Numerical and Experimental Study of the Hydrostatic Pressure Correction in Gas Thermometry: A Case in the SPRIGT

Single-pressure refractive index gas thermometry (SPRIGT) is a new type of primary thermometry, which needs an extremely stable working pressure (stability < 4 ppm). In practice, the pressure control system at room temperature is located above the cold resonator at 5 K to 25 K, and a long pressure tube is used to connect them, which entails a hydrostatic pressure correction (HPC). To this end, a three-dimensional (3D) Computational Fluid Dynamics (CFD) simulation model of the pressure tube has been developed and compared with experimental results. First, to verify the simulation results, the helium-4 gas pressure in the center of the resonator was measured using a determination of the refractive index by microwave resonance coupled with the knowledge of the temperature. Results of simulation and experiment showed good agreement. Thereafter, based on this CFD simulation, the non-linear temperature distribution in the vertical pressure tube and the uncertainty caused by this non-linear phenomenon were calculated. After this, the validity of the isothermal assumption to simplify the calculation of the HPC was verified. Finally, the effect of heating on the pressure was studied and its impact found to be negligible. To the best of our knowledge, this is the first time experimental and simulation results have been compared for the HPC. The results are expected to be more generally applicable to the accurate determination of pressure in cryostats

A second sound thermometer as a temperature transfer standard from 0,7K down to 0,01K

AC

Acoustic Resonator Experiments at the Triple Point of Water: First Results for the Boltzmann Constant and Remaining Challenges

We report on two sets of isothermal acoustic measurements made with argon close to the triple point of water using a 50mm radius, thin-walled, diamond-turned quasisphere. Our two isotherms yielded values for the Boltzmann constant, kB, which differ by 0.9 parts in 106, and have an average value of kB = (1.380 649 6 ± 0.000 004 3)×10-23J · K-1. The relative uncertainty is 3.1 parts in 106, and the average value is 0.58 parts in 106 below the 2006 CODATA value (Mohr et al. Rev Mod Phys 80:633, 2008), and so the values are consistent within their combined (k = 1) uncertainties.JRC.D.3-Knowledge Transfer and Standards for Securit

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