducer. Here, the reflected signal component is received by the second transducer element of the transmitting ultrasonic transducer.

[0030] In both variants, the transmitted signal component is received by the transducer element of the receiving ultrasound transducer.

[0031] According to the invention, both variants are further provided in such a way that the control and evaluation unit is designed in such a way that, in the operating state of the ultrasonic flow meter, it monitors the reception of the reflected signal component and the reception of the transmitted signal component and recognizes one of the following operating states of the ultrasonic flow meter: If the reflected signal component is received and the transmitted signal component is received: ultrasonic flow meter is functional; if the reflected signal component is received but the transmitted signal component is not received: ultrasonic flow meter is functional, measuring tube is empty; if the reflected signal component is not received and the transmitted signal component is not received: ultrasonic flow meter is in fault condition, in particular the transmitting ultrasonic transducer is in fault condition, in particular the transducer element of the transmitting ultrasonic transducer is in fault condition.

[0032] Particularly preferably, the control and evaluation unit is further configured to signal the detected operating state of the ultrasonic flowmeter. This signaling can be achieved, for example, by various optical or acoustic signals, or in other ways known from the prior art.

[0033] In particularly preferred embodiments of the flow meter according to the invention, the ultrasonic transducers are configured with features of the previously described ultrasonic transducer according to the invention. Accordingly, all descriptions made in connection with the ultrasonic transducer according to the invention, with regard to preferred embodiments and their advantages, are also analogously transferable to the ultrasonic flow meter according to the invention and apply accordingly.

[0034] In a particularly preferred embodiment of the ultrasonic flowmeter, the control and evaluation unit is designed such that it evaluates the transmitted signal component as "not received" if the transmitted signal component is below a predefined threshold. This threshold can be, for example, an intensity value or an amplitude value. This design takes into account that the ultrasonic signal propagates even with an empty measuring tube, although it is attenuated to a very high degree. It is therefore conceivable that a small portion of the ultrasonic signal—albeit an extremely small one—can be received even with an empty measuring tube. However, if the transmitted signal component is below the threshold—which may be predefined, particularly by a user—the measuring tube is nevertheless recognized as "empty."

[0035] A method for monitoring the function of an ultrasonic transducer is also described. The ultrasonic transducer comprises a transducer housing and a transducer element, wherein the transducer housing has an ultrasonic window and the transducer element is arranged in the transducer housing and is configured to transmit ultrasonic signals to a signal path and to receive ultrasonic signals from the signal path. The ultrasonic transducer also includes a control and evaluation unit for controlling the transducer element and for evaluating the ultrasonic signals. Furthermore, a buffer element is provided, which is arranged in the signal path of the ultrasonic signals and forms at least a partially reflective boundary layer in the signal path with respect to the surroundings of the buffer element.

[0036] In one variant, a second transducer element is arranged in the transducer housing of the ultrasonic transducer.

[0037] The described method is characterized by the fact that, in a transmission step, an ultrasonic signal is first emitted, whereby the ultrasonic signal is at least partially reflected at the interface. The ultrasonic signal is emitted by the transducer element of the ultrasonic transducer. In a subsequent reception step, the reflected signal component is received by the transducer element of the ultrasonic transducer or by a second transducer element arranged in the transducer housing. In a monitoring step, the reception of the reflected signal component is monitored. If no reflected signal component is received, this absence is detected in a signaling step, and an error condition is indicated.

[0038] The described method provides a very simple way to test the functionality of an ultrasonic transducer without the need for separate test equipment. If a reflected signal component is received, it must have been previously emitted, meaning the transducer element must be functioning correctly. If the reflected signal component is not received, the user must assume that no ultrasonic signal was emitted and that the transducer element is faulty, for example, defective.

[0039] In a preferred embodiment of the described method, a quantity describing the reflected signal component, in particular the intensity of the reflected signal component, is compared with a reference value in a comparison step. If a deviation exceeds a predetermined tolerance value, an error signal is output. This additional method step enables a more comprehensive functional test of the ultrasonic transducer, since it not only monitors whether the transducer element emits an ultrasonic signal, but also whether the emitted ultrasonic signal changes, for example, due to a change in the position of the transducer element within the transducer housing.

