How to test the indoor humidity?

The humidity in the room can be tested with a hygrometer. Measurement methods can be dry-bulb and wet-bulb measurement:

A pair of thermometers with the same shape are used in the parallel device, one is used to measure the temperature, which is called a dry bulb thermometer, and the other is wrapped with absorbent gauze soaked in distilled water, which is called a wet bulb thermometer. When the air is not saturated, the wet bulb needs to consume heat due to surface evaporation, thus reducing the temperature of the wet bulb. At the same time, the wet ball continuously gets heat supply from the air flowing through the wet ball.

When the heat consumed by evaporation of the wet bulb is in balance with the heat obtained from the surrounding air, the temperature of the wet bulb will not continue to drop, resulting in the temperature difference between the dry bulb and the wet bulb. The temperature difference between dry bulb and wet bulb is mainly related to the air humidity at that time.

Of course, the temperature difference between wet and dry balls is also related to other factors, such as ventilation speed, air pressure, wet ball size, wet ball wetting mode and so on. According to the temperature values of dry and wet bulbs and considering other factors, the air humidity at that time can be calculated theoretically.

Extended data

Measurement of air humidity in ancient times

China was the first country to invent the humidity measuring instrument. In the Eastern Han Dynasty, Wang Chong once said in "On Balance and Change" that it would rain if the strings were loose. The looseness of strings is caused by wet weather and elongated strings, indicating that the air humidity is high. It can be seen that ancient stringed instruments can also be used as original air humidity measuring instruments. The "hair" in modern hair hygrometer is actually the miniaturization and accuracy of ancient strings.

Lou Yuanli at the end of Yuan Dynasty and the beginning of Ming Dynasty also said in his book Tian Wu Jia Xing that if the clean strings with good quality suddenly become loose and wide, it is because the piano bed is wet; This phenomenon indicates that it will rain. He also said that if the tone of the harp strings is not well tuned, it also indicates rainy weather. This is actually because loose and wide strings reduce their pitch sensitivity, which is scientific.

In the record of Shi Jiatian, it is mentioned that an instrument is used to hang mud and charcoal on both sides of the balance, and observe the rise and fall of the balance at one end of the charcoal. This is actually the original "hygrometer". The principle is: when the weather is dry, the carbon is light and the balance tends to the soil; When the weather is wet, carbon is heavy and the balance tends to carbon.