The thermographic test is a non-destructive technique based on the physical principle of the energy transmission by radiation, that is through electromagnetic radiation. The wave length of the radiation emitted bt an object depends on its temperature (Wien’s low).
At the regular temperatures of objects, the wave-lengths competing with their-own radiations belong to the spectrum band falling in the infrared (λ included between 0.78 μm and 0,3 μm). Only for temperatures about 6000°k (sun’s surface temperature) the emission take place at the centre of the visible spectrum.
It is called black body that body with an absorption coefficient equal to 1 (it absorbs all the incident radiation) and at the same temperature of a non-black body it emits in a greater copy all the radiations, whatever their wavelength.
It is called grey body that one characterised by an independent emissivity of the wavelength, equal to the absorption coefficient and depending on the temperature only.
Moving on a body’s surface (the bodies that meet each other in the reality can be considered with a good proxy as grey bodies) from a higher temperature point to a lower one, the quantity of radiant energy emitted from the two different regions will vary (according to the Stefan Boltzmann law) and together with it, the wavelength of the emitted radiation will vary as well. The thermo-vision scanner just explore the examined surface using a specific band of wave-lengths and find the radiant energy intensity variation where there is a temperature gradient. Since the the radiant energy is linked to the body temperature only through the emissivity, according to the Stefans’ relation, once the body’s emissivity coefficient is found, it is possible to trace back to the temperature and vice versa: once the temperature is found, it is possible to trace back to its emissivity.
A specific optical scanning device carefully explores the whole camera’s field and reproduces in sequence an electric signal faithfull to the thermal information of the image and proportional to its intensity, which will be reproduced on kinescope.
To each range of variation of the surface temperature will correspond an analogue radiant intensity variation to which the tool will assign a specific colour shade. If the thermal conditions will not be satisfactory to perform the thermography it is possible to heat up through burners.
Main applications
- Individuation of structural lesions
- Malfunctioning of the electrical and hydraulic systems
- Plaster detachment
- Humidity infiltration
- Releases and thermal bridges
- Individuation of the building’s masonry
- Prior evaluation of the costs relating to restoration or change
Main advantages
- Technique absolutely non invasive
- Performing and processing rapidity