Comparison of a Detector-Based Near-IR Radiance Scale to an ITS-90 Calibrated Radiation Thermometer

Integrating-sphere-input InGaAs radiometers (ISIR) have been developed at the National Institute of Standards and Technology (NIST) to extend the detector-based calibration of radiation thermometers from the Si range to the near-infrared (NIR). These near-infrared radiometers are used to determine the reference spectral irradiance responsivity scale based on the primary-standard cryogenic radiometer. The irradiance responsivity scale is then propagated to spectral radiance at the exit port of an integrating sphere. The near-infrared radiation thermometer (NIRT) is calibrated using this detector-based radiance scale. The first phase of this research work is reported here where the relative spectral radiance responsivity of the NIRT has been determined using a monochromator-based system. Thereafter, the relative spectral responsivity of the NIRT is converted into an absolute responsivity using the radiances from the Zn fixed point blackbody. Then, the NIRT is used to extend these calibrations for temperature measurements between 157 A degrees C and 1000 A degrees C. The NIRT has also been calibrated in this temperature range using the five, fixed point blackbodies of the ITS-90. The two different calibration approaches for temperature measurements are compared.