exida explains Blog

Entries tagged with: Dr. William Goble

Getting Realistic Failure Rate Data - Part 3

Over the course of several blogs , I will talk about getting realistic failure rate data, where this failure data comes from, and how different methods of failure data analysis compare. I think if you understand this, you will begin to get a very good feel of what it…

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Getting Realistic Failure Rate Data - Part 4

Over the course of several blogs , I will talk about getting realistic failure rate data, where this failure data comes from, and how different methods of failure data analysis compare. I think if you understand this, you will begin to get a very good feel of what it…

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Getting Realistic Failure Rate Data - Part 5

Over the course of several blogs , I will talk about getting realistic failure rate data, where this failure data comes from, and how different methods of failure data analysis compare. I think if you understand this, you will begin to get a very good feel of what it…

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  • by Dr. William Goble, CFSE
  • Tuesday, August 04, 2015
  • Certification

Getting Realistic Failure Rate Data - Part 6

Over the course of several blogs , I talked about getting realistic failure rate data, where this failure data comes from, and how different methods of failure data analysis compare. I think if you understand this, you will begin to get a very good feel of what it takes…

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High Demand Diagnostic Credit?
  • by Dr. William Goble, CFSE
  • Thursday, January 19, 2017
  • Certification

High Demand Diagnostic Credit?

The IEC 61508 standard states that automatic diagnostics can only lower the dangerous undetected failure rate if those diagnostics execute 100 times faster than the expected demand rate.  That requirement has always seemed excessive to many of us here at exida.  As an accredited Certification Body we…

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How to Calculate Proof Test Coverage
  • by Dr. William Goble, CFSE
  • Thursday, October 16, 2014
  • Certification

How to Calculate Proof Test Coverage

Most engineers who design and verify safety instrumented functions (SIFs) understand how hard it is to design a manual proof test with high effectiveness (also called high proof test coverage). Those folks who understand that a proof test is not likely to detect all failures never use simplified equations…

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I Did Not Lock the Car Door

I Did Not Lock the Car Door

I was driving one of exida’s top risk experts from Europe to a business meeting. We parked and I locked the car door.  He commented “I noticed you did not lock the car door when you parked at the exida office.” He was right. In an area I do…

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I Don’t Want No D*** Diagnostics!

After a false trip incident, I heard a control engineer express his displeasure with the automatic diagnostics in a new safety rated transmitter.  The transmitter diagnostics were annunciated by sending the analog current out of range.  In this case, the current went to 3.6 milliamps.  The problem was that…

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IEC 61508 Functional Safety Certificates - To Accept or not to Accept?
  • by Dr. William Goble, CFSE
  • Thursday, August 10, 2017
  • Certification

IEC 61508 Functional Safety Certificates - To Accept or not to Accept?

I get an email that includes a “certificate” of some sort most every week.  The sender asks “Can I accept this certificate?”  Or the sender might ask “Are these failure rates valid for the process industries?” 

At exida we have some specific criteria we use when performing third party…

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Keep Risk Personal

We are fortunate that Risk Analysts have developed a logical framework of quantitative and semi-quantitative analysis techniques that allow us to assess and optimally mediate risk. And we all know that this is part of the Safety Lifecycle, a series of engineering steps/procedures that represent best safety practices. These…

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Make IEC 61511 into a Cookbook?

IEC 61508 and IEC 61511 are known as “performance” based standards.  Specific design rules, as found in “prescriptive” standards, are not included, allowing for innovation and new technology, as well as creativity and advancement.  However, it does imply that a certain level of competency is required.

Others would strongly…

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Most Failures are Systematic - NOT!
  • by Dr. William Goble, CFSE
  • Wednesday, April 16, 2014
  • Certification

Most Failures are Systematic - NOT!

We have studied hundreds of sets of field failure data from various sources here at exida.  Some of these data sets have indicated differences in failure rates by over an order of magnitude for the same product type.  After tracing through the data collection process for many of…

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NEVER Use B10 Values for PFDavg Calculations

The machine safety community has defined a number called the “B10 number.”  It is a measure of time where 10% of a population of devices should have failed.  Generally it is a measure of expected end of life or “useful life” as defined by the reliability engineering community.

The…

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  • by Dr. William Goble, CFSE
  • Thursday, August 04, 2011
  • Certification

Not Perfect? Not Good

Over the years I have heard good ideas rejected. We have all done this and observed others doing the same. As far as safety equipment, I recall when the first safety certified pressure transmitter, the Moore 345, was released to the market.  Several potential customers said “it doesn’t…

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OREDA Data vs. FMEDA Data

Random vs. Systematic?
  • by Dr. William Goble, CFSE
  • Wednesday, May 07, 2014
  • Certification

Random vs. Systematic?

Most of you know that exida gathers field failure data from many sources including manufacturers’ warranty return data and end user maintenance/failure records.  At this point we have nearly 100 billion unit operating hours of data.  This is probably the largest process industry data set in the world.  And…

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Realistic Failure Rate Data – Necessary

Realistic Failure Rate Data – Necessary

Reliability engineers have known for decades that realistic data must ultimately come from one source, quality field failure data for devices operating in a similar application. 

Perhaps that is why IEC 61511:2016, Clause 11.9.3 states

“The reliability data used when quantifying the effect of random failures shall…

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Replace Before Failure

The solenoid valve manufacturer provides an FMEDA report that lists “useful life = 12 years.”  Useful life is a reliability engineering term that indicates a point in time when the failure rate of a device will begin increasing rather rapidly.  Why do we care about this time interval?  That…

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Root Cause Analysis

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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Setting the Pace

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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