Knowing EMI/EMC for Product Designing

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Knowing EMI/EMC for Product Designing

The world is getting revolutionized with technology, it Is becoming more electronic and developing. All the technologies are driven by a hardware which usually hold hands with the software. The hardware is nothing but a bundled component assembled on a board, called PCB. These PCB should be able to do its work without any disruption due to interference from other devices and without causing interference. Let us know what they are,

EMC (Electromagnetic Compatibility):

Electromagnetic waves are what keeps our devices from constantly interfering with each other. We know that while being in a call on a mobile phone will disrupt a TV set. They are due to interference caused by the waves produced from mobile phone on the hardware of TV. The device needs to be shielded to avoid this.

The design of all electronic enclosures will need to consider two things:

  1. Is the electronic product being designed to operate properly while being affected by self-generated electromagnetic waves?
  2. Is the electronic product generating electromagnetic waves that will negatively affect other products?

All electronic products, again these are what the EPE Designer is designing, are susceptible to interference, and they are generating interference themselves. There are regulations for the frequency specific levels that all electronic products must meet for this generated interference.

EMC Issues:

Electromagnetic Interference (EMI), also called radio-frequency (RFI) when in the radio-frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade the performance of the circuit or even stop it from functioning.

EMC is the ability of the device, equipment, or system function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment.

The main design objective for compliance to EMC requirements will to minimize the size and number of openings.

They are:

  1. Displays (LED/CRT)
  2. Keypads or Membrane Switches
  3. Status Indicators
  4. Cooling Apertures
  5. Box Assembly Seams
  6. Cable or Connector Openings
Shielding the device:

EMI/RFI shielding offers the ability to reduce and control these fields so that they do not cause unwanted interactions.

PCB Design and Layout – where RF and Digital Designers will design the PCBAs to reduce or eliminate noise and susceptibility.

Power Supply Design and Layout – where Power Supply Designers will design the power supplies to reduce or eliminate noise and susceptibility.

Internal Wiring – where the above Designers and Mechanical Designers will work to design interconnects between PCBAs and to enclosure which will not pick-up or induce EMI internally (self-jamming) or externally (violate FCC/CISPR/VDE/Military regulations).

Enclosure Design – where Mechanical Designers will Design a continuously closed conductive envelope in order to prevent outside fields from penetrating the equipment and to prevent internally generated noises from escaping the enclosure.

The enclosure should be the continuous metal surface where PCBA grounds are attached at specific locations. This continuous metal surface can be either “actual” metal (like aluminum, magnesium, or steel) or it can be a conductive coating that has been put onto a non-conductive material (like plastic). Note that, when considering “actual” metal as an enclosure, the designer must take into account that the surface finish on the metal must be conductive. Several common surface finishes for metal are not conductive (enough) to serve as a “continuous metal surface”. Any finish chosen to be conductive, must remain so during the environment (corrosion) and wear (say, due to vibration) that the product will undergo during its expected life.

EMC Standards:

Military Standards:

In solving an EMC problem, both the emitter noise level and susceptor’s noise threshold must be considered. If the susceptor’s lowest signal threshold level can be made greater by at least two times the highest emitter (noise) level (for a 6dB safety margin) then the emitter and the susceptor are considered to be compatible with each other. One way of achieving this type of compatibility is to define not only the maximum allowable emissions level but also the minimum allowable susceptibility threshold level.

The most commonly used military standard for both emissions and susceptibility is MIL-STD-461. There are more than one emission and susceptibility level defined in MILL-STD-461 since the requirement applications vary.

Commercial Standards:

The most common commercial standards are FCC (Federal Communications Commission) as USA based standard and VDE (Verband Der Elektrotechnik) as Germany based standard.