Absolute Radiometry for the MeP-K: The Irradiance Measurement Method

Abstract

The "Mise en pratique for the definition of the kelvin" (MeP-K) as a guide for the realization of the kelvin is presently revised to incorporate the temperature scales in current use as the best formal approximations of the thermodynamic temperature and, additionally, direct methods of thermodynamic temperature measurement. Within the MeP-K, the CCT WG 5 "Radiation Thermometry" develops a document to facilitate the implementation of thermodynamic temperature measurements at temperatures above the silver fixed point (961.78 • C). Three thermodynamic temperature measurement methods, all relying on absolute spectral-band radiometry, are proposed. To make these techniques more accessible for the broader thermometry community, each of these methods is described in detail in an accompanying paper to the MeP-K. These descriptions shall not be understood as a restriction to other possible radiometric methods of thermodynamic temperature measurement. One of the methods of radiometric temperature measurement above the silver point is the absolute measurement of irradiance in a well-defined spectral band. This is a straightforward method, which relies on filter radiometers with known spectral irradiance responsivity and a well-defined observation geometry, without any imaging technique. It has been developed for thermodynamic temperature measurements of precision blackbodies as primary standards for radiometry and thermometry and for the investigation of the uncertainty of the ITS-90 as an approximation of the thermodynamic temperature over a period of nearly 20 years at PTB. The article describes the design of the applied filter radiometers, their calibration chain, and their long-term stability. Additionally, the

Practical Implementation of the Mise en Pratique for the Definition of the Kelvin Above the Silver Point

“…• A filter radiometer, calibrated for irradiance responsivity, is used to measure the radiance of the blackbody in combination with a lens aperture and a single, simple lens-"the hybrid method" [11]. • An imaging radiometer, calibrated for radiance responsivity, comprising a filter radiometer incorporated within an optical system consisting of several lenses and appropriate baffling, is used to measure the radiance of a blackbody-"the radiance method" [12,13].…”

T 90 Measurement of Co-C, Pt-C, and Re-C High-Temperature Fixed Points at the NIM

“…A KE LP4 pyrometer [10] was used to compare the difference between the two cells of each HTFP. The PSP of the NIM was adopted in measuring the ITS-90 values of one selected cell of each HTFP, and the silver point was used as the reference in calibrating the PSP.…”

Results of Long-Term Stability Tests Performed for the Eutectics Co–C and Pt–C

“…80-38) [7] with 650 nm central wavelength and 10 nm bandwidth was selected for temperature measurement. No corrections on the measured values were applied, so short-term stability measurements using the LP-4 pyrometer were performed prior to the actual stability measurements of the Co-C and Pt-C cells.…”