IEC 61000-4-33:2005

Electromagnetic compatibility (EMC) - Part 4-33: Testing and measurement techniques - Measurement methods for high-power transient parameters

Provides a basic description of the methods and means (e.g., instrumentation) for measuring responses arising from high-power transient electromagnetic parameters. These responses can include: - the electric (E) and/or magnetic (H) fields (e.g., incident fields or incident plus scattered fields within a system under test); - the current I (e.g., induced by a transient field or within a system under test); - the voltage V (e.g., induced by a transient field or within a system under test); - the charge Q induced on a cable or other conductor. These measured quantities are generally complicated time-dependent waveforms, which can be described approximately by several scalar parameters, or "observables". These parameters include: - the peak amplitude of the response, - the waveform rise-time, - the pulse width, and - mathematically defined norms obtained from the waveform. This International Standard provides information on the measurement of these waveforms and on the mathematical determination of the characterizing parameters. It does not provide information on specific level requirements for testing. It has the status of a basic EMC publication in accordance with IEC Guide 107.

General Information

• Status: Published
• Publication Date: 26-Sep-2005
• ICS: 33.100.10 - Emission
• ICS: 33.100.20 - Immunity
• Technical Committee: SC 77C - High power transient phenomena
• Drafting Committee: PT 61000-4-33 - TC 77/SC 77C/PT 61000-4-33
• Current Stage: PPUB - Publication issued
• Start Date: 27-Sep-2005
• Completion Date: 15-Dec-2005

Standards Content (Sample)

INTERNATIONAL IEC
STANDARD 61000-4-33
First edition
2005-09
BASIC EMC PUBLICATION
Electromagnetic compatibility (EMC) –
Part 4-33:
Testing and measurement techniques –
Measurement methods for high-power
transient parameters
Reference number
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INTERNATIONAL IEC
STANDARD 61000-4-33
First edition
2005-09
BASIC EMC PUBLICATION
Electromagnetic compatibility (EMC) –
Part 4-33:
Testing and measurement techniques –
Measurement methods for high-power
transient parameters
© IEC 2005 ⎯ Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
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– 2 – 61000-4-33 ” IEC:2005(E)
CONTENTS
FOREWORD.4
INTRODUCTION .6
1 Scope.7
2 Normative references.7
3 Terms and definitions.8
4 Measurement of high-power transient responses .9
4.1 Overall measurement concepts and requirements.9
4.2 Representation of a measured response. 12
4.3 Measurement equipment. 12
4.4 Measurement procedures. 27
5 Measurement of low frequency responses. 27
6 Calibration procedures . 28
6.1 Calibration of the entire measurement channel. 28
6.2 Calibration of individual measurement channel components . 31
6.3 Approximate calibration techniques. 37
Annex A (normative) Methods of characterizing measured responses . 40
Annex B (informative) Characteristics of measurement sensors. 45
Annex C (normative) HPEM measurement procedures . 59
Annex D (informative) Two-port representations of measurement chain components . 62
Bibliography. 69
Figure 1 – Illustration of a typical instrumentation chain for measuring high-power
transient responses . 10
Figure 2 – Illustration of a balanced sensor and cable connecting to an unbalanced
(coaxial) line where I + I = I . 16
out in 1
Figure 3 – Examples of some simple baluns [4b] . 18
Figure 4 – A typical circuit for an in-line attenuator in the measurement chain. 18
Figure 5 – Illustration of the typical attenuation of a nominal 20 dB attenuator for a
50–: system, as a function of frequency. 19
Figure 6 – Typical circuit diagram for an in-line integrator. 20
Figure 7 – Plot of the transfer function of the integrating circuit of Figure 6. 20
Figure 8 – Illustration of the frequency dependent per-unit-length signal transmission
of a standard coaxial cable, and a semi-rigid coaxial line. 21
Figure 9 – Illustration of sensor cable routing in regions not containing EM fields. 24
Figure 10 – Treatment of sensor cables when located in a region containing EM fields. 25
Figure 11 – Conforming cables to local system shielding topology . 26
Figure 12 – Correct and incorrect methods of cable routing. 27
Figure 13 – The double-ended TEM Cell for providing a uniform field illumination for
probe calibration . 29
Figure 14 – Illustration of the single-ended TEM cell and associated equipment. 30
Figure 15 – Dimensions of a small test fixture for probe calibration. 30

