Humidity measurement electric hygrometer

Smith, PR. 1971. The determination of equilibrium relative humidity or water activity in foods A literature review. The British Food Manufacturing Industries Research Association, U.K. Stekelenburg, F.K. and Labots, H. 1991. Measurement of water activity with an electric hygrometer. Ini. J. Food Sci. Technol. 26 111-116. Stoloff, L. 1978. Calibration of water activity measuring instruments and devices Collaborative study. J. AOAC 61 1166-1178. 

Electric hygrometers have been the fastest-growing form of humidity measurement in recent years. They measure the electrical resistance, capacitance, or impedance of a film of moistureabsorbing materials exposed to the gas. A wide variety of sensing... 

Electrical hygrometers typically measure the electrical resistance of a substance, such as hthium chloride or of a semiconductor device which varies with the humidity. The change in resistance is indicated by the calibrated instrument. The response of such an instrument can be slow because the previously absorbed moisture should be completely replaced by the flesh incoming moist air. Also, regeneration of the saturated material may become necessary for fresh readings. 

Many standard lab activities use simple measuring devices such as a thermometer, a clock (or wristwatch, chronometer or stopwatch), a ruler (or micrometer or tape measure), or an electrical meter (e.g. voltmeter, ammeter). Humidity is measured with a hygrometer. 

John Frederic Daniell (1790-1845). English chemist and meteorologist. In addition to invention of the Daniell cell, an improvement over Volta s electric pile, Daniell made contributions to instrumental meteorology through his invention of a dew-point hygrometer that became a standard instrument for measuring relative humidity. 

The main types of instruments measuring humidity in gases are various types of hygrometers (gravimetric, mechanical, condensation, infrared absorbance detector, electric sensor, thermal conductivity, Al203/sili-con, P2O5) and psychrometers. 

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