Working principle of infrared thermometer
The composition and principle of infrared thermometer
Infrared thermometer is composed of optical system, photoelectric detector, signal amplifier, signal processing, display output and so on. The optical system converges the target infrared radiation energy in its field of view, and the size of the field of view is determined by the optical parts of the thermometer and their positions. The infrared energy is focused on the photodetector and converted into 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 instrument internal therapy and the target emissivity.
In nature, all objects whose temperature is higher than absolute zero continuously emit infrared radiation energy to the surrounding space. The size of the infrared radiation energy of an object and its distribution according to wavelength are closely related to 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 on which infrared radiation temperature measurement is based.
A black body is an ideal radiator. It absorbs radiant energy of all wavelengths, without energy reflection and transmission, and its surface emissivity is 1. However, practical objects existing in nature are almost not black bodies. In order to understand and obtain the infrared radiation distribution law, a suitable model must be selected in theoretical research. This is the quantized oscillator model of body cavity radiation proposed by Planck. The Planck blackbody radiation law is derived, that is, the blackbody spectral radiance expressed in wavelength, which is the starting point of all infrared radiation theory, so it is called the blackbody radiation law. In addition to the radiation wavelength and the temperature of the object, the radiation amount of all actual objects is also related to the types of materials that constitute the object, the preparation method, the thermal process, and the surface state and environmental conditions. Therefore, in order to apply the law of blackbody radiation to all real objects, a proportionality factor related to the material properties and surface state must be introduced, namely the emissivity. This coefficient indicates how close the thermal radiation of an actual object is to black body radiation, and its value is between zero and a value less than one. According to the law of radiation, as long as the emissivity of a material is known, the infrared radiation characteristics of any object are known. The main factors affecting the emissivity are yarn: material type, surface roughness, physical and chemical structure and material thickness.
When measuring the temperature of the target with an infrared radiation thermometer, first measure the infrared radiation amount of the target in its waveband, and then calculate the temperature of the measured target by the thermometer. The monochromatic thermometer is proportional to the radiation in the band; the dual-color thermometer is proportional to the ratio of the radiation in the two bands.
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