Low-temperature thermometry below 1 K at PTB

Cryogenic technology based on automated cryogen-free refrigerators has made substantial progress during the last decade making low temperatures easily accessible for a much broader community in science and industry. Along with this development there is a reinforced need in traceable thermometry for the cryogenic range. In this paper we give information about the realization, maintenance and dissemination of the PLTS-2000 at PTB. An updated uncertainty budget is presented for the PLTS-2000 applied for practical dissemination. We report on the investigation of dc-SQUID based noise thermometers which can be used as practical thermometers with a broad working range of more than 3 decades in temperature. On a future stage of development, such noise thermometers are intended to be used for solving the discrepancies in the background data of the PLTS-2000 at its lower end below 0.01 K.