When you point your IR camera at a surface, infrared red energy waves are flooding into the detectors. Some of the waves are a result of the emissivity of the material. Some of the IR waves coming into your infrared camera are the result of reflection off of the target surface. That’s called reflectivity. And in some cases (thin plastic, for example) infrared energy waves are transmitting through a target surface and entering into your thermal imaging detector system. That is called transmissivity. So, we have emissivity, reflectivity and transmissivity. Radiosity is the total of all three components: emissivity, reflectivity and transmissivity. The true temperature of the target surface is found only in one component: emissivity. It’s the job of the thermographer to know the difference.
High Reflectivity off chrome strip
Transmissivity through thin plastic
Due to the highly reflective nature of the surface of the chrome strip around the front window this Fluke IR camera reads -3.0°F, although the ambient temperature is 110°F. Notice the painted door panel. The paint has a high emissivity of 0.95 and therefore gives the thermographer a fairly accurate read of 144.1°F. The image on the right demonstrates the component of transmissivity. Infrared radiation from the man’s face is actually transmitting through the thin plastic. It is not affecting the temperature of the plastic. Radiosity then is all of the infrared radiation coming into your infrared camera: emissivity plus reflectivity plus transmissivity.
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
fax 916-736-1134
rhoff@restcon.com
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
