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ELECTROMAGNETIC INTERFERENCE AND COMPATIBILITY (EMI/EMC) B.SUDHEER K.KRANTHI KUMAR [email protected] [email protected] Cell no: 99...
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ELECTROMAGNETIC INTERFERENCE AND COMPATIBILITY (EMI/EMC) B.SUDHEER

K.KRANTHI KUMAR

[email protected]

[email protected]

Cell no: 9985201865

cell no: 9985201865

III/IV E.C.E. M.V.G.R. COLLEGE OF ENGINEERING, VIZIANAGARAM

ABSTRACT:

The electromagnetic environment is the integral part of the world in which we live. Various apparatus such as radio and television broadcast stations, communication transmitters, and other radar and navigational aids radiate electromagnetic energy during their normal operation. These are intentional and unintentional radiations of electromagnetic energy into the environment. Many appliances, such as automobile ignition systems and industrial control equipment used in everyday life also emit electromagnetic energy although these emissions are not an essential part of normal operation. The electromagnetic environment created by these intentional and unintentional sources, when sufficiently strong, interferes with the operation of many electrical and electronics equipment and systems which degrades the performance of the system. Electromagnetic Interference is nothing but electromagnetic pollution. It is neither seen nor sensed nor audible and hence it is a salient threat.

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INTRODUCTION: EMI/EMC Engineering is a unique and specialized subject. It came into prominence with the tremendous advances in technology and proliferation of variety of electronic instruments and devices which produce electromagnetic emissions. In fact, the world is highly saturated with such emissions from a huge variety of sources. The effect of such sources is spread throughout the electronic spectrum. EMI is defined as the undesirable signal which causes unsatisfactory operation of a circuit or device. EMC is defined as the ability of electronic and communication equipment to be able to operate satisfactorily in the presence of interference and not be a source of interference to nearby equipment. Electromagnetic susceptibility (EMS) is the capability of a device to respond to EMI.

Basic Types of EMI: These are of two types. They are a) Intra-EMI: EMI is said to be intra-EMI if the functional characteristics of one module within an electronic equipment or system is disturbed due to EMI from another module. b) Inter-EMI: EMI is said to be inter-EMI if the functional characteristics of one equipment is disturbed due to EMI generated by equipment. The various methods of electromagnetic interference coupling between an emitter and a receptor are as follows: (1) Radiation coupling, (2) conduction coupling, and (3) combination of radiation and conduction. Let us consider how EMI can travel from its source to a receptor, which may be a device or equipment or system. We can use the term receptor to convey

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that it receives the EMI figure illustrates various mechanisms in which EMI can travel from its source to there receptor. These are: Ø

Direct

path

from

sources

to

receptor (path1) Ø

Direct

radiations

from

source

picked up by the power cables or the signal/control cables connected to the receptor, which reaches the receptor via conduction (path 2) Ø

EMI radiated by the electric power

,signal ,or control cable of the source (path 3& 4) Ø

EMI directly conducted from its

source to the receptor via common electric power supply lines, or via common signal/control cables (path 5) Ø

The EMI carried by various power/signal/control cables connected to the

source, which gets coupled to the power/signal/control cables of the receptors.

SOURCES OF EMI: The

sources

of

electromagnetic interference

are

both

natural and human-made. Natural sources include sun and stars, as well as phenomena

such

atmospherics,

lightning,

thunderstorms, electrostatic On

the

as

and discharge.

other

hand,

electromagnetic

FIG. Other aspects of EMC: (a) electrostatic discharge (ESD), (b) electromagnetic pulse (EMP), (c) lightning, (d) TEMPEST

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interference is also generated during the practical use of a variety of electrical, electronic, and electromechanical apparatus. This interference, which is generated by various equipment and appliance, is human-made.

Celestial electromagnetic noise: The electromagnetic radiation from the celestial bodies such as sun, stars, and galaxies can be attributed to the random motion of charged ions resulting from thermal ionization at very high temperature. The heated parts of the celestial bodies emit thermal noise. They emit broadband as well as narrowband electromagnetic noise. Electromagnetic radiation at certain discrete frequencies has also been detected to emanate from various parts of the sky with varying intensities. Important of them is the radiation from neutral hydrogen clouds, which cover all parts of the sky.

Lightning discharge: Atmospheric electromagnetic noise is caused by electric discharge in the atmosphere. This can be either a localized or an area phenomenon. Strong sources of atmospheric noise are lighting and electrostatic discharge When the field intensity in a charged cloud exceeds the breakdown level, the result will be an electric discharge. This discharge takes place from a cloud to the ground, as well as from one cloud to another.

