Assessmentof the effect of common cause failure and diversity on diagnostic coverage of a self-checking pair

It is important to consider diagnostic coverage (DC) of the automatic diagnosis (AD) scheme in course of the design of highly reliable systems in which redundancy technique is usually applied. Considering the nature of AD is to introduce some form of redundancy, its performance will be affected by common cause failure (CCF). Due to that diversity is an effective antidote for CCF, it is desirable to assess the effect of diversity and CCF on DC. Therefore, a novel method is proposed to quantitatively compare two different AD schemes which include identical redundancy and diverse redundancy based on the protection (data integrity) they provide against CCF in this paper. The AD schemes considered are implemented in the form of self-checking pairs. For the first time, the relationship among diversity, CCF rate and DC is quantified by the proposed method. A two-channel redundant system in which each redundant element employs a self-checking pair is used as an illustration case. The results confirm that the diversity technique increases the DC of the self-checking pair.