Research On Precision Signal Processing Circuit Of Eddy Current Edge Sensors

In this paper,non-contact and high-precision displacement measurement is taken as the research background,focusing on the performance improvement of edge sensors in large astronomical telescopes.An edge sensor with eddy current is introduced in detail of the system design scheme,the core index for edge sensor includes resolution,temperature stability and long-term stability.Probe and circuit of sensor;the design of the main parts such as manufacturing process,method,system analysis of the tem-perature drift compensation of sensor are given.Then,further study of sensor signal processing circuit,the influence of the circuit of sensor of each part is analyzed,this pa-per proposes a noise suppression method of sensor circuit and a circuit of temperature drift compensation,respectively;got the eddy current displacement sensor prototype with a resolution level close to the capacitance displacement sensor and the sensor cir-cuit with excellent temperature stability;A new synchronous demodulation circuit is explored,which is expected to further improve the signal to noise ratio of the sensor,reduce the harmonic component of the terminal output,and improve the actual dynamic range of the sensor.Finally,the prototypes of the designed edge sensor are tested and the LAMOST small system confocal maintenance experiment is carried out,which fully shows the actual performance of the sensor.The main work and contents of this paper are as follows:1)Based on eddy current effect,the basic working principle and equivalent circuit model of eddy current displacement sensor are introduced.The analysis methods of the sensor are given,the analysis method based on COMSOL Multiphysics finite element simulation and MATLAB numerical optimization is proposed to design the electrical parameters of the sensor.Aiming at the core problem of eddy current sensor-thermal drift,the design method and fabrication process of sensor probe are discussed,and the performance differences of single probe,differential probe and pseudo differential probe are analyzed.The basic signal processing circuits of sensors are discussed,and their advantages and limitations are pointed out,which can provide systematic guidance for the design of subsequent sensors.2)According to the application scene of the edge sensor,the design difficulties of the sensor are analyzed,the design scheme of the sensor of probe and signal processing circuit are proposed,the temperature drift characteristics of the sensor are analyzed and the corresponding compensation method is given.The developed sensor prototype is calibrated of system parameter and tested of performance,the LAMOST telescope small system confocal maintain test is carried out,the closed-loop stability of confocal system is preliminary verified,improving the confocal maintain time of the small system,and showing that developed sensors have excellent performance,in the future,the telescope single observation time is expected to boost.3)The resolution characteristics of the eddy current displacement sensor in the full range are analyzed from commercial sensors and experimental prototypes,and the optimal direction to improve the resolution of the sensor is given by derivation of the formula,and a filtering method to suppress the noise of the signal source is proposed.A prototype of differential eddy current displacement sensor with probe material of glass-ceramics is designed,and the noise level of the sensor is measured.The experimental results show that the resolution of the sensor is 5 times higher than the original one.Comparing with some sensor prototypes and commercial products at home and abroad,this sensor prototype has a resolution level comparable to that of capacitive sensors,with a resolution of 0.05 nm at a scale of 20 ?m and a bandwidth of 7.2 Hz.4)In this paper,the temperature drift characteristics of an eddy current displace-ment sensor based on AC bridge are analyzed.This paper introduces the application of ratio measurement in precision measurement and points out its design defects.Then,a compensation method of circuit temperature drift composed of analog circuit is pro-posed,and the principle of compensation is deduced in detail.Finally,the correspond-ing sensor prototype is designed and tested,and the experimental results show that the temperature coefficient of the circuit was suppressed from 243 ppm/? to 5 ppm/?.5)A synchronous demodulation circuit based on sample and hold is proposed.Firstly,the shortcomings of the traditional phase-sensitive detection methods are dis-cussed.According to the measurement circuit of the sensor,the performance of signal detection can be improved by using synchronous sample and hold.The signal transmis-sion characteristics of the circuit are analyzed.Under the same conditions,the circuit can provide a higher dynamic range for measurement.The simulation analysis shows that the output harmonic components of the end of the circuit are suppressed below-60 dB.Finally,a prototype of the eddy current sensor is made and the main performance parameters of the circuit are tested.