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 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…
Read MoreISO 13849-1 Analysis — Part 3: Architectural Category Selection
Post updated 2019-07-24. Ed. You have completed the risk assessment, assigned required Performance Levels to each safety function, and developed the Safety Requirement Specification for each safety function. Next, you need to consider three aspects of the system design: Architectural Category, Channel Mean Time to Dangerous Failure (MTTFD), and Diagnostic Coverage (DCavg). I will discuss selecting…
Read MoreISO 13849-1 Analysis — Part 2: Safety Requirement Specification
This article was updated on 2019-07-24. Ed. Developing the Safety Requirement Specification The Safety Requirement Specification sounds pretty heavy, but actually, it is just a big name for a way to organize the information you need to analyze and design the safety systems for your machinery. Note that I am assuming that you are doing…
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