Method for determining pressure in a vacuum switching tube and pressure measuring device

Abstract

The invention relates to a method for determining a pressure in a vacuum switching tube (1), comprising the steps of: providing the vacuum switching tube, which has a first electrode (3) and a second electrode (4), which have a contact state in which the first electrode and the second electrode are in contact with each other, and a spaced-away state in which the electrodes are spaced apart from each other, and a housing (2) which defines an interior space (26) in which the electrodes are arranged and which maintains a vacuum in the interior space, so that in the spaced-away state the electrodes are electrically isolated from each other by the vacuum; applying an electric field (23) and a magnetic field (24) to the interior space, so that a gas discharge is generated, wherein the orientation of the electric field in the interior space is different from the orientation of the magnetic field; measuring a current (I) of the gas discharge at a plurality of different times (t);Forming a measurement data set (I(t)) from the currents and the times, wherein the measurement data set represents the temporal evolution of the current during the gas discharge; fitting at least a part of the measurement data set with at least one fitting function (43) which has one or more fitting parameters; inferring the pressure from at least one of the fitting parameters.

Description

[0001] The invention relates to a method for measuring pressure in a vacuum switching tube and a pressure measuring device.

[0002] A vacuum switching tube, such as that known from US 3,263,162 A, is designed to perform electrical switching operations under a vacuum. To interrupt an electric current, the two electrodes in the vacuum switching tube are moved from a contact state, in which the two electrodes are in contact, to a spaced-apart state, in which the two electrodes are spaced apart. In the spaced-apart state, the vacuum electrically isolates the two electrodes from each other. To ensure the function of the vacuum switching tube, it is necessary that the vacuum pressure be low. Conventionally, the vacuum pressure is determined using the magnetron method. In this method, electrons are accelerated in an electric field and forced by a magnetic field onto spiral paths, so that the electrons have to travel a much longer path to the anode.Gas molecules struck by these electrons can be ionized, allowing a gas discharge to build up in the vacuum. The current of the gas discharge correlates with the vacuum pressure. The current is characterized by a steep rise to a maximum, followed by a more gradual decline. Traditionally, the current at the maximum is determined and used as a measure of the vacuum pressure. However, the time-resolved current is superimposed with several oscillations. This leads to inaccuracies in determining the current at the maximum, which in turn affects the pressure measurement.

[0003] The object of the invention is therefore to provide a method for measuring pressure in a vacuum switching tube and a pressure measuring device with which the pressure in the vacuum switching tube can be determined with high accuracy.

[0004] The inventive method for determining a pressure in a vacuum switching tube comprises the steps of: b) providing the vacuum switching tube, which has a first electrode and a second electrode, which have a contact state in which the first electrode and the second electrode are in contact with each other, and a separation state in which the first electrode and the second electrode are separated from each other, as well as a housing that delimits an interior space in which the first electrode and the second electrode are arranged, and which maintains a vacuum in the interior space, so that in the separation state the first electrode and the second electrode are electrically isolated from each other by the vacuum; c) applying an electric field and a magnetic field to the interior space, so that a gas discharge is generated, wherein the orientation of the electric field in the interior space is different from the orientation of the magnetic field;d) Measuring the current of the gas discharge at a plurality of different times; e) Creating a measurement data set from the currents and times, wherein the measurement data set represents the temporal evolution of the current during the gas discharge; f) Fitting at least a part of the measurement data set with at least one fitting function having one or more fitting parameters; g) Deducing the vacuum pressure from at least one of the fitting parameters. Using the fitting function and its fitting parameters, a more precise evaluation of the measurement data set is possible compared to simply determining the maximum of the measurement data set, as is conventionally done. This more precise evaluation of the measurement data set also allows the vacuum pressure to be determined with high accuracy.

[0005] It is preferred that in the measurement data set the current intensities rise to a maximum and then fall, whereby the measurement data set has a rising edge that is placed in time before the maximum and a falling edge that is placed in time after the maximum.

[0006] The fitting function preferentially adapts the falling edge. The falling edge is significantly longer than the rising edge, allowing it to be fitted with higher accuracy. This enables the vacuum pressure to be determined with exceptionally high precision. Preferably, the fitting function adapts the falling edge only within a range that is temporally separated from the maximum. This range can be filtered particularly well to remove oscillations superimposed on the gas discharge current. By removing these oscillations, the measurement data set in this range has high accuracy, allowing the fitting function to be adapted with exceptional precision and the vacuum pressure to be determined with exceptional accuracy.

