A RELIABLE SOURCE Testing a product’s operational capabilities

Based on using real life operational data, this kind of life testing accelerates fault conditions by applying operational, failure-causing stresses at levels above those that the product would experience in its application environment: the exaggerated effect ensures optimal anticipation for error within standard operational conditions. The benefit of accelerated life testing is

that it helps detect the design flaws that are most likely to give rise to a product’s ‘infant mortalities’. The disadvantage is that this method may precipitate some misleading failures, and highly accelerated life testing (HALT) may instead provide the answer here.

HIGHLY ACCELERATED LIFE TESTING A key difference between HALT and traditional accelerated life testing is that stress factors, such as high temperatures, are applied directly to the component or sub-assembly under test, and not to the system as a whole. Thermal and mechanical stimuli are also applied separately, and then together, in order to determine the operating and destruct limits of the item under test. Defect analysis is a key stage in the

As the time to market tightens, a product is more at risk of slipping through the net and underperforming. Therefore, testing these products becomes more essential than ever: Chris Bowles, environmental test supervisor at TÜV SÜD, asks how certain tests could be the difference between a reliable and unreliable product

Reliability testing has become an essential element of the design process, as end-users are increasingly demanding electronic products that last longer and deliver value for money. Designers must therefore adopt a more robust approach when ensuring product reliability, whilst also securing a competitive price. The term ‘reliability’ is the ability of an item to perform a required function, in understated conditions, for a stated period of time. Outlining the key terms for this definition, the required function includes the specification of a satisfactory or unsatisfactory operation, while for a complex system, unsatisfactory operation may not be the same as failure. The stated conditions are the total physical environment, including mechanical, thermal and electrical conditions. The stated period of time is the time during which satisfactory operation is desired. With reliability itself, there are varying

ways of measuring this: survivability, availability and maintainability. Firstly, survivability – the probability that an


item will perform a required function without failure – applies only to applications in which failures will not be routinely repaired. Alternatively, availability applies where there is the possibility of both repair and failure, and maintainability refers to the degree to which equipment can be retained in, or restored to, a specified operating condition.

BEYOND LIFE CYCLE TESTING The traditional approach to reliability evaluation has been life cycle testing (which involves tests being carried out within the product’s expected environment), or in fact using actual operational conditions. However, this is an unrealistic approach, as it would be costly and would lengthen a product’s time to market.

Accelerated life testing and environmental stress screenings have therefore become accepted as methods of assessing product reliability: they ensure that a product will not develop faults, identifying any issues.

HALT process and is conducted when the operation and destruct limits are known. The operating limit is defined as the point at which the unit remains operational, but any further increase in stress will result in a recoverable failure. At this stage, all major flaws in the design should be exposed; most may require a simple fix, while others may require major modification. It may also be considered that the design is sufficiently rugged and that no further action is to be taken. There is a common misunderstanding

Chris Bowles, environmental test supervisor at TÜV SÜD

by engineers that HALT tends to lead to ‘over engineered’ products. In fact, a HALT appraisal allows designers to establish the limitations of their product designs and ensure a product’s level of reliability, as expected by the end user. Whatever testing method is chosen,

to remain competitive, companies must select the appropriate techniques for their product that are fast, cost-effective and produce worthwhile results. Without the ability to gauge reliability throughout the design lifecycle, there is no assurance that the final product will meet market expectations. And, on an increasingly technologically level playing field, brand reputation of reliability and longevity is a vital element to differentiate a product from that of any competitors. Keep on top of the market: test to ensure the best.


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