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Calculating the force on a reference mass for the electronic kilogram experiment requires using both absolute and relative gravity meters to measure the acceleration of gravity. Tests have been conducted to achieve an uncertainty of less than 1 part in 108.
The NIST electronic kilogram has had three published results with successively smaller uncertainties. In the present design, there are several measurement components that have uncertainties that are difficult to reduce further. These limiting uncertainties are discussed.
We have measured Newton's gravitational constant with a commercially available mass comparator. In this experiment, the difference of the gravitational force of 13,600 kg mercury on two 1.1 kg copper masses was measured with a relative statistical uncertainty of 16.3times10-6. Including the systematic uncertainties we determine the gravitational constant G to be 6.674 252(122)times10-11 m3kg-1s-2.
After several mechanical improvements, the METAS watt balance has been fully operational during the last 18 months. The reproducibility, alignment issues and the long term stability of the apparatus are discussed.
We have determined the influence of alternative definitions for the kilogram and the ampere on the uncertainty of h, e and mu. This has been achieved with a least-squares adjustment of a limited set of observational equations. We have evaluated the residual errors (and their uncertainties) from this adjustment, and used these to determine expansion factors to achieve results that are self-consistent...
We describe a mass comparison system in which a test mass artifact in air can be directly compared to a standard mass artifact in vacuum using the same high precision comparator balance. The system uses a magnetic levitation technique to couple the weighing pan of the comparator balance in vacuum to the test mass in air. We will discuss motivation, design considerations, and preliminary results.
This paper describes the main progress on the LNE watt balance project since 2004. Development of different parts and structure of the watt balance including starting their assembly are presented.
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...
This paper describes a prototype of a pendulum for deriving the kilogram from the electrical quantities. The equivalent inertial mass of the pendulum is derived from the measurement of the position of the moving assembly and the electrical quantities (electromotive force and current) on a coil as a function of time. The prototype shows the functionality of the method, identifying the operative limits...
The project for the realisation of the kilogram using the ldquosuperconducting magnetic levitation methodrdquo has been continued at MIKES. From the results of the subproject, calorimetric measurements, we have come to the conclusion that the realisation of the kilogram based on the levitation method is difficult with the present knowledge of energy losses in superconductors due to incomplete Meissner...
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