61000-4-33 ” IEC:2005(E) – 3 –
Figure 16 – Electrical representation of a measurement chain, (a) with the E-field
sensor represented by a general Thevenin circuit, and (b) the Norton equivalent circuit
for the same sensor. 31
Figure 17 – Example of a simple E-field probe. 34
Figure 18 – Plot of the real and imaginary parts of the input impedance, Z , for the E-
i
field sensor of Figure 17. 34
Figure 19 – Plot of the magnitude of the short-circuit current flowing in the sensor input
for different angles of incidence, as computed by an antenna analysis code . 35
Figure 20 – Plot of the magnitude of the effective height of the sensor for different
angles of incidence. 36
Figure 21 – High frequency equivalent circuit of an attenuator element . 39
Figure A.1 – Illustration of various parameters used to characterize the pulse
component of a transient response waveform R(t). 41
Figure A.2 – Illustration of an oscillatory waveform frequently encountered in high-
power transient EM measurements. 41
Figure A.3 – Example of the calculated spectral magnitude of the waveform of Figure A.2 . 44
Figure B.1 – Illustration of a simple E-field sensor, together with its Norton equivalent
circuit. 46
~
Figure B.2 – Magnitude and phase of the normalized frequency function F(ZW ) for
the field sensor . 47
Figure B.3 – Illustration of a simple B-field sensor, together with its Thevenin
equivalent circuit . 49
Figure B.4 – Illustration of an E-field sensor over a ground plane used for measuring
the vertical electric field, or equivalently, the surface charge density. 50
Figure B.5 – Illustration of the half-loop B-dot sensor used for measuring the
tangential magnetic field, or equivalently, the surface current density . 52
Figure B.6 – Simplified concept for measuring wire currents . 53
Figure B.7 – Construction details of a current sensor . 54
Figure B.8 – Example of the measured sensor impedance magnitude of a nominal 1 :
current sensor. 55
Figure B.9 – Geometry of the in-line I-dot current sensor . 55
Figure B.10 – Design concept for a coaxial cable current sensor . 56
Figure B.11 – Shape and dimensions of a CIP-10 coaxial cable current sensor. 57
Figure B.12 – Configuration of a coaxial cable I-dot current sensor. 57
Figure D.1 – Voltage and current relationships for a general two-port network . 62
Figure D.2 – Voltage and current definitions for the chain parameters. 63
Figure D.3 – Cascaded two-port networks. 64
Figure D.4 – Representation of the of a simple measurement chain using the chain
parameter matrices. 64
Figure D.5 – Simple equivalent circuit for the measurement chain . 65
Figure D.6 – A simple two-port network modelled by chain parameters . 65
Table A.1 – Examples of time waveform p-norms. 42
Table A.2 – Time waveform norms used for high-power transient waveforms. 42
Table D.1 – Chain parameters for simple circuit elements. 66

– 4 – 61000-4-33 ” IEC:2005(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROMAGNETIC COMPATIBILITY (EMC) –
Part 4-33: Testing and measurement techniques –
Measurement methods for high-power transient parameters
FOREWORD
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all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61000-4-33 has been prepared by subcommittee 77C: High power
transient phenomena, of IEC technical committee 77: Electromagnetic compatibility.
It has the status of a basic EMC publication in accordance with IEC Guide 107.
The text of this standard is based on the following documents:
FDIS Report on voting
77C/156/FDIS 77C/160/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.

61000-4-33 ” IEC:2005(E) – 5 –
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
A bilingual version of this publication may be issued at a later date.

– 6 – 61000-4-33 ” IEC:2005(E)
INTRODUCTION
IEC 61000 is published in separate parts 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
Part 5: Installation and mitigation guidelines
Installation guidelines
Mitigation methods and devices
Part 6: Generic standards
Part 9: Miscellaneous
Each part is further subdivided into several parts and published either as International
Standards or as technical specifications or technical reports, some of which have already
been published as sections. Others will be published with the part number followed by a dash
and a second number identifying the subdivision (example: 61000-6-1).

