ITS-90 non-uniqueness and evaluation of characteristics of new 1000 Ω type platinum resistance thermometers for low-temperature measurement

Abstract

For use in a low-temperature region below the triple point of water (TPW), the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) developed a precise comparison system of capsule-type standard platinum resistance thermometers (CSPRTs) for dissemination of the International Temperature Scale of 1990 (ITS-90). This study compared eight CSPRTs with a reference CSPRT using the comparison system to study non-uniqueness at low temperature. We also evaluated characteristics of a new type of low-temperature PRT with about 1000 Ω of resistance at TPW (PT-1000s), which was recently developed by Netsushin Co, Ltd. to obtain better temperature sensitivity of resistance at a low temperature. The PT-1000 sensor is made from a high-grade platinum wire, similarly to standard PRTs of the ITS-90. We calibrated four PT-1000s based on the ITS-90 and evaluated their characteristics by comparison with a reference CSPRT. Results indicate that the character of the temperature scale of PT-1000s is very close to that of CSPRTs down to 14 K.

ITS-90 reproducibility, xenon fixed point substitution and new interpolating equations between 13.8033 K and 273.16 K

“…The underlying causes of these are variations in SPRT resistance vs temperature characteristics and variations in the calibration point realizations. Variations between different types of interpolating instrument (Type 2 non-uniqueness) are confined to the lowest SPRT temperatures and are treated elsewhere [9,10]. Much of the research into these manifestations of irreproducibility over several decades (see [4,5,[10][11][12][13][14][15][16][17][18][19] and references therein) has been incorporated into formal guidance to the global thermometry community for scale realization and uncertainty budget formulation in the form of the Consultative Committee for Thermometry (CCT) Guide to the Realization of the ITS-90 [20].…”

“…Variations between different types of interpolating instrument (Type 2 non-uniqueness) are confined to the lowest SPRT temperatures and are treated elsewhere [9,10]. Much of the research into these manifestations of irreproducibility over several decades (see [4,5,[10][11][12][13][14][15][16][17][18][19] and references therein) has been incorporated into formal guidance to the global thermometry community for scale realization and uncertainty budget formulation in the form of the Consultative Committee for Thermometry (CCT) Guide to the Realization of the ITS-90 [20]. However, in some respects the data and analysis underlying this guidance are sparse and inconsistent [5], and a broad numerical evaluation of ITS-90 reproducibility, including concrete proposals for its improvement, has remained lacking.…”

“…Experimental studies of NU3 involve the measurement of many SPRTs in isothermal comparator systems, at and between the temperatures of the defining fixed points of the scale [10,11,18,[31][32][33]. In particular, several important aspects of the ITS-90 [4] are based on the Ward and Compton data set of 1979 [31].…”

Special Section on TEMPMEKO 2019: a feature on the XIV International Symposium on Temperature and Thermal Measurements in Industry and Science & IV International Temperature Conference, Beijing (TEMPMEKO & TEMPBEIJING 2019) and Metrology for Meteorology and Climate (MMC 2019)

“…Challenges that need to be addressed are highlighted. As for new progress in conventional thermometers, PT-1000 platinum resistance thermometers, which are newly developed thermometers for industrial low temperature measurements, are evaluated by comparison with a reference capsule-type standard platinum resistance thermometer (CSPRT) in Nakano et al [3]. Pearce et al [4] describe the lifetime extension of Type R and Type S thermocouples by doping the Pt leg with zirconium, which not only restricts grain growth that can lead to breakage, but also counteracts drift due to rhodium contamination by an increase in emf when zirconium is converted to an oxide.…”

“…Finite element analysis is conducted to demonstrate immersion profile improvement methods. The ITS-90 non-uniqueness (types I, II and III) is evaluated in Nakano et al [3] in the low temperature range from the triple point of equilibrium hydrogen (13.8033 K) to the triple point of mercury (234.3156 K) through comparison of eight CSPRTs. The ITS-90 temperature of a high-temperature fixed-point cell of the Co-C eutectic for thermocouple calibration is determined by radiation thermometer measurements and with Pt/Pd and Type S thermocouples in Zheng and Lu [7].…”