Report of the spectral irradiance comparison EURAMET.PR-K1.a.1 between MIKES (Finland) and NIMT (Thailand)

Abstract

A bilateral comparison of the spectral irradiance scales between MIKES (Finland) and NIMT (Thailand) was carried out at 22 wavelengths between 290 nm and 900 nm. MIKES acted as the pilot and link to the results of the key comparison CCPR-K1.a. The spectral irradiance values measured by NIMT generally agree with the key comparison reference value within the expanded uncertainty. Only exceptions are results at wavelengths 300 nm, 450 nm, and 500 nm, where the ratios between the degree of equivalence (DoE) and the expanded uncertainty of DoE (k = 2) are 1.0, 1.4, and 1.2, respectively.

Uncertainty evaluation for linking a bilateral key comparison with the corresponding CIPM key comparison

“…It is a basic property of the division into uncertainties related to the correlated and uncorrelated effects that the contribution by the uncorrelated components can be reduced by investing more effort in the comparison and repeating the measurement cycles several times. spectral irradiance scales between MIKES and NIMT in the spectral range from 290 nm to 900 nm [7]. The pilot and link NMI i of the bilateral comparison is MIKES.…”

“…for the expectation values of the coupled terms in equation (7). All terms corresponding to the defined random variables on the right-hand side of equation ( 12) are now related to uncorrelated effects.…”

“…where the terms ±X ref in equations ( 4) and (7) for D α(i) and D j cancel each other. Since all the terms of equation ( 18) are related to uncorrelated effects, the standard uncertainty of the mutual degree of equivalence can be calculated in a straightforward way,…”

“…A practical example is useful to demonstrate the application of the equations presented. Such an example is provided by a recent bilateral comparison of spectral irradiance scales between MIKES and NIMT in the spectral range from 290 nm to 900 nm [7]. The pilot and link NMI i of the bilateral comparison is MIKES.…”

“…As explained in appendix A, it is straightforward to extend the analysis of the bilateral comparison to a regional comparison by assuming that each participant of the regional comparison has carried out a bilateral comparison with the link NMIs. The results are applied to a practical example of a bilateral comparison EURAMET.PR-K1.a.1 between the Centre for Metrology and Accreditation (MIKES), Finland, and the National Institute of Metrology (NIMT), Thailand [7]. One of the main conclusions of this work is that the uncertainty components related to uncorrelated effects in the measurements of the linking NMIs dominate the additional uncertainty due to the linking process.…”