Overview of EMI / EMC
What is EMI and EMC ?
™ An electromagnetic disturbance which may
degrade the performance of an equipment (device,
system or sub-system) or causes malfunction of
the equipment, is called electromagnetic
interference (EMI).
™ Electromagnetic compatibility (EMC) is a near
perfect state in which a receptor ( device , system
or subsystem) functions satisfactorily in common
electromagnetic environment, without introducing
intolerable electromagnetic disturbance to any
other devices / equipments / system in that
environment.
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SAMEER Kolkata Centre
EMI-EMC Division
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Basic elements of EMI situations
Source /
Emitter /
Culprit
Coupling
Path /
Medium
Receiver /
Receptor /
Victim
™ Interference occurs if the received energy causes the
receptor to function in unwanted manner.
™ Whether the receiver is functioning in wanted or unwanted
manner, depends on the coupling path as well as the
source and victim.
™ The coupling path is to be made as inefficient as possible.
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EMI-EMC Division
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Causes of EMI
™ Sources
™ Refrigerator, washing machine, electric motors.
™ Arc welding machine.
™ Electric shavers, AC, computers.
™ Fast switching digital devices, ICs.
™ Power cords of computers, UPS etc.
™ Air craft navigation and military equipments
™ Victims
™ Communication receivers.
™ Microprocessors, computers.
™ Industrial controls.
™ Medical devices.
™ House hold appliances.
™ Living beings.
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EMI-EMC Division
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Effects of EMI
¾ Momentary disturbance in TV and radio reception
due to operation of mixer-grinder / electric shavers
/ a passing vehicle etc.
¾ Reset of computers and loss of data.
¾ Burn out of sensitive cells / components.
¾ Change of setting of status of control equipments.
¾ Failure of pace maker implanted in a patient due to
a ‘walkie talkie’.
¾ False initiation of electro explosive detonator.
¾ Malfunctioning of flight controlling system due to
use of laptop by passenger.
¾ Biological hazards.
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Radiated Emission and Susceptibility
Noisy
Component
Radiated Emission
Noisy
Component
Radiated Susceptibility
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Conducted Emission and Susceptibility
Noisy
Component
Conducted Emission
Noisy
Component
Conducted Susceptibility
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Purpose and Methodology for EMC System
A system is said to be electro magnetically compatible if :™ It doesn't cause interference with other system .
™ It is not susceptible to emissions from other systems.
™ It doesn’t cause interference with itself.
The methodologies to prevent EMI are
™ Suppress the emissions at source point, best method to
control EMI .
™ Make the coupling path as inefficient as possible.
™ Make the receiver less susceptible to emission.
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EMI-EMC Division
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Common and Differential Mode Noise
L1
(P)
(VCC)
L2
(N)
(VEE)
Idm
Idm
Icm/2
Icm/2
Vdm
Electronic
Circuits
Icm
(Gnd)
™ CM : Interference signal in two lines are
unidirectional and return through ground.
™ DM : Interference signal in two lines are
oppositely directed and thus no ground current
path is required.
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EMI-EMC Division
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EMI control techniques at source
Important techniques to control EMI at source point are
‰
‰
‰
‰
Proper Grounding – single point, multi point or hybrid
grounding depending upon the frequency of operation.
Shielding – Metal barrier is used to suppress coupling of
radiated EM energy into the equipment.
EMI Filtering - used to suppress conducted interference
on power, signal and control lines.
PCB layout – Proper PCB design from the early design
stage is required.
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EMI-EMC Division
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Method of noise coupling
Typical modes of noise coupling are
¾ Conductive coupling through cables.
¾ Coupling through common impedance.
¾ Coupling by radiated E and H field.
¾ Ground loop coupling.
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Objectives of EMC Standards
™ EM spectrum protection.
™ Adequate power quality.
™ Compatibility between collocated electrical and
electronic systems for trouble free operation .
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Standards setting Institutions
™ DOD
-
Department of Defence (USA) -- Immunity and
™ IEC
-
International Electrotechnical Commission (EU)
™ CISPR -
Emission MIL standards
Immunity standards
International Special Committee on Radio
Interference Operating under IEC. -- Emission
Standards.
™ FCC
-
Federal Communication Commission ( EU )
---
Emission standards.
™ BSI
™ VDE
-
British Standard Institution ( UK ) -- Emission
standards.
Verband Deutscher Electrotechniker (Germany) Emission standards.
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Important Immunity Standards
™ IEC 61000-4-2 :
™ IEC 61000-4-3 :
™
™
™
™
™
Electrostatic Discharge immunity test
Radiated radio frequency EM field
immunity test
IEC 61000-4-4 : Electrical fast transient / Burst immunity
test
IEC 61000-4-5 : Surge immunity test
IEC 61000-4-6 : Conducted radio frequency EM field
immunity test
IEC 61000-4-8 : Power frequency magnetic field immunity
test
IEC 61000-4-11 : Voltage Dips, short interruptions and
voltage variations immunity test
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EMI-EMC Division
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Important Emission Standards
™
™
™
™
™
™
™
™
™
CISPR 11 : Industrial, Scientific and Medical equipments
CISPR 12 : Automobiles
CISPR 13 : Audio visual and similar apparatus
CISPR 14 : Household and similar electrical appliances
CISPR 15 : Electrical Lighting and similar equipments
CISPR 22 : Information Technology equipments
FCC Part 15 : Radio Frequency Devices
FCC Part 18 : Industrial, Scientific and Medical equipments
IEC 61000-3-2 : Limits of harmonic current emission (< 16A
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per phase)
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