Method for measuring the surroundings concentration of a light gas with a mass-spectrometric counterflow leak-detecting device

Abstract

A method for determining a surroundings concentration of a light gas with a mass-spectrometric counterflow leak-detecting device (10) that has a mass-spectrometric 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) has a gas outlet open to the atmosphere, wherein the high-vacuum pump (16) and / or the gas detector (12) is / are evacuated with the pre-vacuum pump (24), is characterised in that air from the surroundings of the pre-vacuum pump (24) is introduced into the running pre-vacuum pump (24) or into the inlet-side pre-vacuum region thereof in such a manner that a gas component of the introduced air-gas mixture that is lighter than air, is introduced in the counterflow into the gas detector (12) and is detected there, while the other gas components of the introduced air mixture are fed to the surrounding atmosphere (54) through the exit of the pre-vacuum pump (24).

Description

[0001] Method for measuring the ambient concentration of a light gas using a mass spectrometric flow leak detector

[0002] The invention relates to a method for detecting light gas components in the external environment of a mass spectrometric countercurrent leak detector.

[0003] Mass spectrometric countercurrent leak detection devices typically have: a connection to a test specimen or to a test chamber into which the test specimen is placed, a gas detector in the form of a mass spectrometer connected to the connection, and a high-vacuum pump, usually in the form of a turbomolecular pump, the inlet of which is connected to the mass spectrometer and the outlet to the inlet of a backing pump, the outlet of which pumps the evacuated gas into the ambient atmosphere. The high-vacuum pump typically also has an intermediate gas inlet connected to the test specimen connection or the test chamber connection. In addition, the backing pump can also be connected directly to the mass spectrometer for massive leak detection via a bypass line bridging the high-vacuum pump.The test chamber connection can be connected to the inlet of the backing pump via an additional booster pump, whereby the booster pump can be connected to the intermediate gas inlet of the high vacuum pump.

[0004] To detect leaks, the test chamber connection and the connected test chamber are first evacuated using the backing pump and, if present, the booster pump. The backing pump also generates the required backing vacuum at the outlet of the high vacuum pump so that the high vacuum pump can evacuate the mass spectrometer. As soon as the vacuum required to operate the mass spectrometer is reached at the inlet of the high vacuum pump, a connecting valve in the connection between the test chamber connection and the high vacuum pump is opened, allowing gas to flow from the test chamber into the high vacuum pump and, in countercurrent, through the high vacuum pump into the mass spectrometer, where it is analyzed. In the event of a leak in the test specimen, gas flows from inside the test specimen into the test chamber and from there in countercurrent into the mass spectrometer, where it can be detected.

[0005] For countercurrent leak detection using mass spectrometry, it is often of interest to determine the concentration of certain light gas components in the ambient air. Light gas components are gas components of the ambient air mixture that are lighter than air. Helium, for example, could be one such light gas component.

[0006] Traditionally, the ambient helium concentration is determined using separate gas analyzers. Alternatively, with a mass spectrometric countercurrent leak detector, it is possible to shut off the backing pump and open a gas ballast valve of the backing pump to vent it and thus slow it down. As soon as the backing pump stops, gas can be introduced into the mass spectrometer via the gas ballast valve and a bypass line that bridges the high vacuum pump for massive leak detection, where it can be measured. The bypass line is a direct connection line between the inlet of the backing pump and the mass spectrometer. Such bypass lines for massive leak detection are typically equipped with an additional throttle.

[0007] The invention is based on the object of providing an improved method for determining the concentration of a light gas component in the environment of a mass spectrometric countercurrent leak detector.

[0008] The method according to the invention is defined by the features of patent claim 1.

