Considerations on Immunity Test Levels and Methods with Regard to Functional Safety

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 occur in installations and therefore the systems could potentially be affected. As a consequence a failure of the safety function could arise which might cause harm to people. Thus appropriate immunity against electromagnetic phenomena has to be achieved which is not ensured in any case by complying with normal requirements concerning electromagnetic compatibility (EMC) because they are usually derived from issues of reliability and from economic conditions. Therefore EMC and safety requirements have to be brought together. This paper describes some aspects which have to be considered when merging the topics of EMC and of complex safety-related systems. Particular attention has to be paid to appropriate immunity tests which should reflect both, firstly the potential impact of the electromagnetic phenomena on systems and equipment and secondly the need of highly reliable and accurate test results. One approach to cope with this challenge consists in the introduction of special immunity test levels and test methods in combination with a special performance criterion “Functional Safety” and if necessary by extended immunity test procedures. Furthermore the situation is discussed regarding immunity test levels and safety integrity levels.