DE102022127929A1 - Vibration sensor with spacer for thermal decoupling of the drive - Google Patents

Abstract

The invention relates to a vibration sensor 1 for detecting a fill level or limit level in the interior of a container 3, with a housing 9, a membrane 6 that can be excited to vibrate and a drive 5 for setting the membrane 6 into vibration and/or for sensing a vibration of the membrane 6, wherein the drive 5 is connected to the membrane 6 via a mechanical coupling. The invention is characterized in that the mechanical coupling comprises a spacer 4, so that the drive 5 is arranged at a distance from the membrane 6 for thermal decoupling.

Description

The present invention relates to a vibration sensor according to the preamble of patent claim 1.

Specifically, the invention relates to a vibration sensor for detecting a fill level or limit level in a container, with a membrane that can be excited to vibrate and a drive for setting the membrane into vibration and/or for sensing a vibration of the membrane, wherein the drive is connected to the membrane via a mechanical coupling. The drive is thermally decoupled from the membrane.

Vibration sensors for detecting fill levels or limit levels are known from the state of the art. Such vibration sensors can detect fill levels or limit levels of liquids or bulk materials in containers. For this purpose, the vibration sensors usually comprise a drive that is mechanically coupled to a mechanical coupling, in particular a membrane, in such a way that vibrations can be transmitted from the drive to the membrane and vice versa. Mechanical oscillators similar to a tuning fork are attached to the membrane and are caused to oscillate by the drive. If the mechanical oscillators are immersed in a filling material or liquid, their oscillation behavior changes, which in turn affects the operation of the drive. The changed oscillation behavior of the mechanical oscillators can be detected by the drive and conclusions can be drawn from this as to how high the fill level in the container is or whether a limit level has been exceeded or not reached.

Piezoelectric and/or inductive drives are used as drives. With piezoelectric drives, several piezo elements are usually stacked on top of each other to increase the working travel of the drive. These piezo elements can then be excited to an oscillating change in length by applying an alternating voltage, which is passed on to the mechanical oscillators via the membrane and thus leads to an oscillating movement of the mechanical oscillators. Conversely, vibrations can also be transmitted from the mechanical oscillators via the membrane to the piezo elements, which then lead to an electrical voltage on the piezo elements and can be recorded accordingly.

Inductive drives consist of a magnet and a coil. If an alternating voltage is applied to the coil, the magnet is stimulated to oscillate. The magnet is mechanically coupled to the membrane, so that the vibrations of the magnet cause the membrane to vibrate. Conversely, a vibration transmitted through the membrane to the magnet leads to an electrical voltage in the coil, which in turn can be detected.

It is also possible that the coil is mechanically coupled to the membrane and the magnet is arranged in a fixed location, for example on a housing of the vibration sensor. In this case, the coil itself is stimulated to the oscillating movement in interaction with the magnet, so that the membrane is stimulated to vibrate.

What all these types of drives have in common is that they react to temperature changes by changing their oscillation behavior and can no longer be used above certain maximum temperatures or below certain minimum temperatures. For example, magnets completely lose their magnetic properties above the Curie temperature and the drive can no longer oscillate. Depending on the composition of the magnet, the Curie temperature is between +100°C and +800°C, so the application range of the drives is often limited to +80°C.

Low temperatures of below -100°C to -200°C can have negative consequences for the materials used in the drives. The materials become brittle and therefore no longer have the required mechanical strength, or the devices for suspending the vibrating components lose their elasticity, preventing the vibrating components from moving.

So that vibration sensors can also be used for filling or limit level monitoring of very cold (below -100°C) or very hot (above +100°C) filling materials such as liquid hydrogen at -252°C or liquid nitrogen at -196°C, the object of the invention is to provide a vibration sensor that improves the temperature application range of vibration sensors.

This object is achieved by a vibration sensor having the features of independent claim 1.

Further, particularly advantageous embodiments of the invention are disclosed in the respective subclaims.

It should be noted that the features listed individually in the claims can be combined with one another in any technically reasonable manner (including across category boundaries, for example between method and device) and further embodiments of the invention The description further characterizes and specifies the invention, particularly in connection with the figures.

