Envent 330S-Ex, User Manual

Page: 30 / 71

Envent Engineering Ltd. Page 25 Revision 1
Figure 12. Sample Chamber (Exploded View)
Sensor Block
The sensor block measures the intensity of the LED light reflected off of the H
2
S
sensing tape. It is composed of an electronic board, a red-light emitting diode
and a photodiode, refer to Figure 12. As the tape gets darker due to exposure to
H
2
S, the photodiode receives less light. Less light translates to more H
2
S.
Window & Gasket
These two components seal the small compartment where the H
2
S comes inside
the sample chamber, refer to Figure 12. The window keeps a clear view for the
LED and the photodiode to work properly and isolates them from the sample gas.
The rubber gasket seals the Sample Chamber compartment preventing any
leaks.
Aperture Strip
The sample chamber has a fixed size aperture of ¼ inch (0.635 cm) which is
used for concentrations in between 1 ppm to 16 ppm.
For concentration applications below 1 ppm or above 16 ppm an aperture strip is
installed behind the window in the Sample Chamber, refer to Figure 12. These
aperture strips keep the analysis time to be approximately the same regardless
of the range.
Various sizes of apertures match different measurement ranges. Table 3 shows
the aperture size according to its range.