A New Primary Dew-Point Generator at TUBITAK UME

An implementation of a new low-range primary humidity generator as a part of an international collaboration between TUBITAK UME and VTT MIKES was initiated as a EURAMET Project Number 1259. The dew-point generator was designed and constructed within the scope of the cooperation between TUBITAK UME and VTT MIKES in order to extend the dew-point temperature measurement capability of Humidity Laboratory of TUBITAK UME down to -80 degrees C. The system was thoroughly characterized and validated at TUBITAK UME to support the evidence for dew-point temperature uncertainties. The new generator has a capability of operating in the range of -80 degrees C to + 10 degrees C, but at the moment, it was characterized down to -60 degrees C. The core of the generator system is a saturator which is fully immersed in a liquid bath. Dry air is supplied to the saturator through a temperature-controlled pre-saturator. The operation of the system is based on the single-pressure generation method with a single pass, i.e., the dew-point temperature is only controlled by the saturator temperature, and the humidity-controlled air is not returned to the system after leaving of the saturator. The metrological performance of the saturator was investigated thoroughly at both National Metrology Institutes. The pre-saturator was also tested using a thermostatic bath at VTT MIKES prior to sending them to TUBITAK UME. This paper describes the principle and design of the generator in detail. The dew-point measurement system and the corresponding uncertainty analysis of the dew-point temperature scale realized with the generator in the range from - 60 degrees C to 10 degrees C is also presented.