Abstract
This paper presents an apparatus for the calibration of long-stem platinum resistance thermometers at the argon triple point $$(T_{90} = 83.8058\,\hbox {K})$$ , designed at the Institute of Low Temperature and Structural Research, Poland (INTiBS). A hermetically sealed cell filled at the Istituto Nazionale di Ricerca Metrologica, Italy with high purity gas (6N) is the main element of this apparatus. The cell is placed in a cryostat fully immersed in liquid nitrogen. A temperature-controlled shield ensures the quasi-adiabatic condition needed for proper realization of the phase transition. A system for correcting the temperature distribution along the thermometer well is also implemented. The cell cooling and argon solidification is carried out by filling the thermometer well with liquid nitrogen. A LabVIEW computer program written at INTiBS automatically controls the triple-point realization process. The duration of a melting plateau in the apparatus lasts for about 24 h. The melting width for $$F$$ between 20 % and 80 % was $${<}0.3$$ mK. The reproducibility of the plateau temperature is better than $${\pm }20\,\upmu \hbox {K}$$ .
Highlights
The triple point of argon is one of the low-temperature fixed points of the International Temperature Scale of 1990, ITS 90 (T90 = 83.8058 K) needed for the calibration ofB
Several models of cryostat and systems for the calibration of SPRTs at the triple point of argon were built by different institutions [1,2,3,4,5,6] since more than thirty years
The mechanical part of the cell was made at INTIBS
Summary
Several models of cryostat and systems for the calibration of SPRTs at the triple point of argon were built by different institutions [1,2,3,4,5,6] since more than thirty years. CSPRTs are calibrated in small sealed cells under good adiabatic conditions [7,8,9,10]. At the Institute of Low Temperature and Structure Research (INTiBS), Wroclaw, a new cryostat model for calibration of long-stem SPRTs at the argon triple point was built. The cell is placed in a vacuum chamber immersed in a liquid nitrogen bath allowing realization of the argon triple point and calibration of both types of standard platinum thermometers—long stem and capsule type in a quasi-adiabatic condition. The characteristics of the system and the testing results are reported, showing that reproducible plateaux with the realized temperature spanning
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