EMC in Industrial Automation Systems webinar - May 2020 - Peter Thomas

EMC Awareness for Industrial
Automation Systems
Webinar
Peter Thomas
Control Specialists Ltd
May 2020
www.controlspecialists.co.uk
EMC Awareness for Industrial Control Systems © Control Specialists Ltd – May 2020 Page 2
 Established in 1989, we are an organisation
with ongoing experience in the design,
commissioning and support of programmable
industrial automation systems and the
communication networks used by them.
 Our experience includes utilities (water and
gas), pharmaceutical, logistics, waste disposal
to name but a few
 We also provide training courses on several
areas of industrial automation and are a
PROFIBUS and PROFINET International Training
Centre (PITC).

Online, Instructor-Led Training
We are offering the following, one-day instructor-led online
training courses.
All delegates will have access to the diagnostic equipment on
our live networks.
 PROFIBUS Commissioning and Maintenance
 PROFINET Commissioning and Maintenance
 EMC Awareness for Industrial Automation Systems
For information contact cslsales@controlspecialists.co.uk
Other Webinars
 PROFINET Network Design - 20th May at 10:30 BST
 PROFINET Network Diagnostics - 27th May at 10:30 BST
 PROFINET to PROFIBUS Gateways – 3rd June at 10:30 BST
 PROFIBUS Lightning Surge Protection – 10th June at 10:30 BST
To register contact cslsales@controlspecialists.co.uk

Introduction
 This webinar will provide a brief introduction to the often
complex world of achieving EMC compliance in industrial
automation control systems.
 We have purposely avoided complex mathematical formula
and have limited the depth on each topic to fit within the
one hour time frame to give you the opportunity of asking
questions both during and after the presentation.
 If you are interested in taking this further, then we offer a
one-day online instructor led EMC Awareness training course.
What is EMC?
 Items of electrical and electronic
equipment have been designed to limit
the release of internally-generated
Electromagnetic Interference (EMI) into
its environment.
 Items of electrical and electronic
equipment have been designed to be
capable of operating within the
electromagnetic environment that it
will be installed and used.
Source
Victim
 EMC, Electromagnetic Compatibility, is the term used to ensure
that:

Sources and Victims of EMC
 Lightning strikes.
 High voltage/current mains wiring.
 Drives/inverters.
 Switched mode power supplies.
 Inductive loads such as
contactors/solenoids
 Transmitting devices such as Wi-Fi hubs,
mobile ‘phones etc.
 Computer equipment, for example PCs,
controllers, PLCs, HMI panels etc.
Source
 Signal transmission cables, for example
instrumentation, fieldbus and network
cables etc.
 Computer equipment, for example PCs,
controllers, PLCs, HMI panels etc.
Victim
The EMC Directive and CE
Marking
 The EMC Directive (EMCD) is one of several
directives that is mandatory for an item of
electrical or electronic apparatus to be given a CE
Marking.
 The EMCD requires that all such items of
apparatus meet the following requirements:-
 The electromagnetic disturbance generated
by the apparatus does not exceed a level
specified in harmonised EMC standards. If it
does it may interfere with radio and
telecommunications equipment.
 The apparatus has a level of immunity to
electromagnetic interference that might be
expected during normal use thereby allowing
it to operate as intended.

EMC and Fixed Installations
In an industrial automation environment, these items of electrical
and electronic equipment rarely operate in isolation and will often
interact with other items of equipment installed locally, or
remotely, from it. Such a situation is defined as a “fixed
installation”. Here, the items of equipment will ….
 Often be manufactured by different companies.
 Be installed in wall or floor-mounted cubicles (panels).
 Be very different from one another, e.g. instrumentation,
transformers, lighting, variable speed drives etc.
 Have cabling run along cable tray.
 Often be installed on old sites that pre-date the use of modern
day electronics.
 The use of several EMC-compliant devices in a fixed installation
will only result in an EMC-compliant installation if the system as
a whole has been designed an installed following proven EMC
techniques.
 The EMCD and CE Marking is primarily aimed at discrete
items of apparatus and not for fixed installations.
 The definition of a fixed installation is a combination of
several types of apparatus where applicable devices are
installed and assembled to be used permanently or at a
predefined location.
 The EMCD does however state that fixed installations
shall be installed taking account of good engineering
practices and the information provided by the
respective manufacturers regarding the intended use of
the apparatus.
EMCD and Fixed Installations

