Conformity Magazine- May 2008 - (Page 42) MIL-STD-461F has recently been issued. This is also a test requirement at LRU level that gives a good basis for determining immunity before equipment is integrated into a system. This latest revision includes voltage spike testing (CS106) on power supply interfaces. This is a revised and updated version of the old CS-06 from MIL-STD-461C. An example of a project already incorporating elements of both military and civilian test requirements is the NH 90 Waveform DO160F Voltage Test/ Current Limit Test Category Event Relative Amplitudes Waveform 5A Waveform 4 800V/1600A 5 Multiple Stroke 100%/50% DO160F Voltage Limit/ Current Test 5 Multiple Stroke 14 100%/50% 640V/2000A (Figure 2) helicopter programme. A European joint venture between Eurocopter (France & Germany), Augusta (Italy) and Fokker (Netherlands). As part of the NH 90 test programme, lightning test requirements are based on the U.S. Federal Aviation Administration’s (FAA’s) AC 20-136, which draws on DO160. Changes have been included appropriate to the airframe and its operating environment. Airbus ABD0100.1.2 Voltage Limit/ Current Test A Multiple Stroke 24 100%/50% Boeing D616050-5C Voltage Test/ Current Limit A Multiple Stroke 14 100%/20% 1000V/2000A Why Impulse Testing? Man was never intended to fly, and for man to overcome gravity requires a very complex machine – the airplane. As with all machines, there are many operations required that may, through proper operation, generate electromagnetic interference. Voltage spikes generated by switching of loads on the power lines can affect every piece of equipment with a power interface. The many miles of cables within an aircraft are potential antennas, picking up “noise” and disturbance signals. Apart from the inherent system issues, aircraft, by virtue of the environment they occupy, are extremely susceptible to natural phenomena such as lightning and P-static. Background to the Lightning Environment There are several mechanisms over which the external lightning event is coupled into an aircraft’s systems. In reality, most transients are induced as complex waves through several coupling paths. For practical purposes, these can be narrowed down to two basic mechanisms, resistive coupling and aperture coupling. Resistive Coupling This mechanism produces voltages in loops existing between cables and an aircraft structure. If the structure is highly conductive, the voltages may have the waveshape associated with the external environment. This translates to Number of pulses 14 300V/60A Figure 1: Comparison of waveform parameter specifications for FADEC (fully automatic digital engine controller) (Test Category A = Critical equipment failure which would endanger continued safe flight.) Figure 2: NH 90 Helicopter 2 Conformity mAy 2008
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