Design And Implementation Of Single-axis Digital Fluxgate Magnetometer

Traditional fluxgate adopts analog circuit to process its output signal. As for higheraccuracy and rang of measurement, traditional fluxgate can’t meet the requirement gradually.Meanwhile, unsatisfactory temperature performance is also a big problem. Therefore,digitization is the inevitable trend of it. With the development of digital signal processingtechnology and FPGA device, adopting FPGA to process fluxgate signal will make itstemperature performance better and improve the accuracy and the rang of measurement.Besides, it has the advantages of good vibration, easy modification and high reliability, etc.Based on these advantages, digital fluxgate magnetometer is widely used in each scientificfield, such as aviation, aerospace, geological prospecting and environmental magnetic fieldmonitoring.As for the fluxgate sensor with dual iron core structure, the fluxgate signal is thesuperimposition of even-order harmonic. And the second harmonic is the best one which canreflect the measured magnetic field. So it is necessary to design a specific circuit to extractthe second harmonic.This article mainly analyses fluxgate sensor from two aspects of function andperformance, and presents an appropriate program under the consideration of its arithmeticspeed, resolution and size. The fluxgate signal comes from the drive of the signal stimulus ofFPGA to the sensing head. After frequency selective and power amplification, the signal issampled by AD converter, processed by FPGA and converted to analog signal by DAconverter.This article introduces the structure and fabrication of the sensing head, besides theworking principles and design principles of the fluxgate sensor. Then appropriate ADconversion chip, FPGA chip and DA conversion chip were selected. According to the signalflow, the AD control module, phase sensitive detection module, FIFO module, FIR low passfilter module and DA control module were designed. To prove the correctness of thesemodules, this article conducted simulations by software modelsim. And last the circuit boardwas fabricated, and the feasibility of the program was proved by debugging the circuit.The fluxgate sensor designed in this paper has the following advantages:(1) Compared with the analog magnetic measurement system, it is much stabler and lessdisturbed. And it is harder to be influenced by environment. (2) In this system, the process of rectification, FIFO and filtering can be completed onlyby a FPGA chip, which makes the system little volume and high integration.(3) It is convenient and flexible to modify the system. By using HDL to design the signalprocessing module, the system can be modified by software without changing the circuit.Conforming to the development derection of the fluxgate sensor to high precision,miniaturiazion and digitalization, this paper designed and implemented a digital fluxgatesensor, researched the relevant realization methods and improved the performance of thefluxgate sensor. The experimental results show that the designed fluxgate sensor in this paperhas high precision, good stability and tempreture performance and it can meet the demand ofthe general magnetic field test.