It should also be noted that a conjunction “and/or” used herein, which stands between two features and links them together, is always to be interpreted in such a way that in a first embodiment of the subject matter according to the invention only the first feature can be present, in a second embodiment only the second feature can be present and in a third embodiment both the first and the second feature can be present.

A vibration sensor according to the invention for detecting a fill level or limit level in the interior of a container, in particular an industrial container, for example a container, silo or IBC (= intermediate bulk container) with a housing, a membrane that can be excited to vibrate and a drive for setting the membrane into vibration and/or for sensing a vibration of the membrane, wherein the drive is connected to the membrane via a mechanical coupling, is characterized in that the mechanical coupling comprises a spacer, so that the drive is arranged at a distance from the membrane for thermal decoupling.

The vibration sensor has a housing that is closed off with a membrane on the front side, i.e. towards the product to be monitored. A mechanical oscillator is coupled to the membrane so that vibrations can be transferred from the membrane to the mechanical oscillator and vice versa.

A typical mechanical oscillator can, for example, be constructed like a tuning fork. The two ends oscillate at a characteristic frequency depending on the medium surrounding them.

The vibration sensor is mounted on the container in such a way that the vibration sensor extends into the interior of the industrial container and the mechanical oscillators can come into contact with the contents of the container depending on the fill level. The vibration sensor can therefore use a change in the vibration behavior of the mechanical oscillators to determine a change in the contents of the container surrounding the mechanical oscillators.

In order for the mechanical oscillators to oscillate, they are driven by the drive with the membrane interposed. To do this, the drive carries out an oscillating translational movement along an excitation direction, which is transferred to the membrane. The drive is connected to the membrane via the mechanical coupling to transmit this oscillating movement. The mechanical coupling means that the membrane is rigidly connected to the drive, at least in the excitation direction of the drive.

Depending on the application, high temperatures of, for example, over +100°C or low temperatures of below -100°C can prevail in the container. As described at the beginning, such high or low temperatures are outside the temperature working range of the drive. Outside of this temperature working range, the drive cannot work properly, so it is important to keep the drive within the temperature working range. The mechanical coupling is therefore set up in such a way that the drive is mechanically connected to the membrane, but is thermally decoupled from the membrane.

Thermal decoupling of the drive from the membrane means in the sense of the present application that the temperature of the membrane can be outside the temperature working range of the drive, while only so little heat is transferred via the mechanical coupling that the drive remains within its temperature working range. Assuming that the container contains thermally liquefied hydrogen at -252°C, so that the membrane always has a temperature of below -200°C, the temperature of the drive would not fall below -100°C due to the inhibited heat transfer of the mechanical coupling.

Thermal decoupling between the membrane and the drive can be achieved by using mechanical coupling components that are made, for example, from materials with low thermal conductivities or that inhibit heat transport between the drive and the membrane through certain geometries such as long transfer paths.

For this purpose, the mechanical coupling includes a spacer so that the drive is arranged at a distance from the membrane for thermal decoupling. The spacer transfers the vibrations between the membrane and the drive and thus forms a direct heat or cold bridge. In order to inhibit the heat conduction between the drive and the membrane and to achieve thermal decoupling, it is advantageous if the drive and the membrane are arranged at a distance from each other in the housing of the vibration sensor. This distance is bridged by the spacer.

The present arrangement is therefore particularly suitable for limit level measurements in cryonic liquefied gases, in particular hydrogen, nitrogen or helium.

With the help of the spacer, it is possible, for example, to arrange the drive far outside the container and the membrane with the mechanical oscillators inside the housing, while the mechanical coupling is also ensured by the spacer over larger distances. Far outside the container in the sense of the application means that a side of the drive facing the process is at least 5 cm, preferably at least 10 cm, more preferably at least 20 cm away from an outside of the container facing away from the process.

The distance between the membrane and the drive can preferably be at least 3 cm, 5 cm, 10 cm or 15 cm, or for example a multiple of the drive dimensions. This distance is measured from a side of the membrane facing away from the process to a side of the drive facing the process.

The material from which the spacer is made is preferably a material with low thermal conductivity. Ceramic, for example, is suitable for this. Plastics are also suitable in terms of their thermal conductivity, but the temperature range is often limited compared to ceramic and metal.

