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Glossary of Thermography Terms

Effusivity, Thermal

(e)- A measure of the resistance to temperature change of a material. e is a relevant thermophysical parameter for surface heating or cooling processes as well as in quenching processes.

e = (kρcp)½; [Wmˉ² Kˉ¹ s½]

where K= thermalconductivity,
ρ= bulk density,
cp= specific heat

Emissivity (ε)

The ratio of a target surface’s radiance to that of a blackbody at the same temperature, viewed from the same angle and over the same spectral interval; a generic look-up value for a material. Values range from 0 to 1.0. Also called emittance.

EMI/RFI noise

Disturbances to electrical signals caused by electromagnetic interference (EMI) or radio frequency (RFI). In thermography, this may cause noise patterns to appear on the display and in saved images.

Equalization, Emissivity Equalization

A method for determining the emissivity value in each individual pixel of the image, much used for objects where the emissivity varies from pixel to pixel, e.g. printed circuit boards. The found values are then used for finding the correct temperature in each point of the image.

Equalization Box

A box, in which a test object can be heated up uniformly to a present temperature. Knowing this temperature it is possible to calculate the emissivity in each pixel of the image of the object. Much used for accurate temperature measurements on objects with great emissivity variations over the surface, e.g. transistors, PCBs.

Exitance, Radiant (also called Radiosity)

Total infrared energy (radiant flux) leaving an object surface. This is composed of radiated, reflected and transmitted components. Only the radiated component is related to the surface temperature of the object.

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