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EMC for a change

02 February 2009

Graham Heritage - Technical director

Things are changing in relation to EMC and test equipment but, perhaps surprisingly, the reason for the change is not the introduction of the new European EMC Directive! It’s true that, from 20 July 2009, it will no longer be permissible to declare compliance against the old Directive (89/336/EC). Instead, compliance will have to relate to its replacement – 2004/108/EC. For users and manufacturers of test equipment, however, this makes almost no difference. The changes in the new Directive relate mostly to systems and are, therefore, much more important in fields like process control.

In fact the changes that affect test equipment relate to a new and updated version of the product standard IEC 61326-1. Meeting the requirements of this EMC standard carries a presumption of conformity and is the normal means of compliance with the EMC Directive.

The new version of IEC 61326-1 differs from the old in two key areas. The first is the frequency range for field immunity testing has been extended from 1 GHz to 2.7 GHz. This is to take into account the increasing use of equipment that operates at the higher frequencies.

The second important change is that minimum immunity pass criteria have been set, whereas previously the manufacturer was allowed to choose any one of three criteria.

Radiated and conducted RF immunity must meet the requirements for Criteria A pass. In effect this means that the product must remain within its published specification while being tested. All other tests, except for those involving mains supply interruptions for mains powered equipment, must at least meet the requirements for a Criteria B pass. This allows the equipment under test to go out of specification while being tested.

Tests involving mains supply interruptions must meet at least the requirements for a Criteria C pass, which means that user intervention may be needed to restore the equipment to its normal state.

Suppliers of test equipment like Megger have to test not only new products, but also existing products that they intend to continue selling, to ensure that they meet the new standard. In order to do this, it is likely to that those suppliers will need to purchase additional equipment to extend the scope of their test installations up to 2.7 GHz.

Although the suppliers will undoubtedly do all they can to absorb these additional costs, it is almost inevitable that a proportion will be passed on to their customers. In summary, therefore, the changes to the EMC test regime arguably mean that customers will get a better product, but almost certainly at a higher price.