Conformity Magazine- May 2008 - (Page 46) impulse injected can also have a big influence as to whether the “test” or “limit” value is reached first. Changes in DO-160F The latest DO-160 revision takes into account applications and interpretations applied to a variety of modern airframes. One of the principle changes is the recognition that, although Waveform 5A is defined as a current waveform, the waveshape may also be used for a voltage waveform when the test method specifies lifting the wire shields for direct core wire pulsing. DO-160F now corresponds to the Boeing D6-16050 requirement specifying “waveform 5A may be defined as a voltage test level.” Additionally, DO-160F provides further clarification of the waveform usage. Compare the tables from DO-160F with previous versions and the waveform is no longer the same for voltage and current. In terms of the test equipment, hybrid generator designs can cope with this and future changes. What is a Hybrid Generator? For all test applications without any coupler (PIN, GND injection), the dynamic behaviour of a hybrid generator is well-defined. The advantage of this design is that, independent of the load impedance (e,g., cable length, aluminium or carbon fibre structure), the test results are repeatable and comparable. A hybrid solution is the only generator design that gives comparable test results over the complete EUT load range (Figure 7). To perform cable bundle or cable induced tests, a coupler must be used together with the hybrid generator. It is physically not possible to design a hybrid coupler. Couplers can be optimized either for voltage or for current. Therefore, with two different types of coupler (optimized for either correct open circuit voltage waveform or correct short circuit current waveform), the hybrid generator can be used over a wide load range. Compliant waveforms can be derived for very low loads, for example, cable bundle shield connected to ground on both sides (applicable for aluminium structures), or for high impedance loads, such as cable bundle connected only on one side (carbon fibre structures). A hybrid generator solution with two couplers covers the large load range experienced today and can also be used for future designs. Further advantages of the hybrid generator design are the clean voltage and current waveforms and, as a consequence, clear voltage limits for current tests. Background of Voltage Spike Testing Figure 6: Test/limit definition Any aircraft design includes power generators, distribution and regulation circuits. Inevitably, switching events in the Figure 7: Hybrid voltage and current impulses Conformity mAy 2008
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