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The first phase of the EU collaborative project on sub-kelvin thermometry, ‘ULT Dissemination’, is nearing completion, leading to the development of several thermometers and devices, and the instrumentation needed to disseminate the new Provisional Low Temperature Scale, PLTS-2000, to users. Principal among these are a current-sensing noise thermometer (CSNT), a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second-sound acoustic thermometer and a superconductive reference device SRD-1000. Several partners have set up 3He melting-pressure thermometers to realise the PLTS-2000, and will check it using Pt-NMR, CMN and other thermometers. The scale, which was formally adopted by the Comité International des Poids et Mesures in October 2000, covers the range of temperature from 1 K down to 0.9 mK, and is defined by an equation for the melting pressure of 3He. The SRD employs novel fabrication and detection techniques with up to 10 samples, and is expected to meet the requirement for fixed points below 1 K, formerly filled by the NIST SRM 767 and 768. Other devices included in the project are ruthenium oxide sensors and a self-contained 3He melting pressure thermometer. This paper reviews the project progress to date and indicates the potential for research, metrological and industrial application of the devices developed. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

In the framework of the European Project “Ultra-Low Temperature Dissemination (ULT),” a superconductive reference device (SRD1000) and dedicated external measurement electronics were developed to provide direct traceability to the new Provisional Low Temperature Scale (PLTS-2000). The SRD1000 includes 10 reference points in the temperature range 15 mK to 1 K: W (TC = 15 mK), Be (TC = 23 mK), Ir80Rh20 (TC ≈ 35 mK), Ir92Rh08 (TC ≈ 65 mK), Ir (TC = 100 mK), AuAl2 (TC = 160 mK), AuIn2 (TC = 208 mK), Cd (TC = 520 mK), Zn (TC = 850 mK) and Al (TC = 1180 mK). After extensive research and development in the preparation and in the ultra-low temperature characterization of superconductive reference materials during the past years, eventually a final selection of the materials to be included in the first SRD1000 prototype sensors was made. In this paper, the superconducting transitions observed for the selected materials and the sample preparations are reported, the SRD1000 sensor and external electronics technology are described with some detail, and the ULT facility set up to calibrate the prototype sensors and the future commercial devices is presented. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

In January 2000 a European Project called “MULTICELLS” started, in the field of the realisation of low-temperature standards [1]. In the range from 14 K to 234 K, two competing designs of modular multi-compartment cells (multicells) for the realisation of low-temperature fixed points of the ITS-90 were developed and fabricated by two different partners: BNM-INM and IMGC [2]. The multicells device allows the calibration, in the same run, of up to three thermometers at all the ITS-90 triple points in the low-temperature range, including the mercury point. Several secondary reference points could be optionally added to the system. The limitation of the number of elements is mainly due to thermal effects (thermal homogeneity and response time) and to the dimension of the experimental space of the calorimeter used for measuring the melting curves. In order to reduce the response time, the phase-transition interface of each element of the multicell containing the substance must be in close thermal contact with the thermometers to be calibrated, although the different elements must be easily separated. BNM-INM developed and improved the device in co-operation with the testing partners from other institutes represented by the authors. The technical choices leading to the BNM-INM design are presented and justified. Experimental results on the thermal behaviour of the multicells are given. The tests were performed in accordance with a detailed protocol in order to enable a direct comparison of different designs of the multicells. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

An overview of the main results of an international star intercomparison of low-temperature fixed points is given. Between 1997 and 2002, 52 sealed triple-point cells (STPCs) of the thirteen laboratories represented by the authors have been investigated at PTB. The STPCs are used to realise the triple points of hydrogen, neon, oxygen, and argon, respectively, as defining fixed points of the International Temperature Scale of 1990, ITS-90. The melting curves of all STPCs have been measured on the same experimental equipment, adhering strictly to a single measurement program. This protocol enables separation of the effects influencing the melting curves and direct comparison of the thermal behaviour of the STPCs, which are quite different with respect to design, age, gas source, and filling technology. In the paper, emphasis is given to the typical properties of the four fixed-point substances and to the spread of the STPC parameters. Connections between the star intercomparison and completed and on-going international activities, including the CIPM Key Comparisons, are also discussed. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]