BOREAL LASER GasFinder FC, Operation Manual

Page: 60 / 88

9.6
Boreal Laser Inc. GasFinderFCr Operation Manual — Appendices July 17th 2017
Explanation of R 2 (continued)
A typical plot of concentration versus R
2
will give the following graph:
With lower levels of sample gas, the R
2
s
decrease, and equal zero when there is
no gas present. As the signal from the
gas becomes stronger, the effect of noise,
both electronic and optical, is reduced
and the
R
2
s will increase (i.e., the signal
to noise ratio will increase). The general
shape of the plot is the same for all gases;
however, the x-axis values will depend on
the sensitivity of the instrument to the gas
species being observed.
Use of R 2
The point at which the bend or ‘knee’ of the curve occurs in the plot of R
2
/ ppmm can be
used to determine the sensitivity of the instrument to the gas concentration measurement.
This varies with the instrument and the type of gas but an R
2
of 0.85 is generally agreed to
be the point at which the readings can be considered valid. Below this the readings should
be treated with suspicion.
R2
ppmm