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TEST & MEASUREMENT FEATURE Getting EMC test preparation right


Pete Dorey, principal consultant at TÜV SÜD, looks at the growing importance of functional safety, as devices and machines become increasingly complex


and time associated with EMC testing is vital. The answer to this is to be properly prepared before products are sent to the test laboratory. A test laboratory sees many thousands


T


he majority of electrical products must comply with the


Electromagnetic Compatibility (EMC) Directive 2014/30/EU, as well as other relevant directives, before they can carry the CE marking. Not only does EMC testing ensure that products meet regulatory requirements, it improves product quality and avoids product returns, and early consideration of EMC reduces time-to-market delays for new and upgraded products. Emission tests primarily focus on the


ability of the product not to emit radio frequency energy that would interfere with radio and television broadcast reception and wireless communications, such as mobile phones, WiFi and Bluetooth. Emission tests also include low frequency tests for mains harmonic current, to preserve mains power quality and voltage changes, fluctuations, and flicker tests 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, power surges due to lightning or fast transients due to power switching. Third-party EMC tests and


conformity assessments can help to strengthen a brand’s competitive position in the market, due to improved product performance and reliability, by reducing the chances of failures in use. The two key drivers of brand loyalty and product quality can both be beneficially influenced by such tests; helping to ensure that the product maintains its desirable features when exposed to adverse conditions will support brand loyalty. As manufacturers are under pressure to maintain quality, minimising the costs


of products each year – they will not be familiar with a particular product, so must be briefed fully. A short, but clear general description is therefore vital. It’s particularly important that details are included on the product’s highest internal frequency, as this will allow the laboratory to know the maximum frequency range of radiated emission test. Otherwise, unnecessary test time and laboratory costs will be incurred. Block diagrams should be


included, 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. The laboratory must therefore be informed 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? 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


 TÜV SÜD tuvsud.com ELECTRICAL ENGINEERING | JULY/AUGUST 2019 29


experienced very often, such as electrostatic discharge due to someone touching the equipment). Criteria C allows temporary loss of


Third-party EMC tests and conformity


assessments can help to strengthen a brand’s


competitive position in the market


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. 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. 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 (ie. 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 a 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.


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