This paper describes a quantum realization of the pascal based a helium absolute refractometer at 532 nm. The short-term stability in pressure is ± 2 mPa with a resolution in pressure of this new optical pressure standard is better than 1 mPa with temperature stability about 1 mK. A new design of the refractometer is presented to have better temperature stability and accurate temperature measurements to reach uncertainties in pressure better than current conventional methods.
The measurement of negative gauge pressure is a field of increasing importance in science and industry. One of the main aims of the EMPIR Joint Research Project 14IND 06 pres2vac is to develop guidelines for it. We present a comparison of three different methods for measuring negative gauge pressure: (i) using two absolute pressure measuring instruments, (ii) generating a negative gauge pressure in the bell jar of the pressure balance, and (iii) using a 'hanging piston' pressure balance. The advantages and drawbacks are discussed and some preliminary results presented.
The value of the Planck constant h was determined in 2014 by means of the LNE watt balance experiment. The relative standard uncertainty was 31 parts in 10 8 . This first determination was performed in air with a 500 g mass standard made from XSH Alacrite. The main uncertainty components in air associated with the mass involve the calibration, the mass stability, the buoyancy correction and the magnetic interaction correction. The combined relative uncertainty due to the mass is 7.2 parts in 10 8 . The use in 2016 of a mass standard made from platinum iridium alloy significantly reduces the component of uncertainty arising from the mass standard for a Planck constant measurement either in air or under vacuum. The relative uncertainty due to this contribution is estimated to be about 3 parts in 10 8 in air and one part in 10 8 under vacuum. The future system for the dissemination of the mass unit using the LNE watt balance will be based on a primary realization with three 500 g mass standards made from platinum-iridium alloy, pure iridium and Udimet 720 respectively, coupled with a pool of kilograms made from different materials. Pure iridium and Udimet 720 are new materials to make reference mass standards proposed by CNAM and LNE respectively and have never been used by any NMI for manufacturing mass standards until now. Some new results concerning their surface behavior are given.
Résumé. La nouvelle référence de pression relative dans le domaine de 1,5 à 50 MPa est définie à partir de trois ensembles piston-cylindres (EPC). Ces ensembles de 50 kPa/kg (15,8 mm de diamètre) peuvent être utilisés en jeu contrôlé et sont adaptés pour être montés sur les balances de référence haute pression d'huile, équipées chacune d'un ensemble de masses de 1000 kg. La section effective du premier EPC a été déterminée par des mesures dimensionnelles avec une incertitude relative élargie (k=2) estimée à 1,0 x 10 -5 , puis comparée aux autres ensembles. Par ailleurs, les résultats dimensionnels ont été confirmés à basse pression par comparaison directe avec la référence de 1 MPa. Les coefficients de déformation des ensembles piston-cylindre ont été déterminés expérimentalement avec un ensemble 200 MPa, et comparés aux valeurs théoriques calculées par la méthode des éléments finis (MEF). Le bilan d'incertitude sur la mesure de pression pour cette référence est présentée. L'incertitude élargie est estimée à 15 Pa + 1,2 x 10 -5 x p.Abstract. The new LNE gauge pressure standard in the range 1,5 to 50 MPa, is composed of three pistoncylinders assemblies (PCA). These are 50 kPa/kg controlled clearance piston-cylinder (diameter of 15,8 mm) designed to be adapted on the oil-operated high-pressure reference balances using a 1000 kg mass set. The effective area of the first PCA was determined by dimensional measurements with a expanded (k=2) relative uncertainty estimated to be 1.0 x 10 -5 , and then compared with the other ones. Moreover, the dimensional results were confirmed in the lower pressure range by direct comparison with the 1 MPa reference. The distortion coefficients of the piston-cylinder assemblies were experimentally determined with the 200 MPa unit, and compared with the values calculated by Finite Element Method (FEM). The pressure measurement uncertainty budget for this standard is detailed. The expanded uncertainty is estimated to be 15 Pa + 1.2 x 10 -5 x p.
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