To meet the existing demand for measurements of emittance of opaque and semi-transparent materials, a new facility is being built at NIST around a bench-top Fourier spectrometer. This facility will complement existing capabilities for characterization of sample optical properties, which now encompass specular and directional-hemispherical reflectance and transmittance in the mid-IR. The first stage of the project is focused on opaque samples at medium temperatures, with semi-transparent sample capability and expansion of the temperature range to follow later. The approach selected for direct emittance characterization at temperatures above 500 K is to some extent similar to that employed in existing NIST facilities, sharing the FTIR detection technique and integrating sphere based measurements of hemispherical-directional reflectance. The latter measurement is performed at a single spectral band to allow a radiometric determination of the actual temperature of the sample surface. Design and modeling of the spherical laser reflectometer is the subject of a separate paper presented at this conference. A set of reference blackbodies, which contains four heat pipe furnaces and several interchangeable fixed-point cells, is to be delivered soon. An all-reflective off-axis optical train, designed for low emittance and scatter, has been delivered and is being characterized. To allow direct measurements of emissivity at the temperatures below 500 K, a cryogenically cooled radiometric zero trap and background control measures are being envisioned. Anticipated performance fo the new facility, the optical set up and principles of measurement as well as further development prospects are discussed. Along with a description of the developed methodology of directional emittance capability establishment, a concept of the controlled temperature emittance standard (CTES) is proposed. It is anticipated that such a standard will significantly reduce the ultimate loss of accuracy at the end of the calibration chain and enable end-users with specialized multi-band thermometers, which cannot be directly calibrated against blackbody sources, to train their smart temperature control systems using the material of interest and perform tests on site.
Proceedings Title: International Symposium on Temperature and Thermal Measurements in Industry and Science | 8th | | VDE
Conference Dates: June 19-21, 2001
Conference Location: Berlin, GE
Conference Title: TEMPMEKO
Pub Type: Conferences
directional, emittance, Fourier Transform, hemispherical, infrared, reflectance, spectral, spectrometer, temperature