Low-Temperature-Drift Design of Fluxgate Sensors for Geomagnetic Observation Based on the Two-Stage Magnetic Field Adjustment Method

Fluxgate sensors are used for geomagnetic field observation because of their excellent low-frequency characteristics and reliability. However, fluxgate sensors can experience measurement error caused by the change in ambient temperature during the long-term continuous observation. This article proposes a two-stage magnetic field adjustment method for reducing the sensitivity temperature drift of sensors; the first stage automatically offsets the static magnetic field, so that the measured magnetic field amplitude is suitable for sensor measurement, while the second stage uses a feedback loop with increased feedback resistance to keep the fluxgate probe in a zero magnetic environment. This article puts forth a new experimental test method for nonmagnetic heating that is easily implemented under laboratory conditions. Experimental results show that the designed sensor meets the requirements of a dynamic magnetic field measurement range for geomagnetic observation and that the sensitivity temperature drift is reduced from 118.73 to 23.39 ppm/°C. The dynamic temperature test results demonstrate the improved effect of the proposed method, the outdoor experimental results show that the amount of change in measurement data of the new setup fluxgate sensor is 58% of the change of the internationally advanced Mag-03 sensor under the same external environmental disturbances, and the application of downhole geomagnetic monitoring at a depth of 1 km proves the ability of the proposed method to meet the application requirements of long-term continuous geomagnetic monitoring.