Ionization vacuum measuring cell

Abstract

An ionization vacuum measuring cell comprises an anode (3 A ) and a cathode (4 K ) in a measuring chamber (107). The measuring chamber (107), a housing (101) for a connecting rod (104) of the cathode (4) via a vacuum-tight feedthrough (103). K ) to the outside. The measuring chamber (107) holds the rod (104) in a purely electrically insulating feedthrough (109). The measuring chamber (107) can be replaced in the housing (101) via a detachable plug connection (106).

Description

[0001] In the present description and the claims, we understand the term “feedthrough” to mean a substantially rod-shaped component, The holding arrangement by which this component is held to a plate-shaped second component and protrudes through the plate-shaped component. The feedthrough can be understood as either encompassing the rod-shaped component or not encompassing it, depending on whether it is firmly or detachably connected to this component. In any case, at the feedthrough, the rod-shaped component is in direct contact with a solid body of the feedthrough. Thus, a clear opening in the plate-shaped component through which a rod-shaped component protrudes is not a feedthrough in the sense used here.

[0002] If the bushing is electrically insulated or insulating, it creates electrical insulation between the rod-shaped and the plate-shaped component.

[0003] If the feedthrough is vacuum-tight, then with the inserted rod-shaped component there will be no or practically no gas leakage from one side of the plate-shaped component to the other side.

[0004] DE 42 07 906 A1 discloses a device for igniting a gas discharge in a cold-electrode ionization gauge. WO 2013 / 033851 A1 relates to an ionization vacuum measuring cell; DE 600 03 249 T2 relates to vacuum gauges and more, specifically cold-cathode ionization vacuum gauges; US 2 758 232 A relates to improved vacuum discharge gauges; and WO 2008 / 051603 A2 relates to a method and device for shielding pin insulators in an ionization gauge. First aspect

[0005] The invention, in its first aspect, relates to an ionization vacuum measuring cell. It comprises a housing with a measuring connection for the vacuum to be measured at one end portion of the housing. The measuring connection is an arrangement of one or more openings in the said housing end portion, through which the ambient vacuum atmosphere to be measured extends into the housing.

[0006] A measuring chamber is provided within the housing, i.e., its interior is connected to the aforementioned measuring connection of the housing via a gas flow. This connection is such that, when the ambient pressure changes, the pressure in the measuring chamber adjusts very quickly, virtually instantaneously, to the pressure to be measured. The pressure to be measured is the pressure directly at the measuring connection.

[0007] A first and a second electrode are provided in the measuring chamber. These electrodes are formed substantially coaxially with respect to an axis and are arranged at a distance from one another.

[0008] Between these two electrodes, an ionization chamber is formed in the measuring chamber, in which the gas is ionized upon application of a corresponding electrical potential difference between the electrodes. The first of the electrodes has a substantially cylindrical inner surface as the electrode surface facing the ionization chamber.

[0009] A feedthrough which is both electrically insulating and vacuum-tight is provided for an electrical lead to one of the electrodes or for one of the electrodes itself, with an electrical insulator with respect to parts of the measuring cell which are placed at a different electrical potential than that of the lead through or electrode.

[0010] It is well known that the surfaces exposed to the ionization chamber of such an ionization vacuum measuring cell are subject to deterioration, particularly deposits, which necessitates repeated cleaning. This results in correspondingly long downtimes of the ionization vacuum measuring cell and the processes dependent on its measurement results.

[0011] In order to solve the problem of keeping the ionization vacuum measuring cell operational for a longer period of time, the measuring chamber is now designed as a replaceable component

[0012] Since the measuring chamber contains the first electrode, which has a substantially cylindrical and thus relatively large inner surface, which is freely exposed to the ionization chamber and the corresponding contamination, this inventive design of the ionization vacuum measuring cell ensures that the necessary, time-consuming cleaning, at least of the aforementioned large-area electrode, can be carried out without significantly interrupting the operation of the ionization vacuum measuring cell. The contaminated measuring chamber in the aforementioned cell is replaced with a cleaned or new measuring chamber.

[0013] The modular component concept for the measuring chamber also makes it possible to flexibly use differently designed measuring chambers on one and the same ionization vacuum measuring cell or, conversely, to use one and the same measuring chamber on otherwise differently designed ionization vacuum measuring cells.

[0014] The production of the ionization vacuum measuring cells is made more efficient by the fact that, on the one hand, different measuring chambers with, for example, a uniform external geometry can be manufactured as built-in modules, the other parts of the ionization vacuum measuring cell can be manufactured with a compatible geometry, and, depending on the specific application, the respective ionization vacuum measuring cells can be flexibly assembled with the corresponding measuring chambers as required.

[0015] The measuring chamber is bounded radially outwardly with respect to the axis of the cell, in one example, by the first electrode with the substantially cylindrical inner surface.

[0016] Thus, apart from the end faces, this electrode essentially forms a measuring chamber housing. The ionization chamber is essentially identical to the interior of the measuring chamber.

[0017] In an alternative, the measuring chamber is delimited radially outwards with respect to the axis by a measuring chamber housing which is in contact with an inner surface of the housing in whole, in part or not, and has a substantially cylindrical inner surface which is offset radially outwards from the first electrode.

[0018] The measuring chamber thus has its own housing, which neither forms the electrode nor the housing wall. Nevertheless, the measuring chamber housing can be partially flush with the inner surface of the housing, e.g., guided and held there for replacement. The measuring chamber housing can also be flush with its outer surface completely against the inner surface of the housing. In this design, the housing is practically double-walled in the section where the measuring chamber is located.

[0019] In the second alternative, the measuring chamber is limited, radially outwards with respect to the axis, by at least one axial section of the wall of the housing

[0020] In this variant, the wall of the housing in the section in which the measuring chamber is mounted is formed by the measuring chamber wall or, conversely, the measuring chamber wall is formed there by a part of the housing wall.

[0021] In embodiments of the ionization vacuum measuring cell according to the invention, which can be combined with all embodiments of the ionization vacuum measuring cell according to the invention in every aspect already mentioned and still to be mentioned, unless contradictory, the measuring chamber has a non-vacuum-tight, electrically insulating feedthrough for the electrical supply to one of the electrodes or for one of the electrodes themselves at the end axially facing away from the measuring connection.

[0022] If the aforementioned non-vacuum-tight, electrically insulated feedthrough for the supply to one of the electrodes or for one of the electrodes itself is provided on the measuring chamber at the end facing away from the measuring connection, then the electrically insulated and vacuum-tight feedthrough must also be provided for this supply or this electrode itself, outside the measuring chamber and thus not interchangeable with the latter. However, since both mentioned feedthroughs are intended for the same electrical supply or for the same electrode, the two feedthroughs, on the one hand part of the interchangeable measuring chamber, on the other hand outside the measuring chamber, can be aligned with one another in such a way that, with regard to contamination, the non-vacuum-tight feedthrough on the measuring chamber side shields the vacuum-tight feedthrough located outside the measuring chamber.

[0023] This ensures that the electrically insulating and vacuum-tight feedthrough is shielded from contamination and, when the measuring chamber is replaced, the surfaces of the feedthroughs exposed to the ionization chamber are also replaced.

[0024] It should be noted that the non-vacuum-tight feedthrough on the measuring chamber is significantly simpler and more cost-effective to install than the electrically insulated and vacuum-tight feedthrough, which is not interchangeable with the measuring chamber. However, the more cost-effective, interchangeable feedthrough shields the more complex, more expensive, non-interchangeable feedthrough from contamination.

[0025] In an alternative, the replaceable measuring chamber comprises the electrically insulated and vacuum-tight feedthrough at the end axially facing away from the measuring connection.

[0026] This avoids the need for a second, albeit not vacuum-tight, feedthrough according to the first alternative just mentioned.

[0027] In embodiments of the ionization vacuum measuring cell according to the invention, which can be combined with all embodiments of the ionization vacuum measuring cell according to the invention already mentioned and still to be mentioned under each of the aspects, unless contradictory, the measuring chamber can be pushed into or onto the housing on the measuring connection side until it stops and can be releasably locked on the housing, wherein for this purpose preferably a screw connection or a snap connection is provided between the measuring chamber and the housing or at least one locking element acting axially or radially between the housing and the measuring chamber, preferably a snap ring or a ball locking arrangement.

[0028] In embodiments of the ionization vacuum measuring cell according to the invention, which can be combined with all embodiments of the ionization vacuum measuring cell according to the invention already mentioned and still to be mentioned, unless contradictory, the measuring cell has radially outside the measuring chamber at least a part of a magnetization arrangement which generates a magnetic field in the ionization space.

[0029] By magnetization arrangement we mean an arrangement of permanent magnets with or without passive magnetic field guiding elements, such as yokes, pole pieces, shunts, for example, each made of ferromagnetic material.

[0030] The ionization vacuum measuring cell according to the first aspect of the invention can be virtually any type of such measuring cell. In particular, however, it is a measuring cell in whose ionization chamber, in addition to the electric field, a magnetic field is also generated at an angle to increase the ionization rate. For further details on the latter types of ionization vacuum measuring cells, please refer to the following description.

[0031] The invention further relates to a measuring chamber for an ionization vacuum measuring cell of the type explained above, including all the embodiments mentioned.

[0032] An ionization vacuum measuring cell according to the invention realized today comprises: a) an evacuable housing with a measuring connection for the vacuum to be measured, b) a first and a second electrode which are arranged substantially coaxially and spaced from one another and having a common axis, whereby a measuring chamber is formed between these two electrodes which is arranged in communication with the measuring connection, wherein the first electrode forms the outer electrode and this has a substantially cylindrical surface, and that the second electrode is rod-shaped and lies in the axis.

[0033] It also includes: c) an electrically insulating vacuum-tight feedthrough arranged at one end of the housing on the opposite side of the measuring connection, wherein this feedthrough has an insulator arranged around the axis and the second rod-shaped electrode is passed through this insulator in a sealing manner.

[0034] It also includes: d) at least one permanent magnet ring enclosing the coaxial arrangement of the electrodes, with a magnetization direction aligned substantially radially to the axis and with a ferromagnetic yoke enclosing this permanent magnet ring.

[0035] The yoke is guided away from the permanent magnet ring on both sides in the axial direction and - in longitudinal section - after a predetermined distance from the permanent magnet ring on both sides in the radial direction towards the axis and the first electrode, wherein this first electrode forms the outer electrode of the coaxial arrangement of the electrodes, such that the yoke forms two annular poles on both sides and at a distance from the permanent magnet ring, via which at least some of the field lines of the permanent magnet ring penetrate the first electrode within the measuring chamber, closing, wherein at least partially a tunnel-like magnetic field annular around the axis is formed above the first electrode within the measuring chamber.Directed radially towards the axis, in the area of ​​at least one of the inner poles of the yoke, disc-shaped ferromagnetic conducting means are arranged, which are designed as a first and second pole disc and whose center around the axis each has an opening for the passage of the second electrode and for the passage of the measuring gas, wherein between the lead-through and the second pole disc facing it in the radial area of ​​the insulator and coaxial to the axis a shielding device is arranged to protect the insulator from contamination by dusted particles from the measuring chamber, which forms an ionization space and that at least the first electrode is installed in an exchangeable insert chamber. 2nd aspect

[0036] An ionization vacuum measuring cell always features an ionization chamber that is open to an atmosphere whose pressure is to be measured, but otherwise vacuum-tight. Two electrodes operate within this chamber, generating a high electric field between them. The required electrical potential must therefore be supplied to at least one of the two electrodes via an electrically conductive, vacuum-tight feedthrough, or the electrode itself must be introduced into the ionization chamber via such a feedthrough. If the second electrode is not operated at a reference potential, such as the potential of a cell housing, and the path between the electrodes is therefore electrically floating with respect to the reference potential, then such a feedthrough may also be required for the second electrode.

[0037] Under the second aspect, which does not fall within the subject matter of the claim, a novel electrically insulating, vacuum-tight feedthrough is to be provided in the mentioned ionization vacuum measuring cell.

[0038] This is achieved by the ionization vacuum measuring cell, which includes: a) a housing with a measuring connection for the vacuum to be measured, at one end section of the housing, b) a first and a second electrode in the housing, whereby an ionization space is formed within the housing between these two electrodes, c) an electrically insulating and vacuum-tight bushing for an electrical lead to one of the electrodes or for the electrode itself, with an electrical insulator with respect to other parts of the cell that are not operated at the same electrical potential as the lead or electrode. The said lead or the through-passing electrode is essentially a metal rod in one axis. It comprises the bushing i) a ceramic cylinder coaxial with the axis with an inner surface radially spaced from the rod, ii) a first glass ring fused onto the inner surface on the one hand and the rod on the other, axially set back from an end face of the ceramic cylinder facing the ionisation chamber, iii) a metal connection with a cylindrical opening coaxial with the axis, with the inner opening surface radially spaced from the cylindrical outer surface of the ceramic cylinder, iv) a second glass ring fused onto the cylindrical outer surface of the ceramic cylinder, preferably also axially offset from the end face of the ceramic cylinder facing the ionisation chamber, v) wherein the inner surface of the opening is connected to the second glass ring in a vacuum-tight manner.

