Measuring Humidity

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					              ---- Measuring Humidity ----
1.   Sling psychrometer
      2 thermometers
      1 has a moistened cloth wick around the bulb (this is called
         the ‘wet bulb’)
      Swing around & wet bulb evaporationally cools
         (proportional to how dry the air is)
      Use a table with ‘dry bulb’ and ‘wet bulb depression’
         (dry bulb – wet bulb) to get the dew point or relative
         humidity




2.   Hair hygrometer
      Operates on the principle that hair lengthens as RH increases (e.g. curly hair
        lengthens and get curlier/frizzier on humid days)
      Bundle of hair linked mechanically to a calibrated indictor of 0-100%
      Not as accurate and needs to be recalibrated often




3.   Electric hygrometer
      Electrical conductor coated with a moisture absorbing chemical
      Electric current flow varies with RH
      Used in radiosondes and surface weather stations

				
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posted:10/4/2010
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