Classification and function of thermometer and hygrometer:

Thermometer and hygrometer are used to measure the temperature and humidity of the environment to determine the environmental conditions for product production or storage. It is also used in people's daily life. It is widely used.

Concept of humidity:

When there is a lot of water vapor in the air, we say that the air is humid. Scientists often use relative humidity to describe the amount of water vapor in the air. Simply put, imagine that the air is a towel. If you pour a cup of water, you can use a towel to absorb the water. But in fact, the towel can actually absorb more than a cup of water. Maybe it can absorb five to ten cups of water. The amount of water vapor in the water is only a part of the water vapor that can be in the air, so the relative humidity is a percentage. When the relative humidity is 100%, the air is saturated. Just like a completely wet towel, the air can no longer take moisture. When the relative humidity is 100% and the air is saturated, evaporation and deposition are in equilibrium. Reaching equilibrium again shows the amount of evaporation increase as water precipitation.

Water vapor in the air is called humidity. Because water vapor molecules are so tiny that they cannot be seen, people who study humidity have developed creative ways to measure the amount of water vapor.

History of the hygrometer:

Perhaps Leonardo, a man born in Italy in the 15th century, was the first to come up with an instrument to measure the amount of water vapor in the air. He placed a piece of dry cotton on one side of a celestial being. He then placed an object of exactly the same weight as the cotton on the other side of the celestial being. As the dry cotton absorbs water vapor from the air, it becomes heavier and begins to fall on that side of the celestial being. The difference between the two weights is a measure of the humidity.

Today scientists measure relative humidity using an instrument called a "psychrometer". A "psychrometer" is made of two thermometers strapped together. The bulb of one thermometer is wrapped with a material soaked in water. To begin measuring relative humidity, the psychrometer is rotated until the wrapped thermometer maintains a stable temperature that is always lower than the dry thermometer. The actual air temperature is measured by the dry thermometer. The difference between two temperatures is called "wet-bulb depression" and is the result of evaporation of water from the substance. Scientists record the temperature of the lower dry thermometer and the "wet-bulb depression", and then make a graph to calculate the relative humidity. This is also the working principle of the wet-bulb hygrometer.

Classification of hygrometers:

Classification by measurement method

*Wet-bulb hygrometer

*Dew point hygrometer

*Hair hygrometer

*Coulomb hygrometer

*Electrochemical hygrometer

*Optical hygrometer