February 2013


HP Automation Safety: It’s all about the safety PLC—not!

Focus on the big safety improvements and the real problems. This fundamental concept applies to many tasks in addition to functional safety.

Goble, W., exida LLC

This week I was asked to join a debate about functional safety. The argument was based on a paper that criticized the accuracy of the Markov model used to calculate failure probability of a safety integrity level (SIL) 3 certified safety programmable logic controller (PLC). I was drawn into the argument. While reading the paper, I concluded that this paper could be right. Even though the argument was against the model that I had made some time ago. The old model appeared to be slightly pessimistic, changing the safety PLC result by as much as 10%. I began investigating to identify the exact differences between my model and why it may have been more accurate. Then, I had a flashback. D&#

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