| It is well known that there exist geomagnetic fields around earth due to the fact that the earth we live in is a huge natural magnet.Each object on earth is affected by the geomagnetic field,which affects the distribution of the earth's magnetic field in turn,especially ferromagnetic objects.A stable geomagnetic field under normal circumstances will generate perturbations and cause magnetic anomalies if ferromagnetic object exist in a certain place.The related targets can be detected with the help of magnetic anomalies,such as:iron ore,sunken ships,submarines,ships and so on.The necessary prerequisite to the accuracy of detection is the precise collection of MAD?Magnetic Anomalies Data?.There is no denying that the limited availability;high cost and complexity of operation of the instrument on the market lead to the unreliability.Therefore,this article explores a set of MAD collection system,which is designed to be well behaved,simple to use and affordable.The main research work is divided into following aspects.Firstly,accurate measurement of the frequency signal becomes the key as we use the magnetic field sensor CS-3 to map the magnetic field signal into a frequency signal.Therefore,this paper proposed a high accuracy method of the frequency measurement:we use the TDC to eliminate the error of±1 reference signal period in the frequency measurement on the basis of the traditional equal-precision frequency measurement method,and then utilize the FPGA to calculate to get the exact frequency value.Then,we use the ATmega324PB chip as the core platform,the code is written to control the operation of the chip and receive the frequency value through SPI communication protocol.The ATmega324PB chip processes this value and sents it to the wireless transmitter module.Finally,the receiving program and the interface are written on the PC using C#language,and the data from the wireless module is received and displayed on the interface.At the same time,the data is saved on the PC hard disk for the next data processing to obtain the target information.Thus,this paper designed a MAD collection system and implemented the hardware successfully.The test results show that when the accuracy of the reference frequency reaches 10-8,the measurement accuracy of the system reaches 10-8.When the accuracy of the reference frequency reaches 10-10,the measurement accuracy of the system reaches10-10,and the measurement speed meets the requirements,wireless transmission distance reaches more than 300 meters.The feasibility and convenience of the design scheme is proved and preparation for the practical applications of magnetic anomaly detection is made.It has certain practical value. |
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