[0040] The described method is particularly suitable for monitoring the functionality of the previously described ultrasound transducer according to the invention. Accordingly, all aspects described for the ultrasound transducer can be applied analogously to this method.

[0041] Furthermore, the invention relates to a method for operating an ultrasonic flow meter, wherein the ultrasonic flow meter comprises a first ultrasonic transducer, a second ultrasonic transducer, and a control and evaluation unit. The ultrasonic transducers are configured to transmit an ultrasonic signal to a signal path and / or to receive an ultrasonic signal from the signal path and are operatively interconnected via the ultrasonic signal path. At least one transmitting ultrasonic transducer has a buffer element, wherein the buffer element is arranged in the ultrasonic signal path and forms at least a partially reflective boundary layer in the signal path.The buffer element is formed by the ultrasonic window, wherein the ultrasonic window has an increased thickness, the thickness being defined as the extent of the ultrasonic window along the signal path of the ultrasonic signal, and wherein the buffer element formed by the ultrasonic window extends into or out of the transducer housing.

[0042] The method according to the invention is characterized in that, in a transmission step, the transmitting transducer element emits an ultrasonic signal, wherein the ultrasonic signal is at least partially reflected and partially transmitted at the interface of the buffer element. In a reception step, the transducer element of the transmitting ultrasonic transducer, or a second transducer element arranged within the transmitting ultrasonic transducer, receives the reflected signal component, and the transducer element of the receiving ultrasonic transducer receives the transmitted signal component. In a monitoring step, the control and evaluation unit monitors the reception of the reflected signal component and the reception of the transmitted signal component. In a subsequent signaling step, one of the following operating states of the ultrasonic flowmeter is signaled by the control and evaluation unit: If the reflected signal component is received and the transmitted signal component is received: ultrasonic flow meter is functional; if the reflected signal component is received but the transmitted signal component is not received: ultrasonic flow meter is functional, measuring tube is empty; if the reflected signal component is not received and the transmitted signal component is not received: ultrasonic flow meter is in fault condition, in particular the transmitting ultrasonic transducer is in fault condition, in particular the transducer element of the transmitting ultrasonic transducer is in fault condition.

[0043] The method according to the invention makes it possible to easily distinguish between a fault in a transducer element or an ultrasonic transducer and an empty measuring tube. A particularly preferred embodiment of the method according to the invention is characterized in that the transmitted signal component is then evaluated as "not received" if it is below a predetermined limit value. For example, an intensity value or an amplitude value can be used as the basis for the limit value. This embodiment of the method makes it possible to detect an empty measuring tube even if the transmitted ultrasonic signals are not completely attenuated.

[0044] The method according to the invention is particularly suitable for operating the ultrasonic flow meter described above. Accordingly, all embodiments described for the ultrasonic flow meter can be applied analogously to the method.

[0045] In detail, there are now several possibilities for designing and further developing the ultrasonic transducer and the ultrasonic flowmeter according to the invention. Furthermore, there are several possibilities for carrying out the method according to the invention. Reference is made to the dependent claims and to the description of preferred embodiments in conjunction with the drawing. The drawing shows Fig. 1 an example of an ultrasonic transducer that is not covered by the scope of protection of the claim, Fig. 2 a first embodiment of an ultrasonic transducer, Fig. 3 a second embodiment of an ultrasonic transducer, Fig. 4 a first variant of an ultrasonic flowmeter, Fig. 5 a second variant of an ultrasonic flowmeter, Fig. 6 a fourth embodiment of an ultrasonic transducer, Fig. 7 a fifth embodiment of an ultrasonic transducer, Fig. 8 a method for monitoring the function of an ultrasonic transducer and Fig. 9 a method for operating an ultrasonic flowmeter.

