The Law Of Black Body Radiation Of Infrared Thermometer

A black body is an idealized radiator. It absorbs all wavelengths of radiant energy, without energy reflection or transmission, and its surface has an emissivity of 1. It should be pointed out that there is no real black body in nature, but in order to clarify and obtain the distribution of infrared radiation, an appropriate model must be selected in theoretical research. This is the quantized oscillator model of body cavity radiation proposed by Planck, which is derived Planck’s law of black body radiation, that is, the spectral radiance of a black body expressed in wavelength, is the starting point of all infrared radiation theories, so it is called the law of black body radiation.

The effect of object emissivity on radiation temperature measurement: The actual objects that exist in nature are almost not black bodies. In addition to the radiation wavelength and temperature of the object, the radiation amount of all actual objects is also related to factors such as the type of material that constitutes the object, the preparation method, the thermal process, and the surface state and environmental conditions. Therefore, in order to make the black body radiation law applicable to all actual objects, a proportionality factor related to the properties of the material and the surface state must be introduced, that is, the emissivity. This coefficient indicates how close the thermal radiation of the actual object is to the blackbody radiation, 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 material is known, the infrared radiation characteristics of any object can be known.

The main factors affecting emissivity: material type, surface roughness, physical and chemical structure and material thickness.

When measuring the temperature of a target with an infrared radiation thermometer, first measure the infrared radiation of the target within its band, and then the temperature of the measured target is calculated by the thermometer. The monochromatic thermometer is proportional to the radiation in the band; the two-color thermometer is proportional to the ratio of the radiation in the two bands.