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A comparison of Co-C, Pd-C, Pt-C, Ru-C and Re-C eutectic fixed points
independently manufactured by three different institutes
K. Anhalt, J. Hartmann
Physikalisch- Technische Bundesanstalt Braunschweig und Berlin, Germany
D. Lowe, G. Machin
National Physical Laboratory, Teddington, UK
M. Sadli
CNAM- INM, Paris, France
Y. Yamada, P. Bloembergen
National Metrology Institute of Japan, AIST, Tsukuba, Japan
Abstract. In order to assess the performance and capability
as well as the reproducibility of cell production five
different Metal-carbon (M-C) eutectic cells from three
institutes were measured by radiation thermometry at PTB.
The reproducibility of the melting temperature approached
the requirements set by CCT/CCPR but significant
differences were seen between different manufactures.
Introduction
Metal- Carbon (M-C) eutectics are possible candidates for
thermometric and radiometric fixed-points above the Au
point temperature of 1337.33 K. They are being
manufactured and investigated at a wide number of
institutes. To become recommended temperature fixed
points the repeatability and reproducibility of these systems
have to be carefully investigated so as to guarantee a high
level of world wide equivalence. For this reason a
comparison was carried out at PTB in May 2004 of five
different M-C cells manufactured by CNAM-INM, NPL
and NMIJ within the EU project HIMERT [1].
Outline and experimental setup
In order to assess the performance of the cells with low
uncertainty the relative differences in radiance temperature
of the melting of the M-C cells were determined by
installing them in furnace systems with virtually identical
temperature homogeneity. Measurements were done with
two radiation thermometers.
M-C eutectic cells with Co-C, Pd-C, Pt-C, Ru-C and Re-C
as fixed point material and melting temperatures between
1300 K and 2800 K were manufactured by CNAM-INM,
NPL and NMIJ and brought to PTB. Their outer dimensions
were similar: approx. 25 mm in diameter, 40-50 mm in
length, and a cavity aperture of 3 mm.
Furnace systems As in former comparisons effects of
the furnace on the melting process could not be excluded [2],
two similar Nagano furnaces were supplied by the NMIJ:
Nagano S (VR10-A20) and Nagano M (VR10-A23) [3].
Their equivalence has been investigated prior to the
comparison, showing similar temperature homogeneity for
temperatures up to 2300 K resulting in an equivalent
performance of both M-C cells to be compared.
Radiation thermometers For the radiance measurements
two LP3 radiation thermometers with low size-of
source-effect were used, the LP3 80-46, brought to Berlin
by the BNM-INM, and the LP3 80-05, provided by the PTB,
both with an improved interference filter setup for
measurements at high temperatures characterized by an
effective wavelength of about 650 nm [4].
Experimental procedures During 14 days measurements
in both furnaces were performed. For each cell in each
furnace four melting and freezing plateaus with defined
temperature steps were monitored with both radiation
thermometers resulting in a total of 16 melts and freezes per
day.
For the measurements of the Co-C, Pd-C, Pt-C eutectics
both furnaces were equipped with a cell of the same
material allowing a ‘parallel scheme’ to be established
during one day. The temperatures sensed by the radiation
thermometers never exceeded the melting temperature of
the cell material under investigation by more than 30 K. For
furnace temperatures higher than 2500 K the temperature
homogeneities of the two furnaces are no longer identical;
then the Nagano M furnace provides the best available
conditions. Therefore, the Re-C cells were compared
consecutively in the Nagano M furnace, while on these days
the Nagano S furnace was used to investigate the Ru-C
cells.
Uncertainties
Uncertainty components considered are: cell repeatability,
size-of-source-effect, uncertainty of the inflection point
determination, and the radiation thermometers stability.
Size-of-source-effect The nearly identical
temperature profiles of both furnaces, equipped with an
identical set of radiation shields results in a small
size-of-source-effect (SSE) difference between the cells
(maximum 15 mK for Re-C). Therefore, the signal is not
corrected for the SSE and instead the effect is included in
the uncertainty budget.
Radiation thermometer stability In order to detect
a drift of the radiation thermometers certain cell-furnace
combinations remained unchanged on consecutive days or
were reinstalled during the time of the comparison. From
the difference between such two measurements the stability
of the radiation thermometers can be derived. During the
measurements of Co-C, Pd-C, Pt-C the drift was less than
40 mK for both radiation thermometers. At 2300 K (Ru-C)
and 2750 K (Re-C) larger and significant drifts of up to
100 mK were observed, resulting in higher uncertainties for
Proceedings NEWRAD, 17-19 October 2005, Davos, Switzerland 289