NL2009999C2

NL2009999C2 - Gas analyser and valve assembly for a gas analyser.

Info

Publication number: NL2009999C2
Application number: NL2009999A
Authority: NL
Inventors: Gerard Johannes Cornelis Baarle; Alexei Ofitserov; Ivar Allard Joachim Taminiau; Richard Rijn
Original assignee: Leiden Probe Microscopy B V
Priority date: 2012-12-17
Filing date: 2012-12-17
Publication date: 2014-06-19

Description

GAS ANALYSER AND VALVE ASSEMBLY FOR A GAS ANALYSER

The present invention relates to a gas analyser for analysing a gas flow in a gas flow passage. The 5 invention also relates to a valve assembly to be connected to a vacuum chamber of a gas analyser and/or to a method of analysing a gas flow.

Mass spectrometry is a commonly used technique for analysing the composition of gas flows. The technique is 10 employed in a wide variety of industries and applications, ranging for instance from the chemical industry (in catalysis, metallurgy), process industry and electronics industry (production of semiconductors, etc.) to research laboratories and knowledge institutes. For instance, the 15 analysis results may be used for controlling chemical processes, checking the occurrence of contamination in gas flows, etc.

Mass spectrometers can be used to measure the mass and/or the mass/charge ratio of ionised atoms or other 20 electrically charged particles (herein briefly referred to as particles). A special type of mass spectrometers is the so-called residual gas analyser (RGA). A residual gas analyser is a mass spectrometer that can be connected to a vacuum system and whose functions may be to analyze the 25 gases inside the vacuum chamber. Residual gas analyzers typically may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, and may be used, for instance, to monitor the quality of the vacuum and detect minute traces 30 of impurities in the low-pressure gas environment. Residual gas analysers can also be used to determine the concentrations or absolute partial pressures of the components of a gas mixture.

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Generally, the principle of operation of a residual gas analyser is as follows: a small fraction of the gas particles (molecules) flowing through a flow passage, such as a gas pipe in a chemical plant, is ionized (positive 5 ions), the resulting ions are separated and then detected (i.e. sensed and measured) according to their molecular masses. Figure 1 shows a typical measurement arrangement of a residual gas analyser for analysing the process gas flow in a flow passage 1. The main flow passage 1 may be any 10 conduit, channel, line, vessel, duct tube, etc. wherein a process gas (direction Pi) to be analysed may flow. The gas may be single gas or may be any mixture of two or more gasses .

Referring to figure 1, a flow may be branched off 15 from the (main) passage 1. In some applications only a small portion of the flow is branched off. In other applications the process flow is stopped at (A), which means that the complete process flow is sent through the capillary tube 4.

A portion of the process gas is discharged through 20 an opening 2 in the wall of the passage 1 and flows inside the branch passage 3, i.e. a relatively long capillary tube 4 towards a residual gas analyser 5. The gas flow inside the capillary tube 4 is discharged in a first chamber 5. The first chamber 5 is connected to a discharge pump 6, for 25 instance a turbo pump or a non-turbo pump, for discharging (direction P2) and thereby refreshing the content of the first chamber 5.

Between the first chamber 5 and a second chamber 7 a flow restriction element 8 is arranged allowing a small 30 fraction of the content of the first chamber 5 to enter (in direction P3) the second chamber 7. The second chamber 7 is connected to a further pump 9, for instance a turbo pump, 3 for discharging (direction P4) and thereby refreshing the content of the second chamber 7.

Whereas the flow through the capillary tube 4 has a relatively low flow speed and a relatively high flow rate, 5 the flow through the flow restriction element 8 is relatively fast, but the flow rate through the flow restriction element 8 is considerably smaller than the flow through the capillary tube 4. In fact the flow in the flow restriction element 8 is within the molecular flow regime 10 (free molecular flow), whereas the flow in the capillary tube 4 obviously is not.

The flow restriction element 8 is an element allowing for the controlled flow of gas from the first chamber 5 into the second chamber 6, for instance a small 15 tube, a diaphragm or a pinhole.

The second chamber 7 is connected via a connection element 10 to a residual gas analyzer 11, for instance a mass spectrometer. The gas analyzer is configured to analyze the content of the gas(es) entering through the connection 20 element 10.

Generally the response time is determined by the time delay in the capillary tube 4 rather than the time delay in the restriction 8. The time resolution may be largely determined by the refresh time of the volume of the 25 first chamber 5.

This known measurement arrangement of a residual gas analyser has a number of disadvantages. For instance, the arrangement will only work properly in case of relatively large gas flows, typically in the order of 1-20 30 seem. A bypass flow of 1-20 seem through the capillary tube 4 is needed, while the preferred flow in the gas analyser 11 itself may be a million times smaller.

4

If the flow reduction operation is performed using a capillary tune (having a length of typically 1-3 m and an internal diameter of 50-1000 pm) there is a trade off between response time and gas flow. One can opt for a short 5 response time at the expense of a high gas flow and vice versa. In practice often use is made of a two stage reduction process in order to keep the response time within acceptable limits. Otherwise, when using one long capillary tube, the response time becomes extremely long (typically 10 several minutes). A further problem is that in the long, thin capillary tube 4 separation of gasses may take place. Hence, the response time for different gasses may vary, which may impede the gas analysis operation.

