Electromagnetic Compatibility Basics - EMC-ESD · PDF fileElectromagnetic Compatibility Basics ... Kirchhoff’s Voltage Law U s R1 R2 UR1 U R2 ... “Induction” phenomenon thrives

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in cooperation with

Frits J.K. Buesink, Senior Researcher EMC

[email protected]

Picture or Drawing 20.7 x 8.6 cm

UNIVERSITY OF TWENTE.

TELECOMMUNICATION ENGINEERING.

Electromagnetic Compatibility Basics

Engineering Compatible Equipment and Systems



in cooperation withStoringsmechanismes in Installaties

Definition of EMC

“The ability of the System to Operate according to its Specifications

in its Intended Electromagnetic Environment”

“Without generating Unacceptable Electromagnetic Emissions

into that Environment”

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2




Three Criteria for EMC

1. No (intolerable) emissions into the environment

2. Operate satisfactorily in its EM environment

3. Not cause interference with itself

3




Performance Criteria

what happens when immunity threshold levels are approached?

ASystem continues to work according to specification

Degradation not acceptable

Generally applies to all interference with a continuous nature

BTemporary degradation acceptable, auto recovery.

Usually applies to sporadic interference

to a non-critical function.

CDegradation acceptable. Recovery after manual RESET.

e.g. at mains interruptions. Only for non-critical functions. An

UN

SA

FE

sit

ua

tio

nis

ne

ve

r a

cc

ep

tab

le!

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3




The necessary elements for an interference situation

EMI, ElectroMagnetic Interference model: source – victim and coupling path

Source Victimcoupling pathcoupling path

Coupling path: always electrical interconnections

to tiny.

Emission

Susceptibility(Immunity)

Very large….

this can be demonstrated using:

a noise generator

a radio receiver

and some cables

Effects appear

at any scale

(relative to wavelength)

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All Currents Run in Loops

Kirchhoffs Current Law: basic for the design of component networks

I1 I2

I3

Ia Ib

Kirchhoff’s electrical current law

213 III +=

ba II =

Every current must

have a return path!

As a Designer,

ask yourself:

Where does my

Return Current

Flow?

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4




Common-mode currents dominate the EMC arena

currents, generated by cables’ “desired currents” into CM or ground-loop

Source Load

“Ground”

“Differential-mode” currentIdm

Icm

“Common-mode” current

CM: 98%of all EMI

problems!

Common-mode current is that

part of the return current which

follows a different path than

the designers intended route

CM-currents

can be

created

“elsewhere”

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Demonstration of the Common Mode Current

using the three demonstration cables of slide 1

50 Ω

source (50Ω)

scope

“ground” litz wire

Any Cable

8

50 Ω

amplitude depends on cable quality

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Kirchhoff’s Voltage Law

Us

R1

R2

UR1

UR

2

021 =++ RRS UUU

Inductive EMI Effects: Faraday’s Law

Completes Kirchhoff’s Voltage Law (to suit Maxwell’s equations)

loop 1flux Φflux Φ

Faraday’s Law:

?

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The “Induction” phenomenon

square wave sent over interconnection shows distortion

50

Ω

coax cable

single wire

1. Waveform for fast edge

A B

A

B

signal integrity =

no distortion on

the signal line

10

Ground

Connection

Single

Wire

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“Induction” phenomenon thrives on Magnetic Fields

current in a conductor is only possible when magnetic field exists

50

Ω

coax cable

single wire

1. Waveform for fast edge

A B

A

B

11

Ground

Connection

Single

Wire

LOOP

AREA




The “Induction” phenomenon

“slow” wave sent over interconnection shows no distortion

50

Ω

coax cable

single wire

2. Waveform for slow edge

A B

A

B

signal integrity =

no distortion on

the signal line

12

Ground

Connection

Single

Wire

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Interference: Current in Circuit 1 influences Circuit 2

the coupling path is usually through common-mode currents (or fields)

signal 1

return 1

signal 2

return 2

coupling e.g. through “ground” connections

Circuit 1

Circuit 2

intended (DM) current of circuit 1

intended (DM) current of circuit 2

unintended (CM) current from circuit 1 to circuit 2 (and vice versa)

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Mutual induction: coupling of circuits (loops)

Field loop 1 induces voltage in loop 2 (“Crosstalk”- or: transformer)

I1

loop 1

loop 2

MModel:

flux Φ11

2

12

loop

loop

IM

Φ=

1

11

IL

Φ=

14

8




Mutual induction in practice

two circuits with a common return (“ground”) conductor

source (50Ω)

scope

“ground” litz wire (return)

single wire (source)

single wire (passive)

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50 Ω

B

50

Ω

A





crosstalk created by mutual induction between two loops

source (50Ω)

scope




Only a change in current produces crosstalk!

