Waveform Comparisons Between Qualification Data and Aircraft Measurements

Lightning induced current and voltage pulses are defined in international standards as arising from three distinct coupling mechanisms: capacitive, inductive and resistive. These mechanisms at their simplest give rise to distinct characteristics in the induced wave-shapes relative to the lightning current pulse that caused them. It has long been the practice to decide from a particular induced wave-shape, which was the likely induction mechanism, and compare it in terms of peak amplitude only with the relevant qualification test waveform. This approach fails to take account of the fact that almost all induced waveforms are actually a sum of two or all of the coupling mechanisms, that the coupling is not simple but gives rise to much more complex wave-shapes than the qualification standards would imply, and that there are other critical parameters apart from the peak amplitude. It may also disguise the effect of possible building/rig resonances in test results. In this paper the authors argue that this simple approach is not enough and devise a set of norms encapsulating the properties of current and voltage waveforms in simple quantities that permit a comprehensive comparison between wave-shapes. The characterisation can be done in a standard spreadsheet program provided the two sets of data can be put into a digital form.