An Automated Josephson-Based AC-Voltage Calibration System

Abstract

This paper describes a new calibration system developed at INMETRO to guarantee traceability of lowfrequency alternating current (ac) voltage calibrations (<1 kHz) to a programmable Josephson ac waveform synthesizer. The automated full-synchronous system allows the synchronization of a commercial calibrator or signal synthesizer with a programmable Josephson voltage synthesizer system to be made by employing digital sampling and signal processing techniques, aided by adaptive digital control. It allows accurate determination of the spectral content of ac signals with minimum human intervention. System operation, measurement techniques, and data analysis are detailed. Index Terms-AC voltage, digital signal processing, Josephson, measurement standards, power, spectral analysis. Waldemar G. Kürten Ihlenfeld was born in União da Vitória, Brazil, in 1960. He received the B.Eng. degree from the Federal University of Paraná, Curitiba, Brazil, in 1983, and the M.Eng. and Ph.D. (magna cum laude) degrees in electrical engineering from Braunschweig Technical University, Braunschweig, Germany, in 1994 and 1997, respectively. He was with the Central Laboratory, LAC, Curitiba, from 1983 to 1999, a research institute of the Federal University of Paraná and the Power Utility Company of Paraná. From 1999 to 2013, he was with Physikalisch-Technische Bundesanstalt, Braunschweig, where he was involved in research and development of precision electronic circuits for ac power measurements, and mathematical modeling of sampling systems and investigating electro-thermal modeling of semiconductor devices. He is currently involved in developing sampling systems in the frame of the project Pronametro with the Instituto Nacional de Metrologia, Qualidade e he collaborated with the National Institute of Standards and Technology, Boulder, CO, USA, as a Guest Researcher in Josephson Systems. He is responsible for the dissemination of the Brazil legal volt and for maintaining internationally consistent and traceable voltage standards tied to the SI units. His current research interests include ac and dc Josephson voltage standards and quantum Hall systems and their applications in metrology, ac-dc transfer standards, and power and energy metrology.

Fast synchronous AC-DC transfer measurements with a programmable Josephson AC voltage standard

“…A nanovoltmeter measures the output of a multi-junction TC. The PJVS´ ac voltage determinations of vAC(t) via differential measurements are compared with the calibrator´s dc value adjusted by the computer as described in [3], what allows validation of the ac voltage calibrations as in [1] with a TC.…”

“…This would employ special equations for synchronization to allow coherent sampling. Equations for synchronizing adaptively analog-to-digital converters were presented in [5] and to synchronize their digital-to-analog counterparts in [1] (patent pending). Both algorithms may be employed in order to tackle difficult synchronization issues.…”

“…After developing an automated ac voltage calibration system based on a programmable Josephson ac voltage standard (PJVS) [1] we seek its validation with the help of thermal converters (TCs). Three main tasks are deemed fundamental and are listed in order of importance as follows: (a) The validation of ac voltage calibrations from differential voltage measurements done with the PJVS, (b) the calibration of ac-dc transfer errors of thermal converters and finally, (c) the determination of the measurement limitations of the PJVS by measuring the energy content or rms of a PJVS waveform.…”

“…1 shows the measurement setup. The gray shaded area represents the PJVS calibration system as described in [1]. The ac source is continuously calibrated against the PJVS as described [1].…”

“…The gray shaded area represents the PJVS calibration system as described in [1]. The ac source is continuously calibrated against the PJVS as described [1]. For higher voltages, an inductive voltage divider (IVD) can be used to extend the range of PJVS ac calibrations by measuring at its secondary and by determining kvAC(t), for k (less than 1) being the ration constant of the IVD.…”