National Physical Laboratory

Supply of NPL high temperature eutectic fixed points

These new standards provide UKAS certified ITS-90 temperatures above the copper point, with a range extending up to 2750 °C. The uncertainty of the fixed point temperaturein terms of degrees celsius is 0.05% at k = 2 (i.e. the uncertainty of rhenium carbon at 2474 °C is approximately 1.2 °C). The metal-carbon eutectic cells consist of a blackbody cavity within a graphite crucible containing the eutectic material. The aperture diameter of the blackbody is nominally 3 mm. The estimated effective emissivity of the cavity has been calculated to be 0.9996. The standard design fixed point crucible is 24 mm diameter by 44  mm long, with prices starting from as little as £2,200 (excluding cost of metal). Other designs are possible by arrangement. The fixed-point cells are used by placing the cells within a suitable high temperature furnace and determining the instrument signal at the certified temperature from the melting plateau. (Note that NPL does not routinely supply the furnace but can suggest suitable suppliers). The available cells, along with their fixed-point temperatures are given in the table below.


Fixed point Temperature/ °C
Fe-C 1153
Co-C 1324
Pd-C 1492
Pt-C 1738
Ru-C 1953
Ir-C 2290
Re-C 2474
WC-C 2750

Supply of NPL high temperature eutectic fixed points - Fig 2

Supply and calibration of radiation thermometers using high temperature eutectic fixed points - Fig 1


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Last Updated: 24 May 2016
Created: 12 Dec 2013


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