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Sensors 2017, 17(2), 368;

Uncertainty Analysis in Humidity Measurements by the Psychrometer Method

Department of Bio-industrial Mechatronics Engineering, National ChungHsing University, Taichung 40227, Taiwan
Author to whom correspondence should be addressed.
Academic Editors: Jesús M. Corres and Francisco J. Arregui
Received: 11 December 2016 / Revised: 4 February 2017 / Accepted: 9 February 2017 / Published: 14 February 2017
(This article belongs to the Special Issue Humidity Sensors)
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The most common and cheap indirect technique to measure relative humidity is by using psychrometer based on a dry and a wet temperature sensor. In this study, the measurement uncertainty of relative humidity was evaluated by this indirect method with some empirical equations for calculating relative humidity. Among the six equations tested, the Penman equation had the best predictive ability for the dry bulb temperature range of 15–50 °C. At a fixed dry bulb temperature, an increase in the wet bulb depression increased the error. A new equation for the psychrometer constant was established by regression analysis. This equation can be computed by using a calculator. The average predictive error of relative humidity was <0.1% by this new equation. The measurement uncertainty of the relative humidity affected by the accuracy of dry and wet bulb temperature and the numeric values of measurement uncertainty were evaluated for various conditions. The uncertainty of wet bulb temperature was the main factor on the RH measurement uncertainty. View Full-Text
Keywords: measurement uncertainty; psychrometer constant; dry bulb; wet bulb; humidity; regression analysis measurement uncertainty; psychrometer constant; dry bulb; wet bulb; humidity; regression analysis

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Chen, J.; Chen, C. Uncertainty Analysis in Humidity Measurements by the Psychrometer Method. Sensors 2017, 17, 368.

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