Humidity meter gauge is a physical analysis instrument for measuring gas humidity. Humidity refers to the content of water vapor in the gas. There are two ways of expressing absolute humidity and relative humidity. Absolute humidity refers to the absolute content of water vapor in gases. The most commonly used unit is g/m^3. At a certain temperature and pressure, the water vapor content per unit volume has a certain limit, which is called saturated water vapor content. Relative humidity refers to the ratio of the absolute content of water vapor in gas to the saturated content of water vapor in volume gas at the same temperature and pressure. The commonly used symbol is% R.H. Hygrometers are widely used in many fields, such as ultra-pure metal smelting, textile processing, papermaking and dyeing, food storage and meteorological measurement, etc. Hygrometers are often used to measure or control the humidity of air or industrial process gases.
In Historical Records, a kind of balance device is recorded, with earth and charcoal on both sides of the balance. The book Huainanzi explains this device: when the weather is dry, the charcoal is light, and the balance tilts toward the soil; when the weather is wet, the charcoal becomes heavier, and the balance tilts toward the charcoal. This is the earliest measurement of air humidity.
The earliest hygrometer in Europe appeared in the 15th century. An Italian invented a method of measuring humidity. The principle of this method is the same as that of using the balance device in China. A dry cotton ball is placed at one end of the balance, and weights of the same weight are placed at the other end. When cotton absorbs water vapor in the air, it sinks and the balance tilts to the cotton side. According to the amount of water vapor absorbed by cotton, the content of water vapor in air can be determined.
The humidity meter gauge
used now include hair humidity meter gauge, wet-dry bulb humidity meter gauge and lithium chloride humidity meter gauge. Their principles are different, but the relative humidity is measured.