Verification of Infrared Forehead Thermometer Readings Using a Blackbody Radiator at NMCC-SASO

Abstract

This study presents a verification method for Infrared Forehead Thermometer (IRFT) readings developed at the National Measurement and Calibration Center (NMCC) of the Saudi Standards, Metrology, and Quality Organization (SASO). Six IRFTs from two different models were tested at 38 °C, a temperature threshold for fever according to the World Health Organization (WHO). The IRFT readings were compared against reference radiance temperatures generated by a standard blackbody radiator commonly used for Infrared Ear Thermometer (IRET) calibration. The blackbody was maintained in a temperature-controlled water bath near 38 °C, with its true temperature monitored using a contact standard thermometer (Pt-100). The blackbody’s effective emissivity was calculated as 0.999874, closely matching the default emissivity setting (~ 1.0) of most IRFTs. Instead of using a radiation thermometer, radiance temperatures were calculated from the blackbody’s true temperature measurements using the Sakuma-Hattori Planck III function. When compared to reference radiance temperatures, the laboratory errors in IRFT readings ranged from − 0.20 to 0.09 °C. These values comply with the maximum permissible laboratory error (MPLE) of ± 0.3 °C specified in ASTM E1965-98:2016 for skin IR thermometers. However, when measurement uncertainty (± 0.16 °C) was considered, one IRFT (− 0.20 °C error) failed verification. This was likely due to dust or smudges on the inner lens, which are difficult to clean externally. Further studies are needed to compare and validate these findings using methodologies from other national laboratories.