[0039] Considering the low volume and surface conductivity that must be ensured at the aforementioned feedthrough to ensure its electrical insulation capability, including with respect to leakage currents, even at high voltages or potential differences across the feedthrough, the aforementioned insulation must have a relatively large radial extent relative to the feedthrough axis. The aforementioned radial extent of the feedthrough is ensured cost-effectively with the glass / ceramic insulation. Furthermore, the path for leakage currents is significantly extended by the ceramic cylinder projecting toward the ionization chamber beyond the aforementioned glass rings. This is easily accomplished in manufacturing terms by providing the protruding ceramic cylinder on the one hand and the easily recessed glass rings.The mentioned features of the implementation of the ionization vacuum measuring cell under the second aspect of the present application addressed here, which does not fall under the subject matter of the claim, can be combined with all embodiments of the ionization vacuum measuring cell under the first aspect of the present application, provided that they do not contradict this.

[0040] In an example of the measuring cell of the type mentioned, the electrodes are arranged substantially coaxially with respect to the axis, wherein the first electrode has a substantially cylindrical inner surface as the electrode surface facing the ionization space, radially spaced from the mentioned axis.

[0041] If the second electrode forms the above-mentioned metal rod, then the electrode arrangement is constructed as usual for magnetron cells or cells with an inverted magnetron arrangement, for which reference is made to the following explanations in this regard.

[0042] If the second electrode is ring-shaped, for example on both end faces of the essentially cylindrical inner surface of the first electrode, then the cell is constructed in terms of electrode arrangement as is usual for Penning cells, whereby reference is also made to the following explanations.

[0043] This example of the ionization vacuum measuring cell under the second aspect of the application can also be combined with all embodiments of the measuring cell under the second aspect explained below, but also with all embodiments of the measuring cell under the first aspect of the present application, provided that this does not contradict this.

[0044] In an example of the ionization vacuum measuring cell according to the second aspect of the application, which does not fall within the subject matter of the claim, the second glass ring is fused to the inner surface of the opening. This embodiment can be combined with all previously mentioned and yet-to-be-mentioned embodiments of the measuring cell according to the first and second aspects of the present application, provided they do not conflict with each other.

[0045] In an example of the ionization vacuum measuring cell, which does not fall under the subject matter of the claim, combinable with all the above-mentioned and yet-to-be-mentioned embodiments of the measuring cell under the first and second aspects of the present application, unless contradicted therewith, the second glass ring is sealingly connected to the inner surface of the opening via one or more pairs of a further coaxial ceramic cylinder / a further coaxial glass ring, wherein preferably each further glass ring of a pair is set back with respect to the end face of the further ceramic cylinder of the pair facing the ionization space, onto which end face the further glass ring is fused.

[0046] This creates a series sequence of glass / ceramic up to the inner surface of the metal connection opening, viewed in the radial direction of the feedthrough with respect to the mentioned axis, whereby practically any radial extension of the feedthrough can be easily and cost-effectively manufactured.

[0047] If the aforementioned feedthrough is freely exposed to the ionization chamber on one side, careful attention must often be paid to interfering coating contamination on the corresponding feedthrough surfaces. The longer the radial extension of the feedthrough, the smaller the influence of such an interfering coating. In this embodiment, the additional ceramic cylinder / glass ring pairs are realized with ceramic cylinders offset from the glass rings toward the ionization chamber, at least on some of the pairs. This further extends the leakage current paths.

[0048] Additional sensors, such as Pirani or capacitive diaphragm pressure sensors, are often integrated into ionization vacuum measuring cells. For this purpose, additional feedthroughs for metal pins or rods must be provided on the ionization vacuum measuring cell. This is also the case if both mentioned electrodes are to be operated electrically floating with respect to a cell housing, or if the housing is operated electrically floating and a reference potential such as ground potential is to be applied to one of the mentioned electrodes. For this purpose, a further example of the ionization vacuum measuring cell disclosed under the second aspect is proposed, which does not fall under the subject matter of the claim and which, in turn, can be combined with all the aforementioned and yet-to-be-mentioned embodiments of the ionization vacuum measuring cell under the first and second aspects of the present application, provided that this does not conflict with the above.Accordingly, one or more through-holes are provided through the metal connection, the hole axes of which are either parallel to the mentioned axis of the feedthrough or obliquely angled thereto. The mentioned through-holes always have a directional component of their hole axes that is parallel to the mentioned feedthrough axis. The mentioned one or more through-holes through the metal connection have inner hole surfaces, each of which defines the hole axis, and a metal feedthrough rod is arranged in at least some of the mentioned through-holes, in the respective hole axis. The respective inner hole surfaces and the respective feedthrough rod are sealed with a glass insert.If the metal connections are used in a quasi-standardized manner for different designs of ionization vacuum measuring cells, and with a certain number of the mentioned holes, which are not needed for all designs, it is easily possible to provide some of the mentioned holes specifically for one or the other design of the ionization vacuum measuring cell without a metal feedthrough rod and to seal them with a glass insert.

[0049] The feedthrough described so far comprises a variety of materials extending radially outwards coaxially to the feedthrough axis, including at least one metal rod, then glass of the first glass ring, then a ceramic cylinder, then again glass of the second glass ring and, depending on the design variant, the metal connection or one or more pairs of further ceramic cylinders / glass rings in between. This feedthrough is exposed to high, sometimes inhomogeneous thermal loads, particularly during its manufacture, i.e. melting of the glass, usually provided as glass powder, together with the adjacent surfaces, ceramic or metal, but possibly also in applications subject to high temperatures. The glass / metal / ceramic pairings mentioned lead to high stresses in the feedthrough components, partly due to different thermal expansion coefficients of the materials mentioned and possibly also due to materials that are not absolutely homogeneous in practice.

[0050] This leads to hardly foreseeable distortions at the radially outermost metal connection, which can have serious consequences, especially if, according to the last-mentioned design variant, additional glass-insulated and vacuum-tight feedthroughs are provided at the metal connection, whereby they are by no means necessarily all equally spaced radially with respect to the feedthrough axis and by no means necessarily equally distributed azimuthally at the metal connection.

[0051] Due to the aforementioned stresses in the metal connection, corresponding stresses arise in one or more of the glass inserts, which can lead to hairline cracks in the aforementioned glass inserts. Such cracks do not necessarily occur immediately during or after the aforementioned thermal stress. However, the built-up stresses can lead to the aforementioned cracks occurring much later, during cell assembly or use, due to even minor mechanical stresses such as impacts or blows. These cracks are only detected with great effort when the measuring cell malfunctions.

[0052] In a further example of the ionization vacuum measuring cell, which in turn can be combined with all of the aforementioned embodiments of the ionization vacuum measuring cell under both the first and second aspects of the present application, as well as with the embodiments yet to be explained, provided they do not conflict with them, and which does not fall under the subject matter of the claim, the metal connection comprises an inner ring, which forms the opening of the metal connection with its inner opening. In addition to the aforementioned inner ring, the metal connection further has a further part, which is preferably designed as an outer ring. This further part has a further opening coaxial with the axis of the feedthrough. The inner ring and the further part of the metal connection are connected in a vacuum-tight manner by means of a bridge parting ring.The bridge parting ring is formed either by a connecting seam, preferably a weld or solder seam, or, if the inner ring and the further part of the metal closure are formed as one piece, is formed by a ring web that creates the mentioned one-piece design.

[0053] For the time being, the aforementioned inner ring and the further part of the metal connection with a coaxial opening to the aforementioned inner ring can be considered functionally as two independent parts. The sealing integrity of these two parts is created by the aforementioned connecting seam or the aforementioned ring web. Due to their material (in the case of the connecting seam) or their dimensions (in the case of the web), the latter are capable of acting as stress buffer zones, essentially reducing the stresses generated in the inner ring in a spring-like manner with respect to the further part and distributing them evenly in the aforementioned further part, viewed azimuthally around the feedthrough axis.

[0054] If, with respect to the axis of the feedthrough in the metal connection, through-holes of the aforementioned type are provided with a directional component that is parallel to the feedthrough axis and with inner bore surfaces that each define a bore axis, with a metal feedthrough rod being arranged in at least some of these holes, in the respective bore axis, with the respective inner bore surface and the respective feedthrough rod being sealed with a glass insert, then such feedthroughs are installed in the further part of the metal connection in the latter example. Due to the aforementioned reduction of the stresses in the further part of the metal connection and their homogenization, it was achieved that, despite high temperature stresses on the feedthrough, particularly during its manufacture, the glass inserts on the mentioned feedthroughs in the further part remained unaffected even over long periods of operation, i.e.no stresses leading to cracking occurred or remained.

[0055] It is entirely possible to provide several coaxial rings on the aforementioned metal connection, each connected by a connecting seam, preferably a welded or soldered seam, or by one of the aforementioned ring webs. The last of these rings, usually the radially outermost one or the one axially farthest from the innermost ring, is connected to the further part of the metal connection by one of the aforementioned connecting seams or by one of the aforementioned webs. This creates, if necessary, a bellows-like, vacuum-tight structure between the glass ring and the rigid further part of the metal connection, possibly with the aforementioned additional feedthroughs.

[0056] In further examples of the above-mentioned example of the ionization vacuum measuring cell according to the second aspect of the present application, which does not fall within the subject matter of the claim, the aforementioned inner ring of the metal connection and the opening in the wider part of the aforementioned metal connection are axially aligned with one another or are offset from one another in this direction. The latter allows, if structurally desired, the outer radius of the inner ring to be formed independently of the radius of the opening in the wider part of the metal connection and to support the inner ring and the wider part movably guided radially on one another.

[0057] In a further example of the ionization vacuum measuring cell under the second aspect of the present application, which does not fall under the subject matter of the claim and which can be combined with all embodiments of the ionization vacuum measuring cell under the first aspect of the application as well as with the embodiments yet to be mentioned, unless contradictory, at least the electrically insulated and vacuum-tight feedthrough for the electrical supply to one of the electrodes or for one of the electrodes itself is shielded from contamination towards the ionization chamber by a further non-vacuum-tight, electrically insulating feedthrough.

[0058] As already mentioned, the effectiveness of the aforementioned electrically insulating and vacuum-tight feedthrough is compromised by contamination, such as coating with material sputtered in the ionization chamber. Even if well-designed, particularly with regard to manufacturing and thus manufacturing costs, this feedthrough remains complex due to its dual function. The aforementioned impairment of this complex feedthrough is now shielded in the latter example by an electrically insulating, non-vacuum-tight feedthrough installed between the ionization chamber and the aforementioned dual-function feedthrough. Particularly because the latter is significantly less complex to manufacture, this simpler feedthrough maintains the effectiveness of the aforementioned complex and more expensive dual-function feedthrough over longer operating times.

[0059] In a further example of the ionization vacuum measuring cell, which can be combined with all of the aforementioned embodiments of the measuring cell under the first and second aspects of the present application, as well as with the embodiments yet to be mentioned, unless contradictory, which does not fall within the scope of the claim, an electrically conductive plate arrangement is provided, spaced axially from the electrically and vacuum-tight feedthrough toward the ionization chamber, with an opening coaxial with the aforementioned feedthrough. The electrical lead to one of the electrodes, or one of the electrodes itself, protrudes through this opening toward the ionization chamber.The mentioned opening in the plate arrangement is enclosed by a cylinder projecting upwards from the surface of the plate arrangement facing the feedthrough, which cylinder projects into the ceramic cylinder of the feedthrough without contact or projects beyond the ceramic cylinder of the feedthrough without contact.

[0060] In a currently preferred example, which does not fall within the subject matter of the claim, the ionization vacuum measuring cell comprises: a) an evacuable housing with a measuring connection for the vacuum to be measured, b) a first and a second electrode which are arranged substantially coaxially and spaced apart from one another and having a common axis, whereby a measuring chamber is formed between these two electrodes which is arranged in communication with the measuring connection, wherein the first electrode forms the outer electrode and this has a substantially cylindrical surface, and that the second electrode is rod-shaped and lies in the axis, c) an electrically insulating, vacuum-tight bushing arranged at one end of the housing on the opposite side of the measuring connection, wherein this bushing has an insulator arranged around the axis and the second rod-shaped electrode is passed through this insulator in a sealing manner, d) at least one permanent magnet ring which surrounds the coaxial arrangement of the electrodes, with a magnetization direction aligned substantially radially to the axis and with a ferromagnetic yoke surrounding this permanent magnet ring, wherein the yoke is guided away from the permanent magnet ring on both sides in the axial direction and, after a predetermined distance from the permanent magnet ring - viewed in longitudinal section - is guided on both sides in the radial direction towards the axis and the first electrode, wherein this first electrode forms the outer electrode of the coaxial arrangement of the electrodes, such that the yoke forms two annular poles on both sides and at a distance from the permanent magnet ring, via which at least some of the field lines of the permanent magnet ring close within the measuring chamber, penetrating the first electrode, wherein at least partially a ring-shaped,A tunnel-like magnetic field is formed above the first electrode within the measuring chamber, and in that, in the radial direction, directed towards the axis, in the region of at least one of the inner poles of the yoke, disc-shaped ferromagnetic conducting means are arranged, which are designed as first and second pole discs and whose center around the axis each has an opening for the passage of the second electrode and for the passage of the measuring gas, wherein a shielding device is arranged between the passage and the second pole disc facing it in the radial region of the insulator and coaxially to the axis, to protect the insulator from contamination by dusted particles from the measuring chamber, which forms an ionization space, and in that the insulator comprises a ceramic cylinder with an inner surface facing the second electrode, as well as a glass ring fused onto this and the second electrode.

