Conformity Magazine- May 2008 - (Page 44) the DO-160 voltage waveform 4 definition 6.4/69µs. This voltage waveform can also be present in cable shields derived from the shield current and transfer impedance. Low resistance cables, connected at both ends to a metal airframe structure, will be subject to a current transient, derived from the external lightning event, galvanically coupled between the low inductance airframe and the relatively high inductance cables. Two waveforms result from resistive coupling, and are defined in DO-160 as: • Waveform 5A (40/120µs) models resistive coupling through a composite structure; • Waveform 5B (50/500µs) models resistive coupling through an aluminium structure. Aperture Coupling With metal fuselage designs, aperture coupling was limited to openings in the structure, such as windows. Nowadays, aircraft structures are no longer homogenous, and all new designs have varying degrees of composite materials. Boeing’s 787 “Dreamliner” fuselage uses full composite barrel construction, while Airbus has opted for a metal frame with composite panels. In either case, EM waves can penetrate composite structures more easily, and transients will be induced in the internal electronic systems. The initial lightning stroke (component A) can be coupled as a magnetic field, penetrating an aircraft structure and inducing the DO-160 current waveform 1 (6.4/69µs). Electric and/or magnetic fields penetrating the structure will excite resonances in cables, giving rise to “ringing” waveforms. These are modelled by the DO-160 WF4 Voltage/Current LVL1 - 25/50 LVL2 - 625/125 LVL3 - 150/300 LVL4 - 375/750 LVL5 - 800/1600 LVL1 0 100/4 LVL2 - 250/10 LVL3 - 600/24 LVL4 - 1500/60 WF5A Voltage/Current LVL1 - 20/60 LVL2 - 50/160 LVL3 - 120/400 LVL4 - 300/800 LVL5 - 640/2000 No requirement Standard DO 160F Parameters No. of transients Relative levels Distribution Impulse spacing Event duration Test duration No. of transients Relative levels Distribution Impulse spacing Event duration Test duration No. of transients Relative levels Distribution Impulse spacing Event duration Test duration MS Multiple Stroke 14 strokes 100%/50% random 10 - 200 ms 1.5 s 20 events 24 strokes 100%/50% random 10 - 200 ms 2s 20 events 14 strokes 100%/>20% 10 - 200 ms random 1.5 s 20 events ABD0100.1.2 D6-16050-5/B No requirement LVL1 - 500/1500 LVL2 - 750/2250 LVL3 - 1000-3000 LVL4 - 2000/6000 Figure 3: WF4 and WF5A multiple stroke test requirement Figure 4: Multiple burst event Conformity mAy 2008 Figure 5: Generator impedance definition
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