The document provides an overview of electromagnetic interference (EMI) and electromagnetic compatibility (EMC). It defines EMI and EMC, discusses sources of EMI including natural and man-made sources. Case studies of accidents caused by EMI are presented. Techniques for controlling EMI such as grounding, shielding and filtering are described. Military and civilian EMC standards are also discussed. The document concludes that EMC means that equipment operates correctly in the presence of EMI without itself causing intolerable interference.
6. Accident at Foundry Plant
6
A foundry worker died when the
radio-controlled overhead transporter
dropped a few tons of liquid metal on
him
Cause: an accidental signal from a
radio transmitter was interpreted by
the automatic system as the
legitimate order to get rid of the load
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7. Blackhawk Crashes
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Between 1981 and 1987, five US Blackhawk
army helicopters crashed and killed or injured
all on board when flew too near radio
broadcast transmitters
Cause: insufficient immunity of flight (on-
board) control electronic sub-system against
high intensity radiated fields (HIRF) that
produced uncommanded movements while
flying past radio broadcast towers.
(Source: NASA Reference Publication 1374 July 1995)
8. Unintended Missile Launch
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During a B-52 missile interface
unit test, an uncommanded
missile launch signal took place.
Cause: One of the contributing
factors was crosstalk in the
systems wiring.
The outcome was a yearlong
redesign and test effort
(Source: NASA Reference Publication 1374, July 1995)
9. Some other examples
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Runaway Wheelchairs
Some powered wheelchairs experienced
unintentional movements when police or fire
transmitters were activated nearby.
Although no fatal injuries have been reported,
Authorities have ordered manufacturers of
motorized wheelchairs to shield them from EMI and
to educate users on the potential EMI hazards.
Tornado Fighter Case
A West German Tornado fighter crashed after flying too close to a powerful
Voice of America (Radio) transmitter, in 1984 near Munich, Germany.
(Source: NASA Reference Publication 1374 July 1995)
12. Introduction
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Life of individuals / society is increasingly dependent on errorless
functioning of numerous systems:
Emergency telecommunication systems
Air, maritime, land transportation systems
Safety systems, etc.
Most of such critical systems are controlled by electronic sub-
system hardware or software
EMI can greatly affect the functioning if not controlled properly
13. Definitions
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Electromagnetic interference (EMI) is electromagnetic
energy that adversely affects the performance of
electrical/electronic equipment by creating undesirable
responses or complete operational failure
Electromagnetic compatibility (EMC) is the ability of
electrical or electronic equipment/systems to function in
the intended operating environment without causing or
experiencing performance degradation due to intentional
EMI
14. Difference
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Electromagnetic interference is the degradation
in the performance of a device due to the fields
making up the electromagnetic environment
Electromagnetic compatibility is achieved when
a device functions satisfactorily without
introducing intolerable disturbances to the
electromagnetic environment
EMI/EMC relationship: We control EMI in order to achieve EMC
16. Sources of EMI
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The sources of EMI can be broadly classified into two
groups
Natural sources of EMI
EMI can be caused by natural phenomena
such as electrical storms, rain particles , solar and interstellar
radiation
Manmade sources of EMI
EMI can be caused by man-made sources (Intentional, Unintentional)
Unintentional like commercial radio and telephone communications
Intentional (Jamming, EMP Bombs)
18. EMI depends on what?
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EMI effects depend on
System emissions
System immunity
Degree of coupling
Emission / Source
(Offending
apparatus)
EM Coupling
Immunity
(Victim / Susceptible
apparatus)
19. Effects of EMI
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Sources / Emitters
Radio transmitters
Switching power converters
Motors
High speed digital electronics
Victims / Susceptible equipment
Radio receivers
Detectors
Sensors
Low level analog electronics
Coupling Mechanisms
Conducted
Radiated
Crosstalk
20. Effects of EMI
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EMI can cause malfunctioning of any electronic system
component, especially of integrated circuits
A malfunctioning component can disrupt the operation of
a subsystem or system
Such a disruption in safety-related applications can
provoke an accident or catastrophe
The EMI/EMC problems have been ‘discovered’ first in
military applications in 1950’s and now are more and
more being suffered in civilian applications too
22. EMI control techniques
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To control or suppress EMI, some common
means employed in the design process are
Grounding
Shielding
Filtering etc.
23. Grounding
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GROUNDING is a technique that provides a low
resistance path between electrical or electronic
equipment and the earth or common reference low
impedance plane to bypass fault current or EMI signal
24. Shielding
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The main objective of shielding is to restrict radiations to a
specified region to prevent it from entering into susceptible
devices
The quality of shielding is expressed in the form of shielding
effectiveness of the material.
The shielding of materials can be solids, screens and braids.
They can be in the form of boxes, partitions, cables and
connector shields
26. Some Common Practices
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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
27. EMC Standards
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Military Standards
Military EMC standards are made in order to ensure
system-to-system compatibility in the real time military
environment
MIL-STD 461 and 462
Civilian Standards
The civilian EMC standards are applicable for equipment
used for commercial, industrial and domestic applications
International Special Committee on Radio Interference (CISPR)
Federal Communication Council (FCC), USA
Pakistan Telecommunication Authority (PTA), Pakistan
28. Conclusion
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EMI is a phenomenon while EMC is an
equipment characteristic or a property not
to generate EMI above a certain limit and
not to be affected or disturbed by EMI
The statement "Live and let live" is the best
way to describe EMC
30. References:
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[T1 Telecom Glossary 2000, Radio Regulations 2000]
NASA Reference Publication 1374 July 1995
Armstrong K: EMC-related functional safety; ITEM update 2001, p. 52-59
EUROPEAN EMC Directive
(http://europa.eu.int/comm/enterprise/electr_equipment/emc/guides/english.
pdf)
EUROPEAN RTTE Directive (http://europa.eu.int/eur-
lex/pri/en/oj/dat/1999/l_091/l_09119990407en00100028.pdf)
IEEE Electromagnetic Compatibility Society: http://www.emcs.org/
IEE Guide to EMC and Functional Safety, IEE September 2000 (free)
http://www.iee.org/Policy/Areas/Emc/index.cfm
International Electrotechnical Commission (www.iec.ch )
International Telecommunication Union (www.itu.int)
Mannon J, Johnson E: Radio Waves Spell Trouble for Industry; New
Scientist, 5 May 1983
Moroñ W: Nature and Technology: improving relations; in Struzak R (Ed.)
Global Communications Asia 1997, ISBN 0946393869, p. 259-263
