Test System Based On MATLAB And Lock-in Amplifier

Phase-locked amplification is a technique that can extract the amplitude and phase of a signal at a specific frequency in an extremely noisy environment.Based on the principle of phase-sensitive detection,the lock-in amplification technique uses a signal with the same frequency and fixed phase relationship as the signal to be measured as the reference signal,and measures the amplitude and phase of the signal to be measured relative to the reference signal.As an instrumentation device with rich functions,the lock-in amplifier is widely used in the fields of sensor signal extraction,material physical property testing,and biological signal detection.However,there are many problems in practical applications such as cumbersome parameter settings,low data visualization,imprecise time constants and sensitivity settings in complex tests.To address the problems of manual adjustment of multiple parameters,low automation and inconvenient data processing in testing,a computer-controlled lock-in amplifier testing system is designed by using MATLAB.The main work is as follows:(1)Briefly introduces the functional structure,signal detection principle and key parameters of SR830 lock-in amplifier.In order to better design the system,the noise sources that may affect the system are first analyzed.Then a computer-controlled test system of AC current source and lock-in amplifier is designed.The computer was interconnected with the AC current source and the lock-in amplifier through a GPIB-USB-HS interface card communication.The control,data readout and graphing of the AC current source and lock-in amplifier were implemented using MATLAB program.(2)A dedicated APP was designed based on the MATLAB APP Designer platform,and the design was implemented mainly from the interface control layer,functional layer,and code layer.A variety of controls are arranged in the main interface and parameter setting interface of APP using modular layout,and common measurement and control operations are realized by designing the functions of each module.The status byte of the lock-in amplifier are used to monitor the operation status of the system,and the automatic parameter acquisition function is designed to solve the problem that the parameter setting of the lock-in amplifier is cumbersome and cannot adapt to cross-range testing.Meanwhile,the combination of data extraction and real-time testing realizes the visualization of multi-parameter data comparison and improves the visualization of the system.(3)Use the APP to control the system to test the voltage output signal of the sensor element developed in the laboratory.First,the lock-in effect of the lock-in amplifier with different parameter settings was analyzed to determine the default parameter settings of the lock-in amplifier and the precise parameter settings for different test requirements;then,the voltage signal of the sensor element driven by AC excitation was collected and the variation law of the first and third harmonic components in its output with excitation was analyzed;finally,the common test functions of the APP were combined to Finally,the relationship between the voltage signal and the wind speed is obtained by characterizing the sensor element with the common test function of APP.The innovation of the research is to design a lock-in amplifier test system with MATLAB and apply it to the characterization of the sensor element under AC excitation.The results show that the system enables efficient control of the lock-in amplifier,better extraction of useful signals with precise parameter settings and multi-parameter data visualization functions for functionally complex tests.The test system can be modified by combining the characteristics of the object to be tested.It has the advantages of friendly interface,easy to use and good expandability,thus having good practical application value.