Functional safety of machine controls (BGIA Report 2/2008e)

Abstract: The EN ISO 13849 standard, "Safety of machinery - Safety-related parts of control systems", contains provisions governing the design of such parts. This report describes the essential subject-matter of the standard in its heavily revised 2006 edition, and explains its application with reference to numerous examples from the fields of electromechanics, fluidics, electronics and programmable electronics, including control systems employing mixed technologies. The standard is placed in its context of the essential safety requirements of the Machinery Directive, and possible methods for risk assessment are presented. Based upon this information, the report can be used to select the required Performance Level PL_r for safety functions in control systems. The Performance Level PL which is actually attained is explained in detail. The requirements for attainment of the relevant Performance Level and its associated categories, component reliability, diagnostic coverage, software safety and measures for the prevention of systematic and common-cause failures are all discussed comprehensively. Background information is also provided on implementation of the requirements in real-case control systems. Numerous example circuits show, down to component level, how Performance Levels a to e can be engineered in the selected technologies with Categories B to 4. The examples also provide information on the safety principles employed and on components with well-tried safety functionality. Numerous literature references permit closer study of the examples provided. The report shows that the requirements of EN ISO 13849 can be implemented in engineering practice, and thus makes a contribution to consistent application and interpretation of the standard at national and international level.