Method for measuring ambient concentration of light gas using mass spectrometry countercurrent leak detection device

Abstract

A method for determining an ambient concentration of a light gas includes a mass spectrometry countercurrent leak detection device (10) having a mass spectrometry gas detector (12), a high vacuum pump (16) connected to the gas detector (12), and a pre-vacuum pump (24) connected to the high vacuum pump (16), where the pre-vacuum pump (24) includes a gas outlet to the atmosphere, wherein the pre-vacuum pump (24) serves to evacuate the high-vacuum pump (16) and / or the gas detector (12), characterized in that air from the environment of the pre-vacuum pump (24) is allowed to enter the operating pre-vacuum pump (24) or an inlet-side pre-vacuum region thereof, the pre-vacuum pump (24) is arranged in the gas detector (12) such that gas components, lighter than air, in the admitted air / gas mixture enter the gas detector (12) in a countercurrent manner and are detected in the gas detector (12), while the remaining gas components in the admitted air mixture are conveyed through the outlet of the pre-vacuum pump (24) into the ambient atmosphere (54).

Description

[0001] The invention relates to a method for detecting light gas components in the external environment of a mass spectrometer countercurrent leakage detection device.

[0002] The mass spectrometry countercurrent leak detection device usually includes: a port leading to the sample to be detected or the test chamber where the sample to be detected is located; a gas detector in the form of a mass spectrometer connected to the port; a high vacuum pump usually in the form of a turbomolecular pump, whose inlet is connected to the mass spectrometer and whose outlet is connected to the inlet of the pre-vacuum pump, and whose outlet delivers the evacuated gas to the surrounding atmosphere. In addition, the high vacuum pump usually includes an intermediate gas inlet connected to the sample port or the test chamber port, respectively. In addition, the pre-vacuum pump can be directly connected to the mass spectrometer by bridging the bypass line of the high vacuum pump for large-scale leak detection. The test sample port or the test chamber port can be connected to the inlet of the pre-vacuum pump respectively by an additional booster pump, wherein the booster pump can be connected to the intermediate gas inlet of the high vacuum pump.

[0003] To detect leaks, the test chamber port and the test chamber connected thereto are first evacuated using a pre-vacuum pump and a booster pump (if present). In addition, the pre-vacuum pump generates the required pre-vacuum at the outlet of the high vacuum pump so that the high vacuum pump can evacuate the mass spectrometer. Once the vacuum required to operate the mass spectrometer is reached at the inlet of the high vacuum pump, the connecting valve connected between the test chamber port and the high vacuum pump is opened, allowing gas to flow from the test chamber into the high vacuum pump and into the mass spectrometer in a countercurrent manner through the high vacuum pump for analysis. If the test sample leaks, the gas inside the test sample will enter the test chamber, and then enter the mass spectrometer from the test chamber in a countercurrent manner and can be detected at the mass spectrometer.

[0004] For mass spectrometry backflow leak detection, it is often necessary to determine the concentration of certain light gas components in the ambient air. Light gas components are gas components in air mixtures from the ambient air that are lighter than air. For example, helium is one of these light gas components.

[0005] Traditionally, a separate gas analyzer is used to determine the ambient helium concentration. Alternatively, in a mass spectrometer countercurrent leak detection setup, the fore-vacuum pump can be shut down and the gas ballast valve of the fore-vacuum pump opened for exhaust, thereby slowing it down. Once the fore-vacuum pump is stopped, the gas can be introduced into the mass spectrometer through the gas ballast valve and a bypass line bridging the high vacuum pump for large-scale leak detection, and the gas can be measured at the mass spectrometer. The bypass line is a direct connection line between the fore-vacuum pump inlet and the mass spectrometer. Typically, this bypass line is equipped with an additional throttle valve for large-scale leak detection.

[0006] The object of the present invention is to provide an improved method for determining the concentration of light gas components in the environment of a mass spectrometric counterflow leak detection device.

[0007] The method according to the invention is defined by the features of claim 1 .

[0008] Claim 1 relates to a mass spectrometry countercurrent leak detection device, which has a pre-vacuum pump, a high vacuum pump and a mass spectrometry gas detector. The outlet of the pre-vacuum pump can lead to the atmosphere or, for example, can be connected to an exhaust line that discharges the pumped gas into the atmosphere. The inlet of the pre-vacuum pump is connected to the outlet of the high vacuum pump. The inlet of the high vacuum pump is connected to a mass spectrometer. The intermediate gas inlet of the high vacuum pump is connected to the outlet of the vacuum test chamber and / or the test sample via a separate connecting line. In addition, the ports of the test chamber or the test sample can be connected to the inlet of the pre-vacuum pump via an additional booster pump, respectively, but this is not absolutely necessary. It is conceivable to connect the intermediate gas outlet of the booster pump to the intermediate gas inlet of the high vacuum pump.

