Keywords:relative humidity, humidity generation, uncertainty
The high accuracy and good long-term stability become essential for relative humidity sensors as relative humidity measurements have become more important in many industries. In this study, the uncertainty analysis of the relative humidity generation with the NMIJ two-pressure two-temperature humidity generator was conducted in order to improve the reliability of the calibration and the performance evaluation of relative humidity sensors. Relative humidity in a test chamber of the generator is calculated from dew point and temperature of the moist air. The uncertainty of the temperature and dew point distribution in the chamber, which are two of the major uncertainty components of relative humidity generation and calibration, were estimated. Other uncertainty factors such as the self-heating of thermometers were also evaluated, and the total uncertainty was estimated for the generation of relative humidity from 10 %rh to 98 %rh at 23 °C.