CISPR 11/AMD3/FRAG6
(Amendment)Class and group labelling requirements for ISM equipment
Class and group labelling requirements for ISM equipment
Describes the electromagnetic environment. Intended as a basis to achieve electromagnetic compatibility in system and equipment design, using test standards and mitigation methods which satisfactorily take account of undesirable effects. The report is primarily concerned with characteristics and levels of electromagnetic fields and of non-network-frequency-related conducted emissions from unintentional sources of interference.
Compatibilité électromagnétique (CEM) - Partie 2: Environnement - Section 3: Description de l'environnement - Phénomènes rayonnés et phénomènes conduits à des fréquences autres que celles du réseau
Décrit l'environnement électromagnétique et pourrra servir de base à l'étude de systèmes et de matériels fondée sur l'application de normes d'essais et de méthodes d'atténuation. Ces méthodes tiennent compte de façon satisfaisante des effets indésirables. A pour objet les caractéristiques et les niveaux des champs électromagnétiques et des émissions aux fréquences autres que celles du réseau provenant de sources de perturbations non intentionnelles. Cette publication a le statut d'un rapport.
Electromagnetic compatibility (EMC) - Part 2: Environment - Section 3: Description of the environment - Radiated and non-network-frequency-related conducted phenomena
General Information
Standards Content (Sample)
SLOVENSKI SIST-TP IEC/TR3 61000-2-
3:2004
STANDARD
april 2004
Electromagnetic compatibility (EMC) - Part 2: Environment - Section 3: Description
of the environment - Radiated and non-network-frequency-related conducted
phenomena
ICS 33.100.01 Referenčna številka
SIST-TP IEC/TR3 61000-2-3:2004(en)
© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno
---------------------- Page: 1 ----------------------
RAPPORT
CEI
TECHNIQUE
IEC
1000-2-3
TECHNICAL
Première édition
REPORT
First edition
1992-09
Compatibilité électromagnétique (CEM)
Partie 2:
Environnement
Section 3: Description de l'environnement –
Phénomènes rayonnés et phénomènes conduits
à des fréquences autres que celles du réseau
Electromagnetic compatibility (EMC)
Part 2:
Environment
Section 3: Description of the environment –
Radiated and non-network-frequency-related
conducted phenomena
© CEI 1992 Droits de reproduction réservés —
Copyright - all rights reserved
Aucune partie de cette publication ne peut titre reproduite ni
No part of this publication may be reproduced or utilized in
utilisée sous quelque forme que ce soit et par aucun pro-
any form or by any means, electronic or mechanical,
cédé, électronique ou mécanique, y compris la photocopie et
including photocopying and microfilm, without permission
les microfilms, sans raccord écrit de l'éditeur.
in writing from the publisher.
Bureau Central de la Commission Electrotechnique Inte rn
ationale 3, rue de Varembé Genève, Suisse
Commission Electrotechnique Internationale CODE PRIX "^
International Electrotechnical Commission
PRICE CODE J^
Menutynapoarfaa 3nesrporexwafecaaa
I EC I{ouwaxta
• Pour prix, voir catalogue en vigueur
For price, see current catalogue
---------------------- Page: 2 ----------------------
Oo
1000-2-3 IEC – 3 –
CONTENTS
Page
FOREWORD 7
INTRODUCTION 9
Clause
1 General 11
1.1 Scope and object 11
1.2 Reference document 11
2 General considerations 11
2.1 Coupling between emitting and susceptible devices 13
2.2 Units and decibels 15
3 Source, coupling and susceptor models, and their limitations 17
3.1 Source models 17
3.2 Coupling models 25
3.3 Susceptible device models 35
4 Emission levels and the environment 35
4.1 Conduction environment 35
4.2 Induction field environment 35
4.3 Radiation field environment 37
4.4 Statistical considerations 37
4.5 Implications for limits 37
4.6 Environment implied by invoking of standard limits 37
5. Intentional emitters 43
5.1 Radio transmitters 43
5.2 Other sources of intentional radiation 43
5.3 Carri
er frequency current systems 45
---------------------- Page: 3 ----------------------
1000-2-3 ©IEC – 5 –
Clause Page
6 Unintentional emitters 47
6.1 Physical noise sources 47
6.2 Man–made noise 49
6.3 Atmospherics 51
6.4 Electrostatic discharge 55
6.5 High-voltage and medium-voltage power lines 67
6.6 Low–voltage power lines 75
6.7 Signal and control lines 89
6.8 Appliances 91
