Discussing a design

Do not disturb: the essence of electromagnetic compatibility

Who can still remember watching TV In the seventies and early eighties? Vehicles with spark ignition or radio amateurs could easily mess up the image quality for a brief moment, a harmless example of interference. But what about cases where things could seriously go wrong: imagine a chemical factory, a hospital, or an airplane. With the rapid growth of electronic devices on the globe and technologies with ever increasing switching speeds, it became clear that product design and release needed a different approach. Laws and regulations were introduced, electromagnetic compatibility became part of the process.

What is electromagnetic compatibility?

Electromagnetic compatibility (EMC) is the concept of electronic and electrical devices working as intended in their environment. Electronic products are not allowed to generate electromagnetic disturbances which may affect other devices. On the other hand, equipment should be immune for Electromagnetic Interference (EMI) up to a certain level. EMC deals with problems of noise emission and immunity of electronic and electrical products and systems.

What does EMC consist of?

EMC has two main elements:

  1. Emissions
    EMI emissions should be reduced below acceptable limits.
  2. Susceptibility/immunity
    Electronics should be immune to EMI up to a certain level.
Figure 1: EMI drawing.

Figure 1: EMI drawing.

Emissions are dividable into:

  1. Radiated H-Field
  2. Radiated E-Field
  3. Continuous conducted
  4. Discontinuous conducted

Immunity is dividable into:

  1. Continuous Conducted
  2. Continuous Radiated
  3. Continuous Magnetic
  4. Transient Voltage Dips, Short Interruptions and Voltage Variations
  5. Transient Magnetic
  6. Transient ESD
  7. Electrical Fast Transient

Standards and regulations

Specific tests are needed to verify whether the various emission and immunity aspects of a device are acceptable or not. Regulations mandate tests, which have to be done before the device can be sold in a chosen market. The ‘Standards’ documents define the tests a device must pass in order to prove compliance with these regulations. There are many EMC standards, for example: CISPR, IEC, ISO, SAE, European standards (EN 5X XXX) and American standards (FCC, MIL-STD).

EMC awareness in a product design process

PCB design is one of the key areas where a circuit with a good EMC performance is defined.

During the design, current paths should be identified, as current flows in loops and will look for the path of least resistance. A plan for a proper return path is necessary and one should avoid return path discontinuities and crossing splits. Parasitic EMI antennas (electric and magnetic dipoles) should be identified and taken care of accordingly.

Cables need to be seen as antennas. The tendency is to avoid them as much as possible and use fiber-optics, wireless or infrared instead.

EPR partner and EMC

Electromagnetic compliance and compatibility is a complex subject. If EMI is not addressed in a proper way or if there is no plan to remedy EMC testing failures, one places themselves in a precarious situation. EMC should now be an integral part of any electronics design project. EPR partner can help with the right PCB design, and with getting your device tested at an EMC Test facility.