| #20 Relative Humidity Measurement |
| IRt/c's can be used to accurately and reliably measure actual relative humidity in many situations where there is a convenient source of water and flowing air. |
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| An IRt/c aimed at a wet porous surface with ambient air blowing across the wet surface can actually measure what is called "wet bulb" temperature for that ambient area. (More precisely, wet bulb tem-perature is the equilibrium temperature of the air-water interface when a water film is evaporated. When air is moved over a wet surface, the water cools by evaporation until it reaches wet-bulb temperature, then the cooling stops, no matter how much more air is moved over the surface. The temperature at which the cooling stops is the wet bulb temperature.) |
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| The IRt/c measures the temperature of the air-water interface on a surface directly. The quality of the water or of the absorbing material does not affect the reading, since the IRt/c can directly view the air-water interface, and the wet bulb equilibrium temperature is not materially affected by impurities. |
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| The highest precision method is to employ an IRt/c wired differentially with a conventional thermocouple to measure the quantity "wet bulb depression". The differential pair arrangement guarantees high accuracy, since RH is a strong function of wet bulb depression and a weak function of dry bulb tempera-ture. Standard psychrometric tables, charts, and software algorithms can be used with the data to obtain accurate relative humidity for your environ-mental measurements. |
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