About EMC

What is EMC?

ElectroMagnetic Compatibility: With the proliferation of electronic systems in every aspect of our daily lives, there inevitably comes the problem of compatibility. Listening to the news on AM radio while using an electric razor should not be a problem, as it was in days gone by.


Why do we need EMC?

If EMC design practices are adhered to by both the razor and the radio manufacturers, then listening to the news on an AM radio, while using an electric razor, presents no problem.

Also, worldwide governmental regulations prohibit electronic products from emitting or being susceptible to, Electro-Magnetic Interference.


How do we implement EMC?

Emission, Susceptibility, and Path are the three constituents of EMC, with Emission being the one causing the most incompatibilities, while yielding the greatest number of solutions. Susceptibility on the other hand, is more subtle in its effect and its solutions. Finally, the Path can be the arbiter of both.

The three constituents of EMC are [unwarranted] Emissions, [inappropriate] Susceptibility, and the [unintended] Path between them. The electric razor's motor brushes arcing is a case of unwarranted Emissions; and the AM radio's picking up the noise through the Path(s) (power line, and/or through the air), is the unnecessary Susceptibility.



  • Radiated (electromagnetic field)
  • Inductively coupled (magnetic field)
  • Capacitively coupled (electric field)
  • Conducted (electric current)
Radiated
Radiated EMI is most often measured in the frequency range from 30 MHz to 10 GHz (according to the FCC).
Emission Sources: 
Clocks, clock lines, data lines; switching power supplies,
Susceptibility: 
Clock lines & data lines poorly laid out, improperly terminated;
Solutions:
Solutions: 
Balanced transmission lines, proper terminations, ground planes, shielding, limited rise & fall time drivers
Solutions: 
Shielding, layout, filtering, ground planes, differential line receivers,
Conducted
Conducted EMI is most often measured in the frequency range of several kHz to 30 MHz (according to the FCC).
Emission Sources: 
Power supplies (switching), power rails, motors, relays,
Susceptibility: 
A.C. power cord poorly filtered, power rails poorly decoupled,
Solutions: 
Good bypassing & decoupling practices, layout, ground planes, shielding,
Solutions: 
Good bypassing & decoupling practices, layout, ground planes, shielding, power line filtering,

Regulatory: Residential, Commercial, Industrial, and Military

Entity Standards
USA / FCC Part 15, subpart J
Canada CSA CSA
Japan VCCI VCCI
European EU (European Union) 89/336/EEC EN specifications:
Electronic Equipment Spec. Industrial, scientific and medical equipment EN55011 Broadcast receivers and associated equipment EN55013 Electrical motor-operated and thermal appliances for household and similar purposes, electrical tools and similar apparatus EN55014 Electrical lighting
Military MIL-STD-461/462
Aviation DO-160