[0061] As already mentioned, the features of the ionization vacuum measuring cell explained under the first aspect can be combined with those of the ionization vacuum measuring cell explained under the second aspect, of course provided that such a combination does not lead to contradictions, and thus an ionization vacuum measuring cell is created in which the advantages mentioned are realized both with regard to dismantling and implementation.

[0062] The invention will be further explained in all its aspects below, for example, using further embodiments, examples and figures.

[0063] The figures show: Fig. la in cross-section, schematically and simplified, a first embodiment of a magnetron ionization vacuum measuring cell according to the invention with a ring magnet with axial magnetization, Fig. 1 b in a representation analogous to that of Fig. 1a, a further embodiment of a measuring cell according to the invention, namely a magnetron ionization vacuum measuring cell with two ring magnets spaced apart from each other in the axial direction with radial magnetization, which surrounds an externally surrounding soft magnetic yoke. Fig. 1c in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, namely a magnetron ionization vacuum measuring cell with two ring magnets with axial magnetization, which are positioned oppositely polarized and abutting against each other, Fig. 2a in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, namely a magnetron ionization vacuum measuring cell with a ring magnet with radial magnetization and an externally arranged, enclosing soft magnetic yoke, which has leg-like regions on both sides of the ring magnet and spaced therefrom, each forming an annular pole directed towards a first electrode, wherein a vacuum housing encloses and accommodates the entire arrangement of the measuring cell, Fig. 2b in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, in which the vacuum housing is formed by the yoke itself, Fig. 2c in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, in which the vacuum housing is arranged between the first electrode and the arrangement of the magnet system or the magnetization arrangement, such that the magnet system consisting of permanent magnet and yoke is located outside the vacuum chamber in the region of the atmosphere, Fig. 2d in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, in which the vacuum housing is simultaneously designed as the first electrode, such that the magnet system comprising a permanent magnet and a yoke is located outside the vacuum chamber in the region of the atmosphere, Fig. 2e in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, in which the leg-like regions with the poles are bent towards the first electrode, Fig. 3 in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, in which ferromagnetic conducting means are arranged in the central region of the measuring cell above the poles of the yoke and / or the pole of the ring magnet, Fig. 4 in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, in which the ring magnet and / or the ferromagnetic conducting means associated with the pole are arranged asymmetrically and / or displaceably in the axial direction within the arrangement of the yoke, Fig. 5a shows a plan view of a segment as part of a composite ring magnet in which the magnetization direction is aligned perpendicular to the chord of the segment, Fig. 5b shows a plan view of a segment as part of a composite ring magnet with radially directed magnetization direction, Fig. 5c shows a partial plan view of a ring magnet composed of individual bar magnets, where the individual bar magnets are magnetized in the same direction, Fig. 6a in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, in which two axially spaced ring magnets are shown within the arrangement of the yoke, Fig. 6b in a representation analogous to that of Fig. 1a shows a further embodiment of a measuring cell according to the invention, in which a further ring magnet with axial polarization is arranged on either side of the pole of the radially magnetized ring magnet and oppositely polarized to each other and directed towards the axis within the arrangement of the yoke, Fig. 7 in cross-section and in more detail a further embodiment of a vacuum measuring cell according to the invention, with a feedthrough with shielding device Fig. 8 in cross-section a detailed representation of the feedthrough area with the shielding device according to Fig. 7. Fig. 9 shows schematically and simplified, in longitudinal section, part of the electrically insulating and vacuum-tight bushing, as used in the ionization vacuum measuring cells under the second aspect of the application, which does not fall within the subject matter of the claim, Fig. 10 in a representation analogous to that of Fig. 9, another example of the mentioned electrically insulating and vacuum-tight feedthrough, Fig. 11 using a representation analogous to that of Fig. 9 and Fig. 10, the bushing, in which additional lateral bushings are installed, Fig. 12 schematically and simplified, based on an implementation according to Fig. 11, a first example of precautions not covered by the subject matter of the claim, to participate in the lateral penetrations according to Fig. 11 To eliminate or at least mitigate impairments caused by mechanical stresses, especially thermal stresses, Fig. 13 based on a principle diagram, another example of the precautions according to Fig. 12, Fig. 14 in a representation analogous to that of Fig. 13, another example of the precautions mentioned, namely, as mentioned, to prevent interference with the lateral penetrations according to Fig. 11 to alleviate or even eliminate mechanical stresses, particularly those caused by thermal stresses, Fig. 15 another unclaimed example of the mentioned provisions, in a representation analogous to that of Fig. 13 or 14, Fig. 16 shows a simplified and schematic view of an ionization vacuum measuring cell in which a measuring chamber with a housing part is designed to be exchangeable, according to the first aspect of the present application, Fig. 17 in a representation analogous to that of Fig. 16, an ionization vacuum measuring cell in which the measuring chamber can be replaced by pushing it into or pulling it out of a measuring cell housing, Fig. 18 schematically and simplified, an ionization vacuum measuring cell, in which a measuring chamber is exchangeable, and in which the electrically insulating, vacuum-tight feedthrough with respect to the ionization space is practically completely covered by a non-vacuum-tight feedthrough on the exchangeable measuring chamber, and is thus protected from contamination.

[0064] It is known to use gas pressure measuring cells for vacuum measurement, which are based on the principle of a gas discharge with a cold cathode. Such measuring cells are also known as cold cathode ionization vacuum gauges or Penning cells. In such a measuring cell, a sufficiently high DC voltage is applied between two electrodes (anode, cathode), which can ignite and maintain a gas discharge. The discharge current is then a measure of the pressure to be measured.

[0065] A magnetic field formed in the discharge gap guides the electrons on their path from the negative electrode (cathode) to the positive electrode (anode) along spiral paths, thereby lengthening the electron trajectory. This increases the probability of collision with the gas particles and improves the degree of ionization. This ensures that the discharge burns over wide pressure ranges and behaves stably and reproducibly.

[0066] Vacuum gauges that operate on the principle of gas discharge with cold cathodes can be roughly divided into three classes, which differ mainly in the configuration of the electrodes: 1. Penning cell: The anode is designed as a ring-shaped cylinder enclosing the discharge space, with cathode sheets or plates arranged on both ends of the anode ring. The magnetic field lines run parallel to the axis of the anode ring. 2. Magnetron cell: The anode is designed as a hollow cylinder with a central axis, and the cathode is arranged as a rod at the center or on the axis. The electric field lines therefore run radially. The magnetic field lines run parallel to the cylinder axis. 3. Cell with inverted magnetron arrangement. The cylindrical geometry is similar to that of a magnetron cell, but with the anode as a rod-shaped arrangement in the center and the cathode as a hollow cylinder. The ends of the cylinder are typically also at cathode potential. As with a magnetron, the magnetic field lines run parallel to the cylinder axis, while the electric field lines run radially.

[0067] The space accessible to the gas to be measured within an ionization vacuum measuring cell comprises a measuring chamber within which the ionization space is located between the anode and cathode. Depending on the design of the ionization vacuum measuring cell, the interior of the measuring chamber can thus be identical to the ionization space or include additional spatial areas that are exposed to the gas to be measured, but the gas is not subject to ionization there. As mentioned, the ionization space is located between the anode and cathode and is enclosed by the cathode in inverted magnetron cells, and by the anode in magnetron cells.

[0068] The most commonly used cell design is the inverted magnetron, as it generally produces a more stable measurement signal than the Penning cell in high vacuum, ignites the discharge more easily at low pressures, and the lower measurement range is suitable for lower pressures down to the range 10 -11mbar can be brought.

[0069] The magnetic field required to maintain the gas discharge in the direction of the cylinder axis is generated in the measuring cells due to the required field strengths in the order of up to 10 -1 T (=1000 Gs), generated by permanent magnets, because the power consumption of electromagnets is too high and they would require a large design. The following magnet configurations for inverted magnetron cells are used: A) Ring magnet with axial magnetization, as shown by the magnetization arrangement 105 on the schematic, simplified and exemplary cell shown in Figure 1a. B) Two ring magnets with radial magnetization as shown by the magnetization arrangement 105 on the schematic, simplified and exemplary cell shown in Figure 1b. C) Two ring magnets with axial magnetization, which are arranged with opposite polarity to each other, as shown by the magnetization arrangement 105 on the schematic, simplified and exemplary cell shown in Figure 1c.

[0070] Variant (A) of the magnetization arrangement is the classic variant, with the advantage that such ring-shaped magnets 1 with axial magnetization are simple and inexpensive to manufacture.

[0071] In combination with suitable guide plates made of soft magnetic material, homogeneous useful field lines 14 and thus magnetic flux densities can be achieved in the ionization chamber. The cathode 3 is, as already mentioned, cylindrical and encloses the ionization chamber 20. The anode 4 is arranged in the axis of the cylindrical cathode 3. The entire assembly is enclosed by the annular permanent magnet 1 with axial polarity alignment to axis 7. In Figure 1a, the north pole is designated N and the south pole S. The polarities can also be interchanged within the arrangement. On the front side, the cylindrical cathode, directed towards axis 7, can have further electrode surfaces which are at the same potential and additionally reflect the electrons back into the ionization chamber 20. The ionization chamber has at least one opening which communicates externally with the vacuum chamber P to be measured.Typically, such a measuring cell has a detachable flange connection, directly on the cathode 3 or on a housing 101 (shown in dashed lines), within which the ionization chamber 20 with the electrodes 3 and 4 is located, and outside of which the permanent magnets 1 are arranged. The rod-shaped electrode 4 is guided into the ionization chamber 20 by means of an electrically insulating, vacuum-tight feedthrough 103. The feedthrough rides on the electrode 3 or on the housing 101.

[0072] At the ionization vacuum measuring cell according to Fig. 1a, the housing 101 or the cathode 3 itself forms a measuring chamber 107 within the magnetization arrangement 105 with the permanent magnets 1. The measuring chamber 107 is designed as a replaceable component, preferably not further disassembled without damage. It comprises the cathode 3 and, depending on its design, also at least part of the housing 101. Furthermore, the electrically insulating and vacuum-tight feedthrough 103 with the anode 4 can be part of the replaceable measuring chamber 107. By designing the aforementioned measuring chamber 107 so that it can be temporarily shut down, for example, if cleaning of the measuring chamber becomes necessary, with the ionization chamber 20, a replacement measuring chamber can be quickly installed in the measuring cell.

[0073] The electrically insulating and vacuum-tight feedthrough 103 is advantageously designed, both in a measuring cell concept with a replaceable measuring chamber 107 and in a measuring cell concept with a non-replaceable measuring chamber 107, as will be explained further below, basically with a ceramic cylinder coaxial with the anode 4 and a glass ring that is fused to the anode 4 and the ceramic body. The outer surface of the aforementioned ceramic cylinder is connected via a second glass ring to a metal connection around the anode 4, according to Fig. 1a, for example, the cathode 3 and / or the housing 101. The cathode 3 is usually connected to the housing potential and thus to the reference potential, such as the ground potential of the measuring cell, but can also be operated electrically floating with respect to the housing 101, which then requires a further vacuum-tight, electrically insulating feedthrough for connecting the potential to the cathode 3.

[0074] Variant (B), according to Fig. b, has two radially magnetized magnetic rings spaced apart from each other in the axial direction, which are connected via an annular yoke 2 of the magnetization arrangement 105 made of soft magnetic material for the return of the magnetic circuit. Compared to variant (A), variant (B) has smaller outward stray fields 15, particularly in the radial direction. Part of the generated magnetic field 15 closes outside the ionization chamber and forms a stray field 15, which contributes nothing to the useful field 14. Such external stray fields 15 are disadvantageous because they can disrupt devices and processes located there. Variant (B), with the smaller outward stray field 15, is therefore more advantageous in this regard. However, this also means that less permanent magnet material needs to be used to achieve the same flux densities in the ionization chamber.

[0075] Regarding the interchangeability of the measuring chamber 107 and the design of the electrically insulating and vacuum-tight feedthrough 103, the following applies in connection with Fig. 1a Executed. In Fig. 1b, the feedthrough 103 is part of the replaceable measuring chamber 107.

[0076] Regarding the design of the magnetization arrangement 105, according to the proposal by Lethbridge in EP 0 611 084 A1, ring segments can also be used instead of radially magnetized rings, which generate a radially directed field.

