UK builds most accurate cryogenic current comparator

The National Physical Laboratory and Cryogenic have designed and developed the most accurate electric current comparator, and are offering copies to other measurement labs.

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“This cryogenic current comparator [CCC] provides the world’s most accurate ratio of current. Together with the quantum Hall effect, it allows resistance to be measured to very high accuracy, creating a primary standard of resistance,” said Cryogenic. “If you measure in milliamps or ohms, the CCC can relate this back to primary standards more simply and more accurately than ever before.”

CCCs rely on superconducting materials and a quantum magnetic flux detector in a liquid helium Dewar at 4K to measure current ratio.

“Accurate is better than 1 part in 109. Using the optically-isolated current sources, the resistance bridge can make comparisons between resistors with an accuracy and repeatability of better than 10-8,” said the firm. “It represents a significant accuracy upgrade on any previous system. It has provided, for example, the most accurate measurements to date of the electrical impedance of the quantised Hall effect in graphene.”

It is also claimed to be the first digitally driven CCC, so set-up and measurements are stored on the computer, and to consume less liquid helium than other systems.

“The ultimate goal is to go cryogen free,” said Cryogenic director Jeremy Good. “Cryogenic has pioneered the use of liquid helium-free technology in various areas and we are now extending our know-how to CCCs.”

The comparator is now commercially available from Cryogenic, and the firm already has a contract to install one at Singapore’s national measurement lab.


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