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TitleOn the concept of relative humidity
Publication TypeJournal Article
Year of Publication2006
AuthorsLovell-Smith, J.W., and Pearson H.
Pagination129 - 134
Date Published2006
ISSN00261394 (ISSN)
KeywordsAtmospheric humidity, Gas temperature, Gases, Humidity measurement, Humidity sensors, Problem solving, Saturation (materials composition), Saturation vapor pressure, Sensors, Temperature distribution, Vapor pressure
AbstractStandard definitions of relative humidity ψ of a gas at temperature t and pressure P involve the ratio of some humidity quantity to the same quantity when the gas is saturated at the same temperature and pressure. These definitions do not apply under certain conditions, notably when the gas is pure unsaturated water vapour, and more generally when the theoretical saturation vapour pressure is greater than the actual pressure. The use of impedance-based relative humidity sensors to measure humidity under such conditions is increasingly common and consequently other less well defined definitions may be used over which there is some debate and confusion in the metrological community. In this paper we identify the source of the problem, explore possible definitions and champion a simple and useful definition of relative humidity which extends the traditional definition to cover the whole range. © 2006 BIPM and IOP Publishing Ltd.

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