Vibration sensor

Abstract

The invention relates to a vibration sensor. A transducer device (2) excites a mechanically vibrating unit (1) to perform mechanical vibrations or receives mechanical vibrations from this unit. The transducer device (2) has at least two annular piezo elements (7) which each have two end faces (8, 9) having different electric polarization. The piezo elements (7) are arranged mutually adjacently in a stack in such a way that the end faces (8, 9) having the same polarization are located opposite one another. The piezo elements (7) are contacted by a contact electrode (10) between the end faces (8, 9). The piezo elements (7) are arranged around a sensor (17) designed as a tubular guide structure.

Description

[0001] Vibration sensor

[0002] The invention relates to a vibration sensor. The vibration sensor is preferably used to determine and / or monitor a process variable of a medium. The process variable is, for example, the fill level or density, wherein the medium is, for example, a liquid, a gas, or a bulk solid.

[0003] It is known in the art to use vibration sensors to detect whether liquids or bulk solids have reached or fallen below a certain threshold level. Such sensors also allow, for example, the measurement of the density of the medium. The measuring principle is based on the excitation of a mechanically oscillating unit (e.g., a tuning fork, a single-rod, or a diaphragm) to mechanical vibrations, and the influence of the received vibrations on the interaction of the oscillating unit with the medium. The generated vibrations generally belong to the fundamental mode.

[0004] Piezo drives or piezo actuators are used to generate and receive the oscillations. There are various ways to control the resonant oscillations in a resonator using electronic control. For example, there are electronic solutions with separate excitation and reception components of the piezo drive. This is also known as SE electronics (for transmitter-receiver electronics). The excitation component of the drive generates and supports the resonant oscillations, whereas the reception component receives the oscillations and thus enables feedback from the oscillating circuit. An alternative design involves using only one piezo element, which simultaneously excites and receives the oscillations. This is called single-piezo electronics.

[0005] One issue is to connect the piezo drive in vibration sensors as a force transmitter and force receiver with the mechanically oscillating unit, i.e. a mechanical resonator (such as a tuning fork).

[0006] For example, the following structure is known: The vibration sensor has a housing. In the housing, at least one piezoelectric drive, consisting of a piezoelectric ceramic, is clamped between the sensor membrane and a pressure screw, with a coupling element for the frictional connection between the piezo drive and the sensor membrane. The pressure screw and the housing have corresponding threads so that the piezo drive can be preloaded against the membrane. The harmonic force of the piezo drive acts on the membrane and causes vibrations, for example of the tines, in a fundamental mode of the tuning fork. The restoring force of the preloaded membrane ensures a secure coupling of the piezo drive with the tuning fork, as an exemplary mechanical resonator.

[0007] The problem with the aforementioned design is that the piezo drive incorporates metallic and ceramic components with different thermal expansion coefficients. Therefore, different preloads arise in the piezo drive at different process temperatures. If the diaphragm's restoring force is insufficient, the piezo drive can lose its coupling with the diaphragm and thus the tuning fork, which, in extreme cases, can lead to sensor failure.

[0008] A further problem arises from the design of the aforementioned components. The oscillation frequency of vibration sensors is determined by the stiffness of the membrane and the piezo drive, as well as by the moment of inertia of the tines (in the example of the tuning fork as a mechanically oscillating unit). The more piezo elements and solder lugs are connected in the piezo drive, the more the stiffness of the piezo stack changes due to settling effects or aging, and the more the sensor oscillation frequency drifts.

[0009] The aforementioned effects negatively impact the accuracy of density measurements or the switching behavior in different media. Conversely, it may be necessary to use multiple piezo elements to generate a sufficiently large oscillation amplitude.

[0010] Transducer devices consisting of several stacked piezo elements are disclosed, for example, in DE 10 2019 111 384 B3 or DE 100 28 319 A1. According to EP 1 134 038 A1, a piezo stack is arranged between a pressure screw and a diaphragm in the vibration sensor.

[0011] The invention is based on the object of proposing a vibration sensor which has the widest possible range of applications and the highest possible resistance to aging.

