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Principles of Operation Teledyne API - T100 UV Fluorescence SO2 Analyzer
280
The first stage (Equation 13-1) occurs when SO
2
molecules are struck by photons of the
appropriate ultraviolet wavelength. In the case of the T100, a band pass filter between the
source of the UV light and the affected gas limits the wavelength of the light to
approximately 214 nm. The SO
2
absorbs some of energy from the UV light causing one
of the electrons of the SO
2
molecule to move to a higher energy orbital state.
*
22142
SOhvSO
Ia
nm
(Equation 13-1)
The amount SO
2
converted to
SO
2
* in the sample chamber is dependent on the average
intensity of the UV light (Ia) and not its peak intensity
because the intensity of UV light
is not constant in every part of the sample chamber. Some of the photons are absorbed
by the SO
2
as the light travels through the sample gas.
Darkened
REACTION CELL
filled with SO
2
214nm
Filter
UV
SOURCE
Figure 13-1: UV Absorption
The equation for defining the average intensity of the UV light (Ia) is:
20
SOaxexp1IIa
(Equation 13-2)
Where:
I
0
= Intensity of the excitation UV light.
a = The absorption coefficient of SO
2
(a constant).
SO
2
= Concentration of SO
2
in the sample chamber.
06807C DCN6650