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Chapter 1

Chapter 1. Optoelectronics use IR-Visible-UV Ultraviolet (UV) light Highest frequency Smallest period Very energetic, so bumps electrons to higher orbit Infrared (IR) light Slightly vibrates atoms. UV - Negatives. UV can cause skin cancer and eye damage Fades paint on a car

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Chapter 1

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  1. Chapter 1 • Optoelectronics use IR-Visible-UV • Ultraviolet (UV) light • Highest frequency • Smallest period • Very energetic, so bumps electrons to higher orbit • Infrared (IR) light • Slightly vibrates atoms

  2. UV - Negatives • UV can cause skin cancer and eye damage • Fades paint on a car • Degrades rubber on tires • Tires have coating to absorb UV and dissipate it as heat instead of allowing it to combine with polymer’s molecules • Tires need to be used or dry rot occurs or cracking in tires

  3. UV - Positives • UV kills germs • UV disinfects bacteria by altering DNA in germs • UV sterilizes city waste water • Helps to detect bogus Benjis ($100) • Helps to analyze stamps, rocks, & minerals

  4. UV Classes • UV-V visible 395 to 445 nm • UV-A 320 to 395 nm • Least damaging, but passes through ozone • UV-B 280 to 320 nm • Very harmful, but absorbed in stratosphere • UV-C 200 to 280 nm • Most damaging, but oxygen in stratosphere absorbs most of it • Vacuum UV (VUV) 100 to 200 nm • Man made • More destructive than UV-C

  5. Stratosphere • Ozone layer resides here • Troposphere • Region directly above earth • Sun light hits equator most, so also receives most UV • UV Experimental Index • Used by National Weather Service • Forecasts amount of UV reaching earth’s surface • Index is from 0 to 15 in summer • Also used by Environmental Protection Agency (EPA)

  6. Dobson Unit • Ozone layer • Thickest at the equator and thinnest at poles • Acts as natural shield of UV light • Antarctic ozone hole • Dobson Unit • Measure of ozone • 1 DU is ozone thickness of 0.01 mm at 0o C and 1 atm • Average thickness in U.S. is 300 DU • Uses spectrophotometer to measure.

  7. Ozone (O3) • Colorless • Harsh acrid smell • 90% occurs in ozone layer • Chlorine and Bromine hasten ozone destruction • Single chlorine atom can destroy 100,000 ozone molecules before it leaves stratosphere • Halo carbons destroy ozone. • can remain in atmosphere for up to 120 years

  8. Ozone Destroyers • 80% of ozone destruction occurs from CFCs (Chlorofluorocarbons • Volcanoes also destroy ozone • Mount Pinatubo in Philippines erupted in 1991 and reduced ozone levels by 20%

  9. UV intensity is reduced by the following • Clouds • Rain • Smog • UV affects many animals • Birds detect UV and select mate as to how UV reflects off them • Animals can see UV. Hunters who have washed cloths in laundry detergent are very visible to their prey! • Iguanas use UV to detect edible plants and see territories staked out by other iguanas

  10. Flame Detectors http://www.reliablefire.com/firealarm/flame_detectors.htmlhttp://www.flame-detection.net UV detectors respond to hydrogen fires, but IR detectors don’t. Due to their fast detection capabilities, flame detectors are generally used only in high-hazard areas, such as fuel-loading platforms.

  11. UV Flame Detectors • A UV flame radiates in the 1850 to 2450 angstrom range. (or 185 to 245 nm) • Virtually all fire emit radiation in this band, while the sun's radiation at this band is absorbed by the Earth's atmosphere. (remember the ozone layer) • UV detector is solar blind, so won’t have false alarm due to sun. • Can be used indoors or outdoors. • UV detectors are sensitive to most fires, including hydrocarbon, metals, sulfur, hydrogen, hydrazine, and ammonia. • They detect flames at high speed (3-4 milliseconds) due to the UV high-energy radiation emitted by fires and explosions at the instant of their ignition.

  12. IR Flame Detectors • An infrared (IR) detector basically is composed of a filter used to screen out unwanted wavelengths and focus only on IR. • Main problem is false alarm from radiation of the sun. If inside and shielded from the sun, then works well. Good for bank vaults. • IR detectors are sensitive to most hydrocarbon fires (liquid, gases and solids). • IR detectors respond in less than 50 msec. • IR detectors are less affected by smoke, oil, and certain gases and vapors than UV Detectors.

  13. UV/IR Flame Detector • An ultraviolet/infrared flame detector consists of an UV and single-frequency IF sensor, paired together to form one unit. • A fire alarm is produced only when both sensors detect a fire. • Better false alarm rejection • UV and IR spectral band detectors compare the threshold signal in two spectral ranges and their ratio to each other to confirm the reliability of the fire signal.

  14. IR3 Flame Detectors • IR3 or triple IR spectral band detectors compare three specific wavelength bands within the IR spectral region. • Mathematical techniques are used to correlate the three bands to discriminate between fire and false alarm.

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