How can EMC be achieved
in a fixed installation
 Only using equipment that are known to have been designed
and tested to the relevant EMC standards.
 Ensuring that the equipment is installed in line with
manufacturing guidelines.
 Being aware of the standards that apply in achieving EMC
compliance in an installation.
 Risk accessing the installation against the standards from an
EMC point of view.
 Ensuring that electrical designers and installers are aware of
the techniques of ensuring EMC compliance in a fixed
installation and following them.
 Controlling change during the life cycle of the system to ensure
that EMC-compliance is not compromised.
Standards and Normative
References
 Standards vary from region to region
but the theory behind them is
international.
 One international standard of note is
IEC 61000:5:2 “Electromagnetic
compatibility (EMC). Installation and
mitigation guidelines. Earthing and
cabling”. Many other standards
reference this standard in their
“Normative Reference” section.
 A Normative Reference is a list of one
or more separate standards that have
to be followed in part, or in full, in
order to conform to the standard that
is referencing them.

 In the UK, all people involved in the
design an installation of electrical
installations (commercial or industrial)
have to follow BS 7671: 2018 – The are
commonly known as the IEE Wiring
Regulations.
 From an EMC point of view, BS 7671
contains approximately 6 sides of A4
paper. It does however reference
several other standards.
 Other counties will have their own
equivalent of BS 7671 and the
normative references they quote.
Standards and Normative
References
BS7671:2018 and EMC
Section 444 of BS 7671 states
that “The requirements of
the following standards shall
be applied where
appropriate:”
 BS6701
 BS EN 50310
 BS EN 50174
 BS IEC 61000-5-2
IEC 61000-5-2 is referenced either directly, or indirectly, by the other 3.

BS7671:2018 and EMC
PI Guidelines
• PI released a guideline entitled
“Functional Bonding and Shielding of
PROFIBUS and PROFINET” in 2018
• It is available free of charge to members
of PI from
https://www.profibus.com/download/fu
nctional-earthing-and-shielding/
• The guidelines contain 6 clear
recommendations that network designers
are advised to consider.

Industrial Automation
Emissions
EMC Coupling Paths
 EMI can be transmitted from source to victim via various
coupling paths:
1. Conduction - i.e. via wires, cable screening, surrounding
metalwork.
2. Inductive Coupling – caused by short range magnetic induction.
3. Capacitive Coupling – caused by short range capacitive coupling.
4. Radiated – A combination of inductive and capacitive coupling
applying over larger distances and usually very high frequencies
Source Victim

EMC in Industrial Automation
Systems
Source
 90% caused by power electronics.
 10% other reasons.
Victim
 90% of the problems are due to bad
grounding/reference.
 10% due to bad design, production
faults and aging.
Source – Ghent University 2019
Source
Victim
Examples of Good EMC
Engineering Practice
 In general, evidence of good practice is where installation
techniques have been followed to mitigate against the
possibility of Emissions, Coupling & Radiation and Immunity.
 Emissions – Take appropriate actions to mitigate the source of
disturbances by EMC design, e.g. filters, Shielding etc.
 Coupling and Radiation – Take appropriate actions in respect
of distances, equipotential bonding, selection of cables etc,
shielding etc.
 Immunity – Take appropriate actions to ensure that sensitive
equipment is protected against the various types of
disturbances that might be expected.
 Note – It is not the purpose of the EMCD to ensure
Electromagnetic Compatibility between specific items of
equipment inside the borders of the fixed installation.