61000-4-33 ” IEC:2005(E) – 7 –
ELECTROMAGNETIC COMPATIBILITY (EMC) –
Part 4-33: Testing and measurement techniques –
Measurement methods for high-power transient parameters
1 Scope
This part of IEC 61000 provides a basic description of the methods and means (e.g.,
instrumentation) for measuring responses arising from high-power transient electromagnetic
parameters. These responses can include:
 the electric (E) and/or magnetic (H) fields (e.g., incident fields or incident plus scattered
fields within a system under test);
 the current I (e.g., induced by a transient field or within a system under test);
 the voltage V (e.g., induced by a transient field or within a system under test);
 the charge Q induced on a cable or other conductor.
NOTE The charge Q on the conductor is a fundamental quantity that can be defined at any frequency. The voltage
V, however, is a defined (e.g., secondary) quantity, which is valid only at low frequencies. At high frequencies, the
voltage cannot be defined as the line integral of the E-field, since this integral is path-dependent. Thus, for very
fast rising pulses (having a large high-frequency spectral content) the use of the voltage as a measurement
observable is not valid. In this case, the charge is the desired quantity to be measured.
These measured quantities are generally complicated time-dependent waveforms, which can
be described approximately by several scalar parameters, or “observables”. These
parameters include:
 the peak amplitude of the response,
 the waveform rise-time,
 the waveform fall-time (or duration),
 the pulse width, and
 mathematically defined norms obtained from the waveform.
This International Standard provides information on the measurement of these waveforms and
on the mathematical determination of the characterizing parameters. It does not provide
information on specific level requirements for testing.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-161, International Electrotechnical Vocabulary (IEV) – Chapter 161: Electro-
magnetic compatibility
IEC 61000-2-9, Electromagnetic compatibility (EMC) – Part 2: Environment – Section 9:
Description of HEMP environment – Radiated disturbance
IEC 61000-2-10, Electromagnetic compatibility (EMC) – Part 2-10: Environment – Description
of HEMP environment – Conducted disturbance

– 8 – 61000-4-33 ” IEC:2005(E)
IEC 61000-4-20, Electromagnetic compatibility (EMC) – Part 4-20: Testing and measurement
techniques – Emission and immunity testing in transverse electromagnetic (TEM) waveguides
IEC 61000-4-23, Electromagnetic compatibility (EMC) – Part 4-23: Testing and measurement
techniques – Test methods for protective devices for HPEM and other radiated disturbances
IEC 61000-4-25, Electromagnetic compatibility (EMC) – Part 4-25: Testing and measurement
techniques – HEMP immunity test methods for equipment and systems
3 Terms and definitions
For the purposes of this part of IEC 61000, the following terms and definitions, together with
those in IEC 60050-161 apply.
3.1
electrically small
refers to the size of an object relative to the wavelength of the electromagnetic field. When
the object is much smaller than the wavelength, it is said to be electrically small
3.2
equivalent area
an intrinsic parameter of a magnetic flux sensor (loop) that relates the open circuit voltage of
the sensor to the time rate of change of the magnetic flux density linking the sensor
3.3
equivalent height
an intrinsic parameter of an electric field (dipole) sensor, which relates the measured voltage
across the terminals of the sensor to the E-field component exciting the sensor
3.4
free-field sensor
an electromagnetic field sensor used at a location distant from any scattering body or ground
plane
3.5
high power electromagnetic
HPEM
the general area or technology involved in producing intense electromagnetic radiated fields
or conducted voltages and currents which have the capability to damage or upset electronic
systems. Generally these disturbances exceed those produced under normal conditions (e.g.
100 V/m)
3.6
measurement chain
one or more electrical devices connected together for the purpose of measuring and recording
an electromagnetic signal
3.7
Nyquist frequency
the Nyquist frequency is the bandwidth of a sampled signal, and is equal to half the sampling
frequency of that signal. If the sampled signal represents a continuous spectral range starting
at 0 Hz (which is the most common case for speech recordings), the Nyquist frequency is the
highest frequency that the sampled signal can unambiguously represent

