EMC & Thermal Management
The right approach to EMC test preparation
By Pete Dorey, principal consultant at TÜV SÜD, a global product testing and certification organisation
T
o comply with market requirements and avoid costly recalls, manufacturers in a wide range of industries must ensure that electromagnetic disturbances do not interfere with other users, or with the function of their products. In the EU, the 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. Following Brexit, in the UK this directive has been replaced by the Electromagnetic Compatibility Regulations 2016, and products must comply with this before they can carry the UKCA mark. There is a two-year transition period where products can continue to carry only the CE marking in the UK. Currently, the requirements of the UK EMC Regulations and applicable EMC standards remain the same as those of the EU’s EMC Directive, but may diverge in the future.
Not only does EMC testing ensure that products meet regulatory requirements, it improves product quality and avoids product returns. 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. Early consideration of EMC reduces time-to-market delays for new and upgraded products. It is therefore important to be properly prepared before products are sent to the test laboratory.
In the test laboratory A test laboratory sees many thousands of
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products each year – they will not be familiar with your product, so you must brief them fully. A short, but clear product 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 addresses all product operating 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 minimise 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?
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 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.
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.
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.
www.tuvsud.com/uk Components in Electronics February 2022 23
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