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The present status of an international attempt of several national metrology institutes to determine the Avogadro constant with a relative standard uncertainty better than 2ldr10-8 is presented. To this end, a world-wide collaboration has been set up to produce a 5 kg 28Si single crystal with an enrichment factor greater than 99.985%. Technological steps for the growth of the 28Si single crystal,...
The international community started recently to look for a new way to define the Kelvin. Different experiments around the world have begun. This presentation will describe very briefly the four different techniques currently used for the redetermination of k, namely the measurement of the speed of sound in pure helium-4, the determination deduce of the Doppler profile of the linear absorption line,...
The International Avogadro Coordination aims at determining the Avogadro constant by measuring the molar mass, lattice parameter and density of a 28Si single crystal. As the temperature dependent quantities are measured in different apparatuses, the consistency of the temperature measurements has to be proven. An electronic temperature reference and a standard platinum resistance thermometer (SPRT)...
The following topics are dealt with: fundamental constant, resistance, ac-dc transfer, voltage, power, impedance, magnetic variable, time and frequency measurements and standards; calibration of measurement techniques and set-ups; photonic and magnetic methods; radiofrequency measurement methods.
A new 2-electrode cell for the electro-gravimetric determination of silver has been designed and is now under test. The new set-up allows accurate galvanostatic measurements of the dissolution of the Ag electrode with a strict control on the Ag+ ion concentration in the two sides of the cell solution. The solution stability, the residue recovery, the O2 prevention and the solution filtering process...
This paper presents the French project aiming to determine the von Klitzing constant RK with an uncertainty of one part in 108. The design adopted for a new Thompson-Lampard calculable capacitor and some parts of the impedance comparison measurement chain are presented.
We have developed a Johnson noise thermometry system that is calibrated by precision waveforms synthesized with a quantized voltage noise source (QVNS). Significant improvements to the QVNS and the cross-correlation measurement electronics have dramatically reduced systematic errors and measurement uncertainty. We describe some of these improvements and discuss the potential for this system to contribute...
Within the International Avogadro Project two spheres of highly enriched 28Si crystals have been produced, to perform a new determination of the Avogadro constant NA. As one of the critical tasks the mass of the oxide layer of the spheres has to be measured.
The NPL Mk II watt balance made an initial series of measurements of Planck's constant in the period from October 2006 to March 2007. The results of these measurements differ significantly from those recently published by NIST. Watt balance research at NPL is continuing until March 2008 aiming to reduce the uncertainty associated with the NPL measurement and to further investigate possible sources...
The watt balance compares electrical power and mechanical power to determine Planck's constant h in SI units. If the definition of the kilogram in the SI is altered to fix the value of Planck's constant this will remove the last artefact standard from the SI and the watt balance will provide a way to realise the SI mass unit. At present there are three operational watt balances, with more planned...
A simple setup for the accurate measurement of Johnson noise of a resistor is here presented. The setup is composed of a digital correlation spectrum analyzer, and of a calibration signal source traceable to ac voltage and frequency standards. If resistor temperature is measured, an estimate of the Boltzmann constant kB can be obtained. Presently, measured kB has a relative error below 1times10-3...
A new set of values of the basic fundamental constants has been recommended by the Committee on Data for Science and Technology (CODATA) (http://phvsics.nist.gov/cuu/Constants/). It is based on a least-squares adjustment that incorporates new data that became available before the closing date of 31 December 2006 (known as the 2006 LSA). A number of key advances in experiment and theory have led to...
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