[0009] Claim 1 is based on a mass spectrometric countercurrent leak detection device comprising a backing pump, a high-vacuum pump, and a mass spectrometric gas detector. The backing pump outlet can be open to the atmosphere or, for example, connected to an exhaust line that vents the pumped gases to the atmosphere. The backing pump inlet is connected to an outlet of the high-vacuum pump. The high-vacuum pump inlet is connected to the mass spectrometer. An intermediate gas inlet of the high-vacuum pump is connected via a separate connecting line to a connection for a vacuum test chamber and / or a test specimen. Additionally, the connection for the test chamber or the test specimen could be connected to the backing pump inlet via an additional booster pump—although this is not mandatory.It would be conceivable for an intermediate gas outlet of the booster pump to be connected to the intermediate gas inlet of the high-vacuum pump. The high-vacuum pump is typically a turbomolecular pump. The backing pump is equipped with a gas ballast that is open to the outside atmosphere or discharges into a fresh air line. The gas ballast can be equipped with a selectively switchable valve, allowing it to be opened or closed as required.

[0010] For countercurrent mass spectrometric leak detection, the backing pump is traditionally used to generate the backing pressure at the high vacuum pump outlet, allowing the high vacuum pump to create the required high vacuum inside the mass spectrometer. Gas from the test chamber or the test specimen is introduced into the mass spectrometer via the high vacuum pump's intermediate gas inlet in countercurrent through the high vacuum pump, where it is analyzed. This determines whether the analyzed gas contains a gas component that indicates a leak in the test specimen.

[0011] In order to detect or analyze lighter-than-air gas components from the external environment of the backing pump, the gas ballast valve can be opened or air from the external environment of the backing pump can be admitted into the backing pump through the open gas ballast in such a way that at least one lighter gas component, such as helium, flows out of the backing pump in countercurrent through its inlet and from there into the mass spectrometer, while the remaining gas components are discharged to the environment through the backing pump outlet. Alternatively or additionally, an air inlet can lead directly into the backing pump's forevacuum area, for example, into the connecting line between the backing pump and the high vacuum pump and / or into the bypass line described below for bypassing the high vacuum pump.The invention thus offers the advantage that the analysis of the ambient air, and in particular the measurement of concentrations of light gas components in the ambient air, can be carried out during the actual leak detection with the mass spectrometer without having to interrupt the leak detection process and / or switch off the backing pump. The light gas component to be measured can be introduced in countercurrent from the inlet of the backing pump to the outlet of the high-vacuum pump, through the high-vacuum pump to its inlet, and from there into the mass spectrometer. Alternatively or additionally, the light gas component to be measured can enter the mass spectrometer via a bypass line for massive leak detection that connects the inlet of the backing pump to the mass spectrometer and bypasses the high-vacuum pump. The bypass line can be provided with an additional throttle.Such a bypass line makes it possible to detect particularly large leaks before the high vacuum pump in the mass spectrometer has generated the required high vacuum pressure.

[0012] The light gas component then flows from the gas ballast through the backing pump toward the mass spectrometric gas detector, counter to the pumping direction. The pressure at the outlet of the high-vacuum pump depends only on the speed of the backing pump and not on the proportion of the measured light gas component (e.g., helium) in the ambient air. The measured deviation in the leak rate signal or raw ion current signal of the mass spectrometer depends on the ambient helium concentration or the concentration of the light gas component in the ambient air.

[0013] Light gases, such as helium, flow toward the mass spectrometer in the opposite direction to the pumping direction. The lower the speed of the backing pump, the more helium flows countercurrently through the backing pump's inlet and back into the mass spectrometer. The increase in the light gas component is greater than the total pressure increase in the mass spectrometer due to the different compressions. By changing or modulating the speed of the backing pump, the ambient concentration of light gases, such as helium, can be determined without operating a valve.

[0014] The ambient concentration of the light gas component can be determined during the actual leak detection or after a leak detection of a test specimen, without having to shut down the pumps. The backing pump and the high vacuum pump continue to run, eliminating the time required for shutting down and then restarting the vacuum pumps.

[0015] In the following, exemplary embodiments of the invention are explained in more detail with reference to the figures. They show:

[0016] Fig. 1 shows a first embodiment and

[0017] Fig. 2 shows a second embodiment.

