High-accuracy Weak Magnetic Portable Detection System Based On Magnetometer

In order to achieve high-precision measurement of weak magnetic field, the topicchooses the flux gate sensor to measure weak magnetic field. The flux gate sensor makes useof soft magnetic material in a non-linear zone to modulate the vector of the external weakmagnetic field, and it has a simple physical structure with a small size. Weak magneticdetection has a wide range of applications in the industry. For example, the detection of theground metal mineral resources, the detection of the metal fatigue damage, and themeasurement of the geomagnetic field and so on belong to the weak magnetic field range.Accurate measurement of weak magnetic information is particularly important, therefore highaccuracy, high resolution ratio, removable, and portable measurement equipment becomes thekey technical part of these industries.The existing measurement equipment of weak magnetic field has some shortages, suchas the low sampling rate of the device, and a small number of the stored data although it hasimproved the accuracy greatly, such as the US FVM series. In order to overcome the defectsabove, this thesis proposes that with the flux gate sensor as the front unit, the microprocessoras the system platform, that the system sampling rate is adjustable and the magnetic sensordata detected can be stored is achieved. Flux gate sensor is able to measure the weak magneticfield with high precision, and the microprocessor can be flexible for system control and dataprocessing so that it makes the portability of the entire measurement system possibleultimately.Firstly, this thesis analyzes the mathematical model to measure the vector magnetic withthe flux gate technology. At the same time, it analyzes the effect that the error caused by itsown structural defects of the flux gate probe has on the output accuracy of the magnetic fluxgate sensor.Secondly, based on the mathematical model, it analyzes the differences of the open-loop system and the closed-loop system of the flux gate and designs the LC resonant excitationwith high-frequency transformer core so that it achieves the purpose of the two excitationsignal phase difference π in some way. The LC resonance frequency selective network willfilter the flux gate sensor output signal again. The integrating circuit with the noisesuppression capabilities and cross-correlation characteristics filters the second harmonicsmoothly to obtain the DC component of the magnetic field vector.Furthermore, in order to achieve the portability of the detection system, the SCM withCortex-M4micro controller core will be used in data processing section, and equipped withμC/OS operating system which supports the multithreading, which makes the portability ofthe detection system possible.Finally, the analog conditioning circuitry of the magnetic flux gate sensors in the front ofthe system are calibrated and noise levels and other performance parameters are analyzed.And the sensitivity is29510V/T, the resolution is230nT, and the nonlinear error is0.1246%.Basically, the system achieves the high-precision measurement of the weak magnetic field.