Page 7 - EngineerIt January 2021

GUEST EDITORIAL

Stay Grounded!

By John Wilson, Accreditation & Metrology Services (Pty) Ltd.

he 2020 year has certainly In the electronic instrumentation world where small values are often
been up in the air and it is time required to be measured, these can be seriously distorted by earth loops or
Tfor us to come back down and small currents flowing between different “earths” or grounds and being
be grounded in more ways than one. superimposed on the values being measured. This is very common in
Let us explore being grounded. I am industrial plant applications where the signal wires coming from a remote
not referring to the times I misbehaved part of the plant back to the control room are long and as a result, the earth
and was "grounded" and not allowed potentials of the two systems are likely to be different. Invariably when
out as a child, but often wondered there is an unstable measurement on a plant control system, it is due to
where that phrase came from. It earth loops.
supposedly comes from the term used
in the aircraft and shipping industry, Audio and video equipment earth loops cause all sorts of audio and visual
meaning that the vessel cannot go distortion, along with the classical hum that is so annoying. It is generally
anywhere. In the more classical usage, caused by different grounds and has resulted in the development of optical
someone who is grounded is perceived or wireless connection between the various components to eliminate the
to be sensible or “down to earth”. Even possibility of ground loops.
those in the more esoteric fields of
Yoga, Reiki, Polarity, TRE and other Even in the metrology or calibration world, where ideal conditions are
complimentary healing sciences supposed to exist, earth loops creep in and distort the measurements.
frequently refer to the need to be These come about when two or more instruments are at different earth
grounded. So, what do they mean by potentials and they try to equalise through the signal wires. These
the term? Well, they literally mean for potential differences are known as “Common Mode” (CM) voltages. You
you to go outside and put your feet in may wonder how it is possible to have CM voltages when the instruments
the sand and come down to earth, or are in such a close proximity but incorrectly wired power distribution, poor
be “discharged”. If you don’t believe it, earth connections, wrong power cords and particularly, the wrong
then think about it when you next get a connection of signal leads can lead to perfectly good instruments being
shock from a static discharge - you will defined as faulty or out of specification or worse, faulty equipment
just have had a rapid and classified as being serviceable.
uncomfortable grounding experience.
So, let us go into the New Year
In the electrical world, grounding is with a well-grounded approach
ultra-important for our safety. Without and be sensible about the way we
proper grounding, appliances and live and work. When we feel the
installations can “float” up to high stress levels rising, let us go outside
voltages and cause a shock or and put our feet firmly in
damage when you least expect it. the sand, remember where
Similarly, we are not in control of when we are and be grateful
or where lightning may strike and that we have come
without proper grounding, the results through the waves of
can be disastrous. The correct design the pandemic and
and regular checking of an electrical are ready for
installation and even your home, is whatever may
important for your safety. come next. n

EngineerIT | December 2020 / January 2021 | 5