Redefinition of the Kilogram

For many decades, the kilogram was defined by the so-called International Prototype of the Kilogram – a physical artefact kept at the Bureau International des Poids et Mesures (BIPM) in Sèvres near Paris. Since May 2019, the definition of the kilogram has no longer been based on a physical artefact, but on an unchanging natural constant.

One of the reasons for this redefinition was the recognition that a physical standard can change over the long term. In high-precision mass metrology, even the smallest deviations can play an important role.

• Historical definition of the kilogram based on the International Prototype of the Kilogram
• Redefinition of the kilogram based on natural constants
• Long-term stable and artefact-independent mass scale
• Particular importance for metrology, calibration laboratories and precision applications

Project Silicon Sphere

An important contribution to the redefinition of the kilogram was the Avogadro experiment using nearly perfect silicon spheres. The aim was to determine the number of atoms in highly pure and extremely precisely manufactured silicon spheres and thus establish the connection to the mass scale with the highest accuracy.

Together with the Physikalisch-Technische Bundesanstalt (PTB) and in cooperation with J. Hauser GmbH & Co. KG, HÄFNER was involved in the manufacture and provision of high-precision silicon spheres and the associated special accessories.

This included solutions for handling, storage, transport and cleaning of these sensitive precision bodies. The requirements for roundness, surface finish, cleanliness and safe handling were exceptionally high.

Mass Metrology at the Highest Level

The redefinition of the kilogram is a milestone for the International System of Units (SI). It demonstrates the importance of stable, traceable and globally comparable units of measurement for science, industry, calibration laboratories and national metrology institutes.

For HÄFNER, this project is an example of the combination of precision manufacturing, mass metrology and application-oriented accessories for highly sensitive weights and mass standards.