ATI's Grounding and Shielding for EMC Technical Training Short Course Sampler

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This three-day course is designed for technicians, operators, and engineers who need an understanding of all facets of grounding and shielding at the circuit, PCB, box or equipment level, cable-interconnected boxes (subsystem), system and building, facilities or vehicle levels. The course offers a discussion of the qualitative techniques for EMI control through grounding and shielding at all levels. It provides for selection of EMI suppression methods via math modeling and graphics of grounding and shielding parameters.
Our instructor will use computer software to provide real world examples and case histories. The computer software simulates and demonstrates various concepts and helps bridge the gap between theory and the real world. The computer software will be made available to the attendees. One of the computer programs is used to design interconnecting equipments. This program demonstrates the impact of various grounding schemes and different "fixes" that are applied. Another computer program is used to design a shielded enclosure. The program considers the box material; seams and gaskets; cooling and viewing apertures; and various "fixes" that may be used for aperture protection. .

There are also hardware demonstrations of the effect of various compromises and resulting "fixes" on the shielding effectiveness of an enclosure. The compromises that are demonstrated are seam leakage, and a conductor penetrating the enclosure. The hardware demonstrations also include incorporating various "fixes" and illustrating their impact.

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ATI's Grounding and Shielding for EMC Technical Training Short Course Sampler

