Get to know the working principle of psychrometry. Make a similar measurement with the thermometer in the test set yourself and determine the air humidity based on this. The worksheet also has a calculator for determining air humidity. If possible, compare the result with the reading of an industrially produced air humidity meter.
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Test data
| Dry bulb temperature | ∘C |
| Difference between dry and wet thermometer readings | ∘C |
| Humidity based on my test results | ∘C |
| Humidity measured with an industrial hygrometer | ∘C |
The calculator calculates relative humidity based on the readings of the dry and wet thermometers of the psychrometer. See below for the formula used in the calculator. When using the calculator, enter the data in the table. The answer appears in the last row of the table.
Air humidity according to the readings of the psychrometer thermometers
| Dry thermometer temperature | ∘C |
| Wet thermometer temperature | ∘C |
| Relative humidity |
A psychrometer consists of two thermometers. One is dry, the other is kept constantly wet. A simple way to moisten a liquid thermometer is to wrap a wet cloth around the reservoir and hold it upside down in water. If the air is saturated with water vapor (humidity 100%), the water does not evaporate from the wet cloth, the wet thermometer does not cool down and shows the temperature of the surrounding environment together with the dry one. If the relative humidity is lower, the water from the wet thermometer starts to evaporate, it cools and there is a difference in the temperature readings. The drier the air, the greater the difference. The psychrometer comes with a corresponding table where you can find the humidity corresponding to the temperature difference.
Here we use the following formula to calculate relative humidity
where
and
Source: https://www.1728.org/relhum.htm
Intermediate results:
