Practical EMC and EMI Control for Engineers and Technicians
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Transcript of Practical EMC and EMI Control for Engineers and Technicians
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Practical EMC and EMI Control for Engineers
and Technicians
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Oops ...
Falklands war: HMS Sheffield turned off the missile warning radar - interfered with the satellite communication system. Sunk by a missile
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… oops!
Feb ’99: DC 10 approaching JFK. Banked left, almost caused a crash. CD player in 1st-class suspected.
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Structural Engineering“ … the art of modelling materials we do not
understand, into shapes we cannot precisely analyse, to withstand forces we cannot properly assess, in such a way that the public at large has
no reason to suspect the extent of our ignorance”.
(past Chairman of the Scottish branch of the Institute of Structural Engineers)
Sound Familiar?
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Vocabulary: EMC vs EMI
EMI - Electromagnetic Interference
» This is the PROBLEM
EMC - Electromagnetic Compatibility
» This is the SOLUTION
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Intermittent EMI Sources
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The Need for Standards Standards are needed to control/limit interference
from electronic devices Standards are also needed to make electronic
devices less susceptible to interference Various countries implemented their own
standards Any manufacturer wanting to market goods into
that country, has to comply with the standards
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EMC - the issues
Controlledoutptuts
Control/signalinputs
Disturbing or emitted
surges
Radiated or conducted RF,
emitted harmonics
Radiated EMD
Susceptibilityto EMD
Radiationfrom
outputs
Susceptibilityto EMD
Earth coupling/ bonding
problems
PQ phenomena
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Electromagnetic disturbances(any electromagnetic phenomenon which may degrade performance, without regard
to frequency or coupling method)
Supply voltage» interruptions» dips» surges» waveform distortion» fluctuations
slow rms variations rapid rms variations (flicker)
» Voltage unbalance» Frequency variations» DC in AC networks» Power-line carrier signaling
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Electromagnetic Disturbances Transient overvoltages
» supply lines» signal lines» control lines
lightningswitchingESD (electrostatic discharge)
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Electromagnetic Disturbances
Radio frequency fields» pulsed (radar)» modulated» continuous» coupled directly to equipment» coupled into connected cables
LF magnetic or electric fields NEMP (Nuclear Electromagnetic Pulse)
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Radiated Emissions (RE)
POWERSIGNALS
Conducted Emissions (CE)
POWER
SIGNALS
NOISE
CURRENT
Radiated
Conducted
Emissions
Susceptibility / Immunity
Radiated Susceptibility (RS)
POWERSIGNALS
DISTURBANCE
SIGNAL INJECTED
Conducted Susceptibility (CS)
POWER
SIGNALS
EMC Testing Categories
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Electromagnetic susceptibility The inability of a device, equipment or system to
perform without degradation in the presence of an electromagnetic disturbance
ORImmunity
(to electromagnetic disturbances) The ability of a device, equipment or system to
perform without degradation in the presence of an electromagnetic disturbance
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The compatibility gap
ValvesTransistors
ICs
SwitchgearRadio/Radar/
TV
CellphonesIndustrial
electronics
Decreasing immunity
Increasing emission
EMC Directive
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Emission, immunity & compatibility
Immunity level
Immunity limit
Emission level
Emission limit
Compatibility level
Immunity margin
Emission margin
Compatibility margin
Design margin
Design margin
Independent variable
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Considerations Consequences of EMI
» catastrophicdeath; major injuries; downstream consequences
» criticalminor injuries; extensive damage
» majorminor permanent damage
» minortemporary performance loss
» inconsequentialloss of performance within tolerance;
no human intervention needed
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Test result classification Normal performance within specified limits temporary degradation or loss of function; self-
recoverable temporary degradation or loss of function; requires
human intervention or system reset degradation or loss of function due to physical
damage; software or data corruption
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Levels of Compliance
Self Compatibility
SpecialRequirements
• Harsh Environment• Exceeds Standards• Environment Dominates
• Functional• Just making it work• No EMC design rules
• Self Imposed• Improved Integration / Functionality• Basic EMC design rules• Minimum Specification / Standards
Contractual Compliance
• Electrical & EM Environment (E3)• To Specification• EMC Engineering• Mandatory Testing
Minimum Engineering / In-house standard
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Areas of EMC Engineering Application
PCB’s» Most subtle, but very cost effective
Circuits and Filters» Added circuitry to contain EMI» Adds cost but a necessity for good EMC design
Screening» Enclosures and cables» Brute force - least cost effective
Grounding» Applicable to all three areas above
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DO YOU WANT TO KNOW MORE?
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