Selection of working wavelength of infrared thermometer
In nature, when the temperature of an object is higher than absolute zero, due to the existence of internal thermal motion, it will continuously radiate electromagnetic waves to the surroundings, including infrared rays with a band of 0.75 to 100 μm. Infrared thermometers use Made on this principle.
The wavelength range of visible light is 0.38 to 0.78 microns, and the operating wavelength of industrial infrared thermometers is in the range of 0.65 to 14 microns.
Selection of working wavelength of infrared thermometer
Selecting the working wavelength/band of an infrared radiation thermometer is the first issue that instrument designers must consider. The basis for selecting the working wavelength is multifaceted.
●Determine the working wavelength based on the temperature measurement range
Planck's radiation law shows that for an object close to a black body, the higher the temperature, the greater the energy radiated, and the peak wavelength moves toward the shortwave direction as the temperature increases. Therefore, from the perspective of energy utilization, short wave is generally used for high temperature measurement, long wave is used for low temperature measurement, and medium temperature measurement is somewhere in between.
●Determine the working wavelength based on the emissivity of the object
Generally speaking, the objects to be measured are of various types. It is impossible for a thermometer to meet the requirements of various measured objects at the same time. For those objects that are neither black bodies nor gray bodies, the selection of the working wavelength cannot be determined only based on the measurement range, but mainly based on the change of the emissivity of the measured object with the wavelength.
●Determine the operating wavelength based on the atmospheric transmission spectrum
The infrared radiation thermometer receives the radiation energy of the object being measured and passes through the middle atmosphere. In order to reduce the influence of atmospheric absorption on the measurement results, in addition to considering the above factors when selecting the working wavelength, attention should also be paid to selecting some windows through which the atmosphere transmits radiation. The so-called atmospheric transmission window is not absolutely non-absorbent. The transmittance will decrease as the distance increases. Of course, the distance mentioned here is measured in hundreds of meters. As for the distance of several meters, it will not have a significant impact; the atmospheric window mentioned here is It means that the atmosphere does not contain a large amount of water vapor, smoke, and dust.
Select the working wavelength of the infrared radiation thermometer. Simply speaking, use 8~14 for low temperature and 0.8~1.0μm for high temperature. Other temperature zones are available at 1.6μm, 2.2μm and 3.9μm. Since some materials are transparent at certain wavelengths, infrared energy will penetrate these materials, and a special wavelength should be selected for this material.
