Pressure Measurement at a Test Gas Inlet

Abstract

A device for measuring the pressure at the test gas inlet of a mass-spectrometric leak detector, wherein a mass spectrometer is connected to the inlet of a high vacuum pump, having its outlet connected to the inlet of a pre-vacuum pump, wherein the inlet of the pre-vacuum pump is connected to the test gas inlet, and wherein the inlet of the pre-vacuum pump and at least one intermediate inlet of the high vacuum pump are connected to each other by a connection line comprising a flow throttle.

Claims

1. A method for measuring a pressure at a test gas inlet of a mass-spectrometric leak detector, comprising: connecting a mass spectrometer to an inlet of a high vacuum pump having its outlet connected to an inlet of a pre-vacuum pump via a vacuum line in a gas conducting manner; connecting the inlet of the pre-vacuum pump to the test gas inlet via a pre-vacuum inlet line in a gas conducting manner, wherein from a gas flow from the test gas inlet to the pre-vacuum pump, a partial flow is branched off, throttled, and supplied to at least one intermediate gas inlet of the high vacuum pump; and determining the pressure at the test gas inlet by measuring a test gas partial pressure in said branched-off partial flow by means of the mass spectrometer, wherein the vacuum line comprises an additional pre-vacuum volume to which a pressure measurement device is connected.

2. The method according to claim 1, wherein the pre-vacuum volume is dimensioned in such a manner that, when the vacuum line is closed, the pre-vacuum inlet line is closed, and a high vacuum inlet line connecting the test gas inlet and the at least one intermediate gas inlet is closed, operation to detect massive leaks can be maintained for a sufficient duration of time without pumping of the pre-vacuum volume again.

3. The method according to claim 2, wherein the pre-vacuum volume is dimensioned in such a manner that operation to detect massive leaks can be performed for one hour without interruption.

4. The method according to claim 1, wherein the pre-vacuum volume is larger than 10 cm.sup.3.

5. The method according to claim 1, wherein the partial flow is throttled to a maximum value in a range of 10.sup.5 mbar.Math.l/s to 10.sup.3 mbar.Math.l/s with a pressure difference of about 1000 mbar.

6. The method according to claim 1, wherein a location of the throttling of the partial flow is arranged closer to the inlet of the pre-vacuum pump than to the at least one intermediate gas inlet of the high vacuum pump.

7. The method according to claim 1, wherein the branched-off partial flow is blocked.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Exemplary embodiments of the invention will be described in greater detail hereunder with reference to the Figures. The following is shown:

[0026] FIG. 1 shows a first exemplary embodiment,

[0027] FIG. 2 shows a second exemplary embodiment, and

[0028] FIG. 3 shows a third exemplary embodiment.

DESCRIPTION OF THE INVENTION

[0029] Hereunder, there will first be described those features that are common to the various exemplary embodiments. Substantially, these comprise a leak detection system having a mass spectrometer 12, a high vacuum pump 14, a pre-vacuum pump 16 and a test gas inlet 18.

[0030] The mass spectrometer 12 is connected, via a gas-conducting measurement line 20, to the inlet 22 of high vacuum pump 14. High vacuum pump 14 is a turbomolecular pump. The outlet 24 of high vacuum pump 14 is connected in a gas-conducting manner to the inlet 26 of pre-vacuum pump 16 via a vacuum line 28. Provided in vacuum line 28 is a valve V2 adapted to be closed separately. Via said two vacuum pumps 14,16, the measurement volume of mass spectrometer 12 is evacuated.

[0031] Test gas inlet 18 is connected in a gas-conducting manner to the inlet 26 of pre-vacuum pump 16 via a pre-vacuum inlet line 30 so as to evacuate, by means of pre-vacuum pump 16, a volume (test chamber or test object) connected to test gas inlet 18. Test gas inlet 18 is further connected, via a high vacuum inlet line 32, to the intermediate gas inlet 34 of high vacuum pump 14.

