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Historical EMI/E 3 -Related Incidents Operation Restore Democracy (Haiti-1995) Air wings of USS America & USS Eisenhower replaced with men & helicopters of 10th Infantry Div. and 75th Ranger Regiment. Army aircraft not designed or tested for carrier operation, carriers required to turn off almost all communications and radar surveillance systems. USS Forrestal (Vietnam -1969) ZUNI rocket inadvertently launched by a ship radar 134 dead 27 aircraft destroyed $72M damage to ship ($335M in 2000 dollars) Largest Naval loss of life since WW II Pershing II Nuclear Missile (Germany) Missile motor exploded during routine maintenance Electrostatic discharge identified as the cause 3 dead Blackhawk Helicopter (Germany and USA - 1987) Several potentially fatal incidents and a fatal crash Suspected cause was interference from high power radio transmitters Entire fleet grounded for 3 months during investigation Extensive test and retrofit program necessary Courtesy of Jose Reza HMS Sheffield (Falkland Islands -1982) Hit by undetected EXOCET missile EMI caused degradation of surveillance radar 21 dead, Ship sank 4 days later
ELECTROMAGNETIC ENVIRONMENT EFFECTS (E 3 ) Performance degradation of receiver signal processing circuits Erroneous or inadvertent operation of electromechanical equipments, electronic circuits, components, ordnance, etc. Burnout or voltage breakdown of components, antennas, etc.
ELECTROMAGNETIC ENVIRONMENT EFFECTS (E 3 ) CONTINUED Unintentional denotation or ignition of electroexplosive devices, flammable materials, etc. Personnel Injuries
ELEMENTS OF EMI SOURCES OF EMI COUPLING VICTIM OF EMI
EMI CULPRIT AND VICTIM EMI Source CULPRIT VICTIM Signal Source COUPLING PATH Signal Receiver
CONDUCTED OR RADIATED COUPLING SOURCE COUPLING VICTIM
PRIMARY EMI INTERACTIONS EMI SOURCE (EMITTER) TRANSMITTERS PRIMARY COUPLING MECHANISM RADIATED ANT-ANT RADIATED ANT-CABLE ANT-CASE EMI VICTIM (RECEPTOR) RECEIVERS ELECTRONIC EQUIPMENT RADIATED CABLE-ANT CASE-ANT RECEIVERS ELECTRICAL & ELECTRONIC EQUIPMENT RADIATED CABLE-CABLE CABLE-CASE CASE-CABLE CASE-CASE CONDUCTED POWER LINES SIGNAL LINES GROUND ELECTRONIC EQUIPMENT
EXAMPLES OF NARROWBAND EMI UNITS Conducted Power W dbw dbm Voltage V dbv dbμv Current A dba dbμa Radiated Power Density W/m 2 dbw/m 2 dbm/m 2 Field Strength V/m dbv/m dbμv/m Magnetic Field (H) A/m dba/m dbμa/m Magnetic Flux Density (B) Tesla (Weber/m 2 ) Picotesla (pt) dbpt
EXAMPLES OF BROADBAND EMI UNITS Conducted Power dbm/khz Voltage dbμv/mhz Current dbμa/mhz Radiated Power Density dbm/m 2 /khz Field Strength dbμv/m/mhz Magnetic Field (H) dbμa/m/mhz Magnetic Flux Density (B) dbpt/mhz
Filter Affects on a Pulse V in T in T 1 V 1 V in T in F 1 V 1 = F 1 T in V in T 1 = 1/F 1
Electric-Field Strength vs. Transmitter Distance and ERP*
Walkie Talkie Crashes Equipment
EMI MITIGATION FOR OTHER SYSTEMS Radiated EMI Mitigation Shielding Circuit Design Cable Selection and Layout Conducted EMI Mitagation Grounding Filters, Ferrites, Isolation Transformers, Optical Isolators, etc.
TWO-BOX EMI SEVERAL MILLION COMBINATIONS! MANY WITH AN INFINITE RANGE OF VARIABLES.
MANIFESTATIONS Multiple Sites Battle Force - EME Site System Subsystem Equipment Mother Board PCB Aircraft, Ship or Building Fire-Control Radar, Control System Equipment Racks, Consoles R.F. Receiver, Medical Instrument Main Distribution to PCB Cards to Hold DIPS Components Component DIPS, CHIPS, Relays
COUPLING Conducted power or signal cable coupling Common-ground impedance common-mode coupling Field-to-Cable or Cable-to-Field common-mode coupling Field-to-cable or Cable-to-Field differential-mode coupling Cable-to-Cable differential-mode coupling Case Radiation-Case Penetration
CONDUCTED EMI EMI always start out at the culprit and ends up at the victim as a conducted signal regardless of what goes on between these two points!
Illustration of Common Mode Currents Power Source CMC 1 CMC 2 Load CMC IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 4. Illustration of Common Mode Currents
Illustration of Differential Mode Currents DCM1 Power Source Load DCM2 Figure 3. Illustration of Differential Mode Currents
Illustration of Common and Differential Mode Currents Power Source CMC 1 DMC 1 Load CMC 2 DMC 2 CMC IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 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
Common Mode Currents Resulting From Distributed Capacitance to Ground Power Source CMC 2 1 CMC 2 1 Load CMC 1 IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 6. Common Mode Currents Resulting From Distributed Capacitance to Ground
Common Ground Impedance Common Mode EMI Power Source CMC Load EMI CMC EMI' IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Figure 10. Common Ground Impedence Common Mode EMI
Controlling Conducted EMI Source Power Supplies Motors Inductive Loads High Level Analog Digital Signals Transmitters EM Environment Conducted EMI Victim Analog Equipment Digital Equipment Video Display Recorders Instruments Sensors Control Systems Receivers Applicable EMI Control Techniques Differential Mode Common Mode (Ground Loop) Power Filter Ferrites Isolation Transformers Translent Suppressors Signal Filters Ferrites Isolation Transformers Translent Suppressors Power Filters Ferrites Isolation Transformers Balanced Systems Float Inductor in Ground Signal Filter Ferrite Isolation Transformers Balanced Circuit Float Inductor in Ground Optical Isolator
SIGNAL RETURN? WHAT IS GROUND? CHASSIS REFERENCE? SAFETY WIRE REFERENCE? EARTH REFERENCE?
GROUNDING HIERARCHY
GROUNDING CONDUCTOR IMPEDANCE VS. FREQUENCY
Using Ferrites to Absorb Common-Mode EMI
PRINCIPAL RADIATION SOURCES ON PRINTED CIRCUIT BOARD Radiation from IC dips Logic families clock rates Radiation from ribbon cables Large single-layer board PCB card cage with back plane Multi-layer board
MAGNETIC FIELDS FROM A TWISTED PAIR OF CONDUCTORS (TRANSPOSITION) Area 2 I 1 I 2 Area 1 V ΔV2 ΔV1 R L I 2 I 1
REPRESENTATION OF SHIELDING PHENOMENA FOR PLANE WAVES E y Inside of Enclosure H z Incident Wave H z Outside World E y A H Reflected Wave E y H z E y Metal Barrier B Transmitted Wave E y Attenuated Incident Hz Wave Internal Reflecting Wave
PRINCIPAL BOX SHIELDING COMPROMISES Cover Plate for Access Status Indicator Lamp Holes or Slots for Convection Cooling Screw Spacing = Slot Radiation Forced Air Cooling Panel Meter Potentiometer Connectors Fuse Switch
PP47645A Some System EMC Fix Applications PP47645A