Reliability of 2-out-of-N: G systems with NHPP failure flows and fixed repair times

Vincent M. Dwyer*, Roger M. Goodall, Roger Dixon

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


It is commonplace to replicate critical components in order to increase system lifetimes and reduce failure rates. The case of a general N-plexed system, whose failures are modeled as N identical, independent nonhomogeneous Poisson process (NHPP) flows, each with rocof (rate of occurrence of failure) equal to λ(t), is considered here. Such situations may arise if either there is a time-dependent factor accelerating failures or if minimal repair maintenance is appropriate. We further assume that system logic for the redundant block is 2-out-of-N:G. Reliability measures are obtained as functions of τ which represents a fixed time after which Maintenance Teams must have replaced any failed component. Such measures are determined for small λ(t)τ, which is the parameter range of most interest. The triplex version, which often occurs in practice, is treated in some detail where the system reliability is determined from the solution of a first order differential-delay equation (DDE). This is solved exactly in the case of constant λ(t), but must be solved numerically in general. A general means of numerical solution for the triplex system is given, and an example case is solved for a rocof resembling a bathtub curve.

Original languageEnglish
JournalInternational Journal of Reliability, Quality and Safety Engineering
Issue number1
Publication statusPublished - 1 Feb 2012


  • 2-out-of-N:G
  • Minimal repair
  • NHPP
  • TMR

ASJC Scopus subject areas

  • Computer Science(all)
  • Nuclear Energy and Engineering
  • Safety, Risk, Reliability and Quality
  • Aerospace Engineering
  • Energy Engineering and Power Technology
  • Industrial and Manufacturing Engineering
  • Electrical and Electronic Engineering


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