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EMPIR project’s AC voltage technology featured on cover of IEEE publication

Flare generated from a large flow of electrical current

New project development featured by Institute of Electrical and Electronics Engineers

The project

The volt is the SI unit of electrical potential energy - or the energy needed to make a current flow. While it is possible to trace voltage measurements from direct currents (DC) back to the standard volt unit with universal consistency, this is not the case for voltage measurements made from alternating currents (AC).

To help to solve this measurement challenge, the EMPIR project ‘Waveform metrology based on spectrally pure Josephson voltages’ (15SIB04, QuADC) has developed reliable and traceable AC voltage measurement systems, providing the capability for the first time to manufacture products that require quick analogue-to-digital conversions. The project outcomes will support the traceability of power quality measurements, and as a result, improve the efficiency of power grids across Europe. 

Developing the technology for traceable AC voltage measurements

The new quantum-based measurement system for AC voltage developed during the project has provided direct traceability of AC voltage measurements back to the fundamental SI system, by making use of the Josephson effect representation of the SI volt to ensure worldwide uniformity and no reliance on any physical constraints.

Two project partners, JV and USN, have cooperated to optimise the photodiode mounting procedure for the new system, helping to make it even more reliable. This technology has in fact been highlighted by the IEEE - the world’s largest organisation for technological advancement - and featured on the cover of one of their journals, ‘IEEE Transactions on Components, Packaging and Manufacturing Technology’.

The new photodiode technology has been able to generate the first ever pure-AC voltage signals – an important step towards obtaining a fundamental AC voltage unit. This proof-of-principle experiment has paved the way for developing quantum systems with greater output voltages and superior performance capabilities at higher frequencies, up to the megahertz (MHz) range.

The completed EMPIR project has provided traceability for electrical measurements used in all modern instrumentation, helping to maintain the long-term competitiveness of calibration laboratories across Europe.


This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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