1) Band selection: The radiant energy of the measured object must pass through the atmosphere to reach the instrument, so it is very important to correctly select the working band of the instrument. There are three infrared-transmitting atmospheric windows in the ground atmosphere, namely 1~2.5μm, 3~5um, and 8~14μm. However, the infrared radiation in the coal mine is affected by different gases, coal dust particles, etc., resulting in scattering, absorption and emissivity fluctuations, which make the luminous intensity seriously attenuated and unstable, and have a direct impact on the accurate temperature measurement. The wavelength in the 2.7~3.2p band is the least suitable for use. In addition, there are water vapor, carbon dioxide, methane and other gases in the downhole air. These gases have one or several absorption peaks. Therefore, various factors must be comprehensively considered when selecting the working band. After weighing, if the measurement distance exceeds 8m under the conditions of excavation and mining face, the 3.5~6.0μm band should be used; if the measurement distance is smaller than the 8~14μm band.

 

2) Determination of body emissivity: Strictly speaking, emissivity is not a constant, it is related to the surface properties, temperature, wavelength of radiation, and observation conditions. Therefore, the radiation rate of coal should be measured. A simpler and more accurate method is to measure the surface temperature of the coal with a spot meter or thermocouple. When using the infrared thermal imager to measure again, the value of the emissivity e is continuously adjusted, and the displayed temperature is the point measurement value, and the ε at this time is the emissivity of the measured object. After a lot of work, predecessors have obtained the radiation rate of various common materials. For example, the radiation rate of the coal wall in the coal mine is 0.95, the radiation rate of the shotcrete wall and the rock roadway is 0.92~0.94, and the radiation rate of the roof is generally 093. ~0.95

3) Error analysis and calculation of real temperature: Considering the influence of the environment and the error of the instrument itself, it is necessary to calculate the temperature displayed by the instrument. In the 2-5um band, when the atmospheric absorption rate reaches 20%, the temperature measurement error is about 5.3%; in the 8-13 μm band, when the atmospheric absorption rate reaches 20%, the temperature measurement error is only about 4.5%. When the emissivity measurement error is 20%, the temperature measurement error of the short-wave thermal imager is about 6.5%, while the temperature measurement error of the long-wave thermal imager can reach 9.5%.

Therefore, the calculation of the emissivity of the thermal imager in the working band of 8~13um must be as accurate as possible.