SIST IEC 61786-2:2017

SLOVENSKI STANDARD
01-oktober-2017
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Measurement of DC magnetic, AC magnetic and AC electric fields from 1 Hz to 100 kHz
with regard to exposure of human beings - Part 2: Basic standard for measurements
Mesure de champs magnétiques continus et de champs magnétiques et électriques
alternatifs dans la plage de fréquences de 1 Hz à 100 kHz dans leur rapport à
l'exposition humaine - Partie 2: Norme de base pour les mesures
Ta slovenski standard je istoveten z: IEC 61786-2
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
®
Edition 1.0 2014-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Measurement of DC magnetic, AC magnetic and AC electric fields from 1 Hz to

100 kHz with regard to exposure of human beings –

Part 2: Basic standard for measurements

Mesure de champs magnétiques continus et de champs magnétiques et

électriques alternatifs dans la plage de fréquences de 1 Hz a 100 kHz dans leur

rapport à l'exposition humaine –

Partie 2: Norme de base pour les mesures

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX W
ICS 17.220.20 ISBN 978-2-8322-1970-6

– 2 – IEC 61786-2:2014 © IEC 2014
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 7
3 Terms and definitions . 7
4 General considerations . 8
4.1 Different goals of measurement . 8
4.1.1 General . 8
4.1.2 Characterisation of field levels for compliance with safety standards . 9
4.1.3 Characterisation of spatial variations . 9
4.1.4 Characterisation of temporal variation . 11
4.1.5 Characterisation of frequency content in magnetic field or electric field . 12
4.1.6 Characterisation of population exposure to magnetic field and definition
of metric . 13
4.2 Sources with multiple frequencies . 14
4.2.1 General . 14
4.2.2 Sum of weighted magnitudes . 14
4.2.3 Weighted peak value . 15
4.2.4 Impulse separation . 15
4.2.5 Weighted RMS value . 15
4.2.6 Highest weighted spectral line . 16
4.2.7 Conclusion and recommendation. 16
4.3 Considerations before measurements . 16
5 Measurement procedures and precaution . 17
5.1 AC magnetic field . 17
5.2 DC magnetic field . 18
5.3 AC electric field . 19
6 Measurement uncertainty . 21
7 Measurement report . 22
Annex A (informative) Examples of fields characteristics in typical environments . 24
Annex B (informative) Examples of measurement distances . 27
B.1 IEC 62110:2009 [9] . 27
B.2 IEC 62233: 2005 [10] . 27
B.3 IEC 62311:2007 [11] . 27
B.4 IEC 62369-1:2008 [12] . 27
B.5 IEC/TS 62597:2011 [14] . 27
B.6 IEC 62493:2009 [13] . 28
Annex C (normative) Measurement uncertainty . 29
C.1 Overview. 29
C.2 Assessment of type A uncertainty . 29
C.3 Assessment of type B uncertainty . 29
C.3.1 Non-uniform field . 29
C.3.2 Pass-band limitations . 30
C.3.3 Temperature . 30
C.3.4 Humidity . 30
C.3.5 Location of measurement. 30

C.3.6 Long-term drift . 31
C.3.7 Instrument time constant . 31
C.3.8 Proximity effect of observer (for electric field) . 31
C.3.9 Correction factor . 31
C.3.10 Hysteresis between scales . 31
Annex D (informative) Example of measurement uncertainty . 32
Bibliography . 33

Figure 1 – Magnetic field levels under a 77 kV overhead transmission line (from [9] ) . 10
Figure 2 – Electric field levels under an overhead transmission line (from [9] ). 10
Figure 3 – Example of load variation of 735kV line due to the human activities (daily)
and outdoor temperature (seasonal) . 11
Figure 4 – 50 Hz magnetic field in a high speed train in France . 12
Figure 5 – Waveform (a) and frequency spectrum (b) of magnetic field generated by a
66,04 cm (26 inches) flat-screen LCD television . 13
Figure 6 – Example of DC magnetic field profile above DC underground cable
(calculated at a height of 1 m) . 19
Figure 7 – Observer proximity effects during electric field measurements in vertical
electric field . 20
Figure A.1 – Magnetic field exposure of typical worker (electrician) in North American
power plant (based on 3 days recording) . 25
Figure B.1 – Lighting equipment and measurement distances (from [13]) . 28