Furthermore, the internal volume of the inlet 15 system, defined by the volume of the passage 3 including the volumes of the tubes 8 and 9, is relatively large. This means that a relatively large part of the process flow must be used for the analysing operation and therefore may be lost. Due to the discharge of a relatively large internal 20 volume of gas the process flow through the main passage 1 may be interrupted or at least influenced to some extent.

A further disadvantage of the known gas analysers is that the typical operating pressure range is relatively small. Different pressure ranges in the main passage 1 need 25 differently sized capillary tubes 4 to allow the gas to flow into the vacuum chamber at the operating pressure range of the gas analyser 11. In other words, if a gas analyser is to be used for measuring a gas flow in the main passage in a different pressure range, then the capillary tube 4 should 30 be replaced by a differently sized tube and/or the restriction 8 should be tuned accordingly, leading to a change in flow in the second chamber 7. This may cause a change of the response time of the gas analyser and may 5 reduce the practical application of this type of mass spectrometer for analysing process flows.

It is an object of the present invention to provide a gas analyser and/or a valve assembly for a gas 5 analyser and/or a method of analysing gas wherein at least one of the above identified disadvantages of the existing RGA arrangement has been removed or at least reduced.

It is furthermore an object of the invention to provide a gas analyser and valve assembly that allow for a 10 fast analysis of a process flow.

It is also an object of the invention to provide a gas analyser and valve assembly that may analyze process in a relatively large process gas pressure range.

According to the first aspect of the invention at 15 least one of the objects that is achieved in a gas analyser for analysing a gas flow in a gas flow passage, the gas analyser comprising: - a mass spectrometer comprising a vacuum chamber in which reside: 20 - a ionizer for ionizing particles arriving from a vacuum chamber inlet; - a ion accelerator for accelerating the ionized particles and a mass filter for filtering the ionized particles; 25 - a detector for detecting accelerated and filtered ionized particles; - a valve assembly for leaking a gas portion from the gas flow passage to the vacuum chamber, the valve assembly comprising an inlet and a high pressure outlet to be 30 connected to the gas flow passage and a low pressure outlet connected to the vacuum chamber inlet, the valve assembly further comprising a pressure reduction valve to reduce the pressure of the gas portion leaking from the high pressure 6 inlet to the low pressure outlet and into the vacuum chamber .

In embodiments of the present invention the valve has a small volume at the location where the gas sample is 5 leaked into the ultra high vacuum (UHV) and the badly refreshed volume of the valve assembly is relatively small.

In an embodiment of the invention a three-way valve is arranged in direct fluid contact with the vacuum chamber, so that the response time can be kept to a minimum. 10 The gas analyser according to embodiments of the invention may therefore be configured to perform an essentially real time analysis of the gas flow in the process passage, without needing to disturb the gas flow in the process passage .

15 In embodiments of the invention, for instance when the process gas flow passage is stopped downstream of the opening in the passage providing access to the gas analyzer, the valve assembly may leak the entire gas portion from the low pressure outlet into the vacuum chamber. Essentially all 20 gas particles leaving the low pressure port are then handled in the vacuum chamber so that a reliable analysis can be accomplished. In other embodiments only a fraction of the process gas flow is leaked into the vacuum chamber.

In embodiments of the invention the pressure 25 reduction valve is configured to reduce the pressure at the low pressure outlet to 1.3.10-2 Pa (10-4 Torr) or less, preferably 1.3xl0~4 Pa (10-6 Torr) or less, in order to have the mass spectrometer work at its sweet spot.

In embodiments of the invention the valve assembly 30 is configured to operate at an inlet pressure ranging from lxlO2 Pa to 3xl06 Pa.

In embodiments of the invention the pressure reduction of the valve assembly is controllable. Since the 7 pressure reduction is controllable, no replacement of parts (such as the capillary tubes in existing gas analyzers) is needed when the operating pressures are changed. In some embodiments the pressure reduction is even continuously 5 controllable. Even if large variations of the flow rate or pressure in the passage occur, the pressure reduction may be tuned to enable the gas analyzer to continue the analysis of the gas flow.

In embodiments of the invention the gas analyser 10 comprises a chamber from which a gas sample is taken having an internal volume of smaller than 100 microliter, preferably smaller than 10 microliter (for instance 6 microliter).

In embodiments of the invention the valve assembly 15 is configured to provide a leak rate (qL) of the gas portion leaking into the vacuum chamber between 10_1 and 10~9 Pa 1/s. (at a temperature of about 293 K).

In embodiments of the invention the valve assembly comprises : 20 - a valve body comprising a valve body chamber, an inlet, a high pressure outlet and a low pressure outlet; -a sealing element, for instance a sealing pad, accommodated in the valve body chamber, the sealing element being arranged over the inlet and the high pressure outlet; 25 - a movable element arranged so as to exert an adaptable force on the sealing element for deforming, for instance elastically deforming, the sealing element so as to control the leaking of gas from the inlet via the sealing element to the low pressure outlet.

