Research On Flux-gate Sensor And Its Analog Circuits

Flux-gate magnetometer is continually refined and developed with the development of electronic technology and geophysical science. With the characteristics of high resolution, wide measuring range, simple and reliable, economy and durability, able to directly measure the magnetic field components and suitable for being used in high-speed motion system , the Flux-gate magnetometer's applications are also constantly expanding, for example: in the Earth's magnetic, mineral magnetic measurements, satellite attitude control, and many other related areas , Flux-gate magnetometer occupies an important position.Thesis is a part of "The research on the key technology to Aeromagnetic vector (three-component) measure and prototype development" in one of National 863 Program from China Aero Geophysical Survey & Remote Sensing Center for Land and Resources, and there will be a analog DC signal which is proportional to magnetic field to be measured at the output.The main contents of this article include three parts. They are the research and making of a flux-gate sensor, the design and implementation of flux-gate sensor's analog processing circuits, the difference between closed-loop system and open-loop system of the circuits and the test for them.(1) The research and making of a flux-gate sensorFirst of all,starting from Faraday's law of induction, this thesis indicates working principle of the flux-gate phenomenon ,designs a two-core symmetric structure and derives its EMF expression Through comparison and analysis, it confirms the dual-core structure and designs of its specific structure. Then,by analyzing the affect of the sensor's parameters and the number of turns to sensor, it determines the core material and the structure of dual-core coil frame size and finishes the making of the sensor. And then,it explains the sensor's sensitivity, nonlinear characteristics and accuracy of the sensor's performance,through the spectrum analysis of sensor's output signal and noise signal,it makes out the processing method of the sensor's output signal ---- second harmonic method. (2) The design and implementation of flux-gate sensor's analog processing circuitBased on the making of the sensor and according to the principle of flux-gate sensors, this thesis designs out the sensor excitation circuits and signal processing circuits ,and the circuits finally obtains a analog DC signal proportional to magnetic field to be measured .Excitation circuit includes excitation signal generation circuitry and power amplifier circuit. The excitation signal in thesis is 4.8KHZ square wave produced by crystal. Signal processing circuits mainly contain the LC resonant,preamplifier,bandpass filter,demodulation,low pass filter,Integrator and feedback system. Thesis discusses every circuit modules above in detail from the design principles,design ideas,design details,problems and the improvement of all aspects.(3) The research and the test of closed-loop system and open-loop system of the circuitsFirst, the thesis analyzes the difference between closed-loop system and open-loop system of the circuits theoretically and tests them each, and then tests the circuits of closed-loop system and open-loop system respectively. Under the same condition, use the same method to test the circuits and acquire the data ,then deal with the data separately by quadratic fitting and Non-linear error analysis. Thus ,from the result ,it can be seen that the linearity and error of the closed-loop system are better than the open-loop system's.This thesis completes three main areas of work above,and it finally obtains a analog DC signal whose non-linear error control within 0.2% proportional to magnetic field to be measured and the resolution of the sensor and its circuits is 0.2nT. It is consistent with the requirements of the sub-topic " The research on the key technology to Aeromagnetic vector (three-component) measure and prototype development ", and it takes practical value in the application of aeromagnetic measurements with the flux-gate sensor, laying the foundation for further work.