Measuring and testing – With fluid pressure – Leakage
Patent
1996-02-01
1998-07-28
Brock, Michael
Measuring and testing
With fluid pressure
Leakage
G01M 320
Patent
active
057865299
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a search gas detector, preferably for leak detection instruments, with a gas inlet, with a vacuum pump and an apparatus through which the presence of search gas is recorded. Moreover, the invention relates to a method for operation of a leak detector of this kind.
In the case of high-sensitivity leak detection, chiefly only helium is considered as the search gas. Therefore, in the following text, mainly helium is referred to as the search gas.
In helium leak detection instruments, mass spectrometers are commonly employed as detectors which are set to the mass of helium. Operation of a mass spectrometer requires a high vacuum pump system (high vacuum pump, backing pump etc.) through which the helium entering in the case of a positive test, is removed (refer to DE-A-34 21 533, for example).
From EU-A-352 371 a helium leak detector of the kind affected here, is known. A getter ion pump is employed as the vacuum pump. Even relatively small getter ion pumps are heavy in weight and thus unhandy.
SUMMARY OF THE INVENTION
It is the task of the present invention to significantly reduce the complexity in the generation of the vacuum for search gas detectors, helium detectors for leak detection instruments, in particular.
According to the present invention this task is solved for a search gas detector of the aforementioned kind, by the vacuum pump being an adsorption pump. Adsorption pumps are small and light in weight, so that a leak detection instrument which is equipped with a detector of this kind, is easier to handle.
Since the total operating time of an adsorption pump depends on the quantities of gas which arise, it is expedient that the gas inlet has the property of admitting the search gas in a preferred manner. Thus it is possible to perform an acceptable number of measurements.
The task of the present invention can be solved for a search gas detector of the aforementioned kind, in that the vacuum pump has the property to substantially pump all gases--except the search gas--and where the search gas recording apparatus has the ability to detect an enrichment of the search gas. Also in the case of this solution it is--for capacity reasons--expedient when the gas inlet too has a characteristic which allows a preferred admission of the search gas. In the case of a positive leak test, the search gas enters through the gas inlet. Since the vacuum pump does not pump the search gas, the search gas accumulates and thus gives rise to a pressure increase. Already with a sufficiently sensitive pressure gauge it is possible to determine this pressure increase, and employ it for the formation of measured values.
A preferred method for operating a search gas detector of the aforementioned kind is thus characterised by a vacuum pump having the ability to substantially only pump the components which accompany the search gas--generally air--so that the gas applied to the search gas recording apparatus leads to an increase in the partial pressure and so that the change in the partial pressure may be recorded and evaluated in a differential manner. If this change in the partial pressure occurs by accumulation at the location of the search gas detector, analyses of leaks may be performed at a high sensitivity.
Further positive measurements cause further pressure increases so that the service life also of a helium detector according to this proposal is limited. In order to attain a sufficiently long service life, the admission system must, on the one hand be designed in such a manner that it will practically only let helium pass, so that pressure increases owing to other gases are avoided. On the other hand, the pressure gauge must be extremely sensitive, so that very small pressure increases may be recorded, i.e. so that until the upper pressure limit is attained, as many leak measurements may be conducted as possible.
The gas admission system comprises preferably a polymer diaphragm which separates the high vacuum from a test volume or a sample gas flow. Polymers are a c
REFERENCES:
patent: 3280619 (1966-10-01), Spies
patent: 3867631 (1975-02-01), Briggs et al.
patent: 4419882 (1983-12-01), Ishii et al.
patent: 4459844 (1984-07-01), Burkhart
patent: 4492110 (1985-01-01), Bergquist
patent: 4776207 (1988-10-01), Holme
patent: 5131263 (1992-07-01), Handke et al.
Schoroth Anno
Voss Gunter
Brock Michael
Leybold Aktiengesellschaft
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