A Simple Method to Measure and Correct the Size-of-Source Effect of Infrared Thermometers Using the Emissivity Setting

A source of significant measurement error and uncertainty in infrared thermometers (IRTs) is the size-of-source effect (SSE). The SSE is caused by imperfections in the IRT optical system, resulting in the temperature measurement accuracy being dependent on the target size. If the SSE of an infrared thermometer is known, it can be corrected to achieve more accurate temperature measurements. In this work, a relationship between the SSE, the target emissivity, and the adjustable thermometer emissivity setting is developed. A simple approach to experimentally measure the SSE of an IRT based on this relationship is proposed. The measured SSE can be corrected by making appropriate adjustments to the thermometer emissivity setting, resulting in significantly improved temperature measurement accuracy.