Infrared thermometer consists of optical system, photodetector, signal amplifier, signal processing and display output. The optical system converges the target infrared radiation energy within its field of view. The size of the field of view is determined by the optical components of the pyrometer and its position. The infrared energy is focused on the photodetector and converted to a corresponding electrical signal. The signal passes through the amplifier and the signal processing circuit, and is converted into the temperature value of the measured target after being corrected according to the algorithm of the internal therapy of the instrument and the target emissivity.
In nature, all objects above absolute zero emit infrared radiation energy to the surrounding space. The size of the infrared radiation energy of an object and its distribution by wavelength have a very close relationship with its surface temperature. Therefore, by measuring the infrared energy radiated by the object itself, it can accurately determine its surface temperature, which is the objective basis for infrared radiation temperature measurement.
Blackbody is an idealized radiator that absorbs all wavelengths of radiant energy, no energy is reflected and transmitted, and its surface has an emissivity of 1. However, the actual objects existing in nature are hardly black, and in order to understand and obtain the distribution of infrared radiation, a suitable model must be selected in theoretical research. This is Planck's quantum oscillator model of body cavity radiation. Derived Planck black body radiation law, that is, the wavelength of blackbody spectral radiation, which is the starting point of all infrared radiation theory, it is called the black body radiation law. The radiation amount of all actual objects depends on the wavelength of the radiation and the temperature of the object, and also relates to the types of materials constituting the object, the preparation method, the thermal process, and the surface conditions and environmental conditions. Therefore, in order for the law of blackbody radiation to apply to all real objects, a proportional coefficient, namely the emissivity, must be introduced in relation to the properties of the material and the surface state. The coefficient represents the degree of closeness of the thermal radiation of the actual object to blackbody radiation, with values between zero and less than one. According to the law of radiation, as long as the emissivity of the material is known, the infrared radiation characteristics of any object are known. The main factors influencing the emissivity are: material type, surface roughness, physical and chemical structure and material thickness.
When measuring the target temperature with an infrared radiation thermometer, the infrared radiation amount of the target in its band is first measured, and then the temperature of the measured target is calculated by the thermometer. The monochromatic thermometer is proportional to the amount of radiation in the band; the dual pyrometer is proportional to the ratio of the radiation in both bands.
