Adixen ASM GRAPH - Helium Concentration and Signal Displayed; Spray Method

A 400
T esting methods
GB
00008
-
Edition 05
-
February
02
Helium concentration
and signal displayed
In accordance to the He concentration rate in the gas used for the
leak detection, the signal displayed will change.
Example: signal displayed with a 1x10
-7
mbar.l/s calibrated leak
(with
100 % He) connected to the detector inlet.
% He in the gas used 100 % 10 % 1 %
Signal displayed
on the leak detector
1x10
-7
mbar .l/s
1x10
-8
mbar .l/s
1x10
-9
mbar .l/s
Spray method
(inboard testing)
This involves removing air from the test part, connecting it to the
analyzer and then spraying helium over the outer sur face.
Global test
Spray test
or
par t
spray
probe
He
part
He
detector detector
The part is placed under a
cover, into which helium is
injected.
The leak cannot be located.
Potential leaking
areas are
sprayed with helium.
The leak can be located.
The detector measures the flow of helium penetrating the par t.
Response time
When
spraying starts, the leak signal is not displayed instantaneously
on the analyzer:
there is
a response time which depends on the volume V being tested
and the helium pumping speed S of the system at the opening of the
part, according to the following relation:
T = V/S (T in seconds, V in litres, S in l/s)
T is the time required for the signal to reach 63 % of the final value.
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