Maintenance, upgrades and enhancements

A system is rarely fixed for life: technology "push" and customer "pull" will create opportunities and desires for changes, and the natural degradation of physical structures with time will have a further impact on EMC.

Maintenance

The EMC Directive says very little about ongoing maintenance. The supplier's responsibility is to ensure that he supplies compliant apparatus, and the CE Marking procedures are all geared to the act of "placing on the market". Regulations the user has a responsibility to "take into service" compliant apparatus, but there is very little understanding of the legal position of a product or system that was compliant when it was first used but ceases to be so due to degradation over time.

Such legal niceties raise no dilemma for safety- or mission-critical systems as might be found in the aerospace, military, transport or medical sectors. If a system relies on EMC to be fit for purpose, then it’s reasonable to expect it to remain compatible for the duration of its operational life. Thus for these systems much more than for those which are merely covered by the EMC Directive, through-life EMC related maintenance is an essential part of the control plan. Examples of aspects which should be addressed, along with ways in which they might be controlled.

Note that some failure mechanisms (such as open circuit filter capacitors or surge protection devices) are impossible to detect by functional checks, and some way of testing the system's immunity to "synthetic" interference is needed. Variations on the theme of the IEC 61000-4-4 electrical fast transient burst test can be very useful here.

=== Items to check in periodic maintenance ===

The relevance of upgrades or enhancements

Systems already in the field are often subjected to mid-life upgrades, or changes to the installed configuration. These can take place for a number of reasons:

++ to extend the system's existing capability: e.g., adding more line cards to a telephone exchange

++ to include new functions: e.g., monitoring a new process variable in a production plant

++ to improve the performance or correct deficiencies in existing functions: e.g., a software bug fix

++ to implement a repair: e.g., swapping a faulty board.

With the exception of a repair by replacement of an identical component (and not all apparently similar components are identical in EMC terms), each of these may have EMC implications. As far as the application of the EMC Directive is concerned, the regulations include reconditioning and "modification which substantially alters the EMC characteristics" in their definition of "manufacture", but exclude repairs. A slightly different approach of the EC Guidelines, which introduces the concept of "as-new" apparatus; this is apparatus already taken into service "which is subject to an industrial operation that implies a substantial modification in order to obtain identical (or similar) performance as ... new apparatus placed on the market at the same time". The general principle is that the EMC Directive is re-applied only if the apparatus is to be considered "as-new" and if it’s going to be placed on the market again.

Since in the context of installations the re-con figured system or installation won’t be "placed on the market" again, the conformity assessment procedure for CE Marking won’t apply. What is still applicable is the system builder's original responsibility to ensure that the system or installation meets the Directive's essential requirements. To do this for any but trivial modifications will need some level of EMC analysis. It’s the responsibility of the person making the changes to do this, who could be either the system builder or the user. In the worst case this could require re-testing of the recon figured system, but possibly less onerous alternatives could include documentary proof of the compliance status of newly-introduced items, or their benign nature, or a technical analysis which section that the emissions and/or susceptibilities which are created are negligible.

The same analysis process should be done for upgrades to systems where EMC is an essential part of fitness for purpose, as in safety-critical systems. The difficulty in many cases lies in deciding how relevant a modification is to EMC, and therefore what level of analysis should be undertaken. This difficulty is reduced if the original project documentation included a clear description of the EMC-criticality of all parts of the system, so that changes to any part can be judged against this earlier knowledge.

The trigger for the upgrade analysis process should be built into the change control procedures for the whole system.

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