[0077] The magnetization arrangement according to variant C and Fig. 1c was proposed by Drubetsky & Taylor, US 5,568,053. It results in a field that changes direction relative to the cylinder axis at the height between the two magnetic rings. On the cylinder axis, the field is even zero in this region because the flux densities of the two magnets cancel each other out. The advantage of this arrangement is a smaller stray field compared to variant (A) for a given flux density requirement in the ionization chamber 20. However, the stray field is still significantly present and can cause interference, especially if a strong useful field is to be generated in the ionization chamber 20. In this case, the external stray field also becomes correspondingly stronger and extends further into the outer region.

[0078] Regarding the interchangeability of the measuring chamber 107 and the design of the electrically insulating and vacuum-tight feedthrough 103, the following applies in connection with Fig. 1a Executed. In Fig. 1c, the feedthrough is not part of the replaceable measuring chamber 107, unless it comprises a part of the housing 101 with the feedthrough 103.

[0079] A disadvantage of variant (A) is the relatively strong flux densities, which extend outside the ionization chamber 20, even the measuring chamber 107, and even the entire measuring cell arrangement, where they appear as stray fields 15, as shown in Figure 1a. This has adverse effects on nearby devices and on processes that may occur in the immediate vicinity of the measuring cell during typical use, particularly on processes that involve charge carriers or ionized gas.

[0080] With variant (B), such stray fields 15 are indeed reduced by forming a magnetic circuit outside the ionization chamber 20 and outside the replaceable measuring chamber 107, between the two ring magnets 1, by arranging a guide plate 2 or a yoke made of soft magnetic material on the magnetization arrangement 105. However, significantly disturbing external stray fields 15 continue to form due to the magnetic shunt between the poles N, S at each of the two ring magnets 1, as shown in the Fig. 1b is shown.

[0081] In variant (C), the gas discharge is low due to the small magnetic flux density in the center at the height between the two magnetic rings, which is no longer perpendicular to the electric field axis, and therefore a part of the ionization space 20 in the measuring chamber 107 remains unused. In addition, the magnetic shunt on the outside of the magnets results in a non-negligible disturbing stray field 15, as shown in the Fig. 1c, which has a similar effect to that previously explained for variant (A), according to figure la.

[0082] Inverted magnetrons are frequently used in the coating industry because of their robustness. They have no filament that can burn out or break due to impact. Since magnetron arrays enable a high degree of ionization, there is also an increased problem of contamination of the surfaces exposed to the ionization chamber 20 due to increased sputtering of material from such surfaces and redeposition. Therefore, an attempt will be made to control this problem by constructing inverted magnetrons in such a way that they can be modularly disassembled for cleaning, as already described.

[0083] Plasma discharge splits or activates gases. For example, hydrocarbons are cracked or polymerized via plasma-chemical dissociation reactions. This can also cause fogging of the surfaces mentioned. The measuring chamber becomes dirty. Since this measuring method uses small currents in the range of 10-9 A are measured, even a slight conductive contamination of the bushing 103 can cause leakage currents that distort the measurement or even make it impossible.

[0084] An example illustrates the problem of the required high electrical insulation at a feedthrough 103 of a cold cathode / anode arrangement. At a pressure of 10 -9 mbar, the measuring current is typically 10 -9 A. At an anode voltage of the order of 1 kV, a good insulation resistance value of 10 12 Ω the leakage current has the same order of magnitude as the measuring current.

[0085] Likewise, as mentioned, wall material is sputtered off during operation. This flake can form, either individually or collectively, contaminate the electrically insulating and vacuum-tight feedthrough 103, allow leakage or creepage currents, or even cause short circuits, thus drastically limiting the service life of the measuring cell until cleaning is required.

[0086] Cleaning the measuring cell, whether left intact or disassembled into individual components, can be very laborious and time-consuming. This increases operating costs. Furthermore, after such cleaning, calibration is typically no longer guaranteed, meaning the cells have a greater measurement error.

[0087] However, if, as mentioned, the measuring chamber 107, with or without at least part of a housing 101 and / or with or without feedthrough 103, is directly replaceable as a component, then already calibrated measuring chambers 107 can temporarily take over the operation of the one to be cleaned.

[0088] The increased disassembly of the measuring cell also results in higher production costs, as a disassemblable sealing system is required. Likewise, there is a greater likelihood of leaks occurring after disassembly. This is not the case with a replaceable or even disposable measuring chamber 107, which can be designed to be leak-tight and non-disassemblable.

[0089] Reference can be made to US 5,317,270 and EP 01 540 294 B1.

[0090] As already mentioned, the objects of the present invention, whether solved individually or in combination, include shortening downtimes of the ionization vacuum measuring cell and / or creating a novel electrically insulated and vacuum-tight feedthrough, according to 103, which can be produced in particular with relatively low manufacturing effort and, accordingly, at relatively low manufacturing costs, with high quality in terms of insulation and sealing requirements.

[0091] A well-designed magnetization arrangement for the measuring cell should also be proposed, which includes a magnetron arrangement and in which disruptive magnetic stray fields outside the measuring cell are significantly reduced or even essentially eliminated. The measuring cell should be capable of measuring a wide pressure range and operate reliably and reproducibly. Furthermore, it should be well-designed, compact, and economically manufactured. Contamination occurring during operation, e.g., through self-sputtering, cracking, and the like, should not lead to long and / or frequent downtimes of the measuring cell.

[0092] With regard primarily to the magnetization arrangement on a measuring cell according to the invention realized today under the first and / or second aspect of the present application, the following applies: The measuring cell has a) an evacuable housing with a measuring connection for the vacuum to be measured, b) a first and a second electrode which are arranged substantially coaxially and spaced apart from one another and having a common axis, whereby a measuring chamber is formed between these two electrodes which is arranged in communication with the measuring connection, wherein the first electrode forms the outer electrode and this has a substantially cylindrical surface, and that the second electrode is rod-shaped and lies in the axis, c) an electrically insulating vacuum-tight bushing, arranged at one end of the housing on the opposite side of the measuring connection, wherein this bushing has an insulator arranged around the axis and the second rod-shaped electrode is passed through this insulator in a sealing manner, d) a voltage source connected to the electrodes, e) a current measuring device for evaluating a discharge current formed between the electrodes, which forms a function of the vacuum pressure to be measured, f) at least one permanent magnet ring surrounding the coaxial arrangement of the electrodes, with a magnetization direction aligned substantially radially to the axis and with a ferromagnetic yoke surrounding this permanent magnet ring, wherein: the yoke is guided away from the permanent magnet ring on both sides in the axial direction and, after a predetermined distance from the permanent magnet ring, is guided in the radial direction towards the axis and the first electrode on both sides, wherein this first electrode forms the outer electrode of the coaxial arrangement of electrodes, such that the yoke forms two annular poles on both sides and at a distance from the permanent magnet ring, via which at least some of the field lines of the permanent magnet ring close within the measuring chamber, penetrating the first electrode, wherein at least partially a tunnel-like magnetic field is formed around the axis above the first electrode within the measuring chamber, and that disk-shaped ferromagnetic conducting means are arranged in the radial direction towards the axis, in the region of at least one of the inner poles of the yoke,which are designed as first and second pole discs and whose center around the axis each has an opening for the passage of the second electrode and for the passage of the measuring gas, wherein between the passage and the second pole disc facing it in the radial region of the insulator and coaxial to the axis a shielding device is arranged to protect the insulator from contamination by dusted particles from the measuring chamber, which forms an ionization space.

[0093] In this cell, the measuring chamber is replaceable according to the invention - aspect 1 - and / or the electrically insulating and vacuum-tight feedthrough is formed - aspect 2, which does not fall under the subject matter of the claim.

[0094] The magnetization arrangement mentioned forms a magnetron. In certain cases, the first, outer electrode can be operated as the anode, with the second, inner electrode acting as the cathode. The far preferred arrangement, however, is an inverted magnetron. In this arrangement, the outer, first electrode acts as the cathode, and the coaxial inner electrode acts as the anode. In this arrangement, referred to as an inverted magnetron, the discharge efficiency is significantly better and more stable. The anode, preferably located in the center, is preferably rod-shaped.

[0095] Outside the measuring chamber, the magnetization arrangement always comprises soft magnetic material. The magnetic connection on both sides between the poles runs through the soft magnetic material. This prevents the magnetization arrangement from generating a disruptive stray field to the outside, or at least minimizes such a field. Within the ionization chamber, however, at least two annular, tunnel-like, inward-directed magnetic field configurations form above the surface of the first electrode, each with an axial component. The field lines extend inward from the inner pole of the at least one permanent magnet and penetrate the first electrode, closing on both sides of the magnet via the poles of the soft magnetic or ferromagnetic yoke, in turn penetrating the first electrode.In this process, the field lines at the level of the magnet within the ionization chamber change direction, causing the two adjacent tunnel-like fields to run in opposite polarity. This creates at least two adjacent, torus-like discharges above the first electrode. The electrons rotating within these discharges, viewed in cross-section, oscillate sideways along the field lines and rotate in a circular pattern within the rings in opposite directions. The resulting extended residence time results in a high degree of ionization.

[0096] In order to ensure good insulation and vacuum tightness at the feedthrough 103, it is made of a glass / ceramic composite.

[0097] In addition to an internal glass ring of the feedthrough, a ceramic cylinder is attached to it, which allows the creepage distance to be extended efficiently and cost-effectively. The feedthrough in the anode area must be able to withstand up to 5 kV, which represents approximately the highest anode voltage during operation. Since the lower end of the measuring range of a measuring cell typically reaches 10 -9 mbar the ionization current in the range 10 -10 up to 10 -9 A, the insulation resistance must be in the range 10 13 Ohm so that the leakage current does not limit the sensitivity of the measuring cell with respect to the measuring current.

[0098] The measuring cell as described above, in addition to the provisions under the first claimed aspect and / or the second unclaimed aspect of the application, allows the measuring chamber to be heated to at least 150°C or even to at least 250°C. An overpressure of up to 10 bar is permissible, and the leak rate is better than 1E-9 mbar l / s.

[0099] The feedthrough comprises a metal ring as a metal connection, preferably made of stainless steel, especially non-magnetic stainless steel (1.4435, AISI 316 L). The ring is particularly preferably made of Hastelloy. Hastelloy C-22 (NiCr2 1 Mol 4W, 2.4602) is a nickel-chromium-molybdenum-tungsten alloy. It is highly corrosion-resistant with excellent welding properties.

[0100] Hastelloy B3 (NiMo29Cr, 2.4600) is a nickel-molybdenum alloy with very good resistance to hydrochloric acid and other acids. Both Hastelloys are non-magnetic.

[0101] The bushing's insulator consists of the aforementioned glass / ceramic composite. The glass preferably has a matched thermal expansion coefficient, such as Covar Schott 8250 or BH-7 Nippon glass. The ceramic cylinder is preferably made of Al2O3. This ceramic, surprisingly, allows for an increase in electrical insulation strength beyond that of the glass. The part of the ceramic cylinder projecting beyond the glass insulator should be at least as long as the creepage distance along the glass ring, or longer, in order to sufficiently extend the creepage distance and thereby reduce the leakage current. At the center of the bushing, the rod-shaped anode is sealed to the glass of the glass ring, passed through, and fixed. The anode's diameter is, for example, 1 mm. It is preferably made of Hastelloy C22.

[0102] Additionally, additional feedthrough pins can be arranged on the periphery of the feedthrough, i.e., through the metal connection. They serve to transmit electrical signals to and / or from additional sensors optionally arranged in the housing of the measuring cell, such as Pirani or diaphragm pressure sensors, such as capacitive diaphragm pressure sensors, or they serve to apply potential to the cathode. They also advantageously act as a support for the construction of additional sensors. Such sensors can be particularly advantageously arranged directly in an annular cavity, next to the feedthrough and the protruding ceramic cylinder, in the measuring cell according to the invention or not according to the invention in the aspects of the present application.

[0103] The measuring cell is complemented by at least one second cylinder arranged coaxially to the axis around the center opening of the second pole disk in the direction of the feedthrough. This cylinder overlaps the ceramic cylinder. In the overlap area, the two cylinders are spaced apart such that they do not touch, and a gap is formed in the radial direction. This extends the path for dusted particles from the ionization chamber and shades the feedthrough's insulators. This creates a significant shielding effect that significantly reduces and delays the deposition or contamination of the insulator surfaces at the feedthrough.In addition to the basic design with a pair of cylinders, additional cylinders or several cylinders can be used on only one side or on both sides, which interlock at a distance from each other, thus further extending the path of the labyrinth and further improving the shading effect.

