INFICON T-Guard Leak Detection Sensor - Manual (Page 49)

Operation
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Carrier Gas Measurement
The bigger the chamber and the smaller the total gas flow through it, the longer it
takes for the signal to reach its final value.
The time you need to get a constant signal in Carrier Gas mode depends on the total
gas flow and the volume of the chamber. The time it takes to see 63 % of the signal
is the volume of the chamber divided by the total gas flow.
For example: With a volume of 2 litres and a total gas flow of 20 l/s, you see 63 % of
the signal after 0.1 seconds. After waiting three times as long, you see 95 % of the
signal (0.3 s in this example). After five times as long, you will see 99 % of the signal
Fig. 6-10 Typical helium concentration in an enclosed chamber with a leaky test
sample over time.
Item Description Item Description
1 Helium signal 4 Time
2 Start 5 Rising signal
3 Ambient helium 6 Stable signal, final value
Fig. 6-11 Display of leak rate in Carrier Gas mode with information on the helium
background of the sensor and the environment.