[0046] Fig. 1 shows an example of an ultrasonic transducer 1 that is not covered by the scope of protection of the claim, for a device in Fig. 4 The ultrasonic flowmeter 2 is shown. The ultrasonic transducer 1 has a transducer housing 3 and a transducer element 4. The transducer housing has an ultrasonic window 5 through which ultrasonic waves are emitted or received by the ultrasonic transducer 1. The transducer element 4 is arranged in the transducer housing 3 and serves to transmit ultrasonic signals 6 to a signal path 7 or to receive ultrasonic signals 6 from the signal path 7. In addition, the ultrasonic transducer 1 has a control and evaluation unit 8 for controlling the transducer element 4 and evaluating the ultrasonic signals 6. In the case of the Fig. 1 In the illustrated ultrasonic transducer 1, a buffer element 9 is arranged in the signal path 7 within the transducer housing 3. The buffer element 9 forms a partially reflective boundary layer 10 in the signal path 7, located on the side of the buffer element 9 facing away from the transducer element 4. In the operating state of the ultrasonic transducer 1, the transducer element 4 emits an ultrasonic signal 6, which is at least partially reflected at the boundary layer 10, as shown in Fig. 1 The reflected signal component 11 is indicated by a dashed line. The transmitted signal component 12 is also shown, indicated by a dotted-dashed line. The transducer element 4 receives the reflected signal component 11. The ultrasonic transducer 1 shown has the special feature that the control and evaluation unit 8 is designed to monitor the reception of the reflected signal component 11 when the ultrasonic transducer 1 is operating. If the reflected signal component 11 is received by the transducer element 4, the ultrasonic transducer 1 is functioning correctly. However, if the reflected signal component 11 is not received, i.e., no signal is received by the transducer element 4, the control and evaluation unit 8 detects a fault in the ultrasonic transducer 1.The control and evaluation unit 8 shown is further designed to signal the fault condition. In addition, the control and evaluation unit 8 is designed to compare the intensity of the reflected signal component 11 with a reference value for the intensity of the reflected signal component 11 when the ultrasonic transducer 1 is functioning correctly. If there is a deviation exceeding a predefined tolerance range, the control and evaluation unit detects a fault condition. This is the case, for example, if the transducer element 4 has become detached and its position within the transducer housing 3 has changed.

[0047] The in Fig. 1 The illustrated example of the ultrasonic transducer 1, which is not covered by the scope of the claim, has a buffer element 9 designed as a separate component. The buffer element 9 is formed inside the transducer housing 3 and arranged between the transducer element 4 and the ultrasonic window 5. The reflective boundary layer 10 is formed between the buffer element 9 and the ultrasonic window 5.

[0048] In contrast to the one in Fig. 1 The illustrated embodiments are in the Fig. 2 and 3 Ultrasound transducer 1 is shown, in which the buffer element 9 is formed by the ultrasound window 5. In the case of the Fig. 2 In the illustrated embodiment, the ultrasound window 5 has a thickness d and projects into the transducer housing 3. In the embodiment shown Fig. 3 In the illustrated configuration, the ultrasound window 5 protrudes into the outer space of the ultrasound transducer 1.

[0049] At the in Fig. 3 In the illustrated ultrasonic transducer 1, the buffer element 9 has a coating 13 on its side facing away from the transducer element 4, which serves to improve the reflection properties of the boundary layer 10, e.g. to increase them.

[0050] Fig. 4 shows an ultrasonic flow meter 2, which displays two of the in Fig. 1 The ultrasonic flowmeter 2 has the illustrated ultrasonic transducer 1. It also includes a control and evaluation unit 14. In the illustrated embodiment, both ultrasonic transducers 2 are designed to both transmit and receive ultrasonic signals 6. The two ultrasonic transducers 1 are arranged on opposite sides of the measuring tube 15 and are further offset from each other in the flow direction, as indicated by the arrow. The two ultrasonic transducers are interconnected via the signal path 7. In the illustrated embodiment, the ultrasonic transducers 1 are arranged in transducer pockets 16 of the measuring tube 15.In the operating state of the ultrasonic flowmeter 2, the transducer element 4 of a transmitting ultrasonic transducer 1 emits an ultrasonic signal 6, whereby the ultrasonic signal 6 is at least partially reflected and partially transmitted at the interface 10 of the buffer element 9 of the transmitting ultrasonic transducer 1. The reflected signal component 11 is then received by the transducer element 4 of the transmitting ultrasonic transducer 1, and the transmitted signal component 12 is received by the transducer element 4 of the receiving ultrasonic transducer 1.

