Special features in electronic circuits modeling for fail-safe use

Reliability engineering is becoming increasingly important as we all become increasingly dependent on advanced technology. Consumers want technology, as they want technology that works. Today advanced electronic equipment is used in telecommunication, medical equipment, transportation, railway and similar critical functions. An important issue is the increasing use of complex digital circuitry in safety critical systems and the implications regarding safety assessment. In railway industry the use of ASICs, microprocessors, gate arrays and other highly complex digital devices is seen as a means to provide increased functionality as lower cost with higher reliability and safety. The model must be changed to reflect the modification because of new system elements replace older elements, adding new functions and capabilities. The purpose of the paper is to propose a method for modeling the fail-safe behavior of new conventional electronic scheme for safety-critical applications. The traditional approach as well as the known up to now principles and methods of safety systems synthesis has not solved that problem. A new safety conception has established itself - safety to be looked for on system level instead of on element level. This has considerably changed the modeling principles and methods including even some terms determined for many decades.