Working principle, classification and modern application of infrared thermometer
The temperature measurement principle of the infrared thermometer is to convert the radiant energy of the infrared rays emitted by the object (such as molten steel) into an electrical signal. The size of the infrared radiant energy corresponds to the temperature of the object (such as molten steel) itself. , the temperature of an object (such as molten steel) can be determined. Infrared temperature measurement technology has been developed to scan and measure the temperature of the surface with thermal changes, determine its temperature distribution image, and quickly detect hidden temperature differences. This is the infrared thermal imager. Infrared thermal imaging cameras were first used in the military. In 19 years, TI Corporation of the United States developed the world's first infrared scanning reconnaissance system. After that, infrared thermal imaging technology was successively used in aircraft, tanks, warships and other weapons in Western countries , as a thermal sighting system for reconnaissance targets, it has greatly improved the ability to search and hit targets. The infrared thermal imaging camera produced by the Swedish AGA company is in a leading position in civilian technology. However, how to make the infrared temperature measurement technology widely used is still a problem. It is an application topic worthy of research.
The infrared thermometer is composed of optical system, photoelectric detector, signal amplifier, signal processing, display output and other parts. The optical system gathers 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 its position. Infrared energy is focused on a photodetector and converted into a corresponding electrical signal. The signal passes through the amplifier and signal processing circuit, and is converted into the temperature value of the measured target after being corrected according to the algorithm of the internal treatment of the instrument and the emissivity of the target.
In nature, all objects with a temperature higher than absolute zero are constantly emitting infrared radiation energy to the surrounding space. The magnitude of the infrared radiation energy of an object and its distribution according to the wavelength - have a very close relationship with its surface temperature. Therefore, by measuring the infrared energy radiated by the object itself, its surface temperature can be accurately determined, which is the objective basis for infrared radiation temperature measurement.
A black body is an idealized radiator, which absorbs all wavelengths of radiation energy, has no reflection and transmission of energy, and has an emissivity of 1 on its surface. However, practical objects in nature are almost not black bodies. Qinghe obtained the distribution law of infrared radiation, and in theoretical research, an appropriate model must be selected, which is the quantized oscillator model of body cavity radiation proposed by Planck, and thus derived the law of Planck's black body radiation, that is, the black body expressed by wavelength Spectral radiance, which is the starting point of all infrared radiation theories, is called the law of black body radiation. The radiation of all actual objects depends not only on the radiation wavelength and the temperature of the object, but also on the type of material, preparation method, and thermal process of the object. It is related to factors such as surface state and environmental conditions. Therefore, in order to make the law of black body radiation applicable to all practical objects, a proportional coefficient related to material properties and surface states must be introduced, that is, emissivity. This coefficient represents how close the thermal radiation of an actual object is to the radiation of a 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 material is known, the infrared radiation characteristics of any object are known. The main factors affecting emissivity are: material type, surface roughness, physical and chemical structure, and material thickness. When using an infrared radiation thermometer to measure the temperature of a target, it is first necessary to measure the infrared radiation of the target within its band range, and then the temperature of the measured target is calculated by the thermometer. Monochromatic pyrometers are proportional to the amount of radiation within a band; dual-color pyrometers are proportional to the ratio of the amount of radiation in the two bands.
Infrared temperature measurement adopts a point-by-point analysis method, that is, the thermal radiation of a local area of the object is focused on a single detector, and the radiation power is converted into temperature through the emissivity of the known object. Due to the different detected objects, measurement ranges and usage occasions, the appearance design and internal structure of infrared thermometers are different, but the basic structure is generally similar, mainly including optical system, photodetector, signal amplifier and signal processing, display output and other parts. Infrared radiation emitted by a radiator. Entering the optical system, the infrared radiation is modulated into alternating radiation by the modulator, and converted into a corresponding electrical signal by the detector. The signal passes through the amplifier and signal processing circuit, and is converted into the temperature value of the measured target after being corrected according to the algorithm in the instrument and the target emissivity.
