emc and emi in aircraft and real time

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2. INTRODUCTION:
 Electro magnetics (EM) is a branch of physics or electrical engineering in
which electric and magnetic phenomena are studied.
 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.
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3. EM Signal:
E=Electric field
B=Magnetic field
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E
B

4. ELECTRO MAGNETIC
INTERFERENCE
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Example:
Electromagnetic
interference in
TV signal

6. BASIC ELEMENTS OF EMI
SITUATION
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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 medium is to be made as inefficient as possible.

7. CLASSIFICATION OF EMI:
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8. RADIATED INTERFERENCE
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Narrow band interference usually arises from intentional transmissions such as radio
and TV stations, pager transmitters , cell phones etc. It is a high frequency operation .
Broad band interference usually comes from incidental radio frequency emitters.
These includes electric power transmission lines, electric motors etc. It is a low
frequency operation

9. CONDUCTED INTERFERENCE
 Conducted electromagnetic interference is caused by the physical contact of the
conductors as opposed to radiated EMI, which is caused by induction (without
physical contact of the conductors).
 Electromagnetic disturbances in the EM field of a conductor will no longer be
confined to the surface of the conductor and will radiate away from it.
 This persists in all conductors and mutual inductance between two radiated
electromagnetic fields will result in EMI
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10. Differences between conducted and
radiated interference
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12.  Intra system EMI
causes
 Inter system EMI
causes
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13. 
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Effects of EMI
Momentary disturbance in TV and radio reception due to
operation of mixer-grinder/electric shavers/a passing vehicles
etc
Reset of computers and loss of data.
Change of setting of status of control equipment.
Malfunctioning of flight controlling system due to use of
laptop by passenger.
Biological hazards.

14. Sources of EMI:
The sources of EMI can be broadly classified into two groups
 Natural sources of EMI
example: lightning
 Manmade sources of EMI
example: commercial radio and telephone communications
In specific we can classify as
 Functional: EMI can originate from any source designed to generate
electromagnetic energy and which may create interference as a normal part of its
operation
 Incidental: EMI can originate from man made sources .These sources are not
designed specifically to generate electromagnetic energy but which do in fact cause
interference.
 Natural: EMI can be caused by natural phenomena, such as electrical storms ,
rain particles , solar and interstellar radiation.
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Fig:1
Fig1-lightning hitting
between the
Buildings.

16. EMI CONTROL TECHNIQUES:
To control or suppress EMI, the
three common means employed
in the design process are
Grounding
Shielding
Filtering
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17. Grounding:
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Grounding is the establishment of an electrically conductive
path between two points to connect electrical and electronic
elements of a system to one another or to some reference point,
which may be designated as the ground. .
An ideal ground plane is a zero-potential ,zero-impedance body
that can be used as a reference for all signals in associated
circuitry and to which any undesired current can be transferred
for the elimination of its effects.


18. The purpose of the ground plane
 The main purpose is to provide low grounding
impedance.(the effective resistance of an electric circuit
or component to alternating current, arising from the
combined effects of ohmic resistance and reactance.)
 The secondary purpose is to act as a shield.
 < 1 MHz: Single-point grounding
 > 10 MHz: Multi-point grounding
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Bonding is the establishment of a low-impedance path
between two metal surfaces. Grounding is a circuit concept,
while bonding denotes the physical implementation of that
concept.
Bonds provide protection from electrical shock,
power circuit current return paths, and antenna ground
plane connections, and also minimize the potential
difference between the devices. They have the ability
to carry large fault current.