[0009] The high vacuum pump is usually a turbomolecular pump. The pre-vacuum pump is equipped with a gas ballast which can be vented to the outside atmosphere or to a fresh air line. The gas ballast can include a selective switching valve so that it can be selectively opened or closed.

[0010] For mass spectrometry countercurrent leak detection, a pre-vacuum pump is usually used to generate a pre-vacuum pressure at the outlet of a high vacuum pump so that the high vacuum pump can generate the required high vacuum inside the mass spectrometer. Through the intermediate gas inlet of the high vacuum pump, the gas from the test chamber or from the test sample is allowed to flow countercurrently through the high vacuum pump into the mass spectrometer and be analyzed there. In this process, it is determined whether the analyzed gas has a gas component indicating a leak in the test sample.

[0011] In order to simultaneously detect or analyze light gas components lighter than air from the environment outside the forevacuum pump, the gas ballast valve can be opened or air from the environment outside the forevacuum pump can be allowed to enter the forevacuum pump through the opened gas ballast valve, so that at least one light gas component (e.g., helium) flows out through the inlet of the forevacuum pump in countercurrent and enters the mass spectrometer from there, while the remaining gas components are transported to the environment through the outlet of the forevacuum pump. Alternatively or additionally, the air inlet can be directly connected to the forevacuation region of the forevacuum pump, i.e., for example, to the connecting pipeline between the forevacuum pump and the high vacuum pump and / or to the bypass pipeline for bypassing the high vacuum pump described further below.

[0012] Therefore, the advantage of the present invention is that the mass spectrometer can be used to analyze the ambient air during the actual leak detection, in particular to measure the concentration of light gas components in the ambient air, without interrupting the leak detection and / or shutting down the pre-vacuum pump. In this regard, the light gas component to be measured can flow back from the inlet of the pre-vacuum pump to the outlet of the high vacuum pump, flow to its inlet through the high vacuum pump, and then enter the mass spectrometer from there. Alternatively or additionally, the light gas component to be measured can enter the mass spectrometer by connecting the inlet of the pre-vacuum pump to the mass spectrometer for large-scale leak detection through a bypass line, which bridges the high vacuum pump. The bypass line can be equipped with an additional throttle valve. This bypass line can detect particularly large leaks before the high vacuum pump in the mass spectrometer generates the required high vacuum pressure.

[0013] The light gas components then flow from the gas ballast to the mass spectrometer gas detector via the forevacuum pump in the reverse direction of the pumping direction. The pressure at the high vacuum pump outlet depends only on the speed of the forevacuum pump and not on the proportion of the light gas components (e.g., helium) to be measured in the ambient air. The measurement deviation of the leak rate signal or the ion raw current signal of the mass spectrometer depends on the ambient helium concentration or the concentration of the light gas components in the ambient air, respectively.

[0014] Light gases, such as helium, flow in the direction of the actual pumping of the mass spectrometer. The lower the speed of the forevacuum pump, the more helium will flow back through the inlet of the mass spectrometer in counterflow through the forevacuum pump. Due to the different compressions, the increase in the light gas content is greater than the total pressure increase in the mass spectrometer. By changing or adjusting the speed of the forevacuum pump, the ambient concentration of light gases such as helium can be determined even without activating the valve.

[0015] The ambient concentration of light gas components can be determined during the actual leak detection or after the leak detection of a test sample without shutting down the pump. The pre-vacuum pump and the high vacuum pump continue to run, eliminating the time required to shut down the vacuum pump and then restart it.

[0016] Below, exemplary embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. In the accompanying drawings:

[0017] Figure 1 is a first exemplary embodiment, and

[0018] Figure 2 is the second exemplary embodiment.

[0019] A mass spectrometry countercurrent leak detection device 10 is shown, which comprises a gas detector 12 in the form of a mass spectrometer. The gas detector 12 is connected in a gas-conducting manner to an inlet 14 of a high vacuum pump 16 in the form of a turbomolecular pump. An outlet 18 of the high vacuum pump 16 is connected in a gas-conducting manner to an inlet 22 of a pre-vacuum pump 24 via a connecting line provided with a selectively controllable valve 20. An outlet 26 of the pre-vacuum pump 24 leads to the atmosphere or to an exhaust line.

