Pilot Comparison of Radiance Temperature Scale Realization Between NIMT and NMIJ

Abstract

A pilot comparison of radiance temperature scale realizations between the National Institute of Metrology Thailand (NIMT) and the National Metrology Institute of Japan (NMIJ) was conducted. At the two national metrology institutes (NMIs), a 900 nm radiation thermometer, used as the transfer artifact, was calibrated by a means of a multiple fixed-point method using the fixed-point blackbody of Zn, Al, Ag, and Cu points, and by means of relative spectral responsivity measurements according to the International Temperature Scale of 1990 (ITS-90) definition. The Sakuma–Hattori equation is used for interpolating the radiance temperature scale between the four fixed points and also for extrapolating the ITS-90 temperature scale to 2000 \(^{\circ }\)C. This paper compares the calibration results in terms of fixed-point measurements, relative spectral responsivity, and finally the radiance temperature scale. Good agreement for the fixed-point measurements was found in case a correction for the change of the internal temperature of the artifact was applied using the temperature coefficient measured at the NMIJ. For the realized radiance temperature range from 400 \(^{\circ }\)C to 1100 \(^{\circ }\)C, the resulting scale differences between the two NMIs are well within the combined scale comparison uncertainty of 0.12 \(^{\circ }\)C (\(k=1\)). The resulting spectral responsivity measured at the NIMT has a comparable curve to that measured at the NMIJ especially in the out-of-band region, yielding a ITS-90 scale difference within 1.0 \(^{\circ }\)C from the Cu point to 2000 \(^{\circ }\)C, whereas the realization comparison uncertainty of NIMT and NMIJ combined is 1.2 \(^{\circ }\)C (\(k=1\)) at 2000 \(^{\circ }\)C.