Varian 990 dCLD II, Руководство по эксплуатации

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Model 990 dCLD II Component Leak Detector
6-8
6.2.5 Station Fails to Pump Down
Check the following items:
❑
Is the fixture completely closed?
❑
Is the O-ring on the fixture damaged?
❑
Is the fixture vacuum gauge working?
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Is the fixture manifold plugged with a product or component?
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Are any filters in the vacuum system plugged?
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Does it only pump partially down? This probably indicates a large leak in the system.
❑
Does the roughing pump continually gurgle? This may be difficult to detect with the
pump's oil mist filter in place. Continued gurgling indicates a very large leak in the
system, such as a partially-open fixture or a disconnected or broken valve.
If all of the above check out ok, remove the test fixture and check your vacuum system.
If station will fails to pump down, call Varian Customer Service at 1-800-8VARIAN
(1-800-882-7426).
6.2.6 A High Number of Rejects, Suspected of being False Rejects
This type of problem is the most typical found in any helium leak detection system. While
high levels of rejects can be traced to problems in the test equipment, they are also often
real leaks in the product. Before tearing down the test station, take steps to ensure that the
problem is not a production problem. The first step in this process is to use a
challenge leak .
This is a standard leak shaped like the production part that can be inserted into the produc-
tion line to function like a
bad part. If the station reads the leak within its stated tolerances
and within the actual production cycle, then the problem is not in the station but probably
is in the parts. If the standard leak is substantially out of tolerance, then the problem is most
likely in the station.
Control of helium is one of the most vexing problems in any production environment where
parts are filled with helium then tested in the same room (or building). In normal earth
atmosphere, only 5 parts per million (PPM) of air is helium. This is one of the reasons
helium is used as a leak-test trace gas. For example, in a room containing a closed helium
cylinder, the helium background can rise to 10 to 50 PPM as a result of a leak from the
closed cylinder. In production environments where parts are being filled with helium by
various means and the testing areas are closed due to heating or cooling requirements,
background readings as high as 2000 PPM are possible.