EMC & Thermal Management
EMC and environmental testing in product development
By Richard Poate, senior manager at TÜV SÜD, a global product testing and certification organisation
E
lectromagnetic interference can negatively impact product performance and function in a variety of ways. EMC testing therefore ensures that products meet regulatory requirements and reduces the risk of costly non- compliance, which could require product recalls and cause significant time-to-market delays for new and upgraded products.
The electromagnetic performance of a product is characterised by the design and layout of the product’s circuits, and any protective measures put in place to shield, contain or reduce electromagnetic effects. Measures taken to improve performance such as bonding, shielding and the addition of filters can all be degraded by environmental conditions.
As EMC performance is a regulatory issue, it is understandable that designers and manufacturers focus on this test element first. However, this does not really represent the ‘real world’ use of a product as electromagnetic fields are as much a part of the environment which interacts with a product as temperature, shock, vibration, dust and water ingress. Over the lifecycle of a product, all environmental factors will have a considerable influence over ongoing EMC performance. Examples include degradation of equipment grounding arrangements, reduced effectiveness of compressed or weathered EMC shielding gaskets, and drift or degradation of EMC critical protection components. This means that over a number of years, due to environmental impacts, a product’s EMC performance may change significantly. Designers and manufacturers should therefore be integrating EMC and environmental testing within the product development lifecycle. Simulating product ageing in this way, before EMC testing, will deliver a realistic picture of product performance over its lifetime.
24 February 2021
However, there are no regulatory requirements for artificially ageing a product prior to EMC testing. This is only relevant if a product has a safety function, in which case the EMC standard general methodology for the achievement of functional safety, IEC/TS 61000-1-2, stipulates that ageing should be considered. The standard states that a product’s immunity may be affected by environmental parameters and suggests that testing is used to quantify the impact of stresses, ageing and foreseeable misuse, etc. on the electromagnetic characteristics of a product. The defence and aerospace markets also often have a contractual requirement for EMC integrity over a defined lifespan.
The lifetime EMC integrity of a product cannot be assured if it is tested just once. Therefore, when mission-critical products, such as aerospace, military or rail, are being developed stress screening is often carried out prior to EMC testing. This applies a product’s lifecycle of stress in one test programme. Alternatively, a proportion of a product’s lifecycle stress can be applied to determine whether it is likely to be fit for purpose throughout its lifespan.
Once the product is put into service, a well- defined maintenance schedule, which includes visual and insulation resistance checks, ensures that there are regular reviews of components that might affect EMC performance. In the commercial world, when safety-critical applications are not involved, EMC testing of products remains unusual. This is because, environmental testing usually relates only to packaging and transportation. Stress screening is also often ruled out on cost and time-to- market grounds.
However, environmental factors have been proven to jeopardise EMC over a product’s lifetime, resulting in performance and reliability and potential safety implications. The worst-
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case scenario is that the impaired EMC performance of electronics jeopardises safety. For example, a transient event on a power or signal cable of a large automated system could cause unplanned or unexpected movement and functionality of the system. The larger the system, the more dangerous the unexpected movement becomes, and the unexpected functionality could be extremely hazardous, such as the function of firing metal pins through sheets of steel. It seems that some manufacturers also rely on the breakdown guarantees they provide to end-users, rather than fixing the EMC source of the breakdown at the design stage. Even if EMC presents no risk to safety, designers can add value to a brand by assuring ongoing performance reliability of products. By eliminating the inconvenience of breakdowns, they can use extended warranty periods to gain a competitive advantage with their products. All of this will of course have a substantial impact on the end-users view of a product and the manufacturer’s market reputation.
To assess how a product will react to electromagnetic interference throughout its life, the ideal approach would be that which is suggested in IEC/TS 61000-1-2. This involves applying environmental conditions which simulate the product’s expected life, after which EMC tests should be performed. However, it is important to remember that accelerated environmental tests cannot be relied upon one hundred per cent as unexpected failure modes can still be experienced.
When considering lifetime performance, reliability and safety issues, it is evident that environmental and EMC testing should not be thought of in isolation. Lifetime compliance for quality products will in fact be best achieved if environmental and EMC requirements are considered together from the outset. Designers and manufacturers can therefore help to ensure that the EMC integrity of their products will last a lifetime, thereby enhancing their market reputation for producing reliable products.
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