[0007] It is preferred that the adaptation function adapts the rising edge in addition to the falling edge. This allows for an increase in the number of adaptation parameters, thereby improving the accuracy of determining the vacuum pressure.

[0008] The matching function preferentially adjusts the rising edge. The rising edge is significantly steeper than the falling edge and is therefore particularly suitable for determining a delay after which the gas discharge ignites. The longer the delay, the lower the vacuum pressure.

[0009] It is preferred that one of the adjustment parameters is a delay that specifies the time interval between a time zero point and a generation time, wherein the time zero point is the first time in time at which both the electric field and the magnetic field are applied to the interior, and wherein the gas discharge forms at the generation time.

[0010] It is preferred that in step f) the rising edge is fitted with a further fitting function that has one or more additional fitting parameters, wherein in step g) the vacuum pressure is deduced from at least one of the additional fitting parameters. This allows the accuracy for determining the vacuum pressure to be further increased. It is conceivable to calculate an average of the pressure determined from the fitting parameters and the pressure determined from the additional fitting parameters.

[0011] One of the further adjustment parameters is preferably a delay that specifies the time interval between a time zero point and a generation time, wherein the time zero point is the first time in time at which both the electric field and the magnetic field are applied to the interior, and wherein the gas discharge forms at the generation time.

[0012] In step e), the current intensities measured at different times in step d) are preferably filtered, thereby generating the measurement data set. This smooths the measurement data set, allowing it to be fitted with particularly high accuracy and enabling the pressure to be determined with exceptional accuracy. It is preferred that a low-pass filter be used in step e).

[0013] The method preferably comprises the step of: a) performing a calibration by setting different pressures in the interior of a calibration vacuum switching tube having an interior, generating a calibration gas discharge at each of the different pressures by applying the electric field and the magnetic field to the interior of the calibration vacuum switching tube, and measuring the electric current of the calibration gas discharge at a plurality of different times, wherein a calibration data set is formed from the currents of the calibration gas discharge and the times of the calibration gas discharge, wherein the calibration data set represents the time evolution of the current of the calibration gas discharge, wherein at least a part of the calibration data set is fitted with the at least one fitting function.This allows a characteristic map to be created from which the vacuum pressure can be deduced based on at least some of the values ​​of the adaptation parameters determined in step f). It is also conceivable that the characteristic map is created in such a way that the vacuum pressure can be deduced based on at least some of the values ​​of the adaptation parameters determined in step f) and at least some of the values ​​of the other adaptation parameters determined in step f).

[0014] The interior of the calibration vacuum switching tube is preferably identical in construction to the interior of the vacuum switching tube, except for the presence of a through-hole through which the interior of the calibration vacuum switching tube can be supplied from outside the tube with a gas having different pressures. This allows the characteristic curve to be determined with particularly high accuracy, and consequently, the vacuum pressure can also be determined with particularly high accuracy.

[0015] The pressure measuring device according to the invention is set up to carry out the method.

[0016] The invention will be explained in more detail below with reference to the attached schematic drawings. These show Fig. 1 a section through a vacuum switching tube, Fig. 2 a top view of a pressure measuring device, Fig. 3 several example measurement data sets and Fig. 4 an example measurement data set.

[0017] With reference to Fig. 1, Fig. 2, Fig. 3 to Fig. Paragraph 4 comprises a method for determining a pressure in a vacuum switching tube 1, comprising the steps of: b) providing the vacuum switching tube, which has a first electrode 3 and a second electrode 4, which have a contact state in which the first electrode 3 and the second electrode 4 are in contact with each other, and a separation state in which the first electrode 3 and the second electrode 4 are separated from each other, and a housing 2 which delimits an interior space 26 in which the first electrode 3 and the second electrode 4 are arranged, and which maintains a vacuum in the interior space 26 such that, in the separation state, the first electrode 3 and the second electrode 4 are electrically isolated from each other by the vacuum; c) applying an electric field 23 and a magnetic field 24 to the interior space 26, such that a gas discharge is generated, wherein in the interior space 26 the orientation of the electric field 23 is different from the orientation of the magnetic field 24;d) Measuring the current I of the gas discharge at a plurality of different times t; e) Creating a measurement data set I(t) from the currents I and the times t, wherein the measurement data set I(t) represents the temporal evolution of the current I during the gas discharge; f) Fitting at least a part of the measurement data set I(t) with at least one fitting function 43, which has one or more fitting parameters; g) Inferring the pressure of the vacuum from at least one of the fitting parameters.

