Agilent Technologies Flow Tracker 1000, Reference Manual

Page: 25 / 36

Flow Tracker Series 1000/2000
Reference Manual 25
rate inferred will also be smaller than the actual leak rate. For
these reasons, the accuracy of the reported leak rate can be
quite subjective, and should be regarded appropriately.
Generally, only gases with thermal conductivities substantially
different, either higher or lower than air, can be detected with
this method. The absolute thermal conductivities (at 80 °F,
26.7 °C) of the gases that are selectable in the Flow
Tracker 2000 are shown in
Table 5 .
N O T E
A good rule of thumb is that the actual leak rate is at least the rate
indicated if the appropriate gas is selected.
Table 5 Thermal conductivities
Gas Absolute thermal conductivity
cal/(sec)(cm
2
)(°C/cm) x 10
-6
Detectable Temp
Air 62.20 No 80 °F, 26.7 °C
Nitrogen 62.40 No 80 °F, 26.7 °C
Carbon dioxide 39.67 Yes 80 °F, 26.7 °C
Methane
*
81.83
*
* These gases are technically detectable, however this device is not rated for use
in hazardous areas
80 °F, 26.7 °C
Hydrogen
*
433.92
*
80 °F, 26.7 °C
95-5
Argon-methane Yes 80 °F, 26.7 °C
Helium 360.36 Yes 80 °F, 26.7 °C
N O T E
If the temperature of the gas leak is known, the leak rate and conductivity
can be compensated for temperature. The thermal conductivity of gases
changes in direct proportion to the temperature of the gas. This change is
relatively small and approximately linear at 0.27% per degree Celsius
(greater temp = greater conductivity).