Noise Analysis And Test On The Capacitance Displacement Detection Circuit Of A Precise Accelerometer

High precision accelerometers have a wide range of applications in the field of precision gravity measurement,such as geophysical exploration,earth gravity field aided navigation and so on.However,the variation of the earth's gravity field is very weak,and the requirement for the detection precision is very demanding.Capacitance displacement detection is one of the most common sensing methods in high precision accelerometer.In order to reduce the noise level for a high precision accelerometer,it is of great significance to determine the main source of noises and suppress it through noise analyses and tests on the capacitance-displacement detection circuit.In this paper,based on the establishment of model,theoretical calculation and simulation analysis,the experimental tests were conducted on the typical capacitance displacement detection circuit of a high precision accelerometer.Finally,the main noise sources of the detection circuit are determined.Typical detection circuits for a high precision accelerometer include a capacitance displacement sensor unit,an analog PID control circuit,a feedback actuator and a data acquisition system.In this thesis,the transfer function is derived for each unit of the capacitance detection circuit,and the amplitude-frequency response curve of the transfer function is analyzed,which can be used to guide the subsequent noise analysis and calculation;and then,the noise of each unit of the detection circuit is analyzed,verified in details by the PSPICE software,and compared with each other according to their equivalents on the input end of the accelerometer,taking into account the effects of voltage,current noise and thermal noise of the components in the circuit;finally,the output noise of the detection circuit is verified by grounding the input end,which validates the theoretical analysis.Analysis and test results show that the open-loop noise of the capacitance detection circuit mainly comes from the equivalent input voltage noise of the operational amplifier.The nominal value of the noise of the operational amplifier is about 2 times the measured value,which accounts for the difference between the theoretical prediction and the experimental test.The acceleration detection resolution of the closed loop accelerometer is limited by the data acquisition system,the background noise of which at 0.1Hz is about 7 ng/?Hz,close to the measured background noise of 10 ng/?Hz@0.1Hz.The noise limiting factors of capacitance displacement detection circuit of a typical high precision accelerometer is studied through modeling,calculation and simulation analysis,and experimental test,providing useful knowledge for further optimization of accelerometer noise.