Design And Implementation Of Three-axis Digital Fluxgate Magnetometer

From the beginning of the twenties of last century, there are studies of fluxgate sensors,analog circuits are commonly used in traditional fluxgate sensors, with the extensive application of magnetic field measurement technology, performance requirements of fluxgate sensors are also increasing, traditional analog fluxgate sensor cannot fully applicable to the increasingly stringent requirements of some occasion, also the size and weight of analog fluxgate are relatively large, the hardware circuit is complexity, the temperature performance is poor, and cannot modified expediently. In order to improve the performance of traditional fluxgate sensors, in recent years, digital fluxgate sensors get faster development, researchers have proposed digital fluxgate sensors based on microcontroller and DSP processors, with the development of field programmable gate array(FPGA), FPGA has lower cost and improved performance, making the FPGA as a fluxgate sensor processor become possible, and give full play to its advantages of high-speed processing in parallel. The study of digital fluxgate sensor using FPGA in China is less, so this paper proposed the use of FPGA to design and implement digital three-axis fluxgate sensors in order to achieve higher performance parameters than traditional analog fluxgate sensor.Traditional analog fluxgate sensors commonly use second harmonic detection method for magnetic field measurement, analog circuits typically include driver circuit, the resonant circuit, band-pass filter, phase sensitive detection(PSD) circuit, and low-pass filter circuit,digital three-axis fluxgate sensor designed in this paper was also based on the second harmonic detection method,FPGA has the features of internal programmable logic resources, and basic circuits of traditional analog flux gate sensors were replaced within the FPGA with multiple functional circuit modules, includes a driver module, a phase sensitive detection(PSD) module, a FIR low-pass filter module and by using high precision AD, DA converter to improve accuracy of the sampling data and output data. This paper designed and implemented digital three-axis fluxgate sensor's hardware circuit structure, designed smaller size of fluxgate sensor, making the three-axis fluxgate sensor has smaller size and lower power consumption. This paper also analyzed theoretically the distribution of internal magnetic field of the close-spherical feedback coil which is commonly used in closed-loop three-axis fluxgate sensors,laid the theoretical basis for the realization of three-axis digital fluxgate sensor loop structure, and made functional simulation for the digital PID control algorithm which was commonly used in closed-loop system.This paper used a standard three-axis fluxgate sensor to calibrate the linearity of the designed magetic field sensor's input and output within a certain range of magnetic field.This paper also analyzed the sensitivity and resolution of the flux gate sensor, the result showed that the sensor designed in this paper had high sensitivity and resolution in a certain range of magnetic field.