exida explains Blog

Root Cause Analysis - finding out what happens when a failure occurs, and why it happened in the first place.  There are many reasons for root cause analysis.  The “system” design can be improved to prevent some of the failures from happening again and those who troubleshoot can do…

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Going back in time to the turn of the century (remember 2000?), the amount and quality of failure data threatened to doom the whole probabilistic analysis approach.  I recall a letter in IEEE Spectrum magazine from Patrick D. O’Conner, a well known reliability engineering author, who expressed the…

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In several of our technical papers over the years, we have noticed that failure rates for the manufacturer, model number are different at different sites, even when the processes were quite similar.  When I have mentioned this to end users and manufacturers, often the response is “Yes, I have…

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There have been passionate debates in email and meetings about “Proven In Use” versus IEC 61508 certification. Most debates characterize these evaluation techniques as competing methods.  In 2000 when IEC 61511 was being written there were few IEC 61508 certified products on the market. The…

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I have often heard the question “Who says they can issue a certification?”  This is often accompanied by “Why can’t I certify my own product?”  “Who knows our design better than we do?” Good questions.

The IEC 61508 standard does not require certified products for Functional Safety. …

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Site Specific vs. Product Specific

During a field failure analysis study, it was discovered that the calculated failure rate of a specific device varied by more than 4X depending on installation site.  Particularly, it was one specific site with a high failure rate.  While any reliability engineer…

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In this blog, I will talk about the FMEDA method and how it can generate realistically accurate failure rate data.

The first question we have to ask is “why do you need failure rate data ?”

One of the fundamental concepts in today’s functional safety standard, IEC 61508 and…

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I heard about a “safety certified” PLC in the late 1980s at an ISA SP84 standard committee meeting. The “logic solver” (as they later called it) was the focus of attention in the field of functional safety back then. Many engineers even said, “My system is safe because I…

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I recall the first time I was called an “expert.”  I thought that sounded nice. I spotted a magazine article on safety and thought “I do not have to read that as I am an expert.” I quickly recovered.  The real problem with being called an expert is that…

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I was recently asked how the PFDavg value in an exida FMEDA report was calculated. Those PFDavg values are calculated using the exSILentiaTM program. The person who posed the question was using the equations from Part 6 of IEC 61508 and got a different value. Why?

exSILentia…

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One of the objectives of new performance based standards like IEC 61508 is to allow performance metrics (like PFDavg for low demand systems) to identify the weak links in any proposed design.  Obviously, it is not necessary to put effort into design and spend money on areas…

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I remember the first time I ever saw a spreadsheet program. It was called “VisiCalc" and ran on a Commodore PET computer. My first thought was, “What is that good for?” Then I tried it and was totally hooked. I conclude that the creation of the spreadsheet has changed…

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When I studied Reliability Engineering in graduate school, I was taught that failure rate data came from field failure studies.  I assumed that operating companies always kept accurate records when a piece of equipment failed.  I also assumed that someone would investigate the failures and assign a root cause.…

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exida was recently auditing a systems level project per IEC 61511.  During such audits we check to verify that all equipment used in a safety instrumented function meets systematic capability by either IEC 61508 certification OR justification per reasonable IEC 61511 “prior use” criteria.  Most engineers at…

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As safety professionals, it is our duty to attempt to educate and explain to the public.  Perhaps the biggest challenge is to explain the concept of risk.  Many times after an accident we have heard a politician say something like “We will do whatever it takes to make sure…

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In a marketplace where many of buyers of firmly committed to “proven in use,” many projects are still using 30 year-old logic solver designs.  Proven in use is a valuable concept especially for field equipment where it is hard to evaluate how well a product design will…

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-Han Solo, Star Wars, Episode V: The Empire Strikes Back, 1980

I have enjoyed watching and reading about the actions of the fictional Star Wars character Han Solo over the years.  I recall hearing the above quotation more than once.  And as much as I enjoyed watching this character,…

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