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Topic Title: Microprocessor, integrated circuit Failure Modes IEC61508
Topic Summary: Looking for guidance on the failure modes of microprocessors and ICs as per IEC61508
Created On: 12 January 2014 10:20 AM
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 12 January 2014 10:20 AM
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I am looking for any guidance on failure modes for microprocessors and integrated circuits for carrying out FMEDAs to IEC61508 and typical diagnostic measures for detecting these failures (if possible). Also a description of each failure to give me a better understanding (as I'm not an electronics expert). This is purely involved with hardware failures, not software.
Thanks in advance.
 03 February 2014 04:18 PM
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The reason IEC 61508 was created is that the failure modes of complex components cannot be defined or predicted, so it is necessary to consider the probability of any failure.
 08 March 2014 01:03 PM
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Many of the failure modes of complex components can be defined, which is better than doing nothing.

One of the worst types of failure in a microprocessor (admittedly rare) is when a particular instruction produces the wrong result, but otherwise the processor keeps on working. I have seen this twice in my career, once in a computer motherboard that had been working in a hot environment for many years, and once in a new PLC.

It is technically possible to design algorithms to pick up some subset of this kind of error, that run at the start of each tick cycle or scan, or run two identical processors with the same code stream in parallel. The question is how comprehensive can this be and what are the computing resources required (i.e. cost).

Personally I would start with trying to define the failure modes of the simplest forms of microcontroller first and see what ideas and inspiration this brings to the table.

James Arathoon

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