[0020] Furthermore, the inlet 22 of the pre-vacuum pump 24 is connected to the mass spectrometer 12 via a separate bypass line 28. The bypass line 28 bridges the high vacuum pump 16 and the controllable valve 20 and is provided with a throttle valve 30, thereby enabling large-scale leak detection.

[0021] The leak detection device 10 is also provided with a port 32 for a test chamber or a test sample. In the exemplary embodiment shown, a test chamber 35 is vacuum connected to the port 32. The test chamber 35 receives the test sample to be checked for leaks and is then evacuated. To this end, the port 32 is gas-conductingly connected to a booster pump 34. In this regard, an inlet 36 of the booster pump is gas-conductingly connected to the port 32, while an outlet 38 of the booster pump is connected to the inlet 22 of the pre-vacuum pump via a gas line 42 provided with another valve 40.

[0022] The boost pump 34 is not essential to the present invention. Figure 2 An exemplary embodiment without a boost pump is shown. Figure 2 An exemplary embodiment of Figure 1 The exemplary embodiment of is corresponding to that of , except that the boost pump 34 and the air inlet 53 are missing.

[0023] An intermediate gas line 46 including another selectively operable valve 44 connects an intermediate gas outlet 48 of the booster pump 34 to an intermediate gas inlet 50 of the high vacuum pump 16 .

[0024] The pre-vacuum pump 24 is also provided with a gas ballast valve 52, which is formed separately from the inlet 22 and the outlet 26, and connects the interior of the pre-vacuum pump 24 to an external environment 54 of the pre-vacuum pump 24 and the leak detection device 10. The gas ballast valve 52 can be selectively operated and can be opened and closed.

[0025] A throttle point 51 is provided between the gas ballast valve 52 and the pre-vacuum pump 24 to determine the gas flow rate allowed to flow into the pre-vacuum pump 24 through the gas ballast. According to the present invention, the gas ballast valve 52 can be omitted. In this case, the throttle point 51 is provided only at the inlet of the gas ballast forming the pre-vacuum pump 24. For example, the throttle point 51 can be enabled by selecting a suitable cross section of the gas ballast inlet.

[0026] As an alternative or in addition to the intake of air from the environment 54 via the gas ballast of the pre-vacuum pump 24, the ambient air may also be taken in via a Figure 2 The air inlet 53 shown enters the pre-vacuum region of the pre-vacuum pump 24. Figure 2 In the embodiment, an air inlet 53 is provided, which can be connected to the atmosphere or to a fresh air line, and which leads to the connecting line between the inlet 22 and the valve 20, i.e., to the connecting line connecting the pre-vacuum pump 24 to the high vacuum pump 16. In addition to the gas ballast entering through the pre-vacuum pump 24, Figure 2 Also shown is an air inlet 35, but it is also possible as an alternative not to provide a gas ballast. In this case, the gas ballast on the pre-vacuum pump 24 is omitted. The air inlet 53 is also provided with a throttle valve similar to the throttle point 51 of the gas ballast. Figure 1 This can also be achieved by the exemplary embodiments in .

[0027] During operation, the test chamber 35 is evacuated by means of the pre-vacuum pump 24 and the booster pump 34. The pre-vacuum pump 24 generates the required pre-vacuum at the outlet of the high vacuum pump 16, into which the contents of the mass spectrometer 12 are drawn. At the same time, the pre-vacuum pump 24 also evacuates the mass spectrometer 12 directly via the bypass line 28.

[0028] Once the vacuum pressure required to operate the mass spectrometer 12 is reached, the valve 44 is opened and the valve 40 is closed, so that the leaked gas from the test gas and / or the inside of the test chamber 35 passes through the booster pump 34, the intermediate gas pipeline 36 and in a countercurrent manner through the high vacuum pump 16 into the mass spectrometer 12 and can be analyzed in the mass spectrometer 12.

[0029] In order to be able to quickly and easily determine the gas concentration of the helium content in the ambient air 54, the gas ballast valve 52 is opened while the pre-vacuum pump 24 is still running. In an exemplary embodiment without a gas ballast valve, the gas ballast 52 is permanently opened and connected to the fresh air line. In the simplest case, the gas ballast 52 can be vented to the atmosphere.