Technical Basics
 EMC is a complex subject and can be very technical.
 It is not necessary to have a full knowledge of all of the
theory and formulas to design and install a system that
has good EMC
 However, some technical knowledge will help you
understand more about EMC and how it is achieved in a
fixed installation.
 We will briefly cover the following terminology.
 Resistance and Impedance
 Inductive and Capacitive Coupling
 Frequency and Wavelength
 Differential and Common Mode Currents.
Resistance (R)
 We are all aware that current(i)
flowing in a length of copper cable
will be dependent upon the supply
voltage (v) and the resistance (Ω)
of the cable.
 If the voltage remains constant
then the amount of current will be
dependent upon any variation in
resistance.
 Cables with a larger cross-sectional
area will have more copper and
will therefore have a lower
resistance per metre.
 For a given cable, the resistance
will vary as the ambient
temperature changes.
R
i
V
𝒊 =
𝑽
𝑹

Impedance (Z)
 In AC circuits, i.e. where the
voltage and current are continually
changing, we should really use the
term Impedance.
 Impedance (Z), like Resistance (R),
is measured in ohms, but unlike
resistance, impedance will change
as the frequency of the voltage /
current changes.
Z
i
V
𝒊 =
𝑽
𝒁
Inductance (L)
 Inductance is the property of electrically conductive
materials to oppose any change to the current flowing in
them. The symbol for Inductance is L.
 This is achieved by generating an opposing electromagnetic
force (emf), some times called a back-emf.
 The faster the current changes (higher frequency) the
greater the opposition.
 The symbol of inductance is shown below.
 Although the symbol infers a coil, even straight conductors
have some inductance that at some frequency will become
significant.

Capacitance C
 Capacitance is the ability of a system of electrical
conductors and insulators to store an electrical charge when
a potential difference exists between the conductors. The
symbol for capacitance is C.
 Because the conductors are electrically insulated from one
another, no current actually flows between them.
 However, as the voltage between the two changes faster
(higher frequency), a transient redistribution of electrons
occurs in the adjacent conductor which appears as though it
is conventional current.
Cabling and Impedance
 A cable running in free air can be represented as a resistor in
series with an inductor
 At low frequencies, the inductance effect is negligible and can
be ignored.
 As the frequency of the current increases, L will dominate.
 The formula for current flowing in this cable would be:
XL = Inductive Reactance = 2ΩFL where F is the frequency in Hertz.
As F increases then Z increases and i gets reduces.
LR
𝒊 =
𝑽
𝒁
=
𝑽
𝑹 𝑿𝑳

Cabling and Coupling
 A cable running close to a separate conductor or conductive
material will have capacitance as well as resistance and
inductance.
 In such a situation, a changing voltage in conductor A will
produce a changing voltage in conductor B (capacitive coupling)
and a changing current in conductor A will produce a changing
current in Conductor B (inductive coupling).
 The coupling effects will increase as the frequency increases.
LR
LR
C C
Conductor A
Conductor B
Frequency and Wavelength
 When a sinusoidal signal travels along a cable at a certain speed,
, the period, T, translates to a distance along the cable:
Velocity, v
Wavelength, 
 = vT =
Distance
TimeT

Velocity, v
Wavelength, 
Distance
 Electromagnetic waves traveling in a vacuum do so at the speed of light
‘c’ (c = 2.99 * 108 m/s), but when travelling in copper conductors they
slow down.
 Assuming that electrical signals travel down a copper conductor at 67%
of the speed of light (C), then the wavelength of a 50Hz ac electrical
signal would be:
Wavelength (ƛ) =
∗ .
=
. ∗ ∗ .
= 4017 km
Velocity, v
Wavelength, 
Distance
 If the frequency were to increase to 10MHz, the wavelength would
reduce to:
Wavelength (ƛ) =
∗ .
=
. ∗ ∗ .
∗
= 30m

Accidental Antennas
Metallic structures in
buildings, whose physical
dimensions are > 1/6th of
the wavelength, are
often referred to as
“accidental antennas” by
EMC experts.
Differential Mode Current
 Differential Mode Current (DM) is conventional current that
flows from a voltage source, through a load and back to the
source.
ZLCable
idm

Common Mode Current
 Common Mode Current (CM) is can be caused by capacitive
coupling between one circuit and another.
 Most EMC issues are a result of uncontrolled CM currents.
ZLCable
idm
ZE
icm
Demonstration
 This demonstration will use an Oscilloscope and
Spectrum Analyser to show why a continuous stream
of electrical pulses can cause far more EMC issues
that a sine wave.
 The first part will show you how an oscilloscope
displays a sine wave and a square wave at several
different frequencies.
 The second will show the same signals as displayed
on a spectrum analyser.

