Development of ReFaST Pyrometer for Measuring Surface Temperature With Unknown Emissivity: Methodology, Implementation, and Validation

The accuracy of temperature measurement by optical pyrometer depends largely on the emissivity configuration. However, determination of emissivity is a hard task as it varies with wavelength, temperature, and physical state of the surface. In this paper, we propose a new type of pyrometer named Reflector with a Fast Switching Tube to measure surface temperature as well as emissivity. The invention is featured by a novel reflector equipped with a fast switching tube inside. The tube can be moved to make two measurements, one is to measure intrinsic radiation from the target, and the other is to measure intrinsic and multiple reflectance radiation; then, the emissivity and temperature are solved out simultaneously. For accuracy validation, we make a new type of thermocouple, namely, flat-type thermocouple and measure the surface of it. By measuring the thermocouple immediately, the temperature drop between the measured surface and the thermocouple can be avoided. The measurement difference is 1.0 °C on average compared with the flat-type thermocouple ranging from 600 °C to 900 °C. The measurement uncertainty is evaluated based on a Monte Carlo method, and the standard uncertainty is 1.4 °C at 750 °C.