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hygrometer
hygrometer , instrument used to measure the moisture content of a gas, as in determining the relative humidity of air. The temperature at which dew or frost forms is a measure of the absolute humidity—the weight of water vapor per unit volume of air or other gas at the temperature before cooling. Knowing absolute humidity and air temperature, the observer can calculate relative humidity. The most common type of hygrometer is the dry- and wet-bulb psychrometer . It consists of two identical mercury or electrical thermometers , one of which has a wet cotton or linen wick around its bulb. Evaporating water from the wick absorbs heat from the thermometer bulb, causing the thermometer reading to drop. The difference between dry-bulb and wet-bulb temperatures are compared on psychrometric charts. The temperature at which dew forms, called the dew point, is determined by a dew-point, or condensation-type, hygrometer, which is basically a mirror, usually of polished metal, cooled until dew or frost forms on it. Various cooling methods employ compressed carbon dioxide, dry ice, liquid air, or mechanical refrigeration. When dew or frost forms on the mirror, the temperatures between when dew appeared and when it disappeared is the dew point and is read with optical, electrical, or nuclear techniques. Because human observation varies, photoelectric cells are sometimes used to register the time at which the mirror fogs. Another type of hygrometer works on the principle that electrical resistance varies in a material that absorbs moisture, with the resistance to a current passing between wires measured by special sensors. The most accurate way to measure humidity is with an electric hygrometer, in which a known volume of gas passes over a hygroscopic, or moisture-absorbing, material such as phosphorus pentoxide. It is weighed before and after to determine how much water it took out of the gas. The older types of mechanical hygrometer use human hair, which stretches as it absorbs moisture, with a linkage connecting the center of a bundle of hairs under tension to a pointer. Another uses goldbeater's skin, a membrane from the intestines of oxen. Some materials can determine relative changes in humidity because they change color as they absorb moisture. |
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"hygrometer." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. 14 Feb. 2012 <http://www.encyclopedia.com>. "hygrometer." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. (February 14, 2012). http://www.encyclopedia.com/doc/1E1-hygromet.html "hygrometer." The Columbia Encyclopedia, 6th ed.. 2008. Retrieved February 14, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-hygromet.html |
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hygrometer
hy·grom·e·ter / hīˈgrämitər/ • n. an instrument for measuring the humidity of the air or a gas. DERIVATIVES: hy·gro·met·ric / ˌhīgrəˈmetrik/ adj. hy·grom·e·try / -trē/ n. |
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"hygrometer." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 14 Feb. 2012 <http://www.encyclopedia.com>. "hygrometer." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (February 14, 2012). http://www.encyclopedia.com/doc/1O999-hygrometer.html "hygrometer." The Oxford Pocket Dictionary of Current English. 2009. Retrieved February 14, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-hygrometer.html |
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hygrometer
hygrometer Instrument used to measure the humidity of the atmosphere. One type, the psychrometer, compares the wet and dry bulb temperatures of the air; other types measure absorption or condensation of moisture from the air, or chemical or electrical changes caused by that moisture.
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"hygrometer." World Encyclopedia. 2005. Encyclopedia.com. 14 Feb. 2012 <http://www.encyclopedia.com>. "hygrometer." World Encyclopedia. 2005. Encyclopedia.com. (February 14, 2012). http://www.encyclopedia.com/doc/1O142-hygrometer.html "hygrometer." World Encyclopedia. 2005. Retrieved February 14, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-hygrometer.html |
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hygrometer
hygrometer (hy-grom-i-ter) n. an instrument for measuring the relative humidity of the atmosphere, i.e. the ratio of the moisture in the air to the moisture it would contain if it were saturated at the same temperature and pressure.
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"hygrometer." A Dictionary of Nursing. 2008. Encyclopedia.com. 14 Feb. 2012 <http://www.encyclopedia.com>. "hygrometer." A Dictionary of Nursing. 2008. Encyclopedia.com. (February 14, 2012). http://www.encyclopedia.com/doc/1O62-hygrometer.html "hygrometer." A Dictionary of Nursing. 2008. Retrieved February 14, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O62-hygrometer.html |
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hygrometer
hygrometer An instrument that is used to measure atmospheric humidity. Types include the wet-bulb–dry-bulb, dew-point, and hair hygrometers, and there is one type based on electrical resistance. See also psychrometer.
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MICHAEL ALLABY. "hygrometer." A Dictionary of Ecology. 2004. Encyclopedia.com. 14 Feb. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "hygrometer." A Dictionary of Ecology. 2004. Encyclopedia.com. (February 14, 2012). http://www.encyclopedia.com/doc/1O14-hygrometer.html MICHAEL ALLABY. "hygrometer." A Dictionary of Ecology. 2004. Retrieved February 14, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-hygrometer.html |
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hygrometer
hygrometer Instrument for measuring atmospheric humidity. Types include the wet-bulb—dry-bulb, dew-point, and hair hygrometers, and there is one type based on electrical resistance. See also PSYCHROMETER.
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AILSA ALLABY and MICHAEL ALLABY. "hygrometer." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 14 Feb. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "hygrometer." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (February 14, 2012). http://www.encyclopedia.com/doc/1O13-hygrometer.html AILSA ALLABY and MICHAEL ALLABY. "hygrometer." A Dictionary of Earth Sciences. 1999. Retrieved February 14, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-hygrometer.html |
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hygrometer
hygrometer An instrument that is used to measure atmospheric humidity.
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MICHAEL ALLABY. "hygrometer." A Dictionary of Zoology. 1999. Encyclopedia.com. 14 Feb. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "hygrometer." A Dictionary of Zoology. 1999. Encyclopedia.com. (February 14, 2012). http://www.encyclopedia.com/doc/1O8-hygrometer.html MICHAEL ALLABY. "hygrometer." A Dictionary of Zoology. 1999. Retrieved February 14, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O8-hygrometer.html |
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