16

50 Ω

dt

dIVnoise ~

B

50

Ω

A

9





“common return” = common impedance, largely inductive

source (50Ω)

scope




“Common-Impedance” crosstalk

Phenomenon is referred to as

“Common-Impedance” crosstalk

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50 Ω

B

50

Ω

A





slower risetimes = less crosstalk

source (50Ω)

scope




Note that a slower rise time

produces less or no crosstalk at all!

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50 Ω

dt

dIVnoise ~

B

50

Ω

A

10





thin line: common-impedance is high!

source (50Ω)

scope




19

50 Ω

“Common-Impedance” of wire

is high compared to wide plate

B

50

Ω

A




Cables are used to keep Signal and Return together

field of the return conductor is identical but opposite (if geometry is identical)

H = Magnetic Field [A/m] - H

I

rr

H⋅

Ι≈

π2

Ampere’s Law:

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11




Current carrying conductor always exhibits H-field

minimize fields by locating the return conductor concentric

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external noise source

Inoise

Unoise

1. Coupling into external noise

cable length D

Properties of cables: Transfer Impedance ZT

cable may produce or pick up common mode currents

Idesired

return current flows where?

?

2. Generation of noise in other conductors(e.g. “ground”)

DI

UZ

noise

noiseT

⋅=

[Ohm per meter]

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12




********************“Pig-tails”

effect of geometry changes: fields outside interconnections; CM currents

when

compared…

“Coax is better

than

twin wires”

Coax

Twin

wires

Pig-tail destroys cable symmetry

Fields are

generated

ZT goes UP

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Icm

Use Current Boundary to protect existing “pig-tail”

pig-tails can be acceptable as long as CM currents are kept away from it

H-field

linesWide metal plate

(Current Boundary)

EMC glands

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13




Whether Pacemakers are Indeed this Susceptible?

fields up to 30 kV/m and not just 50 Hz!

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Lightning and Buildings

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Lightning and Buildings

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Insulation in Lightning Protection

keep lightning current on the outside of the building

Exte

rna

l “S

hie

ld”

Inte

rnal w

irin

g

surge

protect

cabinet

1

2

3

4

5

powerdata

RV ⋅Ι≈∆

Ι Ι

Exte

rna

l co

nd

uctin

g s

tru

ctu

re

Current

Boundary

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15




Lightning and Airplanes

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ElectroStatic Discharge

charges built on persons or equipment cause electric sparks (and currents)

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Electric charging by induction

direct contact not necessary!

Teflon

Wool

Printed Circuit Board

- - - - - - - - - - - - - - - - -+ + + + + + + + + + + + + + + +

1. Charging of an insulator

2. Insulated PCB on charged surface

- - - - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - -

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Electric charging by induction

direct contact not necessary!

+ + + + + + + + + + + + + + + +

3.Touch or Ground PCB:

negative charge disappears (spark)

(PCB possibly damaged)

4. Lift PCB: voltage increases! Sparks fly!

- - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - -

+ + + + + + + + + + + + + + + +

PCB

PCBPCB

C

QV = (CPCB decreases)

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Ground self-induction and a fast discharge edge

“Grounding” or “short-circuit” of an ESD source is difficult (better avoid!)

“long” grounding path

neon lamp flashes

on discharge over

“long” grounding path

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in cooperation with

Nuclear ElectroMagnetic Pulse (NEMP)

34Storingsmechanismes in Installaties

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in cooperation with

EMC Rules and Guidelines

a lot of information on EMC engineering can be found on the internet




in cooperation with

EMC Rules and Guidelines

or: buy a book!


ISBN 978-0-470-18930-6

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in cooperation with

Product Development/Program Support

perform engineering & qualification tests

37Engineering Electromagnetic Compatibility

http://www.thales-ecc.nl/onze-expertise/emc/



in cooperation with

The End


http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/gmc-rm001_-en-p.pdf

http://www.engineering.schneider-electric.dk/Attachments/ia/instal/electromagnetic_compatibility_install_guide.pdf

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in cooperation withEngineering Electromagnetic Compatibility

Inductive load switching

Relays, Valves, and PWM motor control systems

V0

SW

L

C(parasitic)

R(parasitic)

Basic model

Ι0

2

2

1Ι⋅⋅= LEnergy

Ιpar

2

2

1VCEnergy ⋅⋅=

22

2

1

2

1VCL ⋅⋅=Ι⋅⋅

L= 0.1 H

C= 100 pF

Ι0 = 1 A

V = 32 kV (!)

Analysis:

Source: Jasper J. Goedbloed, “EMC”

Prentice Hall/Kluwer 1992

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in cooperation withEngineering Electromagnetic Compatibility

High Voltage in Motor arcs and creates Spikes

reason for Electrical Fast Transients (EFT) tests on equipment

am

plit

ud

e

time (µs scale)

breakdown (ns scale)

from EN 61000-4-4

5/50 ns pulses

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Electromagnetic Compatibility Basics - EMC-ESD · PDF fileElectromagnetic Compatibility Basics ... Kirchhoff’s Voltage Law U s R1 R2 UR1 U R2 ... “Induction” phenomenon thrives