What are the relevant theoretical principles of infrared temperature measurement?
In nature, when the temperature of an object is above absolute zero, due to the presence of internal thermal motion;
It will continuously radiate electromagnetic waves in all directions, including infrared radiation with a wavelength range of 0.75 μ m to 100 μ m.
His biggest characteristic is that at a given temperature and wavelength, the radiation emitted by an object has a maximum value, which is called a blackbody, and his reflection coefficient is set to 1;
Other substances with a reflection coefficient less than 1 are called gray bodies, as the spectral radiation power P (λ T) of a blackbody satisfies Planck's law with respect to its absolute temperature T.
At absolute temperature T, the radiation power of a blackbody per unit area at wavelength λ is P (λ T). Based on this relationship, the corresponding relationship curve can be obtained, which leads to:
(1) As the temperature increases, the radiation energy of an object becomes stronger.
This is the starting point of infrared radiation theory and the design basis of single band infrared thermometers.
(2) As the temperature increases, the radiation peak shifts towards the short wave direction (to the left) and satisfies the Wien shift theorem. The wavelength at the peak is inversely proportional to the absolute temperature T, and the dashed line is the line connecting the peak.
This formula tells us why high-temperature thermometers work more at short wavelengths and low-temperature thermometers work more at long wavelengths.
(3) The rate of change of radiation energy with temperature is greater at short wavelengths than at long wavelengths, indicating that thermometers operating at short wavelengths have a higher relative signal-to-noise ratio (sensitivity) and stronger anti-interference ability;
The thermometer should be selected to operate at the peak wavelength as much as possible, especially in the case of low temperature small targets, which is particularly important.
