Thermography technique Essay Example | Topics and Well Written Essays - 1750 words

Thermography technique - Essay Example hence a complete surface temperature map of the object can be obtained in a non-contact manner. With arrogate calibration, it is also possible to get the absolute temperature values of any point on the surface of the object. Standards are required for calibration and these standards are materials of known emissivity in the temperature range of calibration. Infrared refers to a region of spectrum in the midst of the visible and microwave. The infrared spectrum extends from 0.75 mm to 1000 ?m wavelength range. However for practical applications it is the 1 15 ?m wavelength band, which is used. The properties of infrared radiations are similar to those of other electromagnetic radiations like brightness level. These radiations travel in straight lines unfold in vacuum as well as in solid, liquid and gases. These radiations can be optically focussed and directed by mirrors and lenses. The rightfulnesss of geometrical optics are valid for infr ared radiations as well. The energy and frenzy of infrared radiation emitted by an object primarily depends on its temperature and can be calculated victimisation the analytical tools such as Weins law, Planks law and Stefan Boltzmann law. When a body is heated, at that place is an increase in the temperature and emitted energy. The spectrum of infrared radiation emitted by a heated object contains a nonstop band of wavelength over a specific range. The fundamental compares or radiation laws that link the absolute temperature of the emitting object, extreme radiation, the intensity and wavelength are the Planks Law, the Stefan-Boltzmann Law and the Weins Displacement Law. The Planks law describes the spiritual distribution of radiation intensity from a black body and is mathematically expressed as Wm-2sr-1?m-1 .. (1) Where, W? = Blackbody spectral effulgent emittance at wavelength ? (?m) c = 3x108 m/s is the velocity of light in vacuum h = 6.634 x10-34 Js is Planks constant k = 1.4 x10-23 J/K is Boltzmanns constant T is absolute temperature of the full radiator Spectral radiant emittance of a blackbody at various temperatures is shown in Fig.1 1. Fig. 1 Spectral radiant emittance of a blackbody at different temperatures It can be seen in Fig. 1 that total energy radiated by a blackbody i.e. area under the spectral radiant emittance increases with change magnitude temperature of the blackbody. Further it can be seen that maxima of the spectral radiant emittance is shifting towards lower wavelength with increasing temperature of the blackbody. If one differentiates equation (1) with respect to ? and equates the differential to zero then one gets the relationship between the temperature of the blackbody and the wavelength corresponding to the maximum spectral radiance. This relationship is known as Weins law and is mathematically expressed as 2 .. (2) Where, ?max is the wavelength corresponding to the maximum spectral emittance T is absolute temperatur e of the blackbody This equation supports go away ward shift of the spectral emittance peak with increasing temperature of the blackbody as in Fig. 1. Integrating equation (1) with respect to ? between the limits ? = 0 to ? for a given temperature T of a blackbody, one gets total radiant power emitted into a hemisphere from the blackbody. This relationship is known as Stefans-Boltzmann law and is mathematically expressed as Total emittance W/cm2