Uncertainty Analysis for Emissivity Measurement at Elevated Temperatures with an Infrared Camera

The current work describes the measurement of emissivity of rock samples and black paint Pyromark 2500 within the temperature range between 230 ∘ C and 650 ∘ C together with its detailed uncertainty analysis. The infrared camera Optris PI450 was used to obtain the surface temperature of the samples. The described method is based on adjusting the emissivity of the rock sample until the temperature of the rock surface detected by the IR camera matches the temperature of a reference body. The reference body represented the tested rock sample partially coated with Pyromark 2500. The emissivity of the paint was previously determined with a technique described in this work: Pyromark 2500 was applied on a ceramic heater and heated up to a certain temperature that was calculated from measured electrical resistance of the ceramic heater (previously calibrated as a resistance thermometer). The emissivity measurement of rock samples is flexible concerning the type of sample, its size, position relative to the IR camera (distance, observation angle), and environmental conditions. Emissivities of Gotthard granite and Paradiso migmatite are reported, and they are in an agreement with emissivities of some granite samples from literature. The uncertainty of the rock sample emissivity reaches the value of 10 % and the main contribution to it is related to the electrical resistance measurement of the ceramic heater.