Optimal Proof-Testing Intervals with Functional Safety Constraint for E/E/PE Safety-Related Systems

Proof-testing for E/E/PE safety-related systems is known as a periodic inspection and maintenance activity to maintain their designed functional safety in operation. Generally, the proof-testing takes so much cost and time for checking the E/E/PE safety-related systems comprehensively. Therefore, effective proof-testing intervals should be considered based on the rationale for the hazardous risk and maintenance cost. As one of the approaches, there exist methods deriving economic proof-testing intervals minimizing simultaneous the proof-testing cost and the risk at hazardous event occurrence. However, the safety constraint should be needed to consider at the same time since the E/E/PE safety-related systems are required to maintain certain safety level in operation. This paper addresses a mathematical approach for obtaining optimal proof-testing intervals for such practical situations.