[0012] The invention solves the problem by a vibration sensor having at least one mechanically oscillatable unit, a transducer device and a sensor, wherein the transducer device excites the mechanically oscillatable unit to mechanical vibrations and / or receives mechanical vibrations from the mechanically oscillatable unit, wherein the transducer device has at least two piezo elements, wherein the two piezo elements each have two end faces with different electrical polarization, wherein the two piezo elements are arranged adjacent to one another in a stack such that the end faces of the two piezo elements with the same polarization are opposite one another, wherein the two piezo elements are contacted by at least one contact electrode, wherein the contact electrode is arranged between the end faces of the two piezo elements, wherein the at least two piezo elements are designed in a ring shape,wherein the sensor is designed as a tubular guide structure, and wherein the at least two annular piezo elements are arranged around the sensor.,

[0013] The vibration sensor consists of a mechanically oscillating unit and a transducer device. The mechanically oscillating unit can be, for example, a tuning fork, a single-rod, or a diaphragm.

[0014] The transducer device excites the mechanically oscillating unit to mechanical vibrations and / or receives mechanical vibrations from it. It is therefore used to generate and / or receive the vibrations. The transducer device has at least two piezo elements, each with two end faces with different electrical polarization. The two piezo elements therefore have different polarizations (plus or minus, for example) on their respective top and bottom sides. The piezo elements are arranged in a stack such that the end faces of the two piezo elements with the same polarization face each other. Thus, depending on the design, the plus sides or the minus sides face each other. The resulting stack has the same polarization on each of its end faces. For example, if the piezo elements with plus polarization face each other, the stack has two end faces with minus polarization.

[0015] For electrical contact, a contact electrode is provided, which is arranged between the opposite end faces of the two piezo elements and is electrically contacted with the piezo elements.

[0016] The annular piezo elements are arranged around the sensor. For this purpose, the sensor is designed as a tubular guide structure. The sensor can essentially be understood as a pin or rod that serves to thread the piezo elements. Since the tubular shape also entails a longitudinal axis of the sensor, the sensor also defines the longitudinal axis of the transducer device. Therefore, the longitudinal axis runs through the internal recesses of the annular piezo elements, which are thus arranged along the longitudinal axis.

[0017] The ring shape of the piezo elements allows for the inclusion of the sensor, which is preferably used to measure the environment in which the vibration sensor has been placed, or the medium to be measured or monitored. Depending on its design, the sensor can be solidly cylindrical or hollow. The sensor can be, for example, a temperature sensor, a humidity sensor, or a hydrogen sensor. The sensor can have a chip. The sensor can therefore help monitor the process in which the vibration sensor is used. This makes it possible, for example, to compensate for the effects of temperature on the oscillation frequency. Alternatively or additionally, the sensor helps monitor the vibration sensor. For example, increased humidity can serve as a warning signal that the vibration sensor is leaking.This results in a very compact drive with a rigid construction to reduce aging and temperature influences on the mechanical preload of the transducer device. Using the sensor as a guide or threading component also simplifies manufacturing.

[0018] The advantages of the vibration sensor are that it uses a simple and universally applicable transducer device with a very compact piezo stack. This results in minimal aging effects. Furthermore, applications where the sensor can be used at temperatures between -50 °C and +250 °C result in minimal changes in the transducer device's bias voltage. As one of the following designs demonstrates, a temperature sensor can also be easily implemented to compensate for sensor temperature drift and evaluate the process temperature.

[0019] One embodiment consists in the vibration sensor having more than two annular piezo elements, and in the more than two annular piezo elements being arranged around the sensor. In a supplementary embodiment, all piezo elements are annular, and the sensor is located in the internal recesses or openings of the stacked piezo elements.

[0020] The following embodiments refer to the different piezo elements that are arranged together in the stack and around the sensor.

[0021] According to a further embodiment, some of the piezo elements are arranged in a stack such that, for each two adjacent piezo elements, the end faces with the same polarization are opposite each other, and a contact electrode is located between the adjacent piezo elements. In one embodiment, the number of piezo elements is an integer multiple of 2. In an alternative embodiment, the number of piezo elements is an odd number. The contact elements serve to apply electrical signals to the end faces or the electrodes located thereon, or alternatively, to tap electrical signals.

[0022] One embodiment provides for an electrically conductive intermediate element to be arranged between two piezo elements. The electrically conductive element, which, for example, consists at least partially of a metal, electrically connects the end faces of the piezo elements, between which the electrically conductive intermediate element is located. One embodiment consists in the arrangement of an electrically insulating intermediate element between two piezo elements. The electrically insulating intermediate element electrically separates the adjacent piezo elements from one another and thus ensures, for example, that individual functional groups are formed in the stack of piezo elements. The functional groups are, for example, a transmitting unit (or excitation unit) for exciting the mechanical vibrations and a receiving unit for receiving the mechanical vibrations.

