Using a Sling Psychrometer to Measure Relative Humidity
Introduction
A sling psychrometer is a type of hygrometer. Hygrometers are used to measure relative humidity. The psychrometer is made up of two thermometers; one with a dry-bulb and the other with a wet-bulb.
After using the sling psychrometer, the final wet bulb and dry bulb temperatures are converted to determine the relative humidity. The three accepted conversion methods are: psychrometric computer, Skew-T diagram, or temperature conversion chart.
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Things You'll Need
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Instructions
Step 1 - Before attempting any readings, inspect the sling psychrometer to ensure that it is clean and in good condition.
Step 2 - Soak the wick in distilled water (See Tips below).
Step 3 - Swing the sling psychrometer steadily at about 2-3 turns per second. Do not let the instrument get too close to your body, or the measurement might be affected by your body heat. If the wick gets too dry, wet it again and start over.
Step 4 - After about 1 - 1 1/2 minutes, read the wet-bulb temperature. Then, swing the psychrometer steadily for about 1 minute. Read thewet-bulb temperature once more. If the result differs from the first reading, continue swinging for another minute and read again. Repeat as needed until the lowest possible reading is determined.
Step 5 - Read and record the final wet bulb and dry bulb temperatures to the nearest 0.1 degree.
Step 6 - Determine the relative humidity using one of three industry standard practices: psychrometric computer, Skew-T diagram, or temperatureconversion chart.
Tips and Warnings
If the water does not soak in easily, replace the wick.
Always clean and store the barometer in a secure, cool, dry environment.
Be careful to avoid injuries or damage to property when swinging the sling psychrometer.
Photo Credits
Wikimedia Commons and Original Work
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Comments
Some simple sling psychrometers, as the Hubbard unit, place the wet and dry bulbs back-to-back and the evaporative cooling of the wet bulb will affect the dry bulb temperature as well. Glue a thin bit of styrofoam or other insulation to the back of the dry bulb thermometer to serve as a separator and insulator for more accurate results.
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