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“When the number of factors coming into play in a phenomenological complex is too large, scientific method in most cases fails. One need only think of the weather, in which case the prediction even for a few days ahead is impossible.” ― Albert Einstein
“Prediction is very difficult, especially about the future.” – Niels Bohr* We have always had a quest to reduce future uncertainties and know what is going to happen to us, how long we will live, and what may impact our lives. Horoscopes, Tarot
Most reliability engineers are familiar with the life cycle bathtub curve, the shape of the hazard rate or risks of failure of a electronic product over time. A typical electronic’s life cycle bathtub curve is shown in figure 1. [Read more…]
One of the primary questions we answer as reliability engineers is:
How long will it last?
Reliability prediction is the forecast or prognostication attempting to quantify either the time till failure, or expected future failure rate or warranty claims, or required spare parts.
We need to know as we make decisions today about the design or purchase.
All models are wrong, some are useful. ~ George E. P. Box
If you know me, you know I do not like MTBF. Trying to predict MTBF, which I consider a worthless metric, is folly.
So, why the article on predicting MTBF?
Predicting MTBF or creating an estimate is often requested by your customer or organization. You are being specifically asked for MTBF for a new product.
You have to come up with something.
If only we had a crystal ball or another device to predict the future. From the general wondering about the enemies next move, to the soldier hoping their equipment will work. In the corporate boardroom estimating the competitions next move, to the maintenance manager ordering spare parts, we have many uses for knowing the future.
We often look to past performance to provide an indication of the future. Has this mutual fund regularly provided adequate returns? If so, we predict it will going forward. And anyone that has reviewed mutual fund performance also has read or heard the admonishment to not use past performance to estimate future returns. Mutual funds, markets, business and battlefields all change and respond in sometimes unforeseen ways. [Read more…]
Let’s say we have a product that most often fails for one major component. Let’s say a fan (it could be anything, and while I don’t have anything against fans, it’s easy to picture).
Ok, this fan has a data sheet with the classic reliability claim of 50,000 hours MTBF. For those that know about my disdain for MTBF (www.nomtbf.com) rest assured I’m not going to get into it here. The basic approach for estimating the number of failure during any [Read more…]
Just a short post to point to a newly added paper to the reference section. A few years ago I recalled seeing a paper that studied the difference to expect between various parts count methods and actual results. [Read more…]