How to Deal With Emittance
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How to Deal With Emittance
Tip written by: Infraspection Institute
The perpetual question among those using radiometric equipment is, “What emittance value should I use?” In this Tip, we address several options for providing emittance values.
Emittance is a numerical value between 0 and 1.0 indicating an object’s relative ability to radiate infrared energy. Most radiometers allow the user to input emittance values into the radiometer’s computer. Utilizing correct emittance values is imperative for accurate non-contact temperature measurements.
When determining emittance values for a target, there are five accepted ways to obtain an emittance value. These methods are listed below in order of increasing complexity and accuracy.
- Use General Default Values – Organics are generally > 0.80.Metals can vary widely from < 0.1 to > 0.90
- Use Emittance Tables – Be certain to use tables that match your radiometers spectral response and your target’s temperature.
- Estimate Emittance -Choose representative sample and test for emittance value. Use these values whenever similar object is encountered in the future.
- Modify Surface to a Known Emittance Value. Use tape, paint, or powder with known E. Prior to modifying any surface, be certain it is safe to do so.
- Measure Emittance Value – Use subject radiometer to measure target E value. This practice is preferred as it provides the most accurate emittance values.
The procedure for measuring emittance values is described in detail in the Standard for Measuring and Compensating for Emittance Using Infrared Imaging Radiometers available from Infraspection Institute. 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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