[0018] Fig. Figure 1 shows that the vacuum switching tube 1 provided in step b) can have an axial direction 31, a radial direction 32 related to the axial direction 31, and a circumferential direction 33 related to the axial direction 31. The first electrode 3 can be fixedly arranged relative to the housing 2, and the second electrode 4 can be longitudinally displaceable in the axial direction 31 relative to the housing 2. For this purpose, the vacuum switching tube 1 can have a bearing 9 on which the second electrode 4 can slide in and against the axial direction 31. It is conceivable to displace the second electrode 4 mechanically, in particular by using a spring accumulator. Starting from the point in Fig. In the contact state shown in Figure 1, the first electrode 3 and the second electrode 4 can be brought into a spaced-away state by displacing the second electrode 4 away from the first electrode 4 in the axial direction 31. The first electrode 3 can have a first contact surface 7 and the second electrode 4 can have a second contact surface 8, wherein the first contact surface 7 and the second contact surface 8 are arranged in the interior 26. The first electrode 3 can have a thickening at its longitudinal end facing the second electrode 4, and the second electrode 4 can have a thickening at its longitudinal end facing the first electrode 3.The first contact surface 7 and the second contact surface 8 are in contact in the contact state, allowing a current to flow from the first electrode 3 to the second electrode 4, and are spaced apart from each other in the separation state, preventing the current from flowing from the first electrode 3 to the second electrode 4.

[0019] The first electrode 3 can have a first terminal 5 located outside the housing 2, and the second electrode 4 can have a second terminal 6 located outside the housing 2. Electrical conductors can be connected to the first terminal 5 and the second terminal 6 in an electrically conductive manner. The vacuum switching tube 1 can have a bellows 10 which is attached to the bearing 9 and to the first electrode 3, in particular to an electrode projection 25 extending radially 32 from the remaining first electrode 3, enclosing the first electrode 3 and sealing the interior 26 against a vacuum.

[0020] How it looks Fig. As can be seen in Figure 1, the housing 2 can be formed from several sub-housings. The housing 2 can, for example, have a switching chamber housing 14, which is made of or consists of a metal or alloy. The switching chamber housing 14 can completely enclose a switching chamber 13 in the circumferential direction 33, which is part of the interior 26. The first contact surface 7 and the second contact surface 8 are arranged in the switching chamber 13.

[0021] The housing 2 can, for example, comprise a first ceramic housing 17 arranged opposite the axial direction 31 of the switching chamber housing 14, and / or a second ceramic housing 18 arranged in the axial direction 31 of the switching chamber housing 14. The switching chamber housing 14 can be electrically isolated from other components of the vacuum switching tube 1 by means of the first ceramic housing 17 and / or the second ceramic housing 18. It is conceivable that the first ceramic housing 17 and / or the second ceramic housing 18 are formed in one piece or are formed from a plurality of partial ceramic housings 19 arranged side by side in the axial direction 31.

[0022] The housing 2 can, for example, comprise a first flange housing 15, which is arranged opposite the axial direction 31 to the first ceramic housing 17 and is attached to the first electrode 3, and a second flange housing 16, which is arranged in the axial direction 31 to the second ceramic housing 18 and is attached to the bearing 19. The first flange housing 15 and the first ceramic housing 17 can fully delimit a first flange chamber 11 in the circumferential direction 33, which is part of the interior 26. The second flange housing 16 and the second ceramic housing 18 can fully delimit a second flange chamber 12 in the circumferential direction 33, which is part of the interior 26.

[0023] The first flange chamber 11 and the second flange chamber 12 can have a smaller cross-section than the switching chamber 13, the cross-section having a normal that is parallel to the axial direction 31.

[0024] The vacuum switching tube 1 can have two chamber shields 20 attached to the switching chamber housing 14 and projecting into the interior 26, one of the two chamber shields 20 electrically shielding the first flange chamber 11 from switching chamber 13 and against metal vapor, and the other chamber shield 20 electrically shielding the second flange chamber 12 from switching chamber 13 and against metal vapor. The chamber shields 20 can be electrically connected to the switching chamber housing 14. Furthermore, for electrical shielding and shielding against metal vapor, a flange shield 21 can be attached to the first flange housing 15, which projects into the interior 26, and another flange shield 21 can be attached to the second flange housing 16, which also projects into the interior 26.In the area where the partial ceramic housings 19 meet, an intermediate shield 22 can be arranged for electrical shielding and for shielding against metal vapor, with the intermediate shield 22 projecting into the interior 26.

