ELEKTRO MANYETİK UYUMLULUK SLAYT

8/3/2019 ELEKTRO MANYETK UYUMLULUK SLAYT

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EMCThe operation of all items of electrical and

electronic equipment can disturb the operationof other nearby items of electronicequipment.

That disturbance is calledas Electro Magnetic Interference(EMI)

The immunity to effects of EMI is namedElectro Magnetic Compatibility(EMC).


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How Does EMI Affect Electronics? Radiated and conducted interference

Conducted Interference Enters and Exits Equipment throughWiring and Cabling

Radiated Interference Enters and Exits Equipment throughWiring and Enclosure Penetration

Radiated Susceptibility Radiated Emissions

Conducted Susceptibility Conducted Emissions


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Surge Coupling

Lightning and pulse sources cause high-energy transients into power and datacables

IndirectDirect


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Interference couplingmechanisms

coupling path

Directcoupling

Radiatedcoupling

source

victim


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coupling path1. Direct coupling

Coupling viapower or

signal lines

Commonimpedance

coupling

6


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1. Direct coupling

Coupling viapower or

signal lines

7


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Commonimpedance

coupling


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Interference to TV Reception

Two Interfering Signals Injected into TV

No Interference


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The modified DC power supply with significantly improved EMC performance

Circuit diagram of a simple regulated DC power supply


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C5, C6, C7 and C8 provide additional decoupling (effective at high-frequencies)inorder to prevent instability in IC1 and IC2.Without these components, theregulatorcircuits may oscillate at a high-frequency

C9 and C10 provide additional high-frequency decoupling to remove noise present

on theoutput voltage rails.C11, L1, L2, C12 and C13 provide a low-pass supply filter to remove noise and

spurious signals resulting from the harmonics of the switching action of the dioderectifiers. This filter also reduces supply borne noise that would otherwise enter theequipment from the supply

A low-resistance ground connection is introduced to ensure that there is an effectiveconnection between aircraft ground and the equipment chassis


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Effect and causes of EMIThe effects of EMI include

errors in instrument indicationsheterodyne whistles present on audio

signals,

herringbone patterns in video displays,

repetitive pulse noise (buzz) on phonesystems,

desensitising of radio and radar receivers,

false indications in radar and distancemeasuring equipment,

unwarranted triggering of alarms, and so on.


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Sources of EMIFluorescent lights,

Radio and radar transmitters,Power lines,

Window heat controllers,

Induction motors,

Switching and light dimming circuits,

Microprocessors and associated circuitry,

Pulsed high frequency circuits,

Bus cables,

Static discharge and lightning


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Types of interferenceNarrow band interference

is caused by devices generating specificfrequencies

AC power rails, microprocessor clocksradio transmitters and receivers...

Broad band interferenceis caused bydevices generating random frequencies andnoise

Examples ,power supplies ,LCD, switchedmode power supplies, switching powercontrollers, and microprocessor bus

systems

EMI d ti


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EMI reduction

1. Suppress interference at source

Enclose interference source in a screened metalenclosure and then ensure that the enclosure isadequately grounded

Use transient suppression on relays, switches

and contactors

Twist and/or shield bus wires and data bus

connections

Use screened (i.e. coaxial) cables for audio

and radio frequency signals

Check that enclosures, racks are grounded

effectively.


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2. Reduce noise coupling

Separate power leads. Twist and/or shield noisy wires and data bus

connections

Fit an optical fibre data bus where possible Use screened (i.e. coaxial) cables for

audio and radio frequency signals

Keep ground leads as short as possible. Filter noisy output leads.

Physically relocate receivers and sensitive

equipment away from interference source.

3 I i ibili h h ld


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3. Increasing susceptibility thresholds

Limit bandwidth to only that which is strictly

necessary

Limit gain and sensitivity to only that which is

strictly necessary

Ensure that enclosures are grounded and that

internal screens are fitted

Fit components that are inherently less

susceptible to the effect of stray radiatedfields.

Ai ft i i d bli


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Aircraft wiring and cabling

1.Adequate wire separation should be maintainedbetween noise source wiring and susceptible wiring

2.Wire lengths should be kept as short as possibleto maintain coupling at a minimum.

3.Equipment grounds must not be lengthened

beyond design specification.

4. With the aid of the technical manuals, groundingand bondin inte rit must be maintained.

G di


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Grounding

Connecting objects to either a structureor other return path to make circuitcomleted.


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.1 Protect aircraft, crew and passengers against

the effects of lightning discharge 2. Provide return paths for current

3. Prevent the development of RF voltages and

currents

4. Protect personnel from shock hazards 5. Maintain an effective radio transmission and

reception capability

6. Prevent accumulation of static charge.


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BondingElectrical connecting of objects that are not

otherwise adequately connected.1.Equipment bonding: Provide radio frequency

return circuits and to facilitate reduction in

EMI.2.Metallic surface bonding: Connected to the

airframe . Capable of conducting static charges

and lightning strikes.


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3. Static bonds :Connection to the aircraftstructure to dissipate possible static charge


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CONDUCTED EMISSIONSTESTING

Measure Noise on Power Line

Spectrum Analyzer

Product

PowerCord


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RADIATED EMISSIONS TESTING

Test Site: Measure Radiated Noise from Equipment Case

and Cables

Measuring Antenna

Product

3 m or 10 m

SpectrumAnalyzer

Open Area Test Site

Turntable

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ELEKTRO MANYETİK UYUMLULUK SLAYT