Analysis on noise interference of FHD proton magnetometer at Wen’an seismic station

The FHD-2B proton magnetometer at Wen’an station had large F component noise from 2020 to 2021. There is a high correlation between noise interference and temperature, which is generally characterized by high noise in winter and low noise in summer. The surrounding environment, power supply voltage, grounding resistance, power supply line leakage, probe leakage and power frequency interference of the magnetic room were checked respectively, and no interference sources were found. By studying the principle of FHD proton magnetometer, it is found that the harmonic capacitance capacity of FHD proton magnetometer changes with temperature. The capacity is small at low temperature and large at high temperature. The change of the capacity of the harmonic capacitor will affect the center frequency of the oscillation circuit f₀, resulting in increased noise. Since the noise interference of the FHD proton magnetometer at Wen’an station is highly correlated with temperature, it is speculated that the noise interference may be related to the change in the capacity of the harmonic capacitance. We can adjust the inductance L of the probe to correct the influence of the circuit center frequency of the harmonic capacitance capacity transformation. The probe inductance was adjusted several times through experiments, and 34.4 mH was selected as the most appropriate probe inductance value. After the experiment, the noise value of F component decreased, the data curve became smooth, and the noise interference was solved.