Research On Intermittent Fault Mechanism And Diagnosis Technology Of Electrical Connector In Vibration Environment

The intermittent fault(IF)problem is prevalent in complex equipment systems,which brings high cost requirement and security risk.The IF problem has been paid more and more attention by the order,design,test and user departments with the development of diagnostic technology and the popularization of testability engineering.As a primary source of faults,the IF in electric connectors is difficult to be reproduced,tested and diagnosed.In this paper,aiming at the problem that the IF diagnosis is time consuming and costly,and under the support of ministry-level pre-research project and the National Natural Science Foundation of China,the mechanism and influence of IFs in electrical connectors are deeply analyzed.The key technical problems on the diagnosis of electrical connector IF under single-end test are systematically studied.The main contents of this thesis include:1.The parameter architecture and formalization model of the intermittent faultsAiming at the problem of ambiguous comprehension on the cognition of IF,the implications of IF are analyzed,accordingly the IF is strictly defined.The general mechanism of the IF are summarized,also the IF evolving regulations are illustrated.Considering the fact that there is no parameter architecture that can fully characterize the IF,so on the basis of analyzing the behavioral characteristics of IFs,a parametric architecture is established,which includes 14 indexes in the time domain and statistical domain.As the current IF model cannot completely show the dynamic behavior of IF,a construction method for the conditional stochastic Petri net(CSPN)is proposed,and then an IF formalization model based on the CSPN is developed,based on which the IF parameters are solved.2.Study on the influence of vibration stress on the electrical contact resistance(ECR)(1)By way of developing a dynamic model for the electrical connector,the relative displacement between the contact interfaces is analyzed,accordingly the mechanism for the dynamic ECR is illustrated.In view of strong noises in the measured ECRs,a wavelet package transform(WPT)based de-noise method is proposed.This method can filter the noises ranging from low to high frequency.(2)On the aspect of dynamic characteristic of ECR in the vibration environment for the normal electrical connector,a test of normality is performed on the ECRs from different connector pins,and then the laws of ECR change in the early contact state,the ECR resonance characteristic,the influence of vibrational parameters on the ECR statistical indexes,and the ECR characteristics between different degradation-states electrical connectors are analyzed.On the aspect of dynamic characteristic of IF in the vibration environment for the faulty electrical connector,the influence of vibrational parameters and sampling frequency on the intermittence is also analyzed by evaluating and comparing the IF parameters.(3)Firstly an ECR model is established based on the Greenwood-Williamson contact model,and then the mechanism of the dynamic characteristics for the electrical contact is analyzed according to the proposed ECR model and the dynamic model of the electrical connector.3.Study on the influence of ECR on the signal transmissionAiming at the complex transmission performance of electrical contact in high-speed signal transmission,firstly the circuit models for a single-spot contact and the rough surface contact are respectively built,accordingly a circuit model for the electrical connector in the transmission path is established.To know the influence of ECR on the time-domain waveform of the transmitted signal,the impacts of the ECR on the transmitted signal are analyzed based on the telegraph equation in case of impedance matching,and based on the two-port network in case of impedance mismatching,respectively.Accordingly the transfer function and time-domain output waveform with the ECR as the parameter are solved.To extract the fault feature under single-end test,the insertion loss increment(ILI)model for different port-impedance matching cases are developed by introducing in the insertion loss.The measurement method of the ILI,which is taken as the fault feature under single-ended test,is also illustrated.4.Diagnosis method for the electrical connector IFs and working-state assessment methodAiming at the problem of IF diagnosis for electrical connector under single-end test,the ECR fault threshold is determined according to the influence of ECR on time domain waveform,and then the corresponding ILI fault threshold is determined based on the ILI model.Furthermore,the affection of symbol randomness on ILI measurement is analyzed and the corresponding elimination method is illustrated.Consequently an ILI-based IF diagnosis method for electrical connectors is proposed.In terms of working state assessment for the electrical connector,considering the IF intensity,frequency and duration,a cumulative insertion loss increment(CILI)based method is developed for a single IF detection process,while considering the IF frequency and duration,a NN(neural network)-CSPN model based method is developed for the case with long and complex stresses.The validity of the IF diagnosis method for electrical connector under single-ended test is verified both in qualitative and quantitative approach.In this paper,the connotation,definition,parameter architecture and formalization model of intermittent fault are studied,and the influence of vibration stress on ECR and the influence of ECR on signal transmission are deeply analyzed.The diagnosis method of electrical connector IF under single-end test is proposed.Accordingly the difficult engineering problem of the current electrical connector IF diagnosis is scientifically solved,which is of important value to the academic and engineering application.