30 In embodiments of the invention the valve assembly comprises an actuator for actuating the movable element so as to control the leak rate of the valve assembly, either manually or in an automated manner.

8

Gas analysers using a capillary tube to guide the gas to be analysed to the vacuum chamber tend to show a relatively long response time. In order to reduce the response time considerably (while maintaining the gas 5 entering the vacuum chamber within the operating conditions needed to properly operate the analyser), a restriction element may be provided in the supply passage of the gas flow to the vacuum chamber. The supply passage may be embodied to allow for a flow having a relatively large flow 10 speed and high flow rate (with respect to flow in a capillary tube). The restriction element on the other hand is embodied to restrict the flow in the flow passage to such an extent that gas is properly leaked into the vacuum chamber. The restriction element defines a relatively short 15 restriction length, typically 1 cm or smaller, so that the time interval needed by the gas to pass the restriction element is relatively short. This leads to a relatively short overall response time of the system.

In embodiments of the invention the sealing 20 element comprises a circumferential flange. The flange may be pressed onto a valve seat of the valve body by the movable element. The gas flow rate through the valve may be controlled by varying the pressing force on the sealing element.

25 In further embodiments the restriction element is formed by the sealing element and the restriction length is the length of the contact surface between a valve seat of the valve body and the sealing element.

In embodiments of the invention the valve assembly 30 is configured to guide essentially the gas flow from the entire flow passage through the inlet and the outlets. The entire flow is guided through the valve assembly so that a representative detection may be achieved.

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According to another aspect of the invention a valve assembly to be connected to vacuum chamber of a gas analyser and to a gas flow passage is provided, the valve assembly being configured to leak a gas portion from the gas 5 flow passage to the vacuum chamber, the valve assembly comprising: - a high pressure inlet; - a high pressure outlet, both the inlet and the outlet being configured to be connected to the gas flow passage; 10 - a low pressure outlet configured to be connected to the vacuum chamber inlet; - a pressure reduction valve to reduce the pressure of the gas portion leaking to the vacuum chamber.

According to another aspect of the invention a 15 method of operating the gas analyser and/or the valve assembly and/or a method of analysing gas is provided.

Further advantages, characteristics and details of the present invention will become apparent from the following description of several embodiments thereof. In the 20 description, reference is made to the annexed drawings, which show:

Figure 2 a schematic diagram showing an example of a configuration of a gas analyser according to an embodiment of the present invention; 25 Figure 3 an exploded view of an embodiment of the valve assembly according to the invention, in combination with a mass spectrometer according to an embodiment of the invention;

Figure 4 a partly taken away view of the 30 embodiment of the analyser of figure 3, in inserted position;

Figure 5 a side view of a valve assembly according to the embodiment of figures 3 and 4; 10

Figure 6 a longitudinal section through the embodiment of figure 5;

Figure 7 a side view of a sealing element according to an embodiment of the present invention; and 5 Figure 8 a cross-section of the sealing element of

Figure 7.

Referring to figure 2 an arrangement according to an embodiment of the present invention is shown. The figure shows passage 30 through which a gas flow (one or more 10 gasses, herein also referred to as the process flow) 31 flows. The passage 30 comprises essentially a first passage part 40, upstream of the gas analyzer 28, and a second passage part 41, downstream of the gas analyzer 28. The passage parts 40,41 are directly connected to a valve 15 assembly 35. The valve assembly is configured to allow a small portion of the gas flow 31 (flowing into and out of the valve assembly) to enter directly into the vacuum chamber 29 of the residual gas analyser 28.

In embodiments of the invention the upstream 20 passage part 41 is in fluid connection with a high pressure inlet port 36 of a valve assembly 35 (figures 5 and 6). As mentioned above, the valve assembly 35 constitutes a leak unit that is configured to leak a very small amount of gas towards the vacuum chamber 29 of the gas analyser. In the 25 vacuum chamber 29 the leaked in gas particles may be analyzed by the mass spectrometer of the residual gas analyzer 28 .

Basically, in one type of mass spectrometer the gas particles in the vacuum chamber are first ionized, for 30 instance under the influence of electrons emitted from a hot filament. The ionized gas particles are then accelerated and caused to follow a semi-circular trajectory established by the Lorentz force in a uniform magnetic field. The ionised 11 particles are detected by a detector. For a fixed radius of curvature an ionised particle with a particular mass/charge ratio can be isolated and measured by an appropriate combination of the magnetic field and an accelerating 5 voltage.

In practice, it is difficult to achieve very stable and spatially uniform magnetic fields, especially with permanent magnets. In another type of mass spectrometer the use of magnetic fields has been eliminated by a design 10 which uses alternating quadrupolar electric fields (therefore the name quadrupole mass spectrometer), as will be explained hereafter.