6.9 Motors 91
6.10 Digital devices and systems 93
6.11 Radio and television receivers, monitors and video recorders 95
6.12 Fluorescent lamps 97
6.13 Industrial equipment 107
6.14 Traction systems 121
6.15 Ignition systems 121
7 Examples of environments 123
7.1 Residential and commercial environments 123
7.2 Industrial environments 127
7.3 Switching stations 127
7.4 Dedicated telecommunication switching centres 129
7.5 Hospitals 131
Bibliography 133
---------------------- Page: 4 ----------------------
1000-2-3© IEC
– 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
ELECTROMAGNETIC COMPATIBILITY (EMC)
Part 2: Environment
Section 3: Description of the environment -
Radiated and
non-network-frequency-related conducted phenomena
FOREWORD
1)
The formal decisions or agreements of the IEC on technical matters, prepared by Technical Committees on
which all the National Committees having a special interest therein
are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
2)
They have the form of recommendations for international use and they are accepted by the National
Committees in that sense.
3)
In order to promote international unification, the IEC expresses the wish that all National Committees
should adopt the text of the IEC recommendation for their national rules in so far as national conditions will
permit. Any divergence between the IEC recommendation and the corresponding national rules should, as
far as possible, be clearly indicated in the latter.
This section of IEC 1000-2, which has the status of a technical report, has been prepared
by IEC Technical Committee No. 77: Electromagnetic compatibility between electrical
equipment including networks.
The text of this section is based on the following documents:
CD
Report on Voting
77(SEC)103 and 103A 77(SEC)106
Full information on the voting for the approval of this section can be found in the Voting
Report indicated in the above table.
This report is a Technical Repo
rt of type 3 and is of a purely informative nature.
It is not to be regarded as an International Standard.
---------------------- Page: 5 ----------------------
1000-2-3 © IEC –9 -
INTRODUCTION
IEC 1000 is published in separate pa rts according to the following structure:
Part 1: General
General considerations (introduction, fundamental principles)
Definitions, terminology
Part 2: Environment
Description of the environment
Classification of the environment
Compatibility levels
Part 3: Limits
Emission limits
Immunity limits (in so far as they do not fall under the responsibility of the product
committees)
Part 4: Testing and measurement techniques
Measurement techniques
Testing techniques
rt
Pa 5: Installation and mitigation guidelines
Installation guidelines
Mitigation methods and devices
rt
Pa 9: Miscellaneous
Each part is further subdivided into sections which can be published either as International
Standards or Technical Repo rts.
This document has the status of a Basic EMC Publication in accordance with IEC
Guide 107.
---------------------- Page: 6 ----------------------
1000-2-3 © IEC – 11 –
ELECTROMAGNETIC COMPATIBILITY (EMC)
Part 2: Environment
Section 3: Description of the environment - Radiated and
non-network-frequency-related conducted phenomena
1 General
1.1
Scope and object
This Technical Repo
rt describes the electromagnetic environment. It is intended as a
basis to achieve electromagnetic compatibility in system and equipment design, using
test standards (techniques and limits), and mitigation methods (including installation
practices), which satisfactorily take account of undesirable effects that otherwise might
result from unintended electrical and electronic equipment interactions.
This repo
rt is primarily concerned with the characteristics and levels of electromagnetic
fields and of non-network-frequency-related conducted emissions from unintentional
sources of interference. Its application is part of the process of achieving electromagnetic
compatibility of systems; this requires the immunity characteristics of equipment to be
considered together with any normal or special equipment or cable installation practices
that may be required. Trade-offs should be made between physical separation, filtering
and shielding when considering equipment installation and design, in order to achieve
emission and immunity characteristics which meet system requirements.
