exida explains Blog

Entries tagged with: FMEDA

  • by John Yozallinas, CFSE
  • Tuesday, December 17, 2013
  • Certification

12 Days of Christmas: Safety Edition

What’s on your Christmas list?  Instead of relying on Santa, here are some gifts you can expect from a SIL 3 compliant process:

Back to Basics 15 - Architectural Constraints

Back to Basics 15 - Architectural Constraints

Architectural constraints are limitations that are imposed on the hardware selected to implement a safety-instrumented function, regardless of the performance calculated for a subsystem. Architectural constraints are specified (in) according to the required of the subsystem, type of components used, and of the subsystem’s components. (Type A components are simple devices…

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Back to Basics: Failure Rates - FITS

Back to Basics: Failure Rates - FITS

Failures ITime or Failure UnIT

FITs is the number of failures per billion hours for a piece of equipment. 

It is mentioned in both IEC 61508 and IEC 61511 standards as a preferred unit of measurement expressed by 10-9 hours.

Example: 5 FITs is expressed as 5 failures every 10-9 hours (5x10-9). 

When you…

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Back to Basics: Failure Rates - λ

Back to Basics: Failure Rates - λ

The Greek symbol lambda, λ, represents failure rates in functional safety, usually expressed in the unit of measurement of FITS.

λ can be expressed as a total failure rate for a device (λT), or it can be broken down into more specific groupings:

  • Safe detected (λSD)
  • Safe undetected (λSU)
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Back to Basics: Failure Rates - λD

Back to Basics: Failure Rates - λD

The Greek symbol  λD represents dangerous failure rates in functional safety, usually expressed in the unit of measurement of FITs, and can be determined through FMEDAs. (FITs (λ) are failures per billion hours, expressed by 10-9 hours).

λD is the number of dangerous failures per…

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Back to Basics: Failure Rates - λDD

Back to Basics: Failure Rates - λDD

The Greek symbol  λDD is the detectable dangerous failure rate in functional safety expressed in the unit of measurement of FITs which can be determined through FMEDAs. (FITs (λ) are failures per billion hours, expressed by 10-9 hours).

Lambda DD

λDD is the number of…

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Back to Basics: Failure Rates - λDU

Back to Basics: Failure Rates - λDU

The Greek symbol  λDU is the undetectable dangerous failure rate in functional safety expressed in the unit of measurement of FITs which can be determined through FMEDAs. (FITs (λ) are failures per billion hours, expressed by 10-9 hours).

λDU is the number of dangerous undetected failures…

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Back to Basics: Failure Rates - λS

Back to Basics: Failure Rates - λS

The Greek symbol  λS represents safe or spurious failure rates in functional safety expressed in the unit of measurement of FITs which can be determined through FMEDAs. (FITs (λ) are failures per billion hours, expressed by 10-9 hours).

λS is the number of safe…

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Conceptual Design and SIL Verification’s Ultimate Resource

Conceptual Design and SIL Verification’s Ultimate Resource

Cycle Testing for Static Applications? NO!

Cycle Testing for Static Applications? NO!

The failure rates of certain mechanical components used in solenoid valves, actuators, and valves vary substantially depending on operation. Seals such as O-rings, for example have fundamentally different failure modes when used in applications with frequent movement (dynamic) versus applications with infrequent movement (static). 

Static is generally…

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Dare to Be Different

Dare to Be Different

Does Everyone Really Ignore Failure Rates?

Does Everyone Really Ignore Failure Rates?

While discussing functional safety certification of an integrated valve assembly with a manufacturer, exida stated that all devices (actuator, pneumatic parts, valve, etc.) must be IEC 61508 certified. The manufacturer said this was no problem, and provided a set of exida and TÜV certificates. 

Of…

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Duty of Care (Too Good to Be True Failure Rate Data)

Duty of Care (Too Good to Be True Failure Rate Data)

I have received several calls lately to our Australia / New Zealand office about whether it is acceptable to use published failure rates that seem too good to be true.

The person calling is usually doing a SIL verification calculation for an operating plant or for an…

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exida’s Safety Reliability Analysis (SRA) and How It May Help You

exida’s Safety Reliability Analysis (SRA) and How It May Help You

We all know that an FMEDA is only as good as the assumptions made regarding typical design engineering practices and the database used for the failure rates.  Here is the catch, not all products are designed and manufactured per the same rules!  Many manufacturers boast that their…

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Field Data Validation with Predictive Analytics

Who cares about field failure data? Why are we even here?

IEC 61511 – Fundamental Concepts

The fundamental concepts from our functional safety standards are the probabilistic performance based design.  Many of you know that this was terribly controversial when this was first proposed. Even to this day, there…

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FMEDA Predictions
  • by Loren Stewart, CFSE
  • Thursday, September 01, 2016
  • Certification

FMEDA Predictions

The FMEDA technique is performed on a specific device (e.g., ball valve, pressure transmitter, temperature sensor, electronic module, etc.) specified down to the manufacturer and series/model. Based on the specifics of the design, the parts used to execute the design, the design margins, any automatic diagnostics, the…

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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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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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