AGENDA – GROUNDING/BONDING/SHIELDING
Shielding is the proven approach for systems that are impossible to cost effectively EMC harden. Shielding can be used at the PC board level to protect sensitive circuits as well as at the systems level. Larger systems can be placed in shielded rooms or even shielded facilities. Regardless of the size, shielding works the same way. However the grounding, bonding, and cabling approach for larger enclosures will be much different than that used at the PCB level.
Shielding also effectively reduces internal crosstalk and circuit-path coupling as well. In many cases, shielding can eliminate the need for filters. Even if filters are required, a shield provides a superior RF sink and filter input/output isolation. Shielding works . . . plus it doesn’t affect signal integrity! An important factor with today’s ultra high-speed systems! It’s the only suppression component that is not a circuit element, which accounts for shielding being one of the most widely used ways of meeting EMC requirements.
EMC BASICS, CULPRITS, AND VICTIMS
Background Information Terms, Units, Decibels Time to Frequency Conversion Overview of Typical EMI Levels/Coupling Power Line Disturbances Transients - ESD, Lightning, EMP FAST Analysis
GROUNDING/BONDING FOR EMC
Grounding Safety Earthing/Grounding vs EME Coupling Grounding Myths vs Reality Electrical Shock Avoidance (UL, NEC Req's) Lightning Protection Systems Lightning Rods and Earthing Filter Grounding Bonding and Common Impedance Coupling Bond Zo of Round/Flat Conductors & Planes Contact Surfaces Galvanic Corrosion Practical Solutions, from PCB to Room Level Common Zo Coupling Reduction on PCB's Impedance Reduction Multilayer Boards Cable Differential/Common Mode Coupling Field to Wire-Pair and Wire-Pair to Field Twisting Shielding Field to Grnd Loop Coupling & Reduction Common Mode to Diff Mode Conversion Floating & Single Point Grounding Balanced Line Drivers/Receivers Series RF Inductors Double Shielding Shielded Transformers and Baluns Ferrites Optical Coupling
SHIELDING FOR EMC
Shielding Effectiveness (SE) of Barriers Near Field (EF and HF) Far Field/Plane Wave Metal Barrier Performance External/Internal Reflection & Absorption Cavity Amplification Shielding Performance of Typical Metals Low Frequency Magnetic Shielding Conductive Coatings/Metallized Plastics Cable Shields - Balanced Pairs and Coax Cable Shields - Ideal vs Comp. Practices Coaxial Cable Shielding Shielding Effectiveness vs Zt Field Coupling to Coaxial Cables Grounding Rules for Cable Shields Flat Ribbon Cables Connectors and Pigtails Enclosure Shielding - Aperture Leakage General Model for Enclosure SE Calculation of Aperture SE Combination of Multiple Apertures SE of Screen Meshes Conductive Glass Waveguide-Below-Cutoff Effect Honeycomb Air Filters Component Penetrations (Fuses, Switches, Meters, Displays, etc.) EMI Gaskets/Corrosion Control