Environnement AF22e, Техническое руководство, Страница: 26 / 118

Environnement
S.A
AF22e
Duplication prohibited
APRIL 2016
2–6
2.2 MEASUREMENT PRINCIPLE
The radiation intensity absorbed by sulfur dioxide i
a
in the L-length optical chamber follows the Beer-
Lambert law:
i
a
= i
0
x
(1 – e
-
α
LC
)
where :
« i
0
» is the chamber inlet intensity,
«
α
» is the specific SO
2
absorption coefficient,
« C » is the gas concentration to be analyzed.
Likewise, the probability for an excited molecule to fluoresce is given by:
Kf
Kf Kq Kd
+ +
The fluorescence intensity i
f
received by the PM is then expressed in the following form:
f a
Kf
i Gi
Kf Kq Kd
=
+ +
where G is a constant depending on the lit chamber part seen by the PM.
Therefore:
f o
Kf
i Gi
Kf Kq Kd
=
+ +
x
Lc
(1 e )
α −
−
In our case,
α
L C << 1 and 1
−
e
− α
LC
can be developed at first-order as follows:
1 − ≅ +
The result is:
= =
The PM senses radiation directly proportional to SO
2
concentration. This result is the basis of AF22e
measurement technique.