[0032] At a branch-off site 36, a gas-conducting connection line 38 branches off from the pre-vacuum inlet line 30 and enters the high vacuum inlet line 32 at an entering site 40. In this manner, the connection line 38 directly and permanently connects the inlet 26 of pre-vacuum pump 16 to the intermediate gas inlet 34 of high vacuum pump 14, without provision of a valve in connection line 38.

[0033] As closely as possible to said branch-off site 36, connection line 38 comprises a throttle 42 which, with a pressure difference across the throttle from 1000 mbar toward 0 mbar across the throttle, allows for a gas throughput of more than 10.sup.4 mbar.Math.l/s, namely about 2.Math.10.sup.4 mbar.Math.l/s and will prevent a gas throughput higher than the above.

[0034] Throttle 42 is designed as a screen or a capillary.

[0035] The distance of throttle 42 from branch-off site 36 is about a tenth of the distance between branch-off site 36 and entering site 40, i.e. the length of connection line 38.

[0036] Pre-vacuum inlet line 30 comprises, between test-gas inlet 18 and branch-off site 36, a separately closable valve V1. High-vacuum inlet line 32 comprises, between test-gas inlet 18 and entering site 40, a separately closable valve V4.

[0037] In operation, during the initially performed rough evacuation of a volume connected to test-gas inlet 18 (test chamber volume or test object volume), valves V2 and V4 are initially in a closed state and valve V1 is in an opened state. Pre-vacuum pump 16 will then perform the evacuation via test-gas inlet 18.

[0038] In order to make it possible, during this rough evacuation via test-gas inlet 18, to measure the pressure on test-gas inlet 18 without necessitating an additional pressure sensor, a partial flow will be branched off from pre-vacuum inlet line 30 via connection line 38 and be supplied to mass spectrometer 12 via intermediate gas inlet 34 of high vacuum pump 14. With the aid of throttle 42, the partial gas flow will be throttled sufficiently for its evaluation by mass spectrometer 12. With the aid of mass spectrometer 12, the partial pressure of the test gas contained in the branched-off gas flow will be detected. Typically, helium is used as a test gas, wherein the helium partial pressure is measured. From the helium partial pressure, a conclusion is drawn on the total pressure at the inlet flange of the mass spectrometer.

[0039] Mass spectrometer 12 will be evacuated while valve V2 is in an opened state and valves V1 and V4 are in a closed state. As soon as the pressure in mass spectrometer 12 and the pressure measured with pressure measurement device 27 within pre-vacuum volume 29 is sufficiently low for the operation of mass spectrometer 12 (1.Math.10.sup.4 mbar in 12 and <1 mbar in 28), valve V2 will be closed. Then, valve V1 will be opened at the test gas inlet for evacuating the test object. As soon as the total pressure at test gas inlet 18 falls below a sufficient value of about 15 mbar, valve V2 will be opened so that the mass-spectrometric analysis for leak detection will be started. Upon further decrease of the total pressure to a value below 2 mbar, valve V1 will be closed and valve V4 will be opened with the objective to reach the classical counterflow leak detection operation.

[0040] The second exemplary embodiment differs from the first exemplary embodiment by a second intermediate gas inlet 44 of high-vacuum pump 14. Said second intermediate gas inlet 44 is connected to test gas inlet 18 via a gas-conducting line 46 provided with a separately closeable valve V3.

[0041] The third exemplary embodiment according to FIG. 3 differs from the exemplary embodiment according to FIG. 1 in that the branch-off point 36 is arranged between the pump stages 16a, 16b of a multi-stage pre-vacuum pump 16. Generally, the branch-off point can be situated at any desired site in the pre-vacuum connection between test gas inlet 18 and outlet 24 of high-vacuum pump 14.

[0042] By the pressure measurement as provided according to the invention, it is rendered possible, using a mass-spectrometric leak detector, to measure the pressure at the test gas inlet by mass-spectrometric partial pressure analysis already during still high pressures in the pre-vacuum range during evacuation, without requiring an additional pressure sensor for this purpose.