Test gas leak indicator

Details Test gas leak indicator Test gas leak indicator

1996-09-06

1998-10-13

Williams, Herzron E.

Measuring and testing

With fluid pressure

Leakage

G01M 320

Patent

active

058214046

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a process for operating a test gas leak indicator as well as a test gas leak indicator suitable for implementation of this process.
Test gas leak indicators of the kind affected here are connected to a test chamber, for example, which contains one or several test objects. In the case of one test object having a leak, test gas contained within the test object enters into the test chamber and passes from there into the test gas leak indicator through which the test gas is recorded. In the case of a further leak detection method, the test object itself is linked to the inlet of the test gas leak indicator. The test object is sprayed with test gas from the outside. If the test object has a leak, test gas will enter into the test object and then into the test gas leak indicator.
The gas, which in the event of a leak contains the test gas, entering into the test gas leak indicator's inlet may be supplied directly to the sensor (test gas detector) in the test gas leak indicator. When employing helium as the test gas, the test gas leak indicator is commonly a mass spectrometer set to mass 4, which has a relatively low operating pressure thus requiring a high vacuum pump with a downstream backing pump. If the gas, in which the presence of the test gas is to be detected, is applied directly to the mass spectrometer, these pressure conditions must be taken into account. A further possibility is to supply the gas which is to be investigated to the discharge of the high vacuum pump. Possibly present helium passes upstream within the high vacuum pump into the mass spectrometer and is recorded there (counter-flow principle).


SUMMARY OF THE INVENTION

The sensitivity of test gas leak indicators of the described kind is, among other things, limited by the internal test gas or helium background. The cause for this background is, in particular, helium from preceding measurements which has diffused into the seals and/or the oil of the backing pump. Test gas escaping slowly from the seals and the oil passes upstream through the vacuum pumps into the mass spectrometer and thereby causes the undesirable background.
It is the task of the present invention to improve the sensitivity of test gas leak indication.
This task is solved by modulating the gas flow at the inlet of the test gas leak indicator according to the characteristic features of the patent claims. By applying the present invention, non-modulated interference, in particular the non-modulated background of test gas within the instrument, can be eliminated by reliance on the principle of phase-sensitive rectification. There thus exists the possibility of being able to detect very low leak rates even in the presence of high background levels. A further advantage of the process according to the present invention is, that the time response at very low signal levels/leak rates is significantly improved over the state-of-the-art.
Further advantages and details of the present invention shall be explained by referring to the design examples presented in drawing FIGS. 1 to 3.
Shown in drawing FIG. 1 is a schematic design example for a test gas leak indicator operating according to the present invention and
Shown in drawing FIGS. 2 and 3 are alternatives for the devices employed for modulating the gas flow at the inlet.


DESCRIPTION OF THE INVENTION

In the case of the test gas leak indicator according to drawing FIG. 1, the inlet is designated as 2, the line which follows at the inlet 2 is designated as 3 and the test gas leak indicator designed as a mass spectrometer is designated as 4. The high vacuum pump 6 (preferably a turbomolecular pump) is connected via line 5 to the inlet of the mass spectrometer 4. Following at the discharge of the high vacuum pump 6, is a line 7 with valve 8 which connects to the inlet of the backing pump 9. Connected to line 3 are line sections 11, 12 with valves 13, 14. The gas which enters via inlet 2 passes via lines 11, 12 either directly (line 11) or indirectly (line 12) into the mass sp

REFERENCES:
patent: 4510792 (1985-04-01), Morel et al.
patent: 4773256 (1988-09-01), Saulgeot
patent: 5297422 (1994-03-01), Baret
patent: 5369982 (1994-12-01), Holthaus

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