The Design Of Digital Flux-gate Sensor Based On CORTEX-M3

The traditional flux-gate sensors are generally based on analog circuits, with the improved requirements of measurement accuracy and measurement range, the flux-gate sensors based on analog circuits has been unable to meet the measurement needs. Meanwhile,the temperature performance of analog circuits is poor,it resulting in the conventional flux-gate sensor's temperature performance and stability is poor. Therefore, digitizing the flux-gate signal is an effective way to improve the performance of flux-gate sensors. Using the STM32 which based on CORTEX-M3 core to process the flux-gate output signal,the temperature performance of the sensor may be improved, as well as the measurement accuracy and range. It can also decrease the size of sensor, reduce the power consumption and improve the stability. Currently, the flux gate sensors have been widely used in geological exploration, environmental monitoring, aerospace and other fields.The structure of flux-gate probe used herein is similar to ring core, the output signal of this flux-gate probe is superimposition of even harmonic .And the second harmonic is the best one which can reflect the measured magnetic field. Therefore, it is necessary to design a specific circuit to extract the second harmonic and process the signal. This paper systematically analyzes the performance and functionality of the flux gate sensor, consider the operation speed, volume and accuracy and other aspects, presented a reasonable scheme.STM32 produce excitation signal, than the signal input to the probe after power amplifying and the sensor out put the flux-gate signal. After frequency selective, the signal is sampled by A/D converter processed by STM32.In this paper,the working principle of flux-gate signal processing system is discussed in detail. Than The appropriate A/D conversion chip STM32 chip were selected. According to the signal flow inside the STM32, we designed PWM module, A/D acquisition module,FIFO buffer module, phase sensitive detection module, FIR module, D / A module, external storage SRAM module and serial communication module respectively. Among the circuit design process,we did Multisim simulation for each hardware module,and then painted the PCB, debug every hardware module. Compared with the result of Multisim simulation, this article verifies the feasibility of each module, as well as the system.After the design is completed, we tested the stability of the flux-gate sensor and compared the measured values with the theoretical values of eight directions. The results show that the sensor has the stability of 0.4% and the trend of the theoretical values are basically the same with the trend of measured values in eight directions which can adapt to the measurement of magnetic field in general.