Due to the high and low temperatures, non-negligible thermal expansion is to be expected. Since the drive is preloaded against the membrane, if the length of the spacer changes due to a change in temperature, the preload should be maintained as far as possible. This can be achieved by ensuring that the housing around the spacer and the spacer have a similar or even the same thermal expansion, for example by using materials with a similar thermal expansion coefficient; in particular, the same material can be used for the housing and the spacer. Metal is preferred due to its chemical resistance and mechanical properties.

In addition to thermal decoupling through the mechanical coupling, it can also be advantageous if the housing of the vibration sensor is designed in such a way that as little heat as possible is transferred through the wall of the housing and through the interior of the housing. This means that as little heat as possible is conducted towards or away from the drive. For example, cavities in the housing, especially cavities around the mechanical coupling, can be evacuated. This inhibits heat conduction and can at the same time promote the vibration transmission of the mechanical coupling. A material with low thermal conductivity can be used to manufacture the housing.

Advantageous embodiments and variants of the invention emerge from the subclaims and the following description. The features listed individually in the subclaims can be combined in any technically reasonable manner both with each other and with the features explained in more detail in the following description and represent other advantageous embodiments of the invention.

In a preferred embodiment of the vibration sensor, the spacer is designed such that a first heat conduction path from the membrane via the spacer to the drive has a higher thermal resistance than a second heat conduction path from the membrane via the housing to an environment of the housing. The environment is formed by the ambient air around the housing of the vibration sensor.

Preferably, only the part of the housing that is arranged outside the industrial container is taken into account to determine the thermal resistance of the second heat conduction path. Further preferably, only a heat dissipation section of the housing that is located outside the industrial container is taken into account. This heat dissipation section of the housing extends over the housing starting from the industrial container along the excitation direction of the drive and is limited by a plane that is perpendicular to the excitation direction and is located between the drive and the membrane and adjacent to the drive.

The thermal resistance of a heat conduction path depends on the thermal conductivities of the materials along the heat conduction path, as well as on their cross-sectional area and the length of the heat conduction path. The longer the heat conduction path and the smaller the thermal conductivities and cross-sectional areas, the greater the thermal resistance. If the heat is not only transported via the solids, but also transferred to adjacent gases or liquids, for example, the size of the surface over which the heat is transferred to the gas or liquid also plays a role in the thermal resistance of the heat conduction path. The larger the surface to the gas or liquid, the smaller the thermal resistance.

The first heat conduction path runs from the membrane via the spacer to the drive, whereby further components, such as pressure pieces, holders and/or couplings, can be arranged between the membrane and the spacer and between the drive and the spacer, so that the first heat conduction path also runs through these components.

The second heat conduction path runs from the membrane across the housing to the surroundings of the housing, whereby additional components such as holders, additional housing parts and/or couplings can also be arranged between the membrane and the housing, so that the second heat conduction path also runs through these components. Since the second heat conduction path should have as low a thermal resistance as possible, it may be advisable to increase the surface area of the housing, for example by means of cooling fins or additional heat conduction structures. The heat conduction structures can be attached to the inside and/or outside of the housing in order to reduce the thermal resistance from the housing to the surroundings, or they can run parallel to the housing starting from the membrane.

The thermal resistance of the first heat conduction path can be influenced by the component cross-section and the material selection of the spacer. The spacer has the smallest possible component cross-section and is made of materials with the lowest possible thermal conductivities.

The thermal resistance of the first heat conduction path is in particular 20% greater, preferably 50% greater, than the thermal resistance of the second heat conduction path.

In a preferred embodiment of the vibration sensor, the housing is designed to be attached to an opening of the container in such a way that the drive is arranged outside and the membrane is arranged inside the container. It is not absolutely necessary for the entire vibration sensor to detect the fill or limit level to be arranged inside the container. It is important that the mechanical oscillators, which are usually directly connected to the membrane, can be immersed in the filling material. Therefore, at least the membrane is arranged together with the mechanical oscillators inside the container. If the membrane is arranged in an opening of the container and flush with a wall of the container, the membrane is still considered to be arranged inside the container for the purposes of the application.

