What is the role of the blackbody in an infrared thermometer?
(1) An object which, under any conditions, completely absorbs external radiation of any wavelength without any reflection.
(2) An object with an absorption ratio of 1 .
(3) An object that absorbs all incident radiation of any wavelength at any temperature. Any object has the ability to constantly radiate, absorb, and emit electromagnetic waves. Radiation out of the electromagnetic waves in the various bands are different, that is, with a certain spectral distribution. This spectral distribution is related to the properties of the object itself and its temperature, and is therefore called thermal radiation. In order to study the laws of thermal radiation that do not depend on the specific physical properties of the material, physicists have defined an ideal object - black body (black body), as a standard object for the study of thermal radiation. The so-called black body refers to the incident electromagnetic waves are all absorbed, neither reflection nor transmission (of course, the black body is still black body radiation is still to radiate outward).
Kirchhoff's law of radiation (Kirchhoff), in the thermal equilibrium state of the object of the energy radiated and the ratio of the absorption rate and the object itself has nothing to do with the physical properties, only with the wavelength and temperature. According to Kirchhoff's law of radiation, at a certain temperature, the black body must be the radiation capability * big object, can be called a complete radiator. Infrared thermal imaging of electromagnetic waves radiated by different substances are never intersected, this blackbody is just a reference, equivalent to a zero point. But the real world does not exist such an ideal blackbody, so what is used to portray this difference? For any wavelength, the definition of emissivity for the wavelength of a small wavelength interval, the real object of the radiant energy and the same temperature of the black body of the ratio of the radiant energy. Clearly the emissivity is a positive number between 0 and 1. In general, the emissivity depends on the properties of the material, the environmental factors and the observation conditions. If the emissivity is independent of the wavelength, then the object can be called a grey body, otherwise it is called a selective radiator.
Thermal imaging cameras can be affected by external factors in the course of long-term use, resulting in errors, so they need to be calibrated with a grey body.