Table A.1 – Example of field characteristics inside (workers environment) and outside
(public environment) electric substations in a North American utility . 24
Table A.2 – Field characteristics (mT) in different mass transportation system in US:
average and (maximum) . 26
Table D.1 – Example of measurement uncertainty . 32

– 4 – IEC 61786-2:2014 © IEC 2014
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT OF DC MAGNETIC, AC MAGNETIC
AND AC ELECTRIC FIELDS FROM 1 Hz TO 100 kHz
WITH REGARD TO EXPOSURE OF HUMAN BEINGS –

Part 2: Basic standard for measurements

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61786-2 has been prepared by IEC technical committee 106:
Methods for the assessment of electric, magnetic and electromagnetic fields associated with
human exposure.
The text of this standard is based on the following documents:
FDIS Report on voting
106/322/FDIS 106/326/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 61786-2:2014 © IEC 2014
MEASUREMENT OF DC MAGNETIC, AC MAGNETIC
AND AC ELECTRIC FIELDS FROM 1 Hz TO 100 kHz
WITH REGARD TO EXPOSURE OF HUMAN BEINGS –

Part 2: Basic standard for measurements

1 Scope
This part of IEC 61786 provides requirements for the measurement of quasi-static magnetic
and electric fields that have a frequency content in the range 1 Hz to 100 kHz, and DC
magnetic fields, to evaluate the exposure levels of the human body to these fields.
Specifically, this standard gives requirements for establishing measurement procedures that
achieve defined goals pertaining to human exposure.
NOTE Requirements on field meters and calibration are described in IEC 61786-1
Because of differences in the characteristics of the fields from sources in the various
environments, e.g. frequency content, temporal and spatial variations, polarization, and
magnitude, and differences in the goals of the measurements, the specific measurement
procedures will be different in the various environments.
Sources of fields include devices that operate at power frequencies and produce power
frequency and power-frequency harmonic fields, as well as devices that produce fields
independent of the power frequency, and DC power transmission, and the geomagnetic field.
The magnitude ranges covered by this standard are 0,1 mT to 200 mT for AC (1 mT to 10 T for
DC) for magnetic fields, and 1 V/m to 50 kV/m for electric fields.
When measurements outside this range are performed, most of the provisions of this standard
will still apply, but special attention should be paid to the specified uncertainty and calibration
procedures.
Examples of sources of fields that can be measured with this standard include:
− devices that operate at power frequencies (50/60 Hz) and produce power frequency and
power-frequency harmonic fields (examples: power lines, electric appliances…)
− devices that produce fields that are independent of the power frequency. (Examples:
electric railway (DC to 20 kHz), commercial aeroplanes (400 Hz), induction heaters (up to
100 kHz), and electric vehicles.)
− devices that produces static magnetic fields: MRI, DC power lines, DC welding,
electrolysis, magnets, electric furnaces, etc. DC currents are often generated by
converters, which also create AC components (power frequency harmonics), which should
be assessed.
When EMF products standards are available, these products standards should be used.
With regard to electric field measurements, this standard considers only the measurement of
the unperturbed electric field strength at a point in space (i.e. the electric field prior to the
introduction of the field meter and operator) or on conducting surfaces.
Sources of uncertainty during measurements are also identified and guidance is provided on
how they should be combined to determine total measurement uncertainty.

