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Measuring and Compensating for Reflected Temperature – Part 2
Tip written by: Infraspection Institute

Non-contact thermometry provides a means for rapidly measuring object temperatures. To ensure measurement accuracy, all error sources must be considered and properly addressed. With this Tip, we discuss how to measure and compensate for Reflected Temperature using the Direct Method.

Unlike contact thermometry, infrared temperature measurement is subject to several error sources. While many are familiar with emissivity, another common error source is reflectivity. In order to compensate for errors due to reflections, imaging and non-imaging radiometers have inputs for entering Reflected Temperature. Depending upon the make and model of the instrument, this control may be referred to as TAM, Ambient Temp, Background, or Reflected Temperature.

Since all real world objects have emittance values of less than 1.0, some infrared energy will always be reflected from a measured object’s surface. The Reflected Temperature feature found on radiometers will mathematically compensate for this error source provided that it has been properly set by the operator.

Listed below are the general steps for measuring and compensating for Reflected Temperature when using the Direct Method.

• Place imager at desired location and distance from object to be measured
• Aim and focus imager
• Estimate angle of incidence and angle of reflection
• Position imager pointing away from target & parallel to angle of reflection
• With imager focused and its E control set to 1.0, measure average apparent temperature of scene using either area measurement or isotherm feature
• Conduct procedure three times and average results
• Enter averaged value into radiometer’s Reflected Temperature input

When measuring Reflected Temperature, make certain to maintain a safe distance from any hot or energized targets and observe all necessary safety precautions. When entering Reflected Temperature into your radiometer, be sure to access the proper menu as some imagers have inputs for Reflected Temperature as well as ambient air temperature.

The above procedure is described in greater detail in the Standard for Measuring and Compensating for Reflected Temperature Using Infrared Imaging Radiometers. For more information on infrared standards or thermographer training, call 609-239-4788 or visit us online at www.infraspection.com.

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