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Size-of-Source Effect in Infrared Thermometers

Technical Guide 26

The accuracy of most handheld infrared thermometers is severely limited by a phenomenon known as the size-of-source effect (SSE), which arises from scattering and diffraction of radiation within the optical system of the device. The error caused by the SSE can be many times larger than the accuracy quoted in the device's specifications. This guide explains how a calibration laboratory can characterise the SSE and provide information on a calibration certificate to enable users to correct for the SSE and achieve the best accuracy in their measurements.

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