Electrostatic discharge: ESD is a natural phenomenon in which accumulated static electric charges are discharged. This discharge produces electromagnetic interference. The effect of such discharge, which results in electromagnetic interference, could vary from noise and disturbances in audio or measuring instruments to unpleasant electrical shocks to the equipment or persons involved.

Emi from Apparatus and Circuits: The electromagnetic noise or interference generated in electrical, electromechanical, and electronics apparatus is a result of electromagnetic interactions inside such circuits and systems.

Electromagnetic emissions:

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These emissions may be broadly dividend into two categories: (1) intentionally emitted signals, and (2) unintentional electromagnetic emissions during the operation of equipment. While performing its regular function, equipment also often generates certain unintended and undesired electromagnetic emissions. Such emissions could interfere with the operation of other sensitive electronics apparatus. The desire signals emitted by a transmitter could interfere with the operation of other electronic equipment.

Cross-talk in transmission lines: Coupling of electromagnetic energy from one cable to another in multi conductor transmission lines results from magnetic field coupling when the two cables are located close to each other. Magnetic field coupling results from the flux linkage caused by the current flow in one wire and an equivalent loop area formed by another wire and its return path results inductive coupling. Electromagnetic energy transfer or coupling from one transmission line to another due to the above phenomenon is called cross talk.

The devices which are susceptible to EMI are listed below:

EMI receptors

Natural

Man-made Man Animals Plants

Common Receivers Broadcast Relay communication. Radar Telephone Navigation

Consumer & Medical

Industrial Controls Amplifiers Sensors Computers

Biomedical Audio/Hi-Fi Computers Public Address systems

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Ordinance

BIOLOGICAL EFFECTS OF EMI / EMR

EM waves, light, heat, x-ray and gamma rays are all different forms of electromagnetic radiation. However, they differ in their wavelength. These radiations have hazardous effects on men and material. The effects can be divided into two categories. 1. Thermal Effects 2. Non-thermal Effects. 1. Thermal Effects: The damaging levels depend on frequency, ambient temperature, body resistance and weight of individuals. Exposure over an energy density of 10 mw/cm2 at any frequency is considered to be not safe.2. Non-thermal Effects: i)

Minor changes in human blood properties take place.

ii)

Buzzing sound is heard upon exposure to EMR.

iii)

Abnormalities of the chromosome structure occurs..

iv)

Epigastria distress, emotional upsets and nausea have been

noticed. Radiation limits in the frequency range of 0.1 to 100 GHz when personnel are exposed to EM radiations are Ø The average incident power density should not exceed 10 mw/cm2 for exposures greater than 30 seconds. Ø The average incident energy density should not exceed 300 mJ/cm2 for intermittent exposures between 3 and 30 seconds Ø According to IEEE, safe power density level is 2 W/m2.

ELECTROMAGNETIC COMPATIBILITY (EMC) Electromagnetic compatibility (EMC) refers to the ability of electronic devices of different types to operate in their electromagnetic environment without loss of intended function A system is electromagnetically compatible if it satisfies three criteria:

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1. It does not cause interference with other systems. 2. It is not susceptible to emissions from other systems. 3. It does not cause interference with itself.

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.

EMC STANDARDS: These are of two types a) 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. b) 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..

ADVANTAGES OF EMC STANDARDS The advantages are: 1.

Compatibility, reliability and maintainability are increased.

2.

Design safety margin is provided.

3.

The equipment operates in EMI scenario satisfactorily.

4.

Product life and profits are increased.

EMC STANDARDS IN DIFFERENT COUNTRIES S. No.

Standard Name Meaning

Country

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Committee International Special 1.

CISPR (IEC)

Perturbations Radioelectriques – Europe Federal

Communications

2.

FCC

3.

SAE

Society of Automobile Engineers

4.

VG

Military standard

5.

VDE

6.

ISI

Council

Verband

committee

USA Trade

Association

Technical Committee Germany

Deutscher

Electrotecknikev EMI measurements & measuring apparatus

International

Germany

India

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, and mitigation techniques. These are equally important, if not greater, need in the present-day context for circuit designers and engineers engaged in design, installation, and operation of various equipment and system to be adequately conversant with EMI and EMC. This is rational and economical approach when compared to leaving the

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EMI to be tackled and mitigated when such interferences are experienced after the product or system, is assembled

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