A CPLD-based safety concept for industrial applications

Industry demands cost-efficient approaches for the realization of uncomplex safety functions in industrial automation. Therefore new approaches need to be considered. For this purpose the implementation of safety functions in hardware using CPLDs is an option. This approach does, in contrast to microcontroller-based systems, not require the development of startup- and online tests for RAM and CPU. Therefore efforts for design, implementation and verification of these safety integrity measures can be saved as well as hardware resources for the execution of tests. Based on this idea, a CPLD-based safety concept has been elaborated that allows to realize safety functions by exclusively using CPLDs. The safety concept has been derived from normative safety requirements, functional safety requirements as well as other non-functional requirements. The safety concept comprises a CPLD-based redundant failsafe system architecture, safety integrity measures and a precise definition of the safe state and the unsafe state of possible target applications. An industrial power drive system is presented that has been enhanced with uncomplex safety functions to increase its safety integrity. These safety functions are able to avoid the application of power to an electric DC motor, if demanded. They were realized by a fail-safe system. This system adopts the CPLD-based safety concept.