Use of a High-Temperature Integrating Sphere Reflectometer for Surface-Temperature Measurements

Abstract

The National Institute of Standards and Technology (NIST) has developed a new facility for the characterization of the infrared spectral emissivity of samples between 150 and 1,000 • C. For accurate measurement of the sample surface temperatures above 150 • 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: (a) an indirect sample emissivity measurement with an integrating sphere reflectometer and (b) a relative radiance measurement (at the same wavelengths as in (a)) of the sample as compared to a blackbody source. The results are combined with a 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-nearnormal (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 thermocouples and temperature-drop calculations using a knowledge of the sample's thermal conductivity.

Measurements of infrared spectral directional emittance at NIST - A status update

“…Error bars shown in all figures represent expanded uncertainty values (k = 2). Detailed uncertainty budget description can be found in Reference [9]. The results shown are in agreement with the weighted mean and the uncertainties reported for all temperatures and over the entire wavelength range.…”

“…First, the heated-sample emittance is determined at a specific wavelength (900 nm or 1550 nm) using a custom built integrating sphere reflectometer, a filter radiometer and a reflectance standard [9]. Next, a radiance comparison at the same wavelength of the sample and a blackbody of known temperature is made.…”

“…Next, a radiance comparison at the same wavelength of the sample and a blackbody of known temperature is made. From these two results, the surface temperature is calculated with low uncertainty as demonstrated in Reference [9].…”

Temperature-Resolved Infrared Spectral Emissivity of SiC and Pt–10Rh for Temperatures up to 900°C

“…The spectral emissivity of the reference blackbodies has been evaluated by direct comparison of their spectral radiance with the set of fixed-point blackbodies. The spectral emissivities of the fixed-point crucibles have been calculated from the measured emissivity of the graphite crucible material and the geometry of the cavities using Monte Carlo analysis [7,8]. The emittance of the BB cavities was found to be greater than 0.9995 over the wavelength range of interest.…”

A New Spectrophotometer System for Measuring Hemispherical Reflectance and Normal Emittance of Real Surfaces Simultaneously

“…The hemispherical reflectance has been measured by various techniques [7][8][9][10][11][12][13]. In the field of thermal engineering, the hemispherical reflectance has been measured mainly by an integrating sphere technique [7].…”