Sunday, December 6, 2009

Infrared Gas Analyzer

An infrared gas analyzer measures trace gases by determining the absorption of an emitted infrared light source through a certain air sample. Trace gases found in the earths atmosphere get excited under specific wavelengths found in the infrared range. The concept behind the technology can be understood when considering the greenhouse effect. When sunlight hits earths surface, the incoming short wave radiation gets turned into long wave radiation|long wave infrared radiation that is reflected back into space. If there is a thick atmosphere on covering the planet of interest, much of this radiation is absorbed by the "greenhouse gases" in our atmosphere which act as a type of insulative blanket. The infrared gas analyzer works using a similar principle.

Normally, the infrared gas analyzer has two chambers, one serves as a reference chamber while the other chamber serves as a measurement chamber. Infrared light is emitted from some type of source on one end of the chamber, passes through series of chambers that contain given quantities of various gases in question. For example, if the analyzer is designed to measure carbon monoxide and dioxide then these chambers must contain a certain amount of these gases. In the design from 1973 (pictured above), the infrared light is emitted from a source where it passes through the sample gas, a reference gas with a known mixture of the gases in question and then through the "detector" chambers containing the pure forms of the gases in question. When a "detector" chamber absorbs some of the infrared radiation, it heats up and expands. This causes a rise in pressure within the sealed vessel that can be detected either with a pressure transducer or with a similar device. The combination of output voltages from the detector chambers from the sample gas can then be compared to the output voltages from the reference chamber.

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