[0051] The control and evaluation unit 14 of the ultrasonic flow meter 2 is designed such that, during the operating state of the ultrasonic flow meter 2, it monitors the reception of the reflected signal component 11 and the reception of the transmitted signal component 12. Depending on which signal components are received by the transducer elements 4, the control and evaluation unit 14 detects and signals one of the following operating states of the ultrasonic flow meter 2: When the reflected signal component 11 and the transmitted signal component 12 are received: ultrasonic flow meter 2 is functional; when the reflected signal component 11 is received and the transmitted signal component 12 is not received: ultrasonic flow meter is functional, measuring tube 15 is empty; when the reflected signal component 11 and the transmitted signal component 12 are not received: ultrasonic flow meter 2 is in a fault state, in particular the transmitting ultrasonic transducer is in a fault state, in particular the transducer element 4 of the transmitting ultrasonic transducer 1 is in a fault state.

[0052] In the illustrated embodiment of the ultrasonic flowmeter 2, the ultrasonic transducers 1 are arranged according to the in Fig. 1 The illustrated embodiment is designed as follows. However, one of the other configurations or a combination thereof, i.e., a different configuration of the two ultrasonic transducers 1, is also conceivable. The control and evaluation unit 14 is further configured such that it evaluates the transmitted signal component 12 as "not received" if the transmitted signal component 12 is below a predetermined limit value. In this case, an intensity value of the transmitted signal component 12 is used as the limit value.

[0053] Fig. 5 Figure 1 shows an ultrasonic flowmeter 2, designed as a clamp-on ultrasonic flowmeter. The ultrasonic flowmeter 2 is clamped onto the measuring tube 15 from the outside. The clamping mechanism is not shown here, as it is not relevant to the present invention. The ultrasonic flowmeter 2 has two ultrasonic transducers 1. Each ultrasonic transducer 1 has a transducer element 4 and a buffer element 9. The transducer elements 4 are oriented such that they radiate onto the surface of the measuring tube at an oblique angle. This is achieved by the buffer element 9, or buffer elements 9, having a substantially triangular cross-section.In the present illustration, the signal paths of the ultrasonic signals 6 are shown only schematically, as the course of the signal paths 6 depends on the materials used for the buffer element 9, the measuring tube 15, and also the medium transported in the measuring tube 15. The transducer element 4 of the transmitting ultrasonic transducer 2 emits an ultrasonic signal 6, which is reflected at the interface 10 formed between the buffer element 9 and the surface of the measuring tube. Here, the angle of incidence corresponds to the angle of reflection, so that the reflected signal component 11 is reflected at the same angle at which it strikes the interface 10. The reflected signal component 10 then encounters a second interface 10' formed by the buffer element 9.From here, the reflected signal component 11 is reflected back to the boundary layer 10 and from there back to the transducer element 4, which receives the reflected signal component. The transmitted signal component 12 is emitted into the measuring tube 15 and is reflected off the inside of the measuring tube towards the second transducer element 4 of the second ultrasonic transducer 2. This transducer element 4 then receives the transmitted signal component 12.

[0054] In the Fig. 6 is the ultrasound transducer of the in Fig. 5 The ultrasonic flowmeter 2 is shown. The ultrasonic transducer 1 has a housing 3 in which a transducer element 4 is located. The ultrasonic transducer 1 has a buffer element 9 that forms a first boundary layer 10 and a second boundary layer 10' in the beam path of the ultrasonic signal 6. As already mentioned in connection with Fig. 5 As explained, the transducer element 4 emits ultrasonic signals 6, which are partially reflected at the interface 10. The angle of incidence of the reflected signal component 11 corresponds to the angle of incidence of the ultrasonic signal 6. The reflected signal component 11 is reflected to the second interface 10' and strikes it perpendicularly. From here, the reflected signal component is reflected back to the interface 10 and from there back to the transducer element 4. The control and evaluation unit 8 of the ultrasonic transducer 1 is designed to monitor the reception of the reflected signal component 11 and, if it is absent, to detect a fault condition of the ultrasonic transducer 1.

