CO
2
Equations
The measurement of CO
2
is a bit more complicated than for H
2
O because of the influence of
water vapor. There is a slight direct cross sensitivity in the CO
2
signal to H
2
O. This is measured
at the factory and accounted for in the computation of absorptance (equation B-8). There is also
a band broadening effect that is accounted for in the computation of concentration (equation B-
12).
CO
2
absorptance α
c
is computed from
B-8
where V
c
and V
co
are the raw detector signals for sample and reference, Z
c
is the CO
2
zero para-
meter, and X
wc
is a cross sensitivity parameter for the effect of water vapor on CO
2
. Its value is
reported on the calibration sheet as “XS=”.
The empirical pressure correction function g
c
() depends on CO
2
absorptance and pressure:
When P = P
o
, g
c
() = 1.
When P < P
o
Appendix B
Appendix B. Equation Summary B-3
To Next Page
Loading...