[0025] Fig. Figure 1 shows that the electric field 23 applied in step c) can extend from the first electrode 3 and / or the second electrode 4 to the housing 2. Both polarities are conceivable, i.e., the anode can be formed by the housing 2 as well as by the first electrode 3 and / or the second electrode 4. The first electrode 3 and the second electrode 4 can be in contact or in a spaced-apart state. In particular, the electric field 23 can extend to the switching chamber housing 14. The electric field 23 and the magnetic field 24 can enclose an angle in the interior 26, which lies, for example, in the range of 70° to 90°, in particular from 80° to 90° or from 85° to 90°. The electric field 23 can, for example, enclose an angle with the radial direction 32 which lies in a range of 0° to 30°, in particular in a range of 0° to 15° or of 0° to 5°.The magnetic field 24 can, for example, enclose an angle with the axial direction 31 which lies in a range of 0° to 30°, in particular in a range of 0° to 15° or of 0° to 5°, cf. . Fig. 1.

[0026] Alternatively, instead of the electric field 23 applied in step c) extending from the first electrode 3 and / or the second electrode 4 to the housing 2, the first electrode 3 and the second electrode 4 can be arranged in a spaced-apart state, and the electric field 23 can extend from the first electrode 3 to the second electrode 4. Both polarities are conceivable; that is, the anode can be formed by the first electrode 3 or the second electrode 4. The electric field 23 and the magnetic field 24 can enclose an angle within the interior 26, which lies, for example, in the range of 70° to 90°, in particular 80° to 90° or 85° to 90°. The electric field 23 can, for example, enclose an angle with the axial direction 31 which lies in a range of 0° to 30°, in particular in a range of 0° to 15° or of 0° to 5°.The magnetic field 24 can, for example, enclose an angle with the radial direction 32 which lies in a range of 0° to 30°, in particular in a range of 0° to 15° or from 0° to 5°.

[0027] It is conceivable that the magnetic field 24 is switched on first and then the electric field 23. Alternatively, it is conceivable that the electric field 23 and the magnetic field 24 are switched on simultaneously.

[0028] How it looks Fig. 3 and Fig. As can be seen in Figure 4, the currents I in the measurement data set I(t) rise to a maximum 40 and then fall, resulting in a rising edge 41, which occurs before the maximum 40, and a falling edge 42, which occurs after the maximum 40. The rising edge 41 can be steeper than the falling edge 42. This means that the time it takes for the current I to reach the maximum 40 is longer than the time it takes for the current I to return to its value before rising to the maximum. Fig. Figure 3 shows five different measurement data sets I(t), with the first data set I(t) on the left. This first data set is unfiltered. To its right is a second data set I(t), which was obtained by filtering the currents I measured at different times t in step e) using a low-pass filter with a cutoff frequency f1. Frequencies below the cutoff frequency are passed through, while frequencies above the cutoff frequency are removed. To achieve the smoothest possible curve, the cutoff frequency can be, for example, in a range from 1 Hz to 500 Hz, or more specifically, from 1 Hz to 20 Hz.To the right of the second measurement data set I(t) are shown a third measurement data set I(t) filtered by a low-pass filter with cutoff frequency f2, a fourth measurement data set I(t) filtered by a low-pass filter with cutoff frequency f3, and a fourth measurement data set I(t) filtered by a low-pass filter with cutoff frequency f4. The order of the values ​​is f1 > f2 > f3 > f4.

[0029] The maximum I(t) of the first to fifth measurement data sets is shown. Conventionally, the vacuum pressure is determined from the maximum I. It can be seen that the current I of the maximum I depends strongly on the cutoff frequency of the low-pass filter. The matching function 43 determined according to the invention is also shown. Any function can be used for the matching function 43. The matching function 43 can include or consist of one or more exponential functions, a Gaussian function, linear functions, and / or polynomials. A convolution of a Gaussian function with one or more exponential functions is also conceivable.

[0030] In Fig. Figure 3 shows that the fitting function 43 fits the falling edge 42. In a first example, the fitting function 43 can have the form: A(t)=A0e−t−Δt1τ1.

