Influence Factors and Uncertainty Analysis of Relative Humidity Measured by Psychrometer

Abstract

Based on the measurement principle of psychrometer and experimental data, the influence of wind speed on humidity measurement is analyzed, and the uncertainty of humidity measured by psychrometer is evaluated by GUM method. The research results show that under the condition of high temperature and high humidity, the relative humidity measured by psychrometer is not sensitive to wind speed. When the relative humidity is 90%RH and air temperature is 85°C, the difference of relative humidity calculated by using different psychrometer coefficients is 0.03% RH. With the decrease of dry-bulb temperature and relative humidity, the influence of wind speed on relative humidity measurement gradually increases. When the relative humidity is 20%RH and air temperature is 20°C, the difference of relative humidity calculated by using different psychrometer coefficients is 2.64% RH. The main uncertainty of relative humidity measured by psychrometer is introduced by psychrometer coefficient which is a function of wind speed. Measurement uncertainty decreases with the increase of relative humidity while at the same dry-bulb temperature.