2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61786-1:2013, Measurement of DC magnetic, AC magnetic and AC electric fields from
1 Hz to 100 kHz with regard to exposure of human beings – Part 1: Requirements for
measuring instruments
ISO/IEC Guide 99:2007, International vocabulary of metrology – Basic and general concepts
and associated terms (VIM)
ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE Throughout this standard, the words "magnetic flux density" and "magnetic field" will be considered
synonymous.
3.1
average exposure level
spatial average over the entire human body of fields to which the individual is exposed
3.2
correction factor
numerical factor by which the uncorrected result of a measurement is multiplied to
compensate for a known error
Note 1 to entry: Since the known error cannot be determined perfectly, the compensation cannot be complete.
3.3
coverage factor
numerical factor used as a multiplier of the combined standard uncertainty in order to obtain
an expanded uncertainty
Note 1 to entry: For a quantity z described by a normal distribution with expectation m and standard deviation σ,
z
the interval m ± kσ encompasses 68,27 %, 95,45 %, and 99,73 % of the distribution for a coverage factor k = 1, 2,
z
and 3, respectively.
3.4
repeatability (of results of measurements)
closeness of agreement between the results of successive measurements of the same
measurand, carried out under the same conditions of measurement, i.e.:
− by the same measurement procedure,
− by the same observer,
− with the same measuring instruments, used under the same conditions,
− in the same laboratory,
− at relatively short intervals of time.
[SOURCE: IEC 60050-311:2001, 311-06-06, modified –The note to entry has been deleted.]

– 8 – IEC 61786-2:2014 © IEC 2014
3.5
reproducibility (of measurements)
closeness of agreement between the results of measurements of the same value of a quantity,
when the individual measurements are made under different conditions of measurement:
− principle of measurement,
− method of measurement,
− observer,
− measuring instruments,
− reference standards,
− laboratory,
− under conditions of use of the instruments, different from those customarily used,
− after intervals of time relatively long compared with the duration of a single measurement
[SOURCE: IEC 60050-311:2001, 311-06-07, modified –The notes to entry have been deleted.]
3.6
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
3.7
uncertainty of measurement
parameter, associated with the result of a measurement, that characterises the dispersion of
the values that could reasonably be attributed to the measurand
Note 1 to entry: Uncertainty of measurement generally comprises many components. Some of these components
may be estimated on the basis of the statistical distribution of the results of series of measurements, and can be
characterised by experimental standard deviations. Estimates of other components can be based on experience or
other information.
4 General considerations
4.1 Different goals of measurement
4.1.1 General
Magnetic and electric fields can be characterised according to a number of parameters, i.e.
magnitude, frequency, polarization, etc. (see IEC 61786-1:2013, Annex C). Characterisation
of one or more of these parameters and how they might relate to human exposure may serve
as possible goals of a measurement programme. As an aid for readers interested in
developing a field measurement protocol, this subclause provides a list of such possible
measurement goals and possible methods for their accomplishment.
Except in the vicinity of high voltage sources, there is no need to measure the power
frequency electric field, because the electric field will be, at most, a few tens of volts per
metre [3; 22] .
Annex A gives examples of typical field characteristics in different environments.
The goals of a measurement programme, such as those considered below, shall be clearly
defined. A clear definition of goals is required for the determination of instrumentation and
calibration requirements, e.g. instrumentation pass-band, magnitude range, frequency
calibration points, etc. Once the goals have been identified and appropriate instrumentation
has been acquired, a pilot study in the measurement environment of interest may be desirable
___________
Numbers in square brackets refer to the Bibliography.

before decisions are made as to the final measurement methods and associated protocol. The
protocol will describe the step-by-step procedure to follow, using the possible methods
indicated, to accomplish the measurement goals. The protocol may explicitly indicate such
things as instrument requirements (e.g. pass-band, probe size, magnitude range), location of
measurements and duration of measurements. It should then be possible, using the same
protocol, to compare with confidence measurement results obtained in similar electrical
environments.
Possible measurement goals and possible methods for their accomplishment are given in
4.1.2 to 4.1.6.
4.1.2 Characterisation of field levels for compliance with safety standards
Limits on permissible electric or magnetic field levels expressed as resultant values and as a
function of frequency have been indicated in a number of documents, such as [17-19; 21]
necessitating the determination of field levels with the maximum value or spatial value in
specified areas. The choice of measurement location shall be done in consideration of the
possible location of people.
Method: Three-axis meters shall be used to make such measurements of the resultant
magnetic and electric fields. Standards and guidance exist for such measurements near
power lines [4; 9; 15] and electric appliances [10] .
Measurements of magnetic fields near power lines should be correlated with load currents.
Load currents for appliances are either constant or, typically, periodic through a fixed range in
a relatively short time, enabling the determination of the largest resultant magnetic field with
relatively few measurements.
4.1.3 Characterisation of spatial variations
Magnetic and electric fields are not constant around sources. For example, variations of
magnetic or electric fields below power lines are typical (Figures 1 and 2) and can be
calculated.
In Figure 1, non-uniformity is defined by [4; 9] as the maximum value of
( B − B ) / B ×100 (%)
h avg avg
Where
B is the magnetic field level at heights of 0,5 m, 1,0 m and 1,5 m above ground;

