Ulvac HELIOT 301, Инструкция по эксплуатации

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Case 3 High sensitivity test
• Testing conditions
Measure the leak rate of a closed container of about 500 m
λ
.
• Estimated leak rate
Order of E-11 Pa·m
3
/sec
• Recommended setting
Sensitivity H
Fine leak flow
Auto range
Linear display
• Explanation
Hi sensitivity setting is recommended because the estimated leak rate of the test object is on
order of E-11. Since high measurement sensitivity is required, fine leak flow (auto flow) is
recommended.
For display are recommended the linear display that can display each multiplier range
minutely and the auto range that permits automatic changeover.
In this type of test, take time to pump the test object. The important thing is that the
background (leak rate under test before helium is sprayed) is sufficiently low and is stabilized
with respect to the desired leak rate.
Also it is important to minimize the amount of helium to be sprayed to the test object and its
duration. Helium permeates through the O-ring used for the connection of the test port. It
is generally said that helium starts permeating two to three minutes after it is sprayed to the
O-ring and that the amount of permeation is on order of E-8 maximum.
In other words, if a large amount of helium is sprayed or helium is sprayed for an extended
time, the leak rate rises so high that you cannot decide whether the leak rate is due to leakage
or permeation.
The problem of helium permeation can be said of all leak tests. In an application where such
a high sensitivity is required, use great care when making test.