The Design Of Fluxgate Sensor Based On Hysteresis Time Difference And Magnetic Measurement Device

With modern technological advancing, magnetic sensors are developing towards high sensitivity, high resolution, miniature and intelligence. As one of the most important devices in the detection of weak magnetic field, fluxgate magnetic sensor plays a major role. It can measure the weak magnetic field that the range is about 10"10T~10"4T and the resolution is about 10"11 T~10"9T, and also can detect the gradient field and vector field. It is widely used in mineral prospecting, archeology, magnetic field measurement, spacecraft attitude control and other industrial, military and medical fields, and has good development prospects.Traditional fluxgate sensor is based on the general principle of even harmonic which detects the output signal of the even harmonic amplitudes to calculate the measured magnetic field. Its sensitivity subjects to the constraints of fluxgate sensor noise, and requires the use of difference that can inhibit the probe noise or with a compensation coil for reducing the impact of noise. By the level of modern production technology and material constraints, the traditional fluxgates go into the bottleneck of the development.This article will study the design of a new type of fluxgate sensors (namely hysteresis time difference type fluxgate sensor) based on the hysteresis characteristics of magnetic materials and magnetic measurement device. We calculate the time difference between the positive and negative pulse of the induction voltage from fluxgate output, and we can attain the size and direction of the magnetic field. When the excitation current Ie drive magnetic core as the period Te, the core is periodically saturated, and the voltage induced of fluxgate output signal modulate by the magnetic permeability. When the fluxgate is exposed in the zero magnetic fields, the time of negative saturation state is the same with the time of positive saturation state. And therefore the induced voltage signal is a symmetric signal. The time interval between positive pulse and negative pulse is equal to the time between negative pulse and the next period pulse, and the time difference is zero. When the sensor is in the external weak magnetic environment, the time of positive saturation and negative saturation is not the same. Therefore, the induced voltage signal is an asymmetrical signal. The time interval between positive pulse and negative pulse is unequal to the time between negative pulse and the next period pulse, and so the time difference is non-zero. The detection circuit of magnetic measurement device is simpler than that of the traditional fluxgates. Which effectively reduces the size and power consumption, and data processing is also relatively simple. Fluxgate based on hystereis time difference can access to higher resolution and accuracy in the cases of significantly lower power consumption and volume.This paper introduces the background of the study subjects, the development and trend of domestic and foreign fluxgate instrument, and the purpose and significance of the hysteresis time difference magnetic fluxgate and magnetic measurement device are also proposed. In this paper, we also discuss the even harmonics theory, the structure and the measurement circuit of traditional fluxgate. The paper systematically discusses the theory of hysteresis time difference. According to Faraday's law of electromagnetic induction, we establish the mathematical model of the new fluxgate sensor, and derive the sensitivity expressions of the fluxgate to obtain the ways of optimization. With the combination of the simulation and experiment, we analyze the impacts of the driving signal waveform, amplitude and frequency on the sensor sensitivity. Sensor model simulations by using MATLAB tools are presented. We discuss in detail the structure of the sensor probe, core material and production processes on the sensor performance, and give the fluxgate sensor production program in combination with experiments. To hysteresis time difference for the detection of objects, adopting high permeability, high squareness Co-based amorphous alloy for the magnetic-sensitive material, and using PCB technology, we finally complete one single-core probe fluxgate based on hysteresis time difference. Using direct digital frequency synthesis technology, we design a high accuracy excitation signal generator whose waveform can be switched and the magnitude and frequency can be precisely adjusted. We complete the minimum system FPGA circuit, adaptive amplification as well as hysteresis shaping detection circuit. Power circuit, control and display circuit design and the design of magnetic devices system software are accomplished. According to calibration requirements, we design a high accuracy DC magnetic field device to achieve -4x10~4nT~ +4x10~4nT weak magnetic field measurement and calibration in certain circumstances, and test equipment noise, static characteristics, resolution and sensitivity performance.Finally, the paper summarizes the work. In order to improve the system design, we also present its follow-up design and research suggestions.