1.2 Reference document
IEC 1000-2-1: 1990, Electromagnetic compatibility (EMC) – Part 2: Environment –
Section 1: Description of the environment – Electromagnetic environment for low-
frequency conducted disturbances and signalling in public power supply systems.
2 General considerations
There are various approaches that can be used for describing the environment. Classifi-
cation in terms of typical environmental locations such as urban, industrial, residential and
commercial may have some meaning in that each of these tends to imply some general
characteristics of the environment on which compatibility levels may be based. However,
it must be recognized that equipment not normally associated with a particular class of
environment may indeed affect any specific location.
For the above reason, the approach taken in this repo
rt is to state the electromagnetic
levels expected from particular sources or classes of sources. The level expected at a
particular location must then be determined with reference to the sources existing at that
location.
---------------------- Page: 7 ----------------------
1000-2-3 ©IEC – 13 –
At the same time it should be recognized that one cannot always identify all sources
that may affect a particular environment. Such is the case, for example, with conducted
disturbances in a power system generated at large distances, for example large distant
nonlinear industrial loads or unpredictable exceptionally severe lightning strokes. It is
meaningful to make a distinction between public supply and industrial or private networks.
The quality of se rvice at the point of common connection due to remote users will depend
upon the capacity of the network and the loads connected to it that an individual consumer
knows little about. Voltage fluctuations can be caused by load switching as well as by
system faults and lightning strokes. Within a consumer's system, residential or industrial,
the low frequency effects of local loads can be predicted. In general, one would expect
the remote sources to limit the quality of se rvice delivered to a particular consumer
location, and that any given system should perform properly in the absence of local
rvice is otherwise satisfactory. Local
sources. This is assuming that the quality of se
sources can be expected to have more significant effects in possible system and device
degradation.
2.1
Coupling between emitting and susceptible devices
The major reason for considering electromagnetic compatibility is the existence of devices
(equipment, systems) which show susceptibility to electromagnetic emission from other
devices.
Emitting devices
Intentional emissions Unintentional emissions
(disturbances)
(signals)
1
Intentional
Unintentional
coupling paths
coupling paths
EM-environment
Intentional Unintentional
coupling paths coupling paths
In-band signals Out-of-band signals
and disturbances and disturbances
Narrow band Broadband
Susceptible device
c
Figure 1 – Coupling paths between emitting and susceptible devices
---------------------- Page: 8 ----------------------
1000-2-3 ©IEC -15 -
Emitting devices may have intentional emissions, such as a radio-frequency broadcasting
signal, or unintentional emissions, such as the magnetic field produced by the deflection
coils of a video display unit. Through various coupling paths such emission may reach the
site where a susceptible device is located as shown in figure 1, thereby establishing
the electromagnetic environment for that device. The subdivisions shown in this figure are
important for a description of the electromagnetic environment. Moreover, the technical
possibilities available to prevent or solve an interference problem are related to these sub-
divisions, as are also the relevant EMC specifications.
The susceptible device may be exposed to the electromagnetic environment via intentional
coupling paths, such as the aerial of a radio receiver, or via unintentional coupling paths
such as the recording head of a video tape recorder, a signal cable or a mains cable.
Both types of coupling paths, intentional and unintentional, may carry
disturbances
having frequency components in the frequency band designated for the desired signal
of the susceptible device, and disturbances having components outside that band.
The disturbances received may be considered narrow band or broadband. For example,
the disturbance from a switched-mode power supply operating at 40 kHz is narrow band
when measured with a CISPR receiver in the frequency range 10 kHz to 150 kHz since the
receiver bandwidth is 200 Hz and the harmonic components are measured separately
when tuning over the frequency range. However, the same disturbance is broadband for a
video system with a 5 MHz bandwidth because of the harmonics of the 40 kHz signal.
