Thermography bichromatic
Principle :
Based on radiation measurement in two infrared spectral ranges, the bichromatic thermography provides simultaneous access to an emissivity field and temperature field measurement using the gray body hypothesis.
The Bichromatic thermography has several advantages :
The temperature fields obtained with a bispectral camera are more accurate in terms of intensity and spatio-temporal variations.
Emissivity fields reveal surfaces of different natures and physico-chemical transformations.
Examples :
Hot cup in the process of cooling
The temperature field of this hot cup obtained by bichromatic thermography (b) is totally different and fairer than that obtained by traditional thermography with an emissivity of 1 (has), thanks to the consideration of the emissivity field (c).
Observation of the friction track of a brake disc on a test bench
The temperature field is indicative of thermal phenomena such as hot spot locations.
The emissivity field provides information on the physico-chemical evolution of the surface, oxidation, deposits of wear particles…
Bichromatic thermogrpahie VS traditional thermography at two moments of braking
(has) ongoing and (b) at the end. Temperature fields are different in terms of intensity and gradient, than those obtained by traditional thermography for an emissivity of 0,3 and 1. At the end of braking traditional thermograms show a hot spot, while the temperature of the disc is relatively uniform as shown by the bichromatic thermogram. This effect is actually due to an oxidation of the surface of the disc visible on the emissivity field [E.BERTE 2015].