[0018] Shown is a mass spectrometric countercurrent leak detection device 10 with a gas detector 12 in the form of a mass spectrometer. The gas detector 12 is connected in a gas-conducting manner to the inlet 14 of a high-vacuum pump 16 in the form of a turbomolecular pump. The outlet 18 of the high-vacuum pump 16 is connected in a gas-conducting manner to the inlet 22 of a backing pump 24 via a connecting line provided with a selectively controllable valve 20. The outlet 26 of the backing pump 24 is open to the atmosphere or discharges into an exhaust line.

[0019] The inlet 22 of the backing pump 24 is also 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 30 to enable massive leak detection.

[0020] The leak detection device 10 is further provided with a connection 32 for a test chamber or a test specimen. In the illustrated embodiment, a test chamber 35 is vacuum-connected to the connection 32. The test chamber 35 accommodates a test specimen to be tested for leaks and is then evacuated. For this purpose, the connection 32 is gas-conductingly connected to a booster pump 34. The inlet 36 of the booster pump is gas-conductingly connected to the connection 32, while the outlet 38 of the booster pump is connected to the inlet 22 of the backing pump via a further gas line 42 provided with a further valve 40.

[0021] The booster pump 34 is not essential to the invention. Fig. 2 shows an embodiment without a booster pump. The embodiment of Fig. 2 corresponds to that of Fig. 1 except for the missing booster pump 34 and the air inlet 53.

[0022] An intermediate gas line 46 having a further selectively actuatable valve 44 connects an intermediate gas outlet 48 of the booster pump 34 with an intermediate gas inlet 50 of the high vacuum pump 16.

[0023] The backing pump 24 is further provided with a gas ballast valve 52, which is separate from the inlet 22 and the outlet 26 and connects the interior of the backing pump 24 with the external environment 54 of the backing pump 24 and the leak detection device 10. The gas ballast valve 52 is selectively operable and can be opened and closed.

[0024] Between the gas ballast valve 52 and the backing pump 24, a throttle point 51 is provided, which determines the gas flow admitted into the backing pump 24 through the gas ballast. According to the invention, the gas ballast valve 52 can be omitted. In this case, only the throttle point 51 is provided at the inlet forming the gas ballast of the backing pump 24. The throttle point 51 can be made possible, for example, by selecting a suitable cross-section for the gas ballast inlet.

[0025] Alternatively or in addition to the intake of air from the environment 54 via the gas ballast of the backing pump 24, the ambient air can also be admitted into the backing region of the backing pump 24 via an air inlet 53, as shown in Fig. 2. In Fig. 2, an air inlet 53 is provided as an exemplary embodiment, which can be open to the atmosphere or connected to a fresh air line and which opens into the connecting line between the inlet 22 and the valve 20, i.e., into the connecting line connecting the backing pump 24 to the high vacuum pump 16. The air inlet 35 is shown in Fig. 2 in addition to the air inlet via the gas ballast of the backing pump 24, but can also be provided without the gas ballast as an alternative. In this case, the gas ballast on the backing pump 24 is omitted. The air inlet 53 is also provided with a throttle similar to the throttle point 51 of the gas ballast.The same is also possible with the embodiment in Fig. 1.

[0026] During operation, the test chamber 35 is evacuated using the backing pump 24 and the booster pump 34. The backing pump 24 generates the required backing vacuum at the outlet of the high vacuum pump 16, into which the high vacuum pump 16 evacuates the contents of the mass spectrometer 12. Meanwhile, the backing pump 24 also directly evacuates the mass spectrometer 12 via the bypass line 28.

[0027] As soon as the vacuum pressure required for the operation of the mass spectrometer 12 is reached, the valve 44 is opened and the valve 40 is closed so that test gas and / or leakage gas from the interior of the test chamber 35 passes through the booster pump 34, the intermediate gas line 36 and in counterflow through the high vacuum pump 16 into the mass spectrometer 12 and can be analyzed there.

[0028] To quickly and easily determine the helium gas concentration in the ambient air 54, the gas ballast valve 52 is opened while the backing pump 24 is still running. In the embodiment without a gas ballast valve, the gas ballast 52 is permanently open and, if necessary, connected to a fresh air line. In the simplest case, the gas ballast 52 can be open to the atmosphere.

