Selection of Working Wavelength for Infrared Thermometer
In nature, when the temperature of an object is higher than absolute zero, due to the existence of its internal thermal motion, it will continuously radiate electromagnetic waves to the surroundings, including infrared rays with a band of 0.75-100 μm. Infrared thermometers use made on this principle.
The wavelength range of visible light is 0.38 to 0.78 microns, and the working wavelength of industrial infrared thermometers is in the range of 0.65 to 14 microns.
Selection of Working Wavelength for Infrared Thermometer
Selecting the working wavelength/working band of the infrared radiation thermometer is the first problem that the instrument designer should consider. There are many reasons for choosing the working wavelength.
●Determine the working wavelength according to 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 radiated energy, and the peak wavelength moves to the short wave direction as the temperature increases. Therefore, from the perspective of energy utilization, short waves are generally used for high temperature measurements, long waves are used for low temperature measurements, and medium temperature measurements are in between.
●Determine the working wavelength according to the emissivity of the object
Generally speaking, the objects to be measured are various. 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 body nor gray body, the choice of working wavelength cannot be determined only according to the measurement range, but mainly according to the change of emissivity of the measured object with wavelength.
●Determine the working wavelength according to the atmospheric transmission spectrum
The infrared radiation thermometer receives the radiant energy of the object to be 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-absorbing, and the transmittance will decrease as the distance increases. Of course, the distance mentioned here is in hundreds of meters. As for the distance of a few meters, it will not have a significant impact; the atmospheric window mentioned here is It means that the atmosphere does not contain a lot of water vapor, smoke and dust.
Select the working wavelength of the infrared radiation thermometer, simply speaking, use 8-14 for low temperature, and 0.8-1.0 μm for high temperature. Other temperature zones can choose 1.6μm, 2.2μm and 3.9μm. Since some materials are transparent at a certain wavelength, infrared energy will penetrate these materials, and a special wavelength should be selected for this material.
