EMC & Circuit Protection
EMC test preparation - minimise cost & optimise time to market
Pete Dorey, a principal consultant at TÜV SÜD Product Service and TÜV SÜD BABT, talks about the processes of EMC testing for finished electronic products
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 and power cables, conducted interference and a range of transient interference events such as electrostatic discharges, power surges due to lightning or fast transients due to power switching.
Pete Dorey W
hether they are battery or mains powered, the vast majority of finished electronic products must
comply with the Electromagnetic Compatibility (EMC) Directive 2014/30/EU (amongst others) before they can carry the CE marking and be sold in the European Union market. To comply with market requirements and avoid costly recalls, manufacturers in a wide range of industries, such as consumer products, medical devices, industrial machinery, railway, automotive, aerospace and military equipment must ensure that electromagnetic disturbances do not interfere with other users, or with the function of their products.
Minimise cost maximise revenue Not only does EMC testing ensure that products meet regulatory requirements, it reduces the risk of costly non-compliance, which would require product recalls, and cause significant time-to-market delays for new and upgraded products. If a buyer is loyal to your brand, it means that they will always buy from you, or at least consider you first. Provided that the service and product quality is maintained, it is unlikely that brand-loyal customers will consider alternative suppliers. The features and characteristics of a product determine its desirability. If these features do not degrade and the product continues to fulfil its purpose when exposed to a range of adverse conditions, especially those that would not be expected in normal use, a lasting belief in the product’s quality is formed. 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 therefore 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 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.
Minimising test times
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. 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 maximises the 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?
Pass or fail? 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
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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.
Hardware and software 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/disconnected to allow the test set-up to be moved between facilities i.e. avoid soldered connections. 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. Electromagnetic interference 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.
www.tuv-sud.co.uk Components in Electronics September 2017 15
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