61000-4-33 ” IEC:2005(E) – 9 –
3.8
pre-pulse
refers to a portion of an impulse-like transient waveform that occurs at a time before the time
of the primary peak
3.9
sensor
a transducer that senses a particular electromagnetic quantity (such as an electric or
magnetic field, a current or a charge) and converts it into a voltage or current that can be
measured. Typically, this is the first element in a measurement chain for EM measurements
3.10
waveform norm
a parameter that is determined from a mathematically well-defined operation on a waveform
or signal (such as an integration of the waveform), which yields a scalar number that permits
a comparison of various waveforms or their effects
3.11
waveform parameter(s)
a single parameter that denotes a waveform characteristic (such as the rise time of the
waveform), which is difficult to cast into the waveform norm formalism, yet which is useful in
describing a response
3.12
–dot
a suffix (as in I-dot), which denotes the derivative with respect to time of the quantity (I),
implying that the measurement is proportional to the time rate of rise of the response (I)
4 Measurement of high-power transient responses
This standard is concerned with the measurement and description of high-power transient
signals resulting from a high altitude nuclear detonation (referred to as the high altitude
electromagnetic pulse – HEMP) or from the use of a transient source (or pulser) producing
high-power electromagnetic (HPEM) fields. Typically, the physical quantities being measured
include the electric (E) and magnetic (H) fields in (or near) a facility or test object, or the
induced current and charge (or voltage) on conducting wires entering into the facility or test
object.
This clause of the standard describes the overall measurement techniques for these transient
responses, and in Annex A, suggests several waveform parameters and norms that shall be
used to characterize the measured responses. Many of the measurement methods and
equipment may also be used for measuring time harmonic (i.e., frequency domain) signals;
however, this application is not considered further in this document, as we shall be concerned
with only the measurement of transient signals.
4.1 Overall measurement concepts and requirements
The measurement of transient response quantities is realized by using a number of transient
signal processing elements linked together in a sequential manner. Referred to as a
“measurement chain”, this collection of equipment will detect, process, transmit and record
measured transient responses, so that they can be used after the test is finished to analyse a
measured quantity or the electrical behaviour of the system under test.
Figure 1 shows two typical instrumentation chains that shall be used for measuring high-
power transient responses. The measurement chain shown in Figure 1(a) contains the
following elements.
– 10 – 61000-4-33 ” IEC:2005(E)
Waveform
Fibre optic
Fibre optic digitizer
receiver
transmitter
Sensor Balun Attenuator Integrator
Coaxial cable
Data acquisition
Fibre optic cable
and control
IEC  1432/05
(a) Instrumentation chain using a coaxial cable and fibre optics
Waveform
digitizer
Sensor
Integrator
Attenuator
Balun
Coaxial cable
Data acquisition
and control
IEC  1433/05
(b) Instrumentation chain with only coaxial signal lines
Figure 1 – Illustration of a typical instrumentation chain
for measuring high-power transient responses
– Coaxial cable – this element provides an electrical connection between the various
elements of the measurement chain, at a constant impedance (typically 50 :). An
alternative to this element is the fibre-optics transmission system discussed below.
– Sensor – a device that converts the measured quantity (EM field, current, or charge) into a
voltage that can be measured.
– Balun – a device that operates as a matching transformer to ensure that the sensor is well
adapted (matched) to the coaxial signal line. This device also helps to suppress common-
mode signals.
– Attenuator – a signal reduction device installed in-line to reduce the sensor signal strength
if it is too large.
– Integrator – an active or passive device to integrate in time the sensor output. This is
needed because in some cases, a sensor will respond to the time rate of change (e.g., the
derivative) of the measurement quantity. (Signal integration can also be performed in
software.)
– Fibre optics transmitter – a device to convert the measured fast transient electrical signal
to a modulated optical signal, which can be transmitted away from the vicinity of the
sensor to a distant recording device.

