A review of precision AC voltage and current measurements

Technological changes affecting the AC voltage measurements are discussed. These have been in both commercial instruments and in the potential for new standards. The main changes are: (a) the improved stability and increased range of commercial instruments; (b) the requirements for the calibration of non sinusoidal waveforms; (c) the potential for improved national standards for AC voltage generation and measurement. These changes lead to requirements for the extension in range of present calibration facilities for AC voltage as well as AC/DC transfer. There is also a requirement for the calibration of non sinusoidal waveforms. The development of new standards will initially support existing standards and ultimately provide better standards and better traceability to the primary DC standards. The Josephson array system could provide a primary standard of AC voltage. At NPL the AC voltage standard will provide a working standard which will provide the starting point for the extension to other voltages and frequencies.