  1. 1. Professional Development Short Course On: Grounding and Shielding for EMC Instructor: Dr. William G. Duff (Bill)ATI Course Schedule: http://www.ATIcourses.com/schedule.htm http://www.aticourses.com/intro_to_grounding_shielding.htmATIs Grounding and Shielding for EMC:
  2. 2. www.ATIcourses.comBoost Your Skills 349 Berkshire Drive Riva, Maryland 21140with On-Site Courses Telephone 1-888-501-2100 / (410) 965-8805Tailored to Your Needs Fax (410) 956-5785 Email: ATI@ATIcourses.comThe Applied Technology Institute specializes in training programs for technical professionals. Our courses keep youcurrent in the state-of-the-art technology that is essential to keep your company on the cutting edge in today’s highlycompetitive marketplace. Since 1984, ATI has earned the trust of training departments nationwide, and has presentedon-site training at the major Navy, Air Force and NASA centers, and for a large number of contractors. Our trainingincreases effectiveness and productivity. Learn from the proven best.For a Free On-Site Quote Visit Us At: http://www.ATIcourses.com/free_onsite_quote.aspFor Our Current Public Course Schedule Go To: http://www.ATIcourses.com/schedule.htm
  3. 3. What Is Ground?• Earth Ground• Power Ground• Signal ground• Safety Ground• Return• Reference Level
  4. 4. Ground Means any ReferenceConductor Used for a Common Return
  5. 5. Grounding Misuse and Myths• Reasons for Grounding Are Not Clear• The Word "Grounding" is Often Misused when other Words are Meant, such as: Connect to Bonding Return Path Earthing• Many Myths Exist, such as: "Lower Impedance is Always Better" "Use Grounds for Digital-Circuit Reference" "Use Separate Safety, Instrument & System Gnd.• Reasons for Grounding Are Not Clear
  6. 6. Grounding for EMC• Ground Circuits, Equipments, Systems, Cables, Shields• Common Mode and Differential Mode Coupling• Avoid Ground Loops• More Grounds are not Better
  7. 7. Interconnected Equipment Having 29Questions = 229 = 500,000,000 Answers
  8. 8. Effects of Shared Ground Impedance• Common Source or Common Ground Impedance Coupling• EMI and signal use same impedance• Shared impedance provides path for EMI to couple from a source to a victim.• Minimizing the shared ground impedane will help mitigate the problem.• A single point ground may help.
  9. 9. Common Ground Impedance Common Mode EMI CMC Power Source Load CMC EMI EMI IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 10. Common Ground Impedence Common Mode EMI
  10. 10. Illustration of Common Mode Currents CMC 1 Power Source Load CMC 2 CMCIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 4. Illustration of Common Mode Currents
  11. 11. Illustration of Differential Mode Currents DCM1 Power Source Load DCM2 Figure 3. Illustration of Differential Mode Currents
  12. 12. Illustration of Common and Differential Mode Currents CMC 1 DMC 1 Power Source Load CMC 2 DMC 2 CMC IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 5. Illustration of Common and Differential Mode Currents Illustration of Common and Differential Mode Currents Illustration of Common and Differential Mode Currents
  13. 13. PRINCIPAL RADIATION SOURCES ON PRINTED CIRCUIT BOARD Radiation from IC dips Logic families clock rates • Large single-layer board • PCB card cage with back plane • Multi-layer board Radiation from ribbon cables
  14. 14. Common Mode Radiated EMI Radiated EMI CMC 1 Power Source Load CMC 2 CMCIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 11. Common Mode Radiated EMI
  15. 15. Ground-Loop CouplingConverts Common Mode Voltage to Differential-Mode Voltage
  16. 16. Using Ferrites to Absorb Common-Mode EMI
  17. 17. Added Feed-Thru Capacitors -Help Reduce ESD and RF Susceptibility Note: Max Cap Value Must Support Data Bandwidth C < 1/ωR
  18. 18. Coupling Rejection Offered by Twisting Wire Pair
  19. 19. SHIELDING APPLIES TO ALL LEVELS• Components • Systems• Circuits • Cables• Functional Stages • Platforms• Equipments • Buildings
  20. 20. CONCEPTUAL ILLUSTRATION OF FIELD INTENSITIES VS. SOURCE TYPE AND DISTANCE High Current Corresponds to Low Current Corresponds to Low Impedance High Impedance High E Low E Monopole Eθ Eθ Loop Hθ Low H I High H Hθ V Near Far Near Far Field Field V Field Field High-Impedance Source Low - Impedance, Electric-Field Source and Wave Magnetic - Field Source and Wave
  21. 21. FIELD IMPEDANCE AS A FUNCTION OF DISTANCE FROM SOURCE
  22. 22. ELECTRIC FIELD VS SOURCE DISTANCE
  23. 23. SUMMARY Near Field Far FieldElectric Fields Plane Waves Are Generated for allZ > 377 OhmsRadiated From High Source Impedances forImpedance Sources Distance Greater ThanMagnetic Fields Approximately 1/6 of a WavelengthZ < 377 OhmsRadiated from LowImpedance Sources
  24. 24. REPRESENTATION OF SHIELDING PHENOMENA FOR PLANE WAVES Ey Inside of Enclosure Hz Incident WaveA Ey Transmitted Wave Ey B H Ey Attenuated Hz Incident Hz Ey Hz Reflected Wave Wave Internal Reflecting Outside World Metal Wave Barrier
  25. 25. SHIELDING EFFECTIVENESS (SE) SEdB = 20 log10(Eoutside/Einside) SEdB = 20 log10(Houtside/Hinside)where: E = Electric-field Strength H = Magnetic-field Strength SEdB = RdB + AdB where: RdB = Reflection Loss in dB AdB = Absorption Loss in dB
  26. 26. REFLECTION LOSS ( K + 1)2 ZW RdB = 20 log10 ,K = VSWR 4K Zb  Zw  ≅ 20 log10  , K ≥ 10  4 Zb Where : E Zw = wave impedance = H jω μ jω μ Zb = barrier impedance = = σ + jω ε σfor ω ε < < σ
  27. 27. REFLECTION LOSS (RdB) OF PLANE WAVES VS FREQUENCY 3kHz 30kHz 300kHz 3MHz 30MHz 300MHz 200 200 150 150 Copper 100 100 Iron* 50 Hypernick* 50 0 1kHz 10kHz 100kHz 1MHz 10MHz 100MHz 0 Radio Frequency Valid for thickness > 3 δ δ = Skin Depth * Permeability assumed constant with frequency
  28. 28. ABSORPTION LOSS, A Current Density 0.066 δ= mm f MHz μ r σ r δ t AdB = 8.68 t / δ = 131 t f MHz μ r σ r where t = thickness in mm f MHz = frequency in MHz μ r = permeability relative to copper σ r = conductivity relative to copper
  29. 29. ABSORPTION LOSS VS FREQUENCY
  30. 30. PRINCIPAL BOX SHIELDING COMPROMISES Holes or Slots Screw Spacing Cover Plate for Convection Cooling = Slot Radiation for Access Status Indicator Lamp Forced Air Cooling Panel Meter Potentiometer Connectors Fuse Switch
  31. 31. SLOT AND APERTURE LEAKAGE L t h  t << h Shield MaterialSE (dB) •  Log Frequency •λ / 2
  32. 32. Reducing Radiation Coupling by Shielding Cable Wires
  33. 33. To learn more please attend ATI course Grounding and Shielding for EMC Please post your comments and questions to our blog: http://www.aticourses.com/blog/ Sign-up for ATIs monthly Course Schedule Updates :http://www.aticourses.com/email_signup_page.html

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