BOREAL LASER GasFinderMC-2, Operation Manual

Page: 60 / 90

9.6
Boreal Laser Inc. GasFinderMC Installation 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 considered to be
the point at which the readings can be considered valid. Below this the readings should be
treated with suspicion.