Development of High-precision Cave Thermometer and Actual Measurement Characteristics at Huailai Seismic Station

In order to study the variation characteristics of cave temperature, a high-precision cave temperature instrument with a resolution of 0.000 1 ℃ was designed and developed. It was measured in Huailai deformation cave with annual variation of 0.06 ℃ and daily variation of 0.01 ℃（Statistics in 2019）. Through the analysis of the daily and monthly temperature curve, correlation analysis, period and amplitude spectrum under normal conditions, it is found that the temperature of Huailai cave is not affected by the air temperature, and is positively correlated with the air pressure, which has the tidal effect of periodic variation; the main factors causing the sudden change of the cave temperature are: man-made entering the cave, the rotation of the calibration motor, especially the sudden change of the air pressure in the process of rainfall, which causes the change of the cave temperature;"Heat expansion and cold contraction" makes the temperature of the cavity interfere obviously with the daily variation of the cavity's strain extensometer. The trend transition of the station strain observation in March 2020 is caused by the slight change in cave temperature. Future observations should utilize the existing cavern conditions, deploy high-precision temperature observations, reduce interference, and accumulate cave（ground）temperature change data to better identify and discover topographical abnormalities.