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.