© 2022 by the author. Licensee MDPI, Basel, Switzerland.De Lucas Veguillas, Javier2024-02-262024-02-262022-10-28Sensors 22(21): 8284(2022)https://www.mdpi.com/1424-8220/22/21/8284http://hdl.handle.net/20.500.12666/943Javier de Lucas Veguillas [0000-0001-9030-6721] Data access requests from academic investigators can be directed to the corresponding author.An experimental procedure for characterizing the size-of-source effect (SSE) is proposed. Such an effect is the cause of one of the main influence variables generating uncertainty in the measurement, both in calibration and use, of direct reading radiation thermometers (RT). The procedure and uncertainty calculation described in the paper are aligned in terms of metrological traceability, with the requirements generally imposed to ensure the accuracy of measurements in industry and science. Results of application and validation of this particular procedure with equipment, including black body (BB) sources normally used in radiation thermometry calibration laboratories in the industrial field, are shown.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttps://creativecommons.org/licenses/by-nc-nd/4.0/Radiation thermometerThermometryIndustrial calibrationMetrologyTraceabilityBlackbodyEmissivityinfo:eu-repo/semantics/article10.3390/s222182841424-8220info:eu-repo/semantics/openAccess