Chapter 3 - Main Parameters

Last edit: 20/06/2023

In Chapter 3, the parameters used in both IEC 62061 and ISO 13849-1 are described.

IEC 62061 introduced, in the new edition, the important Failure Rate λNE, or No Effect Failure, that does not contribute to the SFF of the subsystem.

DC, SFF, MTTFD, CCF are explained in detail. The importance of HFT (Hardware fault Tolerance) is highlighted and, linked to that, the Route 1H and the Proof Test concepts are presented.


Here the book paragraphs:

  • Failure Rate (λ)
  • Safe Failure Fraction (SFF)
  • Diagnostic Coverage (DC)
  • Safety Integrity and Architectural Constraints
  • Mean Time to Failure (MTTF)
  • Common Cause Failure (CCF)
  • Proof Test
  • Mission Time and Useful Lifetime