61000-4-33 ” IEC:2005(E) – 11 –
– Fibre optics cable – a non-conducting fibre cable that can be routed in and around the
system under test to permit the transmission of the optical signal to the distant optical
receiver.
– Fibre optics receiver – a device that receives the modulated optical signal from the
transmitter, demodulates it and recovers the imbedded information from the sensor.
– Waveform digitiser – this is the detector in the measurement chain, which receives the
sensor electrical analogue signal, converts it into a stream of digital data and then passes
these data on to a recording device.
– Data acquisition and control computer – the main logic processor to conduct the
measurements and store and analyse the results.
Additional information on each of these elements in the measurement chain will be provided
later in this clause.
Not all of the elements of the measurement chain in Figure 1(a) are always necessary. For
example, the attenuator shall be required only if the sensor response is so large that it tends
to over-drive the fibre optics (FO) transmitter and cause signal distortions. Similarly, some
sensors may have a self-contained integrator, so that the integrator element in the
measurement chain shall be omitted.
Figure 1(b) illustrates a case where the entire measurement chain is interconnected only by a
coaxial cable. The FO system is not present in this case, perhaps due to some special feature
of the signal being measured:
– the dynamic range of the desired signal is larger than that provided by the FO
transmit/receive equipment,
– the measured pulse is much faster than the transmission capabilities of the FO system, or
– perhaps the cost of the FO system is prohibitive.
Regardless of the configuration of the measurement chain, there are several basic
measurement principles that must be recognized during the course of performing the
measurements. These are as follows.
– The measurement sensor always perturbs the EM field in its vicinity (or influences the
local current and/or charge densities). It can be shown that if a sensor were designed to
not perturb the field, it would register a zero response.
– The use of a measurement chain can “load” the system or circuit being measured, so that
the obtained reading may not be the true response.
– The measurement chain can be used to measure both near field and far field responses.
Typically, a field sensor will measure only one of the three orthogonal E- or H-field
components, and whether the observation point is in the near-zone or the far zone is
unimportant in describing the responses. In the far-zone, the E/H ratio of the principal
(transverse) field components is equal to the impedance of free-space (377 :), but in the
near zone this E/H relationship is not maintained.
– The sensor shall be calibrated to provide a suitable relationship between its electrical
output and the response quantity it is measuring.
– In addition to the sensor, the remainder of the measurement chain can also add errors to
an EM field quantity being measured, and such errors shall be minimized. Such errors can
arise both from secondary scattering from the measurement equipment (which adds an
error in the fundamental EM field quantities being measured), and from a perturbation of
the response provided by the sensor as it propagates through the measurement chain
(say, from external common-mode currents on a coaxial cable affecting the internal signal
through the shield transfer impedance). The use of the FO transmission system is one way
of minimizing this unwanted perturbation. Other ways include a careful routing of the
coaxial cable so as to minimize pick-up, the use of ferrite beads on the coax to attenuate
induced currents, additional shielding over the coaxial lines, and keeping the length of the
coax line as short as possible.

– 12 – 61000-4-33 ” IEC:2005(E)
– Calibration procedures shall be applied to all elements of the measurement chain. The
integrator functions ideally only over a particular frequency band. The coaxial cable has
increasing loss as the frequency increases. Each of these facts shall be taken into
account in developing an end-to-end calibration of the measurement chain.
– The measurement system noise shall be determined and its effects on the measured
response quantities shall be quantified.
– Once a “raw” waveform is measured and digitised by the recording device, the calibration
function shall be applied and a “corrected” response waveform determined.
– After the corrected waveform is determined, it shall be summarised by one or more
waveform parameters, or norms, identified in Annex A.
Details and requirements for each of these measurement chain elements will be discussed
in 4.3.
4.2 Representation of a measured response
The measured, corrected and digitised waveform that is ultimately recorded by the data
acquisition computer is usually a complicated function of time. To easily distinguish between
one waveform and another, and to relate a particular waveform to a possible effect on a
system or facility, one or more scalar numbers representative of the waveforms shall be used.
In this manner, only a few numbers, as opposed to the entire data record of the transient
waveform, can summarize the essence of a waveform.
In describing the response waveform in this manner, there are two classes of numbers that
shall be used. Waveform parameters are numbers that are immediately obvious from an
examination of the transient response, such as the peak amplitude. Waveform norms, on the
other hand, are mathematically defined scalar parameters that require a numerical processing
of the total waveform. The energy contained in the waveform is an example. In this clause of
the standard, each of these types of waveform parameters is defined.
Annex A of the present standard provides additional information on how measured transient
waveforms can be characterized.
4.3 Measurement equipment
As noted in Figure 1 there are four major elements to the measurement system. These
include:
– the response sensor that measures an electrical parameter (EM field component, a
current, or a charge) and converts it into a voltage;
– the transmission system that transports the measured voltage from the sensor to the
detection equipment;
– the detection (or digitisation) system that takes the received voltage response and
converts it into a digital format for processing and storage; and
– the computer controlling the measurement process and performing data processing and
storage.
4.3.1 The measurement chain
Each of these measurement chain elements can affect the amplitude and wave shape of the
recorded signal, and it is important to understand and control such perturbations. As an
example, consider the case of a transient EM field described by its E-field component E (t)
o
striking the field sensor in Figure 1(a), and producing a transient response at the recording
1)
device given as R (t). As noted in [1] , the relationship between the transient
measured
response and excitation is given by a convolution (*) operation as
—————————
1)
Figures in square brackets refer to the Bibliography.

