National Physical Laboratory

Kibble balance: Metrology community honours late Dr Bryan Kibble

The global metrology community has paid tribute to the late Dr Bryan Peter Kibble, who worked at the National Physical Laboratory (NPL). Dr Kibble's famous invention, the watt balance, is being renamed after him in a unanimous decision by the Consultative Committee for Units (CCU). Invented in the 1970s, the device measures the Planck constant in SI units enabling the redefinition of the SI unit of mass: the kilogram, which is proposed for 2018.

Dr Kibble and Dr Ian Robinson working on the Kibble balance at NPL
Dr Kibble and Dr Ian Robinson working on the Kibble
balance at NPL

Kibble began working as a senior postdoctoral fellow at NPL in 1967 where he became interested in the SI unit of current, the ampere, which was then measured using a piece of equipment known as a current balance.

The accuracy obtainable using the current balance was limited and it was very difficult to use. To avoid these problems, Kibble invented a new way of linking the mechanical and electrical units. This watt balance, combined with a measurement of the SI ohm, produced more accurate measurements of the ampere. The watt balance is now named the Kibble balance.

Kibble continued to improve his invention, and a second model was built in 1990. In conjunction with quantum mechanical measurements of voltage and resistance, and measurements of the acceleration due to gravity, it was capable of accurately measuring the Planck constant. A worldwide consensus value of the Planck constant will be used to redefine the SI unit of mass: the kilogram.

Dr Kibble worked tirelessly in his field until his death in April 2016, and his achievements were lauded by his peers as a pivotal steps for metrology. He was known for his gentle nature and patience as a teacher.

The formal redefinition of the kilogram is due to happen in 2018 and, though he is not alive to bear witness to it, Dr Kibble's legacy will live on in metrology: a fitting tribute for a man who loved his work.

Read more about the Kibble balance

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Last Updated: 22 Jul 2016
Created: 21 Jul 2016

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