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Why Imagers & Radiometers Disagree

As the awareness of non-contact temperature measurement has increased, spot radiometers have become common tools in the workplace. Discrepancies frequently arise when temperatures taken with spot radiometers are compared to temperatures obtained with an imaging radiometer.

Advances in technology and increased sales volume have allowed several manufacturers of spot radiometers to offer a number of models priced below $100. Lower cost, combined with a greater awareness of infrared thermometry, has allowed most maintenance personnel to incorporate spot radiometers into their toolboxes.

When a thermographer reports temperatures obtained with an imaging radiometer, maintenance personnel will frequently attempt to cross-verify reported temperatures with a spot radiometer. In such situations, discrepancies are common as the spot sizes of imaging radiometers and spot radiometers often vary widely. In order to ensure measurement accuracy and avoid discrepancies, one should bear the following in mind:

• For accurate temperature measurement, radiometers must be operated correctly and in accordance with manufacturer’s instructions
• Radiometer accuracy can degrade over time or with physical stress
• Spot radiometers will generally have spot measurement sizes that are larger than imaging radiometers
• When spot measurement sizes vary between instruments, reliable cross-verification is not possible

To avoid discrepancies, personnel who utilize infrared radiometers should be trained in the proper use of their test equipment along with its limitations. Personnel must also understand how the characteristics of infrared instruments affect the accuracy of observed temperatures. Lastly, using cross-verification of temperatures should be avoided when radiometer capabilities differ from each other.

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