Operating Manual PG11 / PGE11 Page 10
1.4 Detection principle of PG11 and PGE11
PG11 is using an Optical Detection principle. The basic working principle is illustrated in the drawing below
and consists of the following basic parts:
A. Infrared light (2 – 6 µm region) is generated at the
light source
and directed at the
B.
sapphire lens
focusing the light so it is passing through the
C.
gas
to be measured. The gas will absorb some wavelengths depending on the type of gas. The
higher concentration of the gas the more light is absorbed. After passing through the gas the
remaining light is
D. reflected by a
mirror
and back through the gas again reaching the lens directing the light at
E. the
light sensors
. The light sensors will measure what wavelengths that have been absorbed and how
much light has been absorbed. Based on this information the Gas Detector can decide if the target
gas is above the
alarm level
.
In addition to the basic principles described above there are more functions in the detector that are
compensating for changes for example by temperature and component aging over time.
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