[0104] In one embodiment of the invention under the first claimed aspect and / or second, unclaimed aspect, the cathode electrode is designed as a separate tubular part or cylinder, for example in the form of a sheet metal, which is held at a distance from the inner wall of a housing (see 101) by pole discs arranged on both sides of the tubular part, whereby a gap-shaped line is formed laterally between the housing and the tubular part and thereby encloses the measuring chamber (see 107). The pole discs have webs on their periphery around the circumference, which allow the measuring gas to be guided from the measuring inlet through the gap to the feedthrough. This arrangement also forms an embodiment of an exchangeable measuring chamber according to the invention, which can be easily exchanged and replaced if the measuring chamber becomes too dirty.The replaceable measuring chamber can also be made of different materials depending on the measuring cell's application in different processes. For example, the cathode in the replaceable measuring chamber can be made of titanium sheet. The properties of the sputtered titanium allow unwanted gases to be trapped or pumped away. The pumping effect can be incorporated into the firmware for calibrating the measuring cell, if necessary.

[0105] Let us now turn to the other figures and examples.

[0106] An embodiment of an ionization vacuum measuring cell 30 with a magnetron magnetization arrangement 105 is, for example, in the Fig. 2a schematically, simplified and shown in cross-section.

[0107] A housing 101 has a measuring port 8, which can be connected to the vacuum to be measured, whereby the housing 101 is evacuated accordingly. The connection between this housing 101 and the container with the vacuum to be measured can be established, for example, via a sealing flange 11. The vacuum measuring cell 30 comprises the housing 101, with two electrodes 3, 4 and a magnetization arrangement 105, which, in the present embodiment, the housing 101 encloses. The magnetization arrangement 105 includes a permanent magnet ring 1 and a yoke 2 made of ferromagnetic material. The ferromagnetic material can comprise both metallic materials (ferromagnetic) and ceramic materials, such as ferrites.

[0108] The first and a second electrode 3, 4 are arranged essentially coaxially and spaced apart from one another and have a common axis 7. This creates the ionization chamber 20 between these two electrodes. This, in turn, is arranged in communication with the measuring connection 8. The first electrode 3 forms the outer electrode and has a substantially cylindrical surface. The second electrode 4 can also be cylindrical or rod-shaped and is advantageously arranged in the center, along the axis 7.

[0109] Both electrodes can be electrically supplied via vacuum-tight electrical feedthroughs 105A, 105K on the housing 101. For this purpose, a voltage source is connected to the electrodes 2, 3. Current measuring means 17 are used to evaluate a discharge current, the discharge that develops between the electrodes 3, 4. This discharge current corresponds to a function of the vacuum pressure to be measured and is electronically evaluated and fed for further use. At least one permanent magnet ring 1 surrounds the coaxial arrangement of the electrodes 3, 4 with the magnetization direction 13 aligned essentially radially to the axis. This permanent magnet ring 1 is further enclosed by a yoke 2, which is made of ferromagnetic material to guide the magnetic field.The yoke 2 is guided away from the permanent magnet ring 1 on both sides in the axial direction and, after a predetermined distance d from the permanent magnet ring 1, is guided on both sides in the radial direction towards the axis 7 and the first electrode 3. This creates a type of U-shaped yoke in cross-section, which forms poles 9a and 9b on both sides and at a distance from the permanent magnet ring 1. The first electrode 3 is the outer electrode of the coaxial arrangement of electrodes 3, 4. At least some of the field lines of the permanent magnet ring 1, the useful field lines 14 which determine the discharge, thus close above the pole of the permanent magnet ring 1 and the respective pole 9a, 9b of the yoke 2 within the ionization chamber 20, penetrating the first electrode 3, wherein an annular, tunnel-like magnetic field 14 is preferably formed above the first electrode 3 within the ionization chamber 20. When arranged according to the . Fig. 2a, a tunnel-like magnetic field 14 is formed on both sides of the permanent magnet ring 1, i.e. two ring-shaped or torus-shaped magnetic fields 14 with opposite polarity of the field lines.

[0110] The outer first electrode 3 is preferably operated as a cathode and the inner second electrode 4 as an anode.

[0111] The permanent magnet ring 1 is magnetized in the radial direction and preferably contains magnetic material from the group of rare earths, such as neodymium, samarium, etc. To simplify production, the ring can also be assembled from individual parts, such as segments and / or individual rectangular magnets, which are then arranged in a ring-like manner, as shown in the Fig. 5a to 5c. The magnetization occurs in the direction of the arrow, in the case of the segment of the Fig. 5a in a uniform direction or in the case of the segment of the Fig. 5b in the radial direction. In the case of Fig. 5c, individual, for example rectangular magnets, are arranged in a ring-like arrangement. The length h is then preferably longer than the width of the individual piece. The thickness of the magnetic ring 1 is preferably not greater than the width h.

[0112] The shape of the U-shaped yoke 2 is at least partially angled in the sectional plane in which the axis 7 lies, such that in the axial direction at a distance d on both sides of the permanent magnet ring 1, the resulting legs of the yoke 2 point radially towards the axis 7 of the measuring cell 30 and form an annular pole 9a, 9b on each side there, which is guided towards the first electrode 3. Preferably, the angle is formed at a right angle, as shown in the Fig. 2a to 2d, 3, 4 and 6. The poles 9a, 9b of the yoke and the inner pole of the permanent magnet ring are preferably equally spaced from the axis 7. However, in certain cases they may be offset from each other, as is the case, for example, in the Fig. 2b. There, for example, one pole 9b of the yoke 2 is guided towards the axis 7 in the lower area. It is advantageous if all poles are arranged as close as possible to the area of ​​the first electrode 3 in order to be able to guide and use the magnetic field optimally. The poles 9a, 9b of the yoke are preferably arranged such that the magnetic field 14 passes through the first electrode 3 there. The useful magnetic field 14 thus leads away from the pole of the permanent magnet ring 1 through the first electrode 3 and closes in an arc within the ionization space 20 above the two poles 9a, 9b of the yoke 2, where it is again guided through the first electrode 3. The passage of the magnetic field through the first electrode 3 leads to a high discharge efficiency.In certain cases, one or both poles 9a, 9b of the yoke 2 can also be arranged in such a way that the field lines 14 only partially or not at all pass through the first electrode 3, as is the case, for example, in the . Fig. 2b in the upper part for the one pole 9a. In the lower part of the Fig. 2b, the yoke 2 is angled towards the axis in such a way that there too the field lines 14 again pass through the first electrode 3. It is advantageous if this angled arrangement occurs on both sides of the cylindrical first electrode 3. In this case, the first electrode 3 forms a type of closed cylinder which only has an opening 8 for the supply of the measuring gas P and, if necessary, means for holding the second electrode within this cylinder with an electrical, possibly also vacuum-tight feedthrough for feeding the second electrode. In addition to the angled design of the yoke 2, at least parts thereof can also be guided at least partially in an arc shape in the radial direction towards the first axis 7 or towards the electrode 3, as is shown in the Fig. 2e is shown.

[0113] In the example shown the Fig. 2a, the elements of the measuring cell 30, the magnetization arrangement, and the two electrodes 3, 4, are enclosed by the vacuum-tight housing 101. This housing 101 has an opening 8 and a connection 11, preferably designed as a flange, with which the measuring cell 30 can be sealingly connected to the vacuum volume to be measured.

[0114] In the embodiment according to Fig. 2a, as mentioned, the housing 101 encloses the magnetization system 105. Thus, the replaceable measuring chamber 107 is radially delimited by the electrode 3 with respect to the axis 7. To replace this measuring chamber 107, whose interior essentially corresponds to the ionization chamber 20, the electrically insulating and vacuum-tight feedthrough 103 Awith the electrode 4 on the housing 101, which is not part of the replaceable measuring chamber 107. In a further embodiment (not shown here), the measuring chamber 107 also includes the electrode 4 and the electrically insulating and vacuum-tight feedthrough according to 103 A designed to be replaceable, in that the mentioned bushing is attached to the electrode 3, and not to the housing 101. As in Fig. 2a, the opening 8 of the housing 101 is designed so large that the measuring chamber 107 can be replaced through the opening 8. Otherwise, and if the opening 8 is as for example in Fig. 2b, it is easily possible to, as shown in Fig. 2b shown in dash-dotted lines, the flange 11 as housing part 101 a to be releasably unscrewed and removed from the remaining housing 101 in order to replace or exchange the measuring chamber 107.

[0115] Another possible further design of the measuring cell 30 with the housing 101 is shown in the Fig. 2b. Here, the yoke 2 of the magnetization arrangement 105 is simultaneously designed as a vacuum-tight housing 101 with connecting means 11 arranged thereon. The yoke 2 can also be only part of the housing 101. In this case, the housing 101 can be made partly of a soft magnetic or ferromagnetic material and partly of a non-magnetic material, such as inox.

[0116] Here, too, the replaceable measuring chamber is radially defined on the outside by electrode 3. The feedthrough 103A, along with electrode 4, is part of the replaceable measuring chamber 107.

[0117] In another variant, according to the Fig. 2c, the housing 101 can be arranged between the first electrode 3 and the magnetization arrangement 105, such that the magnetization arrangement 105 is located entirely outside the vacuum-enclosing housing 101. This has the advantage that the materials of the magnetization arrangement 105 cannot contaminate the ionization chamber 20, which could adversely affect the measurement result.

[0118] The replaceable measuring chamber 107 is defined radially outwardly by the housing 101, or at least a portion thereof. The feedthrough 103A rides on the housing 101, meaning that the electrode 4 and the feedthrough 103A, along with the housing 101, are also part of the replaceable measuring chamber 107.

[0119] In the variant after the Fig. 2d shows that the first electrode 3 can also be designed as a vacuum-tight housing 101. This also allows the magnetization arrangement 105 to be vacuum-separated from the ionization chamber 20 and also allows a compact, simple design of the measuring cell 30. The permanent magnet ring 1 can be arranged asymmetrically in the axial direction within the yoke 2 between its legs with the two poles 9a, 9b or even displaceable, as shown in the Fig. 4 is shown with arrows 18 indicating the direction of movement. This allows the properties of the magnetization arrangement 105 and thus the discharge to be specifically influenced, or irregularities to be corrected. In most and preferred cases, the permanent magnet ring 1 is arranged centrally relative to the poles 9a, 9b of the yoke 2, so that the poles 9a, 9b of the yoke 2 are arranged symmetrically relative to the permanent magnet ring 1.

[0120] The replaceable measuring chamber 107 in Fig. 2d is radially delimited on the outside by the electrode 3. The feedthrough 103A rides on the electrode, whereby the electrode 4 and the feedthrough 103A are also part of the replaceable measuring chamber 107.

[0121] The magnetic field, which is directed inwards from the poles, can be influenced with additional conductive agents to further optimize the discharge.

[0122] For example, ferromagnetic conductive means 6 can be arranged in the radial direction towards the axis 7, in the area of ​​the inner pole of the permanent magnet ring (1), as shown in the Fig. 3 and Fig. 4. Ferromagnetic conducting means 5a, 5b can also be arranged, for example, in the radial direction toward the axis 7, in the region of at least one of the inner poles 9a, 9b of the yoke 2. Such conducting means can be manufactured as sheet metal parts or plate-like parts made of soft magnetic or ferromagnetic material, which are, for example, disc-shaped. Openings are provided therein as required to guide the second electrode 4 through and / or to enable gas exchange.

[0123] Comparing the representation of Fig. 3 with the shape of the electrode 3 according to Fig. 1c, then it is immediately apparent that the ferromagnetic conducting means 5a and 5b can easily contact the front parts of the Fig. 1c shaped electrode 3, because such conductive means 5a and 5b do not lose their conductivity with respect to the magnetic field by being placed on the electrical potential of the electrode 3.

[0124] The same applies to the Fig. 3 shown conductive means 6. They can also be easily mounted on the electrode 3.

[0125] However, these conductive means 5a, 5b and / or 6 can thus be part of the replaceable measuring chamber 107 by being exchanged with the mentioned one electrode 3, which is in any case part of the mentioned replaceable measuring chamber 107.

[0126] A further embodiment of the magnetization arrangement 105 is shown in the Fig. 6a, in which two permanent magnet rings 1, axially spaced from one another and with opposite poles, are arranged within the yoke 2. This arrangement generates a particularly powerful annular magnetron field between the two poles of the permanent magnet rings 1 above the first electrode 3 within the ionization chamber 20. On either side of this, a further annular field then runs, which is closed off by the two poles 9a, 9b of the yoke 2, thus preventing stray fields from escaping to the outside. If necessary, it is also possible to use more than two permanent magnet rings 1, the polarity of which is arranged alternately, although two permanent magnet rings 1 are preferred.

[0127] The replaceable measuring chamber 107 in Fig. 6a is radially delimited on the outside by the electrode 3. The feedthrough 103 rides on the electrode 3, whereby the electrode 4 and the feedthrough 103 are also part of the replaceable measuring chamber 107.

[0128] A further embodiment of the magnetization arrangement 105 is shown in the Fig. 6b.

[0129] Between the legs and the poles 9a, 9b of the yoke 2 and the permanent magnet ring 1, a further ring magnet 21a, 21b is arranged, which is magnetized in the axial direction and which is arranged within the magnet system in the area towards the axis 7. Preferably, the thickness of the magnet ring 21 in the radial direction is at most half the width h of the permanent magnet ring 1. With this arrangement, very high flux densities of the magnetic field tunnel above the first electrode 3 can be achieved. Of course, such a ring magnet 21 can also be advantageously arranged between two permanent magnet rings 1 according to the previously described embodiment according to the Fig. 6a.

