If you didn’t get a chance to read the last blog (blog #026) it would be good to go back and take a look at it. It discusses the subject of “emissivity”. Since we learned that “emissivity” is connected with “accuracy” it would be nice to be able to change the surface characteristics of a highly reflective material (low emissivity) so that we can get an accurate surface temperature reading. Can we do that? YES! How? There are several ways: (1) adjust the camera emissivity if it has that feature capability (2) paint the surface (3) cover the surface with a high emissivity tape (electrician tape, masking tape, etc).
Let me refer to the 3rd edition of the NonDestructive Testing HANDBOOK, Volume 3, Infrared and Thermal Testing by the American Society for Nondestructive Testing. (This would be a good publication to have in your library if you are serious about thermography.) In chapter 5 (Noise in Infrared Thermography), Part 3 (Techniques to Increase Emissivity) you’ll find the above three suggestions. In chapter 10, Part 4 under “Infrared Thermographic Equipment Operation” a caution is noted when adjusting the emissivity in the camera. On page 296 it says: “Set or use the correct emissivity and be particularly cautious with emissivity settings below 0.5.”
Polished copper has a very low emissivity and thus the surface temperature reading will be inaccurate. The image below shows two copper tubes, one with cold water and one with hot water. Notice the temperatures before modifying the surface for increased emissivity:
The surface temperature difference between the cold tube and the hot tube shows a difference of only 8° F. In the next images you’ll see the results of adding electrician tape (brown) to the back side of the same tubes. Notice the surface temperature differences in this image.
I quickly turned the tubes around exposing the sides with the electrician tape. Now the surface emissivity is in the 90’s and the temperature difference in the two tubes is 102° F. A significant effect, wouldn’t you say?
How’s your comfort level in thermography?
(The above comments represent my opinion).
Rod Hoff / Restoration Consultants Inc
Thermography Instructor / IR camera sales
3284 Ramos Circle, Sacramento CA 95827
toll free 888-617-3266 ext 301
Provider of Fluke TiS, TiR, TiR1, Ti, Ti25, TiR27, Ti27, TiR29, Ti29, TiR32, Ti32, TiR3, and TiR4 infrared cameras.
See DEMO www.moistureview.com/demo.html