Vacuum leakage-detection system and method for evacuating a test connection

Abstract

The invention relates to a vacuum leakage-detection system (10) comprising: a test connection (12) for connecting a test object to be tested or a test chamber receiving the test object; a Roots pump (16) which is vacuum-connected to the test connection (12) for transporting a gas flow through the test connection (12) and the Roots pump (16); and a gas detector (18) which is connected to the test connection (12) for detecting a test gas in the transported gas flow. The vacuum leakage-detection system is characterized in that the Roots pump (16) has a flushing device (20) which is designed to determine the moisture content of the transported gas flow and to supply a flushing gas to the Roots pump (16) on the basis of the determined moisture content in order to thereby avoid condensation of the moisture in the interior of the Roots pump (16).

Description

[0001] Vacuum leak detection system and method for evacuating a test port

[0002] The invention relates to a vacuum leak detection system for detecting a gas leak in a test object and a method for evacuating a test connection.

[0003] A vacuum leak detection system has a test port that can be evacuated by a vacuum pump, to which the test specimen or a test chamber containing the test specimen can be connected to evacuate the test specimen or the test chamber containing the test specimen. A gas detector is provided for analyzing the evacuated gas stream to detect any possible leakage gas.

[0004] When evacuating a test specimen or a test chamber containing the test specimen, moisture contained in the evacuated gas can condense in the vacuum pump. The condensed water vapor can cause damage to the vacuum pump, for example, through corrosion or by impairing the effectiveness of lubricants or sealants in the vacuum pump.

[0005] Oil-sealed vacuum pumps feature a feature known as gas ballast, which prevents vapor from condensing inside the pump. To achieve this, a precisely defined amount of air, known as gas ballast, is introduced to reduce the pump's compression ratio from a maximum of 10:1.

[0006] The invention is based on the object of creating an improved vacuum leak detection system in which the risk of condensation of water vapor is reduced, and of providing a corresponding method.

[0007] The vacuum leak detection system according to the invention has a test port that is vacuum-connected to a vacuum pump to evacuate the test port and a test object or test chamber connected to the test port. The gas stream drawn from the test port is transported by the test port through the vacuum pump, the outlet of which may be open to the atmosphere. A gas detector is provided and configured to analyze gas from the transported gas stream and detect a possible leak gas or a test gas. The vacuum pump is a Roots pump, which typically has no sealant or less sealant than other types of vacuum pumps, such as oil-sealed rotary vane pumps, diaphragm pumps, or scroll pumps. However, a Roots pump is more susceptible to rust due to the limited or non-existent sealant.

[0008] To reduce the risk of rust formation caused by water vapor condensing in the Roots pump, the Roots pump is equipped with a purging device designed to measure the moisture content in the transported gas stream and to supply a purge gas to the Roots pump depending on the measured moisture content. Additionally, the purge device can be designed to measure the pressure of the gas in the transported gas stream and to change the purge gas supply depending on the measured pressure. The higher the measured moisture content or pressure, the more purge gas is supplied to the Roots pump to transport the water vapor out of the Roots pump without the water vapor condensing inside the Roots pump. The moisture content is preferably measured at the outlet of the Roots pump.In Roots pumps, it was previously unknown to provide a gas ballast valve that opens or closes depending on the moisture content of the pumped gas. The invention is based on the idea of ​​providing a controlled purge gas supply in a Roots pump depending on the measured moisture or pressure.

[0009] The purging device can be provided with a purge port that is open to the atmosphere to supply air as purge gas and / or that is designed to connect a purge gas source. The purge port is connected to the Roots pump via a purge gas path. The purge gas path can be connected to the Roots pump via an intermediate gas inlet that opens into the Roots pump between the inlet of the Roots pump and the outlet of the Roots pump. The purge gas path can have a controllable or adjustable purge valve that is automatically actuated depending on the measured moisture content or the measured gas pressure.

[0010] In particular, a first purge gas path and a second purge gas path parallel to the first purge gas path can be provided, which are connected to the Roots pump depending on the measured moisture content or pressure. For this purpose, the two purge gas paths can be connected to different ports of the valve, which can be a three-way or two-way valve. The valve then switches between the first purge gas path and the second purge gas path depending on the measurement result. The two purge gas paths can open into the same purge port or into separate, different purge ports.