Inside the container, the low or high temperatures mentioned above prevail, from which the drive must be decoupled. Outside the container, on the other hand, moderate temperatures usually prevail, for example in the range of -20°C to +60°C. It is therefore advisable to arrange the area of the vibration sensor with the drive outside the container so that no high or low temperatures affect the drive from the outside.

In a further preferred embodiment of the vibration sensor, the spacer has a substantially cylindrical shape with a length and a diameter, the length being a multiple of the diameter. The larger the cross-section of the spacer and the shorter its length, the more or faster the heat can be transferred from one end of the spacer to the other end. Therefore, the cross-section and thus the diameter should be as small as possible in relation to the length of the spacer so that as little and as slowly as possible the heat is conducted from one end of the spacer to the other end and thus between the membrane and the drive.

The shape of the cross-section is hardly important, so that in addition to a circular cross-section, an oval, rectangular, square or polygonal cross-section is also possible. It is important that the cross-sectional area is small compared to the length of the spacer. It can also be provided that the spacer has a very small cross-section at one point along its length, seen in the direction of excitation, in order to inhibit heat transport there as much as possible, while the remaining cross-sectional areas of the spacer can be larger.

In a further preferred embodiment of the vibration sensor, the spacer is designed as a hollow body. As already explained, a small cross-sectional area of the spacer leads to low heat conduction. It can therefore be advantageous if the cross-sectional area is reduced by a hollow in the spacer. A round tube or rectangular tube can be used for this purpose for the spacer, whereby the ends of the spacer can be closed or open. Since the thermal conductivity of a hollow spacer is reduced as well as the mass, the vibration behavior of the spacer is also improved at the same time, so that vibrations between the membrane and the drive can be transmitted more precisely due to the reduced inertia. If the ends of the spacer are closed, the spacer can be filled with a medium with very low thermal conductivity, such as a gas, in particular a chemically inert gas or a protective gas or with sodium, or it can also be evacuated.

In a further preferred embodiment of the vibration sensor, the spacer is mounted in the housing of the vibration sensor in an oscillating manner. Depending on the length of the spacer, it can be advantageous if the spacer is not only mounted by the coupling with the membrane and the drive, but is also mounted in the housing. Since the spacer must be able to follow the vibrations of the membrane and the drive, the mounting should, if possible, enable the spacer to oscillate in the direction of excitation of the drive. Movement of the spacer transverse to the direction of excitation, for example due to deflection of the elongated spacer, can be prevented or at least limited by the mounting.

In a further preferred embodiment of the vibration sensor, the spacer is mounted in the housing so that it can vibrate using at least one damping element, whereby the damping element preferably dampens vibrations in an excitation direction of the drive significantly less than orthogonal and/or oblique to the excitation direction. To detect fill or limit levels, only vibrations of the spacer in the direction of the excitation direction and thus perpendicular to the membrane are used. These vibrations along the excitation direction are also called useful modes. All other vibrations of the spacer that do not occur in the direction of the excitation direction or perpendicular to the membrane can interfere with the detection of the fill or limit level by the vibration sensor. These vibrations are referred to as interference modes. The damping element therefore dampens the useful modes significantly less than the interference modes.

If the amplitudes of the wanted and spurious modes are used for comparison, the damping element preferably dampens the amplitudes of the wanted modes by a factor of 3, 5, 10 or 20 less than the amplitudes of the spurious modes. In a preferred embodiment, the damping element reduces the amplitudes of the wanted modes by less than 5%, preferably less than 3%, while the amplitudes of the spurious modes are reduced by at least 90%, preferably at least 95%.

The damping can be achieved, for example, by designing the damping element as a damping spring. A particularly advantageous design of the damping spring is a diaphragm spring, as this allows movements perpendicular to the diaphragm plane very well and dampens movements parallel to the diaphragm plane very well. If such a diaphragm spring is used parallel to the diaphragm of the vibration sensor, the useful modes can act perpendicular to the plane of the diaphragm spring and are therefore almost not damped, whereas the interference modes all have high movement components orthogonal to the direction of excitation and thus parallel to the plane of the diaphragm spring, which are therefore strongly damped.