For the analysis of gasses in a gas flow flowing in a gas flow passage use can be made of residual gas 15 analysers (RGA's). An RGA is typically a mass spectrometer of small physical dimensions that can be connected directly to a vacuum system and its function is to analyse the gasses inside the vacuum chamber. A small fraction of the gas particles in the gas flow are ionised and the resulting 20 ionised particles are separated, detected and measured according to their molecular masses. RGA's can be used to identify the different molecules present in a residual gas environment and can be used to determine the concentrations or absolute partial pressures of the components of a gas 25 mixture.

Figures 3 and 4 show an example of a residual gas analyzer (RGA) 11 that can be combined with a valve assembly 35 according to an embodiment of the present invention. RGA 11 comprises a probe assembly 14 comprising an ionizer 17, a 30 quadrupole probe 18 and a detector unit 19. The detector unit 19 comprises a flange 20 that may be attached to a flange 21 of a tubular cover 22. At the other side of the flange 20 the casing of a control unit 15 may be attached.

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The control unit 15 may contain the electronic circuitry and the power supply for operating the gas analyzer.

The tubular cover 22 further comprises a mounting flange 23 for mounting with a corresponding flange 24 of a 5 vacuum port 25 of the vacuum chamber 29. As is shown in figures 3 and 4, a first end of the probe assembly 14 may be inserted into the tubular cover 22 until the flange 20 of the probe assembly 14 abuts the flange 21 of the tubular cover 22. In this position the probe assembly 14 is attached 10 to the tubular cover 22 and the vacuum chamber 29.

Positively charged gas particles (ions) are produced in the ioniser 17 by bombarding residual gas particles in the vacuum chamber 29 originating from the valve assembly 35 with electrons derived from a heated 15 filament (not shown). The filament is heated to incandescence with an electrical current. The filament is the source of the electrons used in ionising the gas particles (molecules). The emitted electrons are accelerated by an ion accelerator and are directed to the entrance of 20 the particle mass filter. The ionized particles are filtered by the probe 18, more specifically by its quadrupole mass filter 26, where they are separated based on their mass to charge ratio. Ionised particles that successfully pass through the quadrupole mass filter 26 are then focussed 25 towards the detector unit 19 which is configured to detect the particles.

The quadrupole mass filter 26 comprises four rods (schematically shown in figures 2 and 3). During operation a two-dimensional (X-Y) electric field is created between the 30 rods (electrodes) with the two opposite rods connected together electrically. Ionised particles enter the filter along the Z-axis and start oscillating in the X and Y directions. The ionised particles are separated based on 13 their mass to charge ratio by the lateral forces resulting from the electric potentials applied to the rods. Separation of a specific mass requires setting of suitable RF and DC voltages such that only the ionised particles of interest 5 have stable trajectories down the probe 18 and reach the detector unit 19.

In figures 5 and 6 the valve assembly 35 is shown in more detail. In the arrangement shown in these figures, the entire process flow 31 flowing through the passage 40 10 (in directions P4 and P5, figure 3) is fed to the gas analyser 11. To this end the passage 30 comprises a first part 40 upstream of the valve assembly 35 and a second part 41 downstream of the valve assembly 35. The upstream passage part 40 is connected to a high pressure input 36 while the 15 downstream passage portion 41 is connected to a high pressure output 38. A third port 44 is provided as well. Inside the valve assembly 35 an inner volume or space is formed. The third port 44 is a low pressure output port and provides the earlier mentioned gas that is leaked towards 20 the vacuum chamber 29 of the residual gas analyser 11.

The valve assembly 35 comprises a generally tubular element 37. Inside the tubular element 37 an inner volume or space 39 is formed. A membrane 48 is positioned in the space 39 of the tubular element. The membrane 48 is 25 attached to the inner wall of the tubular element 39 and is made of material that is essentially impermeable to gas. Consequently, essentially no gas passes from a lower compartment 50 of the inner space 39 to an upper compartment 51 of the same.

30 Inside the upper compartment 51 and extending in a generally longitudinal direction is arranged a pressure control rod 55. The pressure control rod 55 is at one end attached to the upper wall 56 of the tubular element 37 in 14 such a way that the rod may be moved up and down (respectively in direction P6 and P7) so that the rounded end 58 of the pressure control rod may exert a force upon the membrane 48. More specifically the pressure control rod 55 5 may exert a force upon a block 64 that is integrated with the membrane 64. The rounded end 58 of the pressure control rod ensures that the force exerted on the membrane is always in a downward direction.

In the lower compartment 50 a movable sealing pad 10 60 is provided. The sealing pad is shown in more detail in figures 7 and 8. The sealing pad 60 comprises a centre part 61, at the bottom of which a small circumferential flange 62 is formed. The circumferential flange 62 has a flattened edge (as is shown in the cross-section of figure 8) or a 15 rounded edge. The sealing pad 60 further comprises at the top of the centre part 61 a bar 63 that may be attached to the block 64. To this end the bar may be threaded. The bar 63 of the sealing pad connected to the block 64 is located so that the pressure control rod 55 contacts the membrane 48 20 exactly at the position of the block 64. In this manner the rod 55 may exert a pressure on the block 64 and thereby on the entire sealing pad 60 when the rod is moved downwardly (direction P7) . Exertion of a force on the sealing pad 60 by moving the rod 55 causes the edge of the circumferential 25 flange 62 to be pressed against the seat 65.

