ABSTRACT

This chapter deals with the description of some general principles of infrared radiation, followed by the definition of some of the basic terms and design configurations. It provides the description of newer developments in the field of infrared analysis, such as the use of tunable crystals and multiple internal reflection configurations. Infrared absorption is a technique that can be used successfully for continuous chemical analysis of a process. Infrared analysis is, therefore, most straightforward when the component molecules of the sample have significantly different atomic groupings. Most industrial process analyzers use nondispersive infrared (NDIR) designs. The NDIR technique is most sensitive and selective for small molecules whose spectral fine structure is resolved under ambient conditions. There are NDIR analyzers that use two detectors filled with two different gases, such as carbon monoxide and a hydrocarbon. In NDIR and Gas filter correlation analyzers the characteristics of the gas-filled cells vary with temperature.