Therefore, in a further preferred embodiment of the vibration sensor, the at least one damping element is designed as a diaphragm spring whose width and length or whose diameter is many times greater than its thickness.

It has been shown that good results can be achieved with conventional vibration sensors and damping elements in the form of diaphragm springs made of spring steel, in particular spring steel 1.4310, stainless steel, in particular stainless steel 1.4301 or steel, in particular steel C22, with a thickness of 0.1 mm to 1.0 mm and an outer diameter of 20 mm to 50 mm. Full-surface diaphragm springs with a thickness of 0.2 mm have shown particularly good results. The diaphragm springs can be designed as a flat cylindrical disk, or be plate-shaped or have a concentric wave structure.

Good results were also achieved with regard to the damping effect with partially perforated diaphragm springs with a thickness of 0.4 mm. Therefore, in a further preferred embodiment of the vibration sensor, the at least one damping element in the form of a diaphragm spring has at least one through-opening in the direction of the drive direction.

In a further preferred embodiment of the vibration sensor, the at least one damping element has an inner ring for connection to the spacer and an outer ring for connection to the housing, wherein the inner ring is connected to the outer ring via at least one, preferably four webs.

The damping element has an inner ring, by means of which it can be connected directly or indirectly to the spacer. In this way, the damping element can be easily connected to the vibrating spacer with a sufficient distance to the membrane of the vibration sensor. By arranging the damping element at a distance from the membrane, an improved damping behavior for the spacer is achieved, since the spacer has a pivot point in the plane of the membrane due to the coupling with the membrane. The interference modes of the However, due to the distance from the membrane, the damping element has an improved point of attack with a large lever, so that the vibrations of the disturbing modes can be effectively dampened.

In order to further improve the damping effect of the damping element, it can have an outer ring by means of which it can be connected to a housing of the vibration sensor that is fixed relative to the membrane. The outer ring can, for example, be welded to the housing of the vibration sensor or clamped between a shoulder of the housing and a screw-in sleeve. The damping element is preferably welded to the housing, whereby a particularly stable fastening of the damping element can be achieved by means of a circumferential weld. In this way, the damping element is fixed in both the axial and radial directions, which can further improve the damping effect. The connection can also be made using a sintering process or a metal injection molding process (MIM process for short), which offers the same advantages as welding.

A plurality of resilient webs can be arranged on the inner ring, which extend at least in sections in the radial direction. By designing the diaphragm spring with such resilient webs, a damping characteristic of the diaphragm spring can be influenced. In particular, it is possible in this way to design the diaphragm spring in such a way that it dampens to different degrees in different directions in the diaphragm plane. Diaphragm springs designed with webs are particularly easy to handle if the webs extend from the inner ring to the outer ring. The spring webs can extend in particular radially, spirally or meanderingly.

In a preferred embodiment, four webs are arranged at right angles to one another on the inner ring, with two opposite webs having identical dimensions. Such a symmetrical embodiment is useful because vibration sensors of the type in question are typically constructed rotationally symmetrically. It also makes it possible to design the diaphragm spring in such a way that it can dampen interference modes occurring in a preferred direction particularly well, for example.

This can be achieved, for example, by making two first webs running in the direction of a connecting line between two mechanical vibration elements arranged on the membrane on a side opposite the drive wider than the two second webs running perpendicular to them. Since paddles that are aligned parallel to one another and perpendicular to the connecting line between their attachment points on the membrane are typically used as mechanical vibration elements, certain interference modes occur preferentially in the direction of the connecting lines of the attachment points of these mechanical oscillators. In order to be able to dampen these interference modes particularly effectively, it is useful if the corresponding webs are made stronger, in particular wider. For example, the first webs can have a width of 6 mm and the second webs a width of 4 mm, with the webs in typical vibration sensors typically having a length between 3 mm and 5 mm, in particular between 3.5 mm and 4.5 mm.

Depending on the geometry of the spacer, it may be advantageous if a damping element is arranged halfway along the length of the spacer, with the length of the spacer being measured along the excitation direction of the drive. In this way, the first vibration mode of the spacer is effectively damped by the damping element. In order to effectively dampen the subsequent second mode, third mode, fourth mode, etc., further damping elements can be provided along the length of the spacer, each arranged at the locations of the amplitudes of the various modes.

