What is the role of black body in infrared thermometer?
(1) An object that completely absorbs external radiation of any wavelength without any reflection under any conditions.
(2) Objects 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 continuously radiate, absorb, and emit electromagnetic waves. The radiated electromagnetic waves are different in each band, that is, they have a certain spectral distribution. This spectral distribution is related to the characteristics of the object itself and its temperature, so it is called thermal radiation. In order to study the laws of thermal radiation that do not depend on the specific physical properties of matter, physicists have defined an ideal object—a black body—as a standard object for thermal radiation research. The so-called black body means that all incident electromagnetic waves are absorbed, with neither reflection nor transmission (of course, a black body still radiates outward).
Kirchhoff's radiation law (Kirchhoff), the ratio of energy radiated by an object in thermal equilibrium to its absorption rate has nothing to do with the physical properties of the object itself, but is only related to wavelength and temperature. According to Kirchhoff's radiation law, at a certain temperature, a black body must be the object with the greatest radiation ability, and can be called a complete radiator. The electromagnetic waves radiated by different substances in infrared thermal imaging never intersect. This black body is just a reference object, equivalent to a zero point. But such an ideal black body does not exist in the real world, so what is used to describe this difference? For any wavelength, the emissivity is defined within a small wavelength interval of the wavelength. The radiated energy of the real object is the same as that of a black body at the same temperature. ratio of radiated energy. Obviously the emissivity is a positive number between 0 and 1. Generally, the emissivity depends on the material properties, environmental factors and observation conditions. If the emissivity is independent of wavelength, the object can be called a gray body, otherwise it is called a selective radiator.
Infrared thermal imaging cameras will be affected by external factors during long-term use, causing errors, so they need to be calibrated with a black body.
