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DPT & Relative Humidity Charts
Handy Dandy Earth Science Reference Tables Page 747
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Weight of Water Vapor in Air Relative Humidity =
: The ratio of the air’s actual water content to its potential water vapor content at a given temperature. Relative Humidity Weight of Water Vapor in Air Relative Humidity = Weight of Potential Water Vapor in Air at Saturation Basically, relative humidity tells you how saturated the air is with water.
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A psychrometer is used to measure relative humidity.
The dry bulb measures the air temperature The wet bulb gives a measure of how unsaturated the air is—the evaporation of water from the wet bulb lowers the temperature reading (and the evaporation depends on the saturation of the air)
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Dewpoint Temperature: The temperature the air would have to be cooled to saturate the air (causes water to condense
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The “Dry Bulb” Don’t let it fool you. It is just a thermometer.
It measures the air temperature. Duh! 20°C
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The “Wet Bulb” Has a little wet booty tied to the bottom.
Gets cool when water evaporates. 12°C Wet Booty
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A Dry Day… A lot of moisture will evaporate.
The wet bulb will be a lot cooler than the dry bulb. 20°C 20°C 14°C 12°C 8°C Difference between wet bulb & dry bulb is 12 °C.
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A Humid Day… A little bit of moisture will evaporate.
The wet bulb will not be much cooler than the dry bulb. 20°C 14°C Difference between wet bulb & dry bulb is 6 °C.
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Page 747 & 750 of your Handy Dandy Earth Science Reference Tables
Warning #1: Be sure to READ the correct chart: DPT or RH Warning #2: Dew Point Temperature IS NOT “Difference between wet bulb and dry bulb”. Warning #3: The wet bulb temp IS NOT the DPT.
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Dry-bulb temperature is your air temperature.
20 °C
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14 °C
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4 °C
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Subtract (the difference) between the dry bulb and wet bulb
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20°C 14°C 20-14=6
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18°C 16°C 18-16=2
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Put it all together 20°C 8°C 20-8=12 Relative Humidity = 11%
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14°C 10°C 14-10=4 Relative Humidity = 60%
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The Dew Point Chart works the same way
14-10=4 Dew Point = 6°C
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Try These. 58% 17 °C 86% 4 °C 57% 4 °C 91% 16 °C 100% 14 °C 45% -9 °C
Dry Bulb Wet Bulb R Humidity DPT 26°C 20 °C 6 °C 5 °C 12 °C 8 °C 18 °C 17 °C 14 °C 0 °C -3 °C 58% 17 °C 86% 4 °C 57% 4 °C 91% 16 °C 100% 14 °C 45% -9 °C
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More Difficult. 82% 18 °C 45.5% -.5 °C 100% 17 °C 20% -17 °C 69%
Dry Bulb Wet Bulb R Humidity DPT 21°C 19°C 11°C 6 °C 17 °C 17°C 2°C -3 °C 9°C 6.5 °C 70°F 60 °F 82% 18 °C 45.5% -.5 °C 100% 17 °C 20% -17 °C 69% 3.5 °C 15 °C 21 °C 52% 11 °C(50 °F)
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