INRiM report on the evaluation of Fe-C HTFP cells performed in the framework of the WP1: Realisation and dissemination of the redefined kelvin above 1300 K (EMPIR project 18SIB02). Real-K "Realising the redefined kelvin”.

A total of seven iron-carbon (Fe-C) high temperature fixed point (HTFP) cells of the hybrid type, respectively supplied by: 3 from CEM (Centro Español de Metrología), 2 from PTB (Physikalisch-Technische Bundesanstalt) and two from LNE-Cnam (Laboratoire Commun de Métrologie), were evaluated at INRiM in the period of time from Feb. 16th, 2021 to Mar. 24th, 2021 accordingly to the rules defined in the Protocol of WP1 of the EMPIR project Real-K [2]. The purpose of the measurements performed consisted in the comparison, evaluation and selection of the cells for the thermodynamic temperature campaign and traceability exercise, respectively. Considering that only one horizontal three-zone high-temperature furnace was available in the laboratory, consequently the Fe-C cells performance evaluation has been conducted following the procedure described as “alternative case” in the paragraph 3.2 of the protocol. The stability of the INRiM primary standard radiation thermometer, used to derive the differences between the cell’s transition temperature, has been constantly monitored during all the measurements with respect to the freezing temperature of the copper fixed point.