Determination of Emissivity by Using Reflected Thermal Radiation

Abstract

The determination of emissivity is crucial in any temperature measurement using radiation thermometry. Without this knowledge, large measurement uncertainties result. There is a lack of information on emissivity for common materials. Where there are databases, these databases often give emissivity for a specific material in a range or give emissivity for different conditionings of the material. This information may not apply to certain uses of the material. This creates quite a bit of doubt for anyone making measurements in the field. What is needed is a method to determine emissivity for a material object in the field. In 2011, Yamada and Ishii discussed a method that was set up in a fixed geometry to determine the emissivity of a specular object. In this paper, a method is discussed to determine the emissivity of both specular and diffuse objects using a thermal radiation source. The theory is presented. Then, practical measurements which were made are discussed. These measurements are compared to emissivity determined by other methods.