29.09.2005
After having been used for more than 17 years, the comparator balance of PTB used so far as prototype balance is replaced by a high-resolution 1 kg vacuum mass comparator of the latest generation.
Prototype balances are of special importance for the dissemination of the unit of mass and the realisation of the mass scale. They are used to compare the mass of the 1 kg stainless steel primary standards with the national kilogram prototype made of platinum-iridium. In addition, this balance will be used at PTB for the realisation of the mass scale in the range from 1 kg to 100 g and for mass determinations within the scope of international comparison measurements (key comparisons) as well as for the performance of calibrations for other National Metrology Institudes (NMIs), calibration laboratories and industry.
Handing over of the new prototype balance on July 8, 2005 (from left to right: Dr. Roman Schwartz, head of PTB Department 1.1 "Mass"; Roland Nater, head of the Metrology Division of Mettler-Toledo AG; Martin Firlus, collaborator of PTB Working Group 1.11 "Realisation of Mass")
The new prototype balance (type M_one, Mettler-Toledo AG) is the metrological basis for the future safeguarding of and reduction in the attainable measurement uncertainties stated in the CMC tables of the BIPM for the mass scale of the PTB in the range from 1 mg to 5 t and the quantities derived from it as, for example, force, torque, pressure, density. For the applications stated, it offers essential improvements, e. g. an automatic weight-changing mechanism with 6 positions (so far 4 positions), a reduction in the standard deviation to maximally 0.4 µg (so far 2 µg), and the possibility of determining the mass of measurement objects with clearly larger dimensions, compared with conventional 1 kg mass standards. The latter is a prerequisite for the new system being used for the mass determination of 1 kg silicon spheres in air and vacuum within the scope of the Avogadro Project dealing with the determination of the Avogadro constant and the redefinition of the kilogram. Use of larger buoyancy artefacts also allows improvements in the determination of the air density for the required air buoyancy corrections to be expected, which will lead to a reduction in the uncertainty for both the link-up of stainless steel standards to the national kilogram prototype and for the mass determination of other bodies.
Contact person:
Michael Borys, FB 1.1, AG 1.11, E-mail: michael.borys@ptb.de