Research On Impedance Spectrum Measurement Method Based On Impedance Matching

Impedance spectroscopy is an important parameter for analyzing the frequency characteristics of an object,which represents the characteristic curve of the object’s impedance varying with frequency.Impedance spectrum measurement system is usually used to measure the impedance value of the measured object in a certain frequency at multi-frequency points.It is widely used in electrochemical analysis,biomedicine,material detection and other fields,and has important research value.Based on vector volt-ampere method,this paper designs an embedded system impedance spectrum measurement method based on frequency scanning,and analyses the problems of low measurement accuracy and complex signal processing circuit in traditional impedance measurement method,and puts forward some corresponding improvement measures.The specific research contents are as follows:Firstly,the measurement principle of vector voltammetry is described in detail,and the error model of impedance measurement is established.The influence of reference resistance on impedance measurement error is verified by theoretical analysis and experiment.Therefore,an impedance matching idea to reduce measurement error is proposed,and the overall design of impedance spectrum measurement scheme based on impedance matching is established.Secondly,according to the impedance matching method,the impedance spectrum measurement module circuits such as electronic switch switching circuit,negative voltage switching circuit and differential amplifier circuit are designed.The step-by-step measurement of system impedance and measured impedance is realized,the measurement error of measured impedance caused by system impedance is eliminated,and the symmetrical circuit is used to overcome the vulnerability of traditional impedance measurement circuit to space electromagnetic noise.Disadvantage of interference.Thirdly,the main control chip STM32 is used to generate sinusoidal signals,design impedance matching algorithm and data acquisition and fitting functions.Non-integer periodic sampling and least squares sin-fitting of the whole period are adopted to improve the accuracy of data fitting and shorten the fitting time.Sin-fitting signal is expressed by vector,which simplifies the calculation of vector ratio between output and input.The impedance matching algorithm realizes the automatic switching of the best reference resistance and improves the accuracy of impedance measurement.In addition,the host computer communicates with STM32 through serial port,which realizes the functions of reference resistance pair switching,frequency change of excitation signal,real-time display of data acquisition,signal processing and data storage.Finally,the impedance spectrum measurement experiment of the analog electrolytic cell was carried out,and the step-by-step measurement of the amplification factor,system impedance and parallel impedance of the system was completed,and the impedance spectrum of the electrolytic cell was deduced.By comparing and analyzing the traditional impedance spectrum measurement experiment of fixed reference resistance,it is proved that the impedance spectrum measurement system based on impedance matching has higher measurement accuracy.