Infrared systems : flame detector

Abstract

Nature of infrared radiation: Infrared radiation is an electromagnetic radiation similar in nature to visible light. In the electromagnetic spectrum the infrared region occurs adjacent to the red end of the light spectrum (about 0.78 μm) and extends to the region of very short microwaves (about 150 μm) (see fig. 1.1.). Hence the prefix “infra” meaning “below” the red. It is, in effect, “light" having wavelengths too long for our eyes to see. Our sense of touch, however, detects these wavelengths and our brain interprets and tells us that “this is hot”. Infrared radiation is another name for radiant heat (heat that radiates from a source such as the sun, an electric bulb, or a candle flame). It is not necessary that the source emit visible light. An electric iron, for example, does not become even red bot, yet it is an abundant producer of infrared. In fact, infrared radiation is generated by vibration and rotation of the atoms and molecules within any material whose temperature is above absolute zero. […] Application of infrared radiation: After a century of steady advances, the utility of infrared techniques is no longer confined to spectros copy nor is it used just for devices for night vision and rifle sighting, or for infrared heating. There is developing a fascinating variety of applications of electromagnetic radiation constituting the spectrum from about 1 μm to about 1000 μm (i.e. up to very-high-frequency radar). The list of applications is long, ranging from missile defence and fire detection to meteorology and medical diagnostics. But however, varied the applications, infrared systems can be broken down into four basic units, namely an infrared source, an optical system, a radiation detector and an arrangement for presenting the data. […] The system can be of two types either passive or active. Passive systems are used in most applications, the object of interest is in this case the source which is seen by its self-emission. In active systems, a controlled source is used to illuminate the object under observation. Before going into details about the basic units mentioned above which make up any infrared system it is necessary to review first the underlying physics.