[0023] One embodiment provides that the vibration sensor has at least two contact electrodes, and that the two contact electrodes are electrically connected to one another via a connecting unit. The connecting units connect the contact electrodes and thus also the adjacent end faces of the piezo elements. In one embodiment, the contact electrodes are provided as solder lugs. The two contact electrodes are preferably located partially within the stack of more than two piezo elements or are connected to one end face of the stack of piezo elements.

[0024] One embodiment consists in that a subgroup of the more than two piezo elements serves to excite the mechanically oscillatable unit to mechanical vibrations, and another subgroup of the more than two piezo elements serves to receive mechanical vibrations from the mechanically oscillatable unit. In this embodiment, two different subgroups of piezo elements are located in a stack. One group serves to generate, and another group serves to receive, the mechanical vibrations of the mechanically oscillatable unit.

[0025] One embodiment provides that one subgroup and the other subgroup each comprise the same number of essentially identically designed piezo elements. In this embodiment, the excitation group and the reception group are symmetrical.

[0026] An alternative to the aforementioned configuration is that one subgroup and the other subgroup each comprise a different number of essentially identically designed piezo elements. This configuration creates an asymmetry. Thus, for example, more piezo elements are used to excite vibrations than to receive them.

[0027] In a further embodiment, at least some of the piezo elements serve to excite and receive the mechanical vibrations. In this embodiment, at least some of the piezo elements perform the dual function of both exciting and receiving vibrations. In one embodiment, all piezo elements serve to excite and receive the mechanical vibrations.

[0028] One embodiment provides that the vibration sensor further comprises a housing, that the transducer device is arranged in the housing between a pressure screw and a diaphragm, and that the mechanically oscillatable unit is coupled to the diaphragm. In this embodiment, the transducer device is clamped between a pressure screw and a diaphragm. The mechanically oscillatable unit is coupled to the diaphragm. The mechanically oscillatable unit can be a tuning fork, a single rod, or the diaphragm itself.

[0029] One embodiment consists in that the transducer device has a coupling element, that the coupling element has a recess, and that the sensor opens into the recess. The coupling element is preferably located on an end face of the stack of piezo elements.

[0030] The invention is explained in more detail with reference to the following figures.

[0031] Fig. 1 shows a section through a schematically illustrated vibration sensor,

[0032] Fig. 2 shows a spatial representation of a ring-shaped piezo element,

[0033] Fig. 3 shows a section through a first schematic design of a stack of piezo elements,

[0034] Fig. 4 shows a section through a second embodiment of a stack,

[0035] Fig. 5 shows a section through a third embodiment of a stack,

[0036] Fig. 6 shows a section through a fourth embodiment of a stack,

[0037] Fig. 7 shows a section through a fifth embodiment of a stack,

[0038] Fig. 8 shows a section through a sixth embodiment of a stack,

[0039] Fig. 9 shows a section through a seventh embodiment of a stack,

[0040] Fig. 10 shows a section through a first schematic embodiment of a converter device and Fig. 11 shows a section through a second embodiment of a converter device.

[0041] Fig. 1 shows the basic structure of a vibration sensor. Located in the housing 3 is a transducer device 2, which is clamped between a pressure screw 4 and a diaphragm 5. Between the transducer device 2 and the diaphragm 5 is a coupling element e, which in the illustrated embodiment is designed as a spherical shell facing the diaphragm 5. Therefore, the transducer device 2 can rotate about its axis of rotation when screwed in without strong torsional forces occurring that could destroy the piezoceramic elements of the transducer device 2. In the example, the mechanically oscillatable unit 1 is a tuning fork with two prongs. It can be seen that the transducer device 2 is designed and arranged such that its longitudinal axis is perpendicular to the diaphragm 5.

[0042] Fig. 2 shows an annular piezo element 7 made of a ceramic material, for example lead titanate zirconate. The end faces 8, 9 are each coated with a metal (not shown here) as electrodes for electrical contact, and the piezo element 7 is polarized in the direction of the height of the element 7. Compression results in an electrical charge at the electrodes on the end faces 8, 9. The polarity of the piezo element 7 is designated by a sign (- or +). In the example, a positive charge results on the upper end face 8 (indicated by the plus sign) and a negative charge on the lower end face 9 (indicated by the minus sign).