• 1 eine Schnittdarstellung eines Vibrationssensors, angeordnet in einer Öffnung eines Behältnisses mit einem durch ein Distanzstück thermisch entkoppelten Antrieb,
• 2 ein Dämpfungselement ausgeführt als Membranfeder in einer Draufsicht,
• 3 ein durch zwei Dämpfungselemente in einem Gehäuse eines Vibrationssensors schwingend gelagertes Distanzstück.

The present invention is explained in detail below using exemplary embodiments with reference to the accompanying figures. They show:

• 1 a sectional view of a vibration sensor arranged in an opening of a container with a drive thermally decoupled by a spacer,
• 2 a damping element designed as a diaphragm spring in a plan view,
• 3 a spacer that is mounted in a vibration sensor housing by two damping elements.

In the figures, unless otherwise stated, the same reference symbols designate the same components with the same function.

1 shows a sectional view of a vibration sensor 1, arranged in an opening 2 of a container 3 with a drive 5 thermally decoupled by a spacer 4.

The drive 5 of the vibration sensor 1 is mechanically coupled to a membrane 6 via the spacer 4. Two mechanical oscillators 7 are arranged on the membrane 6 and can oscillate like a tuning fork. In order to set the mechanical oscillators 7 in vibration, the drive 5 can move the spacer 4 back and forth in an oscillating direction A of the drive 5. This oscillating movement of the spacer 4 is transferred to the membrane 6, which in turn then excites the mechanical oscillators 7 to oscillate. Conversely, vibrations of the mechanical oscillators 7 can also be transferred to the drive 5 in this way. The vibration behavior of the mechanical oscillators 7 depends heavily on the density of the medium surrounding the mechanical oscillators 7. If the mechanical oscillators 7 are immersed in a filling material 10 in the container 3, in this case liquid hydrogen, whose density is significantly higher than that of the gaseous hydrogen otherwise in the container, the oscillation behavior changes, which in turn can be detected via the drive 5. In this way, the filling level or limit level of the filling material 10 in the container 3 can be detected.

The spacer 4 is mounted in a cylindrical housing 9 of the vibration sensor 1 by means of two damping elements 8. The damping elements 8 enable the spacer 4 to move along the excitation direction A of the drive 5 without significantly dampening the movement in the excitation direction A. However, a movement of the spacer 4 transverse to the excitation direction A is largely dampened or prevented by the damping elements 8.

The spacer 4 allows the drive 5 to be arranged at a significant distance from the membrane 6 or the mechanical oscillators 7 within the housing 9 of the vibration sensor 1. The spacer 4 can only conduct a small amount of heat due to its small cross-section and its great length, so that in this way the drive 5 is arranged essentially thermally decoupled from the membrane 6. For the application of a vibration sensor 1 for liquid hydrogen as filling material 10, the length of the spacer 4 is in a range from 5 to 45 cm, while the diameter is 3 to 10 mm, in particular the spacer 4 has a length of 10 cm and a diameter of 5 mm. In addition, the housing 9 of the vibration sensor 1 is fastened in the opening 2 of the container 3 in such a way that the membrane 6 with the mechanical oscillators 7 are arranged inside the container 3, while the drive 5 is arranged outside the container 3. In this arrangement, as little heat or cold as possible is transferred from the filling material 10 to the drive 5, so that the vibration sensor 1 can also be used for filling materials 10 with very high temperatures, such as over +200°C, or very low temperatures, such as below -200°C, without the drive 5 having to be operated outside its permissible temperature range, such as ± 100°C.

Both a first heat conduction path W1 from the membrane 6 to the drive 5 and a second heat conduction path W2 from the membrane 6 to the surroundings of the housing 9 are shown. The first heat conduction path W1 runs over the spacer 4 and the second heat conduction path W2 over the housing 9. The two heat conduction paths W1 and W2 have different thermal resistances. The thermal resistance of the first heat conduction path W1 is increased compared to the thermal resistance of the second heat conduction path W2 due to the geometric design of the spacer 4 and its material properties.

