India joins global initiative on World Metrology Day, logging in new ‘kilogram’ and other base SI units

India joins global initiative on World Metrology Day, logging in new ‘kilogram’ and other base SI units

NEW DELHI, May 20: With countries across the globe saying goodbye to original kilogram (kg) by introducing redefined International System of Units on the World Metrology Day, India’s National Physical Laboratory (NPL) – country’s national measurement body – too on Monday adopted the new system and launched a campaign to create awareness among users on how the new kilogram and three other base units will work in the country without affecting their day-to-day works.
The new kilogram (unit of weight) and three other new base units – ampere (electric current), Kelvin (temperature) and mole (amount of substance such as atoms) – will now not be based on ‘physical artefacts’ but on ‘constants of nature’ (quantum standards).
It means their values will never change and countries will not have to copy their internationally accepted prototypes. In any case, the change is not a matter of worry as scientists use the same mass of old kg while scientifically redefining new kg.
There are seven base SI units. While second (time), meter (length) and candela (unit of luminous intensity) have long been based on ‘constants of nature’ (quantum standards), the redefined units of remaining four were introduced globally on Monday.
Metrologists from over 60 countries, including India, had agreed for the change at the General Conference on Weights and Measures in Versailles, France in November last year.
Asked whether existing instruments need immediate calibration in view of the change, DK Aswal, director of the NPL, said, “No, we don’t need that. The proposed changes in the unit definition have been designed to have no immediate consequences.”
He told TOI, “Length is already being measured in terms of speed of light. Time is also being currently measured using redefined units. For mass, we will use Kibble balance (electromechanical measuring instrument) of other National Measurement Institutes (NMIs) till we build our own.”
About its implication, Aswal said this “may not change anything drastically”, but it will matter when it comes to measurements less than a kg. For instance, measuring smaller diamonds or precious metals.
The change can be better understood from an example of kg. Currently, kg is defined as equal to weight of a human-made small polished platinum-iridium cylinder, cast in 1879. It has been kept at the International Bureau of Weights and Measures in Sevres near Paris in France since 1889. It’s called ‘international prototype kg’ (IPK). It is copied by countries across the globe for use through calibration of instruments.
This IPK has, however, lost around 50 micrograms (about the mass of an eyelash) since it was created due to contamination or cleaning. But, it is still used as ‘one kg’ as per old definition despite losing weight. Under new scientific system, the one kg will always remain one kg as it is not based on ‘physical artefact’. The same principle applies to other units, ensuring constant value and universality.
In simple terms, one standard bag of flour will contain as much flour as it ever did under new definition kg – it means it’ll not change even a bit for ever.
The NPL, as its national responsibility, has prepared documents, recommending incorporation of the changes in the NCERT textbooks and in syllabi of metrology courses in IITs, NITs and other academic institutes.
Officials here said the redefined SI Units would not change the values in real term for day-to-day works. It will, however, guarantee their stability and universality in long run and help in coming out with accurate data in all sectors including environment for measuring pollutants. All future measuring instruments will come with factoring in redefined units, they added. (TNN)