Research On Key Technologies Of Digitalization Of Vertical Pendulum Tiltmeter

In the field of earthquake prediction,topographic deformation observation is an important research direction.Earth tilt is a kind of crustal deformation,so the tiltmeter used to observe the solid tidal deformation has certain guiding significance for the prediction of earthquake precursors.At present,the overall size of the domestic active vertical pendulum tiltmeter is smaller,and the installation and debugging are more convenient.The differential capacitance displacement detection in the instrument is realized by an analog circuit.The gain stability of the analog circuit is weak,and the degree of automation is not high enough.The circuit can achieve very good results in these aspects.At the same time,the digital circuit is better than the analog circuit in terms of ease of debugging and signal fidelity.Therefore,this paper proposes a digital circuit based on a vertical pendulum tiltmeter.This article starts with the mechanical part of the vertical pendulum tiltmeter and briefly describes the main structure,components and parameters of the key components of the instrument.The transfer function of the mechanical part of the instrument is calculated by analyzing the movement of the pendulum body,and then the amplitude-frequency phase-frequency curve of the system is obtained,and the model of the mechanical part is determined.Next,the circuit part of the vertical pendulum tiltmeter is analyzed,and the differential capacitance sensor,the core component of the circuit part,is analyzed and calculated.Simulation software is used to simulate the circuit part of the instrument.By setting different capacitance values to simulate different positions of the pendulum,the system output voltage corresponding to the different positions is measured,and the simulation output conforms to the actual situation in the instrument circuit.At the same time,the equation between the output voltage and the tilt angle is fitted by the least square method,which verifies that the output and input have a good linear relationship within the full range of the instrument.Based on the above research,a digital circuit based on the vertical pendulum tiltmeter is designed,which mainly includes four parts: sine wave generation module,ADC,digital synchronous detection,and digital low-pass filter.The processing process of the digital circuit is: through sine wave The generator module generates a sine wave with a known frequency,amplifies the sine wave through the operational amplifier in the analog circuit,and uses the ADC to extract it after the signal conditioning circuit.Then the collected main channel signal and reference channel signal(ie sine wave)Generate the signal generated by the module)display the two-channel waveform data and calculate the phase difference,convert the phase difference into the time difference,use the microcontroller to delay the main channel signal,and then retain the first half cycle of the signal to complete the digital synchronous detection After that,the signal is digitally low-pass filtered.The above modules have been implemented through the STM32F103 single-chip microcomputer.