Safety Integrity Levels Model for IEC 61508 -- Examination of Modes of Operation --

Eiichi KATO  Yoshinobu SATO  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E83-A    No.5    pp.863-865
Publication Date: 2000/05/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section LETTER (Special Section on Reliability Theory and Its Applications)
safety integrity level,  modes of operation,  frequency of harmful event,  safety-related system,  programmable electronic,  functional safety,  

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The present paper modifies the algorithm to estimate harmful event frequencies and examines the definition of modes of operation in IEC 61508. As far as the continuous mode concerns, the calculated results coincide with those obtained based on the standard. However, for the intermediate region of medium demand frequencies and/or medium demand durations, the standard gives much higher harmful event frequencies than the real values. In order to avoid this difficulty, a new definition of modes of operation and a shortcut method for allocation of SILs are presented.