Electrical standards of measurement. Part 1: D.C. and low-frequency standards

The paper reviews recent developments in electrical masurement techniques in the context of the UK national standards maintained by the National Physical Laboratory. Part 1 describes the primary electrical standards, their derivation from the SI units, and their relation to the standards maintained by the International Bureau of Weights and Measures. From the primary standards a number of working standards are derived and used for the calibration of other laboratories´ reference standards. These include the essential step of a.c./d.c. transfer. In recent years there have been a number of important advances in the techniques of accurate measurement, including the development of independent means of monitoring the stability of the primary standards and of improved null detectors, ratio devices and thermal voltmeters. These have found application not only in electrical standards but also in the measurement of the magnetic properties of materials. Parts 2 and 3 of this paper extend the discussion of standards to the microwave and submillimetre-wave regions.