Research On The Electronmagnetic Interference And Airworthiness For Aircraft EWIS Wiring

With the development of avionics, airborne electronic equipments are becoming more digitized. Frequency band is constantly broadening, and also the power, the sensitivity and the complexity of network equipment is increasing. All of this result in very poor aircraft electromagnetic compatibility environment, which bring about more and more electronic equipments failures and affect flight safety finally. And in fact, 90%of the reasons of the equipment or system performance descending result from electromagnetic coupling among large and complex cable interconnection. Therefore, the research on the electromagnetic interference of aircraft wring and its airworthiness is of practical significance. Extensive cable electromagnetic interference researches have done abroad from the 1960 s. Firstly, using the electromagnetic coupling circuit theory in low-frequency situation and the transmission line theory in high-frequency situation, the low-frequency electromagnetic coupling circuit model and high frequency transmission line model are built in this paper to analyze the factors that affect the electromagnetic coupling, such as the distension between wires, height from the reference ground, pigtail effect and shielding method. Then, based on above analysis and the real electromagnetic interference problem of aircraft cables, adopt the EMC studio simulation software to build various types of cable models in the real aircraft electromagnetic environment.With the EMC studio to simulate this models, kinds of relationships of cable EMI caused by the cable spacing, height from the reference ground level, grounding of the shield and the pigtail effect, the wire harness in the treatment of idle and a variety parallel to the earth conductor at different frequencies are summed. The simulation results validate the theory. Finally, this paper chose the power line, the coaxial cable between transmitter and antenna in the bunch of cables connected VOR and other equipments in Boeing 737, and uses the EMC studio to simulate this cables model. Based on FAR25 and RTCA DO-160 F and other relevant airworthiness standards, airworthiness is verified combined with the cable EMI simulation result, several related suggestions are given to reduce electromagnetic interference between cables or wires. In order to meet the airworthiness standards of FAR25, those suggestions can be as a reference to the design of aircraft wiring to improve the electromagnetic compatibility of aircraft electronic systems.