[0043] Figure 3 shows two piezo elements 7 used for a vibration sensor with single-piezo electronics 18. This means that the piezo elements 7 are connected to or operated by such electronics 18 as if they were only a single element. These are ring-shaped piezo elements 7. The polarization of the electrodes is indicated here by the plus and minus signs.

[0044] The piezo elements 7 contact a contact electrode 10 located between them with their (+) electrodes, which may be a so-called solder lug, for example. During production, electrically conductive material is introduced between the piezo elements 7 and melted so that the piezo elements 7 are soldered together and electrically connected. The contact electrode 10 is contacted by an electrical conductor 11, which in turn is connected to an electronics unit 18. The electronics unit 18 generates the electrical signals with which the mechanically oscillatable unit 1 is excited and / or receives the electrical signals that the transducer device 2 generates from the mechanical vibrations. The (-) electrodes of the piezo elements 7 are electrically conductively connected to the metallic housing 3 (see Fig. 1) and are therefore short-circuited. Alternatively, a separate electrical conductor can also be connected to the (-) electrodes.In principle, the sign of the electrodes arranged in the center of the stack and facing each other is irrelevant. Thus, as shown here, both the (+) electrodes and the (-) electrodes can be facing each other.

[0045] In this exemplary embodiment, two piezo elements 7 are electrically connected in parallel to form a single piezo element in a resonant circuit of the vibration sensor with electronics 18 for fundamental wave excitation. Such drives are inexpensive to manufacture and characterized by high rigidity. Furthermore, they can be operated over a wide temperature range with essentially no loss of mechanical preload.

[0046] In an alternative embodiment, only one piezo element 7 is used. To achieve this from the embodiment shown in Fig. 3, one of the illustrated piezo elements 7 is replaced by a ring made of an insulating material, e.g., a non-conductive ceramic (e.g., aluminum oxide, steatite, or zirconium oxide).

[0047] Fig. 4 shows a variant for supplying the vibration sensor with more energy. The number of piezo elements 7 is an integer multiple of 2. The even number of piezo elements 7 are connected in parallel, so that the same polarizations are adjacent to each other. The top and bottom end faces of the stack (here each with a minus sign) can be short-circuited (as in the variant in Fig. 3). Here, they are connected to the electronics (not shown) via an electrical conductor 11. The positive electrodes located within the stack are contacted via an electrical conductor 11, as in the embodiment in Fig. 3.

[0048] Figure 5 shows a structure of the transducer device, in which one part of the piezo elements 7 serves to generate and another part to receive the mechanical vibrations. Two piezo elements 7 are provided in each case, so that the two subgroups of the stack are essentially identical. This results in a symmetrical structure. Therefore, the choice of which subgroup—whether the upper or lower one—serves to receive or generate the mechanical vibrations can be freely selected.

[0049] An electrically conductive ring 12 is located between the two groups of piezo elements 7. The contact electrodes between the piezo elements 7 are each connected via their own electrical conductor 11 to an electronic unit 18 (not shown here) designed as feedback electronics, which generates appropriate excitation signals and evaluates or further processes the received signals. On the right side, it is indicated that the end faces of the two upper piezo elements 7 are electrically connected to each other by a connecting unit 14.

[0050] In the embodiment of Fig. 6, an electrically insulating intermediate element 13 is located between the sub-assemblies, each consisting of two piezoelectric elements 7. This element consists, for example, of a dielectric ceramic (such as aluminum oxide, non-polarized piezoelectric ceramic, steatite, zirconium oxide, etc.). The electrically insulating intermediate element 13 can—like the electrically conductive intermediate element 12 in the embodiment of Fig. 5—serve to compensate for the axial and vertical stresses in the receiving sub-assembly that arise from the excitation sub-assembly of the piezoelectric elements.

[0051] The annular intermediate elements 12, 13 are optimized for the application in terms of their material and thickness. Such rings can be made of duralumin, for example, to compensate for the low expansion coefficient of the ceramic of the piezo elements. It has proven particularly advantageous if the intermediate elements 12, 13 are made of the same material as the coupling element e (see Fig. 1). The (-) electrodes of the piezo elements 7 or the contact electrodes 10 between the immediately adjacent piezo elements are electrically connected to one another via connecting units 14.