The terms broadband and narrow band are always determined by the bandwidth over
which the disturbance is detected or measured. Hence, the same source can be both
broadband and narrow band.
2.2 Units and decibels
The decibel (dB) was originally defined as the ratio r of two powers P1 and P2
dissipated
in a resistance R expressed as a logarithmic unit as follows:
V^/R -
r(dB) = 10 logo Pi - 10 login
20 log 10
Vi
2 \
V2/ 2
R
where P 1 and P2
are measured or determined under identical conditions. Hence, r can
be expressed in terms of the associated voltages V1 and V2
as indicated in the above
equation.
If V2
is chosen to be a unit value, for example 1 NV, and V1
is expressed in terms of that
unit, then r gives the magnitude of
V1 expressed in "dB with respect to 1 pV", normally
abbreviated to r (dB(pV)). This latter approach is widely used in the field of EMC. Hence,
if Yis a unit value then X(dB(Y)) is defined as:
X(dB(Y)) = 20 IogiorXl
Y
---------------------- Page: 9 ----------------------
1000-2-3
© IEC –17 –
Certain conventions exist for the choice of Y. Here are some examples:
a)
In the case of conducted emissions, the voltage is expressed in dB(pV), i.e.
decibels above 1 pV; and the current in dB(pA), i.e. in decibels above 1 pA. For
example, 120 dB(pV)
corresponds to 10 6 pV or to 1 V.
b)
In the case of radiated emission, the electric field strength is expressed in dB(pV/m)
and the magnetic field strength in dB(pA/m). For example, 34 dB(pV/m) corresponds
to 50 pV/m. In statutory measurements and CISPR recommendations, the magnetic
field strength
H at frequencies below 30 MHz is usually expressed in dB(pV/m), the
unit of the electric field strength E, where dB(pA/m) would be more appropriate.
In such cases, the magnetic field
H expressed in dB(pA/m) and in dB(pA/m) satisfies
the relation:
H (dB(p.A/m)) = H (dB(pV/m)) – 51,5 (dB(S2))
where 51,5 dB(S2) = 20 when Z0 = 377 S2 and Z0 =
E/H.
log10Z0
The wave impedance Z0
= 377 S2 applies only to the case of a plane electromagnetic
wave. However, this is not relevant here as the measurement display is calibrated in such
a way that the signal induced by the magnetic field H in the magnetic field antenna, is
interpreted as a signal produced by an electric field of strength
E = Z0H. See also 3.1.2.
In the case of large conducted disturbances, the use of nonlinear surge diverters
precludes the application of dB units and analytical methods which are based on a linear-
ity hypothesis.
3 Source, coupling and susceptor models, and their limitations
When electrical and electronic devices and coupling paths are examined in detail,
they can be found to be extremely complex. In order to deal with them in a practical
way, simplification is necessary. This is done through the method of developing models.
Disturbance sources emit by mechanisms of conduction, induction and radiation. Coupling
paths may occur through conduction, induction or radiation, and most usually by com-
binations of these phenomena.
3.1 Source models
3.1.1
Conducted emissions
For conducted emission, the source can often be considered as a two-po
rt or three-
terminal device. Figure 2 shows noise sources in differential mode (VDM) and in common
IM
mode (V). Connection points 1 and 2 can be identified as, for example, the neutral and
the phase of a mains connection, or as the connection points of a desired signal of a
control line. Connection point 0 represents the reference of the source, formed for
example by the protective earth, the steel reinforcement in a building, or a metal chassis.
In many cases it may be necessary to consider the source as an N-port network, as in the
case where a multi-wire flat cable is involved.
---------------------- Page: 10 ----------------------
1000-2-3 © IEC 19 -
-
Phase Neutral
IEC 829/92
Figure 2 - Source model for conducted emission
(Source loaded by and Z12)
ZL1
The voltages VDM and are complex voltages having desired as well as disturbance
VcM
components. However, the desired voltage from the source, whether this is a power line
or a signal line, is predominantly represented in. the VDM component. The disturbance
voltage components of VDM and VcM may be of equal importance.