61000-4-33 ” IEC:2005(E) – 13 –
R (t) E (t)
T(t) , (1)
measured o
where T(t) is the impulse response of the measurement system. Given the measured
response R (t), the goal is to determine the excitation E (t) , and [1] represents this
measured o
process symbolically as the deconvolution (1/*) operation
E (t) R (t) (1/
) T(t) . (2)
o measured
In [1], various techniques that may be used to evaluate this deconvolution operation to
determine E (t) are discussed, with one of them being recasting equations (1) and (2) in the
o
frequency domain through the use of Fourier transforms, and then using the transfer function
concept [2] to deconvolve the excitation function.
Denoting the Fourier transforms of the measured transient response and the excitation E-field
~
~
at the sensor by R (f ) and , respectively (see Annex A), the frequency domain
E (f )
measured o
equivalent of equation (1) is expressed as
~ ~ ~
R (f ) T(f )E (f ), (3)
measured o
where now the convolution operation becomes a simple multiplication by the Fourier spectrum
~
of the transfer function T(f ) . In the frequency domain, the deconvolution operation of equation
(2) is given as the inverse of equation (3) as
~ ~ ~
1
E (f ) T (f ) ˜ R (f ) . (4)
o measured
NOTE In this standard, transient quantities are represented using the notation F(t), and the corresponding Fourier
~
spectral density is .
Ff
~
This deconvolution is easily carried out, as long as the transfer function spectrum T(f ) is not
zero at any real frequency f. Once the spectrum of the excitation field is determined, the
transient behaviour of this field component may be determined by taking an inverse Fourier
transform.
As noted in Figure 1(a), the measurement chain consists of several different elements, each
~
of which contributes to the overall transfer function . Because each element in the chain is
T(f )
designed to function at a constant impedance level (typically 50 ohms), the end-to-end
~
transfer function of the measurement chain can be evaluated as the product of individual
T(f )
complex-valued, frequency dependent transfer functions for each element in the measurement
chain. In this manner, the overall transfer function is given as
~ ~ ~ ~ ~ ~ ~
T (f ) T (f )˜T (f )˜T (f )˜T (f )˜T (f )˜T (f ) . (5)
digitiser fibre optics integrator attenuator balun sensor
To determine the spectrum of the excitation field from equation (4) it is necessary that the
~
transfer function be known. Methods for determining this transfer function accurately
T(f )
(both in magnitude and phase over a wide frequency range) will be discussed in Clause 6 of
this standard. In many instances, however, the various transfer function components in
equation (5) are designed to be very simple functions of frequency or even constants over a
wide frequency band, and this makes the overall transfer function very simple.
Subclause 4.3.2 in this standard and Annex B discuss several different types of sensors that
provide output responses that are related to an excitation function (like an incident field or
induced current.) The responses of these sensors are seen to be of two basic types: one
which has an output that is approximately proportional to the excitation quantity and another,

