Low Frequency Vibration Sensor Design For Micro-vibration Signal Detection

Low-frequency vibration sensors have significant applications in the field of micro-motion monitoring and oil and gas exploration.The survey found that the current domestic still mainly rely on natural frequency greater than 5Hz passive vibration sensors to pick up the vibration signal,but the market is in urgent need of excellent performance of low-frequency vibration sensors.In reducing the natural frequency by changing the mechanical structure,it needs to increase its mass and volume,which brings great inconvenience to engineering applications.Therefore,designing low-frequency vibration sensors with low cost,small volume,high sensitivity and low own noise without changing the mechanical structure has become a research difficulty in the current sensor field.Based on the moving-coil vibration sensor,this paper develops the low-frequency vibration sensor design from three aspects:low-frequency compensation method with force balance feedback,adaptive genetic algorithm to optimize the analog filter circuit parameters and system performance testing and verification.The field of microseismic places higher demands on the lower limit of low frequency,temperature stability,sensitivity level and noise level of vibration sensors.In this paper,based on the analysis of the kinetic model and electromechanical model of the moving coil vibration sensor and the study of the basic principles,advantages and disadvantages of the force balance feedback method to expand the low frequency characteristics of the moving coil vibration sensor,a Lippmann-type force balance feedback low frequency compensation circuit is designed based on the frequency response curve and performance parameters of the PS-5GR moving coil vibration sensor;then the dynamic matching impedance circuit based on the negative temperature coefficient resistor is designed to improve the stability of the system frequency response performance of the vibration sensor in a wide range of temperature changes;then the gain adjustment circuit is designed on the basis of the analysis of the low frequency expansion preamplifier circuit,which improves the sensitivity of the vibration sensor,and at the same time realizes the variable sensitivity function to adapt to the needs of different sensitivity sensors in engineering applications;finally,for the low frequency vibration sensor low own noise requirements,analysis of microseismic signal and sensor system noise,from the circuit design,device selection point of view to propose the corresponding design means,so that the sensor has a low own noise.The low-frequency compensation circuit designed based on the force-balanced feedback technique requires an analog filter circuit as a post-stage circuit to achieve the purpose of improving the gain at low frequency points and flattening the frequency response curve.In order to solve the need for rich priori knowledge and complex and variable parameters for analog filter design,this paper designs an improved adaptive genetic algorithm for circuit parameter search.Genetic individuals are tracked under a typical filter circuit structure to adaptively adjust the parameter search strategy to achieve automatic optimization of the secondorder narrowband bandpass filter and fourth-order low-pass filter circuit parameters,and the reliability of the algorithm optimization is verified using simulation tests.In order to verify the actual performance of low-frequency vibration sensors in terms of own noise,low-frequency compensation and low-frequency gain,firstly,the self-noise and actual environmental noise of the system were tested to verify the low own noise level of the equipment;secondly,through the ultra-low frequency sensor calibration system,the designed low frequency vibration sensor was proven to have low frequency monitoring capability;then the designed low frequency vibration sensor was tested in a standard testing facility through a vertical vibration device;finally,field tests showed that the designed low-frequency vibration sensor has potential industry applications in terms of low-frequency signal pickup capability compared to the PS-5GR and industry standard vibration sensors.