1. Source Requirements for IR Analysis: For basic, non-dispersive infrared (NDIR) gas analyzers used in industrial settings, the source needs to be rugged, inexpensive, and capable of emitting a broad range of mid-to-long infrared wavelengths.
2. The Hot Wire Spiral: The most common source for a "simple" IR analyzer is a Hot wire spiral (also called a nichrome or kanthal wire). When an electric current passes through this resistive spiral, it heats up and glows, emitting infrared radiation according to Black-body radiation principles. It is preferred for simple devices because it does not require the complex pre-heating or delicate handling associated with more advanced sources.
3. Why not the others?:
• Tungsten lamp: Primarily emits visible and near-infrared light; it is not suitable for the mid-infrared region where most gas absorption occurs.
• Nernst glower: An excellent IR source made of ceramic oxides, but it is considered a more "advanced" and delicate source used in high-end lab spectrophotometers rather than "simple" industrial analyzers.
• Mercury arc lamp: Used for ultraviolet (UV) or far-infrared applications, but not for standard gas analysis in the mid-IR range.