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Supporting the definition and realisation of the kilogram

The Kibble balance, formerly known as the watt balance but later renamed after Bryan Kibble who developed the apparatus at the National Physical Laboratory (NPL) in the 1970s, is an instrument that compares electrical and mechanical power. It allows the SI unit of mass to be realised in terms of quantum electrical units; Josephson voltage and quantum Hall resistance, in relation to a fixed value: the Planck constant.  

Current iterations of the Kibble balance, including the world-leading NPL MkII Kibble balance which is now at The National Research Council in Canada, were designed primarily to measure the Planck constant with relation to the pre-2019 mass scale.  

NPL's next-generation balance has been specifically designed to realise the unit of mass following the revision of the SI. It employs novel operational principles and mechanical design features which result in a balance that is cost-effective, easier to manufacture and more convenient to use than current methods. It aims to match or surpass the current level of accuracy achievable. 

Notable features of NPL's next-generation Kibble balance include a novel guidance mechanism to minimise errors resulting from the misalignment of the coil in the magnetic field. It has been specifically designed for multiple unit production with the intention of widely distributing the means to realising the unit of mass, enhancing the resilience of the global mass scale. This will make the global mass scale much more robust.  

A locally realisable Kibble 

Looking forward, NPL will work towards creating Kibble balance instruments that provide SI traceable mass and force measurements at the point of need, such as in production processes. Additionally, we plan to miniaturise the device for applications in pharmaceutical research, biotechnology, personalised medicine, environmental monitoring, microfabrication, and robotics. 

NPL has developed designs and knowledge for prototype miniaturised Kibble balances with traceability to the SI kilogram, which have been demonstrated in the laboratory. This technology could enable mass measurements to be made where traceable mass calibrations are otherwise difficult to achieve. The Technical Readiness Level (TRL) 3 prototype table-top Kibble balance, measuring roughly 20cm x 20cm, could be developed and scaled for mass measurements up to the tens of grams range.  

We are looking to partner with industrial and research stakeholders to translate this capability into instruments suitable for industrial applications. For more infomation please use the “contact us” button below. 

Electronics and software for Kibble systems 

NPL has also developed unique electronics and software for running Kibble balance systems. The electronics and software are interchangeable between different Kibble-type sensors and can substantially reduce the space and complexity of the subsystems required.   

Find out more about NPL's Calibration of weights service

Find out more about NPL's Technical consultancy service

Find out more about NPL's Manufacture and supply of transducers service

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