Cryocooler Operation of a DC Voltage Standard Based on High Temperature Superconductor Josephson Junctions

A commercially available Josephson voltage standard based on high temperature superconductor Josephson junctions with a liquid nitrogen free cooling is presented. The results of the calibrations of an electronic DC reference Fluke 732B and a Keithley nanovoltmeter 2182 with uncertainties equal to a few parts in 10
⁸
demonstrate the suitability of the application of a N4-21 in the highest-level metrology. The implementation of a link between Josephson junctions and Zener diodes largely eliminates the uncertainty contributions associated with Zeners non-linear drift, environmental effects and the impact due to shipping.