Uncertainty evaluation of humidity sensors calibrated by saturated salt solutions

This study evaluates the sources of uncertainty for two types of humidity sensors. The standard humidity environment was made by several saturated salt solutions. These uncertainty sources include predicted values of calibration equation, reference humidity source, temperature variation effect, nonlinear and repeatability, and resolution source. The study also dealt with the effect of calibration methods and calibration equations on the uncertainty. The polynomial calibration equation had better predictive performance than the linear equation for two types of humidity sensors.The uncertainty analysis shows that the predicted uncertainty is the main source for combined uncertainty. No significant difference of the uncertainty for resistive sensor was found between classical method and inverse method. However, the predicted uncertainty of inverse method is significantly lower than that of classical method for capacitive humidity sensor.