Use of a High Temperature Integrating Sphere Reflectometer for Surface Temperature Measurements
Leonard M. Hanssen, Claus Cagran, A Prokhorov, Sergey Mekhontsev, V B. Khromchenko
NIST has developed a new facility for the characterization of the infrared spectral emissivity of samples between ambient and 1000 C. For accurate measurement of the sample surface temperatures above 300 C, the system employs a high temperature reflectometer to obtain the surface temperature of the sample. This technique is especially useful for samples that have significant temperature gradients due to the thermal conductivity of the sample and the heating mechanism used. The sample temperature is obtained through two measurements: (1) an indirect sample emissivity measurement with an integrating sphere reflectometer and (2) a relative radiance measurement (at the same wavelengths as in (1)) of the sample as compared to a blackbody source. The results are combined with knowledge of the blackbody temperature and Planck s law to obtain the sample temperature. The reflectometer s integrating sphere is a custom design that accommodates the sample and heater to allow reflectance measurements at temperature. The sphere measures the hemispherical-near-normal (8 ) reflectance factor of the sample compared relative to a previously calibrated room temperature reference sample. The reflectometer technique of sample temperature measurement is evaluated with several samples of varying reflectance. Temperature results are compared with values simultaneously obtained from embedded thermometers and temperature drop calculations using knowledge of the sample s thermal conductivity.