Redefined Units Of Measurement

By admin May 25, 2019 09:47

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World’s scientific and technical community, has unanimously adopted the resolution to redefine four of the seven base units, the kilogram (SI unit of weight), Kelvin (SI unit of temperature), mole (SI unit of amount of substance), and ampere (SI unit of current).

  • It has now enabled scientists and researchers to base the SI units entirely on fundamental properties of nature, which will ensure their ongoing refinement and improvement for years to come.
  • The fundamental constants are invariants of time and space and successfully replaced the artifact based units, and aptly opened up the new era for quantum world by linking all seven base units to fundamental constants/quantum standards.

Measurement standards

  • It was only in 1875, with the creation of BIPM, that measurement began to be standardised internationally.
  • The BIPM reports to the General Conference on Weights and Measures (CGPM), to which India became a signatory in 1957.
  • The original definitions for the most basic units were uncomplicated. Until 1875, the metre was defined as 1/10 million of the distance between the North Pole and the Equator.
  • The second was initially based on the length of a day of 24 hours; in 1956, the standard was set to a fraction of the solar year.
  • It was only in the middle of the 20th century that the more complex definitions began to be adopted.

The New Definitions

  • Since 1967, the second has been defined as the time it takes for a certain amount of energy to be released as radiation from atoms of Caesium-133. This became the basis of all measures of time, and is used in atomic clocks.
  • The purpose of system units is to enable worldwide coherence of measurements.
  • The International System of Units (SI) was formalised in 1960 and has been updated several times to account for development in measurement technology.

World Metrology Day (WMD)

  • The new SI is being implemented worldwide from 20th May 2019 i.e. the World Metrology Day.
  • The World Metrology Day (WMD) is celebrated annually on 20th May as the Metre Convention was signed by representatives of seventeen nations on May 20, 1875.
  • The Convention set the framework for global collaboration in the science of measurement and in its industrial, commercial and societal applications.


  • CSIR-NPL, the National Metrology Institute (NMI) of India has started the R&D efforts in establishing the new SI, alongside the international implementations.
  • CSIR-NPL introduced redefined SI Units to nation in terms of constant of nature through a series of events & by delivering lectures.
  • As a national responsibility and keeping in view of the importance and recognition of new revision of SI, the CSIR-NPL has recommended the proposed changes to be incorporated in syllabi of textbooks, metrology courses and other academic institutes.
New definitions for the kilogramme

  • Until now, kilogramme has been defined as the mass of a platinum-iridium lump, the so-called Grand K, which is kept in a secured vault on the outskirts of Paris.
  • It has been the world’s one true kilo, against which all others were measured, since 1889.
  • The new definition of kg involves accurate weighing machines called ‘Kibble balance‘, which uses Planck’s Constant to measure the mass of an object using a precisely measured electromagnetic force.

Planck constant is a physical constant that is the quantum of electromagnetic action, which relates the energy carried by a photon to its frequency.


  • Unlike a physical object, the formula cannot pick up particles of dust, decay with time or be dropped and damaged.
  • The new SI System will be helpful in bringing in accuracy while dealing with international trade, biotechnology, high-tech manufacturing and human health and safety.
  • It will spare nations the need to occasionally send their kilos back to France for calibration against the Grand K.
  • The proposed changes in the unit definition have been designed to have no immediate consequences.
  • The unit redefinitions represent a profound change of perspective and they are expected to form the foundations of improved measurements for decades to come.

The fundamental constants are invariants of time and space and have successfully replaced the artefact based units, and aptly opened up the new era for quantum world by linking all seven base units to fundamental constants or quantum standards.

Quantum computing, artificial intelligence (AI), Industry 4.0, space enabled communications, are some of the international challenges of the near future and it is necessary, to make the triumphs to meet the above challenges with the support of quantum metrology based quality infrastructure.

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By admin May 25, 2019 09:47