Theory
91518 Multigas Analyzer Service Manual 3-8
Figure 3-6: CO
2
and N
2
O absorbance
Identification of anesthetic agents and the calculation of their concentrations is performed by measuring
absorptions at five wavelengths in the 8 to 9 µm band (Figure 3-7) and solving the concentrations from a set of
five equations.
The measuring accuracy is achieved using numerous software compensations. The compensation parameters
are determined individually for each gas measuring unit during the factory calibration.
Figure 3-7: Infrared absorbance of anesthetic agents
The infrared radiation source is a 4-W filament, surrounded by thermal isolation. The lamp unit is gas tight. A
hole in the isolation allows the radiation to pass into to a 4-mm conical measuring chamber.
From the measuring chamber, the infrared radiation passes into seven tubular light guides with a reflective
inner surface. A thermopile detector with an optical filter is located at the other end of each light guide.
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