[0130] The replaceable measuring chamber 107 in Fig. 6b is radially delimited on the outside by the electrode 3. The feedthrough 103 rides on the electrode 3, whereby the electrode 4 and the feedthrough 103 are also part of the replaceable measuring chamber 107.

[0131] All bushings 103 on the embodiments according to the Fig. 1a to 6b can be inventively designed even without an interchangeable measuring chamber 107, in that the feedthroughs 105 are then designed as metal / glass / ceramic / glass composite feedthroughs of the type already mentioned, as will be described later. However, the embodiments with interchangeable measuring chambers 107 can easily be combined with the feedthroughs designed as mentioned.

[0132] The measuring cells 30 described so far are operated, for example, with a voltage of 3.3 kV between the two electrodes 3, 4, i.e., between cathode 3 and anode 4. The preferred range for the operation of the measuring cell 30 is between 2.0 kV and 4.5 kV.

[0133] Below are dimensions for the important parts.

[0134] The second electrode 4 (anode): - Length of the anode within the measuring space: for example 20 mm, with the preferred range of 10 to 30 mm. - Anode diameter: for example 1.0 to 1.5 mm, with the preferred range of 1.0 to 5.0 mm. - Material: non-magnetic (also para- or diamagnetic).

[0135] The first electrode 3 (cathode): - Length of the cathode: for example 20 mm, with the preferred range of 10 to 30 mm. - Diameter of the cathode: for example 20 to 25 mm, with the preferred range of 15 to 35 mm. - Material: non-magnetic (also para- or diamagnetic).

[0136] The permanent magnet ring 1: - Height in axial direction: for example 5.0 mm, with the preferred range of 3.0 to 10 mm. - Width h in radial direction: for example 5.0 mm, with the preferred range from 3.0 to 10 mm.

[0137] Dimensions of the entire measuring cell (external dimensions): - Length of the measuring cell (without electrical connections): for example 54 mm, with the preferred range from 25 to 70 mm. - Diameter of the measuring cell: for example 30 to 50 mm, with the preferred range of 25 to 80 mm.

[0138] Magnetic field: The flux density on the cylinder axis, measured within the measuring chamber in the axial direction, is in the range of 10 mT (milli Tesla) to 300 mT, preferably in the range of 60 to 130 mT.

[0139] Stray field 15: - Less than 2.0 mT at a distance of 30 mm in radial direction from the outer edge of the measuring cell 30, preferably less than 0.5 mT. - Less than 2.0 mT at a distance of 30 mm from the front or rear edge in the axial direction of the measuring cell 30, preferably less than 0.5 mT.

[0140] In both cases, the stray field cannot reach zero as its lowest values. In the best case, these lowest achievable limits are at most approximately 0.01 mT, corresponding to 0.1 Gauss, which is roughly the same order of magnitude as the Earth's magnetic field measured at the Earth's surface.

[0141] It has been shown that with the high ionization power of this magnetron cold cathode vacuum measuring cell, more material is dusted off the electrode surfaces. Therefore, good protection of the insulators of feedthrough 103 against recoating by such dusted material particles is particularly important.

[0142] As already mentioned several times, it is particularly advantageous if the first electrode, the cathode, is designed as part of a replaceable measuring chamber that can be easily installed, for example, at the measuring connection side, into or onto the rest of the measuring cell, e.g., inserted, thus forming a replaceable unit. Replacement occurs when a certain undesirable degree of contamination is present, which undesirably impairs the measurement accuracy or the reliable operation of the measuring cell is no longer guaranteed.

[0143] A measuring cell according to the invention in a variant is now described on the basis of the Fig. 7 and Fig. 8 described in more detail.

[0144] It includes: a) an evacuable housing 101 with a measuring connection 8 for the vacuum to be measured, b) a first and a second electrode 3, 4, which are arranged substantially coaxially and spaced apart from one another and with a common axis 7, whereby the ionization chamber 20 is formed between these two electrodes, which is arranged in communication with the measuring connection 8, wherein the first electrode 3 forms the outer electrode and this has a substantially cylindrical surface, and that the second electrode 4 is rod-shaped and lies in the axis 7, c) an electrically insulating vacuum-tight feedthrough 103 arranged at one end of the housing 101 on the opposite side of the measuring connection 8, wherein this feedthrough has an insulator 41, 41' arranged around the axis 7 and the second rod-shaped electrode 4 is passed through this insulator in a sealing manner, d) at least one permanent magnet ring 1, which surrounds the coaxial arrangement of the electrodes 3, 4, with a magnetization direction 13 aligned substantially radially to the axis and with a ferromagnetic yoke 2 surrounding this permanent magnet ring 1, wherein the yoke (2) is guided away from the permanent magnet ring 1 on both sides in the axial direction and, after a predetermined distance d from the permanent magnet ring 1, is guided on both sides in the radial direction towards the axis 7 and the first electrode 3, wherein this first electrode 3 forms the outer electrode of the coaxial arrangement of the electrodes 3, 4, such that the yoke 2 forms two annular poles 9a, b on both sides and at a distance from the permanent magnet ring 1, via which at least some of the field lines of the permanent magnet ring 1 close within the ionization chamber 20, penetrating the first electrode 3,wherein a tunnel-like magnetic field 14, annular around the axis 7, is formed at least partially above the first electrode 3 within the ionization chamber 20, and wherein, directed radially toward the axis 7, in the region of at least one of the inner poles 9a, b of the yoke 2, disc-shaped ferromagnetic conducting means 5a, 5b are arranged, which are designed as first and second pole disks 5a, 5b and whose centers around the axis 7 each have an opening 31, 31" for the passage of the second electrode 4 and for the passage of the measuring gas, wherein a shielding device 42, 60 is arranged between the passage 103 and the second pole disk 5b facing it in the radial region of the insulator 41, 41' and coaxial with the axis 7 to protect the insulator 41, 41' from contamination by dusted particles from the ionization chamber 20.

[0145] Out of Fig. 7 (see also Fig. 3 and Fig. 4) it can be seen that the conductive means 5a, 6 and 5b are connected to the electrode 3 and form the measuring chamber 107. This is removable or replaceable as a component with respect to the housing 101 by pulling it out through the measuring connection 8, wherein the electrode 4 rides with the feedthrough 103 on the housing 101 and thus, in this embodiment, is not part of the replaceable measuring chamber 107. The measuring chamber 107 is itself held in the housing 101 in an extendable manner by the action of the magnetization arrangement, including the plate-shaped conductive means or pole disks 5a, 5b, 6 on the measuring chamber 107, wherein, as in Fig. 7, a snap ring 68 can additionally be provided to block the positioning of the inserted measuring chamber 107 in the housing 101.

[0146] At the feedthrough 103, the cylinder 42, which also acts as a shield and insulator, is a ceramic cylinder. The insulator 41' is a glass ring fused to the cylindrical inner surface of the ceramic cylinder 42 on the one hand and to the electrode 4 on the other.

[0147] The insulator 41 is a second glass ring, which is fused on the one hand to the cylindrical outer surface of the ceramic cylinder 42, and on the other hand to a metal connection 43 formed as a ring or the inner surface of an opening provided therein that is coaxial with the axis. Fig. 7, the invention is realized in a combined manner under both aspects 1 and 2.

[0148] The signal evaluation at the measuring cell according to Fig. 7 is carried out by connecting a voltage source 16 to the electrodes 3, 4, wherein the discharge current of the discharge formed between the electrodes 3, 4 is evaluated by means of current measuring means 17. This measured discharge current forms a function of the vacuum pressure to be measured.

[0149] Magnet holders 70 can be arranged on both sides of the permanent magnet ring 1, opposite the yoke 2, in order to hold the permanent magnet ring 1 precisely in position. This arrangement with permanent magnet ring 1, yoke 2, and magnet holder 70 can also be designed as a structural unit that can be easily pushed over the tubular housing 101. A shoulder serving as a stop for positioning can be provided accordingly on the outer circumference of the housing 101. As mentioned, the ionization chamber 20 or the replaceable measuring chamber 107 is advantageously limited in length on both sides at the end and spaced from one another in the axial direction 7 by a first and a second pole disk 5a, 5b.These are each arranged in the area of ​​the two poles 9a, 9b of the yoke 2, wherein, if necessary, the inner wall of the tubular housing 101 as electrode 3 or an additionally inserted cylindrical electrode body along the inner wall of the housing 101 encloses and laterally delimits the ionization chamber 20.

[0150] If the inner wall of the housing 101 forms the electrode 3, then it is advantageous to design the axial section of the housing forming the electrode as part of the exchangeable measuring chamber 107, e.g. by axial screw connections to the Fig. 7 dotted lines p.

[0151] The first 5a and second pole disks 5b, together with the first electrode 3, 3', which surround the axis 7 with the second electrode at a distance, form and thus delimit the measuring chamber 107. Advantageously, a further pole disk 6 is provided in the region of the pole of the permanent magnet ring 1. This divides the measuring chamber 107 into two ionization chambers 20, 20'. It is advantageous if the division is carried out such that the third pole disk 6 and the permanent magnet are arranged centrally, whereby the two ionization chambers 20, 20' are arranged symmetrically with respect to the third pole disk 6 and have approximately the same dimensions.

[0152] The ferromagnetic conducting means directed radially in the region of the inner pole of the permanent magnet ring 1 towards the axis 7 is designed as a third pole disc 6 and also has an opening 31' in the center for the passage of the second electrode 4.

[0153] When using more than one permanent magnet ring 1 according to the Fig. 6a, additional pole discs can be used in the area of ​​each pole of the permanent magnet rings, thus creating additional ionization spaces. Alternatively, pole discs can also be omitted above the poles of the permanent magnet rings. The preferred arrangement is shown in the Fig. 7 and Fig. 8, with three pole discs and a single permanent magnet ring 1, particularly in a symmetrical configuration. The pole discs are advantageously circular.

[0154] The Fig. The advantageous embodiment of the measuring chamber 107 shown in Figure 7 consists in that the first electrode 3 is designed as a separate, preferably sheet-metal-shaped, cylinder, arranged coaxially spaced from the inner wall of the tubular housing 101. A gap 63 is thereby formed between them. The electrode cylinder 3 encloses the measuring chamber 107 and is connected, on both sides, to the first and second pole discs 5a, 5b. The width of the gap 63 is relatively small compared to the measuring chamber diameter, but sufficiently large to achieve a sufficient conductance for the passage or distribution of the measuring gas from the measuring inlet 8 through the entire ionization chamber 20, 20' into the area of ​​the feedthrough 103.

[0155] The first and second pole disks 5a, 5b, as well as possibly the third pole disk 6 or further, preferably two of them, rest at their periphery on the inner wall of the housing 101, wherein in the region of the gap 63, webs 35 are formed on the periphery of the pole disks with interrupting areas or openings. Through these openings at the edge of the pole disks, a connection is created from the measuring inlet 8, via the coaxial gap 63 along the electrode cylinder to the feedthrough 103. This design of the measuring chamber, with the electrode cylinder, together with the pole disks 5a, 5b, 6, thus forms a unit that can be inserted into the housing and is therefore easily replaceable, the aforementioned replaceable measuring chamber 107. This measuring chamber 107 can now be easily replaced as needed if the ionization chamber 20, 20' has an intolerable level of contamination after a certain period of operation.For further simplification, as mentioned, a stop for the measuring chamber position, e.g. a positioning shoulder 61, can be provided on the inner wall of the housing 101.

[0156] When replacing, the measuring chamber 107 is simply pushed into the housing 101 via the measuring inlet 8 until it stops against this positioning shoulder 61. The measuring chamber 107 can then be additionally secured in position on the side of the measuring inlet 8 with a fixing element, for example a snap ring 68.

[0157] It is advantageous if at least some of the pole disks have at least one additional opening, preferably a plurality of openings 32, 32', in addition to the central opening 31, 31', 31". If there are a plurality of openings, for example bores, these should be distributed evenly, in particular in a ring shape. In this case, it is advantageous if, in particular, the first pole disk 5a, which faces the measuring inlet 8, and possibly the third pole disk 6, have at least one such additional opening 32, 32', which are distributed over the disk. With these additional openings, the permeability for the measuring gas into the ionization chamber 20, 20' is increased.

[0158] For certain cases, an ignition aid 33 (see Fig. Fig. 8) can be arranged, which can better initiate the ignition of the discharge. This consists, for example, of a small metal part, such as a plate with sharp edges or points, on which a voltage pulse causes field emission of free charge carriers.

[0159] As already mentioned, it is very important for reliable long-term function of the measuring cell to shield the insulator parts 41, 41', 42 (glass / ceramic / glass) of the bushing 103 particularly carefully. A particularly suitable design is described in the Fig. 7 and, in detail, Fig. 8 elected.