[0029] To determine the gas concentration of the helium portion of the ambient air, the speed of the vacuum pump is modulated or at least changed between two different operating states, for example, switching between the final speed of the backing pump 24 and a reduced speed. The changed pump speed results in a change in the helium partial pressure and the total pressure at the inlet 22 of the backing pump 24. A change or signal swing for the helium portion can then be measured in the measurement signal of the mass spectrometer 12 because the helium from the backing pump 24 enters the mass spectrometer 12 either via the bypass 28 or in counterflow through the high vacuum pump 16. The supply of air flowing from the environment 54 into the backing pump 24 can be influenced, in the case of a gas ballast valve 52, by opening and closing the gas ballast valve 52.

[0030] Gas components of the ambient air that are lighter than the average of the gas components of the ambient air will flow out of the backing pump in countercurrent through the inlet 22 and from there flow in countercurrent through the high vacuum pump 16 and / or through the bypass line 28 into the high vacuum of the mass spectrometer 12, where they can be measured. In contrast, gas components of the ambient air that are heavier than the ambient air are returned to the environment 54 via the outlet 26 of the backing pump 24. In this way, helium from the ambient air 54 enters the mass spectrometer 12 and can be analyzed there without having to switch off the backing pump 24, the high vacuum pump 16, and / or the booster pump 34.

[0031] Alternatively or in addition to the gas ballast of the backing pump 24, an air inlet for supplying ambient air directly into the backing area of ​​the backing pump 24 may be provided, for example as an air inlet 53 in the connecting line between the backing pump 24 and the high vacuum pump 16, between the inlet 22 and the valve 20 and / or in the bypass line 28.

Claims

Claims: A method for determining the ambient concentration of a light gas using a mass spectrometric countercurrent leak detection device (10) comprising a mass spectrometric gas detector (12), a high-vacuum pump (16) connected to the gas detector (12), and a backing pump (24) connected to the high-vacuum pump (16), wherein the backing pump (24) has a gas outlet open to the atmosphere, and wherein the high-vacuum pump (16) and / or the gas detector (12) are evacuated by the backing pump (24), characterized in that air from the environment of the backing pump (24) is admitted into the running backing pump (24) or into its inlet-side backing area such that a gas component of the admitted air-gas mixture, which is lighter than air, is introduced countercurrently into the gas detector (12) and is detected there.while the remaining gas components of the introduced air mixture are supplied to the surrounding atmosphere (54) through the outlet of the forevacuum pump (24). Method according to claim 1, characterized in that the gas component that is lighter than air is neon, helium, hydrogen, or deuterium. Method according to claim 1 or 2, characterized in that the lighter gas component is introduced into the gas detector (12) in countercurrent flow through the high-vacuum pump (16) or through a bypass line (28) bridging the high-vacuum pump (16) and connecting the forevacuum pump (24) to the gas detector (12) for massive leak detection. A method according to any one of the preceding claims, characterized in that the backing pump (24) has an open gas ballast through which air from the environment (54) of the backing pump (24) is admitted into the running backing pump (24). A method according to any one of the preceding claims, characterized in that a separate air inlet (53) is provided in the A forevacuum section is provided upstream of the inlet (22) of the forevacuum pump (24), through which air from the environment of the forevacuum pump (24) is admitted into its forevacuum section. A method according to one of the preceding claims, characterized in that, to determine the ambient concentration of the light gas component of the admitted air-gas mixture, the rotational speed of the forevacuum pump is varied and the proportion of the light gas component is determined from the resulting change in the measurement signal of the gas detector (12). A method according to the preceding claim, characterized in that the rotational speed of the forevacuum pump is varied from a first rotational speed value to at least a second rotational speed value different from the first, and the response of the measurement signal representing the partial pressure of the gas component is evaluated.A method according to any of the preceding claims, characterized in that the backing pump (24) is a rotary piston and / or claw pump. A method according to any of the preceding claims, characterized in that the analysis of the gas component from the environment. the forevacuum pump (24) with the gas detector (12) during the analysis of the test chamber gas. Method according to one of the preceding claims, characterized in that the forevacuum pump (24) is not deactivated during the measurement of the light gas component from the environment of the forevacuum pump (24).

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