2 shows a damping element 8 designed as a diaphragm spring. The base body of the damping element 8 corresponds to a cylindrical disk whose diameter is a multiple of its height. The damping element 8 is provided with four through openings 11 and a centrally arranged passage for the spacer 4, so that a shape is formed from an outer ring 12 and an inner ring 13, wherein the outer ring 12 and the inner ring 13 are connected via four resilient webs 14. The webs 14 allow the inner ring 13 to move relative to the outer ring 12 in the excitation direction A with little resistance, so that the vibrations of the spacer 4 in the excitation direction A are only very slightly dampened, while vibrations transverse to the excitation direction A can be very strongly dampened by the webs 14.

3 shows a spacer 4 which is mounted in a housing 9 of a vibration sensor 1 by means of two damping elements 8. The damping elements 8 correspond to the 2 shown damping element 8 with an outer ring 12 and an inner ring 13, which are connected to each other via webs 14. The damping elements 8 are each clamped against a shoulder in the housing 9 by a screw-in sleeve 15 and are thus firmly connected to the housing 9 via the outer ring 12. The spacer 4 also has two shoulders, which serve as a counter bearing for the inner ring 13 of the damping element 8. In the 3 is the diameter of the spacer 4 for forming the shoulders for the inner ring 13 in the area between the damping elements 8 is increased compared to the two ends of the spacer 4. However, it is just as effective if the diameter of the spacer 4 is only increased in the area of the two shoulders. This would save additional weight and thus improve the vibration behavior.

List of reference symbols

1

Vibration sensor

2

opening

3

container

4

Spacer

5

drive

6

membrane

7

mechanical oscillator

8th

Damping element

9

Housing

10

Filling material

11

Passage opening

12

Outer ring

13

Inner ring

14

web

15

Screw-in sleeve

A

Excitation direction of the drive

W1

first heat conduction path

W2

second heat conduction path

Claims (10)

Vibration sensor (1) for detecting a fill level or limit level in the interior of a container (3), with a housing (9), a membrane (6) that can be excited to vibrate, and a drive (5) for setting the membrane (6) into vibration and/or for sensing a vibration of the membrane (6), wherein the drive (5) is connected to the membrane (6) via a mechanical coupling, characterized in that the mechanical coupling comprises a spacer (4), so that the drive (5) is arranged at a distance from the membrane (6) for thermal decoupling. Vibration sensor (1) after Claim 1 , characterized in that the spacer (4) is arranged such that a first heat conduction path (W1) from the membrane (6) via the spacer (4) to the drive (5) has a higher thermal resistance than a second heat conduction path (W2) from the membrane (6) via the housing (9) to an environment of the housing (9). Vibration sensor (1) according to one of the Claims 1 until 2 , characterized in that the housing (9) is adapted to be fastened to an opening (2) of the container (3) such that the drive (5) is arranged outside and the membrane (6) inside the container (3). Vibration sensor (1) according to one of the Claims 1 until 3 , characterized in that the spacer (4) has a substantially cylindrical shape with a length and a diameter, the length being a multiple of the diameter. Vibration sensor (1) according to one of the Claims 1 until 4 , characterized in that the spacer (4) is designed as a hollow body. Vibration sensor (1) according to one of the Claims 1 until 5 , characterized in that the spacer (4) is mounted in an oscillating manner in the housing (9) of the vibration sensor (1). Vibration sensor (1) after Claim 6 , characterized in that the spacer (4) is mounted in the housing (9) in an oscillating manner by means of at least one damping element (8), wherein the damping element (8) preferably dampens vibrations in an excitation direction (A) of the drive (5) substantially less than orthogonal to the excitation direction (A). Vibration sensor (1) after Claim 7 , characterized in that the at least one damping element (8) is designed as a diaphragm spring whose width and length or whose diameter is many times greater than its thickness. Vibration sensor (1) according to one of the Claims 7 until 8th , characterized in that the at least one damping element (8) has at least one through opening in the direction of the drive direction (A). Vibration sensor (1) according to one of the Claims 8 until 9 , characterized in that the at least one damping element (8) has an inner ring for connection to the damping element (8) and an outer ring for connection to the housing (9), wherein the inner ring is connected to the outer ring via at least one web.

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