Aerospace, Military and Defence
Avionics equipment and electromagnetic compatibility (EMC)
By Andrew Lawson, EMC chief engineer at TÜV SÜD, a global product testing and certification organisation
A
vionics platforms and installations have high power intentional transmitting sources and other sources of interference. They must
therefore 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. Unfortunately, all avionics electromagnetic phenomena are not covered in a single standard.
RTCA DO-160 is an avionics environmental standard and includes EMC test methods and limits for equipment, which are outlined below. RTCA DO-357 is the User Guide to RTCA DO-160. RTCA 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.
RTCA DO-160 Section 1 - Purpose & Applicability
Section 1 requires the equipment performance standards to be specified, which define the minimum functional performance of different categories of equipment. The manufacturer can either adopt an RTCA or EuroCAEMOPS, or specify their own equipment specification. These equipment performance standards are required during susceptibility testing to ensure that the equipment continues to function correctly.
RTCA DO-160 Section 2 - Definition of Terms - General
Section 2 requires the severity of limits, known as ‘categories’, to be decided. DO-160 lists categories for each test. Due to the large number of possible categories, they are not listed here but reference should be made to the
20 March 2023 ● 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
DO-160 standard and the DO-357 User Guide.
RTCA DO-160 Section 3 – Conditions of Tests
Section 3 provides the general test requirements. This describes how to set up the equipment and the test facility and test equipment requirements. Since these apply to all the environmental tests, some will not be applicable to EMC e.g. combining test conditions.
RTCA DO-160 Tests
Section 15 to 25 specify the EMC test requirements. Some tests are subdivided into multiple sub tests which correspond to separate tests in other standards. When writing test plans it is easier to consider these sub-tests as tests in their own right as they have their own test method and limit. Section 19 is a good example as it comprises five different tests.
Contents of a test plan
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
Components in Electronics
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
The choice of test facility depends on a range of factors such as accreditation, price, capability, location, and good reputation. Choosing an accredited 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. UKAS accredited test facilities are given on the UKAS website:
https://www.ukas.com/find-an- organisation/
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.
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