Briefly describe the working principle of infrared thermometer
Infrared thermometer by the optical system, photodetector, signal amplifier and signal processing, display output and other components. Optical system convergence of its field of view of the target infrared radiation energy, the size of the field of view by the thermometer's optical components and their location to determine. The infrared energy is focused on the photodetector and transformed into a corresponding electrical signal. This signal is converted into the temperature of the target by amplifiers and signal processing circuits and corrected for the target emissivity according to the algorithms used in the instrument.
In nature, all objects with temperatures above absolute zero are constantly emitting infrared radiation energy into the surrounding space. The size of an object's infrared radiation energy and its distribution by wavelength - and its surface temperature have a very close relationship. 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 thermometry.
Blackbody is an idealised radiation body, it absorbs all wavelengths of radiant energy, no energy reflection and transmission, the emissivity of its surface is 1. However, the existence of the actual objects in nature, almost all are not blackbody, in order to clarify and obtain the law of distribution of infrared radiation in the theoretical study must choose the appropriate model, which is the Planck put forward by the body of the cavity radiation of the quantisation of the vibronic model, which led to the derivation of the Planck's law of blackbody radiation, that is, expressed in wavelengths of the blackbody spectral radiance, which is the starting point of all infrared radiation theory, it is called the law of blackbody radiation. All the radiation of the actual object in addition to relying on the wavelength of the radiation and the temperature of the object, but also with the composition of the object's material type, preparation methods, thermal processes, as well as the surface state and environmental conditions and other factors. Therefore, in order to make the blackbody radiation law applicable to all real objects, it is necessary to introduce a proportionality coefficient, i.e., emissivity, which is related to the nature of the material and the state of the surface. This coefficient expresses the proximity of the thermal radiation of a real object to the blackbody radiation and has a value 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 emissivity are in: material type, surface roughness, physical and chemical structure and material thickness.
When using infrared radiation thermometer to measure the temperature of the target first of all to measure the target in its band range of infrared radiation, and then by the thermometer to calculate the temperature of the target to be measured. Single-colour pyrometers are proportional to the amount of radiation in the band; two-colour pyrometers are proportional to the ratio of the amount of radiation in the two bands.