[0160] As already mentioned, the ceramic cylinder projects beyond the one insulating part 42, 41', preferably both insulating parts designed as glass rings 41' and 41. A metallic retaining ring 43, acting as a metal connection, is sealingly connected to the second insulating part 41, i.e., fused to the second glass ring. The metal connection 43, ring-shaped here, carries the feedthrough 103. The metal connection 43 is sealingly connected at the periphery at 45 to one end of the housing 101, which is opposite the measuring inlet 8. The connection at 45 to the housing 101 is advantageously welded, in particular laser welded. A particularly suitable material for the metal connection 43 is stainless steel (Inox), although non-magnetic steel is preferred in order not to unduly influence the discharge in the ionization chamber. The housing 101 is also preferably made of a non-magnetic, stainless steel (Inox).

[0161] At least one second cylinder 60 is arranged coaxially to the axis 7 around the center opening 31 of the second pole disk 5b in the direction of the feedthrough 103. This second pole disk 5b is positioned relative to the feedthrough 103, and the two cylinders 42, 60 are dimensioned in length and diameter such that the second cylinder 60 protrudes into the first, spaced apart from it. Both cylinders are arranged coaxially to one another and to the axis 7. In the area of ​​overlap b, the two cylinders 42, 60 are radially spaced from one another such that they do not touch, and a gap a is formed in the radial direction. This gap a forms an insulation path in the vacuum. With such an arrangement, the creepage path on the surface of the insulators is extended, creating shadowing areas into which dusted material from the ionization chamber cannot reach.The surface of the insulators, namely the glass rings and the ceramic cylinder in the exemplary embodiment, remains protected from contamination at least in some areas, but at least the path via conductive coatings and consequently for possible leakage currents from the second electrode 4 to the housing 101 is interrupted.

[0162] As mentioned, according to the invention, glass is used as the insulating material for both insulator parts 41, 41'. Since the cylinder 42 in the inventive design of the bushing 103 is made of ceramic, i.e. also of an insulating material, the shielding effect is further improved. The insulating material of the cylinder 42 is ceramic. The second cylinder 60 on the second pole disk 5b, on the other hand, is advantageously made of a metal, which is advantageously not ferromagnetic. In addition to the use of a single pair of interlocking cylinders 42, 60, another or even several further interlocking cylinders can be used to further improve the shielding effect. The solution shown according to the Fig. 7 and Fig. 8 with a single pair of cylinders 42, 60, however, is a particularly suitable and cost-effective design.

[0163] The immersion depth or overlap b of the two cylinders 42, 60 is, for example, 1.0 mm, with a preferred range of 0.1 mm to 3.0 mm. The distance (gap) a between the two cylinders 42, 60 in the radial direction is, for example, 0.5 mm, with a preferred range of 0.2 mm to 10.0 mm.

[0164] In the inventive design of the feedthrough 107, the first cylinder consists of a ceramic, such as aluminum oxide, with a specific resistance at 20°C of > 10E17 Ohm m, 10E13 Ohm m at 200°C (FRIALIT F99.7, Friatec Electrical Feedthroughs and Insulating Tubes, Ceramic Metal Composite Components, 1126 / 3 2 VII 04 Gr., Brochure 1279). In the inventive design of the feedthrough 103, the material used for the first and second insulator parts 41, 41' is a glass such as Schott 8250 log, whose electrical volume resistance at 250°C is 10.0 ohm cm (Brochure Schott Technical Glasses, Physical and Technical Properties, 90491 English 04100.7 kn / lang, 2010), corresponding to 10E12 Ohm m.

[0165] An annular chamber 47 can now additionally be formed between the second pole disk 5a, the feedthrough 103, the centrally arranged shielding device, realized by the cylinders 42, 60, and the inner wall of the housing 101, in which chamber, for example, an additional vacuum sensor 48 is arranged. The use of a Pirani sensor or a diaphragm pressure sensor is particularly suitable as the additional vacuum sensor 48. These sensors are small in design and can be elegantly accommodated in this annular chamber 47 in the area of ​​the feedthrough 103. They are also reliably protected from unwanted deposits from the ionization chamber by the shielding device 42, 60, i.e., in the inventive embodiment, the ceramic cylinder 42 and the metal cylinder 60.

[0166] Additionally, for example, the Pirani measuring cell in particular can be provided with an additional protective arrangement 49. The additional feedthrough elements required for such measuring cells, feedthrough rods or pins 44, can be easily provided in combination with the feedthrough 103. Such feedthrough rods 44 can, for example, be integrated directly into the insulator part 41 and / or, preferably, also into the metal connection 43. With such additional vacuum sensors 48, the application range of the vacuum measuring cell 30 can be significantly expanded. Such a combination measuring cell makes it possible to significantly expand the precisely measurable vacuum pressure range.

[0167] An embodiment of the ionization vacuum measuring cell according to the invention, for example according to the Fig. 7 and Fig. 8 includes: a) an evacuable housing with a measuring connection for the vacuum to be measured, b) a first and a second electrode which are arranged substantially coaxially and spaced apart from one another and having a common axis, whereby an ionization space is formed between these two electrodes in a measuring chamber which is arranged in communication with the measuring connection, wherein the first electrode forms the outer electrode and this has a substantially cylindrical surface, and the second electrode is designed as a rod and lies in the axis, c) an electrically insulating and vacuum-tight feedthrough arranged at one end of the housing on the opposite side of the measuring connection, wherein the feedthrough has an insulator arranged around the axis and the second electrode is passed through this insulator in a sealed manner. The measuring cell further comprises a measuring chamber in or on the housing, containing at least the first electrode.

[0168] The measuring chamber is designed as a replaceable component and / or the electrically insulating and vacuum-tight feedthrough comprises a ceramic cylinder coaxial with the axis, with an inner surface radially spaced from the rod, and a first glass ring fused onto the inner surface on the one hand and the rod on the other, axially set back from an end face of the ceramic cylinder facing the ionization chamber. The feedthrough then further comprises a metal connection with a cylinder opening coaxial with the axis, with the inner surface of the opening radially spaced from the cylindrical outer surface of the ceramic cylinder. The feedthrough then further comprises a second glass ring fused onto the cylindrical outer surface of the ceramic cylinder, axially set back from the end face of the ceramic cylinder facing the ionization chamber, wherein the opening inner surface is connected to the second glass ring in a vacuum-tight manner. In both mentioned alternatives and their combination, according to the first and second aspects of the present application and Their combination further comprises the measuring cell d) at least one permanent magnet ring enclosing the coaxial arrangement of electrodes, with a magnetization direction aligned substantially radially to the axis, and with a ferromagnetic yoke enclosing this permanent magnet ring, wherein the yoke is guided away from the permanent magnet ring on both sides in the axial direction and, after a predetermined distance from the permanent magnet ring, is guided on both sides in the radial direction towards the axis and the first electrode. This first electrode is the outer electrode of the coaxial arrangement of electrodes, such that the yoke forms two annular poles on both sides and at a distance from the permanent magnet ring, via which at least some of the field lines of the permanent magnet ring close within the ionization chamber, penetrating the first electrode.A tunnel-like magnetic field, which is at least partially annular around the axis, is formed above the first electrode within the ionization chamber. Furthermore, in the region of at least one of the inner poles of the yoke, disk-shaped ferromagnetic conducting means are arranged, directed radially towards the axis, in the region of at least one of the inner poles of the yoke. These disks are designed as first and second pole disks and whose centers around the axis each have an opening for the passage of the second electrode and for the measurement gas to pass through. A shielding device is arranged between the lead-through and the second pole disk facing it in the radial region of the insulator and coaxial to the axis to protect the insulator from contamination by dusted particles from the ionization chamber.

[0169] This measuring cell according to the invention can be further developed as follows: A) in that in the sectional plane in which the axis lies, the yoke is at least partially curved in the radial direction towards the first electrode. B) in that in the sectional plane in which the axis lies, the yoke is at least partially angled, preferably at right angles, in the radial direction towards the first electrode. C) in that at least two permanent magnet rings with opposite magnetization directions are arranged within the yoke with the two poles spaced apart from each other in the axial direction, each pair of permanent magnet rings forming a further annular and tunnel-like magnetic field above the first electrode. D) in that two permanent magnet rings with opposite magnetization directions are arranged within the yoke with the two poles spaced apart from each other in the axial direction. E) in that the housing encloses both the permanent magnet ring with the yoke and the two electrodes. F) because the yoke forms part of the housing. G) in that the housing is arranged between the first electrode and the permanent magnet ring with the yoke such that the permanent magnet ring and the yoke are arranged separated from the vacuum. H) in that the first electrode is designed as a housing. I) in that the at least one permanent magnet ring is arranged at an unequal distance from the poles in the axial direction within the yoke J) in that the at least one permanent magnet ring is arranged displaceably in the axial direction within the yoke relative to the poles K) in that ferromagnetic conducting means are arranged in the region of the inner pole of the permanent magnet ring in a radial direction towards the axis and are designed as a pole disk which has an opening in the center for the passage of the second electrode. L) in that the first and second pole discs together with the first electrode, which surrounds the axis with the second electrode at a distance, form the measuring chamber M) in that the bushing has an at least two-part insulator in the center, which seals around the second rod-shaped electrode with the first insulator part, wherein the second insulator part surrounds the first in a ring-shaped manner in the radial direction to the axis and at least one first cylinder is sealingly arranged between them, which coaxially surrounds the axis and projects beyond the insulation parts on both sides, wherein a metallic connection is sealingly connected to the second insulator part and carries the bushing and is sealingly connected to one end of the housing N) in that at least one second cylinder is arranged coaxially to the axis around the center opening of the second pole disc in the direction of the feedthrough, which second cylinder projects into the first cylinder with an overlap, wherein in the region of the overlap the two cylinders are arranged at a distance from each other in such a way that they do not touch each other and a gap is formed in the radial direction O) in that at least one of the two insulator parts is made of glass. P) in that the first cylinder consists of an insulating material, preferably a ceramic Q) in that the second pipe section (60) is made of a metal that is not ferromagnetic R) in that the first electrode is designed as a separate sheet-metal-shaped cylindrical part and is arranged coaxially spaced from the inner wall of the housing, forming a gap therebetween, and, enclosing the measuring chamber, is closed on both sides by the first and second pole discs, respectively S) in that the pole discs rest on the periphery of the inner wall of the housing and form webs in the area between the gap of the first electrode and the housing with interrupting areas that provide a connection from the measuring inlet to the feedthrough T) in that the sheet-metal cylinder part together with the pole discs form a measuring chamber unit that can be inserted into the housing and is therefore exchangeable U) in that the first pole disc and possibly the third pole disc have at least one further opening, preferably more, which are distributed over the disc to increase the permeability for the measuring gas into the ionization space V) in that an annular chamber is formed between the second pole disc, the bushing, the centrally arranged shielding device and the inner wall of the housing, in which an additional vacuum sensor is arranged W) in that the additional vacuum sensor is a Pirani sensor or a diaphragm pressure sensor.

[0170] In Fig. 9 is a simplified longitudinal representation of a good further development of the already based on the Fig. 7 and Fig. 8 presented feedthrough 103. In the axis 110 of the feedthrough 103 lies the metal rod 112, which is to be electrically insulated and vacuum-tight, according to Fig. 7 e.g. electrode 4 or an electrical supply to one of the electrodes in the ionization chamber.

[0171] A ceramic cylinder 114 is cast coaxially to the axis 110 and fused to the metal rod 112 via a glass ring 116. The outer cylindrical surface of the ceramic cylinder 114 is in turn connected to the metal connection 120 via a second glass ring 118. For this purpose, the metal connection 120 has an opening 122 coaxial with the axis 110, and the further glass ring 118 is, as mentioned, cast on the one hand to the outer surface of the ceramic cylinder 114 and on the other hand to the cylindrical opening surface of the opening 122.

[0172] As further schematically shown in Fig. 10, several pairs of first glass rings 116, 116a, 116b and associated ceramic cylinders 114a, 114b may be provided if necessary to further increase the electrical insulation of the feedthrough 103.

[0173] As already shown by Fig. 7, cylinders may be provided on the ionization vacuum measuring cell on the ionization chamber side, as shown in Fig. 10 at 125 dashed, and correspondingly cylinder 60 of Fig. 7, which project beyond the ceramic cylinders 114 of the bushing 103 inside these cylinders 114 or outside these cylinders 114 without contact.

[0174] Based on implementation 103 according to Fig. 10 and in the same representation shows Fig. 11 the bushing 103 is supplemented with one or more lateral bushings 130 with bushing rods 132, e.g. for the additional pressure sensors according to 48 of Fig. 7 and / or for applying potential to the second or another electrode in the ionization chamber. The lateral feedthroughs 130 are provided in the metal connection 120. Their axis 134 is usually parallel to the axis 110, but in certain applications can be arranged at an oblique angle to the axis 110, but in any case with a directional component parallel to the axis 110.

[0175] The lateral feedthroughs 130 are each formed by a bore 136 through the metal terminal 120, in which the rod or pin 132 to be passed through is arranged coaxially. The rod or pin 132 is fused to the metal terminal 120 by the glass of a glass insert 138, is vacuum-tight in the bore 136, and is electrically insulated from the wall of the bore 136.

