In the 1980’s, there was a raging debate in the functional safety committee about redundancy versus diagnostics. Some said functional safety could only be achieved with redundant systems. This was strongly supported by Triple Modular Redundant (2oo3) safety PLC vendors. 

Others argued that diagnostics would be an equal or better solution using PLC architectures like the 1oo2D.  Yet no method was available to show the impact of diagnostics quantitatively.

ISA S84.01 was published with Probability of Dangerous failure rate limits per SIL level. A Draft of IEC 61508 was being created, but there was no predictive method to assign a number to the ability of a device (element) to perform automatic self-diagnostics. Also, no predictive method to determine failure rates of a device as a function of failure mode. Qualitative arguments over the pros and cons of various design options.

Functional safety is a critical aspect of many industries, including automotive, aerospace, and medical devices. To ensure that these systems operate reliably and safely, they must be designed and tested in a structured manner. One tool developed that could be used for this purpose is Failure Modes Effects and Diagnostic Analysis (FMEDA):

  • To provide device/element level failure rates as a function of each failure mode.
  • To measure the effectiveness of automatic diagnostic functions.
  • To use quantitative reliability analysis to make design decisions in multiple failure mode situations.
  • To show that resulting designs were better than alternatives.
  • To show that hardware designs meet the requirements of functional safety standards (IEC 61508).

FMEDA is a process that is used to analyze the failure modes of a system, including its components, to identify the potential causes of failures and the effects that these failures could have on the system. This process involves examining the design of the system, the components that make up the system, and the operating environment of the system to identify potential failure modes.

FMEDA is typically used in the context of safety-critical systems, where a failure could result in harm to people or damage to property. By identifying potential failure modes and their effects, designers can develop strategies to mitigate these risks and ensure that the system operates safely.

In conclusion, FMEDA is a powerful tool that is used to ensure the safety and reliability of complex systems. By identifying potential failure modes and their effects, designers can develop strategies to mitigate risks and ensure that these systems operate safely. So please join us for our webinar – What is an FMEDA to learn more and ask questions.

Tagged as:     Redundancy     PLC     Paddy Healy     IEC 61508     FMEDA  

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