Determining Size of Source for Handheld Infrared Thermometers – Theory and Practice

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Determining Size of Source for Handheld Infrared Thermometers – Theory and Practice (144.02 KB)

Infrared (IR) thermometry is a very useful form of temperature measurement. It has advantages over contact thermometry. These advantages typically include a quicker response time and not having to interfere with the system being measured. However, it is typically not as accurate as contact thermometry. Part of the difference in accuracy is due to the fact that IR thermometers themselves are not as accurate as contact thermometers. The other part of the difference can be due to the user not controlling factors which can cause greater uncertainty of measurement. Major uncertainties in IR thermometry can be a result of emissivity, repeatability and size of source effect (SSE). Size of source (sometimes referred to as spot size) can be especially difficult because information on size of source is difficult to find.

This paper discusses size of source as it applies to IR thermometers. It covers experimentation done on handheld IR thermometers to determine size of source using accepted practices. It also compares this data to manufacture’s specifications given with the tested instruments. It demonstrates how to apply this knowledge to account for the uncertainty caused by not having a source of proper size and shows how to apply this data to an uncertainty budget.

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