Scientists create scales for the new kilogram

Scientists create scales for the new kilogram

Technology News |
By Christoph Hammerschmidt

The Physikalisch-Technische Bundesanstalt (PTB) is developing a so-called Planck scale together with the Technische Universität Ilmenau. It works according to the principle of electromagnetic force compensation: A weight force on one side of the balance is balanced by an electromagnetic force on the other side. Weight pieces, so-called mass standards, the scales that hitherto give an indication how much the mass is actually on the scale, are then no longer needed. A first prototype of the Planck scale will be available to scientists at the end of the year. Thus, it checked which development steps are still necessary to make the balance suitable for industrial use. This could be the starting shot for the development of a whole new, industry-capable generation of scales.

The development of the Planck scale will be pushed forward by the imminent redefinition of the kilogram: the international prototype kilogram, a small metal cylinder in a safe near Paris, will soon be disused. A kilogram definition comes into its own on the basis of an indestructible and unchanging natural constant: the Planckian quantum of action “h”. The name “Planck balance” refers to this constant. Once the value of h has been established internationally, masses can be determined solely by measuring electrical quantities.

A further advantage of the Planck scale is the continuous measuring range. Although the first prototype will only reach a measuring range of 1 mg to 100 g, the planned successor will already range from 1 mg to 1000 g. Comparable scales could be used directly for industrial weighings, as so-called primary standards, since a calibration with normal weights is omitted. In the long term, the Planck scale could achieve higher accuracy even with small masses than with previous normal weights for industrial use.

While PTB is already mulling the practical consequences and chances of the new kilogram definition, the redefinition itself is still not complete. On a global scale. two experiments are being pursued to achieve the goal of a kilogram definition based on natural constants: the Avogadro experiment, in which the number of atoms is to be determined in an almost perfectly spherical crystal of isotopic silicon, and the kibble scale (or Watt scale), in which the weight of a mass in the gravitational field of the earth is compensated by an electromagnetic force. In both experiments, the value of the Planckian quantum of action is determined so that both approaches meet on the target line. While the PTB mainly follows the path across the silicon globe, the US NIST and the Canadian NRC favor the kibble scale. However, in order to be able to offer both paths in the future transfer of the mass units to the industry, PTB, together with the Technical University of Ilmenau, launched the prototype development of a Planck scale (as an industrial variant of a kibble scale).

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