Improved Cryogenic Current Comparator setup with digital double current source

Resistance calibration at PTB, Germany´s national metrological institute (NMI), has been based on Cryogenic Current Comparators (CCC´s) for almost two decades. So far, comparisons in the ensemble of normal resistors with nominal values from 1 Omega up to 1 MOmega and with the quantum Hall resistance R_K-90 are performed by means of two complementary setups for high- or low-ohmic resistors, respectively. To replace both setups, we designed a new LHe probe equipped with an optimized PTB dc SQUID sensor as well as a digital state-of-the-art double-current source. In this paper, we describe basic features and highlight the advantages of the new system.