INFICON T-Guard Leak Detection Sensor - Manual (Page 50)

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Operation
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(0.5 seconds in this example). By increasing the total gas flow, the measurement will
be quicker but for the price of a lower sensitivity. The smallest displayable leakage
rate increases when the total gas flow is increased.
In order to save time, you can calibrate and measure with a shorter time than needed
for the final leak rate value. But then the completely identical timing for calibration
and each measurement is very important. This method is called Dynamic Measure-
ment.
Like in the Accumulation mode, a GROSS measurement will be done before the
FINE measurement of the leak rate to avoid helium contamination of the Wise
Technology™ Sensor.
5.3.2.1 Hints for a good measurement:
• Minimize the chamber volume but do not let the test sample touch the walls.
• Place the inlet for external air in the chamber opposite the connection of T-
Guard™ Leak Detection Sensor.
• Use fans inside the chamber to have a good mixture of helium and air
everywhere.
• Do not make the outside air inlet too big. Helium must not leave the chamber
there.
• Lead the same ambient air into the chamber and the reference line.
• For a trigger leak rate of 1·10
-5
mbar l/s, do not use a total flow higher than 3000
sccm. For a trigger leak rate of 1·10
-4
mbar l/s, do not use a total flow higher than
30,000 sccm. For a trigger leak rate of 1·10
-3
mbar l/s, do not use a total flow
higher than 300,000 sccm.
• After closing the chamber and applying helium to the test object, wait for a certain
time, which amounts to:
INFICON strongly recommends this kind of set-up for Carrier Gas Measurement:
3 x chamber volume (in ccm)
Carrier gas flow (in ccm per seconds)
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