Pressure transducer for determining and / or monitoring a first pressure of a medium

Abstract

The invention relates to a pressure transducer (1), comprising - a first pressure sensor (3), - a process adapter (6) having a membrane system (7) with the first separating membrane (8) and a second separating membrane (9), which are arranged with respect to one another in such a way that the first separating membrane (8) faces the medium (24) and the second separating membrane (9) faces away from the medium (24), and a first intermediate space (10) is enclosed between the first separating membrane (8) and the second separating membrane (9), said intermediate space having a vacuum, - a sensor unit (14) having a carrier (15), a vacuum tube (2), a second pressure sensor (16) and a communication unit (17), wherein the sensor unit (14) is pressure-tightly fastened to the pressure transducer (1) by means of the carrier (15) and is arranged such that the vacuum in the first intermediate space (10) can be monitored by means of the second pressure sensor (16), wherein the vacuum tube (2) extends through the carrier (15) and projects into the vacuum in a first end region (2a) and is hermetically sealed in a second end region (2b).

Description

[0001] Pressure sensor for determining and / or monitoring the initial pressure of a medium

[0002] The invention relates to a pressure sensor for determining and / or monitoring a first pressure of a medium.

[0003] In pressure measurement technology, absolute pressure, differential pressure, and gauge pressure sensors are known. Absolute pressure sensors determine the prevailing pressure of a process medium absolutely, i.e., relative to a vacuum, while differential pressure sensors determine the difference between two different pressures of the process medium or media. With gauge pressure sensors, the pressure of the process medium to be measured is determined relative to a reference pressure, where the prevailing atmospheric pressure in the vicinity of the gauge serves as the reference pressure.

[0004] Pressure sensors have a pressure-sensitive measuring element, the so-called pressure sensor, on whose first and second surfaces pressure is applied. In the case of relative or absolute pressure sensors, the pressure of the process medium to be measured acts on the first surface of the pressure sensor, while an absolute or reference pressure acts on the second surface. In the case of differential pressure sensors, a first and a second pressure of the process medium are applied to each surface. The measuring element bends depending on the relative pressure, which is formed by the difference between the pressures applied to the two surfaces. This bending is converted by an electronic unit into an electrical signal dependent on the relative pressure, which is then available for further processing or evaluation. A distinction is made, among other things, between capacitive and piezoresistive pressure sensors.A large number of such pressure sensors are manufactured and distributed by companies of the Endress+Hauser Group.

[0005] A ceramic pressure sensor, for example, comprises a ceramic base body and a ceramic measuring diaphragm, which is pressure-tightly bonded to the base body by means of an active brazing alloy, forming a measuring chamber. Furthermore, the pressure sensor typically includes a transducer for converting pressure-dependent deformation of the measuring diaphragm into a primary electrical signal, as well as a primary signal path extending through the base body. The transducer can be, for example, a capacitive or a resistive transducer. The primary signal path usually includes at least one electrical feedthrough through the base body. Silicon chips, which are generally bonded to a silicon substrate, are also known as pressure sensors instead of ceramic ones.

[0006] In the case of absolute and relative pressure sensors, the pressure of the medium is measured by means of one, and in the case of differential pressure sensors by means of two, pressure-sensitive diaphragms facing the process. Each diaphragm has an associated diaphragm bed, which typically serves to emboss the diaphragm and to limit its movement in case of overload. Additionally, a pressure transmission medium is used, which transmits the pressure of the medium acting on the diaphragm to one of the two surfaces of the pressure sensor via a pressure transmission path.

[0007] If the diaphragm breaks or is damaged, the medium can penetrate the pressure sensor and contaminate and / or even damage it. To prevent this, German patent application DE 19949831 B4 discloses the use of a diaphragm system consisting of two parallel diaphragms, one facing the medium and the other facing the pressure fluid. A vacuum-sealed space is provided between the two diaphragms. A detection device monitors any changes in the vacuum within this space. Currently, it is common practice to connect the vacuum port for applying the vacuum to the process adapter.

[0008] It is therefore an object of the present invention to provide a pressure sensor and a method in which the vacuum connection is integrated into the pressure sensor in a simple manner.

[0009] The problem is solved according to the invention by a pressure sensor according to claim 1 and a method according to claim 11.

