Kibble, Bryan P. Division of Electrical Science, National Physical Laboratory, Teddington, Middlesex, United Kingdom.
- Working principle
- Advantages of this approach
- Links to Primary Literature
- Additional Readings
An electromechanical apparatus for establishing the watt as an SI electrical unit. Prior to January 1, 1990, there were voltage units in use in the United States, France, the United Kingdom, Russia, and so on which differed from each other (and, with hindsight, from the SI volt) by up to 9 parts per million (ppm). These units were based on results from various current balances. Then results obtained from a different kind of apparatus at the National Physical Laboratory in the United Kingdom and the National Institute for Science and Technology in the United States, which were based on the simple principle described below, enabled the electrical units to be put on a sound SI basis. The accuracy in deriving the SI unit of voltage in this way was considered to be better than 0.2 ppm. Since that date these apparatuses have continued to be refined, and others are being developed in metrological laboratories, with the more ambitious objective of defining the kilogram in terms of fundamental physical constants instead of having to rely on a carefully preserved artifact, the cylinder of platinum-iridium alloy kept at the International Bureau of Weights and Measures. To do this, the accuracy achieved by the apparatus will have to be demonstrated to be of the order of 0.01 ppm. See also: Current balance; Electrical units and standards
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Its dedicated editorial team is led by Sagan Award winner John Rennie. Contributors include more than 9000 highly qualified scientists and 42 Nobel Prize winners.
MORE THAN 8500 articles and Research Reviews covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 17,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information