21. Shielding:
 The purpose of shielding is to confine radiated energy to a specific region
or to prevent radiated energy from entering a specific region.
 Shields may be in the form of partitions and boxes as well as in the form of
cable and connector shields.
 Shield types include solid, nonsolid (e.g., screen), and braid, as is used on
cables. In all cases, a shield can be characterized by its shielding
effectiveness.
 The shielding effectiveness is defined as
SE=10 log incident power density
transmitted power density
 where the incident power density is the power density at a measuring point
before a shield is installed and the transmitted power is the power density
at the same point after the shield is in place.
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22. Shielding:
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23. Filtering:
 An electrical filter is a network of lumped or distributed constant resistors,
inductors, and capacitors that offers comparatively little opposition to
certain frequencies, while blocking the passage of other frequencies.
 Filter provides the means whereby levels of conducted interference are
substantially reduced.
 The most significant characteristic of a filter is the insertion loss it provides
as a function of frequency.
 Insertion loss is defined as
IL=20 log V2/V1
 Where V1 is the output voltage of a signal source with the filter in the
circuit,
 V2 is the output voltage of the signal source without the use of the filter.
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24. Filtering:

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25. ELECTRO MAGNETIC
COMPATIBILITY
 Electromagnetic compatibility (EMC) is the branch of
electrical science which studies the unintentional generation,
propagation and reception of electromagnetic energy with
reference to the unwanted effects (Electromagnetic
interference, or EMI) that such energy may induce.
 The goal of EMC is the correct operation, in the same
electromagnetic environment, of different equipment which
use electromagnetic phenomena, and the avoidance of any
interference effects.
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26. ECM
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.
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.
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27. The methodologies used 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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28. COUPLING MECHANISM:
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The basic arrangement of noise source, coupling path and victim, receptor or sink is
shown in the figure below. Source and victim are usually electronic hardware devices,
though the source may be a natural phenomenon such as a lightning strike, electrostatic
discharge(ESD)

