EMC and environmental testing should not be separate
30 January 2013
It is not unusual for different products to be sent for separate electromagnetic compatibility (EMC) and environmental tests, with no correlation between the two results. As EMC testing is a regulatory issue, it is often done first and environmental testing much later in the product development cycle. However, EMC is simply another environmental issue, because electromagnetic fields are as much a part of the environment as dust, temperature, vibration, or water ingress.
Indeed, over the lifecycle of a product, environmental factors will have a considerable influence over ongoing EMC performance. Examples include screws working loose due to vibration, EMC shielding being degraded due to distortion of panels or fixings over time, and moisture ingress and corrosion affecting bonding impedance. It therefore makes sense for designers and manufacturers to integrate EMC and environmental testing into any risk management strategy while developing products.
As all of these environmental factors can jeopardise a product’s EMC performance later in life, lifetime reliability and availability is best achieved by simulating ageing before EMC testing. Using environmental testing in this way ensures that EMC test results are a more realistic indicator of a product’s lifetime performance.
There is evidence to confirm that environmental factors can jeopardise EMC over a product’s lifetime, resulting in performance, reliability and even safety implications. For example, documented cases have motorbikes and cars stalling in the vicinity of cellular base stations, and radio key fobs refusing to work. However, there are no regulatory requirements to use environmental testing techniques for the artificial ageing of a product, so the EMC testing of samples conditioned in this way is unusual.
Even when mid-life impaired EMC is no risk to safety, designers will add value by assuring ongoing performance, availability and reliability. By eliminating the inconvenience of breakdowns and having the ability to offer extended warranty periods, a competitive advantage will be gained.
Designers that want to ensure that their products are of a high quality could learn from markets such as defence and aerospace. As these sectors often have a contractual requirement for EMC integrity over a defined lifespan, stress screening is usually carried out prior to EMC testing. Secondly, products are tested against a defined build standard, and that standard is maintained through the quality management process. Thirdly, a well-defined maintenance schedule ensures that the EMC performance is monitored throughout a product’s lifetime.
The rail industry is another good example of how lifetime EMC integrity can be assured in an environment where safety is paramount. In this industry, preparation of a safety case takes into account both environmental and EMC issues, with maintenance packages designed to optimise ongoing compliance. For example, a well-defined maintenance schedule, including visual and insulation resistance checks, ensures regular surveillance of components that could affect EMC performance.
In addition, products in these types of markets are much more likely to be upgraded during the product’s lifetime. This means that periodic re-design and re-testing are the norm. However, upgrades and refurbishments can create uncertainties. For example, train owners may secure regulatory and contractual compliance at the outset, but train operators can make changes, such as introducing passenger information systems, which may compromise the product’s EMC performance. As there is a regulatory requirement that EMC performance must be maintained over the life of the product, there may be a legal requirement for the owner to check their product when any changes are made by the operator.
If there are still grey areas in industries where safety is a high priority, you also have to question the lifetime integrity of electronic products developed in the commercial world. Competitive pressures often prompt manufacturers to do the legally bare minimum in their testing practices, which usually means that environmental testing is only considered for packaging and transportation. Stress screening prior to EMC testing is therefore often ruled out on cost and time-to-market grounds. Typically, the kind of arguments made are along the lines of – ‘does it really matter if the EMC performance of a consumer electronic device is impaired by the effects of vibration over a period of years?’
For producers who want to ensure that their reputation with their customers remains positive in terms of a product’s reliability throughout its working life, it is important that environmental and EMC testing should not be thought of as isolated events. In many cases, RF testing should also be taken into account, if the product under consideration is an intentional radiator.
Lifetime compliance therefore means that environmental and EMC requirements must be considered together from the start of the product development process. This approach maximises the value of any investment made in EMC testing by helping to ensure that the EMC integrity of products will last a lifetime.
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