Measurement of Relative Humidity and Hygrometer Calibration in Low Temperature Environments

It has been always difficult in measurement of relative humidity and hygrometer calibration in low temperature. Current hygrometer calibration in laboratory is usually done in normal temperature. Though most hygrometer tests have been temperature compensated with temperature coefficient offered, it is still not easy to guarantee the accuracy of hygrometer in environment several tens of degrees below zero, the error of those hygrometers unknown. The calibration method discussed in this paper is fit for calibration temperature 0 °C to -40°C, reliable and accurate.