Where are the fundamental changes from EN 954-1? Previously the focus was on the architecture of the control system. Ultimately this was converted into "categories". By contrast, the structure in the new standard EN ISO 13849-1 is simply stated on a qualitative basis. This means that quantitative variables such as the mean time to a dangerous failure (MTTFd), diagnostic coverage (DC) and common cause failures (CCF) have been added. Together, these parameters affect the performance level that can be achieved. Varying them also enables you to identify the optimum configuration. Due to these parameters, the new standard also considers aspects such as probability of failure and fault detection capabilities. These don't just refer to the logic section. On a safety control system for example; the whole safety function is considered, from sensor to actuator. This overall assessment is nothing new in itself, but it does now have a different priority: as a result of the rigorous assessment in accordance with EN ISO 13849-1, it is now fully established and stipulated. The focus may now be on components such as valves for example, which were considered a lower priority under EN 954-1. In accordance with the new standard, these must now be included in the calculation with their characteristic data and reliability values.
Machinery in the European Economic Area must comply with the Machinery Directive. The CE mark is the visible seal on the machine, which documents conformity with the Machinery Directive. The change to the Machinery Directive takes place Dec 31, 2011.
If a manufacturer does not want to use the standards to comply with the Machinery Directive, there is a more costly alternative, but for most manufacturers it is cost prohibitive and much slower to put into practice.
SOURCE Pilz Automation
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