This is a summary of the Consultative Committee for Thermometry (CCT) Key Comparison CCT-K3, i.e. the comparison of realizations of the fixed points of the International Temperature Scale of 1990 (ITS-90) over the range 83.8058 K to 933.473 K. The differences in the realizations of the various fixed points in this range of the ITS-90 and the uncertainties of those differences are given for the fifteen standards laboratories participating in the comparison.
An Oxford Instruments Radiox cryogenic radiometer was recently installed at the Bureau International des Poids et Mesures (BIPM). The first measurements were aimed at characterizing the performance of the system. The Radiox was then compared with the cryogenic radiometer of the French Institut National de Métrologie (INM), a CRI LaseRad, at the BIPM by successive measurements of the power in a laser beam at two wavelengths: 647 nm and 476 nm. The radiometers differed in these measurements by 1,9 parts in 10 4 , the uncertainties in each being smaller than 1 part in 10 4 .
The photodiode self-calibration technique requires the application of a water drop to the surface of the photodiode to be calibrated. By adsorption of water in the silicon oxide the reflectivity and hence the sensitivity of the photodiode changes. We show that the reflectivity of the detector can be restored to its former value by cleaning with pure ethanol. Influences of the room humidity on photodiode responsivity are discussed.
The spectral responsivity scales of eighteen national standards laboratories have been compared within the wavelength range 250 nm to 1000 nm using two different types of silicon photodetector. Overall, good agreement was found between the scales of the participating laboratories, although some large deviations were also observed, especially in the ultraviolet.
The sensitivity of a series of silicon trap detectors has been measured as a function of beam polarization. Measurements and numerical simulation show that very small departures from the ideal orientation of the photodiodes mounted in the trap induces a significant sensitivity to the state of polarization of the beam. Consequences of this polarization dependence for the use of trap detectors as transfer detectors in high-accuracy applications, particularly in cryogenic radiometry, are discussed.
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