[0055] An alternative design of an ultrasound transducer 1 is in Fig. 7 The ultrasonic transducer 1 is shown here with a first transducer element 4, which is designed and used for transmitting and receiving ultrasonic signals. However, the ultrasonic transducer 1 also has a second transducer element 4', which is used to receive the reflected signal component 11. In contrast to the one shown in Fig. 6 In the illustrated embodiment, the reflected signal component 11 is not reflected back to the transducer element 4, but is received by the transducer element 4'. The control and evaluation unit 8 is then designed to monitor the reception of the reflected signal component 11 by the second transducer element 4'. If the reflected signal component 11 is absent, the control and evaluation unit 8 detects an error condition.

[0056] Fig. 8 shows a method 100 for functional monitoring of an ultrasonic transducer, as used in the Fig. 1 bis 3 and 6The process is illustrated. In a transmission step 101, an ultrasound signal is emitted, whereby the ultrasound signal is at least partially reflected at the interface. In a reception step 102, the reflected signal component is received by the transducer element. In a monitoring step 103, the reception of the reflected signal component is monitored, and in a signaling step 104, an error condition is signaled if a reflected signal component is not received.

[0057] Fig. 9 shows a method 200 for operating an ultrasonic flow meter, as described in Fig. 4The process is illustrated. In the illustrated method, an ultrasonic signal is emitted by the transmitting transducer element in a transmission step 201, whereby the ultrasonic signal is at least partially reflected and partially transmitted at the interface of the buffer element. In a reception step 202, the transducer element of the transmitting ultrasonic transducer receives the reflected signal component, and the transducer element of the receiving ultrasonic transducer receives the transmitted signal component. In a monitoring step 203, the control and evaluation unit monitors the reception of the reflected signal component and the reception of the transmitted signal component. In a signaling step 204, one of the following operating states of the ultrasonic flowmeter is signaled by the control and evaluation unit: If the reflected signal component is received and the transmitted signal component is received: ultrasonic flow meter is functional; if the reflected signal component is received but the transmitted signal component is not received: measuring tube is empty; if the reflected signal component is not received and the transmitted signal component is not received: ultrasonic flow meter is in a fault state, in particular the transducer element of the transmitting ultrasonic transducer is in a fault state.

[0058] In the described method, the transmitted signal component is considered "not received" if it falls below a predefined threshold. This threshold is defined as an intensity value of the transmitted signal component. Reference sign

[0059] 1 Ultrasonic transducer 2 Ultrasonic flow meter 3 Transducer housing 4 Transducer element 4' Second transducer element 5 Ultrasonic window 6 Ultrasonic signal 7 Signal path 8 Control and evaluation unit 9 Buffer element 10 Boundary layer 10' Second boundary layer 11 Reflected signal component 12 Transmitted signal component 13 Coating 14 Control and evaluation unit 15 Measuring tube 16 Transducer pocket 100 Procedure 101 Transmit step 102 Receive step 103 Monitoring step 104 Signaling step 200Procedure 201Transmit step 202Receive step 203Monitoring step 204Signaling step 1

Claims

1. Ultrasonic transducer (1) for an ultrasonic flowmeter (2), comprising a transducer housing (3) and a transducer element (4), wherein the transducer housing (3) has an ultrasound window (5) and wherein the transducer element (4) is arranged in the transducer housing (3) and is designed to emit ultrasonic signals (6) to a signal path (7) and designed to receive ultrasonic signals (6) from the signal path (7), and comprising a control and evaluation unit (8) for controlling the transducer element (3) and evaluating the ultrasonic signals (6), wherein a buffer element (9) is arranged in or on the transducer housing (3) within the signal path (7) such that the buffer element (9) forms at least one at least partially reflective boundary layer (10) in the signal path (7), wherein, during operation of the ultrasonic transducer (1), the transducer element (4) emits an ultrasonic signal (6), wherein the ultrasonic signal (6) is at least partially reflected at the boundary layer (10) of the buffer element (9), and wherein the reflected signal component (11) is received by the transducer element (4), and wherein the control and evaluation unit (8) is designed such that, when the ultrasonic transducer (1) is in operation, it monitors the reception of the reflected signal component (11) and, if no reflected signal component (11) is received, detects an error state of the ultrasonic transducer (1), characterized in that the buffer element (9) is formed by the ultrasound window (5), and that the ultrasound window (5) has an increased thickness, wherein the thickness is defined as the extent of the ultrasound window (5) along the signal path (7) of the ultrasonic signal (6), and that the buffer element (9) formed by the ultrasound window (5) protrudes into the transducer housing (3) or protrudes out of the transducer housing (3).

