The Research Of Conducted Interference In Data Transmission System Based On Fault Tree

The thesis promotes a new method to analysis conducted interference, which is complex, hidden and more reasons and more result, and then adapts fault tree method for solving and calculating the public impedance, electrostatic interference and crosstalk between lines in data transmission system, and also designs a practical software to resolve the interference.According to the three basic elements of conducted interference and the principle to construct fault tree, the thesis determines the conducted interference of the data transmission system as the top event of fault tree. Line receiver, code transformer, modulator and output filter directly result in conducted interference, which are connected with the top event with and gate as the middle event. Microwave switch, signal line and power-enlarging source are treated as middle events or basic events to construct the second layer of fault tree. Continued like this layer by layer until all events turn to be basic events.In the thesis, using downlink method to get the minimum cut set of the formal fault tree is determined as the reason of conducted interference. Begin with the top event, the input events of AND gate were lined up and that of OR gate were lined down, and go to the deepest layer. The minimum cut set of the formal fault tree can be obtained through comparing the results.The thesis constructs the formal fault tree with the above method. Through solving its minimum cut set, we get the basic reason for data transmission system failure, and also develop a practical fault diagnosis software, and then from the view of three elements of conducted interference make analysis and calculation for the system failure and discussed the solving methods. For example, for a 0.3m AWG14 conducted line, its impedance is 0.4Ω, which is rather larger; while for a more wider and flatter conducted line with the same material, its impedance is 0.2Ω, which can replace the former one to meet the requirement of ground impedance. Under the VC++6.0 platform, the part used as filter function gets 50 dB quickly, which is the restraining value for the 27MHz conducted interference noises for 2-level LC filter with the band-pass filter in 1.5MHz cutoff frequency.The content in the thesis can be applied on the following two fields: in the stage of Electromagnetic Compatibility designing of systems or equipments and in the stage of diagnosing, investigating and solving the conducted interference occurring after putting to use. In this way, the failure reason won't be missed, thus it has strong practicality, and the software makes the interference solving process a lot of convenience for the engineers.