Teledyne 100E - UV Light Path and Components

Theory Of Operation Model 100E Instruction Manual
164 045150102 Rev XB1
The second stage of this reaction occurs after the SO
2
reaches its excited state (SO
2
*).
Because the system will seek the lowest available stable energy state, the SO
2
* molecule
quickly returns to its ground state (Equation 10-3) by giving off the excess energy in the
form of a photon (hν). The wavelength of this fluoresced light is also in the ultraviolet
band but at a longer (lower energy) wavelength centered at 330nm.
nm3302
kF
2
hvSO*SO +→
(Equation 10-2)
Obviously the more SO
2
that is present in the sample gas the more fluorescence will be
detected in the sample chamber. Unfortunately there are several other factors that also
can affect the amount of fluorescence detected by the analyzer.
For instance, the amount of SO
2
* is dependent on the average intensity of the UV light
and not its peak intensity because some of the photons are absorbed by the SO
2
as the
light travels through the sample gas.
Figure 10-1: UV Absorption
The equation for defining the average intensity of the UV light (Ia) is:
()()
[]
20
SOaxexp1IIa −−=
(Equation 10-3)
Where:
•
I
0
= Intensity of the excitation UV light.
•
a = The absorption coefficient of SO
2
.
•
SO
2
= Concentration of SO
2
in the sample chamber.
•
x = The distance between the UV source and the SO
2
molecule(s)
being affected (path length).