When you point your IR camera at a surface, infrared 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, your camera is picking up infrared energy waves resulting from emissivity, reflectivity and transmissivity. Radiosity is the total of all three components. Radiometric cameras will combine all three components to give a temperature readout. Is it accurate? 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.
Due to the highly reflective nature of the surface of the chrome strip around the front window of this car the Fluke IR camera reads -3.0°F, although the ambient temperature is 110°F. The -3.0°F reading is a result of the combined infrared radiation from that which is emitted from the chrome and that which is reflected off of the chrome. Outer space is very cold and the reflection of outer space is corrupting the temperature read out. Now, 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. So, in this case the camera is receiving all three components of radiosity: emissivity, reflectivity and transmissivity. To be comfortable in using an infrared camera you need to be aware of what your camera is receiving in the form of infrared energy waves.
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