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EMC TESTING


Pete Dorey, Principal Consultant at TÜV SÜD Product Service, explains how to take the right approach to preparing for EMC testing.


❱ ❱ Increasing numbers of products will visit EMC test chambers on the path to certification


M


anufacturers in a wide range of industries are increasingly being required to ensure that electromagnetic


disturbances do not interfere with other users, or with the function of their products. Therefore, the majority of electronic products must comply with the Electromagnetic Compatibility (EMC) Directive 2014/30/EU, as well as other appropriate requirements, before they can carry the CE marking. Emission tests primarily focus on the


ability of the product not to emit radio frequency energy but also include low frequency tests for mains harmonics and to avoid lighting flicker. Emissions may radiate from the product or be conducted over power leads. Immunity tests ensure that the product functions correctly in the presence of radiated fields from transmitters, conducted interference via cables and a range of transient interference events such as electrostatic discharges.


HELPING THE LABORATORY Test laboratories see many thousands of products each year – they will not be familiar with your product, so you must brief them fully. A short, but clear general description is therefore vital. It’s particularly important to include details on the product’s highest internal frequency, as this will allow the laboratory to know the maximum


10 /// EMC Testing Vol 1 No. 2


frequency range of radiated emission tests. Otherwise unnecessary test time and laboratory cost will be incurred. Include block diagrams, which detail


the test configurations, data paths and various product functions. This will ensure that the test laboratory covers all the possible configurations of the product, none will be missed and no unnecessary tests done. If possible select a single mode of


operation that addresses all product operating frequencies and functions as this enables the laboratory to do a single set of tests that will cover the ‘worst case scenario’. It is also important to know the cycle time it takes the product to run through all of its functions as this impacts on the speed of testing. It is also vital to understand at exactly


what point a product has failed an immunity test, so that the test condition or test frequency of failure can be identified. You must therefore inform the laboratory about what performance criteria indicates that the product has failed during the tests. Is it that the display no longer works, the interface fails, voice becomes distorted, or warning lights indicate a malfunction etc?


TEST CRITERIA There are three performance criteria A, B and C that are specified in the EMC standards and each immunity test has one criteria specified. Criteria A requires


Pathway to successful EMC Testing


the product to continue operating as normal at all times and applies to tests for continuous EMC phenomena (like immunity to adjacent mobile phones). Criteria B allows some degradation during the test condition and applies to tests for transient immunity (EMC not experienced very often, such as electrostatic discharge due to someone touching the equipment). Criteria C allows temporary loss of function and applies to severe transient immunity which is infrequent, such as a power surge or voltage interruptions. Of course permanent loss of function is a failure! For immunity tests therefore, the manufacturer must define the performance criteria for their product as this determines a test pass or fail.


OTHER REQUIREMENTS The laboratory also needs equipment to support the product under test, such as laptops for monitoring the product’s performance. Any such equipment must not introduce excessive EMC interference, it must be sufficiently immune itself and must be easily connected/disconnected to allow the test set-up to be moved between facilities. External interface cables need to be at


least 10m in length, so that they reach any remote equipment that is located outside the chamber. Local interface cables must terminate in shielded loads (i.e. inside metal boxes that stop interference) inside the chamber.


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