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Controlling EMI to improve reliability

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Edited by the Electronicstalk editorial team Jan 22, 2007

The second edition EMC Directive, 2004/108/EC, includes specific requirements for "fixed installations", and for the equipment/systems supplied to them.

The costs of digital processing, wired and wireless datacommunications and solid-state power conversion are continually decreasing as their functionality continually increases.

As a result these electronic technologies are increasingly used in a wide range of applications, often displacing proven electromechanical, mechanical, hydraulic or pneumatic technologies.

For example, control panels now often contain powerful programmable logic controllers (PLCs) or personal computers (PCs); touchscreen colour displays; variable-speed AC motor drives and a variety of other switch-mode power convertors; pulsewidth-modulated (PWM) servomotor drives; and wired and/or wireless datalinks (Ethernet, Profibus, ASI etc.).

But all electronic technologies are inherently prone to suffering from inaccuracy, malfunction, even damage when interfered with by electromagnetic (EM) phenomena during real-life operation.

The continued shrinking of the silicon features in electronic devices generates most of the improvements in cost and functionality - but at the price of making them more susceptible to EM interference (EMI).

The intensity and frequency range of real-life EM phenomena are continually increasing, due to the growing use of digital, switch-mode, and wireless technologies, and especially due to mobile radiocommunications (cellphones, walkie-talkies, vehicle mobile radio, Wi-Fi, Bluetooth etc) and the use of variable speed motor drives.

This worsening EM environment, combined with the increasing EM susceptibility of electronics, means electronic reliability is decreasing - with increasingly important consequences for downtime, cost of ownership, warranty costs, customer satisfaction, safety risks, and exposure to product liability litigation.

A new guide from REO (UK) describes practical engineering techniques that panel builders can use to control EMI and improve reliability.

The European EMC Directive (89/336/EEC, amended) can be viewed as an attempt to control this problem through legislation, although it does not cover safety issues.

Unfortunately, it is unclear about how it should be applied to installations or custom equipment/systems, and this has led to it being effectively ignored by most companies active in those areas.

However, on 1st July 2007 the second edition EMC Directive, 2004/108/EC, will replace 89/336 - and it includes specific requirements for "fixed installations", and for the equipment/systems supplied to them.

2004/108 defines fixed installations as: "A particular combination of several types of apparatus and, where applicable, other devices, which are assembled, installed and intended to be used permanently at a predefined location".

This covers all installations from the smallest residential electrical installations through hotels, public buildings, entertainment venues and factories to national infrastructure (eg electrical, telephone, road and railway networks).

It includes all commercial and industrial installations.

Private installations, such as multimedia setups in the home, are not subject to the same constraints as professional ones.

Providing the individual installer uses only apparatus that is compliant with the EMC Directive and follows its manufacturer's instructions - then 2004/108 requires no additional EMC compliance work.

However, any professional who creates a fixed electrical installation - or supplies custom-designed equipment/systems to such installations - must, by law, comply with the specific requirements in 2004/108 from 1st July 2007, including the creation of the EMC compliance documentation.

2004/108 requires a "responsible person" to be appointed for each fixed installation - ensuring that it complies with the directive and that good EMC engineering practices are employed.

They must also document how they achieved EMC compliance, and keep those documents ready for inspection by EMC enforcing authorities.

Relying solely on purchasing products that carry the CE marking will not achieve "due diligence" in compliance with 2004/108, either for custom equipment/system manufacturers, or for fixed installations themselves.

In all fixed installations, it will be necessary to assess the electromagnetic environment, ensure that the EMC characteristics of the purchased equipment/systems are suitable for that environment, and then to follow the supplier's EMC installation, operation and maintenance instructions whilst using good EMC engineering practices.

2004/108 does not require custom-engineered equipment/systems to pass any EMC tests, or carry the CE marking for EMC compliance - but it does require all such equipment/systems to be supplied to their fixed installations with documents that: identify the fixed installations they are intended for (eg name, address); give their manufacturers' names and addresses (or that of their agents or EU importers); uniquely identify them (eg type number, batch number, serial number); identify the EMC characteristics of the fixed installations for which they are intended; and indicate the precautions to be taken for incorporating them into the fixed installations so as not to compromise the conformity of those installations with 2004/108's EMC Protection Requirements.

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