Post updated 2019-07-24. Ed. Fault Consideration & Fault Exclusion ISO 13849-1, Clause 7 [1, 7] discusses the need for fault consideration and fault exclusion. Fault consideration is examining the components and sub-systems used in the safety-related part of the control system (SRP/CS) and making a list of all possible faults. This is a non-trivial exercise!
Read MoreISO 13849-1 Analysis — Part 7: Safety-Related Software
Post updated 2019-07-24. Ed. Safety-Related Software Up to this point, I have been discussing the basic processes used to design safety-related parts of control systems. The underlying assumption is that these techniques apply to the design of hardware used for safety purposes. The remaining question focuses on the design and development of safety-related software that…
Read MoreISO 13849-1 Analysis — Part 6: CCF — Common Cause Failures
Post updated 2019-07-24. Ed. What is a “Common Cause Failure”? There are two similar-sounding terms that people often get confused: Common Cause Failure (CCF) and Common Mode Failure. While these two types of failures sound similar, they are different. A Common Cause Failure is a failure in a system where two or more portions of the…
Read MoreISO 13849-1 Analysis — Part 5: Diagnostic Coverage (DC)
Post updated 2019-07-24. Ed. What is Diagnostic Coverage? Understanding Diagnostic Coverage (DC) as used in ISO 13849-1 [1] is critical to analyzing the design of any safety function assessed using this standard. If you missed a previous part of the series, read it here. In the last instalment of this series discussing MTTFD, I mentioned…
Read MoreISO 13849-1 Analysis — Part 4: MTTFD – Mean Time to Dangerous Failure
Post updated 2019-07-24. Ed. Functional safety is all about the likelihood of a safety system failing to operate when you need it. Understanding Mean Time to Dangerous Failure, or MTTFD, is critical. If you have been reading about this topic, you may notice that I am abbreviating Mean Time to Dangerous Failure with all capital…
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