Environnement AS32M, Техническое руководство, Страница: 32 / 186

Environnement
S.A
AS32M
Duplication prohibited
DECEMBER 2013
2–8
2.3 DESCRIPTION OF THE MAIN MODULES
For all this section and its sub-sections, refer to .
A pump mounted at the end of the fluid circuit draws the sample through a Teflon tube connected to
the rear panel of the analyzer. Protection against dust is ensured by a Teflon diaphragm filter.
2.3.1 DRYER
Refer to Figure 2–5.
The Perma-Pure dryer uses a permeation-distillation drying process. The dryer is made of two
concentric tubes; the internal tube is made of a special water-permeable polymer. The molecules are
transferred through this tube from the side where the water content is the highest to the side where it
is the lowest. To ensure a lower partial pressure of water on the outside of the polymer tube, the tube
periphery is placed under vacuum and rinsed by the exhaust flow leaving the tube.
Figure 2–5 – Perma-Pure dryer
2.3.2 PARTICLE FILTER
After drying, the sampled gas passes through a particle filter made up of microfibers of borosilicate
glass. This filter retains 99.5% of the particles with an aerodynamic diameter greater than 10 nm,
avoiding the optical interference caused by the light scattering induced by particles of greater size than
the emission wavelength (450 nm).
2.3.3 OPTICAL CAVITY
The optical cavity is a hollow stainless steel cylindrical chamber, closed at each end by a high
reflectivity mirror. The luminous source placed before the inlet mirror of the cavity is a light-emitting
diode (L.E.D.) that emits at 450 nm. The beam of light is focused by a convergent lens placed between
the LED and the inlet mirror. The photons transmitted by the outlet mirror of the cavity are detected by
a phototube placed behind this mirror. Between the outlet mirror and the detector, a convergent lens
focuses the beam on the detector, and a band-pass interference filter centered at 450

10 nm
enables selection of photons with a wavelength between 440 and 460 nm.
2.3.4 GAS INLET SOLENOID VALVE ASSEMBLY
An assembly of two 3-way solenoid valves allows selection of one of three analyzer inlets: sample,
zero air, or span gas. ". Protection against dust is provided by a Teflon filter (PTFE) connected to the
"sample" inlet.
N a f i o n