Evaluation of sophisticated hardware architectures for safety applications

Standards and guidelines give advice on the development of qualitative and quantitative criteria to evaluate safety related systems. Success of many modern applications is highly dependent on the correct functioning of complex computer based systems. In some cases, failures in these systems may cause serious consequences in terms of loss of human life. Systems in which failure could endanger human life are termed safety-critical. The SIS (Safety Instrumented System) should be designed to meet the required safety integrity level as defined in the safety requirement specification (safety requirement allocation). Moreover, the SIS design should be performed in a way that minimizes the potential for common mode or common cause failures (CCF). The purpose of this paper is to describe the calculation of MTTF-values for a 2004-architecture with the help of Markov-models. In the paper equations are indicated for PFD for normal and common-cause-failures. The results are high availability and a high reliability.