Preferably the material of the sealing pad 60 is slightly softer than the material of the seat 65. In embodiments of the invention the valve seat is made of metal while the sealing pas is made of copper. The valve seat 65 30 may for instance be formed by a flat steel surface. In other embodiments alternative materials and/or shapes may be employed.

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The sealing pad 60 is formed so that the circumferential edge 62 is positioned around the earlier mentioned high pressure inlet ports 36 and 38. In this manner the internal chamber 69 inside the sealing pad 60 may 5 sealed from the lower compartment 50. By varying the force exerted by the rod 55 on the valve seat 65, the pressing force of the flange 62 on the valve seat 65 may be varied. Depending on the actual force the amount of gas (i.e. volume per time interval or flow rate) inside the chamber 69 formed 10 between the bottom of the central part 61 of the sealing pad, the flange 62 and the upper part of the valve seat 65, flowing towards the lower compartment 50 may be varied. In other words, by moving up and down the rod 55, the flow rate of gas originating from the gas flow passage and leaking 15 from the gas sample chamber 69 to the compartment 50 and from the compartment 50 out of the low pressure outlet port 44 into the vacuum chamber 29 of the gas analyser can be tuned.

The restriction length of the sealing element 60 20 is defined by the length (thickness) of the contact surface between the circumferential flange 62 of the sealing element and the valve seat 65. The contact surface may be very small. In embodiments of the invention wherein the thickness of the circumferential flange 62 is about 0,5 mm, the 25 restriction length may be as small as 0,1 mm or smaller.

The downward and upward movement of the rod 55 is accomplished by operating an adjustment mechanism 70. The mechanism comprises a generally L-shaped lever 71. The rod is attached inside the internal space 39 to the wall of the 30 tube 37 by a pivot 72. Pivot 72 is slightly off axis with respect to pressure control rod 55. Consequently, the pressure control rod 55 moves down and up (and slightly sideways as well) if the lever 71 is moved. More 16 specifically, when rod 55 is pivoted with respect to the pivot 72, the rod edge 58 moves to increase or reduce the pressure force on the membrane 48. Pivoting of the rod can be accomplished by changing the orientation of the lever 5 (i.e. an outer end of which is attached to the upper end of the rod) with respect to the wall of the tubular element 37. This change of orientation can be accomplished by operating an adjustment mechanism. The adjustment mechanism may comprise an adjustment screw 76. When the screw is operated, 10 the distance between the free end of the lever 71 and the wall of the tubular element 37 is changed, which change causes an upward or downward movement of the rod. The slight lateral movement of the rod is accommodated by the rounded end of the rod 58. This configuration provides for a very 15 high sensitivity of the movement of the lever and thereby enables the operator to change the leak rate of the valve very accurately.

In the embodiment described in connection with figures 5 and 6, the flow 31 through the flow passage 30 is 20 passed entirely through the valve assembly. In other embodiments, the flow to the high pressure inlet port 36 is branched off of from the (main) passage 30. The gas that is not leaked into the low pressure output but rather is discharged through the high pressure output port 38 can be 25 returned to the (main) passage 30 through a separate discharge line or can be discharged elsewhere.

Since in the valve assembly the low pressure outlet 44 is connected to the vacuum chamber of the gas analyser, either directly or through a relatively short 30 passage (tube, line, hose, channel, etc.), the response time (i.e. the time between a certain gas constituent entering the valve assembly and the time at which this constituent is 17 detected by the detector) may be reduced considerably relative to known gas analyzers.

The gas leaking from the gas sample chamber 69 of the sealing element into the vacuum compartment 50 is 5 eventually discharged through the low pressure outlet port 44. The flow in the first and second passage parts 40,41 and in the chamber 69 essentially is a viscous flow. Due to the restriction element (for instance the sealing pad) the gas flow in compartment 50 and through outlet 44 is essentially 10 a molecular flow. This means that the gas molecules move at a relatively high speed inside the compartment 50. For instance, the average velocity of a nitrogen molecule in vacuum conditions and at room temperature is about 470 m/s. Consequently, the time delay from the entering the 15 compartment 50 to reaching the vacuum chamber of the gas analyser is very short. For instance, if the distance between the sealing element of the valve assembly and the gas analyser is about 10 cm, the time delay is only about 0.2 ms .

20 The time resolution appears to be proportional to the volume from which a gas sample is taken times the pressure inside this volume divided by the flow (i.e. the refresh rate of the volume). If the flow rate is low and a high pressure is allowed, then the volume of gas sample 25 chamber should be very small to provide a good time resolution. In embodiments of the invention the volume of the compartment 69 therefore is typically in the order of 100 μΐ or less, preferably 10 μΐ or less. This is considerably smaller than the internal volume that is 30 present in the known gas analysis systems.

The construction of the valve assembly 35 enables the reduction of the pressure at the low pressure outlet (output port 44) to 1.3xl0“2 Pascal or less, or even to 1.3 18 1CT4 Pascal or less, which are typically values that may be easily handled by the RGA 11. The input pressure (i.e. the pressure in the upstream part 40 of the passage 30) may be as high as 1x10s to lxlO6, preferably even ranging from lxlO2 5 Pascal to 3xl06 Pascal.

