BOREAL LASER GasFinder FC, Руководство по эксплуатации

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9.4
Boreal Laser Inc. GasFinderFCr Operation Manual — Appendices July 17th 2017
Appendix C — Explanation of ppmm
Gas concentration is measured in ppm, ‘parts per million’ by volume. If a room measuring 100m
x 100m x 100m (1 million cubic metres) has 10 cubic metres of air replaced by a pure gas, then
the gas concentration is expressed as 10 ppm. Open path monitors, like the
GasFinderFCr ,
measure the total amount of a specifi c gas such as HF in the path of the laser beam between
the transmitter unit and a refl ector. This is a ‘total path’ measurement. The units are ‘parts per
million metres’, or ‘ppmm’.
A uniform background concentration of 10 ppm over 50 m gives a reading of 500ppmm .
10ppm x 50m = 500ppmm
When the 500 ppmm is divided by 50 m the result is a value of 10 ppm, which is the ‘path
averaged’ concentration.
A concentrated cloud of 50 ppm, 10 m in diameter, in a background of 0 ppm also gives a
reading of 500 ppmm. 50ppm x 10m = 500ppmm
Retrorefl ector
Remote Head
10ppm
50m
50ppm 50ppm
50m
10m
Remote Head
Retrorefl ector