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EMC

EMC. Mohamed Mokdad Ecole d’Ingénieurs de Bienne. Agenda. Current situation EMC Theorie Equipement interaction Sprectrum allocation National & International The twisted pair. Why EMC?.

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EMC

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  1. EMC Mohamed Mokdad Ecole d’Ingénieurs de Bienne

  2. Agenda • Current situation • EMC Theorie • Equipement interaction • Sprectrum allocation • National & International • The twisted pair

  3. Why EMC? • WHAT IS EMC?ElectroMagnetic Compatibility: With the proliferation of electronic systems in every aspect of our daily lives, there inevitably comes the problem of compatibility. Listening to the news on AM radio while using an electric razor should not be a problem, as it was in days gone. • WHY DO WE NEED EMC?If EMC design practices are adhered to by both the razor and the radio manufacturers, then listening to the news on an AM radio, while using an electric razor, presents no problem.Also, worldwide governmental regulations prohibit electronic products from emitting or being susceptible to, Electro-Magnetic Interference.

  4. Routers ISP1 ISP2 Edge Corporate Point-to-point Microwave Core Transport ADM ATM Switch/ IP giga-router PSTN/ISDN Internet ATM/FR Access Netzwerk-Architektur Transport

  5. Current access technologies • Wired • Analog / twisted pair • Digital / twisted pair • CATV • xDSL • Powerline • Wireless • WLL • Mobile ?

  6. The EMC issues • EMC • Very critical (Very costly in manufacturing) • Electromagnetic Pollution • Spectrum allocation • Licencing process • Limited ressource • E.g. OFCOM role in UMTS

  7. EM waves

  8. EM Fields Principles • Antenna receives all signals in the air • Depending on emitted power and • Cabling acts as antennas • In receiving power and • In emitting power • Antenna is optimised for frequency ranges • Filtering helps selecting bands • E.g. Radio station selection

  9. Spectrum and media • Wireless • Services are allocated frequency bands • Wired • Services have to be • Immune against neighbouring services • Not disturbing for neighbouring services • How • Cabling is radiating power • Cabling is capting electromagnetic fields

  10. Perturbations • Magnetic Flux = (Flux Density) x (Loop Area) • For a steady state signal of frequency f, the induced voltage in the loop is: Induced Voltage = j  2  x π x (f ) x (Flux) ; where  • π = 3.14159; and j denotes 90 degree phase angle • f = Frequency of the magnetic field

  11. Induction Concept

  12. E.g. 2G Mobile telephony Spectrum

  13. E.g. 3G Mobile telephony Spectrum

  14. Le régulateur

  15. Frequency vs. Wavelength wavelength x frequency = speed of light= 300 000 000

  16. Spectrum Allocation 10 000 cm  3 MHz

  17. EMC Design • Sprectrum optimised allocation • Global coordination (ITU) • Cabling optimisation (Immune/No Radia.) • Coupling reduction • Design and emitted Power (Reach range) • Filtering – Costly by manufacturing • Passive • Active

  18. Analogique ISDN HDSL 2 paires HDSL 3 Paires ADSL VDSL HDSL 1 paire Spectrum usage in access network 0 -20 -40 -60 Densité spectrale [dBm/Hz] -80 -100 -120 -140 1 10 100 1000 10000 100000 Fréquence [kHz]

  19. An Example: The Twisted Pair

  20. Tight Twisting

  21. The Result When current flows in a wire, an electromagnetic field is created which can interfere with signals on adjacent wires. As frequency increases, this effect becomes stronger. Each pair is twisted because this allows opposing fields in the wire pair to cancel each other. The tighter the twist, the more effective the cancellation, and the higher the data rate supported by the cable. Maintaining this twist ratio is the single most important factor in any successful UTP installation.

  22. Definitions • dB • R [dB] = 10 log10 A/B-3 dB ► A/B = ½ 10-3/10 = A/B • dBm • x [dBm] = 10x/10 [mW]10 dBm ► 10 mW20 dBm ► 100 mW • Log2(X) = Log10(X)/Log10(2)

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