Furthermore the pressure reduction of the valve assembly is easily controllable. For instance in the embodiment shown in figures 5 and 6, the pressure reduction is controlled by operating the adjustment mechanism 70.

10 Accordingly, the assembly can be used effectively in quite a large pressure range, without essentially needing to make constructional adjustments to the arrangement.

As discussed earlier, the leaking rate of the gas flowing from the valve assembly into the vacuum chamber 29 15 for further analysis by the mass spectrometer may be easily controlled. In the embodiments shown in figures 5 and 6 the flow rate or leaking rate can be controlled by operating the adjustment mechanism 70. The adjustment arrangement makes it possible to control the leak rate on the fly, i.e. without 20 substantially disturbing the process gas flow through the main flow passage and thereby without essentially influencing the process that is to be controlled.

In a further embodiment of the invention, control of the leak rate of the valve assembly may be performed in a 25 continuous manner. For instance the leak rate may be gradually increased or decreased, for instance to render more accurate analysis results.

In some of the embodiments described so far the leaking rate is controlled manually, for instance by an 30 operator operating the adjustment mechanism. In other embodiments, however, the leaking rate is controlled by an electronic controller, for instance a computer or similar electronic device, which is configured to control an 19 electric motor that operates the adjustment mechanism. The controller may or may not be connected to the control of the mass spectrometer or to one or more flow sensors for sensing the flow rate in the main passage.

5 In embodiments of the invention ionization takes place by bombarding residual gas particles (molecules) with electrons derived from a heated filament. However, other ionisation techniques are also conceivable, such as a fast atom bombardment (FAB) technique, electrospray ionisation, 10 or matrix assisted laser desorption/ionisation (MALDI).

The present invention is not limited to the embodiments described herein. The rights sought are determined rather by the following claims, within the scope of which numerous modifications, adjustments and additions can be envisaged.

15 20

CLAUSES

1. Gas analyser for analysing a gas flow in a gas flow passage, the gas analyser comprising: 5 - a mass spectrometer comprising a vacuum chamber in which reside: - a ionizer for ionizing particles arriving from a vacuum chamber inlet; - a ion accelerator for accelerating the ionized 10 particles and a mass filter for filtering the ionized particles; - a detector for detecting accelerated and filtered ionized particles; - a valve assembly for leaking a gas portion from the 15 gas flow passage to the vacuum chamber, the valve assembly comprising an inlet and a high pressure outlet operatively connected to the gas flow passage and a low pressure outlet operatively connected to the vacuum chamber inlet, the valve assembly further comprising a pressure reduction valve to 20 reduce the pressure of the gas portion leaking from the high pressure inlet to the low pressure outlet and into the vacuum chamber .

2. Gas analyser as claimed in claim 1, wherein the 25 pressure reduction valve is configured to reduce the pressure at the low pressure outlet to 1.3.10 Pa (10 Torr) or less, preferably 1.3xl0~4 Pa (10 6 Torr) or less.

3. Gas analyser as claimed in any of claims 1-2, 30 wherein the valve assembly is configured to operate at an inlet pressure ranging from lxlO2 Pa to 3xl06 Pa.

21 4. Gas analyser as claimed in any of the preceding claims, wherein the pressure reduction of the valve assembly is controllable.

5 5. Gas analyser as claimed in any of the preceding claims, wherein the gas analyser is configured to analyse the gas flow by determining the mass/charge ratio of the ionized particles reaching the detector.

10 6. Gas analyser comprising a chamber from which a gas sample is taken having an internal gas sampling volume of smaller than 100 microliter, preferably smaller than 10 microliter .

15 7. Gas analyser as claimed in any of the preceding claims, wherein the valve assembly is configured to provide a leak rate (qL) of the gas portion leaking into the vacuum chamber between 10-1 and 10~1 Pa 1/s.

20 8. Gas analyser as claimed in any of the preceding claims, wherein the leak rate of the valve assembly is continuously controllable.

Gas analyser as claimed in any of the preceding 25 claims, the valve assembly comprising: - a valve body comprising a valve body chamber, an inlet, a high pressure outlet and a low pressure outlet; -a sealing element, for instance a sealing pad, accommodated in the valve body chamber, the sealing element 30 being arranged over the inlet and the high pressure outlet; - a movable element arranged so as to exert an adaptable force on the sealing element for deforming, preferably elastically deforming, the sealing element so as 22 to control the leaking of gas from the inlet via the sealing element to the low pressure outlet.

10. Gas analyser according to claim 9, wherein the 5 sealing element comprises a circumferential flange pressed onto a valve seat of the valve body.

11. Gas analyser as claimed in any of the preceding claims, comprising a restriction element in the 10 supply of the gas flow to the vacuum chamber, the restriction element being configured to control the leaking of gas into the vacuum chamber and/or defining a restriction length smaller than 1 cm, preferably smaller than 1 mm.

