EC-24.6 Electromagnetic Interference and Compatibility
You can identify the source, the coupling path and the victim in an interference problem, apply the standard design measures that reduce emission and improve immunity, and describe what a compliance test actually involves.
Before:EC-2. Electromagnetics and Transmission LinesEC-17. Industry and Research Experience
A product that interferes with other equipment, or that fails when other equipment interferes with it, cannot legally be sold in most places. The subject looks like a collection of superstitions until it is organised around one structure: there is always a source, a path and a victim, and breaking any one of the three solves the problem. Most of the effective measures are decisions made during layout and cost nothing.
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Source, coupling path and victim, and why naming all three matters
Interference problems are frequently attacked by adding filters at the victim when the cheap fix was at the source. Identifying all three parts before changing anything is what makes the work systematic.
NPTEL: EMI, EMC and Signal Integrity — Principles, Techniques and Applications (IIT Kharagpur) · CourseConducted and radiated emission, and the frequency ranges each covers
Below about thirty megahertz noise mostly escapes along cables and above it mostly radiates, so the two are measured differently and fixed differently. Knowing which one a failure is halves the search.
NPTEL: EMI, EMC and Signal Integrity — Principles, Techniques and Applications (IIT Kharagpur) · CourseCommon mode against differential mode, and why cables radiate
A small common-mode current on a long cable radiates far more efficiently than a large differential current in a loop on the board. That is why so many emission failures are cured at the connector.
NPTEL: EMI, EMC and Signal Integrity — Principles, Techniques and Applications (IIT Kharagpur) · CourseFiltering, ferrites and shielding, and where each belongs
A filter attenuates along a conductor, a ferrite adds loss to common-mode current and a shield blocks a radiated path, and using the wrong one wastes money without helping. Each has a frequency range in which it is effective.
Immunity: electrostatic discharge, bursts, surges and fields
Compatibility is a two-way requirement, and the tests inject energy into a product to see whether it keeps working. Protection has to be at the connector, before the energy reaches anything delicate.
NPTEL: Electronic Packaging and Manufacturing (IIT Kharagpur) · CourseWhat a compliance test is, and pre-compliance on your own bench
Formal testing happens in a laboratory with a calibrated chamber and is expensive to repeat, so problems are best found earlier with a near-field probe and a spectrum analyser. The rough measurement will not certify anything and will find most failures.
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