Demonstration Setup
Oscilloscope
Spectrum Analyser
Waveform Generator
EMC Good Engineering
Practice
There are several techniques that can be
followed to provide evidence of good EMC
practice in industrial automation systems.
These include:-
 Ensuring adequate separation between
cables of different categories.
 Terminating the shields of all shielded
cables at both ends to a low impedance
bonding network.
 Avoiding the use of “pig tails” on cable
shield and ensuring 360o termination using
clamps or dedicated EMC glands.
 Ensuring the low impedance bonding of all
cubicles (panels) to the same low
impedance bonding network.
 Terminating the shields of shielded cable on
entry / exit to all cubicles.
 And many more …..

Cable Categorisation
 Cable Categorisation is the technique of grouping cables
carrying similar electrical signals into separate categories and
then ensuring that there is some physical distance between
the cables in each category.
 Typical categories might include sensitive cables (CAT I) , low
voltage cables (CAT II), high voltage cables (CAT III) and
cables at risk of direct lightning strikes (CAT IV).
 Recommended Cable separation distances are stated in
several standards and, in some cases, differ from one another
in terms of exact numbers.
 A typical separation distance between the categories above
would be between 100mm and 150 mm.
 However, the latest release of 50174-2, section 6.2.1 provides
a method of making a more informed calculation that may
result in much smaller distances.
Cable Categorisation
 Typical cable separation distances:
Cables in
category I
Cables in
category II
Cables in
category III
Cables in
category IV
≥20cm
≥10cm ≥10cm
≥50cm
≥50cm
≥50cm

Use of cable trays
 When laid in a single cable tray the different categories should
be separated by the recommended distances:
10cm10cm
Cat III Cat II Cat I
 When separated by earthed steel partitions with a steel lid, the
bundles can be placed next to each other:
Cat III Cat II
Cat I
• All channels and partitions must
be properly earthed.
• Use flexible bonding links
protected against corrosion.
• Braided straps are better than
solid metal.
Cable Shielding
The shield of a cables serves two purposes, depending upon the
application.
 In network cables, the shield prevents externally generated
EMI from reaching internal conductors.
 In Variable Speed Drive motor cables, the shield prevent
internally-generated EMI from escaping into the local
environment.

Shield Termination
 For the shield of a cable to perform its task, a current must
flow in it. Therefore it MUST be terminated at both ends.
 However, this is not always done because of concerns of
creating ground loops. This would not be an issue in
modern-day networks used in a correctly designed EMC-
compliant bonding network.
 In the UK, this techniques is called “grounding” or
“earthing” the shield. This is an unfortunate terminology as
both have nothing whatsoever to do with EMC as we will
explain on the following page.
 Depending on the frequency of the currents flowing in the
shield, the shielding effect will be due either an opposing
magnetic field created by the shield current or the skin
effect in the shield.
Shield Termination
If the earthing or grounding of a shield at both ends was vital for
EMC, the only way to achieve EMC in an aircraft containing
shielded cables would be as follows:-
Earthing has nothing to do with EMC. Earthing is a safety-related
matter.

The magnetic field caused by the current in conductor 1 will
induce a current in the shield of conductor 2 but only if:
1. It is terminated at BOTH ends and …
2. The bonding infrastructure has a low impedance
How duel-end termination
of a shied works.
Bonding Infrastructure
 The correct method therefore is to
terminate the shield at both ends to a
common, low impedance bonding
infrastructure.
 The fact that the bonding
infrastructure itself is “earthed” or
“grounded” is a safety requirement
and nothing whatsoever to do with
achieving good EMC.
 A bonding infrastructure that meets
the requirements of both safety and
EMC is called a MESH Common Bonded
network (MESH-CBN) and is described
in 50310.
 Such a system avoids long lengths of
bonding cable that would limit the
flow of high frequency currents.