15 12. Gas analyser as claimed in claims 10 and 11, wherein the restriction element is essentially formed by the sealing element and the restriction length is the length of the contact surface between a valve seat of the valve body and the sealing element.

20 13. Gas analyser as claimed in claim 11, comprising an actuator for actuating the movable element.

14. Gas analyser as claimed in any of the 25 preceding claims, wherein the valve assembly is configured to leak the entire gas portion from the low pressure outlet into the vacuum chamber.

15. Gas analyser as claimed in any of the 30 preceding claims, the valve assembly being configured to guide essentially the gas flow from the entire flow passage through the inlet and the outlets.

23 16. Gas analyser as claimed in any of the preceding claims, wherein the ionizer is configured to bombard leaked-in particles from the gas flow with electrons and/or wherein the ion accelerometer and mass filter are 5 formed by a quadrupole filter for generating alternating quadrupolar electric fields, the quadrupole filter preferably comprising four parallel metal rods.

17. Gas analyser as claimed in any of the 10 preceding claims, wherein the ionized particles are ionized atoms and/or other electrically charged particles.

18. Valve assembly to be connected to vacuum chamber of a gas analyser and to a gas flow passage, the 15 valve assembly being configured to leak a gas portion from the gas flow passage to the vacuum chamber, the valve assembly comprising: - a high pressure inlet; - a high pressure outlet, both the inlet and the outlet 20 being configured to be connected to the gas flow passage; - a low pressure outlet configured to be connected to the vacuum chamber inlet; - a pressure reduction valve to reduce the pressure of the gas portion leaking to the vacuum chamber.

25 19. Valve assembly as claimed in claim 18, wherein the pressure reduction of the valve assembly is controllable and/or wherein the leak rate of the valve assembly is continuously controllable.

20. Valve assembly as claimed in any of claims 18-19, comprising a chamber from which a gas sample is taken, 30 24 the chamber having an internal volume of smaller than 100 microliter, preferably smaller than 10 microliter.

21. Valve assembly as claimed in any of the claims 5 18-20, the valve assembly comprising: - a valve body comprising a valve body chamber, an inlet, a high pressure outlet and a low pressure outlet; -a sealing element, for instance a sealing pad, accommodated in the valve body chamber, the sealing element 10 being arranged over the inlet and the high pressure outlet; - a movable element arranged so as to exert an adaptable force on the sealing element for deforming, preferably elastically deforming, the sealing element so as to control the leaking of gas from the inlet via the sealing 15 element to the low pressure outlet.

22. Valve assembly according to claim 21, wherein the sealing element comprises a circumferential flange pressed onto a valve seat of the valve body.

20 23. Valve assembly as claimed in any of claims 18-22, comprising a restriction element in the supply of the gas flow to the vacuum chamber, the restriction element being configured to control the leaking of gas into the 25 vacuum chamber and/or defining a restriction length smaller than 1 cm, preferably smaller than 1 mm.

24. Valve assembly as claimed in claims 22 and 23, wherein the restriction element is formed by the sealing 30 element and the restriction length is the length of the contact surface between a valve seat of the valve body and the sealing element.

25 25. Method of analysing a gas flow in a gas flow passage, the method comprising: - leading a gas flow through a high pressure inlet into a gas sample chamber of a valve assembly according to any of 5 the preceding claims; - leaking gas from the gas sample chamber into a compartment and from the compartment to a low pressure outlet; - leading the leaked gas from the low pressure outlet 10 to the vacuum chamber of a mass spectrometer; - ionizing gas particles in the vacuum chamber; - accelerating the ionized particles and filtering the s ame ; - detecting accelerated and filtered ionized particles. 15 26. Method of operating a gas analyser and/or valve assembly as claimed in any of the claims 1-24.

Claims

A gas analyzer for analyzing a gas flow in a gas flow passage, the gas analyzer 5 comprising: a mass spectrometer comprising a vacuum chamber in which are housed: an ionizer for ionizing particles arriving from a vacuum chamber inlet; 10 an ion accelerator for accelerating the ionized particles and a mass filter for filtering the ionized particles; a detector for detecting accelerated and filtered ionized particles; 15 a valve assembly for leaking a gas portion from the gas flow passage to the vacuum chamber, the valve assembly comprising an inlet and high pressure outlet operatively connected to the gas flow passage and a low pressure outlet operatively connected to the vacuum chamber inlet, the valve assembly further comprising a reduction valve for reduce the pressure of the gas portion leaking from the high pressure inlet to the low pressure outlet and into the vacuum chamber.

A gas analyzer according to claim 1, wherein the pressure reduction valve is adapted to reduce the pressure in the low pressure outlet to 1.3 x 10 "2 Pascal (10 ~ 4 Torr) or less, preferably 1.3 x 10" 4 Pascal (10 "6 Torr) or less.

A gas analyzer according to any of claims 1-2, wherein the gas assembly is configured to operate at an inlet pressure in the range of 1 x 102 Pascal to 3 x 106 Pascal.

