Construction and Evaluation of Non-contact Fixed-point Cells

V. Žužek, V. Mlačnik and J. Bojkovski Metrology Institute of the Republic of Slovenia/University of Ljubljana-Faculty of Electrical Engineering/Laboratory of Metrology and Quality Adoption of radiation thermometer calibration capability using fixed points at ULFE/LMK. Four miniature fixed-point cells for pyrometric use have been filled and tested in scope of the MultiFixRad project, namely: copper, iron-carbon, cobalt-carbon and palladium-carbon eutectic alloy cells. Methods and infrastructure for fixed-point realisation were adopted at MIRS/ULFE/LMK in scope of the MultiFixRad project (22RPT03). Miniature graphite cells were filled with copper, iron-carbon, cobalt-carbon and palladium-carbon alloys. A vertical furnace was used for cell filling and a horizontal furnace for fixed point realisation. Argon (5N purity) was used for oxygen purging. A high flow of argon is required to prevent oxidation to graphite cells. Furnace opening was narrowed to force laminar flow of argon and to prevent convective intrusion of oxygen into the furnace. Plateaus were characterized programatically from smoothened numeric derivatives: The freezing plateaus of pure metal cells are characterized at the negative zero pass of the first derivative (on graph downward turn after infliction). The melting plateau of eutectic cells is characterised at the positive zero pass of the second derivative (when graph switches between slowing down and speeding up). Results of various furnace parameter combinations (Figure 3) indicate that fast rates (step change) at high temperature deviations (5 to 10 °C) above and bellow melting point were found ideal for robust realisation. Construction and Evaluation of Non-contact Fixed-point Cells Figure 1: Constructed fixed point cell, oxidised paladium-carbon cell and the calibration furnace view. Figure 2: Fe-C plateau analysis using the numeric first and second derivative (smoothened) with characterised time of plateau (blue circle) and result of polynomial fit method (red circle). Figure 3: Stability analysis of multiple fixed point realisations. The paladium-carbon cell exhibited oxidation problems; furnace parameters will be optimised in the future.