Voltage calibration systems using Josephson junction arrays

The realization of the SI definition of the volt depends on experiments that relate the primary electrical units to mechanical units of length, force, and power. The development of large arrays of Josephson junctions is allowing an ever increasing number of laboratories (currently 25) to maintain intrinsic Josephson voltage standards at an accuracy near 0.05 ppm. The fundamentals of Josephson voltage standards and how computer control makes these standards simple to use in a variety of applications are reviewed. The accuracy and stability of voltage standards based on the Josephson effect far surpass those of all other voltage-standard devices. The voltage generated is independent of environmental and material characteristics because it is based on a fundamental constant, the ratio of the elementary charge to Planck´s constant. International agreement on the value of this constant ensures uniformity and reproducibility throughout the world