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SUMMARY THE PRESERVATION of signals and equipment are gener-ally characterized by the term Electromagnetic Compatibility (EMC), whose essence will translate in its own grounding system. The proper EMC im-provement in the installation of automation and control systems ensures a significant reduction of the risks and costs associated with failure of equipment, whose conse-quences can be disastrous, thus justifying a systematic approach for the grounding sys-tem as it is not effective to elect a few “rules of thumb” to solve all would be scenarios.
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1. THE ROLE OF THE GROUNDING 20212
SYSTEM AND ITS OBJECTIVES
Automation and control systems are
dependent on electronics to meet their
needs in the various processes. When the
equipment associated with these processes
are damaged or have a malfunction due to
electromagnetic disturbances, there will be
risks related to safety and financial losses.
The proper operation of automation and
control systems is thus directly related to
the integrity of the equipment and signals,
this integrity being generally characterized
by the term Electromagnetic Compatibility
(EMC), which can be defined as the ability
of a device, unit of equipment or system to
function satisfactorily in its electromagnetic
environment without introducing itself in-
tolerable electromagnetic disturbances to
that environment.
The best cost-effective approach to such
a proper EMC configuration requires each
item of equipment and its interconnections
to comply with specific EMC standards
which, however, may not be enough to an-
swer for all needs in a particular installation
when additional protective measures are so
to be implemented.
Practically all protective measures to
avoid Electromagnetic Interference (EMI)
are directly related to the grounding system.
Indeed, all different electrical-electronic
technologies existing in an Industrial Plant
will necessarily converge into the grounding
system and it is therefore in the grounding
system where the noise coupling problems
occur and thus it is in the grounding system
where they must to be solved.
The essence of electromagnetic compat-
ibility for automation and control systems
will thus be translated into its own ground-
ing system which can be understood as an
(single) electrical circuit, which goes from
the earth electrode subsystem to compo-
nents in printed circuit boards, including
all the installed protective measures, whose purpose aims
to conciliate different commitments: Safety for the power
system, Protection against lightning, and Control of elec-
tromagnetic interference.
To meet this goal (safety, protection against lightning
and interference control) the grounding system would be
an ideal plan with zero impedance where different signal
levels could be mixed without any interference. But the ideal
is not real, and what is done is the simulation of this ideal
behavior through a proper design of the grounding system for
a specific installation, aiming at two complementary goals:
1st Safety Grounding - to guarantee that dangerous
voltages due to power fault or lightning discharge could not
cause any harm to people or to the installation itself, being
its design based mainly on industrial frequencies and sup-
ported by the electrode system;
2nd EMC Grounding - to avoid electromagnetic interfer-
ence, external to the system (both that from a third party
into the installed electronic system or vice-verse) as well as
internal to the system, being its design no more related to the
electrode system but directed to the high frequency behavior
of all system interconnections in order to:
a. prevent electromagnetic disturbances to be coupled