A mechanical indicator that displays the relative humidity of a space. Traditional non-electronic analog hygrometers are generally accurate to about 10% while electronic digital versions are accurate to less than 5%. Vigilant hygrometers are accurate to 2%.
Any of several instruments used for measuring atmospheric humidity. Some types of hygrometers are: 1) psychrometer - measures the temperature difference between a wet-bulb and a dry-bulb thermometer. A sling psychrometer is mounted in a frame, then whirled in the air for ventilation. 2) hair hygrometer - measures the expansion and contraction of a human hair that is mounted under tension. A gold beater's skin hygrometer uses a proteinaceous membrane for the same type of measurement. 3) dew-point hygrometer - measures the temperature for the formation and evaporation of dew that is observed using a photoelectric cell. 4) diffusion hygrometer - measures the diffusion of water vapor through a porous membrane. 5) lithium chloride hygrometer - measures the temperature and electrical conductivity of a hygroscopic salt that becomes conductive when it absorbs water. - from Boston MFA Conservation and Art Materials Dictionary http://www.mfa.org/conservation/qsearch.htm (May 3, 2001)
The generic term for instrument that measures humidity. A specific type of hygrometer is a psychrometer. It consists of two thermometers, one wet bulb, one dry bulb. The wet bulb cools in relation to the moisture in the air.
Any instrument that measures the water vapor content of the atmosphere. There are six basically different means of transduction used in measuring this quantity and hence an equal number of types of hygrometers. These are 1) the psychrometer, which utilizes the thermodynamic method; 2) the class of instruments that depends upon a change of physical dimensions due to the absorption of moisture ( see hair hygrometer, torsion hygrometer, goldbeater's-skin hygrometer); 3) those that depend upon condensation of moisture ( see dewpoint hygrometer, frost point hygrometer); 4) the class of instruments that depend upon the change of chemical or electrical properties due to the absorption of moisture ( see absorption hygrometer, electrical hygrometer, carbon-film hygrometer element, dew cell); 5) the class of instruments that depend upon the diffusion of water vapor through a porous membrane ( see diffusion hygrometer); and 6) the class of instruments that depend upon measurements of the absorption spectra of water vapor ( see spectral hygrometer). Middleton, W. E. K., and A. F. Spilhaus, 1953: Meteorological Instruments, 3d ed., rev., Univ. of Toronto Press, 105â€“116.
Hygrometers are instruments used for measuring humidity. A simple form of a hygrometer is specifically known as a "psychrometer" and consists of two thermometers, one of which includes a dry bulb and the other of which includes a bulb that is kept wet to measure wet-bulb temperature. Evaporation from the wet bulb lowers the temperature, so that the wet-bulb thermometer usually shows a lower temperature than that of the dry-bulb thermometer, which measures dry-bulb temperature.