What does a sling psychrometer measure?

A sling psychrometer is a device specifically designed to measure relative humidity in the air. It consists of two thermometers: a dry bulb thermometer that measures the air temperature and a wet bulb thermometer that is moistened with water. When air flows over the wet bulb, the evaporation of water cools the bulb, and the temperature difference between the two thermometers can be used to calculate the relative humidity.

The principle behind its operation relies on the fact that the amount of cooling that occurs in the wet bulb is dependent on the humidity of the air. In drier conditions, more evaporation takes place, leading to a larger temperature difference between the two thermometers, and consequently, this indicates lower relative humidity. Conversely, in more humid conditions, less evaporation occurs, resulting in a smaller temperature difference and indicating higher relative humidity. This relationship allows the sling psychrometer to be an effective and practical instrument for determining the moisture content in the air.