Research On Digital Technology Of Three-axis Fluxgate Sensor

The fluxgate sensor is a weak magnetic vector measurement sensor with high sensitivity,measurement accuracy,small size and light weight.Especially in recent years,with the wide application of weak magnetic measurement technology,the consumer market needs a large number of magnetic measuring devices with excellent performance and low cost.However,the performance of the signal processing circuit of the conventional analog fluxgate sensor is susceptible to temperature,electromagnetic interference and difficulty in integration,making the digital fluxgate sensor with strong anti-interference ability,high integration and low cost have become a trend in technological development.Based on the analysis of the traditional analog fluxgate sensor theory,this paper deeply studies the signal characteristics of the fluxgate probe under the premise that the fluxgate probe of the double core structure provides excitation signals for the cosine wave and square wave voltage source,It was found that the waveform of the excitation signal does not affect the theoretical no-load sensitivity of the fluxgate probe.By comparing and analyzing three common effective signal detection methods,such as time difference method,peak method and second harmonic method,it is determined that the second harmonic method is used to extract the effective signal.By studying the specific implementation method of phase sensitive detection and filtering in the digital domain,the influence of the feedback link on the system characteristics,the PID closed-loop control theory,and the commonly used magnetic compensation driving principle,another key technology for the digitization of this paper is proposed:a full digital closed loop feedback technique for A-E and PWM cascade modulation.A closed-loop full digital fluxgate system simulation model based on Simulink simulation software is established,which verifies the rationality of digital theory.Based on the previous digital theory research,a three-axis full digital fluxgate sensor prototype was designed using industrial grade dsPIC microcontroller.Finally,the prototype is debugged,mainly including the determination of the excitation frequency and the duty cycle of the excitation signal,the setting of the PID link parameters,and verifying the performance of the equivalent DAC with A-E and PWM cascade modulation.The nonlinearity of the equivalent DAC is 0.001%,which is approximately equal to the nonlinear error of DAC8812B,which proves that the method of implementing equivalent DAC in this paper is effective.Through testing on prototypes and performance,the measurement range of the prototype is±50000nT,linearity 10-2,noise less than 0.1nT,resolution 78nT,bandwidth DC-80Hz,which meets the design specifications of this paper,which verifies the feasibility and rationality of the digital technology of this paper,and the performance of the prototype meets the performance requirements of magnetic fluxgate sensors for magnetic instruments in the consumer market.