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BIPM-PTB lay groundwork for intercomparison of AC Josephson voltage standards

Over the last decade, considerable research activity on alternating current (AC) quantum voltage references has been carried out to meet the demand for applied AC measurements in industry and in scientific research.

One such project, the EURAMET EMPIR project ACQ-PRO: “Towards the propagation of AC quantum voltage standards” seeks to develop measurement and research capacity by providing access to AC quantum voltage references. Increasing the number of NMIs using these standards will encourage research and development on electrical metrology for industrial applications.

The BIPM is contributing to these objectives by using its own transportable AC Josephson Voltage Standard to develop a comparison protocol for a future series of BIPM on-site comparisons. This AC Josephson Voltage Standard was provided to the BIPM by the NIST as the outcome of a cooperative research and development agreement. Over a two-week period in August 2017, the BIPM collaborated with the German NMI, PTB (Physikalisch-Technische Bundesanstalt), in an on-site measurement campaign at the PTB in Braunschweig.  The BIPM transportable quantum voltage standard was compared to the PTB AC quantum voltage standard using an AC signal generator which served as a transfer standard. The measurand was the root-mean-square voltage of the signal generator, at 1 V and 6.5 V, at the frequency of 62.5 Hz.

After solving issues related to ground loops and electromagnetic interference, the best configuration of the measurement setup resulted in the following relative voltage difference:

ΔU/U = 0.3 ppm at 6.5 V and ΔU/U = 0.2 ppm at 1 V with an associated relative Type A uncertainty of 0.3 ppm at 6.5 V and of 0.9 ppm at 1 V.

This pilot comparison enabled both participants to better understand the behavior of their own measurement setup. Among the parameters for consideration were those linked to the design of the protocol for a future BIPM comparison of AC quantum voltage standards. More specifically, the present study demonstrated that different approaches for the phase adjustment of the AC signals can easily lead to systematic errors in the final result.

The BIPM looks forward to carrying out a similar pilot study in 2018 with the National Physical Laboratory in the UK.

Dr. Stephane Solve operating the BIPM AC traveling quantum voltage standard in the PTB laboratories (Braunschweig).

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