h
B is the arithmetic mean of the three levels.

avg
– 10 – IEC 61786-2:2014 © IEC 2014

untransposeduntransposed
5,0
1,1,5 m5 m
4,5 90
A A
1,1,0 m0 m
AA AA
4,0 0,0,5 m5 m
B B
BB BB
-
Non-uniformity 70
3,5 C C
CC CC
3,2 m 3,2 m
3,0
2,5
40 3,0 m
2,0
3,5 m 3,5 m
1,5
1,0
3,0 m
0,5
0 3,8 m 3,8 m
–10
0,0
–30 –20 –10 0 10 20 30
Distance  (m)
Conductor
transposedtransposed
7,0
1,1,5 m5 m
phase sequencephase sequence
6,0 1,1,00m m
C
AAA  CC
6,0 m
0,0,5 m5 m
B B
BB BB
non -
Non-uniformity
5,0 70
C A
CC AA
4,0
1,0 m
3,0
G.L.
2,0
Distance  (m)
1,0
0,0
–30 –20 –10 0 10 20 30
77 kV, double-circuit, vertical configuration
Distance  (m)
IEC
Figure 1 – Magnetic field levels under a 77 kV overhead transmission line (from [9])
3,2 m 3,2 m
Phase sequence
phase sequencphase sequencee
3,0 m
AAA  AAA  A C
AA CC
3,5 m 3,5 m
Electric Field (V/m)
BBB  BBB  B B
BB BB
800 C C C A
CC CC CC AA
3,0 m
UntranspoUntransposedsed transposetransposedd
700 3,8 m 3,8 m
Conductor
11,0 m
1,0 m
G.L.
–30 –20 –10 0 10 20 30
- 30 - 20 - 10 0 10 20 30
Distance x  (m)
Distance (m)
distance x (m)
77 kV, double-circuit, vertical configuration
IEC
Figure 2 – Electric field levels under an overhead transmission line (from [9])
The spatial distribution of magnetic fields away from power lines or single identifiable sources
is typically unknown.
Alternating magnetic fields in most environments will be non-uniform because of the spatial
dependence of the fields from the source currents. It is noteworthy that static magnetic fields
also show considerable spatial variability in residences [29].
Method: The magnetic field components shall be recorded as a function of coordinate position
when characterising spatial variation. Standards exist for carrying out such measurements
Electric field  (V/m)
Magnetic field  (mT) Magnetic field  (mT)
Non-uniformity  (%) Non-uniformity  (%)

