The FMEDA Based DC Calculation for Railway Safety Computer

This paper presents a new algorithm to compute the Diagnostic coverage (DC) for railway safety computer using the Failure modes effects and diagnostic analysis (FMEDA) theory. The importance to work out the DC accurately is stressed. A certain type of railway safety computer's output element is taken as an example to show how the DC is worked out using the FMEDA method. The probability of dangerous failures per hour (PFH) of one certain safety computer is obtained considering the DC. The final results show that the DC is 99.6% and the PFH of the safety is 1.165 fit, which means 1.165 dangerous failures may occur during 1 billion hours' working time, running up to the requirement of the Safety integrity level 4 (SIL4). This paper provides an example to come up with the DC for safety computer, thus making the PFH calculation more accurate and so is the Safety integrity level.