Research On The Noise Characteristics And Signal Processing Method Of Low Frequency Piezoelectric Acceleration Sensor

Piezoelectric accelerometer is one type of sensor for vibration signal measurement,which is widely applicated in many fields such as automobile manufacturing, aerospace engineering, etc. With the development of science and technology, the requirement of acquiring and processing vibration signal, especially for the low frequency signal becomes increasingly demanding. As a result of the disadvantages of the traditional piezoelectric accelerometer, such as narrow application range, long time response, it couldn’t accurately measure the low-frequency and weak vibration signal. At present, the high precision measurement of low frequency weak vibration signal is still a problem for domestic and foreign researchers. Base on the research of background noise of piezoelectric accelerometer, then analysis the experimental data, and corresponding noise reduction methods, in this paper a IEPE(Integrated Electronics Piezoelectric sensor) has been developed. The IEPE has the features of wide range for frequency response, high sensitivity, etc. They are widely applicated in weak signal measurement field. Therefore, it is a great significance to keep the measured signal from background noise of the accelerometer, and makes the piezoelectric accelerometer has higher class precision and sensitivity.This paper focus on the application examples of piezoelectric accelerometer in different fields, represent by the IEPE accelerometer, researched the features of piezoelectric accelerometer background noise, by established the noise model, to design the piezoelectric accelerometer low noise system, my major works as following:(1) Based on the piezoelectric effect, derived the piezoelectric equation of cylindrical ceramic material, research on the working principle of the piezoelectric accelerometer;based on the piezoelectric materials type to study the performance parameters of the piezoelectric materials. According to the structure and position of piezoelectric element, to analysis the features of various types of piezoelectric accelerometer(compress type, shear type and bending type). Through the study of IEPE accelerometer structure and power supply mode, discovered the IEPE accelerometer with encapsulated structures have strongability to against electromagnetic induction interference under high temperature environment, their two wires working model will not affected by the thermocouple, so they have small temperature drift, easy to decentralized collection and centralized control,thereby improving the anti-interference and measurement accuracy.(2) Based on the basic theory and characteristics of noise, the source of piezoelectric accelerometer noise is researched. The piezoelectric transformer internal noise including the mechanical thermal noise that produced by mechanical resonance system and the electrical noise that produced by the piezoelectric element. For analysis the piezoelectric transformer internal noise types, to design the IEPE accelerometer charge amplifier circuit and establish each noise model. Use the principle of the-Y(35) transformation during the noise analysis of T bias network, thereby reduced the difficulty of modeling. Meanwhile,base on this noise model, the spectral density expression of the background noise was derived. It provided the theory basis for design low noise piezoelectric accelerometer.(3) Research on the charge amplifier of the developed low noise IEPE accelerometer,the features of amplitude-frequency characteristics and low-frequency cut-off frequency of the circuit were tested. Through the study of the noise characteristics of the circuit by experiments, compared the experimental testing results and theoretical value to verify the validity of the theoretical formula. The experimental prototype is tested, the output noise is collected, and the noise power spectrum is analyzed. Based on the experimental testing result and noise spectral density formula, summarized the technical requirements of the low noise accelerometer.(4) Based on the theory of wavelet analysis, the noise of the accelerometer output signal was disposed. Due to the shortcomings of the traditional wavelet transform,research on the signal de-noising method of acceleration sensor based on wavelet morphology. Use Matlab for the method test, then achieved good results.