near power lines [4; 9; 15] and electric appliances [[9]]. While such measurements can be
made with survey meters, instrumentation incorporating "measurement wheels" is available
for characterising spatial distributions of magnetic fields in environments where physical
obstructions do not hinder the movement of the wheel. As the wheel rotates, it periodically
triggers a three-axis magnetic field meter to record the resultant magnetic field. Software
provided with such instrumentation permits the generation of plots of magnetic field profiles,
equifield contours, statistical analyses of the field levels, etc [2; 26]. As for characterisation of
field levels for compliance with safety limits, such data will not take the temporal variations of
the field profiles into account without repeated measurements.
4.1.4 Characterisation of temporal variation
Because magnetic fields are produced by load currents and ground return currents that can
vary greatly with time, the temporal variations of magnetic fields can easily exceed a factor of
2.
Under a power line, the magnetic field depends on the load of the line. For single circuit lines
or double circuit lines operated in parallel, the magnetic field is directly proportional to the
load of the line. Figure 3 gives an example of the load of a 735 kV line and the outdoor
temperature. In this case, the load is influenced by human activities (daily cycle) and by
outdoor temperature (season cycle) and by the place of the line in the network. Moreover, the
magnetic field level can vary with the sagging of the conductors because of heating due to
large current loads and environmental conditions [16] .
IEC
Figure 3 – Example of load variation of 735kV line due to
the human activities (daily) and outdoor temperature (seasonal)
Method: Three-axis and single-axis magnetic field meters are available with output
connections that can be used in combination with commercially available data loggers to
record the variation of magnetic field levels at one or more locations, as a function of time.
Three-axis exposure meters and magnetic field waveform capturing instrumentation can also
be used to periodically record field levels. Because of the dependence of magnetic field levels
on load currents, which can vary daily, weekly, seasonally (Figure 3), etc., the challenge is to
determine a time interval for recording measurements that will capture enough variations of
the field to obtain a valid statistical description. Conducting an initial pilot study in the
measurement environment of interest can be useful for addressing the question of
measurement sampling time.
Finding the temporal maximum of the magnetic field by measurement is not easy. For some
simple situations, such as under single circuit power lines, this may be estimated by recording
the current during the magnetic field measurement and extrapolation to the maximum load.

– 12 – IEC 61786-2:2014 © IEC 2014
An additional consideration should be taken into account when measurements are performed
in electric mass transportation systems or other areas where there are variable speed motors.
For example, in trains, the magnetic field can be a function of the speed of the train (see
Figure 4).
IEC
NOTE Broadband = 40 Hz – 800 Hz, harmonics = 100 Hz – 800 Hz.
Figure 4 – 50 Hz magnetic field in a high speed train in France
For the electric fields, unlike spot measurements of magnetic fields from power lines, the
measured values will not change greatly because the voltages remain nearly constant.
However, the electric field level can vary with the sagging of the conductors because of
heating due to large current loads [16] .
4.1.5 Characterisation of frequency content in magnetic field or electric field
Since (1) electric and magnetic fields from electrical equipment often contain power-frequency
harmonics or frequencies unrelated to the power frequency, and (2) electric and magnetic
field limits have been set as a function of frequency [17-19; 21], characterisation of the
frequency content can be an important goal.
An example of a magnetic field that is rich in harmonics and that is produced by a common
electrical appliance is shown in Figure 5. Figure 5a shows a waveform of the horizontal
component of the magnetic field 10 cm away from the surface of the front-centre of an
operating 66,04 cm (26 inches) flat-screen LCD television. The harmonic components in the
field are indicated in Figure 5b, which shows a frequency spectrum for the waveform in
rd
Figure 5a. It is shown that the fundamental frequency is 50 Hz and significant levels of 3 and
th
5 harmonics are included.
0.1
0.3 0.1
0.3 0,1
0,3
FFuundandammeentntaall f frreequequencncyy:: 50 50 H Hzz
00.20.,22
0.000,.00888
0,1
0.1
0.1
0,06
0.00.066
0,04
0.00.044
-0.1-0.1
-0,1
0.00.022
0,02
-0.2
-0.2
-0,2
-0,3
-0.3
-0.3
--0.00.022 --0.00.011 00 00.0.011 0.00.022
-0,02 -0,01 0,01 0,02
00 505000 10100000 15150000 20200000
TimTime (sec)e (sec)
FFrequrequeenncycy (Hz) (Hz)
IEC
IEC
(a) (b)
Figure 5 – Waveform (a) and frequency spectrum (b) of magnetic
field generated by a 66,04 cm (26 inches) flat-screen LCD television
Method: Commercially available single-axis and three-axis magnetic field meters are
sometimes provided with output connections that give an output voltage proportional to the
magnetic field strength.
Such instrumentation, in combination with commercially available spectrum analysers, can be
used to characterise the frequency components in the magnetic field. Alternatively, wave-
capturing instrumentation has software that enables the determination of the frequency
content from the recorded data. Magnetic field meters which can be switched to indicate rms
field values of the power frequency and one or more harmonic frequencies are also available.
More modern electric and magnetic field meters include a spectrum analyser.
It should be noted that the frequency content of magnetic fields produced by variable speed
electrical equipment, e.g. electric mass transportation systems, can change as a function of
speed [5].
The electric field of AC power systems has low total harmonic distortion.Therefore the
harmonics of power frequency electric field are negligible [9].
4.1.6 Characterisation of population exposure to magnetic field and definition of
metric
A number of epidemiological studies on occupational or residential exposure, that have
examined the possibility of health effects from exposure to power frequency magnetic fields,
have been conducted. From the magnetic field measurements, different statistic indicators
can be defined.
Method: A more precise assessment of exposure is determined by wearing a small three-axis
exposure meter that periodically records the field at a location of interest on the body.
Estimates of human exposure shall be made from a combination of spatial and temporal
variation measurements and information which describes patterns of human activity [31].
Commercially available three-axis exposure meters that can be worn on the body can be used.
Such instrumentation periodically records the resultant magnetic field value for periods of time
extending to several days, depending on the frequency of sampling of the magnetic field,
memory storage capacity and battery life. The sampling rate will depend in part on the model
assumed for the interaction between the field and subject. The data collected can be
downloaded to a computer, and software provided with the instrumentation or specially
developed, is used to determine exposure to the parameters such as TWA (time weighted
average), geometric mean, and several percentile values.
MMagneagnetticic FFieield (ld (mmTT))
MagneMagnettic Fic Field (ield (mmTT))

