Typical Electromagnetic Interference Test And Analysis Of Toshiba’s CVU002-D0 Encoder

To solve the typical electromagnetic interference(EMI)problem that the Toshiba’s CVU002-D0 encoder suffered in the Brazilian urban rail transit trains,according to the idea of "the check of EMI source and coupling path--the analysis of the formation mechanism of EMI--the establishment of measures for solving EMI",a detailed study is carried out.Firstly,through theoretical analysis,radiation immunity test in the laboratory and field strength measured on site,the radiation coupling of EMI coupling path is excluded and it is determined that the interference comes from conduction coupling.Through three kinds of conduct immunity tests(electrostatic,electrical fast transient,surge)performed in the laboratory,it is checked and confirmed that the signal type of EMI is the surge that the internal circuit port of CVU002-D0 encoder suffered.According to the immunity test circuit topology of the surge on the internal circuit port,the voltage and the effective value of the voltage that the surge signal couples to the internal circuit port of the encoder are obtained.The direct cause of the burning of the resistance and MOS tube at the output port of the encoder pulse signal is found out.Then,the parts of the system on the train which may produce this interference signal are investigated one by one.Meanwhile,combined with the results of site survey and the characteristics of the train grounding system,it is confirmed that the EMI source on the train is the transient current entering the vehicle body.Based on the principle of self-inductance calculation in electromagnetic theory and considering skin effect,the internal and external self-inductance parameters of the vehicle body in the equivalent circuit formed by the contact line and the vehicle body are derived.Combined with the relevant resistance of the vehicle body and the instantaneous current collected on the spot,the unbalance voltage of vehicle body is calculated.In addition,according to the characteristics of two-core shielded cable,the capacitive coupling model of the unbalance voltage of vehicle body is established and the formation mechanism is analyzed.Finally,from the perspectives of reducing the EMI source and improving the immunity of the encoder,the measures to solve the problem of EMI are put forward and verified effectively by the tests in site and in the laboratory.The research results show the following conclusions:The interference source can be significantly reduced by concatenating flat gasket whose equivalent resistance is 50mΩ to the end of the protective earthing wire which is connected to the vehicle body.The immunity of the encoder can be greatly enhanced by adding transient voltage suppressor(TVS tube)inside the internal circuit port of the encoder.