An Introduction to EMC  

   Formulas  

   Electromagnetism

EMC - Electromagnetic Compatibility

The ability of a device or system to function without error in its intended electromagnetic environment.

EMC is a term used to describe the interaction of electrical and electronic equipment with its electromagnetic (EM) environment and with other equipment. EMC deals with emissions and immunity of electronic devices. All electrical devices generate emission and are susceptible to EM phenomena such as lighting-induced transients, electrostatic discharges, electrical fast transients, radiofrequency fields generated by transmitters and hand-held communication devices. Moreover, an electronic device can be also susceptible to self-generated interferences. A good EMC design will minimize both susceptibility to, and generation of EM disturbances.
 

EMI - Electromagnetic Interference

Electromagnetic emissions from a device or system that interfere with the normal operation of another device or system

There are three essential elements to any EMC problem:

1. Source of an electromagnetic phenomenon
2. Receptor (or victim) that cannot function properly due to the electromagnetic phenomenon
3. Path between them that allows the source to interfere with the receptor.

Each of these three elements must be present although they may not be readily identified in every situation. Electromagnetic compatibility problems are generally solved by identifying at least two of these elements and eliminating (or attenuating) one of them.

Potential sources of electromagnetic compatibility problems include radio transmitters, power lines, electronic circuits, lightning, lamp dimmers, electric motors, arc welders, solar flares and just about anything that utilizes or creates electromagnetic energy.

Potential receptors include radio receivers, electronic circuits, appliances, people, and just about anything that utilizes or can detect electromagnetic energy.

Methods of coupling electromagnetic energy from a source to a receptor fall into one of four categories.

• Conducted (electric current)
• Inductively coupled (magnetic field)
• Capacitively coupled (electric field)
• Radiated (electromagnetic field)

Coupling paths often utilize a complex combination of these methods making the path difficult to identify even when the source and receptor are known. There may be multiple coupling paths and steps taken to attenuate one path may enhance another.

EMI Test Plans, Procedures, and Reports

Clear, accurate test procedures and test reports ensure your EMI tests are properly performed and documented. This translates to less time in the EMI lab, clearer test data interpretation, and more repeatable test results.

EMC Glossary and Links

• ACES - Applied Computational Electromagnetics Society
• AEMCLAP - Automotive Electromagnetic Compatibility Laboratory Accreditation Program
• ANSI - American National Standards Institute
• APLAC - Asian Pacific Laboratory Accreditation Cooperation
• CENELEC - European Committee for Electrotechnical Standardization)
• CISPR 22 - Emission Limits for Class A Devices. CISPR is a committee of the International Electrotechnical Commission (IEC), which promulgates standards in order to facilitate trade between countries. Many countries have adopted EMC requirements based on IEC standards. The IEC has published a guide titled, "EMC: The Role and Contribution of IEC Standards" (pdf 331kB), which provides a good overview of EMC standardization efforts.
• CSA - Canadian Standards Association
• EEC - European Economic Community
• EIA - Electronic Industries Association
• EMC - Electromagnetic Compatibility
• ESA - Electrostatics Society of America
• ESD - Electrostatic Discharge
• EMI - Electromagnetic Interference
• EMI - Injection Molding (protective coatings for ESD and radiated electromagnetic interference)
• EMP - Electromagnetic Pulse
• ETSI - European Telecommunications Standards Institute
• FCC - Federal Communications Commission (U.S.A.)  The FCC Rules and Regulations, Title 47, Part 15, Subpart B regulates "unintentional radio-frequency devices". Most products regulated by Part 15, Subpart B fall into one of two categories. Class A devices are those that are marketed for use in a commercial, industrial or business environment. Class B devices are those that are marketed for use in the home. Class B limits are more stringent than Class A limits and the Class B certification process is administratively more rigorous than the Class A verification process. The radiated and conducted EMI test procedures are defined in the ANSI Standard C63.4. FCC Rules and Regulations, Part 15, only regulates radio frequency emissions. Currently there are no FCC regulations pertaining to product immunity to electromagnetic fields. See FCC Limits.
• HEMP - High altitude nuclear Electromagnetic Pulse
• HF - High Frequency
• HV - High Voltage
• IEC - International Electrotechnical Commission
• IEEE - Institute of Electrical and Electronics Engineers
• ISO - International Organization for Standardization
• ITE - Information Technology Equipment
• LF - Low Frequency
• LV - Low Voltage
• MIL-STD-461 - EMC requirements for products that are marketed for use by the US military that includes limits for radiated and conducted immunity as well as radiated and conducted emissions M461E.pdf (970 kB) . This and other U.S. Military Standards can be obtained from the US The Department of Defense Single Stock Point for Military Specifications, Standards and Related Publications.
• NARTE - National Association of Radio and Telecommunications Engineers
• NEMP - Nuclear Electromagnetic Pulse
• NIST - National Institute of Standards and Technology (U.S.A.)
• NSSN - National Resource for Global Standards
• PLT - Power Line Transient
• RES - Radiated Electromagnetic Susceptibility
• SAE - Society of Automotive Engineers
• VCCI - Voluntary Control Council for Interference (Japan)
• VDE - Verband Deutscher Elektrotechniker