Surface moisture content can be measured directly using IR analyzers. When light hits a surface, moisture absorbs IR radiation in the region of 1.8 microns. So IR absorbance correlates with actual surface moisture.
Today, it’s the capability of people, not equipment, that limits application. Thermal imagers rapidly are becoming more economical and easy to use, but the camera is only as good as the person using it.
Take time to examine your processes, understand your materials, and think about how the properties you wish to assess relate to thermal characteristics. Then, having the full picture, you can make the most of thermal imagers.
Emissivity basics
All objects emit IR (thermal) radiation. The intensity of the radiation depends upon the temperature and nature of a material’s surface. At a given temperature, an object that has an emissivity of 1 would provide perfect or so-called blackbody radiation. Of course, in the real world, there are no perfect radiators and materials produce lower emissivities. When a thermal imager observes the thermal radiation from real objects, part of what it sees is reflected from the object’s surface, part is emitted by the object, and part may be transmitted through the object.
L. Terry Clausing, P.E., is an American Society for Nondestructive Testing Level III certified specialist in thermography at TrendFormers, Cincinnati, Ohio. E-mail him at [email protected].