– 14 – IEC 61786-2:2014 © IEC 2014
Past human exposures in specified areas should be estimated by having surrogates wearing
exposure meters perform activities that were conducted in the past in the specified areas [27-
28; 30]. This approach assumes that the magnetic field sources have not changed
significantly over time.
4.2 Sources with multiple frequencies
4.2.1 General
If a source is not producing a single sinusoidal field, the field produced can be described as a
superposition of sinusoidal fields with different frequencies. The spectrum of the field may
consist of discrete spectral components or it may be continuous. Examples of sources
producing a discrete spectrum are distribution power lines and AC/DC converters. These
examples also have a harmonic spectrum, which means that spectral components occur only
at integer multiples of one fundamental frequency. A non-harmonic discrete spectrum may be
produced by two or more independent generators. In a continuous spectrum there are no
discrete spectral components visible because it consists of an infinite number of spectral lines
with infinite small spaces. The spectrum of a single impulse or burst is an example of a
continuous spectrum. Also thermal noise produces a continuous spectrum. Of course discrete
and continuous spectra may be superposed in a real spectrum.
The goal of this subclause 4.2 is to show how non-sinusoidal fields can be compared with the
reference levels of existing guidelines or standards.
In the frequency range up to 100 kHz, the guidelines are based on short term effects such as
stimulation of the nervous system [17-19; 21]. The other known biological effect is the
thermal effect which can be neglected below 100 kHz. Reference [25] gives a very good
summary of the literature dealing with neurophysiological effects of electromagnetic fields.
The guidelines define basic restrictions to characterise neurophysiological effects. As these
basic restrictions are not measurable quantities, the guidelines introduce reference levels for
external fields. Basic restrictions and reference levels are frequency dependant.
With the reference level we have a practical model which is valid for external sinusoidal fields.
The reciprocal of the reference level curve can be seen as a transfer function from the
external fields to the biological effect. If the spectrum of the external field strength multiplied
with this transfer function results in value below one, we assume that the external field is in
compliance with the corresponding safety standard.
The concept of transfer function can also be applied to non-sinusoidal fields. The
multiplication of the spectrum of the external field with the transfer function results in a
spectrum which is relevant for the exposure and which can be called the weighted spectrum.
For a discrete spectrum this means that the field strength of each spectral component is
divided by the reference level at the frequency of the spectral line. The question is now how
to add the weighted spectral lines. The following methods are published.
4.2.2 Sum of weighted magnitudes
In references [19], [21] and [18] it is proposed to add the magnitudes of the weighted spectral
lines.
For example, reference [21] proposes the following criteria for magnetic field:
10MHz
H
j
≤1
∑
H
R, j
j=1
where
H is the magnetic field strength at frequency j
j
H is the reference level at frequency j defined in reference [21]

