Reliability and MTBF: We Think We Know What We Mean, But Do We?


Reliability and MTBF: We Think We Know What We Mean, But Do We?

In this article published by EDN, Jeff Smoot, CUI’s VP of Application Engineering and Motion Control, discusses the common misconceptions that occur when talking about reliability and mean time between failures (MTBF) of various products and components.

Jeff Smoot begins the article by saying that terms like “reliability” and “MTBF” are generally discussed with casual disregard to what is truly meant. Noting that often individuals wrongly assume that MTBF equates to the expected life of a product.

He then highlights this example, “A product whose intrinsic failure rate is 1 in a million (i.e. 10-6) failures per hour has, by definition, an MTBF of one million hours. However the probability of it lasting 1 million hours (i.e. x=1 on the graph) is just 36.7%, which pretty much scotches any false assumption that MTBF equates to expected life. Indeed, further inspection of the graph shows that the probability of surviving more than 500,000 hours is only just over 60%, while a more respectable 90% reliability figure only equates to 100,000 hours.”

Ultimately, he concludes that figures for a product’s reliability or MTBF do not guarantee life expectancy and should be treated with some caution. However, they are still useful in providing a consistent approach for comparing products as long as you have an understanding of where that data is coming from.

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