Measuring shell resonances of spherical acoustic resonators

International audienceCoupling between gas and shell is a concern in the experiment used at LNE-CNAM to determine the Boltzmann constant kB by an acoustic method. As the walls of real resonators are not perfectly ridig, some perturbations occur in the frequency range of the acoustic resonances measured within helium gas contained in the caivity. As a contribution for a better understanding of the phenomenon, we have built an experiment to measure the shell modes of the spherical resonators in use in our laboratory. We report here a work in progress to assess these modes using a hammer blow method together with modal analysis. The study is carried out with air-filled, copper-walled, half-litre quasi-spherical resonator in the frequency range from 1 Hz to 20 kHz. Our results show that the shell modes expand into multiple resonances of similar modal shape, including the "breathing" mode. We confirm the observations reported in other works [4,6] of shell perturbations at other frequencies than the breathing frequency

The IMERAPlus Joint Research Project For Determinations Of The Boltzmann Constant

Abstract. To provide new determinations of the Boltzmann constant, k, which has been asked for by the International Committee for Weights and Measures concerning preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole, an iMERAPlus joint research project has coordinated the European activities in this field. In this major European research project the Boltzmann constant has been determined by various methods to support the new definition of the kelvin. The final results of the project are reviewed in this paper. Determinations of the Boltzmann constant k were achieved within the project by all three envisaged methods: acoustic gas thermometry, Doppler broadening technique, and dielectric constant gas thermometry. The results were exploited by the interdisciplinary Committee on Data for Science and Technology (CODATA) in their 2010 adjustment of recommended values for fundamental constants. As a result, the CODATA group recommended a value for k with a relative standard uncertainty about a factor of two smaller than the previous u(k)/k of 1.7×10 −6

The European Metrology Programme for Innovation and Research project: Implementing the new kelvin 2 (InK2)

The International System of Units (SI) is to be redefined with implementation set to be on World Metrology Day (20th May 2019). Under the auspices of the Consultative Committee of Thermometry (CCT) the world thermometry community has been working together to ensure a smooth and effective redefinition of the kelvin. A large part of that activity has been coordinated through the European Metrology Programme for Innovation and Research: "Implementing the new kelvin" projects. This paper describes the InK2 project contribution

The absolute salinity of seawater, its real components and its measurands

Salinity is an essential quantity to calculate many of physical properties of oceans, but It is also a quantity hardly definable considering the complexity of the middle in its bio-geo-chemical composition and the imperfections of the existing measurement techniques. The TEOS-10 gives several definitions to the notion of absolute salinity, usable in function of the properties to study, but they are based on the concept of a constant elemental composition of seawater, so that, if its major inorganic components are well known, its real composition vary in time and space and its determination is still a challenge. Most of salinity calculations are based on conductivity measurements. This communication reviews other techniques which are used or could be used to assess the absolute salinity of seawater, and question about the mesurand of these techniques and the possibility to redefine the concept of salinity from physical properties

An Adiabatic Calorimeter for the Realization of the ITS-90 in the Cryogenic Range at the LNE-CNAM

The LNE-CNAM, in cooperation with the IPN, has recently developed a new cryogen-free adiabatic calorimeter, to realize the International Temperature Scale of 1990 (ITS-90) in the temperature range between 6 K and 84 K. The new calorimeter, cooled by a closed-cycle Gifford-McMahon refrigerator, is equipped with three thermal shields and two separate vacuum chambers, to minimize the effect of parasitic heat fluxes. The inner adiabatic chamber can accommodate either a multi-compartment cell--containing the triple points of hydrogen, neon, oxygen, and argon, to realize the ITS-90 between 14 K and 84 K--or a comparison block for thermometers, the calibration of rhodium-iron (RhFe) thermometers between 6 K and 24 K. The use of a cryogen-free system and a fully computer-controlled measurement chain allow long lasting experiments and good thermal control, resulting in a substantial reduction of the measurement uncertainties. The new adiabatic calorimeter has been successfully tested at the LNE-CNAM. The overall standard uncertainties in the realization of the ITS-90 have been reduced from 2.08 mK to 0.37 mK at the hydrogen triple point, from 1.40 mK to 0.30 mK at the triple point of neon, and are maintained below 0.26 mK at the triple points of oxygen and argon. In the temperature range between 6 K and 24 K, calibrations of rhodium-iron resistance thermometers have been carried out with a standard uncertainty of the order of 0.80 mK

A Closed-cycle Refrigerator for Realizing Low-Temperature Fixed Points

In order to accommodate the MULTICELLS Project output devices, a cryogen-free refrigerator has been designed and built at the Istituto di Metrologia “G.Colonnetti” (IMGC). The cryostat is a Gifford-McMahon refrigerator with two cooling stages. With the wiring and radiation loading on the shields, the lowest temperature of the second stage is about 10 K. The refrigerator has been designed as an adiabatic calorimeter: it can be used to reproduce the cryogenic ITS-90 defining fixed points (triple points) or to perform accurate thermometer comparisons at low temperatures. In order to prevent serious damage to capsule-type resistance thermometers, the mechanical vibrations due to the moving piston have been measured at the cold tip and in the experimental chamber. To reduce the vibration level at the thermometer wells, the experimental apparatus has been appended by means of carbon reinforced fibres: a reduction of the vibrations of about one order of magnitude has been observed. The cryostat is interfaced with a system for process control and data acquisition. Therefore, triple point temperature measurements have been carried out automatically, with values for the heat capacity measured at temperatures close to the phase transition points. The main measurement steps include the approach to the phase transition and temperature measurement at the triple point. During the approach, a MATLAB routine using a statistical hypothesis test is used for the phase transition detection. The temperature control system, implemented in a LabVIEW™ program running on a PC, monitors and controls the temperature of the whole system during the measuring process. This paper describes firstly the design and the construction of the cryostat. The operational characteristics of the refrigerator and its performance during the triple point measurements are also presented. Finally, as an example of the thermometer calibration at a cryogenic gas fixed-point of the ITS-90, the realisation, during development of the system, of the neon triple point with an expanded uncertainty of the order of 0,1 mK is reported