This is defined in 3.4.4 of IEC 61508-4 as an E/E/PE safety-related system, in which the failure modes of each individual component are well defined and the behaviour of the system under fault conditions can be completely determined.
An example is a system comprising one or more limit switches, operating one or more contactors to de-energize an electric motor, possibly via interposing electromechanical relays.
This text contains extracts from the IEC Functional Safety Zone. All such extracts are copyright of International Electrotechnical Commission © 2005, IEC, Geneva, Switzerland. All rights reserved. IEC has no responsibility for the placement and context in which the extracts are reproduced. This notice takes precedence over any general copyright statement.
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