2. Ultrasonic transducer (1) for an ultrasonic flowmeter (2), comprising a transducer housing (3) and a transducer element (4), wherein the transducer housing (3) has an ultrasound window (5) and wherein the transducer element (4) is arranged in the transducer housing (3) and is designed to emit ultrasonic signals (6) to a signal path (7) and designed to receive ultrasonic signals (6) from the signal path (7), and comprising a control and evaluation unit (8) for controlling the transducer element (3) and evaluating the ultrasonic signals (6), wherein a buffer element (9) is arranged in or on the transducer housing (3) within the signal path (7) such that the buffer element (9) forms at least one at least partially reflective boundary layer (10) in the signal path (7), wherein a second transducer element (4') is arranged in the transducer housing (3), wherein, during operation of the ultrasonic transducer (1), the transducer element (4) emits an ultrasonic signal (6), wherein the ultrasonic signal (6) is at least partially reflected at the boundary layer (10) of the buffer element (9), wherein the second transducer element (4') is arranged in the transducer housing in such a manner that the reflected signal component (11) is received by the second transducer element (4'), and wherein the control and evaluation unit (8) is designed such that, when the ultrasonic transducer (1) is in operation, it monitors the reception of the reflected signal component (11) and, if no reflected signal component (11) is received, detects an error state of the ultrasonic transducer (1), characterized in that the buffer element (9) is formed by the ultrasound window (5), and that the ultrasound window (5) has an increased thickness, wherein the thickness is defined as the extent of the ultrasound window (5) along the signal path (7) of the ultrasonic signal (6), and that the buffer element (9) formed by the ultrasound window (5) protrudes into the transducer housing (3) or protrudes out of the transducer housing (3).

3. Ultrasonic transducer (1) according to claim 1 or 2, characterized in that the buffer element (9) forms at least one second, at least partially reflective boundary layer (10') in the signal path (7), wherein, during operation of the ultrasonic transducer (1), the reflected signal component (11) is reflected from the first boundary layer (10) to the second boundary layer (10').

4. Ultrasonic transducer (1) according to any one of claims 1 through 3, characterized in that a coating (13) that enhances partial reflection is applied to the boundary layer (10) formed by the buffer element (9)-or, if multiple boundary layers (10, 10') are formed, to at least one of the boundary layers (10, 10').

5. Ultrasonic transducer (1) according to any one of claims 1 through 4, characterized in that the control and evaluation unit (8) is designed such that, when the ultrasonic transducer (1) is in operation, it compares a parameter describing the reflected signal component (11), in particular, the intensity of the reflected signal component, with a reference value and, in the event of a deviation beyond a predetermined tolerance range, outputs an error signal.

