Study On Iepe Accelerometer Noise Floor Characteristics

As the preferred choice to measure vibration acceleration, the IEPE accelerometer isoccupying an important status in many areas, especially in the field of low frequencyvibration measurement. With the unceasing progress of technology, the low frequencyvibration signal measurement gets more and more attention. Both in the industrial marketand military applications accelerometers with a lower measurement frequency are hopedto meet the need for low frequency vibration signal detection. Due to the weakness of thelow frequency vibration signal, it is necessary to take advantage of the low noiseaccelerometers to ensure that the desired signal is not covered by the noise floor of theaccelerometer. Therefore, the research about the noise floor characteristics of IEPEaccelerometer has great significance to guide the design of low noise accelerometer andimprove the signal-to-noise ratio of the accelerometer.In this paper, two important components of IEPE accelerometers, which are thepiezoelectric transducer and the charge amplifier, are used as the research objects toanalyze the noise floor of IEPE accelerometers systematically.Firstly, based on the working principle of piezoelectric transducer, the mechanicalmodel of piezoelectric transducer, the spring-mass-damped mechanical harmonicoscillator with single-degree freedom，and the electrical model of the piezoelectric elementare established. Then, two major noise sources, which are the mechanical-thermal noiseand the electrical-thermal noise of piezoelectric transducer, are analyzed and modeledseparately, and the noise spectral density expression of piezoelectric transducer isdeduced.Secondly, the IEPE accelerometer charge amplifier circuit with junction field effecttransistor (JFET), which meets the technical specifications, is designed as the core element.In the circuit, the main noise sources including the resistor thermal noise, the shot noise,the channel thermal noise and the1/fnoise, are studied and their corresponding noisemodels are established. The internal noise source is converted to the input by using theE n Innoise model construction method. Meanwhile, the Y-transform principle is introduced into the noise analysis of the T-bias network, reducing the noise analysisdifficulty, and the noise spectral density expression for the IEPE accelerometer chargeamplifier circuit is deduced.Finally, the noise of the piezoelectric transducer and the circuit is superimposed, andeventually gets the noise floor expression of the IEPE accelerometer. In the meantime, thenoise floor of IEPE acceleration is studied in experiments, and the experimental dataobtained in experiments are compared with the theoretical calculation values obtained bythe expression, verifying the validity and accuracy of the theoretical expression. Inaddition, the theoretical expression is used to analyze the key factors which influence theaccelerometer noise. The accelerometer low noise design principles summarized providesthe theoretical basis for improving the signal-to-noise ratio of the accelerometer.