A hygrometer is an instrument used to measure the humidity of air or some other gas, which is the amount of water vapor it contains. There are several types of hygrometers that are used to measure humidity, including:
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Mechanical hygrometers: These use organic substances such as goldbeaters skin or human hair that contract and expand in response to humidity. The contraction and expansion of the hair element in a mechanical hygrometer causes the spring to move the needle on the dial.
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Electrical hygrometers: These measure the change in electrical resistance of a thin layer of lithium chloride or a semiconductor device as the humidity changes.
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Dew-point hygrometers: These consist of a polished metal mirror that is cooled at a constant pressure and constant vapor content until moisture just starts to condense on it. The temperature of the metal at which condensation begins is the dew point.
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Psychrometers: These use two thermometers, one of which is covered with a wet wick. The difference in temperature between the two thermometers is used to calculate the relative humidity.
Hygrometers are used in a variety of settings, including residential settings to assist in humidity control, the coating industry, manufacturing industries, hospitals, incubators, agricultural production and storage, humidors, museums, and meteorology. They are also used to prevent mold and mildew development in bathrooms, kitchens, and other "wet" areas.
