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  What is EMC ?
An acronym for Electromagnetic Compatibility, EMC is the ability for devices (or systems) to function as intended within their electromagnetic environment, without interfering with other devices, and without being susceptible to interference from other devices.

EMC engineering is is the art and science of effectively dealing with electromagnetic interference (EMI).

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Why All The Concern Over EMI and EMC?

When the flight crew instructs passengers to turn off notebook computers and other personal electronic devices prior to aircraft takeoff and landing, it is due to concerns over  EMC. It is widely known in the civil aviation community that electromagnetic radiation from laptop computers can interfere with some onboard navigation systems potentially causing unpredictable aircraft behavior.

When patient monitoring equipment in a hospital intermittently gives erroneous readings whenever someone nearby uses a mobile phone, that's an EMC issue. Many hospitals now prohibit the use of mobile phones in certain patient care areas.

When an electric wheelchair loses control and heads into busy traffic because a nearby pedestrian talks on a walkie talkie, that's an EMC issue. Tests by the U.S. Food and Drug Administration have shown some types of electric wheelchairs are susceptible to RF fields in the order of 5 V/m to 15 V/m. The FDA's Center for Devices and Radiological Health has since launched new initiatives to raise EMI immunity standards for wheelchairs.

Although some EMC hazards can have life threatening consequences, most of us witness EMC situations more often than we think. For example, your TV reception is garbled whenever someone turns on the vacuum cleaner. Your computer crashes during a lightning storm or power surge and valuable data is lost.  You overhear a voice conversation in your stereo or there is an annoying hum or buzz that won't go away. The portable radio next to your computer always sounds better when you turn off your computer. These are just a few of the many common EMC situations which lead to degraded performance or reliability. Although some EMC situations have obvious and repeatable symptoms, like the poor radio reception in the example, other symptoms may be much more elusive and may well be hidden. This may give rise to functional safety issues which can be a potential liability concern for equipment manufacturers.

Another reason why EMC is gaining much attention lately is due to the proliferation of electronic devices. All electronic devices emit electromagnetic interference to varying degree and; all electronic devices are also susceptible to interference, to varying degree. This fact has not eluded governments and authorities concerned about possible impact on communication and other safety-critical systems. Electronics play a big role in our everyday lives and are used in everything from industrial process control, automobiles, personal communications, medical diagnostics, to air traffic control systems. With this increased reliance on electronics, and due to the numerous documented EMC events, the effect of electronic systems on public safety is becoming more apparent and better recognized than ever before. In many cases, failure of electronic systems to perform as intended may lead to disastrous consequences involving potential loss to life and property.

In an effort to control the EMC performance of electronic devices, governments worldwide have enacted, or are in the process of introducing legislation, requiring most electronic devices for domestic consumption to pass minimum EMC performance standards. This trend will likely continue as more new electronic devices come on the market, adding to the already polluted electromagnetic environment around many major cities.

 

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How Do I Know If I Have An EMC Problem? 

This is a difficult question to answer. The symptoms of EMC problems are usually not obvious to the uninitiated, and are often masked by other equipment operational or performance issues. The complex relationship between circuit layout, bandwidth, grounding and shielding all play an integral part in determining overall system compatibility in a given electromagnetic environment. Having said that, many EMC problems are typically characterized by erratic or unexplained system behavior, or even malfunction, sometimes triggered by the operation of other electrical-electronic equipment which functions may be entirely unrelated to those of the victim circuits. Certain natural phenomena such as lightning and electrostatic discharge can also trigger EMC-related symptoms in susceptible systems. In every EMC problem, there is always a source of interference, a victim circuit, and a coupling path involved. No matter how complex an EMC problem may first appear, the good news is, it can usually be systematically diagnosed and reduced to a simpler problem for which practical solutions can be sought. The first step in dealing with any potential EMC issues is to contact a qualified EMC professional.