[0176] If, as is usual, several lateral feedthroughs 130 are provided, which are arranged to provide as direct an electrical access as possible to components on the ionization chamber side, these lateral feedthroughs 130, for optimal positioning, do not all need to be radially equally spaced with respect to the feedthrough axis 110, nor do they need to be equally distributed along the periphery, i.e. azimuthally with respect to the axis 110.

[0177] If holes 136 are provided in the metal connection 120 which are not needed for a feedthrough 130 for a specific application, such a hole 130 can be provided as shown in dashed lines at 130 o in Fig. 11 shown, it must be sealed vacuum-tight by means of a fused glass insert.

[0178] When considering Fig. 11 it is readily apparent that the feedthrough 103 is relatively easy to manufacture by appropriately positioning the rod 112, cylinder 114, metal connection 120 and feedthrough rod 134, providing powdered glass in the corresponding openings / bores and melting it. It is also apparent that the feedthrough 103 is already subjected to high thermal, partly inhomogeneously distributed loads during production. Various material pairings are present, namely metal / glass, then glass / ceramic, ceramic / glass, glass / metal, metal / glass and finally glass / metal. These pairings of different materials, the possibly staggered formation of the actual fusions at the fusion zones, ieMaterial transitions, as well as inhomogeneities in the respective materials, particularly glass and ceramic, which can never be ruled out, along with different thermal behavior of the materials, can lead to high stresses developing in the glass inserts 138 of the lateral feedthrough 130. These can lead to cracks, such as hairline cracks, appearing in the glass inserts 138 during thermal loading or during cooling, or only much later, e.g., during mechanical impact loading during operation of the measuring cell. These cracks massively reduce, if not eliminate, both their vacuum tightness and their electrical insulation capacity.

[0179] The problem of high stresses in the glass inserts 138 at the lateral bushings 130 in the metal connection 120 was basically solved by, as in Fig. 12 schematically shows the metal connection 120 in two parts 1201 and 120 which are "movable" relative to each other within limits and primarily in the radial direction. a The lateral bushings 130 are provided on the outer part 120 with respect to the axis 110. The integrity of the two parts as a metal connection 120 is ensured by a connecting section 145 of the two parts 120 acting as a stress buffer. i , 120 a This buffer zone, which can be provided along a separation gap 140 between the mentioned parts of the metal connection 120, is designed as a material zone bridging this gap all the way around and can comprise relatively ductile metal and / or can be designed so thin that it absorbs the stresses practically like a spring and is homogeneously distributed into the outer part 120 a of the metal connection 120. Thus, in the unclaimed embodiment according to Fig. 12 the metal connection 120 through an annular gap 140 coaxial with the axis 110 of the bushing 103 into an inner part 120 i and an outer 120 a divided, preferably both made of the same metal. In the outer part 120 a rides the or rides the already based on Fig. 11 presented lateral feedthrough 130. The integrity of the metal connection 120 is ensured by the bridge section 145 acting as a buffer zone in Fig. 12 circled, obtained.

[0180] Instead of an annular gap 140, as shown schematically in Fig. 13, the inner 120 i and outer 120 a Parts of the metal terminal 120 may be designed such that they extend along at least one plane E, perpendicular to the axis 110, to which the two parts 120 i and 120 a adjacent to each other, can move radially. As shown in Fig. 13, the integrity of the part 120 including vacuum tightness can be formed by a circumferential connecting seam, such as a weld or solder seam 150. Advantageous in the basic embodiment according to Fig. 13 is that the two parts are guided in the radial direction of expansion and therefore cannot bend against each other, which leads to bending stresses, particularly on the glass ring 118 according to Fig. 10 and subsequent ceramic cylinder.

[0181] In the unclaimed embodiment according to Fig. 13 is actually the coaxial gap 140 according to Fig. 12 is designed as a spatial area open towards the axis 110, which with respect to the radial displaceability of the outer part 120 a regarding the inner part 120 i , which takes over the splitting function and therefore in Fig. 13 is also designated 140.

[0182] In the unclaimed embodiment according to Fig. 14, as will now be readily apparent to the person skilled in the art, the embodiments according to Fig. 12 and Fig. 13. On the one hand, the two parts are guided in their radial relative expansion movement along two planes E1 and E2, perpendicular to the axis 110 of the bushing. On the other hand, a multi-part annular gap 140 is provided, which is radially divided into offset sections and ensures the required relative radial mobility to absorb the stresses. According to Fig. 14, the integrity of the metal connection 120 is ensured by at least one connecting seam, such as a weld or solder seam, running around the axis 110, and if necessary, on the side of the metal connection 120 facing away from the seam 150, as in 150 b in Fig. 14, another connecting bridge must be created, e.g. segmented. It must be pointed out that the bridge section, which ensures the integrity of the metal connection 120, must be electrically conductive if the two parts 120 are to be connected. a and 120 b be operated at the same electrical potential as usual and ensure vacuum tightness.

[0183] Instead of a connecting seam, the bridge section can be Fig. 15, by means of webs 1451 or 1452, which are created by incorporating the gap structure 140 into the material of the metal connection 120. Of course, a combination of connecting seam and connecting web made of the material of the metal connection 120 is also possible.

[0184] As already mentioned several times, the ionization vacuum measuring cell according to one aspect of the invention has a measuring chamber which can be removed from the measuring cell as a replacement part by simple manipulation and replaced, for example, by another measuring chamber. Fig. Figure 16 shows a schematic and simplified representation of one of the possible implementations. The replaceable measuring chamber 107 with measuring gas connection 8 comprises, as shown in dashed lines, one electrode 3 and thus, apart from the second electrode, the ionization chamber and furthermore according to Fig. 16 a section 101 b of the housing 101. The measuring chamber 107, the housing section 101 coaxial with respect to axis 7 b is connected to the remaining housing part 101 at a connection zone 152 a connected, such as by means of a bayonet lock, a screw connection, etc. The interchangeability of the measuring chamber 107 is in Fig. 16 indicated by the double arrow AU.

[0185] The electrically insulating and vacuum-tight bushing 103 can (not shown in Fig. 16) on the remaining housing part 101 a or on the measuring chamber 107. In the latter case, the electrode inserted through the aforementioned feedthrough 103 is also replaced along with the measuring chamber 107.

[0186] In the embodiment as simplified and schematically shown in Fig. As shown in Figure 17, the measuring chamber 107 is inserted into the housing 101 on the side of the measuring gas connection 8 and secured therein. With magnetization arrangements as described, this often already provides sufficient self-fixation of the measuring chamber 107 in the housing 101. In this embodiment, too, the feedthrough 103 can be firmly connected to the housing 101 or to the replaceable measuring chamber 107.

[0187] If additional locking of the measuring chamber 107, which is preferably inserted against the stop on the housing 101, is required, this can be achieved by locking means such as a snap ring or bolt through the wall of the housing 101 or ball-lock connections, etc.

[0188] As already mentioned, the electrically insulating and vacuum-tight feedthrough 103 is extremely sensitive to contamination. If, as in Fig. 18 is shown in a highly simplified and schematic manner, the exchangeable measuring chamber 107 does not include the mentioned feedthrough 103, but the latter is firmly connected to the housing 101, then the feedthrough in Fig. 18, the rod designated 104 can also be introduced into the measuring chamber 107, there into the ionization chamber, in an electrically insulated manner. For this purpose, an electrically insulating, non-vacuum-tight feedthrough 109 is provided at the measuring chamber 107. Therefore, an electrically insulating feedthrough 109 is provided coaxially with axis 7 and thus feedthrough 103 at the measuring chamber 107, through which the rod 104 is guided snugly when inserted into the measuring chamber 107. Fig. 18 is only an example of a measuring cell constructed in the manner of a Penning cell with cathode 4 K and anode 3 A If necessary, to ensure the interchangeability of the measuring chamber 107, as shown schematically in Fig. 18 at 106, sections of the rod 104 are coupled by detachable plug connections.

[0189] With the bushing 109 practically adjacent to the rod 104, the bushing 103 is highly effectively protected from contamination from the ionization chamber.

Claims

[1] Ionization vacuum measuring cell comprising: a) a housing (101) with a measuring connection (8) for the vacuum to be measured at one end section; b) a measuring chamber (107) in the housing (101) which is gas-flow-connected to the measuring connection (8); c) a first and a second electrode (3, 4) in the measuring chamber (107), which are arranged substantially coaxially with respect to an axis and spaced apart from one another, whereby an ionization space (20) is formed in the measuring chamber (107) between these two electrodes, wherein the first electrode (3) has a substantially cylindrical inner surface as the electrode surface facing the ionization space (20), d) an electrically insulating and vacuum-tight feedthrough (103) for an electrical supply to one of the electrodes or for one of the electrodes itself, with an electrical insulator, characterized bythat the measuring chamber (107) is designed as an exchangeable component and is limited radially outwards with respect to the axis by a) a measuring chamber housing, which is in contact with an inner surface of the housing (101) in whole, in sections or not, and has a substantially cylindrical inner surface which is offset radially outwards from the first electrode (3), or b) at least one axial section of the wall of the housing. [2] Ionization vacuum measuring cell according to claim 1, characterized by that the measuring chamber (107) has, at the end axially remote from the measuring connection (8), a non-vacuum-tight, electrically insulated feedthrough for the supply to one of the electrodes or for one of the electrodes themselves, or a feedthrough which is both electrically insulated and vacuum-tight. [3] Ionization vacuum measuring cell according to one of claims 1 to 2, characterized bythat the measuring chamber (107) is pushed onto or into the housing (101) on the measuring connection side until it stops and is releasably locked on the housing (101), wherein for this purpose a screw connection or a snap connection is preferably provided between the measuring chamber (107) and the housing (101) or at least one locking member acting axially or radially between the housing (101) and the measuring chamber (107), preferably a snap ring. [4] Ionization vacuum measuring cell according to one of claims 1 to 3, characterized by that at least part of a magnetization arrangement (105) is provided radially outside the measuring chamber (107), which generates a magnetic field in the ionization space (20). [5] Ionization vacuum measuring cell according to one of claims 1 to 4, characterized by that the measuring chamber (107) cannot be dismantled without destruction. [6] Ionization vacuum measuring cell according to one of claims 1 to 5, which is constructed as an inverted magnetron cell. [7] Measuring chamber (107) for an ionization vacuum measuring cell according to one of claims 1 to 6, wherein the measuring chamber (107) is designed as a component with a measuring chamber housing and a first and a second electrode (3, 4) are arranged in the measuring chamber (107), substantially coaxial with respect to an axis and spaced from one another, and wherein an ionization space (20) is formed in the measuring chamber (107) between these two electrodes. [8] Ionization vacuum measuring cell comprising: a) an evacuable housing (101) with a measuring connection (8) for the vacuum to be measured, b) a first and a second electrode (3, 4) which are arranged substantially coaxially and spaced apart from one another and with a common axis (7), whereby a measuring chamber is formed between these two electrodes, which is arranged in communication with the measuring connection (8), wherein the first electrode (3) forms the outer electrode and this has a substantially cylindrical surface, and that the second electrode (4) is rod-shaped and lies in the axis (7), c) an electrically insulating vacuum-tight feedthrough (103) arranged at one end of the housing (101) on the opposite side of the measuring connection (8), wherein this feedthrough has an insulator (41, 41') arranged around the axis (7) and the second rod-shaped electrode (4) is passed through this insulator in a sealing manner, d) at least one permanent magnet ring (1) surrounding the coaxial arrangement of the electrodes (3, 4), with a magnetisation direction (13) aligned substantially radially to the axis and with a ferromagnetic yoke (2) surrounding this permanent magnet ring (1), characterized bythat the yoke (2) is guided away from the permanent magnet ring (1) on both sides in the axial direction and, after a predetermined distance from the permanent magnet ring (1), is guided on both sides in the radial direction towards the axis (7) and the first electrode (3), wherein this first electrode (3) forms the outer electrode of the coaxial arrangement of the electrodes (3, 4), such that the yoke (2) forms two annular poles (9a, b) on both sides and at a distance from the permanent magnet ring (1), via which at least some of the field lines of the permanent magnet ring (1) penetrate the first electrode (3) within the measuring chamber, wherein at least partially a tunnel-like magnetic field (14) is formed around the axis (7) above the first electrode (3) within the measuring chamber, and that directed in the radial direction towards the axis (7), in the region of at least one of the inner poles (9a, b) of the yoke (2),disc-shaped ferromagnetic conducting means (5a, b) are arranged, which are designed as first and second pole discs (5a, b) and whose center around the axis (7) each has an opening (31, 31') for the passage of the second electrode (4) and for the passage of the measuring gas, wherein between the passage (103) and the second pole disc (5b) facing it in the radial region of the insulator (41, 41') and coaxial to the axis (7) a shielding device (42, 60) is arranged to protect the insulator (41, 41') from contamination by dusted particles from the measuring chamber, which forms an ionization space (20), and that at least the first electrode (3) is installed in an exchangeable insert chamber.

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