– 14 – 61000-4-33 ” IEC:2005(E)
in which the sensor output response is proportional to the time rate of change (derivative) of
the excitation.
For the first type of sensor, the transient response of the device is given as
V (t) K E (t) (6a)
out sensor o
and the corresponding frequency domain spectral representation is
~ ~
V (f ) K E (f ) , (6b)
out sensor o
where K is a characteristic constant of the sensor.
sensor
For the second type, or differentiating sensor, the output is given as
d
V (t) K E (t) , (7a)
out sensor o
dt
and the frequency domain spectrum is
~ ~
V (f ) j 2S f K E (f ). (7b)
out sensor o
For the case when a differentiating sensor is used, it is necessary to provide some sort of an
integration function to recover the excitation function from the derivative signal provided by
the sensor. This can be provided either by an integrating circuit element in the measurement
chain (described more fully in 4.3.5), or by a post-processing of the computed response using
numerical methods. If a hardware integration of the signal is to be used, the integrator
provides an output that is proportional to the integral of the input signal, and in the frequency
domain, this is expressed as
~ ~
V (f ) K V (f ) , (8)
out integrator in
j 2S f
where K is a characteristic constant for the integrator component.
integrator
Thus, when a differentiating sensor is used in the measurement chain, the measured
response from equation (3) can be represented as
~ ~ ~
R (f ) T(f )E (f )
measured o
~
§ 1 ·
¨ ¸
| K ˜ K ˜ K ˜ K ˜ K ˜ j 2S f K E (f ) (9a)
digitiser fibre optics integrator attenuator balun sensor o
¨ ¸
j 2S f
© ¹
~
| K E (f )
o
and if a self-integrating sensor is used, the measured response is
~ ~ ~
R (f ) T(f )E (f )
measured o
~
|K ˜ K ˜ K ˜ K ˜K E (f )
(9b)
digitiser fibre optics attenuator balun sensor o
~
| K E (f )
o
61000-4-33 ” IEC:2005(E) – 15 –
The scalar coefficients of the components (K ) in equations (9a) and (9b) are typically
i
provided by the manufacturers of the measurement chain components and are often used
without further calibration. However, for accurate measurements of such HPEM fields, each of
these components shall be calibrated before being used in a measurement program.
Regardless of the type of sensor used in the measurement, the overall transfer function K is
used to compute the excitation function spectrum as
~ ~
1
E (f ) K ˜ R (f ) . (10)
o measured
Because K is frequency independent, the resulting transient response is given as
–1
E (t) = K ˜ R (t). (11)
o measured
In many practical cases involving transient signals having fast rise times, the frequency range
~
of interest is such that the transfer function T (f ) is not a constant over the frequency band.
Consequently, equations (10) and (11) are not suitable for determining the excitation from the
measured response. In such cases, it shall be necessary to determine the overall complex-
valued transfer function of the measurement chain by calibration methods, and then use
equation (4) to compute the excitation function.
4.3.2 Response sensors
As discussed in 4.3, the first element in the measurement chain of Figure 1 is the EM sensor,
which interacts with the local EM field (or current, or charge) and produces a voltage output.
The design of a sensor has been described in detail by Baum [3, 4], where the following
requirements are set out for an “ideal” sensor.
a) It is an analogue device which converts the electromagnetic quantity of interest to a
voltage or current (in the circuit sense) at some terminal pair for driving a load impedance,
usually a constant resistance appropriate to a transmission line (cable), terminated in its
characteristic impedance.
b) It is passive.
NOTE As discussed in Annex B, it is also possible to have sensors that are active; however, the passive sensor is
viewed as being simpler to calibrate, and thus, are often viewed as being more desirable than the active sensors.
c) It is a primary standard in the sense that, for converting fields to volts and current, its
sensitivity is well known in terms of its geometry; i.e., it is “calibratable by a ruler” [5]. The
impedances of loading elements may be measured and trimmed. Viewed another way, it
is, in principle, as accurate as the standard field (voltage, etc.) in a calibration facility. (A
few percent accuracy is usually easily attainable in this sense).
NOTE This requirement is for the “ideal” sensor, in which there is a simple geometrical relationship between the
field component being measured and its output signal. This simplifies the sensor calibration procedures. For other
types of sensors that are not “calibratable by the ruler”, the calibration process must be accomplished as described
in 6.2.2.
d) It is designed to have a specific convenient sensitivity for its transfer function, which is
often expressed as an equivalent area or an effective height.
e) Its transfer function is designed to be simple across a wide frequency band. This may
mean “flat”, in the sense of volts per unit field or rate of rise of the field, or it may mean
some other simple mathematical form that can be specified with a few constants (in which
case more than one specific convenient sensitivity number is chosen).

– 16 – 61000-4-33 ” IEC:2005(E)
In using such sensors, it is important to keep in mind that there can be significant voltages
developed within the sensor and on the sensor cables. If the quantity being measured is too
large for the sensor design, there can be corona or arcing within the sensor, which will cause
a misreading of the response, or possibly damage within the sensor. Thus, the sensor shall
be carefully selected for the expected response level to be measured.
Annex B provides more details on the representations of the transfer functions for different
types of EM field sensors. Additional details of the physical realization of sensors also are
provided in Annex C of IEC 61000-4-23.
4.3.3 Baluns
When a balanced EM sensor, like a dipole antenna, is fed with coaxial cable, it is possible
that a portion of the induced antenna current will flow on the exterior surface of the cable
shield. Such currents can flow around the outside cases of measurement equipment and
couple energy into the power lines or into the ground connection. This can result in
unpredictable equipment performance and unintended interference to other equipment. Figure
2 illustrates such a connection, where it is evident that a portion of the current from the
sensor (I ) flows in an uncontrolled manner on the exterior of the coaxial cable and the
out
equipment enclosure. I can also be considered to be the common mode portion of the cable
out
current.
I
1 I
out
Balanced
I
in
–I I
1 in
R
EM sensor L
–I
Balanced line
C
p
I
out
Unbalanced line
(coax)
Equipment enclosure
IEC  1434/05
Figure 2 – Illus
...