Inficon T-Guard Leak Detection Sensor Manual do Utilizador descarregar pdf (Página 50)

48 Operation

jina85e 5.fm Technical Handbook(1112)

(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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