Sunlight
The sun emits an enormous amount of energy, which could be harmful to human beings if not for the vapours and gases in the atmosphere, like water (clouds), ozone, and other vapours and gases in the air, through which the sunlight is filtered. In the figure it can well be seen that "cold" CO2 filters the solar radiation around 4.3 µm. The Infrared detector which uses this frequency is therefore solar blind. Not all manufacturers of flame detectors use sharp filters for the 4.3 µm radiation and thus still pick up quite an amount of sunlight. These cheap flame detectors are hardly usable for outdoor applications. Between 0.7 µm and approx. 3 µm there is relatively large absorption of sunlight. Hence, this frequency range is used for flame detection by a few flame detector manufacturers (in combination with other sensors like ultraviolet, visible light, or near infrared. The big economical advantage is, that no expensive sapphire detector windows but quartz windows can be applied. These electro-optical sensor combinations also enable the detection of none-hydrocarbons like hydrogen fires without the risk of false alarms, caused by artificial light or electrical welding.
Read more about this topic: Flame Detection
Famous quotes containing the word sunlight:
“Prostration is our natural position. A wormlike movement from a spot of sunlight to a spot of shade, and back, is the type of movement that is natural to men.”
—Wyndham Lewis (1882–1957)
“Semi-Saracenic architecture, sustaining itself as if by miracle in mid air; glittering in the red sunlight with a hundred oriels, minarets, and pinnacles; and seeming the phantom handiwork, conjointly, of the Sylphs,... the Fairies,... the Genii, and ... the Gnomes.”
—Edgar Allan Poe (1809–1849)
“‘The key is in the window, the key is in the sunlight at the
window—I have the key—Get married Allen don’t take drugs—the key is in the bars, in the sunlight in the window.
Love,
your mother’”
—Allen Ginsberg (b. 1926)