The source housing is filled with 'Zero Gas' if the air would otherwise interfere. For some
applications, this is provided by a chemical held in a glass container screwed into the side of the
housing.
The detector output is a maximum for the Zero Gas condition and falls towards minimum (zero)
with increasing concentration (absorption). The instrument automatically compensates for
variations in output by adjustments made during zero and span cycles. Failure of either
adjustment can be due to a source or detector problem.
Motor
Soda Lime
Infrared
Source
Rotating
Shutter
Spacer
Cell
Window
nalysis
Cell
Window
Thermistor
Detector
Thin
Film
Filter
Figure 14 - The Single Beam analysis bench
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