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 select the working band of the instrument correctly. There are three infrared-transmitting atmospheric windows in the ground atmosphere, namely 1~2.5pm, 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, which seriously attenuates and becomes unstable in luminous intensity, which has a direct impact on the accurate temperature measurement. The wavelength in the 2.7~3.2μ band is the most unsuitable 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 the advancing and mining face, the 3.5~6.0pm band should be used; if the measurement distance is smaller than the 8~14μm band.

 

2) Determination of coal emissivity: Strictly speaking, emissivity is not a constant, it is related to the surface properties, temperature, radiation wavelength, and observation conditions. Therefore, the radiation rate of coal should be measured. A relatively simple and accurate method is to measure the surface temperature of coal with a monthly spot meter or a thermocouple. When using the infrared thermal imager to measure again, continuously adjust the value of emissivity e to make it display the temperature as a point measurement value, and s at this time is the emissivity of the object to be measured. After a lot of work, predecessors have obtained the emissivity of various common materials. For example, the emissivity of the coal wall in the coal mine is 0.95, the emissivity of the shotcrete wall and the rock roadway is 0.92~0.94, and the emissivity of the roof is generally 0.93. ~

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 45%. When the emissivity measurement error is 20%, the temperature measurement error of the short-wave thermal imager is about 65%, while the temperature measurement error of the long-wave thermal imager can reach 9.5%. Therefore, the measurement of the emissivity of the thermal imager in the working band of 8~13um should be as accurate as possible.