[0052] Figure 7 shows a variant with an asymmetrical distribution of excitation and reception subassemblies. The upper four piezo elements 7 are used for excitation and have an electrical conductor 11 for connection to the electronic device. The lower two piezo elements 7 are used to receive the mechanical vibrations. They have their own electrical conductor 11 for outputting the electrical signals resulting from the mechanical vibrations. When installed, the reception component is thus closer to the membrane. An annular, electrically insulating intermediate element 13 is located between the two subassemblies.

[0053] Fig. 8 shows a configuration of the stack of piezo elements 7, in which two piezo elements 7—arranged here at the top—serve to excite the vibrations, and a piezo element 7 located underneath and separated by an electrically insulating intermediate element 13 serves to receive the vibrations. The drive group is connected via a conductor 11, and the receiving group via a separate electrical conductor 11. The use of the groups of piezo elements 7 is fixed, and interchanging their functions is not possible. In the drive group, the end faces are also connected to one another via an electrically conductive connecting unit 14.

[0054] The design of Fig. 9 is identical to the design of Fig. 4 with respect to the stack of piezo elements 7. The difference is that in the variant of Fig. 9, the electrical conductor 11, which is connected to negative, also contacts the end face of the lowest piezo element 7. This makes it possible to measure this structure even when not installed, since all piezo elements 7 are fully contacted. In the variant of Fig. 4, the lowest piezo element is contacted via the housing.

[0055] Fig. 10 shows a compact unit comprising coupling element 6, transducer device 2, and pressure screw 4. The transducer device 2 may consist of any number of piezo elements, which are not shown individually here. The piezo elements are ring-shaped, and in the central, continuous recess there is a pin 16, which here projects into a recess 15 of the coupling element 6. The pin 16 supports production as an assembly aid by simplifying the threading of the piezo elements. The pin 16 can, for example, be made of a dimensionally stable plastic, which may contain glass fibers or inorganic fillers. Examples are polytetrafluoroethylene (PTFE) with 30% glass fiber or polyetheretherketone (PEEK) with a glass fiber content of between 0% and 30% glass fiber. Other examples of possible materials are polyphenylene sulfide (PPS), polysulfone (PSU), or thermosets with or without fillers.Alternatively, the pin 16 consists at least partially of a ceramic.

[0056] In the embodiment of Fig. 11, the same basic structure can be seen as in Fig. 10: The transducer device 2 is located between the pressure screw 4 and the coupling element e with the spherical section. A pin-shaped sensor 17 is located through the recesses in the pressure screw 4 and the piezo elements 7 of the transducer device 2 into the recess 15 of the coupling element 6. The piezo elements 7 are thus located around the sensor 17 along the longitudinal axis of the transducer device 2 and the sensor 17. During production, the sensor 17 therefore serves to thread on or as a guide structure for the piezo elements 7. The sensor 17 thus fulfills the same purpose as the pin 16 in the embodiment of Fig. 10, but has the additional advantage that the sensor 17 remains in the transducer device 2 and allows the measurement of a measured variable - in this case the temperature.Sensor 17 has a hollow tube containing the sensor components or contact leads. In this case, sensor 17 is a temperature sensor with two electrical connection leads. The measured values ​​from temperature sensor 17 can be used to compensate for the reversible temperature drift of the relative oscillation frequency caused by the process temperature. For a mechanically oscillating unit or a stainless steel housing, this drift lies between approximately -0.0003 1 / K and -0.0002 1 / K.

[0057] The tubular section of the sensor 17, around which the piezo elements 7 are located, is electrically non-conductive and preferably made of a ceramic. For example, it is an aluminum oxide ceramic, which has a relatively high thermal conductivity and reliably insulates the electrodes of the piezo elements 7 from each other. The actual measuring component of the temperature sensor 17 is, for example, a measuring resistor (e.g.,

[0058] Pt100, Pt500 or Pt1000).