Panel Design
There is little point in going to the effort of good
EMC design if the cubicles themselves do not
follow a similar design route. Such a route would
include:-
 Internal design laid out with EMC in mind.
 Ensuring a low impedance bond between the
cubicle and the bonding network.
 Minimising the number of aperture’s.
 The use of EMC-compliant bonding between
panel sides and doors, e.g. braided straps as
opposed to wire.
 Making sure that painted surfaces do not result
in high impedance connections.
 360o Termination of the shields of shielded
cable on entry / exit to the cubicles.
But what about existing
Installations?
 What we have covered so far is a high-
level introduction to some of the proven
techniques that can be used as evidence
of good engineering practice in achieving
EMC in a new installation.
 The same techniques apply in existing
installations but the existing bonding
infrastructure may be one designed for
conventional electrical safety, i.e. “star”
earthing.
 Such a bonding network is considered
bad for EMC at all frequencies.
 This does not mean that you need to
implement a site-wide improvement. But
it does mean that you may need to
implement local improvements.

Variable Speed Drives (VSD’s)
 Variable Speed Drives are becoming a
more and more popular way of
controlling the speed of induction
motors.
 There are many good reasons for using
them but they have the potential of
creating significant EMC compliance
issues if they and the cables to / from
them are not installed correctly.
 The simplest way of doing this is to
ready the manufacturers installation
guidelines and following them.
 Unfortunately this is not always done.
 The most common method of varying the frequency of the supply
to the motor is to employ a technique known as Pulse Width
Modulation (PWM).
 High-speed solid-state switches (Thyristors or Insulated Gate
Transistors) are used to rapidly switch the current in pulses. A
narrow pulse is equivalent to a low voltage and a wide pulse is
equivalent to a high voltage.
 You will know from the earlier demonstration that such pulses
will produce harmonics at multiples of the switching frequency.
 Although the switching frequency of a Variable Speed Drive is
between 2 and 16 KHz. The emissions as a result of PWM can go
up into MHz.
PWM Voltage
to Motor
Equivalent
synthesized
sine wave
VSD’s and EMC

 Supply Harmonics and Filtering.
 Potential damage to bearings.
 Choice of Motor Cable – Construction, Installation and
Shielding.
Consequently, despite their obvious advantages, several factors
need to be considered when using VSD’s:
Variable Speed Drives
A common source of high
frequency bonding currents
The four channels of the
EMC INspektor were
connected as shown.

A common source of high
frequency bonding currents
Summary
 Be aware of the EMC standards that apply to the design and
installation of electrical installations in your region and those
regions that you, or the installation, will be operating in.
 Ensure that the relevant people in your organisation are
sufficiently trained for the design and installation of your
fixed installations from an EMC point of view.
 Risk-access your particular situation/ application against these
standards.
 Document the risk assessment.
 Follow good engineering practice.
 Have a change control procedure in place.

 Using the term impedance, rather than resistance, where EMC is
concerned is important.
 A knowledge of the frequency of concern(s) will be very useful,
i.e. what are the likely frequencies of any emissions in the
installation?
 Currents (DM or CM) will always flow in loops and will prefer low
impedance loops over higher impedance loops.
 EMC will be made easier by having CM currents flow in small loops.
 As the physical dimensions of building infrastructure components
become > 1/6th of the wavelength of the “frequency of concern”,
they can resonate and become “accidental antennas”. These
should be avoided.
 Remember that it is improvements to the bonding infrastructure
and not the earthing / grounding that will make a difference to
EMC.
Summary
Peter Thomas
Chairman of PI Training Centres and Technical Officer – PI UK
www.linkedin.com/in/petermthomas
peter.thomas@controlspecialists.co.uk
www.controlspecialists.co.uk
Tel +44(0)1925 824003

EMC in Industrial Automation Systems webinar - May 2020 - Peter Thomas

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