Exploring the Size-of-Source Effect of Transfer Radiation Thermometers by Various Methods

To estimate the proper corrections to temperature values observed while aiming to radiation sources of different sizes, one must be aware of σ, the parameter that assesses the size-of-source effect (SSE) of a radiation thermometer, as a function of the diameter d of a radiation source. Since there is no known mathematical function to relate them, it is difficult to obtain σ as a function of d. The direct method to evaluate σ typically calls for a set of several apertures with increasing diameter. It is desirable to develop methods that produce accurate approximations with fewer apertures to speed up and reduce the cost of evaluating σ. With a constrained number of apertures, we demonstrate in this study an approach for obtaining an approximation to σ as a function of d. Indeed, we explore the SSE in both direct and indirect methods, as well as investigating the non-uniformity of the used source for further future correlation studies. In direct method, we developed the proper equations for calculating σ, and we presented the collected data and show that the SSE function values agree to within 0.08%. In indirect method, the SSE function found to be less than 0.3%.