[0059] For the version with temperature sensor 17, the coupling element 6 is at least partially made of a hard but thermally conductive alloy, e.g., so-called aircraft aluminum or duralumin. Examples include EN AW-7022 or EN AW-7075 with a yield strength greater than 200 MPa. The use of an aluminum alloy is particularly advantageous for piezo elements 7, since such an alloy, due to its generally high coefficient of expansion, can compensate for the typically rather low coefficient of expansion of a piezo ceramic. Such compensation is particularly important if the housing of the vibration sensor is made of stainless steel. For example, stainless steel 316L has a thermal expansion coefficient of 17 * 10-6 1 / K. A piezoceramic has an expansion coefficient of approximately 6 * 10-6 1 / K and aluminum alloy EN AW-7022 has a coefficient of 23.6 * 10-6 1 / K.Therefore, to match the expansion coefficients of the ceramic piezo elements to the 316L stainless steel housing, the aluminum coupling element should have a thickness of 1.66 mm for every 1 mm of the piezo elements' thickness. This prevents preload losses at high application temperatures.

[0060] In the embodiment shown in Fig. 11, the coupling element 6 is a one-piece component with a spherical end at the bottom and a disc-like end at the top. The upper diameter is equal to the diameter of the piezo elements 7.

[0061] In the embodiment shown in Fig. 10, the coupling element 6 ends in a spherical shape. The upper end has a smaller diameter than the piezo elements 7. To ensure the compensation of the expansion coefficients discussed above, a metal disc 19 is provided, which in this example is located between the coupling element 6 and the piezo elements 7.

[0062] In an alternative embodiment, the metal disc 19 is located below the pressure screw 4 or within the stack of piezoelectric elements 7. The thickness and material of the metal disc 19 should generally be selected to optimize the balance between the expansion coefficients of the housing and the piezoelectric ceramics. Reference symbols for a mechanically oscillating unit

[0063] converter device

[0064] Housing

[0065] pressure screw

[0066] membrane

[0067] coupling element

[0068] Piezo element

[0069] front side

[0070] front side

[0071] contact electrode electrical conductor electrically conductive intermediate element electrically insulating intermediate element

[0072] Connection unit

[0073] recess

[0074] Pen

[0075] sensor

[0076] Electronics unit

[0077] metal disc

Claims

Patent claims 1. A vibration sensor comprising at least one mechanically oscillatable unit (1), a transducer device (2), and a sensor (17), wherein the transducer device (2) excites the mechanically oscillatable unit (1) to mechanical oscillations and / or receives mechanical oscillations from the mechanically oscillatable unit (1), wherein the transducer device (2) comprises at least two piezo elements (7), wherein the two piezo elements (7) each have two end faces (8, 9) with different electrical polarization, wherein the two piezo elements (7) are arranged adjacent to one another in a stack such that the end faces (8, 9) of the two piezo elements (7) with the same polarization are opposite one another, wherein the two piezo elements (7) are contacted by at least one contact electrode (10), wherein the contact electrode (10) is arranged between the end faces (8, 9) of the two piezo elements (7),wherein the at least two piezo elements (7) are ring-shaped, wherein the sensor (17) is designed as a tubular guide structure, and wherein the at least two ring-shaped piezo elements (7) are arranged around the sensor (17).

2. Vibration sensor according to claim 1, wherein the vibration sensor has more than two annular piezo elements (7), and wherein the more than two annular piezo elements (7) are arranged around the sensor (17).

3. Vibration sensor according to claim 2, wherein a subgroup of the piezo elements (7) serves to excite the mechanically oscillatable unit (1) to mechanical vibrations, and wherein another subgroup of the piezo elements (7) serves to receive mechanical vibrations from the mechanically oscillatable unit (1).

4. Vibration sensor according to one of claims 1 to 3, wherein the vibration sensor has at least two contact electrodes (10), and wherein the two contact electrodes (10) are electrically connected to one another via a connecting unit (14).

5. Vibration sensor according to one of claims 1 to 4, wherein the vibration sensor further comprises a housing (3), wherein the transducer device (2) is mounted in the housing (3) between a pressure screw (4) and a membrane (5), and wherein the mechanically oscillatable unit (1) is coupled to the membrane (5).

6. Vibration sensor according to one of claims 1 to 5, wherein the transducer device (2) has a coupling element (6), wherein the coupling element (6) has a recess (15), and wherein the sensor (17) opens into the recess (15).

7. Vibration sensor according to one of claims 1 to 6, wherein the sensor (17) is designed to be electrically insulating at least in a region which is located in the piezo elements (7).

8. Vibration sensor according to one of claims 1 to 7, wherein the sensor (17) is a temperature sensor.

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