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Hygrometers are the most accurate way to measure humidity and can use hair, psychrometry, electrical resistance, or chemicals. Satellites provide the most accurate global readings.
There are various methods of measuring humidity, most of which use a device called a hygrometer. The hygrometer can work in various ways, depending on the type, and is the most accurate method of determining air humidity. Some are connected to other devices called humidifiers, which are connected to humidifiers and dehumidifiers and help control the level of humidity in the air.
One type of hygrometer uses hair, usually human hair, which is attached to levers inside the unit. When the humidity in the air increases, the hair lengthens and then contracts when it decreases. The levers are usually connected to a dial that displays the humidity reading.
Other methods of measuring humidity using a hygrometer include the psychrometer and electrical hygrometers. Both methods are quite accurate, although the electric version is more sophisticated in design. There are also chemical hygrometers that are similar in effectiveness.
A psychrometer, also known as a two-bulb hygrometer, works by using two thermometer bulbs. A light bulb is dry and measures the air temperature. The other bulb is covered with a substance, usually wick or muslin, and then moistened. After being moistened, the bulb is exposed to moving air, either by a fan or by throwing the psychrometer into the air. As water evaporates into moving air, the temperature on the thermometer will decrease. The amount of temperature drop helps tell the amount of moisture in the air.
This method of measuring humidity is similar to swimming on a hot, breezy day. Before entering the water, the temperature feels warm even with a breeze. If one jumps into the water and gets wet and then comes back out, the breeze suddenly feels very cool. This is called evaporative cooling. In general, the lower the air humidity, the greater the drop in temperature.
Electrical hygrometers work by measuring the electrical resistance of a particular substance. Most substances, such as lithium chloride, have varying resistances to an electric current based on the humidity in the air. These differences are then calculated to display the humidity.
Chemical hygrometers work by using a chemical and exposing it to air. The chemical will be measured before being exposed and then again after. Any changes in weight indicate how much moisture there is in the air.
While hygrometers are fairly accurate methods of measuring humidity, the most accurate way to test humidity on a global scale is through the use of satellites. Specialized satellites can detect the exact humidity in the troposphere, thus providing accurate readings on weather conditions around the world. They are able to track sudden changes in humidity and weather conditions to predict storms, wind and weather changes.