[0011] It is crucial that the two purge gas paths have different flow resistances. The internal flow resistance of the second purge gas path should be higher than the internal flow resistance in the first purge gas path. This means that, when the moisture content is higher, the first purge gas path can be used to supply purge gas to the Roots pump, delivering a larger amount of purge gas than via the second purge gas path. Similarly, when the moisture content is lower, the second purge gas path with a higher flow resistance can be connected to the Roots pump, delivering a smaller amount of purge gas. Similarly, arrangements with more than two purge gas paths, each with different flow resistances, are also conceivable. These can be connected to the Roots pump as required, depending on the measurement results.

[0012] Preferably, below a first limit value of the measured humidity, the flow of purge gas through the purge valve is throttled to less than 1,000 sccm, preferably less than 500 sccm, and particularly preferably less than 100 sccm, but at least approximately 10 sccm, preferably at least 50 sccm, e.g., to a value of approximately 70-80 sccm. This ensures that a small amount of purge gas is supplied to the Roots pump even when the moisture content of the transported gas stream is sufficiently low, in order to prevent backflow of gas from the atmosphere, e.g., helium, into the Roots pump.

[0013] Above a second limit value for the moisture content of the gas in the transported gas stream, the inflow of purge gas into the Roots pump is increased to at least 10,000 sccm and preferably to at least 50,000 sccm. To measure the moisture content of the gas in the transported gas stream, a humidity sensor can be provided at the outlet or in the region of the outlet of the Roots pump or at another position in the vacuum line connecting the test connection to the Roots pump in order to measure the humidity of the gas supplied to or discharged from the Roots pump. To measure the gas pressure of the gas in the sucked-in gas stream, a pressure sensor can be provided at the inlet or in the region of the inlet of the Roots pump.

[0014] The purging device is equipped with a control device to which the measurement results from the humidity sensor or the pressure sensor are fed. The control device is designed to evaluate the measurement results and, depending on the evaluation, to change the amount of purge gas supplied to the Roots pump. For example, depending on the evaluation, a purge valve in the purge gas path connecting the purge connection to the Roots pump can be actuated. The control device can be designed as a computer or microprocessor that controls and actuates a servomotor of the purge valve.

[0015] The Roots pump can be part of a multi-stage turbomolecular vacuum pumping system, with the Roots pump forming the backing pump of the turbomolecular vacuum pumping system. The inlet of the Roots pump is connected to the outlet of a turbomolecular pump, whose inlet is connected to the gas detector.

[0016] The gas detector can then be a mass spectrometer, so that the vacuum leak detection system can be a mass spectrometric vacuum leak detection system. The gas from the test port can be fed to the mass spectrometer according to the countercurrent principle, in countercurrent through the turbomolecular pump. For this purpose, the test port can be connected to at least one intermediate gas inlet of the turbomolecular pump via an intermediate gas line. The intermediate gas line can branch off from a vacuum line that connects the test port to the inlet of the Roots pump. The inlet of the Roots pump is connected to the outlet of the turbomolecular pump by another line, which can be referred to as the forevacuum line.

[0017] In the method according to the invention, the moisture content of the gas in the gas stream drawn from the test port by the Roots pump is measured, and a quantity of purge gas is supplied to the Roots pump depending on the measured moisture content. The purge gas is supplied using the purge device. The higher the measured moisture content of the gas, the more purge gas can be supplied to prevent or reduce condensation of the water vapor in the drawn-in gas stream within the Roots pump. For this purpose, moisture content limits can be applied when controlling the purge valve.

[0018] In the following, exemplary embodiments of the invention are explained in more detail with reference to the figures. They show:

[0019] Fig. 1 shows a first embodiment and

[0020] Fig. 2 shows a second embodiment of the invention.

[0021] In both embodiments, the vacuum leak detection system 10 has a test port 12 that is vacuum-connected to a Roots pump 16 via a vacuum line 14. The Roots pump 16 evacuates the test port 12 via the vacuum line 14. A test specimen can be directly connected to the test port 12, so that the connected test specimen is evacuated. In the event of a leak in the test specimen, gas from the atmosphere surrounding the test specimen flows into the test specimen as leakage gas and is evacuated by the Roots pump 16. Alternatively, a test chamber that accommodates the test specimen to be tested can be connected to the test port 12. In the event of a leak in the test specimen, gas from the interior of the test specimen then passes through the leak into the test chamber and is evacuated by the Roots pump 16 via the test port 12.

