Using a two-temperature - Two-pressure humidity generator for the in-situ calibration of chilled mirror hygrometers for a wide temperature range

The necessary calibration of chilled mirror hygrometers used as reference standards in humidity calibration can be done in-situ parallel to the calibration process using a humidity generator controlled by sensors traced back to the national standards. A two-temperature - two-pressure humidity generator allowing a dew point from -20degreesC up to 70degreesC and a working temperature up to 80degreesC has been developed. All pressures and temperatures are measured using sensors being traceable to the pressure and temperature standards with very low uncertainties. The calibration of the chilled mirror system which is normally used for humidity calibration of hygrometers can be done in-situ using the physical parameters of the humidity generator. The design of the system, the calibration procedure, and the uncertainty are discussed.