[0010] With regard to the pressure sensor, the task is solved by a pressure sensor for determining and / or monitoring the initial pressure of a medium, with

[0011] a first pressure sensor which can be subjected to the first pressure of the medium on a first surface,

[0012] a process adapter with a membrane system comprising a first separation membrane and a second separation membrane, which are arranged such that the first separation membrane faces the medium and the second separation membrane faces away from the medium, and a first, vacuum-filled space is enclosed between the first and second separation membranes, wherein the first and second separation membranes are pressure-tightly attached to the process adapter at a circumferential edge, forming a pressure chamber between the second separation membrane and the process adapter, and wherein the membrane system is designed to transmit the first pressure to the pressure chamber.

[0013] a pressure transfer path designed to transfer the initial pressure from the pressure chamber to the first surface,

[0014] a sensor unit comprising a carrier, a vacuum tube, a second pressure sensor and a communication unit, wherein the sensor unit is attached to the pressure sensor in a pressure-tight manner by means of the carrier and is arranged such that the vacuum in the first space can be monitored by means of the second pressure sensor, wherein the second pressure sensor and the communication unit are electrically connected to each other and are arranged on a surface of the carrier facing the vacuum, wherein the vacuum tube extends through the carrier and projects into the vacuum in a first end region and is hermetically sealed in a second end region.

[0015] According to the invention, the vacuum connection is provided in the sensor unit. The vacuum connection thus does not need to be integrated as a separate connection in the process adapter, but is advantageously integrated into the sensor unit and the carrier. This means that the vacuum connection or vacuum tube and the second pressure sensor for monitoring the vacuum are located in the same unit. This simplifies the manufacture of the pressure sensor and, in particular, reduces the number of welds required for integrating the second pressure sensor and vacuum tube compared to conventional pressure sensors. The vacuum tube can be designed as a capillary or as a hollow cylinder. The vacuum tube can have a crimped section.

[0016] The sensor unit is pressure-tightly attached to the pressure transducer by means of the carrier, so that in the event of a leakage of the first separating diaphragm, the medium cannot pass through the sensor unit into the interior of the pressure transducer and potentially escape from the pressure transducer. The pressure-tight arrangement of the carrier within the pressure transducer ensures the overload resistance of the sensor unit even at high initial pressures of the medium. The communication unit and the second pressure sensor are located within the vacuum. The second pressure sensor is designed to monitor the vacuum. The pressure transducer thus enables vacuum monitoring via the second pressure sensor while maintaining the pressure resistance of the sensor unit. The first and / or second pressure sensor can be configured to output a measured value. The first pressure sensor can be located in a measuring unit of the pressure transducer.The pressure sensor can include an evaluation unit, which is specifically designed to process a measured value from the first pressure sensor and / or the second pressure sensor. The evaluation unit can be electrically connected to the first pressure sensor and / or the second pressure sensor. The carrier can be designed to establish an electrical connection between the communication unit and the evaluation unit of the pressure sensor. The communication unit can be designed to transmit a measured value from the second pressure sensor to the evaluation unit. The first pressure sensor and / or the second pressure sensor can be piezoresistive pressure sensors, for example, silicon chips. The sensor unit can be arranged on the process adapter or another component of the pressure sensor.

[0017] The first space is vacuum-sealed or evacuated. The absolute pressure in the first space is zero, whereby "zero absolute pressure" as used in the application refers to a technically feasible vacuum with a pressure of less than 100 mbar, and in particular less than 10 mbar.

[0018] In one embodiment, the second end region is hermetically sealed by means of a crimp and a seal. The seal is achieved in particular by means of a welded or soldered connection.

[0019] In one embodiment, the second pressure sensor and / or the communication unit is configured to output a loss of vacuum and / or an error signal in the event of a leak in the first separating membrane. If the first separating membrane leaks, medium will enter the first space. Depending on the type of medium entering, its pressure, and its velocity, the second pressure sensor will initially output a measured value that correlates with a loss of vacuum in the first space, thus indicating that a leak in the first separating membrane has occurred. If the pressure of the incoming medium exceeds the measuring range of the second pressure sensor, the second pressure sensor may output an error signal.On the other hand, the ingress of medium can cause a short circuit in the electrical connections between the second pressure sensor and the communication unit, resulting in the communication unit issuing an error signal. In one embodiment, the communication unit is configured to transmit a measured value from the second pressure sensor to an evaluation unit of the pressure transducer.

