Levitated superconductor model for kilogram: With the kilogram “shedding and gaining” weight over the last 100 years, India has now proposed to adapt a new method to maintain its accuracy

Syed Akbar
Hyderabad: With the kilogram “shedding and gaining” weight
over the last 100 years, India has now proposed to adapt a new method
to maintain its accuracy.

At present, India has “artifact-based national standards” for the
kilogram. The National Physical Laboratory (NPL-CSIR), Delhi, has
proposed to go for the “levitated superconductor” approach during the
12th five-year plan to give a new definition to the kilogram.

The international scientific community could not arrive at a consensus
on the redefinition of the kilogram after it found that the
international prototype of the kilogram had gained or lost weight
since it was first defined in 1889. India’s proposal to adapt the
“levitated superconductor” approach may help the international
community in redefining the kilogram.

“The levitated superconductor approach relates the kilogram to
electrical quantities by levitating a superconducting body in a
magnetic field generated by a superconducting coil, and measuring the
electrical current required in the coil. This research is expected to
pave the way for the barrier of the artifact based on international
standard of mass with quantum standard,” said Dr AK Bandyopadhyay,
chief scientist, apex level standards and industrial metrology,
NPL-CSIR.

Emphasing the need for the accuracy of the kilogram, Dr Bandyopadhyay
pointed out that since mass is the base quantity and it is connected
with volume, density, force, pressure etc. any confusion in the
definition would drastically effect the measurement, science &
technology, international trade and commerce.

“In the pharmaceutical industries, 1mg is required to be measured for
various drug components where any increase in the relative uncertainty
may cost a substantial error in the measurement and may result in the
failure of drug delivery. Similarly, in the nano force measurement,
which is very common in the atomic and subatomic level, increase in
the uncertainty in measurement may affect the overall performance of
the instrument,” he added.

The NPL has gained expertise in providing an internationally traceable
mass measurement from 1 mg to 2000 kg.

Since 1889, the SI system defines the unit to be equal to the mass of
the international prototype of the kilogram, which is made from an
alloy of platinum and iridium of 39 mm height and diameter, and kept
at the International Bureau of Weights and Measures. It is known as
“official standard”, Dr Bandyopadhyay said.

It is found that by comparing this “official standard” with its
“official copies”, which are made of roughly the same materials and
kept under the same conditions in different countries including India,
the mass of the “official standard” appears to be changing relative to
the mass of its copies.