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Electromagnetic Compatibility (EMC) is not a
household word, even in this era of pervasive use of
technological jargon. EMC relates to a discipline or a
branch of scientific investigation that clearly falls
under the category of specialty engineering. The
development of sophisticated electronic apparatus in
recent decades has made it necessary to devote time and
energy to this field in order to assure that
electrical/electronic equipment operates in its intended
function and in its assigned environment. In other
words, in this modern day and age where computers and
microprocessors are ubiquitous in everything that uses
electrical power, compatibility in an electromagnetic
environment has become an important part in the use of
electronic gadgetry.
The military with its rapid advancements of modern
electronic equipment, particularly during war times,
recognized a need to seriously address the EMC issue
long before equipment manufacturers did. Today, in a
world of digitization and where even appliances are
provided with a computer, national and international
regulatory agencies have set up EMC requirements for
equipment to be marketed. The increased use of the upper
frequency spectrum and the super sensitivity of modern
circuitry make it imperative to control the associated
electromagnetic interference (EMI). Failing to do so,
may result in a serious EMC problem.
EMC problems manifest themselves in a variety of
situations.
-Household appliances, such as mixers or vacuum cleaners
cause static in an AM radio or TV
-Fluorescent lights destabilize the sync circuits in
video displays
-Lightning can cause damage in telephone equipment as
well as in other electronic apparatus
-High power transmitters and radars interfere with car
radios and other sensitive equipment
-Lab Tops interfere with aircraft electronics during
take-off and landing
These are just a few examples of EMC problems with
various consequences encountered in our daily lives. As
can be seen, an EMC problem is always comprised of three
elements, the source (culprit), the receptor
(victim) and the path between them, which may be a wire
(conductor) or just the intervening air space.
Identification of these elements is a first step to the
solution of the problem.
To dig deeper into the details of this vast field of EMC
which deals with the emissive as well as the immunity
issues of electrical/electronic equipment, installed on
aircraft, on board ship or on the ground,
would be beyond the scope of this article. Books
and papers on the subject are available to the reader
who desires to study in greater depth the many aspects
of EMC.
The following two examples, however, further illustrate
the existing need to control interference during the
design phase of equipment to avoid later embarrassment
or even tragedy. Once the box is installed,
it is often difficult to fix the problem, and it
is always costly.
In the waning months of WW II, German submarines
suffered a hard blow due to a peculiar EMC phenomenon,
according to the report of Karl Dönitz, commander of the
U-Boats, in his book “Ten years
and twenty days.” He related an incident that
caused perplexity and the greatest of concern in the
German submarine command. U-Boats had sunk Allied
shipping, destined to relief England’s shortage
of food and materials, during the many months of
the raging “Battles of the Atlantic.” The Allies had
finally gained the upper hand in the struggle to protect
the convoys. Radars installed on aircraft enabled
the search crew to detect U-Boats traveling on
the surface during recharging of their batteries. The
ensuing battle often ended with the loss of a submarine,
since it had little chance to dive away in time.
To alleviate this untenable situation, U-Boats were
outfitted with a radar detection receiver. This device
issued warning signals in the boat allowing ample time
for it to slip beneath the surface. Unfortunately,
the designers had neglected to subject the radar
receiver to interference testing prior to installation
on the boats. The receiver radiated an interference
signal via its antenna, soon detected by Allied pilots.
No longer did they have to turn on their radars,
the boats would betray their own positions. Numerous
losses of U-Boats was the result, and all because
electromagnetic interference had gone uncontrolled.
The second example to be cited here, has a personal
touch. Not as tragic as the WW II story, but it was
embarrassing as it was humorous. It happened during sea
trials of the Boeing-built military hydrofoil boat. As
the boat “flew” across the Puget Sound waters on its
foils, the Navy captain had ordered crew members to
observe equipment operation and report any failure,
malfunction or false dial indication while the boat went
through its maneuvers. All of a sudden the boat abruptly
dropped on its hull without a prior command from the
bridge! What happened? Everybody was dumbfounded. The
captain immediately ordered everybody to remain at his
station and report his last five minute activity.
This revealed that the executive officer had
flushed the toilet during that period !! But what did
that have to do with landing the boat on its hull? An
analysis team came up with the answer rather quickly.
Flushing the toilet activated a pump who’s wiring was
routed next to the input wiring of the computer,
which controlled the flaps on the foils. The
computer had reacted to an interference signal,
generated by the pump and coupled into the computer
input port.
A typical EMC problem. Here the three elements were: the
pump the source, the computer the victim and the path
between them the closely coupled wiring. Due to the
humorous aspects of this episode,
the story spread within the EMC community of this
country like wildfire. For a brief period of time, the
toilet was in control of boat operation.
These two incidents, occurring in a time span of over
forty years, demonstrate that the advancement of
modern technology did not eliminate EMI. It is
just as important today as it was yesterday to make the
effort of incorporating control measures early in the
design phase to assure compatible system operation.
Unfortunately, management is sometimes reluctant to
allot the required time and money.
Electromagnetic interference always stands in the way of
electromagnetic compatibility, it is like a side effect
in the operation of electronic gear, and as a colleague
of mine aptly called it one time, it is “bad electricity!" |
©
2006 All content property of European Weekly unless where otherwise
accredited
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