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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.

❱ ❱ Thousands of new products are being tested for EMC immunity in such chambers to ensure they meet CE Marking requirements

question of delivering hardware to the laboratory, other factors also need to be considered such as providing the testing body with information about how the product works, what its failure modes are and other related information as well as providing periphery equipment that will be needed to perform a full evaluation. A test laboratory sees 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 frequency range of radiated emission test. If this isn’t done, then unnecessary test time and laboratory cost is likely to 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 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 RESULTS 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 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

OTHER REQUIREMENTS Do not assume that the laboratory can provide everything to support the product, such as laptops for monitoring the product’s performance, and ensure that there are spare power packs and batteries. Of course, any such equipment must not introduce excessive EMC interference, it must be sufficiently immune itself, and must be easily connected or disconnected to allow the test set-up to be moved between facilities. An example of a poorly prepared product in this respect is the use of soldered connections. Tests are performed in a chamber and

so 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. Special product test software may be required to achieve a single mode of operation to exercise all functions, and so must be written ahead of time and verified. Poor EMC can negatively impact

product performance and function in a variety of ways. EMC testing helps to ensure that your device will continue to function as expected in the intended EMC environment. Good preparation helps streamline the test process in the laboratory and ensures that the product’s time-to-market is optimised and costs minimised. n

Pete Dorey is a Principal Consultant at TÜV SÜD Product Service, a global product testing and certification organisation, and at its sister company, TÜV SÜD BABT, a major radio and telecommunications certification body on the world arena. TÜV SÜD Product Service analyses over 20,000 products each year in Europe,

Asia-Pacific and the Americas, ensuring that products are safe, reliable and compliant and minimising liability risks for manufacturers, importers and retailers. TÜV SÜD Product Service’s sister company, TÜV SÜD BABT, focuses on radio

and telecommunications certification and is a Notified Body under the European Union’s Marine Equipment, Radio Equipment and Machinery Directives.

EMC Testing 2018 Vol 1 No. 1 /// 3

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