Use of a Furnace for a Thermal Radiation Source

Infrared thermometers are being designed to measure higher temperatures. To meet the calibration needs for these instruments, higher temperature sources are needed. Most of the infrared thermometer models reaching higher temperatures have a narrow field of view, meaning that there is the possibility of using a cavity thermal radiation source instead of a flat-plate thermal radiation source for their calibration. One possibility for the use of a cavity is designing the cavity for use inside of a furnace. This can present several challenges such as knowing the emissivity of the cavity. This issue is further clouded by the temperature uniformity on the cavity walls. This paper discusses placing a cavity inside a standard thermocouple calibration furnace. It discusses testing that was done to qualify the cavity. It then speaks to steps that may be taken in the future to improve this design.