Gas analyzer according to one of the preceding claims, wherein the pressure reduction of the valve assembly is controllable. 5

5. Gas analyzer according to any of the preceding claims, wherein the gas analyzer is designed to analyze the gas flow by determining the mass / charge ratio of the ionized particles reaching the detector.

A gas analyzer comprising a chamber from which a gas sample is taken with an internal gas sample volume of less than 100 μΐ, preferably less than 10 μΐ. 15

7. Gas analyzer as claimed in any of the foregoing claims, wherein the valve assembly is designed to provide a leakage rate (qjJ of the gas part leaking in the vacuum chamber between 10-1 and 10-9 Pascal 1 / s.

A gas analyzer according to any one of the preceding claims, wherein the leak rate of the valve assembly is continuously controllable.

9. Gas analyzer as claimed in any of the foregoing claims, the valve assembly comprising: - a valve body comprising a valve body chamber, an inlet, an outlet and a low-pressure outlet, - a sealing element, for example a sealing block, housed in the valve body chamber, the sealing element arranged over the inlet and the high pressure outlet; a movable element arranged to exert an adjustable force on the sealing element for elastically deforming the sealing element to control the leakage of gas from the inlet via the sealing element to the low pressure outlet.

The gas analyzer of claim 9, wherein the sealing element comprises a circumferential flange that is pressed onto a valve seat of the valve body.

11. Gas analyzer as claimed in any of the foregoing claims, comprising a restriction element in the supply of the gas flow to the vacuum chamber, wherein the restriction element is designed to direct gas leakage into the vacuum chamber and / or defines a restriction length of smaller than 1 cm, preferably smaller than 1 15 mm.

12. Gas analyzer according to claim 10 or 11, wherein the restriction element is essentially formed by the sealing element and the restriction length is the length of the contact surface between the valve seat of the valve body and the sealing element.

13. Gas analyzer according to claim 11, comprising an operating element for operating the movable element.

14. Gas analyzer as claimed in any of the foregoing claims, wherein the valve assembly is designed to leak the entire gas part from the low-pressure outlet to the vacuum chamber.

A gas analyzer according to any one of the preceding claims, wherein the valve assembly is adapted to guide the gas flow of substantially the entire gas flow passage through the inlet and outlets.

16. Gas analyzer according to one of the preceding claims, wherein the ionizer is designed to bombard leaked particles from the gas flow with electrons and / or wherein the ion accelerator and the mass filter are formed by a quadrupole filter for generating alternating quadrupolar electric fields, the quadrupole filter preferably comprises four parallel metal bars.

17. Gas analyzer according to one of the preceding claims, wherein the ionized particles are ionized atoms and / or electrically charged particles.

18. A valve assembly operably connectable to the vacuum chamber of a gas analyzer and to a gas flow passage wherein the valve assembly is configured to leak a gas portion from the gas flow passage to the vacuum chamber, the valve assembly comprising: a high pressure inlet; a high pressure outlet; wherein both the inlet and the outlet are configured to be operatively connected to the gas flow passage; a low pressure outlet configured to be operatively connected to the vacuum chamber inlet; a pressure reduction valve to reduce the pressure of the gas portion leaking into the vacuum chamber.

The valve assembly according to claim 18, wherein the pressure reduction of the valve assembly is controllable and / or can be continuously controlled in the leakage speed of the valve assembly. 5

A valve assembly according to any one of claims 18-19, comprising a chamber from which a gas sample is taken, wherein the chamber has an internal volume of less than 100 μΐ, preferably less than 10 μΐ. 10

A valve assembly according to any of claims 18-20, wherein the valve assembly comprises: - a valve body comprising a valve body chamber, an inlet, a high-pressure outlet and a low-pressure outlet; A sealing element, for example a sealing block, housed in the valve body chamber, the sealing element being arranged over the inlet and the high pressure outlet; a movable member arranged to exert an adjustable force on the seal member for deforming, preferably elastically deforming, the seal member to direct gas leakage from the inlet through the seal member to the low pressure outlet. 25

The valve assembly of claim 21, wherein the sealing element comprises a circumferential flange that is pressed onto the valve seat of the valve body.

A valve assembly according to any of claims 18-22, comprising a restriction element in the gas flow supply to the vacuum chamber, the restriction element being designed to control the leakage of gas into the vacuum chamber and / or defining a restriction length which is smaller than 1 cm, preferably smaller than 1 mm.

A valve assembly according to claim 22 and 23, wherein the restriction element is formed by the sealing element and the restriction length is the length of the contact surface between a valve seat of the valve body and the sealing element.

A method for analyzing the gas flow in the gas flow passage, the method comprising: - passing the gas flow through a high pressure inlet into a gas sample chamber of a valve assembly according to any one of the preceding claims; 15. gas leakage from the gas sample chamber into the compartment and from the compartment to a low pressure outlet; - directing the leaked gas from the low pressure outlet to the vacuum chamber of the mass spectrometer; 20. ionizing gas particles in the vacuum chamber; - accelerating the ionized particles and filtering them; the detection of accelerated and ionized particles. 25

A method for operating a gas analyzer and / or a valve assembly according to any of claims 1-24. 30