High Speed And Precision Inductance Measurement System Based On Double Excitation Auto-balancing Bridge

As an important parameter in electromagnetic measurement,the fast and accurate measurement of inductance is of great importance in the measurement and calibration of inductors and the design and production of high-precision inductive sensors.Although the traditional coaxial AC bridge can achieve high-precision measurement of inductance,it has narrow band width and low measurement efficiency,while the commercial impedance analyzer can achieve fast measurement of inductance under wide band width,but its maximum relative uncertainty is only 5×10^-4,which is difficult to meet the demand of high precision impedance measurement.In order to meet the requirements of fast and high precision measurement of inductance,this paper proposes a method of inductance measurement based on double excitation auto-balancing bridge,focusing on four aspects of key technologies:high-precision bridge excitation source,high-speed real-time voltage information acquisition and transmission,efficient bridge automatic balancing algorithm and high-precision voltage ratio calculation method to carry out the research work.The system prototype is developed and verified by experiments.The main research work is as follows:1.Aiming at the demand of fast and high precision inductance measurement,the common inductance measurement principle is analyzed and compared,and a high precision inductance measurement scheme based on double excitation auto-balancing bridge is proposed.The circuit principle,measurement method and measurement process of the scheme are introduced,and the key technologies of the scheme implementation are pointed out.2.Based on CORDIC algorithm and FPGA,two DDS excitation signal sources are designed,which realizes the output of high-precision sinusoidal excitation signal with adjustable amplitude,phase and frequency with low resource consumption;The inductance measurement module based on FPGA+ARM+upper computer architecture is designed.While ensuring the high-speed real-time transmission of voltage signals of the bridge,high-speed multi-point FFT calculation and inductance measurement results display are realized by upper computer.3.In order to meet the requirements of fast automatic bridge balancing,an iterative balancing algorithm based on the fastest descent method is proposed.The convergence speed of the algorithm is improved,and the automatic balance of the double excitation bridge can be realized in the time range of 110～330ms in actual measurement.Aiming at the measurement error caused by the initial phase change of the excitation signal and non-integer periodic sampling,a bridge voltage signal processing method based on the all-phase Fourier Transform algorithm（ap FFT）was proposed.The influence of the initial phase and signal frequency change on the bridge voltage ratio calculation was analyzed and compared.Compared with the traditional FFT,The minimum estimation error of signal parameters by all-phase FFT is only 6.316×10^-13,and the high-precision calculation of bridge voltage ratio can be realized without any correction measures.4.A high precision inductance measurement system based on double excitation auto-balancing bridge is developed,and inductance measurement experiment and measurement uncertainty evaluation are carried out.The results show that the relative error of inductance measurement results of this system is very small compared with that of commercial digital bridge,and the optimal measurement relative uncertainty at different frequencies can reach 9.98×10^-5.