Estimation and evaluation of the 1004-architecture for safety related systems

In the standard IEC 61508 miscellaneous architectures for safety related systems are introduced. Depending on the required safety, reliability and availability levels several architectures such as 1oo2-, 2oo2-, 1oo3-, and 2oo3-architectures can be selected. In this paper, the concept and calculation of a novel architecture is presented. The 1oo4-architecture (one out of four) represents an advanced safety architecture, which is 3-failure safe. This means that at least one of the four channels have to work correctly in order to trigger the safety function. In order to classify the quality of the proposed architecture for safety related systems the PFD-value is calculated. Additionally, the Markov-model for a 1oo4-architecture is introduced and the MTTF-value for this architecture is calculated. The results are high safety and high reliability.