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Compensating for Reflected Temperature
Tip written by: Infraspection Institute

When performing infrared temperature measurements, reflected infrared energy can be a significant error source. This potential error source can be overcome by using the proper radiometer and test procedure.

All thermographers have experienced reflected energy when inspecting low emittance targets. For qualitative imaging, single-point reflections may be avoided by changing viewing angle.

With quantitative imaging, failing to compensate for reflected energy can account for significant measurement errors. The infrared energy received by a radiometer is the sum of emitted, reflected and transmitted energy (E+R+T=1.0). For targets with a transmittance of zero, the error sources are emittance and reflectance. Using a quality radiometer, reflected energy can be measured and compensated for by using the Reflector Method described below.

1. Set radiometer Emittance control to 1.00
2. Locate radiometer at desired distance from target to be measured
3. Aim and focus imager
4. Position diffuse reflector in front of, and parallel to, face of target
5. Measure apparent temperature of reflector surface and remove reflector
6. Enter value obtained in Step 5 into radiometer’s computer under reflectance input – commonly labelled Background, TAmbient, or Reflected Temperature.

Lastly, be sure to maintain a safe working distance from any energized or potentially dangerous targets.

The topic of reflected temperature is covered in depth in the Infraspection Institue Level II Certified Infrared Thermographer training course. Copies of Infraspection Institute’s Standard for Measuring and Compensating for Reflected Temperature Using Infrared Imaging Radiometers are available in PDF format from the Infraspection Online Store.

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