The Research Of Capacitance Measurement Method Based On Chaos Theory

This paper is based on the drilling strain gauge project of Beijing National Earthquake Infrastructure Service. The research is aimed to solve the problem of high precision micro displacement measurement caused by earthquake. We learn traditional detection methods and chaos theory, and propose two chaotic methods: the chaotic method based on phase diagram and the chaotic method based on the generalized Floquet exponent.From the analysis and simulation of the capacitance sensor and the traditional method, we can see that the reason why the precision can not be enhanced is that the signal is too weak while the noise is strong, and the circuit is too complex. In order to enhance the precision of capacitance measurement, we utilize the sensitivity to initial and the noise-resistance of chaos to propose two methods.The first method is the chaotic method based on phase diagram. Input the signal to be detected into the Duffing chaos system. And then calculate the amplitude of the weak signal through observing phase diagram and adjusting the driving force. Simulation shows that when0ω =10rad/ s, the signal to noise ratio(SNR) of this method reached-76 db while SNR of lock-in amplifier method was-30 db. This method is more accurate than lock-in amplifier method both in the detection accuracy and noise resistance.The second method is the chaotic method based on the generalized Floquet exponent. Calculate the relation between the the generalized Floquet exponent and the driving force. And then estimate the amplitude of the weak signal through the linear fitting. Simulation results show that this method has a relative error 7.7% when SNR is-20.79 db, the frequency is 10rad/s and the sample rate of noise is 0.01 s. It is 417.8% lower than lock-in amplifier method in the detection. The noise resistance of this method is also satisfactory when SNR drops.At last we draw the conclution and propose some aspects of future research.