Designing for Life for the World in which we live
Designing for Life for the World in which we live
Ken Webb, TÜV Product Service/BABT
Published: January 2006 - EMC Compliance Journal
Manufacturers generally view electromagnetic compatibility (EMC) testing and environmental testing as separate functions if, in fact, they consider environmental testing at all. But in reality, EMC is 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, etcetera. It therefore makes sense to look at integrating EMC and environmental testing in any risk management strategy.
In practice, where EMC testing and environmental testing are carried out it is not unusual for separate test items to be sent for assessment. Frequently, EMC testing comes first and environmental testing much later in the development timecycle, with no correlation between the two sets of results. The inclination to measure EMC performance first is understandable. It is a regulatory issue, and by submitting a pristine product for testing the best possible results can be expected.
However, over the lifecycle of a product, environmental factors can have a considerable influence on EMC 
performance. Examples include screws working loose due to vibration, EMC shielding being degraded due to distortion of panel or fixings over time, and moisture ingress and corrosion affecting bonding imped-ance. All of these effects can jeopardise the product’s EMC perform-ance and integrity later in life, with reliability, availability and even safety implications. Lifetime reliability and availability is best assured by conditioning to simulate ageing before EMC testing, ensuring that EMC results present a more realistic picture of lifetime performance.
Combined testing in critical applications
While there are no regulatory requirements to artificially age the product prior to EMC testing, products destined for critical applications, such as defence and aerospace, often have a contractual requirement for EMC integrity over a defined lifespan. How can lifetime EMC integrity be assured in these industries, when equipments are generally tested only once, for qualification?
Firstly, 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 checks, insulation resistance checks etcetera - ensures regular surveillance of components affecting EMC performance. In addition, products for these markets are much more likely to be upgraded during the project lifetime, so that periodic re-design and re-testing is the norm, although his does not ensure that non-compliant EMC products are being used.
In the rail industry, preparation of a safety case similarly takes into account environmental and EMC issues, and maintenance packages are designed to optimise ongoing compliance. However, upgrades and refurbishments can raise uncertainties. Train owners may secure regulatory and contractual compliance at the outset but train operators can make changes, for example introducing passenger information systems, which may compromise EMC performance. Over a period of years, EMC performance may change significantly. With the 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 when changes are made.
Automotive is another industry where performance and safety can be impaired by changes in the 
electromagnetic environment induced by insufficient attention during servicing, or the addition of product-enhancing and value-added facilities not essential to the product’s 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 manufacturers to cut corners in their testing practice.
Risk in commercial applications
Outside of safety critical applications, EMC testing of conditioned samples is unusual. In the commercial world, environmental testing usually relates to packaging and transportation. Stress screening is often ruled out on cost and time-to-market grounds. And does it really matter if the EMC performance of a washing machine is impaired by the affects of vibration over a period of years?
There is anecdotal evidence to confirm that environ-mental factors can jeopardise EMC over a product’s lifetime with 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 keyfobs refused to work. The worst-case scenario is that impaired EMC performance jeopardises safety. Roadside and trackside signals and signs are examples of products where harsh environmental conditions can influence EMC performance with the potential to create a hazard.
Even where mid-life impaired EMC is no risk to safety, manufacturers will add value by assuring ongoing performance, availability and reliability, eliminating the inconvenience of breakdowns, and allowing extended warranty periods to gain competitive advantage.
Regulatory influences
While pre-conditioning remains outside regulatory requirements, two EU Directives may in future impact manufacturers views on their testing regime. Firstly, the new Product Warranty Directive, which came into force on January 2006, compels manufacturers of goods destined for the EU to increase their warranty period from one to two years. The second is the Physical Agents Directive which comes into force in 2008 to protect people in the workplace. Many products currently in the early stages of development will be required to meet the EMF requirements of the Directive - through life if the possibility of litigation is to be avoided.
EMF in general is an emotive issue, with the ongoing argument about the danger of excessive exposure not only in the workplace but also to the man in the street. A question of liability comes in here. Who will assume responsibility a few years down the line if compliance is compromised by through-life environmental influences - the manufacturer who has not taken reasonable steps to ensure lifetime compliance? Will manufacturers face the possibility of litigation years after they believed that they had safely discharged their responsibility for product compliance?
The solution - designing for life
In the light of lifetime performance, availability, reliability and, ultimately, safety issues it is important that environmental and EMC testing should not be thought of as isolated events. In some cases, environmental, EMC and RF testing should not be separated. In the Bluetooth era, there may well be a case for designing a washing machine for lifetime EMC and RF performance if it is not going to cause the fridge to order the wrong beer somewhere down the line.
Lifetime compliance will be best achieved if environmental and EMC requirements are considered together from the outset. Consultation with a testing advisory service at the earliest stage in the design process will provide information on a comprehensive, cost-effective approach to testing for lifetime compliance, and lead to a lifecycle review highlighting any measures required down the line to maintain compliance.
By these means, manufacturers can increase the value of EMC testing, helping to ensure that the EMC integrity of their products will last a lifetime, enhancing their reputation for reliability in their marketplace, and minimising the risk of litigation.