[0031] In this example, A0, Δt1, and τ1 are the fitting parameters. It is conceivable that, as is also the case in Fig. As shown in Figure 3, the fitting function 43 adjusts the falling edge 42 only within a range that is temporally separated from the maximum 40. This range can, for example, be located at a distance from the maximum 40 that lies within a range of 0.1 s to 5 s.

[0032] It is conceivable that the adjustment function 43 adjusts not only the falling edge 42 but also the rising edge 41. For this to be possible, the adjustment function could have a sum, where one term of the sum is a rising function and another term of the sum is a falling function.

[0033] It is conceivable that the fitting function 43 adapts the rising edge 41. In a second example, the fitting function 43 can have the form: B(t)=B0(1−e−t−Δt2τ2).

[0034] In this example, B0, Δt2 and τ2 are the fitting parameters.

[0035] One of the adjustment parameters can be a delay Δt (see below). Fig. 4), which specifies the time interval between a time zero t0 and a generation time t1, where the time zero t0 is the first time at which both the electric field 23 and the magnetic field 24 are applied to the interior space 26, and where the gas discharge forms at the generation time t1. It is conceivable to set t0=0. Furthermore, it is conceivable that the adjustment parameters Δt1 and Δt2 mentioned in the first and second examples represent the delay Δt.

[0036] It is conceivable that in step f), the rising edge 41 is fitted with a further fitting function that has one or more additional fitting parameters, whereby in step g), the vacuum pressure is deduced from at least one of these additional fitting parameters. Any function can be used for the further fitting function. The further fitting function can include or consist of one or more exponential functions, a Gaussian function, linear functions, and / or polynomials. A convolution of a Gaussian function with one or more exponential functions is also conceivable.One of the further adjustment parameters is a delay Δt, which specifies the time interval between a time zero point t0 and a generation time t1, where the time zero point t0 is the first time in time at which both the electric field 23 and the magnetic field 24 are applied to the interior 26, and where the gas discharge forms at the generation time t1.

[0037] The method can comprise the step of: a) performing a calibration by setting different pressures in the interior of a calibration vacuum switching tube having an interior, generating a calibration gas discharge at each of the different pressures by applying an electric field and a magnetic field to the interior of the calibration vacuum switching tube, and measuring the electric current I of the calibration gas discharge at a plurality of different times t, whereby a calibration data set is formed from the currents I of the calibration gas discharge and the times t of the calibration gas discharge, wherein the calibration data set represents the time evolution of the current I of the calibration gas discharge, wherein at least a part of the calibration data set is fitted with the at least one fitting function. The different pressures can, for example, be in a range of 10 -9 mbar up to 10 -3The pressure can be measured in mbar. It is also possible to adjust the calibration data set using the additional adjustment function. A characteristic curve can be created from at least one of the calibration adjustment parameters and optionally from at least one of the other calibration adjustment parameters, from which the pressure can be read.

[0038] The calibration data set can be formed by filtering the current intensities I measured at the different times t in step a), in particular by means of the low-pass filter.

[0039] The interior of the calibration vacuum switching tube can be identical in construction to the interior 26 of the vacuum switching tube 1, except for the presence of a through-hole through which the interior of the calibration vacuum switching tube can be supplied from outside the calibration vacuum switching tube with a gas having different pressures. The walls that delimit the interior 26 of the vacuum switching tube 1 preferably comprise the same material or materials as the walls that delimit the interior of the calibration vacuum switching tube.

[0040] Fig. Figure 2 shows a pressure measuring device 50 configured to perform the method. The pressure measuring device 50 may include a voltage source 51 configured to generate the electric field 23. The pressure measuring device 50 may include a magnet 52, in particular a permanent magnet and / or a coil, configured to generate the magnetic field 24. Reference symbol list 1 vacuum switching tube 2 cases 3 first electrode 4 second electrode 5 first connection 6 second connection 7 first contact surface 8 second contact surface 9 warehouses 10 bellows 11 first flange chamber 12 second flange chamber 13 Switching chamber 14 Switch chamber housings 15 first flange housing 16 second flange housing 17 first ceramic housing 18 second ceramic housing 19 partial ceramic housings 20-chamber screen 21 Flange screen 22 Intermediate screen 23 electric field 24 Magnetic field 25 electrode protrusion 26 Interior 31 Axial direction 32 Radial direction 33 Circumferential direction 40 Maximum 41 rising flank 42 falling flank 43 Adjustment function 50 Pressure measuring device 51 Voltage source 52 Magnet f x Cutoff frequency I electric current t time I(t) measurement data set t0 Time zero t1 Production time Δt delay