R,j
This method usually overestimates the exposure because it does not use the phase
information of the spectrum.
4.2.3 Weighted peak value
An ICNIRP statement [20] showed clearly that the sum of weighted magnitudes method is only
a worst case estimation because the phase of the weighted spectral lines is not taken into
account. It is proposed to take the phase of the source spectrum into account and transform
the weighted spectrum into the time domain. The peak value of the resulting weighted time
domain signal is finally the relevant exposure measure. For the magnitude of the transfer
function the reciprocal of the reference level curve is used. The phase of the transfer function
is derived from the steepness of the reference level curve.
A method which works completely in the time domain is also proposed in reference [20]: in
this method the time domain signal of the field is convolved with the impulse response of a
weighting filter. The transfer function of this weighting filter is identical to the transfer function
already described for the frequency domain method. Again the peak value of the weighted
time domain signal is the relevant exposure measure.
Mathematically there is no difference between the two proposed methods because
multiplication in the frequency domain is exactly the same as convolution in the time domain.
In Clause 8 of IEC 62311:2007 [11] the weighted peak method is also described in detail. The
weighted peak method using the convolution approach is already available in commercial
measurement instruments. These instruments work in real time, are very easy to use and can
be used for arbitrary signals. Especially pulses, bursts or noise-like signals can be evaluated
in the sense of references [20] and [11].
4.2.4 Impulse separation
For signals with arbitrary temporal behaviour an evaluation of the time domain signal is
proposed in 5.3.2 of reference [1] . It is described in detail for magnetic fields only. The time
domain signal of the field is divided into a sequence of single impulses. From the duration of
each impulse a corresponding frequency is calculated which is used to select the proper
reference level for each impulse. In the general case the peak value of the time derivative of
each magnetic field impulse must then be compared with the peak value of a sinusoidal signal
at the reference level multiplied with its corresponding angular frequency.
In many cases this procedure gives the same results as the weighted peak method described
in references [20] and [11] if the same reference levels are applied, if the impulses are
separated correctly and if the corresponding frequencies of the impulses are extracted
correctly. The reason for this similarity is that the same physical and neurophysiological
effects are the basis of both methods. The interpretation of these effects is however
somewhat different. The task to separate the time domain signal into single impulses and to
extract the relevant parameters is not an easy one and not well defined. Therefore, the
reproducibility of this method is not good.
4.2.5 Weighted RMS value
In [10] it is proposed to add the squares of the magnitudes of the weighted spectral
components in a first step and then take the square root of this sum in a second step as a
measure of the actual exposure. According to Parseval’s theorem the RMS value of the
weighted time domain signal is exactly the same. In reference [10] an averaging time of one
second is proposed for the time domain method. This method was introduced to avoid the
overestimation which could occur by summing the magnitudes directly. Also in reference [11]
the frequency domain version of this method is proposed as a mean of avoiding

– 16 – IEC 61786-2:2014 © IEC 2014
overestimation. However there is no neurophysiological rationale for this approach. Therefore
this procedure might underestimate the real situation.
4.2.6 Highest weighted spectral line
In reference [1] the absence of additive effects of different spectral components regarding the
neurophysiological effects is assumed. According to 5.3.3 of reference [1] it is sufficient to
show compliance of each spectral component separately if the spectrum consists of a limited
number of harmonics and if the amplitudes of these harmonics decay with frequency. For the
rationale of this approach reference [8] is cited in reference [1]. It is worth noting that [8] is
only an abstract. It is also worth noting that the method described in 5.3.2 of Ref. [1] can give
much more conservative results.
4.2.7 Conclusion and recommendation
We have seen that there is a broad range of methods to assess fields with multiple
frequencies. From the current point of view the weighted peak method should be used
because it has the lowest risk for overestimation as well as for underestimation. It also
produces stable and predictable results with a minimum of work for the operator.
...