Design and implementation of weak magnetic measurement based on magnetoresistive sensors

In order to obtain real-time and accurately magnetic parameters, a micro digital magnetometer based on HMC1001 magnetoresistance sensors was designed. The paper detailedly illustrates the working principle and design scheme of the system. The data acquisition module adopts 24 bit sigma-delta A/D converter AD7732 to sample magnetic signals of three sensors. FPGA is applied as main master controller to perform the data acquisition and transmission. Finally, the sampled data are transmitted to the upper computer through RS485 interface in asynchronous serial mode. According to the analysis of writing and reading time diagrams of AD7732, the paper also introduces the software design of data collection. Through the use of parallel processing capabilities of FPGA, three-channel analog signals are sampled in parallel, which realizes the real time acquisition and transmission of magnetic signals. The test result showed that tricomponent magnetic resistance magnetometer has the good performance in linearity, noise level and long-term stability. Compared with traditional magnetometer, this system has advantages such as high reliability, high precision and low power consumption. It can be applied successfully in the detection of weak geomagnetic field signal.