The relatively simple lumped representation in figure 2 is valid when the connection
points 1, 2 and 0 are at such short distances from each other that, at all frequencies to be
considered, no wavelength or field-induction effects play a noticeable role. The common-
mode source amplitude and impedance are represented by VcM and ZcM respectively.
The differential-mode source amplitude and impedance are represented by two sources
of amplitude Y2 VDM and by the impedances ZDM1 and ZDM2 . It should be noted that,
in general, Z is not equal to ZDM2 . Equal values occur only by chance or when special
DM1
measures have been taken in the construction of the system involved. If the source
is unloaded (ZL1 = Z= L2 ZL12 = co), the nodal point K is in the "electrical middle", however
Z
this is not normally the case when the source is loaded because of
L1 # ZL2 # ZL12.
As a result, the common-mode current /cm may be determined by both VcM and
VDM.
The current /cm is equal to the half vector- sum of / 1 and /2, like VcM in figure 3 is half the
vector -sun of V1 and V2.
An example of the relation between the open-circuit voltages V V1 and V2 is
,
DM VcM,
given in figure 3.
IEC 830/92
V V. and V2 for the unloaded situation
Figure 3 - Relation between
cM , VDM,
---------------------- Page: 11 ----------------------
1000-2-3 © IEC –21 –
In figure 4 relations are given between the voltages V Vi and 172 , for the loaded
cM, VDM,
situation.
/ Z
2 DM2
+
(/1 12)ZC M
IEC 831/7'
Figure 4 – Relations between the voltages V V and 172 , for the loaded situation
cM, VDM,
Low-level conducted disturbance voltages are typically measured using an artificial
network having a well-defined load impedance. For example, the CISPR V-terminal
network has ZL12 = with =
and 150 0, or 50 S2 II 50 pH or 50 S2 // 5 pH.
ZL1 = ZL2 ZL1
These values are considered to relate to the (average) absolute value of the impedance
presented by the real mains, which depends, among other things, on the mains current
for which the network has been designed. It is important to note that the artificial mains
networks mentioned here are not valid for all applications, for example the case of the
propagation of transients.
It must therefore be recognized that measurements of emission from sources are of a
limited nature. For example, to determine compliance with a conducted emission limit, the
measurement is made with a specified terminating impedance. No direct measurement of
the source impedance is made. Thus, when a given source is placed in a circuit which
presents an impedance to it which is different from the measurement impedance, the
actual emission will differ from that measured. Such variations must be anticipated by
system EMC engineers when designing compatible systems.
3.1.2
Radiated emissions
Radiated emission levels are usually stated in terms of electric (E) and magnetic field (H)
levels, expressed in dB(pV/m) and dB(pA/m). Particular sources differ in the relative
magnitudes of each of these components and their variations with distance.
In the so-called far-field region of a source the distance between the source and the point
of obse rvation of the field is much larger than X
/(2n), where X is the wavelength of the
field, and larger than the dimensions of the source. At such distances, and in the absence
of nearby reflecting objects, the E and H fields are perpendicular to each other and perpen-
dicular to the direction of propagation of the wave. In addition, there is a fixed relation
between the magnitudes of E and H, which makes statements of electric field strength and
magnetic field strength equivalent. In the far field and free space E/H = 377 S2 and the field
levels fall off inversely with distance from the source.
---------------------- Page: 12 ----------------------
1000-2-3 © IEC – 23 –
In the near-field region of the source, the distance between the source and the point of
observ
ation is either much smaller than X /(2n) or smaller than the dimension of the source
or both. The relation between the E and H fields now depends on the wavelength of the
disturbances, the actual position in the near-field region and the type of source.
A simple model used for radiation is the dipole which may be of electric or magnetic types,
(see figure 5). This model exhibits an inverse cubed variation of the field strength of its
dominant component (electric field for an electric dipole, magnetic field for a magnetic
dipole) at nearfield distances. For such sources a statement of the "dipole strength" would
enable calculation of the field components (both electric and magnetic) at any distance.
