Research On Intermediate Frequency Magnetic Field Measurement System Based On Waveform Data Sampling

With the widespread application of alternating magnetic field, magnetic field measurement has made a great progress. It has been applied to geophysics, space technology, military engineering, industry, biology, medicine, archeology and many other fields. At present, many products related to magnetic measurement have been sold in the market. But because of the constraint of magnetic field sensors, most products just measure the average of the center of a large spatial region, resulting in a lower resolution, a large measure scale. These products can also not achieve to measure continuously and display the measure result of spatial point.This topic follows the research of the National Natural Science Foundation Project, research on new method of metal ions inducing hyperthermic oncocogy. With waveform data sampling as the core, the thesis uses single chip arm microprocessor and FIFO memory to complete the data processing and the measurement of magnetic field intensity. The problem of nonlinear error and low sensitivity introduced by rectifying and filtering has also been solved. Through signal reconstruction theory, we reconstruct the signal from the sampled waveform data and display it. In time domain, the reconstruction signal can vividly and visually reflect the change characteristics of the magnetic field in the measured point.Firstly the thesis elaborates the background and significance of the topic and summarizes the state of the art of alternating magnetic field measurement at home and abroad. Secondly the thesis discusses the current methods of measuring alternating magnetic field, determines the theoretic basis for system measurement and analyzes the problem of intermediate frequency magnetic field measurement device based on waveform data sampling. Thirdly in order to overcome the nonlinear error introduced by rectifier filter, we propose a design scheme of intermediate frequency magnetic field measurement system which is based on waveform data sampling. Fourthly the thesis illustrates the design of key hardware circuits, including signal adjusting module, data acquisition module, power module, frequency detection and shaping circuit, and the USB interface circuit, presents the process of software implementation and studies the algorithm of waveform display. Lastly, we debug the whole system, analyze the measurement precision of the system and the problem with waveform display and proposes modified method.The system adopts microcontroller LM3S1958based on ARM(?) CortexTM-M3and introduces embedded real-time operating system μC/OS-Ⅱ. According to different hardware circuit, μC/OS-11creates different user tasks and then completes the task scheduling so that the resource on chip LM3S1958can be made full use of. The preemptive task scheduling strategy of μC/OS-11ensures the real time requirement of the task. The experiment results show that the intermediate frequency magnetic field measurement system based on waveform data sampling has good measurement precision, consistence and stability. The waveform display system uses software synchronous trigger and there is no obvious distortion. Futhermore, the system is of strong real-time, so it can satisfy the requirement of intermediate frequency magnetic field measurement.