[0020] In one embodiment, the communication unit is configured as a printed circuit board with one or more contact surfaces, wherein the second pressure sensor is electrically, and in particular mechanically, connected to the printed circuit board by means of one or more contact surfaces. The second pressure sensor can be arranged on a surface of the printed circuit board facing the support or on a surface of the printed circuit board facing away from the support.

[0021] In one embodiment, the communication unit is electrically connected to the carrier. The carrier can have at least one connection pin for this purpose, by means of which the carrier and the communication unit are electrically connected. Preferably, the carrier can have at least two connection pins; one of the connection pins can be used to supply a voltage to the communication unit, and the other connection pin can be used to transmit data.

[0022] In one embodiment, the carrier is a cable gland. The cable gland can be configured to provide an electrical connection to the communication unit. The cable gland can have a base plate and at least one connection pin, in particular arranged perpendicular to the base plate and insulated from the base plate. The base plate and / or the at least one connection pin can be metallic.

[0023] In one embodiment, the support is connected to the pressure sensor by a pressure-tight weld. The support can be made of a metal. If the support is configured as a current feedthrough, a base plate of the current feedthrough can be welded to the pressure sensor.

[0024] In one embodiment, the pressure sensor has a pressure transmitter with a base body and the pressure transmission path arranged in the base body, which is designed to transmit the first pressure from the pressure chamber to the first surface.

[0025] In one embodiment, the pressure sensor has a sleeve that is pressure-tightly connected to the process adapter and the pressure transmitter and at least partially surrounds the pressure transmitter, so that a second space is formed between an outer wall of the pressure transmitter and an inner wall of the sleeve. This second space is fluidically connected to the first space via a channel located in the process adapter. The sleeve allows the sensor unit to be positioned at the second space, thus enabling the sensor unit to be located at a distance from the medium.

[0026] In one embodiment, the sensor unit is arranged on or inserted into the sleeve. The sleeve may have a recess that connects the sensor unit to the second cavity. The carrier can be pressure-tightly connected to the sleeve. Alternatively, the sensor unit can be arranged in an interior space within the sleeve. The carrier can also be pressure-tightly connected to this interior space. Inserting the sensor unit into the sleeve offers the advantage that the sensor unit is protected from environmental influences.

[0027] With regard to the method, the problem is further solved by a method for sealing a vacuum tube in a pressure sensor according to one of the previous embodiments, wherein the method comprises at least the following steps:

[0028] Applying a vacuum to the first gap using the vacuum tube,

[0029] Crimping the vacuum tube in a crimp area of ​​the vacuum tube, so that the vacuum is enclosed in the first space,

[0030] Sealing the vacuum tube in the second end area of ​​the vacuum tube, so that the vacuum in the first space is hermetically enclosed.

[0031] According to the invention, the vacuum in the first cavity is hermetically sealed by crimping and then sealing the vacuum tube after applying a vacuum to the first cavity. Crimping alone is sufficient to seal the vacuum; however, sealing is additionally performed to ensure the vacuum is maintained permanently. Crimping and sealing can also be performed simultaneously: the vacuum tube is crimped in the crimp area while the second end area is sealed. The second end area connects directly to the crimp area. The vacuum tube can be connected to a vacuum unit, particularly a vacuum pump, which is designed to apply a vacuum to the first cavity.

[0032] The embodiments of the method according to the invention apply mutatis mutandis to the pressure sensor according to the invention and vice versa. In an optional first process step, a pressure sensor can be provided, the first intermediate space of which is to be evacuated and whose vacuum tube, in particular, is not yet sealed. The further components can already be present in the pressure sensor, at least insofar as access to the vacuum tube for vacuuming, crimping, and sealing is possible. In particular, the sensor unit can already be pressure-tightly attached to the pressure sensor; the process adapter can already include the diaphragm system. The pressure transmitter, the pressure sensor, and / or, if applicable, the sleeve can also already be arranged in the pressure sensor.

[0033] In one embodiment, the first cavity is purged with a gas before it is subjected to a vacuum. The gas can be a noble gas or nitrogen. For purging with the gas, the vacuum tube can be connected to a delivery unit, for example a pump, which is designed to deliver the gas into the first cavity.

[0034] In one embodiment, sealing is achieved by means of a welding or soldering process.

[0035] In one embodiment, the vacuum tube is shortened after crimping such that an uncrimped section facing away from the vacuum is removed. Crimping typically takes place in a central area of ​​the vacuum tube. Any portion of the vacuum tube extending beyond the crimped area can be removed after crimping by cutting it off.

