EMC and functional safety - Considerations on compatibility, immunity and safety integrity levels

Safety functions are more and more carried out by electrical, electronic or programmable electronic systems. Such systems are exposed to electromagnetic phenomena like they typically exist in installations and could therefore be affected. As a consequence a failure of the safety function could arise which might cause harm to people. Thus appropriate immunity has to be achieved which is not ensured in every case by complying with normal EMC requirements because they are usually derived from issues of availability and of economic circumstances. Therefore the topics of EMC and safety requirements have to be merged in order to ensure the reliability of a safety-related system when being exposed to electromagnetic disturbances. This paper describes an approach how to establish proper function and/or reaction of such safety functions by introducing particular immunity levels in combination with a special performance criterion "Functional Safety". A particular challenge results from the fact to take into account requirements related to the different safety integrity levels. This situation is considered and discussed regarding the determination of appropriate immunity test levels.