There seems to be a bunch of confusion surrounding systematic capability and random capability.  I will try to clear up the confusion by explaining what is all considered and what the IEC standard says about both. 

Systematic Capability

  • Development process/quality system requirements depend on certification SIL level, higher SIL level means more stringent requirement
    • For software architecture design, Fault Detection not required for SIL 1, Recommended for SIL 2, Highly Recommended for SIL 3
  • Systematic capability indicates level of development process/quality system considered
  • If product systematic capability is SIL 3, the development process considered meets IEC 61508 SIL 3 requirements, therefore product can be used in SIL 3 applications
  • If product systematic capability is SIL 2, product can only be used in SIL 2 applications
  • SIL capability of SIL 3 does NOT mean that the product can be used without any redundancy in SIL 3 applications

Random Capability

  • Product specific performance requirements
    • Probability of failure for an entire SIF
    • Minimum Hardware Fault Tolerance for an element
  • Probability of failure limits apply to entire SIF, achieved SILPFD cannot be concluded for single product
    • exida certificate specifies that probability of failure must be verified for each application
  • Minimum element Hardware Fault Tolerance can be specified if product constitutes a complete element
    • Actuator is a component in an element, achieved SILAC cannot be concluded
    • Transmitter can be complete element, achieved SILAC is specified
  • Certificate lists Type A or Type B equipment type
  • SILAC specified for HFT = 0 and HFT=1
  • Certificate identifies Minimum HFT method applied, i.e. Route 1H or Route 2 H

Why does it matter?

Each exida certificate shows both the systematic and random capabilities.

Both the systematic capability and the random capability are important for end users to know if they are meeting the required risk reduction for their system. So if your certificate is not showing BOTH systematic and random capabilities, you are only getting half of the story!

Tagged as:     SILAC     SIF     Route 1H     Loren Stewart     exida Certification  

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