[0022] In both embodiments, at least a portion of the gas evacuated from the test port 12 is fed to a gas detector 18, which is vacuum-connected to the Roots pump 16 and the test port 12. In both embodiments, the gas detector 18 is designed for gas analysis in order to detect a leakage gas and / or a test gas.

[0023] In both embodiments, the Roots pump 16 is connected to a purging device 20, which is designed to automatically supply a purge gas to the Roots pump 16. For this purpose, the purge device 20 has a purge connection 22, which is connected to an intermediate gas inlet 26 of the Roots pump 16 via a purge line 24. The purge connection 22 is open to the atmosphere to draw in air as the purge gas.

[0024] The flushing line 24 is provided with a flushing valve 30 which can be actuated by a control device 28.

[0025] In the area of ​​the outlet of the Roots pump 16, the vacuum line 14 is provided with a sensor 32, which is designed as a humidity sensor to measure the moisture content of the gas transported by the Roots pump 16. The measurement result of the sensor 32 is transmitted electronically to the control device 28, which actuates the purge valve 30 depending on the transmitted measurement result. The control device 28 can be a microprocessor or computer. In addition, the sensor can be designed to measure the pressure of the gas at the outlet of the Roots pump 16 in order to actuate the purge valve 30 depending on the measured pressure. Alternatively or in addition to the pressure measurement at the outlet, a pressure sensor (not shown in the figures) can be provided at the inlet of the Roots pump 16 and connected to the control device 28.

[0026] In the embodiment shown in Fig. 2, the purge valve 30 is opened or closed by the control device 28 depending on the measurement result, or it changes the flow rate through the purge line 24 to a greater or lesser value. All embodiments have in common that when a threshold value of the measured moisture content or the measured gas pressure is exceeded, a larger amount of purge gas is supplied than below this or another threshold value.

[0027] Thus, in the exemplary embodiment according to Fig. 2, the control device 28 detects that a threshold value has been exceeded and then opens the purge valve 30, for example by driving a servomotor of the valve to open it. As a result, when the threshold value is exceeded, purge gas in the form of air flows through the purge connection 22, e.g., at a flow rate of more than 50,000 sccm, into the interior of the Roots pump 16, preventing water vapor from condensing within the Roots pump 16. If the measured moisture content falls below a threshold value, the purge valve 30 closes the flow down to a residual value of approximately 70-80 sccm to prevent air from the environment of the Roots pump 16 from flowing back into the gas detector.

[0028] In the embodiment according to Fig. 1, the purge valve 30 is a three-way / two-way valve which connects a first purge gas path 34 of the purge line 24 and a second purge gas path 36 of the purge line 24, which is different from the first purge gas path 34, to the Roots pump 16.

[0029] The first purge gas path 34 connects the purge connection 22 to a first connection of the purge valve 30. The second purge gas path 36 connects the purge connection 22 to a second connection of the purge valve 30. A third connection of the purge valve 30 is connected to the intermediate gas inlet 26 of the Roots pump 16.

[0030] Depending on the measurement result of the measurement signal received from sensor 32, control device 28 switches between the first and second connections, so that either the first purge gas path 34 is connected to the Roots pump 16 or the second purge gas path 36 is connected to the Roots pump 16. The first purge gas path 34 enables a high flow rate of more than 50,000 sccm of purge gas. The second purge gas path 36 is provided with a throttle 54 that limits the flow rate to approximately 70 sccm if the measured moisture content is below a threshold value.

[0031] The embodiment shown in Fig. 1 is a mass spectrometric leak detector in which the gas detector 18 is a mass spectrometer and the Roots pump 16 forms the backing pump of a two-stage vacuum pumping system 38. The main pumping stage of the vacuum pumping system 38 is a turbomolecular pump 40, whose inlet is connected to the gas detector 18 and whose outlet is connected to the inlet of the Roots pump 16 via a backing line 42. The backing line 42 is provided with a valve 44 that can be closed to pre-evacuate the test port 12, for example, after changing a test specimen, in order to evacuate the test port 12 only through the Roots pump 16.

[0032] Two intermediate gas lines 46, 46a connect the vacuum line 14 and thus the test connection 12 with respective intermediate gas inlets 48, 48a of the turbomolecular pump 40. Both intermediate gas lines 46, 46a are each provided with selectively actuable intermediate gas valves 50, 50a for selectively opening or closing the respective intermediate gas line 46, 46a.

