On balancing safety and reliability of hybrid and `Bi-duplexed' systems

Having defined the parameters necessary to the determination of a system, the author considers five systems (four hybrid systems with and without stop signal and a new redundancy scheme called Bi-duplexed redundant system) and the author compares these systems from both safety and reliability points of view, according to the complexity of the functional units. No hypothesis is made on the law of degradation of these functional units and of the additional circuits. However, this law must be the same for the two kinds of circuits.