Research On In-situ Calibration Technology Of Low Frequency Vibration Sensor

Magneto-electric low-frequency vibration sensors play an important role in vibration measurement in civil and hydraulic engineering,lifeline engineering,disaster prevention and mitigation,aerospace and other fields.However,the sensor in the transportation process encountered impact,moisture and strong electromagnetic field interference and other situations will be severely deformed in spring,rust and demagnetization and other issues,so that the main technical indicators of the sensor changes,which is not allowed in major engineering and high-precision vibration measurement,the sensor must be calibrated before installed on the actual measurement site.High precision portable small vibration table,and on-site calibration technology without the use of vibration table are the two methods to realize in-situ calibration.Improving the calibration accuracy of these two methods is important for providing the accuracy of the measured data of engineering vibration.Based on the analysis of the principle of small vibration table and the principle of self-calibration method of magneto-electric low-frequency vibration sensors,this paper studies the problems such as large distortion of low-frequency acceleration of small vibration table,self excitation of traditional relative feedback vibration table and large high-frequency error of self-calibration method.The following work has been carried out:(1)The problem of self-oscillation caused by excessive damping of the relative speedometer feedback vibration table is studied in detail,and the influence of the relative speedometer and exciter related parameters(electromechanical coupling coefficient,inductance and internal resistance),spring stiffness,kinematic part mass,circuit parameters and power amplifier gain of the vibration table on the calibration system are analyzed.Aiming at the problem of self-oscillation,a method was given to reduce the formant of the vibration table,which reduced the formant of the small vibration table by appropriately superimposing the differential link in the feedback loop,and further improved the damping ratio of the small vibration table by continuing to increase the damping,and improve its low frequency characteristics.(2)Aiming at the problems of complex structure,high cost and limited travel of the relative speedometer feedback vibration table,a method for extracting feedback signals from the coil of the vibrator(uneven constant bridge method)is proposed,which experimentally proves that this method can expand the low frequency characteristics of the vibration table and improve the waveform distortion of the vibration table.(3)Aiming at the problem of large self-calibration error in the high-frequency band of magneto-electric sensors,a self-calibration circuit for low-frequency vibration sensors is proposed.On the basis of analyzing the mathematical model of the built-in coil calibration method,a new calibration circuit is proposed,and the experiment proves that the self-calibration accuracy of the sensor in high-frequency has been greatly improved after using the self-calibration circuit,and the relative error of the sensor is less than 5% compared with the high-frequency calibration result of the sensor in the laboratory.(4)Aiming at the problem of uneven distribution of magnetic flux density of single magnet magnetic circuit structure,a dual magnet closed magnetic circuit structure is given,and the magnetic circuit structure is analyzed and calculated.The results show that the magnetic circuit structure solves the problem of uneven distribution of magnetic induction intensity of single magnet magnetic circuit structure,and provides a reference for the research and development of new magneto-electric sensors.In addition,the effect of the installation angle of the traditional horizontal vibration sensor on the sensitivity and amplitude frequency characteristics of the sensor has been studied and experimented,which provides a basis for improving the accuracy of sensor calibration.(5)The vibration calibration software of the low-frequency vibration sensor is designed.In view of the existing calibration process,the sampling rate is too high,the low SNR,collision and the low calibration efficiency,the functions of automatic sampling rate,automatic narrowband filtering and collision avoidance software have been added,which provide convenience for on-site offline calibration of small vibration table.