EMC - ElectroMagnetic Compability
Compliance with the EMC Directive is mandatory for all electronic and electrical products.
The essential requirements
“Equipment shall be so designed and manufactured as to ensure that: (a) the electromagnetic disturbance generated does not exceed the level above which radio and telecommunications equipment or other equipment cannot operate as intended; (b) it has a level of immunity to the electromagnetic disturbance to be expected in its intended use which allows it to operate without unacceptable degradation”. The essential EMC requirements for products are based on two aspects: emission and immunity. Problems to other products are caused by (excessive) emission(s) of a product; and suffering from nearby products is due to insufficient immunity from a product in its EMC environment. The objective is to make sure that products can operate in the same environment in a compatible way without mutual interference.
EMC problems in the real world
An example of a real-life EMC problem was reported by OFCOM, UK regulator and competition authority. A well-known brand of wireless baby-phones caused interference to aircraft communication when planes were approaching airports. It was however not the wireless technology in the baby-phone but the plugin adapter with a switch-mode power supply that caused the problem. The power supply emitted disturbances on radio channels used by National Air Traffic Services. The troubled area was overflown with a specially equipped aircraft (!) to locate the source of the problems. A specially equipped road vehicle was then sent to identify the house concerned. A recall of the faulty power supply had to be performed. It was a lot of trouble for a low-cost electronic item, but flight safety required it.
EMC design
The main challenge that manufacturers face when dealing with EMC is that the disturbances may be caused by unexpected sources (like the disturbances from the baby-phone power supply). And because these disturbance sources are unintentional, they are often overlooked during the design of a product. Disturbances travel via air, so larger products are often more challenging than smaller ones. Disturbances also are conducted via cables, so more and/or longer cables are often bad news for designers trying to establish EMC compliance. The complexity of a product has impact on its EMC behaviour; it is harder to comply with the EMC requirements for products that contain advanced electronics or microprocessors running at high frequencies. EMC solutions like metal enclosures, shielded cables, filters or ferrite cores are possible but obviously result in higher costs.
EMC testing
Testing according to harmonised EMC standards is typically chosen to show compliance. A very specific product standard such as for alarms or taximeters might be applicable, but in many cases standards for larger product groups are applicable e.g. for lighting, tools, multimedia or household appliances. In those rare cases where no product standard is available one can always apply generic standards. Fortunately, all EMC standards describe just two hands full of phenomena for which basic standards are available that describe test methods. A complete EMC test program is often finished within two days.
Guidance
The European Commission issued a GUIDE on EMC. It deals with a number of practical issues that will be of interest to manufacturers and other stakeholders.
