New whitepapers for aerospace testing
Testing electronic systems for the aerospace industry follows the basic requirements specified in RTCA DO-160 and EUROCAE ED-14. A leading manufacturer of test equipment and member of the SAE and EUROCAE standard committees, EMC PARTNER publish three white papers on our website. We hope they provide useful information on the complexities of indirect lightning testing. All whitepapers are free to download. Please leave your comments on one of our social media channels: Twitter / LinkedIn
Here we go with our latest 3 whitepaper articles:
Overview and Experiences with RTCA/DO160 Level 5 avionics requirements
Aircraft design and assembly is a global phenomena. Sub systems are designed, manufactured and tested in multiple locations, only being shipped to the aircraft assembly plant on demand. This global process requires comparable tests producing identical results no matter where in the world they are performed. Standardisation of test methods and equipment go a long way to achieving these objectives. The RTCA DO160 is ideally suited to fulfil this standardisation role.
Two sections of DO160 deal with lightning effects and there is a close relationship between them.
- Section 22 (Lightning induced transient susceptibility)
- Section 23 (Lightning direct effects).
Section 22 specifies requirements for equipment level tests using indirect lightning effects, section 23 deals with direct lightning strikes.
Tests on individual LRUs (Line Replaceable Units) are treated as stand alone black boxes. They can be sold to multiple aircraft manufacturers who require a baseline performance. This is provided by testing to the “generic” DO-160 section 22 requirements.
Direct lightning effects covered by section 23 of DO160 are performed on whole aircraft usually in only a few locations (aircraft manufacturers) and therefore has very specific space requirements. The external or direct lightning event is characterised by high current discharges reaching 200kA and described as a „four component“ test, there being four distinct phases to the lightning event.
The generation of such discharges requires large and very expensive test equipment and a lot of space. This type of testing is certainly more representative of the real event, but poses additional problems in evaluating the effects and assessing any latent damage that may have occurred to equipment, cabling or interfaces. This task could. Show Document
Indirect Lightning testing and the influence of couplers
Indirect lightning tests described in RTCA DO-160 section 22 and EUROCAE ED14 define wave shapes and amplitudes for current and voltage impulses when applied using PIN injection and Cable Bundle methods.
Cable Bundle testing relies on a test system comprising impulse generator and coupling device. Because of the range of frequencies and impulse types, inductive couplers made from different materials are necessary to ensure energy transfer while maintaining wave shape integrity at the point of injection (coupler secondary).
Source impedance of a test system in general is defined as z = v(t) / i(t)
This is, however, only true when both the voltage (v) and current (i) waveforms are in phase. This is true for indirect lightning generators configured for PIN injection and Ground Injection.
Once a coupler becomes part of the test set-up, such as for Cable Bundle tests, the open loop voltage waveform is influenced by the coupler saturation characteristics.
In this situation, the conditions required for z(source) are no longer met (waveforms are altered). The system impedance is now referred to as a „virtual“ impedance which can only be resolved mathematically and has no relation to the actual generator source impedance. Show Document
Indirect Lightning Cable Bundle Testing using Waveform 3
RTCA/DO-160 and EUROCAE ED-14 section 22 describe testing of indirect lightning into cable bundles using waveforms derived from high energy fields caused by waveform D lightning transients in the vicinity of an aircraft. Waveform 3 frequencies depend upon the length of the system and the length of the cables. Longer cables can sustain only lower frequency oscillations (inversely proportional to length). Standard requirements are for waveform 3 1MHz and 10MHz to give the same current response into low impedance cable bundles. However, for technical reasons it is (nearly) impossible to build a waveform 3 (WF3) generator for 1MHz and 10MHz having the same source impedance and delivering the cable bundle limit current required. This paper will discuss reasons why the 10MHz generator source impedance is higher than for 1MHz, what the consequences are for WF3 limit. Show Document