New International Systems of Units to come into force from May 20, 2019

Speed Post News Network

New Delhi : The 26th meeting of the General Conference on Weights and Measures (CGPM), which was held during November 13-16, 2018 at Palais des Congrés, Versailles, France, voted for the redefinition of 130 years old “Le grand K – the SI unit of kg” in terms of the fundamental Planck’s constant(h). The new definitions will come into force on May 20, 2019. The CGPM is the highest international body of the world for accurate and precise measurements.

The CGPM comprises 60 countries including India and 42 Associate Members. At this meeting India was represented by  Avinash K Srivastava, Secretary, Department of Consumer Affairs, Government of India, Dr D K Aswal, Director, National Physical Laboratory (NPL), New Delhi, and Dr T D Senguttuvan, Head Planning, Monitoring & Evaluation, NPL.

The International Bureau of Weights and Measures (BIPM), the main executive body of CGPM, has the responsibility of defining the International System of Units (SI). This revision of the SI is the culmination of many years of intensive scientific cooperation between the National Metrology Institutes (The national Physical Laboratory for India) and the BIPM.

Out of five draft resolutions, the revision of the International System of Units and the definition of timescales are the important. The most important is the resolution on the revision of International System of Units. The definition of the seven base units namely, second, metre, kilogram, ampere, Kelvin, mole and candela has been changed from being linked to artefacts to being based on the fundamental constants on nature.

Notably the definition of kilogram has been changed from being the mass of prototype sanctioned by the 1st CGPM held in Paris in 1889 and deposited at the BIPM to the Planck constant which is a physical constant. Likewise, the definition of metre has been changed to link it to the speed of light. There is a change in definition of time also. The change in the definition will result in uniform and worldwide accessible SI system for international trade, high- technology manufacturing, human health and safety, protection of environment, global climate studies and the basic science under-pinning these. The units are expected to be stable in the long term, internally self-consistent and practically realisable being based on the present theoretical description of nature at the highest level, according to a PIB release.

The International prototype of kilogram (IPK) is kept at the BIPM, Paris, and serves as the international standard of kilogram. It is made of 90% platinum and 10% iridium and is a cylinder of 39 mm diameter and 39 mm height. Replicas of the IPK are made of the same material and used at BIPM as reference or working standards and national prototype of kilogram (NPK), kept at different National Metrology Institutes (NMIs).