Improvements in the realization of the triple point of water in metallic sealed cells at LNE-Cnam
Since 2008, LNE-Cnam has been working on the development of metallic sealed cells for the water triple point, temperature 273.16 K. The objective is to perform calibrations of capsule-type standard platinum resistance thermometers employing adiabatic calorimetry techniques, in order to get the lowest possible level of measurement uncertainty. After the realization of a preliminary prototype, the full system composed of new cells and an adiabatic calorimeter has been significantly improved. New cells have been manufactured, an ameliorated calorimeter has been built and improved procedures have been set up to clean, fill and seal the cells. Despite a remaining discrepancy of about 0.8 mK between metallic and traditional water triple point cells, the reproducibility of metallic cells has been improved to 0.1 mK. This paper describes the new devices developed and the results obtained. This work has been developed within the frame of the European metrology research program (EMRP) joint research project ‘SIB10 NOTED’. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.