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

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

4. 4 But why do we sling it around and around?

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

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7. 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. 8 What influences how much the wet-bulb temperature goes down? Humidity Temperature

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

11. 11 Now we can calculate relative humidity!

12. 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. 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!

14. For Help: AMSTI-GLOBEThe GLOBE Program www.amsti.org/globewww.amsti.org/globe www.globe.govwww.globe.gov Judy ReevesLynn VaughanAMSTI-GLOBEResource Specialist judy@amsti.orglynn@amsti.org Robin NelsonJerry CobbsAMSTI-GLOBE AdministratorTechnology Specialist robin@amsti.orgjerry@amsti.org