29. There are four basic coupling mechanism :
1. Conductive
2. Capacitive
3. Magnetic/Inductive
4. Radiative
Conductive coupling:
Conductive coupling occurs when the coupling path between the source and the
receptor is formed by direct contact with a conducting body, for example a
transmission line, wire, cable or metal enclosure.
. Capacitive coupling:
 Capacitive coupling occurs when a varying electrical field exists between two
adjacent conductors typically less than a wavelength apart, inducing a change
in voltage across the gap.
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30. Radiative coupling:
 Radiative coupling or electromagnetic coupling occurs when source and
victim are separated by a large distance, typically more than a wavelength.
 Source and victim act as radio antennas: the source emits or radiates
an electromagnetic wave which propagates across the open space in
between and is picked up or received by the victim.
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31. Layout design
 In simple non-critical devices, the layout design is often
enough.
◦ Especially, if there are no cables to/from the device.
 About 90 % of post-design EMC-problems are caused
by poor layout design!
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32. Good layout design
 Split the system in parts
 Choose grounding points well and minimize the
grounding impedance.
 Remember that every conducting part can carry
interfering currents!
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33. Splitting the system in parts
 Decide which parts are critical vs. non-critical.
 Place the parts which are neither sensitive nor
sources for interference, into separate locations
even on their own circuit boards.
 For example, linear power supplies, non-clocked
logic circuits and power amplifiers are usually
immune to interference.
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34. Ferrite chokes
 Very common in data cables.
 Adds series inductance to cable.
 Effective on frequencies 1-1000 MHz (approximately).
 Disadvantage: relatively low attenuation (10-20 dB).
 Advantage: easy to add afterwards.
 Ferrite choke attenuates also fast transients caused by
ESD.
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36. Electromagnetic Interference in airplane
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37.  EMI is a major problem in modern digital avionics
systems, and it is getting worse.
 The most common Natural EMI source is
Lightning.
 Three basic EMI sources:
1. Transients
2. 400 Hz power
3. Radio Frequency
Ten specific EMI sources:
1. Electrostatic 6. Magnetic field(400Hz)
2. 1 MHz Resonant frequency 7. Computer clock/Data signals
3. Voltage potential drop 8. Switching Regulators
4. Inductive switching transient 9. HF/VHF
5. Electric field (400 HZ) 10. Super high frequency
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38. 
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39. EMC CRITICALITY CATEGORIES
Category 1:
Electromagnetic compatibility (EMC) problems that
could result in loss of life, loss of vehicle , Mission abort,
or unacceptable reduction in system effectiveness.
Category 2:
EMC problems that could result in injury, damage to
vehicle, or reduction in system effectiveness that could
endanger mission success.
Category 3:
EMC problems that could result in annoyance, minor
discomfort, or no reduction in system effectiveness.
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40. Examples of alleged Electro-magnetic
interference (EMI) based incidents
●CRJ200 First Officer reports compass system
malfunctions during initial climb. When passengers are
asked to verify that all electronic devices are turned off the
compass system returns to normal.
●MD88 crew has problem on VHF com radio. The static
stopped when the passengers were asked to turn off their
electronic devices
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42. EMI management?
●Today aircraft type designs such as the Boeing 787,
Airbus A350 and A380 are designed taking EMC into
account
Today cabin systems:
●Equipment qualification for new systems is constantly
updated –where equipment qualification for installed
aircraft systems stay on the original qualified status.
●System configuration and age of the aircraft defines
qualification level of the equipment on board
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43. Guidance and regulations
Guidance Material:
●RTCA/DO -313 Certification Guidance for Installation of Non-
essential, Non- required Aircraft Cabin Systems & Equipment
●RTCA/DO-160 Environmental Conditions and Test Procedures for
Airborne Equipment
●EUROCAE ED14 Environmental Conditions and Test Procedures for
Airborne Equipment
●RTCA/DO-294 Guidance on Allowing Transmitting Portable
Electronic Devices (T-PEDS) on Aircraft
●EURAOCAE ED-130 Guidance for the use of Portable Electronic
Devices (PEDs) on Board Aircraft
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44. NEED FOR EMC STANDARDS:
 The EMC standards are required for trouble free co-existence
and to ensure satisfactory operation.
 They are also required to provide compatibility between
electrical, electronic, computer, control and other systems.
 Standards are required as manufacturer-user interaction and
user’s knowledge on EMI are limited.
 They are also required for establishing harmonized standards
to reduce international trade barriers and to improve product
reliability and life of the product.
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45. EMC STANDARDS:
These are of two types
 Military Standards :
Military EMC standards are made in order to ensure system-to-system
compatibility in the real time military environment. Military standards
are more stringent than civilian standards. Most of the military standards
are broadly based on MIL-STD 461 and 462.
 Civilian Standards:
The civilian EMC standards are applicable for equipments used for
commercial, industrial and domestic applications. The emission
standards are specified to protect the broadcast services from
interference..
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46. ADVANTAGES OF EMC
STANDARDS
The advantages are:
Compatibility, reliability and maintainability
are increased.
Design safety margin is provided.
 The equipment operates in EMI scenario
satisfactorily.
 Product life and profits are increased.
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47. EMC STANDARDS IN DIFFERENT
COUNTRIES:
Sl
no
Standard
name
Meaning Country
1 CISPR(IEC) Committee International
Special
Perturbations Radioelectriques
– Europe
International
committee
2 FCC Federal Communications
Council
USA
3 SAE Society of Automobile
Engineers
Trade Association
Technical Committee
4 VG Military standard Germany
5 VDE Verband Deutscher
Electrotecknikev
Germany
6 ICT EMI measurements &
measuring apparatus
India
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48. CONCLUSION:
 The fact that EMI was recognized as a problem of significant practical
concern three-quarters of a century ago generally suggests that by now this
must be a well-understood field, and solutions to problems are
consequently a routine technology.
 The position is that a great deal of theoretical, analytical and practical
information is today available to understand EMI, have graduated from the
traditional EMC fixes based on trail and error approach.
 EMC has developed into a very interdisciplinary subject.
 Many problems and topics in this field are how ever still open for further
research.
 There is aerial need for further research on several aspects of EMC .These
include characterization of interferences, measurements techniques etc...
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49. REFERENCES:
 “aircraft digital electronics and computer system ” a textbook by MIKE
TOOLY.
 “DIGITALAVIONICS SYSTEM ” a textbook by CARY.SPITZER
 http://www.arrl.org/tis/info/rfigen.html RadioFrequency
Interference/ElectroMagnetic Interference, ARRL
 http://www.kyes.com/antenna/interference/tvibook.html
INTERFERENCE HANDBOOK
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