[0036] The invention will be explained in more detail with reference to the following figures, Figs. 1-4. They show:

[0037] Fig. 1: a first embodiment of the pressure sensor according to the invention.

[0038] Fig. 2: one embodiment of the membrane system.

[0039] Fig. 3: one embodiment of the sensor unit.

[0040] Fig. 4: a second embodiment of the pressure sensor according to the invention.

[0041] Figure 1 shows a schematic embodiment of a pressure sensor 1 according to the invention. The pressure sensor 1 comprises a first pressure sensor 3, a process adapter 6, and a sensor unit 14. The first pressure sensor 3, which can be subjected to the first pressure p1 of the medium 24 on a first surface 4 and, in particular, to a second pressure on a second surface 5, especially one opposite the first surface 4, can be arranged in a measuring unit 35 of the pressure sensor 1. The second pressure can be ambient pressure, absolute pressure, or another pressure of the medium 24. The pressure sensor 3 can be connected to an evaluation unit 28, which determines the first pressure p1 based on a measured value generated by the pressure sensor 3. The evaluation unit 28 can be connected to a display unit 29, which can be configured to display the first pressure p1.

[0042] The process adapter 6 has a membrane system 7, which is arranged on the medium side and shown in detail in Fig. 2. The membrane system 7 comprises a first separating membrane 8 and a second separating membrane 9, which are arranged relative to each other such that the first separating membrane 8 faces the medium 24 and the second separating membrane 9 faces away from the medium 24, and a first intermediate space 10 is enclosed between the first separating membrane 8 and the second separating membrane 9. The first intermediate space 10 is evacuated or has a vacuum. The first separating membrane 8 can be pressurized with the first pressure p1. The first separating membrane 8 and the second separating membrane 9 are each pressure-tightly attached to a circumferential edge 11a, 11b on the process adapter 6, so that a pressure chamber 12 is formed between the second separating membrane 9 and the process adapter 6. A membrane bed 26 can be associated with the second separating membrane 9.

[0043] The membrane system 7 is configured to transmit the initial pressure p1 to the pressure chamber 12. The process adapter 6 can include a section of the pressure transmission path 13, which is fluidically connected to the pressure chamber 12. The pressure transmission path 13 can be configured to transmit the initial pressure p1 from the pressure chamber 12 to the first surface 4. A further section of the pressure transmission path 13 can also be arranged in the measuring device 35.

[0044] The sensor unit 14 comprises a carrier 15, a second pressure sensor 16, and a communication unit 17, as shown by way of example in Fig. 3. The sensor unit 14 can be arranged on the first space 10 or on a second space 18 of the pressure transducer that is fluidically connected to the first space 10. The sensor unit 14 is pressure-tightly attached to the pressure transducer 1 by means of the carrier. For example, the sensor unit 14 can be arranged on the process adapter 6 and connected to the first space 10. The second pressure sensor 16 and the communication unit 17 are electrically connected to each other and arranged on a surface of the carrier 15 facing the vacuum. The second pressure sensor 16 is configured to monitor the vacuum in the first space 10. The sensor unit 14 further comprises a vacuum tube 2 by means of which the first space 10 is pressurized with vacuum.

[0045] In Fig. 3, the communication unit 17 is shown by way of example as a printed circuit board 19, which has one or more contact surfaces 32. The second pressure sensor 16 is electrically and, in particular, mechanically connected to the printed circuit board 19 by means of at least one of the contact surfaces 32, for example, by means of a solder joint. The carrier 15 is shown by way of example as a current feedthrough. The current feedthrough can have a base plate 34 and one or more connection pins 20. The communication unit 17 can be electrically connected to the carrier 15, for example, by means of at least one connection pin 20. The carrier 15 can be connected to the pressure sensor 1 by means of a pressure-tight weld. For example, the base plate 34 can be pressure-tightly welded to the pressure sensor 1. The vacuum tube 2 is, in particular, a capillary.A first end region 2a of the vacuum tube 2 protrudes into the vacuum, and a second end region 2b is hermetically sealed. This prevents the vacuum from escaping from the first space 10. The second end region 2b can have a crimp area 36 and a seal 37. Thus, when closing the vacuum tube 2, it can first be crimped in the crimp area 36 and then sealed, e.g., by soldering or welding. The sealing can also take place during the crimping process.

