A psychrometer is used by refrigeration engineers to measure:

• A. Relative Humidity Level of the Atmosphere
• B. Temperature
• C. Pressure
• D. Dew Point

Answer: (A)

A psychrometer measures how humid the air is by using two thermometers: a dry-bulb and a wet-bulb. The wet-bulb thermometer has its bulb wrapped in a wick kept wet. As air flows over it, water evaporates from the wick, cooling the bulb. The amount of cooling depends on how much moisture the air can still hold. In drier air, evaporation is greater and the wet-bulb temperature reads much lower than the dry-bulb. In more humid air, evaporation slows and the two readings are closer together. By looking at the difference between these two temperatures along with the dry-bulb temperature, you can determine the relative humidity, usually using a chart or a calculation.

So the main use of a psychrometer in refrigeration work is to establish the relative humidity of the surroundings. It’s true the device provides temperature readings as part of the process, but those readings are used to derive humidity, not to measure air temperature directly. It doesn’t measure pressure directly, and while dew point can be inferred from the humidity and temperature, the primary function is assessing relative humidity.