Resistance bridge based on the cryogenic current comparator in a transport dewar

An optimized resistance bridge based on the Cryogenic Current Comparator (CCC) with SQUID readout has been developed. The bridge can be used for routine secondary resistance calibrations as well as for the traceability of 100 /spl Omega/ to the quantum Hall resistance. The CCC-SQUID, shielding and wiring are mounted in a telescopic insert, fitted in a low-evaporation rate, transportable liquid He dewar, with an autonomy of around 1 month. A difference compensator method is used to balance the bridge. A new, more reliable and self-standing bridge electronics has been fabricated and tested. An uncertainty in the comparison of resistors at least one order of magnitude better than room temperature CCs is expected.