Electromagnetic compatibility (EMC) testing and environmental testing are often viewed as separate functions, meaning that it is not unusual for separate products to be sent for test assessment. Frequently, EMC testing comes first and environmental testing much later in the product development cycle, with no correlation between the two sets of results.
The inclination to measure EMC performance first is understandable, as it is a regulatory issue and by submitting a pristine product for testing the best possible results can be expected. However, in reality it is unlikely to be delivering the best long-term value to both manufacturers and those that purchase their products.
EMC is in fact just another environmental issue. Electromagnetic fields are as much a part of the environment which interacts with a product as temperature, shock, vibration, dust and water ingress. It therefore makes sense for designers and manufacturers to look at integrating EMC and environmental testing into any risk management strategy when developing products.
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, as well as moisture ingress and corrosion affecting product bonding. All of these effects can jeopardise the product’s EMC performance and integrity later in life, resulting in reliability and safety implications. Lifetime reliability is therefore best assured by simulating product ageing before EMC testing is done to ensure that the results present a more realistic picture of a product’s lifetime performance.
A lesson learned
While there are no regulatory requirements to artificially age a product prior to EMC testing, manufacturers that want to ensure that their consumer products are of a high quality could learn from those that supply the defence and aerospace markets, as these often have a contractual requirement for EMC integrity over a defined lifespan.
However, even with such ‘mission critical’ products, how can lifetime EMC integrity be assured when equipment is still generally tested only once? Firstly, in these markets stress screening is often 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, including visual and insulation resistance checks, ensures that there is regular surveillance of components that will affect the EMC performance of a product.
In the rail industry, preparation of a safety case similarly takes into both account environmental and EMC issues. However, while maintenance packages are designed to optimise ongoing compliance, upgrades and refurbishments can also 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. Over a number of years of use, the product’s EMC performance may change significantly.
The automotive industry is another area where performance and safety can be impaired by changes in the electromagnetic environment induced by insufficient attention during servicing, or the addition of product-enhancements not essential to its core function.
If there are grey areas, even in applications where the safety of people is a high priority, how many more are there in the commercial world, where competitive pressures can prompt some manufacturers to cut corners in their testing practice?
Risk in commercial applications
Outside of safety critical applications, EMC testing of conditioned samples remains unusual. This is because in the commercial world, environmental testing usually relates only to packaging and transportation. Stress screening is also often ruled out on cost and time-to-market grounds. The arguments that apply are along the lines of: ‘does it really matter if the EMC performance of a washing machine is impaired by the effects of vibration over a period of years?’
In fact, there is anecdotal evidence to confirm that environmental factors can actually jeopardise EMC over a product’s lifetime, resulting in performance, reliability and even safety implications. There are documented cases where motorbikes and cars have stalled in the vicinity of cellular base stations, and radio key fobs refused to work. The worst-case scenario is that the impaired EMC performance of electronics jeopardises safety. For example, roadside and trackside signals and signs can be affected by harsh environmental conditions that can influence EMC performance with the potential to create a hazard.
Even when mid-life impaired EMC is no risk to safety, manufacturers will add value by assuring ongoing performance reliability of their products. By eliminating the inconvenience of breakdowns, they can use extended warranty periods to gain a competitive advantage with their products.
The solution - designing for life
In the light of lifetime performance, reliability and safety issues, it is therefore evident that environmental and EMC testing should not be thought of as isolated events. Lifetime compliance for quality products will in fact be best achieved if environmental and EMC requirements are considered together from the outset.
One approach is that consultation with a testing advisory service at the earliest stage in the design process will provide manufacturers with information on a comprehensive, cost-effective approach to testing for lifetime compliance. It should also lead to a product lifecycle review which will highlight any measures required down the line to maintain a product’s compliance.
By these means, manufacturers can increase the return-on-investment that they get from their EMC testing. Helping to ensure that the EMC integrity of their products will last a lifetime can only enhance their reputation in their marketplace for reliability, as well as minimise the risk of a backlash or litigation from dissatisfied consumers.l
Jean-Louis Evans, managing director at TÜV Product Service, a global product testing and certification organisation, and at its sister company, British Approvals Board of Telecommunications (BABT), the world’s leading radio and telecommunications certification body.