Cryogenic Voltage Standard at PTB
For several years precise 2e/h measurements via the ac Josephson effect have been routinely carried out at the Physikalisch-Technische Bundesanstalt (PTB) [1,2] and other standard laboratories throughout the world. The total (1σ) uncertainty obtained for 2e/h is 4 parts in 108. This accuracy should also be guaranteed between the different measurement apparatus for 2e/h determinations in the various standard laboratories. This comparison can be realized by two conceivable procedures. In one case electrochemical standard cells are transported from one laboratory to another and the EMF’s of the cells are compared with the local Josephson reference voltages. During the 1973 intercomparisons at BIPM the results of NBS, NML, NPL, and PTB agreed to within ± 2 parts in 107, yielding an accuracy which was evidently limited by the use of thermo-regulated electrochemical transport standards. On the other hand improvement of the consistency of the data can be achieved by transporting Josephson apparatus as was done for the first time between BIPM and PTB.
KeywordsSpot Welding AlMg Alloy Balance Detector Temperature Dependent Resistivity Null Detector
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