Research On Signal Processing Technology Of High Precision Low Frequency Quartz Flex Accelerometer

The quartz flex accelerometer is a key component in the fields of inertial navigation and guidance,low-frequency vibration measurement and microgravity vibration isolation.These fields of application put forward urgent high-performance,miniaturization,and digitization requirements for the quartz flex accelerometer.The high-precision signal processing of the quartz flex accelerometer is based on the principle of moment balance and the use of servo circuit.The performance of the servo circuit is one of the key factors restricting the performance improvement of the quartz flex accelerometer.In the prior art solutions,the hybrid integrated analog servo circuit has low accuracy due to the integrated circuit technology problems,while the discrete component servo circuit has low integration and low utility because it transmits capacitance signals which are highly susceptible to parasitic capacitance.In addition,the manufacturing and assembly errors will cause the header mathematical model parameters and design values to be inconsistent,leading to lack of design basis for servo circuit controller parameters.Moreover,there is no theoretical basis for servo circuits design and optimization because of the lack of a comprehensive theoretical model to reveal the mechanism of servo circuit noise.In this paper,aiming at the above-mentioned application requirements and problems in the existing technology,a high-accuracy and high-integration digital quartz flex accelerometer signal processing solution with adaptive control capability is proposed,and the servo circuit system is designed and developed.The main research works are as followings:Firstly,a digital signal processing scheme that takes both precision and integration into consideration is proposed.The differential capacitance detection circuit is used as a high-precision front-end circuit and built into the integrated header,while the high-precision signal demodulation and digital servo control circuit is set back.The current signal is transmitted between the front circuit and the rear circuit,which could overcome the inherent defect that the parasitic capacitance seriously affects the signal quality when transmitting the capacitive signal.At the same time,the integration of the quartz flex accelerometer is improved in this scheme.A current bridge differential capacitance detection circuit is used to directly convert the information of the deflection angle of the quartz pendulum to a proportional current signal,which theoretically realizes an ideal linear sensing characteristic.In the back-end circuit,the high-precision demodulation method is used to demodulate the output signal of the integrated header,and the A/D and D/A conversion links are introduced to realize the digital servo control of the accelerometer.Secondly,the system model of quartz flex accelerometer is analyzed,and the open-loop model identification method is used to obtain the mathematical model of the header,and the parameters of the PID controller are designed based on the identification results.The adaptive PID control algorithm which takes the above parameters as the initial parameters is applied to set the PID parameters to the best.The final experimental results show that the control strategy can achieve good control effects.Thirdly,a thorough servo circuit noise model is established,and the influence of the key parameters in the servo circuit on the additive noise carried by the deflection angle signal is quantified.Based on the noise analysis results,the circuit parameters are optimized.After the optimization,the root-mean-square of the equivalent additive noise carried by the deflection angle signal is only 164.54?V(7)rms(8).Combined with the transfer function of the quartz flex accelerometer system,it is estimated that the equivalent voltage noise of the total output of the servo circuit is about 84.17?V(7)rms(8).Finally,the integration of quartz flex accelerometers is accomplished with the high-performance servo circuit system and integrated header mechanical structure.An experimental system was set up to test the sensor performance parameters.The experimental results indicate that the one hour stability at 0g and ±1g is 25 ?g,17 ?g and 16 ?g respectively,the resolution is 10 ?g,the nonlinearity is 0.028%,the bias repeatability(short-term)is 36 ?g,and the scale factor repeatability(short-term)is 33 ppm.The quartz flex accelerometer with the integrated signal processing method proposed in this paper has good performance indicators and technical advantages.