However, it is more usual to measure the dominant component at a fixed distance, without
making reference to the source strength.
IEC 833/92
A = loop area
IEC 832/92
Figure 5a — Electric dipole Figure 5b — Magnetic dipole
strength = 1- le strength =
A • Im
Figure 5 – Electric and magnetic dipole elements
In case of radio transmitters, the gain of the antenna in the intended coupling path and the
net power Pt transferred to the antenna are usually known. As the antenna gain is always
directional with respect to the antenna, the gain normally referred to is that associated
with the direction of maximum radiation.
The effective or equivalent radiated power, ERP, of an antenna is defined as:
ERP =
GrPt
where
Gr is the antenna gain relative to the maximum directivity Gh of a half wave dipole.
---------------------- Page: 13 ----------------------
1000-2-3 ©IEC - 25 -
r in the far field of the
The electric field strength produced by an antenna at a distance
antenna is expressed as:
E - ZGh • ERP - 7
ERP
r
1 4nr2
where G = 1,64 h and Z, the wave impedance of the medium, equals 377 SZ in free space.
It follows that:
ZGh
- 7
'h
4n
The term "effective or equivalent isotropically radiated power, EIRP', is also used for the
antenna. The relation between ERP and EIRP is given by:
EIRP = Gh ERP.
3.2
Coupling models
The phenomena involved in transferring electromagnetic energy from a source to a suscep-
tor are, in general, very complex. Exact calculation of the energy transferred in particular
cases may therefore be difficult. However, in many cases the important coupling may be
described in terms of comparatively simple models. These models are divided into three
main classes: common-impedance coupling, coupling by induction (near-field) and radia-
tive (far-field) coupling.
3.2.1
Common-impedance coupling
This type of coupling is also referred to as conductive coupling. It occurs when currents or
a portion of the currents associated with a source and susceptor share a common path.
Typically the common path may be represented by a resistance, an inductance or a capa-
citance or by a combination of any of these. Two of many examples that can be cited are
the sharing by the source and receptor of 1) a common power mains, and 2) a common
ground current return path.
Resistive coupling
The resistive part of the common impedance Re is determined by the conductor
material and by the skin effect as a result of which the resistive part becomes frequency
dependent. For a straight round conductor of diameter d one has:
when
Rc /R =d/4S S«d
dc
and Rc /Rdc 1 if S»d
where is the d.c. resistance of the conductor and S the skin depth given by:
Rdc
where co is the angular frequency of the signal, p the permittivity and a the conductivity of
the conductor material.
---------------------- Page: 14 ----------------------
1000-2-3 ©IEC _ 27
Reactive coupling
The reactive part of common-impedance coupling can be produced by a common induc-
tance. The common inductive reactance XL can then be written as:
XL =w
LL
where L L
is the inductance of the conductor. The value of LL depends on the shape
of the current loop and its surroundings. However, as a rule of thumb, one can say
that LL = 1 pH/m (or 1 nH/mm). In many electromagnetic interference problems
XL » Rc.
For transient events, this is always the case, in spite of the emphasis given to massive
earthing conductors.
3.2.2 Coupling by induction
Coupling by induction occurs when voltages or currents are induced in the circuits of the
susceptor by local electric or magnetic fields or combinations of these emanating from the
source. Examples are control circuits located in the vicinity of a large power transformer,
arc furnace or welder and closely spaced (and parallel) transmission circuits such as a
power line and a telecommunications line.
---------------------- Page: 15 ----------------------
1000-2-3 ©IEC — 29 —
a) Electric field coupling
Electric field or capacitive coupling occurs when electric fields from one circuit impinge
on another. For the low-frequency approximation it is appropriate to describe this type
of coupling with a coupling capacitance. The magnitude of the capacitance depends
primarily on the actual situation, i.e. on the shape of the circuits and on the surround-
ings of the circuits. An example is given in figure 6, where the coupling capacitance
C12
per unit length is given between the wires (of diameter d) of two parallel loops at a
distance D, using the ground plane as a common return, for three values of the loop
height.