[0033] The vacuum line 14 has a vacuum valve 52 between the test port 12 and the Roots pump 16, downstream of the intermediate gas lines 46, 46a in the flow direction from the test port 12 to the Roots pump 16. The vacuum valve 52 can be closed as soon as a sufficient vacuum pressure has been generated at the test port 12. When the intermediate gas valves 50 or 50a are open, gas from the test port 12 passes through the respective intermediate gas inlet 48, 48a into the interior of the turbomolecular pump 40 and from there, when the high vacuum in the gas detector 18 is sufficiently low, flows in countercurrent through the turbomolecular pump 40 into the gas detector 18. In this case, either the intermediate gas valve 50 or the intermediate gas valve 50a is open, while the other of the two intermediate gas valves 50, 50a is closed. The vacuum leak detection system according to Fig. 1 then forms a mass spectrometric vacuum leak detector according to the countercurrent principle.

[0034] The second purge gas path 36 is provided with a flow restrictor 54, which causes the internal flow resistance of the second purge gas path 36 to be significantly higher than that within the first purge gas path 34. Preferably, the second purge gas path 36 results in a gas flow of less than 100 sccm, for example in the range between approximately 70 - 80 sccm, while the first purge gas path 34 results in a gas flow of more than 50,000 sccm.

Claims

Claims 1. Vacuum leak detection system (10) with a test connection (12) for connecting a test object to be tested or a test chamber accommodating the test object, a Roots pump (16) which is vacuum-connected to the test connection (12) for transporting a gas flow through the test connection (12) and the Roots pump (16), and with a gas detector (18) connected to the test connection (12) for detecting a test gas in the transported gas flow, characterized in that the Roots pump (16) has a purging device (20) which is designed to determine the moisture content of the transported gas flow and to supply a purging gas to the Roots pump (16) depending on the determined moisture content, in order to thereby prevent condensation of the moisture inside the Roots pump (16).

2. Vacuum leak detection system (10) according to claim 1, characterized in that the purging device (20) is designed to determine the moisture content of the transported gas stream at the outlet of the Roots pump (16) and to change the amount of purge gas supplied depending on the determined moisture content.

3. Vacuum leak detection system (10) according to one of the preceding claims, characterized in that the purging device (20) has a humidity sensor (32) for measuring the moisture content of the transported gas stream.

4. Vacuum leak detection system (10) according to one of the preceding claims, characterized in that the purging device (20) has a purging connection (22) connected to the Roots pump (16), which is open to the atmosphere and / or is designed to be connected to a purging gas source.

5. Vacuum leak detection system (10) according to one of the preceding claims, characterized in that the purging device (20) is provided with a purging valve (30) which can be controlled as a function of the measured moisture content in order to automatically control the amount of purging gas supplied.

6. Vacuum leak detection system (10) according to the preceding claim, characterized in that the purging device (20) has a first purge gas path (34) connecting the purge connection (22) to the purge valve (30) and at least one further second purge gas path (36) connecting the purge connection (22) to the purge valve (30) parallel to the first purge gas path (34), the internal flow resistance of which second purge gas path is greater than that of the first purge gas path, wherein the purge valve (30) is designed to selectively connect the first or the at least second purge gas path to the Roots pump (16).

7. Vacuum leak detection system (10) according to one of the preceding claims, characterized in that the Roots pump (16) forms the backing pump of a turbomolecular vacuum pumping system (38) which has a turbomolecular pump (40) whose inlet is connected to the gas detector (18) and whose outlet is connected to the inlet of the Roots pump (16).

8. Vacuum leak detection system (10) according to the preceding claim, characterized in that the test connection (12) is connected via a Vacuum line (14) is connected to the inlet of the Roots pump (16) and the turbomolecular pump (40) has at least one intermediate gas inlet (48) which is connected to the vacuum line (14) via an intermediate gas line (46).

9. Vacuum leak detection system (10) according to one of the preceding claims, characterized in that the purging device (20) opens into an intermediate gas inlet (26) of the Roots pump (16) between its inlet and outlet.

10. A method for evacuating a test port (12) of a vacuum leak detection system (10) according to any one of the preceding claims, comprising the steps: Transporting a gas stream through the test connection (12) and the Roots pump (16), Measuring the moisture content of the transported gas stream and Changing the quantity of purge gas supplied to the Roots pump (16) with the purge device (20) as a function of the measured moisture content in order to prevent condensation of the moisture inside the Roots pump (16).

11. Method according to the preceding claim, characterized in that at a higher moisture content in the transported gas stream, a larger quantity of purge gas is supplied than at a lower moisture content.

Images