Claims

Method for determining a pressure in a vacuum switching tube (1), comprising the steps: b) providing the vacuum switching tube (1) having a first electrode (3) and a second electrode (4) having a contact state in which the first electrode (3) and the second electrode (4) are in contact with each other and a separation state in which the first electrode (3) and the second electrode (4) are separated from each other, and a housing (2) having an interior space (26) in which the first electrode (3) and the second electrode (4) are arranged and which maintains a vacuum in the interior space (26) such that in the separation state the first electrode (3) and the second electrode (4) are electrically isolated from each other by the vacuum;c) Applying an electric field (23) and a magnetic field (24) to the interior space (26) such that a gas discharge is generated, wherein the orientation of the electric field (23) in the interior space (26) is different from the orientation of the magnetic field (24); d) Measuring a current (I) of the gas discharge at a plurality of different times (t); e) Forming a measurement data set (I(t)) from the currents (I) and the times (t), wherein the measurement data set (I(t)) represents the temporal evolution of the current (I) during the gas discharge; f) Fitting at least a part of the measurement data set (I(t)) with at least one fitting function (43) which has one or more fitting parameters; g) Deducing the pressure of the vacuum from at least one of the fitting parameters. Method according to claim 1, wherein in the measurement data set I(t) the current intensities (I) rise to a maximum (40) and then fall, whereby the measurement data set (I(t)) has a rising edge (41) which is arranged temporally before the maximum (40) and a falling edge (42) which is arranged temporally after the maximum (40). Method according to claim 2, wherein the adaptation function (43) adapts the falling flank (42). Method according to claim 3, wherein the adaptation function (43) adapts the falling flank (42) only in a region which is arranged temporally spaced from the maximum (40). Method according to claim 3 or 4, wherein the adaptation function (43) adapts the rising flank (41) in addition to the falling flank (42). Method according to any one of claims 2 to 4, wherein the adaptation function (43) adapts the rising flank (41). Method according to any one of claims 1 to 6, wherein one of the adjustment parameters is a delay (Δt) which specifies the time interval between a time zero point (t0) and a generation time (t1), wherein the time zero point (t0) is the first time in time at which both the electric field (23) and the magnetic field (24) are applied to the interior space (26), and wherein the gas discharge forms at the generation time (t1). Method according to one of claims 3, 4 or 7, wherein in step f) the rising flank (41) is adapted with a further adaptation function which has one or more further adaptation parameters, wherein in step g) the pressure of the vacuum is inferred from at least one of the further adaptation parameters. Method according to claim 8, wherein one of the further adjustment parameters is a delay (Δt) which specifies the time interval between a time zero point (t0) and a generation time (t1), wherein the time zero point (t0) is the first time in time at which both the electric field (23) and the magnetic field (24) are applied to the interior (26), and wherein the gas discharge forms at the generation time (t1). Method according to any one of claims 1 to 9, wherein in step e) the current intensities (I) measured at the different times (t) in step d) are filtered, thereby forming the measurement data set (I(t)). Method according to claim 10, wherein in step e) filtering is carried out using a low-pass filter. A method according to any one of claims 1 to 11, comprising the step: a) performing a calibration by setting different pressures in the interior of a calibration vacuum switching tube having an interior, generating a calibration gas discharge at each of the different pressures by applying the electric field and the magnetic field to the interior of the calibration vacuum switching tube, and measuring the electric current (I) of the calibration gas discharge at a plurality of different times (t), wherein a calibration data set is formed from the currents (I) of the calibration gas discharge and the times (t) of the calibration gas discharge, wherein the calibration data set represents the time evolution of the current (I) of the calibration gas discharge, wherein at least a part of the calibration data set is fitted with the at least one fitting function. Method according to claim 12, wherein the interior of the calibration vacuum switching tube is identical in construction to the interior (26) of the vacuum switching tube (1) except for the presence of a through-hole, via which the interior of the calibration vacuum switching tube can be supplied from outside the calibration vacuum switching tube with a gas having different pressures. Pressure measuring device configured to perform a method according to any one of claims 1 to 13.

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