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ELECTROMAGNETIC INTERFERENCE AND COMPATIBILITY

ELECTROMAGNETIC INTERFERENCE AND COMPATIBILITY. By Dr. Sisir K Das, Head of EMC Chief Editor of EMC Journal, SEMCE(I) 2nd Cross Road, CIT Campus, Taramani Chennai - 600 113 <sisirdas@hotmail.com>. DEFINITIONS. EMI:

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ELECTROMAGNETIC INTERFERENCE AND COMPATIBILITY

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  1. ELECTROMAGNETIC INTERFERENCE AND COMPATIBILITY By Dr. Sisir K Das, Head of EMC Chief Editor of EMC Journal, SEMCE(I) 2nd Cross Road, CIT Campus, Taramani Chennai - 600 113 <sisirdas@hotmail.com>

  2. DEFINITIONS • EMI: is a phenomenon in which the production of RF energy causes an unwanted response or malfunction in an electronic equipment. • Sources: Natural - Lightning, Electrostatic Discharge (ESD) Manmade-Electric switches, high power communication /radar, transmitters, power lines, automobiles, Arc welders, computers and so on. • Victims: Receivers, microprocessors, industrial controls, medical devices, etc.

  3. Ship Radio & TV Broadcast Lightning Radar Power Line Handy Talkie Tele communications Mobile Radio Ignition Conducted noise Electric Motors AC power circuit Electronic equipment is subjected to a variety of electromagnetic interference sources. Careful design is required to guarantee compatibility with environment- Intersystem EMI RE CE

  4. EXAMPLE - Intersystem EMI Electric field coupling Antenna Magnetic field coupling Conductive coupling Common impedance coupling Oscillator Speaker RF Amplifier Mixer IF Amplifier Detector Audio Amplifier Power Supply

  5. 2  A 20dB/decade 2A  f1 / f A 40dB/decade 2A  f1 / f . f2 / f T f2 tr 0 f1 tr 1/  1/ tr sinpf  sinpftr V = A -------- --------- pfpftr  is the width at 50% height V is peak voltage Frequency band is control by fastest switching edge For 0f f1, V = 2 A For f1 <f f2 ,V = 2A f1/f For f > 1/ptr f1 f2 V = 2At ---- x ----- f f NOISE COMPUTATION IN FREQUENCY DOMAIN

  6. Coupling Path Victim of EMI EMI Source (Emitter) (Media) (Receptor) A BASIC EMI SITUATION Impedance? Impedance? Impedance? Voltage measuring device - high impedance circuit Voltage generative device - high impedance circuit E-field source/victim - high impedance circuit Current measuring device - low impedance Current generating device - low impedance H-field source / victim - low impedance

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