Functional safety analysis of reliable control systems using decision by majority

Fault detection and reliable control theory are for design of safety-related systems. They should be realized in systems comprising electrical and/or electronic and/or programmable electronic components, which are called electrical/electronic/programmable electronic systems (E/E/PE systems). The IEC (International Electrotechnical Commission) is preparing the international standard for functional safety of such E/E/PE safety-related systems, IEC 61508, which is planned to be adopted by the ISO (International Organization for Standardization). It uses safety integrity levels to specify the target safety level of functions to be implemented by E/E/PE safety-related systems. The author has presented a framework of tolerance against sensor failures consisting of the following aspects: (a) reliable stability against sensor failures using decision by majority among redundant sensors, and (b) fault detection mechanism for redundant sensors. This paper analyzes its functional safety according to the policy of the IEC 61508. A great deal of effort will be made on safety analysis especially based on the international standard in the field of control theory. This paper is the first step to such studies