15
0
10
D (mm) 100
LEC 834192
Figure 6 — Capacitance per unit length as a function of conductor separation
---------------------- Page: 16 ----------------------
1000-2-3 ©IEC — 31 —
It also shows that
Figure 6 clearly shows the influence of the surroundings on C12 .
C12
varies rapidly with D but that for Did > 10 the coupling capacitance does not vary much
with D. Note that for sufficiently high values of h the equation for the coupling capa-
citance reduces to:
7CE
C _ F/ m
(h —>
12
(2D)
In
d
which is the equation for the capacitance between the wires in the absence of a ground
plane.
The above example applies equally to two cables running parallel to a metallic plane,
i.e. a shield or conduit, which forms the reference for the common-mode voltages on
the cables.
In cases where the feedback from the receptor circuit to the emitter circuit is negligible
and the circuits are small compared with the wavelength under consideration, the dis-
turbance caused by capacitive coupling can be represented in the receptor circuit by a
current source. The current source can be approximated by
1c
= joC12 V
where V
is the driving voltage at the emitter side of
C12.
b) Magnetic field coupling
Magnetic field or inductive coupling occurs when magnetic fields from one circuit
impinge on another. An appropriate quantity to describe this type of coupling is the
mutual inductance. Its value depends greatly on the actual situation, for example on
the shape of the circuits and on the surroundings of the circuits, as in the case of the
coupling capacitance.
In cases where the feedback of the receptor circuit to the emitter circuit is negligible
and the circuits are small compared with the wavelength under consideration, the dis-
turbance caused by the magnetic coupling can be represented in the receptor circuit by
a voltage source. The voltage source can be approximated by:
V1 = joM12 1
where M12 is the mutual inductance between the two circuits involved and / the driving
current in the emitter circuit. This can also be written as j0)B 1 A2 where A2 is the area of
the receptor loop and B 1 the flux density produced by the emitter loop in the receptor
loop. In the last relation it is assumed that B 1 is a constant over the area A2.
A very useful model is one that accounts for the magnetic field in the vicinity of a parallel
wire transmission line. Its magnitude as a function of parallel wire spacing and the
distance from the wires is shown in figure 7. If the distance is large compared with the
separation, the field strength falls off as 1/r 2. If the distance is small compared with
the spacing, the field is calculated as for a single wire (the closest wire).
---------------------- Page: 17 ----------------------
1000-2-3 © IEC – 33 –
Magnetic sources such as transformers, relays, etc. will produce field strengths
attenuated as the third power of the distance.
40 -120
µo /L
1.r«d:Bo_—
2nr
^
^`^.
20 µo/Ld 140
d
IL
2.l»r»d:B= ► .
2nr2
d=
1m
160
0
^^^^^^ ^ r
Fe ld on axis, , ^^^
normal to plane
6
0
of lines
180
- 20--r
= distance above
plane
B
^
*
200
-40—
^
o
o l
60 ^ — -220
^
c.-
0 0
7J
0 ,
o-
^ o!
-8 0 240
o-
O
^O.
0
00
^
0^
^
-100
0,001 0,01 01 1,0
10,0 100,0
r (m)
IEC 835/92
Figure 7 – Flux density from parallel conductors
c) Mixed coupling
In many cases the coupling mechanisms discussed in the preceding subclauses occur
simultaneously. Which of the three mechanisms will dominate depends on the actual
situation. Only in a limited number of cases it is possible to indicate whether capacitive
coupling will dominate over magnetic coupling, or vice versa. An example is the case of
coupling between two parallel wires. Assuming the receptor circuit to be terminated by
its characteristic impedance on both ends, magnetic coupling dominates if the emitter
circuit is terminated with an impedance lower than the characteristic impedance and
capacitive coupling dominates if that impedance is higher.
3.2.3 Radiative coupling
Radiative coupling may be the primary means of coupling when the source and the
susceptor are relatively far apart i.e. in the far-field situation. The coupling mechanism
by elec
...
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