Blackbody is an ideal radiator. It absorbs radiant energy of all wavelengths, without energy reflection and transmission. Its external emissivity is 1. It should be pointed out that there is no real blackbody in nature, but in order to understand and obtain the infrared radiation dispersion law, it is necessary to choose a suitable model in theoretical research. This is the quantum oscillator model of body cavity radiation proposed by Planck. Then, the law of Planck blackbody radiation is derived, that is, the blackbody spectral radiance indicated by the wavelength. This is the starting point of all infrared radiation theories, so it is called the blackbody radiation law.
Impact of object emissivity on radiation temperature measurement: Practical objects that exist in nature are hardly black bodies. The amount of radiation of all practical objects depends not only on the radiation wavelength and the temperature of the object, but also on the types of materials that make up the object, the method of preparation, the thermal process, and the appearance and environmental conditions. Therefore, in order to make the black body radiation law applicable to all practical objects, it is necessary to introduce a share factor related to the nature of the data and appearance, that is, the emissivity. This coefficient indicates the closeness of the thermal radiation of the practical object to the radiation of the black body, and its value is between zero and a value less than 1. According to the law of radiation, as long as the emissivity of the data is known, the infrared radiation characteristics of any object are known.
The main factors affecting emissivity: data type, surface roughness, physical and chemical structure, and data thickness.
When measuring the temperature of a target with an infrared radiation infrared thermometer, first measure the amount of infrared radiation in the target's band, and then calculate the temperature of the target with the infrared thermometer. Monochromatic infrared thermometers share the amount of radiation in the band; dual-color infrared thermometers share the amount of radiation in the two bands.
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