[0030] In order to determine the gas concentration of the helium content in the ambient air, the speed of the vacuum pump is adjusted or at least varied between two different operating states, for example, alternating between a terminal speed and a reduced speed of the forevacuum pump 24. The change in the pump speed leads to a change in the helium partial pressure and the total pressure at the inlet 22 of the forevacuum pump 24. In the measurement signal of the mass spectrometer 12, a change in the helium content or a signal deviation can be measured, because helium from the forevacuum pump 24 flows back into the mass spectrometer 12 via the bypass line 28 or via the high vacuum pump 16. In the case of the gas ballast valve 52, the air supply flowing from the environment 54 into the forevacuum pump 24 can be influenced by opening and closing the gas ballast valve 52.

[0031] Gas components of ambient air that are lighter than the average value of the gas components of ambient air will flow countercurrently out of the pre-vacuum pump through the inlet 22 and from there countercurrently through the high vacuum pump 16 and / or through the bypass line 28 into the high vacuum of the mass spectrometer 12, where these gas components can be measured. In contrast, gas components of ambient air that are heavier than ambient air return to the environment 54 through the outlet 26 of the pre-vacuum pump 24. In this way, helium from the ambient air 54 enters the mass spectrometer 12 and can be analyzed in the mass spectrometer 12 without having to shut down the pre-vacuum pump 24, the high vacuum pump 16 and / or the booster pump 34.

[0032] As an alternative or in addition to the gas ballast of the pre-vacuum pump 24, an air inlet can be provided to supply ambient air directly to the pre-vacuum area of ​​the pre-vacuum pump 24, for example as an air inlet 53 allowing ambient air to enter the connecting pipeline between the pre-vacuum pump 24 and the high vacuum pump 16, between the inlet 22 and the valve 20 and / or into the bypass line 28.

Claims

1. A method for determining an ambient concentration of a light gas, comprising a mass spectrometer countercurrent leak detection device (10) having a mass spectrometer gas detector (12), a high vacuum pump (16) connected to the gas detector (12), and a pre-vacuum pump (24) connected to the high vacuum pump (16), wherein the pre-vacuum pump (24) comprises a gas outlet to the atmosphere, wherein the pre-vacuum pump (24) is used to evacuate the high vacuum pump (16) and / or the gas detector (12), It is characterized in that Air from the environment of the fore-vacuum pump (24) is allowed to enter the fore-vacuum pump (24) in operation or the fore-vacuum region on its inlet side, so that gas components lighter than air in the air / gas mixture allowed to enter enter the gas detector (12) in a countercurrent manner and are detected in the gas detector (12), while the remaining gas components in the entering gas mixture are transported to the surrounding atmosphere (54) through the outlet of the fore-vacuum pump (24).

2. The method according to claim 1, characterized in that The gas component that is lighter than air is neon, helium, hydrogen or deuterium.

3. The method according to claim 1 or 2, characterized in that: The light gas component enters the gas detector (12) in a countercurrent manner through the high vacuum pump (16), or enters the gas detector (12) by bridging the high vacuum pump (16) and connecting the pre-vacuum pump (24) to a bypass line (28) of the gas detector (12) to perform large-scale leak detection.

4. The method according to any one of the preceding claims, characterized in that The pre-vacuum pump (24) includes an open gas ballast, allowing air from the environment (54) of the pre-vacuum pump (24) to enter the operating pre-vacuum pump (24) through the open gas ballast.

5. The method according to any one of the preceding claims, characterized in that A separate air inlet (53) is provided upstream of the inlet (22) of the pre-vacuum pump (24) in the pre-vacuum region, allowing air from the environment of the pre-vacuum pump (24) to enter the pre-vacuum region thereof through the air inlet (53).

6. A method according to any one of the preceding claims, characterised in that The speed of the pre-vacuum pump is varied in order to determine the ambient concentration of the light gas component of the air / gas mixture admitted, and the proportion of the light gas component is determined from the resulting change in the measurement signal of the gas detector (12).

7. The method according to any one of the preceding claims, characterized in that The speed of the pre-vacuum pump is changed from a first speed value to at least a second speed value different from the first speed value, and a response of the measurement signal representing the partial pressure of the gas component is evaluated.

8. The method according to any one of the preceding claims, characterized in that The pre-vacuum pump (24) is a Roots pump and / or a claw pump.

9. The method according to any one of the preceding claims, characterized in that During the analysis of the test chamber gas, the gas composition of the environment from the pre-vacuum pump (24) is analyzed by the gas detector (12).

10. The method according to any one of the preceding claims, characterized in that The pre-vacuum pump (24) is not deactivated during measurement of the light gas component of the environment from the pre-vacuum pump (24).

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