High Resolution Magnetometer Signal Acquisition System

High precision geomagnetic field data plays an important role in the space science research.The fluxgate magnetometer,measuring constant or low frequency magnetic fields by using the magnetization saturation characteristics of a soft core material,is one of the most widely used geomagnetic detecting instruments.The high resolution signal acquisition system is developed in this thesis.Together with a front-end of fluxgate sensor,this system can collect the synchronous measurement of three axis magnetic field data.The main work includes:1)Study on the fundamental principle of fluxgate magnetometerBy introducing and deriving the analytical solution of output voltage of fluxgate sensors,the basic mathematical modeland the schematic block diagram of the fluxgate magnetometer are developed,providing the basis and scheme for the subsequent hardware circuit design.2)Design of fluxgate magnetometer signal acquisition systemBased on the fluxgate principle,we design the hardware circuit,including the power supply,the CPU load circuit,three 24bitChannel AD acquisition and the serial communication modules.Combined with the Electro Magnetic Compatibility(EMC)theory,the optimization of the circuit is implemented to reduce the noise.Meanwhile,the system software design is completed,including the system initialization and the underlying driver of each function module.3)The prototype and performance testingThe principle prototype of our signal acquisition system for fluxgate mag-netometers is developed.Its overall performance is tested,including the measu rement range,measurement errors,linearity,resolution,sampling frequency and noise test.The test results show that,the measurement range of the X,Y,Z three channels can be±81980nT,±82320nT and±82210nT,with the voltage input range±10V for all of the three channels,corresponding to a resolution better than 0.040nT.The maximum value is 0.004%FS for the nonlinearity,0.007%for the average deviation and 27.187pT/(?)(at1Hz),27.184pT/(?)(atlH z)and 27.186pT/(?)(atlHz)for the noise of X,Y,and Z channel.The samplin-g frequency can be 50.3Hz.4)Fluxgate magnetometer data processing and analysis methodsThe processing and analysis methods of geomagnetic field data is investigated.Based on the fluxgate magnetometer data from the magnetosphere multiscale satellite mission(MMS),the spectral characteristics of the electromagnetic ion-cyclotron wave(EMIC)are examined by using FFT and WAVELET.And a digital filter is conducted to remove the background noise and distinguish the EMIC waves in different bands.The signal acquisition system designed in this thesis,with the features of high-resolution,low noise,multiple functionality extension interfaces and high cost performance,can provide technical supports for the high precision magnetic field measurement in the future.