Design and Implementation of Safety Functions on a Novel CPLD-Based Fail-Safe System Architecture

In the case of a fault fail-safe systems achieve and maintain a safe state for people, environment and property. These systems are usually realized using microcontroller-based architectures. With respect to cost per unit and development effort for fail-safe systems, industry has to consider new approaches. An option is to realize simple safety functions using architectures that include CPLDs. A novel hardware architecture for embedded fail-safe systems is the outcome of recent research efforts at SIEMENS. This architecture is homogeneously redundant and contains, in contrast to similar systems, exclusively two CPLDs instead of microcontrollers. This paper is presenting design and implementation of the very first fail-safe system based on this architecture. This system targets the market of industrial automation. The fail-safe system enhances a power converter with safety functions. To achieve the required safety integrity, adequate measures able to detect random and permanent faults, are implemented. The novel fail-safe system adheres to the draft of the second edition of the IEC 61508, which includes requirements for the realization of safety functions using CPLDs, the IEC 61800-5-2 and the EN ISO 13849.