[0046] The second pressure sensor 16 and / or the communication unit 17 can be configured to output a loss of vacuum and / or an error signal in the event of a leakage of the first separating membrane 8. The communication unit 17 can be electrically connected to the evaluation unit 28, for example by means of the carrier 15, which can be configured as a current feedthrough. The communication unit 17 can be configured to transmit a measured value from the second pressure sensor 16 to the evaluation unit 28. The evaluation unit 28 can be configured to detect a leakage based on the measured value transmitted by the communication unit 17 and, in particular, to send a warning about the leakage to the display unit 29. The display unit 29 can be configured to display the warning about the leakage.The evaluation unit 28 can also be designed to detect a leak based on an error signal from the communication unit 17 and, in particular, to send a warning about the leak to the display unit 29.

[0047] The pressure sensor 1 can have a pressure transmitter 21 with a cylindrical base body 21a and the pressure transmission path 13 arranged therein, which may be filled with a pressure transmission fluid. The pressure transmitter 21 can be arranged between the measuring unit 35 and the process adapter 6. The pressure sensor 1 can further have a sleeve 22. The sleeve 22 surrounds the pressure transmitter 21 at least partially, so that a second space 18 is formed between an outer wall 21b of the pressure transmitter 21 and an inner wall 22a of the sleeve 22. As shown in Fig. 4, the sleeve 22 can surround the pressure transmitter 21 from its first end region 30 to its second end region 31. The sleeve 22 can be pressure-tightly connected to both the process adapter 6 and the pressure transmitter 21, in particular by means of a weld, especially an orbital weld. The weld points are shown as black, round dots.

[0048] The second space 18 is arranged, in particular, coaxially with the pressure transmission path 13. The second space 18 can be arranged such that it surrounds the pressure transmission path 13. The base body 21a of the pressure transmitter 21 can be cylindrical. The inner wall 22a of the sleeve 22 can be cylindrical. The second space 18 can essentially be in the form of a hollow cylinder.

[0049] The process adapter 6 can have a channel 23, which is arranged and configured such that the channel 23 fluidically connects the first intermediate space 10 with the second intermediate space 18. The channel 23 can lead from a region between the circumferential edges 11a, 11b of the first separating membrane 8 and the second separating membrane 9 to an end face 6a of the process adapter facing the pressure transmitter 21. As shown by way of example in Fig. 1, the channel 23 can initially have a section arranged perpendicular to the end face 6a in the region between the circumferential edges 11a, 11b of the first separating membrane 8 and the second separating membrane 9, which opens into an inclined section that finally leads to the second intermediate space 18.

[0050] The sensor unit 14 can be inserted into the sleeve 22, as shown in Fig. 1, or arranged on the sleeve 22, as shown in Fig. 4. In both cases, the sensor unit 14 is pressure-tightly connected to the sleeve. In the second case, the sensor unit 14 can be arranged in a recess 27 of the sleeve 22. Reference numeral list

[0051] 1 pressure sensor

[0052] 2 vacuum tubes

[0053] 2a first end area

[0054] 2b second end area

[0055] 3 first pressure sensor

[0056] 4 first area

[0057] 5 second area

[0058] 6 process adapters

[0059] 6a Front face of the process adapter

[0060] 7 Membrane system

[0061] 8 first separating membrane

[0062] 9 second separating membrane

[0063] 10 first space

[0064] 11a circumferential edge of the first separating membrane 11b circumferential edge of the second separating membrane 12 pressure chamber

