Environnement AF22e, Technical Manual, Page: 30 / 118

Environnement
S.A
AF22e
Duplication prohibited
APRIL 2016
2–10
Analysis
The HC-molecule free sample to be analyzed, is sent to a reaction chamber to be irradiated by an
ultraviolet radiation centered at 214 nm, which is the SO
2
molecule absorption wavelength.
A photodiode measures the ultraviolet radiation generated by the UV lamp. This measurement is used
during signal processing to compensate any variation of UV energy.
Molecules restore a specific fluorescence in the ultraviolet. The fluorescence is optically filtered between
300 and 400 nm to eliminate some interfering gases. The fluorescence is detected by the PM tube
placed near the reaction chamber.
At each « zero-ref » start, a shutter is placed between the UV lamp and the reaction chamber inlet. This
electrical zero corresponds to the PM tube darkness current and the preamplifier offset voltage. Taking
account the electrical zero in signal processing removes any risk of temperature and over-time drift.