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2 A Sling Psychrometer is used to measure relative humidity. Get yours today!

3 Psychrometer Parts: Dry Bulb ThermometerDry Bulb Thermometer Wet Bulb ThermometerWet Bulb Thermometer Reservoir and StockingReservoir and Stocking WETDRY

4 But why do we sling it around and around?

5 What happens to your skin when you sweat and then stand in a breeze?

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7 As the wet-bulb thermometer goes through the air 1. Water evaporates 2. Energy is used; water changes from liquid to vapor 3. Wet-bulb temperature goes down

8 What influences how much the wet-bulb temperature goes down? Humidity Temperature

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10 Using our wet- and dry-bulb temperatures, we can consult tables made by scientists… …to determine humidity and saturation value.

11 Now we can calculate relative humidity!

12 Partial Relative Humidity Chart for 30° C Difference Between Dry Bulb and Wet Bulb Temperatures Relative Humidity None100% 0.5°96% 1.0°93% 1.5°89% 9.0°44% 9.5°42% 14.5°19% 15.0°17% 18.0°5% Fortunately, we don’t have to do all this every time…

13 On the side of the psychrometer is a sliding scale which calculates relative humidity for us. Align the dry-bulb reading with the wet-bulb reading. The arrow will point to the relative humidity reading on the center scale. It’s easy!

For Help: AMSTI-GLOBEThe GLOBE Program Judy ReevesLynn VaughanAMSTI-GLOBEResource Specialist Robin NelsonJerry CobbsAMSTI-GLOBE AdministratorTechnology Specialist