Hardware redundant vital computers - Demonstration of safety on the basis of current standards

Abstract

A 2 out of 2 computer is used as an example to discuss the safety strategy of hardware redundant vital computers. One prerequisite for safety is a short fault disclosure time. A maximum fault disclosure time is standardised in ENV 50129. ENV 50129 contains a note which recommends a measure how to fulfil the standard’s requirement. This paper analysis whether the standard’s requirement is consistent with the safety target or not, and whether the measure is suitable to meet the requirement. Alternative requirements and measures are recommended.