[0065] 13 Pressure transmission path

[0066] 14 Sensor unit

[0067] 15 carriers

[0068] 16 second pressure sensor

[0069] 17 Communication unit

[0070] 18 second space

[0071] 19 printed circuit board

[0072] 20 connection pins

[0073] 21 pressure transmitters

[0074] 21a Basic body

[0075] 21b Outer wall of the pressure transmitter

[0076] 22 Sleeve

[0077] 22a Inner wall of the sleeve

[0078] Channel 23

[0079] 24 Medium

[0080] 26 Membrane bed

[0081] 27 recess

[0082] 28 evaluation units

[0083] 29 Display unit

[0084] 30 first end area of ​​the pressure transmitter

[0085] 31 second end area of ​​the pressure transmitter

[0086] 32 Contact surface Base plate Measuring mechanism Crimp area Sealing

Claims

Patent claims 1. Pressure sensor (1 ) for determining and / or monitoring a first pressure (p1) of a medium (24), with a first pressure sensor (3) which can be subjected to the first pressure (p1) of the medium (24) on a first surface (4), a process adapter (6) with a membrane system (7) comprising a first separation membrane (8) and a second separation membrane (9), which are arranged such that the first separation membrane (8) faces the medium (24) and the second separation membrane (9) faces away from the medium (24), and a first vacuum-filled intermediate space (10) is enclosed between the first separation membrane (8) and the second separation membrane (9), wherein the first separation membrane (8) and the second separation membrane (9) are pressure-tightly attached to a circumferential edge (11) on the process adapter (6) to form a pressure chamber (12) between the second separation membrane (9) and the process adapter (6), wherein the membrane system (7) is designed to transmit the first pressure (p1) to the pressure chamber (12). a pressure transmission path (13) configured to transmit the first pressure (p1) from the pressure chamber (12) to the first surface (4), a sensor unit (14) with a carrier (15), a vacuum tube (2), a second pressure sensor (16) and a communication unit (17), wherein the sensor unit (14) is attached to the pressure sensor (1) in a pressure-tight manner by means of the carrier (15) and is arranged such that the vacuum in the first intermediate space (10) can be monitored by means of the second pressure sensor (16), wherein the second pressure sensor (16) and the communication unit (17) are electrically connected to each other and are arranged on a surface of the carrier (15) facing the vacuum, wherein the vacuum tube (2) runs through the carrier (15) and projects into the vacuum in a first end region (2a) and is hermetically sealed in a second end region (2b).

2. Pressure sensor (1) according to claim 1 , wherein the second end area (2b) is hermetically sealed by means of a crimp and a seal.

3. Pressure sensor (1) according to one of the preceding claims, wherein the second pressure sensor (16) and / or the communication unit (17) is configured to output a loss of vacuum and / or an error signal in the event of a leakage of the first separating membrane (8).

4. Pressure sensor (1) according to one of the preceding claims, wherein the communication unit (17) is designed to transmit a measured value from the second pressure sensor (16) to an evaluation unit (28) of the pressure transducer (1).

5. Pressure sensor (1) according to one of the preceding claims, wherein the carrier (15) is a current feedthrough.

6. Pressure sensor (1) according to claim 5, wherein the current passage has a base plate (34) and at least one connection pin (20) arranged perpendicular to the base plate (34) and insulated from the base plate.

7. Pressure sensor (1) according to one of the preceding claims, wherein the support (15) is connected to the pressure sensor (1) by means of a pressure-tight weld.

8. Pressure sensor (1) according to one of the preceding claims, wherein the pressure sensor (1) has a pressure transmitter (21) with a base body (21a) and the pressure transmission path (13) arranged in the base body (21a), which is designed to transmit the first pressure (p1) from the pressure chamber (12) to the first surface (4).

9. Pressure sensor (1) according to one of claims 7-8, wherein the pressure sensor (1) has a sleeve (22) which is pressure-tightly connected to the process adapter (6) and the pressure transmitter (21) and surrounds the pressure transmitter (21) at least partially, so that a second space (18) is formed between an outer wall (21b) of the pressure transmitter (21) and an inner wall (22a) of the sleeve (22), wherein the second space (18) is fluidically connected to the first space (10) by means of a channel (23) arranged in the process adapter (6).

10. Pressure sensor (1) according to claim 9, wherein the sensor unit (14) is arranged on the sleeve (22) or inserted into the sleeve (22).

11. Method for sealing a vacuum tube (2) in a pressure sensor (1) according to any one of claims 1-10, wherein the method comprises at least the following steps: Applying a vacuum to the first space (10) by means of the vacuum tube (2), Crimping the vacuum tube (2) in a crimp area (36) of the vacuum tube (2) such that the vacuum is enclosed in the first space (10), Sealing the vacuum tube (2) in the second end region (2b) of the vacuum tube (2) so that the vacuum in the first space (10) is hermetically enclosed.

12. Method according to claim 11, wherein the first space (10) is purged with a gas before the first space (10) is subjected to a vacuum.

13. Method according to one of claims 11-12, the sealing is done by means of a welding or soldering process.

14. Method according to one of claims 11-13, wherein the vacuum tube (2) is shortened after crimping such that an uncrimped area facing away from the vacuum is removed.

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