6. Ultrasonic flowmeter (2) for determining the flow rate of a flowing medium, comprising a first ultrasonic transducer (1), a second ultrasonic transducer (1), and a control and evaluation unit (14), wherein the ultrasonic transducers (1) are designed to emit an ultrasonic signal (6) along a signal path (7) and / or to receive an ultrasonic signal (6) from the signal path (7), and are operatively connected to one another via the signal path (7) of the ultrasonic signal (6), characterized in that at least the ultrasonic transducer (1) designed for use as a transmitter includes a buffer element (9), that the buffer element (9) is arranged in the signal path (7) of the ultrasonic signal (6) within or on the transducer housing (3), that the buffer element (9) forms at least one at least partially reflective boundary layer (10) in the signal path (7), that the buffer element (9) is formed by the ultrasound window (5), and that the ultrasound window (5) has an increased thickness, wherein the thickness is defined as the extent of the ultrasound window (5) along the signal path (7) of the ultrasonic signal (6), and that the buffer element (9) formed by the ultrasound window (5) protrudes into the transducer housing (3) or protrudes out of the transducer housing (3), that, when the ultrasonic flowmeter (2) is in operation, the transducer element (4) of the emitting ultrasonic transducer (1) emits an ultrasonic signal (6), wherein the ultrasonic signal (6) is at least partially reflected at the boundary layer (10) of the buffer element (9) and is partially emitted, that either • the reflected signal component (11) is received by the transducer element (4) of the emitting ultrasonic transducer (1), and the transmitted signal component (12) is received by the transducer element (4) of the receiving ultrasonic transducer (1), or • a second transducer element (4') is arranged in the transducer housing of the ultrasonic transducer (1) designed for transmission, and that the reflected signal component (11) is received by the second transducer element (4') of the emitting ultrasonic transducer (1), and the transmitted signal component (12) is received by the transducer element (4) of the receiving ultrasonic transducer (1), and that the control and evaluation unit (14) is designed such that, when the ultrasonic flowmeter (2) is in operation, it monitors the reception of the reflected signal component (11) and the reception of the transmitted signal component (12), and detects and signals one of the following operating states of the ultrasonic flowmeter (2): • upon receiving the reflected signal component (11) and receiving the transmitted signal component (12): the ultrasonic flowmeter (1) is functional, • upon receiving the reflected signal component (11) and failing to receive the transmitted signal component (12): measuring tube (15) is empty, • if the reflected signal component (11) is not received and the transmitted signal component (12) is not received: the ultrasonic flowmeter (2) is in an error state; specifically, the transducer element (4) of the emitting ultrasonic transducer (1) is in an error state.

7. Ultrasonic flowmeter (2) according to claim 6, characterized in that at least one ultrasonic transducer (1) is designed in accordance with the features of any one of claims 1 through 5.

8. Ultrasonic flowmeter (2) according to claim 6 or 7, characterized in that the control and evaluation unit (14) is designed such that it evaluates the transmitted signal component (12) as "not received" if the transmitted signal component (12) falls below a predetermined threshold value.

9. Method (200) for operating an ultrasonic flowmeter, wherein the ultrasonic flowmeter comprises a first ultrasonic transducer, a second ultrasonic transducer, and a control and evaluation unit, wherein the ultrasonic transducers are designed to emit an ultrasonic signal along a signal path and / or to receive an ultrasonic signal from the signal path and are operatively connected to one another via the signal path of the ultrasonic signal, wherein at least the ultrasonic transducer designed for transmission comprises a buffer element, the buffer element is arranged in or on the transducer housing within the signal path of the ultrasonic signal, and the buffer element forms at least one at least partially reflective boundary layer within the signal path, wherein the buffer element (9) is formed by the ultrasound window (5), and wherein the ultrasound window (5) has an increased thickness, wherein the thickness is defined as the extent of the ultrasound window (5) along the signal path (7) of the ultrasonic signal (6), and wherein the buffer element (9) formed by the ultrasound window (5) protrudes into the transducer housing (3) or protrudes out of the transducer housing (3), wherein, in an emitting step (201), the emitting transducer element emits an ultrasonic signal, wherein the ultrasonic signal is at least partially reflected and partially transmitted at the boundary layer of the buffer element, wherein, in a receiving step (202), the transducer element of the emitting ultrasonic transducer or a second transducer element arranged within the emitting ultrasonic transducer receives the reflected signal component, and the transducer element of the receiving ultrasonic transducer receives the transmitted signal component, wherein, in a monitoring step (203), the control and evaluation unit monitors the reception of the reflected signal component and the reception of the transmitted signal component, and wherein, in a signaling step (204), the control and evaluation unit signals one of the following operating states of the ultrasonic flowmeter: • upon receiving the reflected signal component and receiving the transmitted signal component: the ultrasonic flowmeter is functional, • upon receiving the reflected signal component and failing to receive the transmitted signal component: the measuring tube is empty, • upon failing to receive the reflected signal component and failing to receive the transmitted signal component: the ultrasonic flowmeter is in the error state, in particular, the transducer element of the emitting ultrasonic transducer is in the error state.

10. Method (200) according to claim 9, characterized in that the transmitted signal component is evaluated as "not received" if the transmitted signal component falls below a predetermined threshold value.