Gas passage with selectively acting penetration surface and...

Details Gas passage with selectively acting penetration surface and... Gas passage with selectively acting penetration surface and...

1997-12-08

2001-08-21

Lipman, Bernard (Department: 1713)

Gas separation: apparatus

Apparatus for selective diffusion of gases

C096S007000

Reexamination Certificate

active

06277177

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a gas passage with a selectively acting penetration surface. Moreover, the present invention relates to a process for manufacturing a selectively acting gas passage. Gas passages of this kind are employed in measurement or analytical instruments, for example. It is aimed at admitting lighter gases with a high preference and heavier gases with a lower preference into a measuring instrument, for example.
As disclosed in DE-A-43 26 265, for example the entire contents of which are incorporated by reference, a leak detector is known, the test gas detector of which is equipped with a selective admission system. Helium is used as the test gas. The selective admission comprises a penetration surface formed by a separating wall or a diaphragm, in which the permeability for helium is by many decades higher than the permeability for other gases. For example, quartz, quartz glass (SiO
2
), Pyrex glass or also polymer diaphragms made of FEP, for example, offer these properties.
Generally, measuring and analytical instruments should be of high sensitivity and offer a short response time. In a test gas detector according to incorporated DE-A-43 26 265 it is therefore a design target to let as much helium as possible penetrate the penetration surface in a time which is as short as conceivable. This is only possible when on the one hand the penetration surface is as large as possible and when on the other hand it is as thin as possible. This is opposed by the fact that generally the penetration surface will be exposed to a differential pressure. The internal volume of the measuring instrument is evacuated whereas atmospheric pressure prevails outside. Because of the load imposed by the differential pressure there are limitations as to the size and thickness of the penetration surface.
SUMMARY OF THE INVENTION
It is the task of the present invention to create a selectively acting gas inlet which may be exposed to relatively high pressure differentials, and which none-the-less offers a relatively large and relatively thin penetration surface.
This task is solved by the present invention in that the selectively acting penetration surface be formed by a plurality of adjacent windows. In the case of this solution the individual windows of the penetration surface are very small. The smaller the surface area of the windows, the thinner the window forming layer, diaphragms, or the like may be in order to withstand the prevailing pressure differential. If, for example, 200 square windows made of quartz glass having a length of sides of 0.7 mm are provided, then these form a total penetration surface of 0.98 cm
2
. A penetration surface of this kind may already be loaded with a differential pressure of one atmosphere when the thickness of the individual windows amounts to about 5 to 10 &mgr;m.
It is known that heating of a material reduces the response time and increases the gas throughput. In the case of a gas inlet according to the present invention it is possible through the planar arrangement to bond—by means of metal structures produced by thin-film technology—heating coils to the windows. Thus there exists the possibility of restricting the heat to the individual windows. The risk that glued joints in the vicinity may degrade or develop leaks does not exist.
Preferably the windows forming the penetration surface are made of quartz, quartz glass or similar materials (Pyrex glass, for example) since these may be manufactured with methods known from thin-film technology at reasonable cost.


REFERENCES:
patent: 3828527 (1974-08-01), Briggs et al.
patent: 3939695 (1976-02-01), Booth
patent: 5661229 (1997-08-01), Bohm et al.
patent: 0 264 594 B1 (1987-08-01), None
patent: 0264594 (1988-04-01), None
patent: 0 352 371 A2 (1988-11-01), None
patent: 8908489 (1989-09-01), None
patent: WO 95/04922 (1995-02-01), None
patent: 9513860 (1995-05-01), None

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