DS-FEB23-PG46_Layout 1 16/02/2023 10:06 Page 1
FEATURE
MILITARY, AEROSPACE & DEFENCE
EMC FOR AVIONICS
Electromagnetic compatibility (EMC) with natural and
man-made sources is essential for avionics platforms and
installations. Andrew Lawson, EMC chief engineer at TÜV SÜD comments
they must be designed to ensure EMC with the natural and man-made electric, magnetic and electromagnetic environments in which they are to be deployed. They must also offer compatibility with natural environment sources. Manufacturers need to ensure their products meet safety legislation for the products and their use in safety related applications, and EMC standards contribute to ensuring equipment functional safety. However, EMC testing alone does not provide safety assurance as it would not be practical to test for all conditions. This means it does not consider foreseeable faults, misuse, ageing, production tolerances, environmental factors, full range of EM phenomena and levels over lifecycle, and testing uncertainty. Therefore, the focus should be on design and risk analysis to identify how EMC susceptibility would cause the product to fail, the consequences (does it fail safe/unsafe?) and any design mitigations. Unfortunately, all avionics electromagnetic phenomena are not covered in a single standard. RTCA DO-160 is an avionics environmental standard and therefore includes a wide range of non-EMC phenomena, as well as EMC test methods and limits for equipment. RTCA DO-357 is the User Guide to DO-160. DO-357 provides additional background information for the associated test procedures and requirements of DO-160. It also includes the rationale for requirements, guidance in applying the requirements, commentary, possible troubleshooting techniques and lessons learnt from laboratory experience.
A
EMC GENERAL TEST REQUIREMENTS A screened room must be used for both RF emission and susceptibility measurements to provide a low level of ambient noise (emissions)
46 DESIGN SOLUTIONS FEBRUARY 2023
s avionics platforms and installations have high power intentional transmitting sources and other sources of interference,
and to prevent radiated interference infringing the Wireless Telegraphy Act (susceptibility). Some low frequency and conducted tests do not require a screened room. A basic screened room has the disadvantage that it is a metal box and will resonate at certain frequencies, increasing the measurement uncertainty (40 dB has been quoted). To improve the performance of the screened room, an RF absorber is attached to the walls to provide absorption of the RF energy to prevent reflections and resonances. Choosing an accredited test facility is not
usually mandatory but reduces the risk to the client who will otherwise have to satisfy themselves that a non-accredited facility has performed the testing correctly.
TEST PLAN CONTENTS A control plan or procedure may be produced at the start of a project and is normally used for large or complex systems. It demonstrates to a purchaser a defined EM strategy and contractual compliance. It provides EMC guidance throughout the project lifecycle. It also defines the EM management organisation, responsibilities, EMC requirements, design approach, test and qualification programme. The test plan or procedure provides all the
information to enable a test facility to perform the tests. Generally, there is one test plan per equipment/system. The test report is produced by the test
facility as a record of the tests carried out. This demonstrates how the equipment complies with the test standard against the requirements of the control plan/test plan, and hence contractual requirements. Guidance on the content of these documents is provided in DO-160, which requires the test categories and minimum performance standards (specification) to be documented on an Environmental Qualification Form, examples of which are given
in DO-160 Annex A. The cost of testing and timescales can become excessive unless good engineering judgment is applied in the form of a technical rationale for the selection of tests.
TEST PLAN GENERIC CONTENT • Description of equipment under test - Power supply, interfaces, cable lengths, size and weight
• Modes of operation - Exercise all functions for emission and susceptibility • Test configuration and layout - Block diagram and layout on the bench/floor, grounding arrangement • Drive and support equipment • Test requirements and rationale (any tailored requirements) • Susceptibility performance criteria and method of monitoring - Parameters to be monitored, failure criteria • Sweep speed, dwell time and susceptibility modulations • Test procedures and limits • QA, documentation, safety & security. In order to achieve consistency throughout the phases of EMC testing it is essential to formalise the details of the test plan/procedure for the project. A test plan/procedure should therefore be developed and agreed with the client project manager prior to the commencement of EMC testing and shall be sufficiently detailed to enable any test to be repeated by another approved test house. Without a formalised test plan/procedure the results of the EMC test may vary considerably due to possible variations in the test arrangement, thus obscuring the effects of any modifications during development of the equipment to the production stage.
TÜV SÜD
www.tuvsud.com/en/industries/aero- space-and-defence
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64
