Shipboard Electromagnetic Environment Control

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Nov 16, 2013 (3 years and 11 months ago)

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Shipboard EM/EMI/EMC & RADHAZ



InField Scientific Inc. and Her Majesty the Queen in Right of Canada

2
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1


2.

Introduction to Shipboard EME, EMC and EMI







This section introduces shipboard electromagnetics, electromagnetic
compatibility (EMC) and interference (EMI). It emphasizes the importance of
controlling the electromagnetic environment (EME) and gives
examples of EMI
problems onboard ships. This section also introduces the three EMI phases
shown in the above diagram: source, coupling path and victim. Each of these
phases will be described in detail throughout the course.



Definitions



Shipboard EMI Probl
ems and Trouble Shooting



Shipboard EMC Analysis



A Two Box System


2.1

References:


Law, P. E.:
Shipboard Electromagnetics,
Artech House, Boston

Paul, C.R..:
Introduction to Electromagnetic Compatibility,
John Wiley & Sons, Inc.,
New York, 1992

White, D.:
A Ha
ndbook Series on Electromagnetic Interference and Compatibility,
Interference Control Technologies, Inc., Gainesville, Virginia, 1994

2.2

Definitions:

EMC

-

Electromagnetic Compatibility. A system is electromagnetically compatible if:



It does not cause interf
erence TO other systems.



It is not susceptible to interference FROM other systems.



It does not cause interference with itself.

EMI

-

Electromagnetic Interference: Any electromagnetically induced degradation,
obstruction or interruption to the performanc
e of electronic equipment.

Source

Cou
pling path

Victim



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EME

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Electromagnetic environment including all EM fields, equipment, conductors,
shielding, cabling, etc... in the physical region of concern.

HERP

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Electromagnetic Radiation Hazards to Personnel.

HERF

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Electromagnetic Radiati
on Hazards to Fuel.

HERO

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Electromagnetic Radiation Hazards to Ordnance.

RADHAZ

-

Electromagnetic Radiation Hazards to Personnel including RF Burn.

RF Burn

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Radiation burns to personnel as a result of contact currents on conducting
surfaces.

TEMPEST



(
Transient ElectroMagnetic Pulse Emanation Standard) A standard to
control electromagnetic emission or interception of CLASSIFIED data.
TEMPEST standards state the required levels of signal attenuation.

EMC may be concerned with a system consisting of sin
gle piece of equipment,
electrically interconnected equipments or a suite of equipment located within a specific
location such as a single compartment or the entire ship, Figure 2.2
-
1.

EMC may also be concerned with c
ompatibility between two or more system
s, such as
two ships, a ship and an aircraft or two communication systems on a single ship. This is
referred to as
Intersystem EMC,

Figure 2.2
-
2.
















Figure
2.2
-
1
:
EMC may be concerned with comp
atibility within a single system or
a single ship.




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Figure
2.2
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2
:

Intersystem

EMC refers to compatibility between two or more
systems, such as a ship and an aircraft.





























Figure
2.2
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3
: Hierarchy of EME Terms.


EME

RADHAZ

EMC

EMI

IMI

BBN

TEMPEST

External Sources

Other

Other Ships

HERO

HERF

HERP

RF Burn



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2.3

EMI Problems

EMI problems are divided into three phases: interference that originates from a source,
is propagated (radiation, conduction, penetration, etc…) through a coupling pat
h and
interferes with the victim.





Figure
2.3
-
1
: Three phases of EMI.


A modern warship environment is arguably the most severe example of congestion of
electronic and electrical systems, containing ro
ughly the equivalent of a small city’s
electronics systems within the confines of a football field. Added to this is the fact that
modern electronics systems are much more sensitive than their earlier predecessors,
making them much more susceptible to EMI

degradation.



To make matters worse
-

COTS, Commercial Off The Shelf equipment is now
being used on warships. This equipment doesn’t meet the military standards for
electromagnetic control.


EMI effects on the victim may range from:



distorted videos



c
rackling audio



navigational malfunctions



system failure



system burnout



fuel ignition



ordnance detonation; …

Source

Coupling path

Victim



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SHIP SAFETY BULLETIN


































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SHIP SAFETY BULLETIN CONTINUED


































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Figure
2.3
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2
: Degraded SATCOM antenna pattern. A sample, degraded antenna
reception pattern from a SATCOM antenna is shown here. The notch between
125


慮搠ㄸd


was “worked around” by installation of a complementary antenna;
the

combination provides a full 360


SA呃OM 捯v敲慧攠eCO Gui摥].













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Figure
2.3
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3
: Radar causing interference to landing system [CO guide]


















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Figure
2.3
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4
: Radar interference to navigation satellite receivers [CO guide].












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Figure 2.3
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5: Link 11 to Radar EMI [CO guide]



慤慲 to 呁CAN I湴敲f敲敮捥

Powerful radars such as the air search fleet radars have produced interference to
TACAN navigation systems. The coupling mechanism is direct leakage into the TACAN
controller cables which were exposed to radar illumination.


Resolution to the problem was to place the victim cable in a properly grounded conduit
and to run the exposed ca
ble within the mast structure wherever possible.



Power Supply Interference to Navigation Systems

High current switching power supplies have introduced harmonic signals into navigation
system cables, resulting in navigation system problems. Coupling into

the victim cable is
most likely due to common ground connections, grounding arrangements on the
navigation system cabling and cable to cable coupling between the power supply lines
and the navigation system cables.


The EMI situation was alleviated by obs
erving proper cable segregation and separation
guidelines. Power and communication cabling must be separated in all situations. The
navigation system antenna lead must be separated from all power leads both on the
exterior of the ship and within interior

cableways.


This was a particular concern with the OMEGA Navigation Systems that have been
replaced on the CF Navy vessels.



Interference from Ventilator Fan

In another reported incident, operation of a simple ventilator fan speed controller on the
USS I
owa interfered with the main gun (triple 16”) turret rotation.



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2.4

Trouble
-
shooting


Inevitably, despite the best EMC procedures, EMI problems cannot be totally
avoided in so complex an environment as a ship. It is expected that during the
implementation, te
st and inspection phases some EMI problems may arise.

One of the major concerns when trouble shooting is that the fix will cause different EMI
problems or move the problem to another frequency. The difficulty here is that the new
EMI is unknown while th
e original one was at least known. Not only is all of the effort in
identifying the EMI problem lost, but, one also introduces unknown dangers by causing
additional EMI.

Trouble shooting is a very difficult task, the following basic procedure is used to
i
nvestigate EMI problems:

Victim Identification:
The victim should be identified as narrowly as possible without
excluding any components that may be adversely affected by the EMI.

Problem Identification:

Research databases of other ships to determine if t
his problem
has been reported and/or solved elsewhere. Secondly, determine if the problem
is in fact an EMI problem or may be attributed to mechanical, electrical or
electronic malfunction.

Source Identification:
This may be accomplished by selectively a
ctivating and
deactivating potential sources individually and in combination while monitoring
the reported EMI problem. It is important to determine whether the source is an
intentional emitter
-

such as a transmitter; or, whether it is an unintentional
e
mitter.

Coupling Path Identification:
The coupling path is the link between the source and the
victim. In many instances, blocking the coupling path by shielding, adding RAM
(RADAR Absorbing Material), screening or by relocating one of the systems
solves

the EMI problem. Identification of the coupling paths is therefore a key
step in trouble shooting EMI problems.

Problem Correction:
Once the victim, source and coupling paths are identified
practical EMC solutions may be applied. These solutions will i
nclude one or
many of the following techniques filtering, grounding, bonding, shielding, adding
RADAR absorbing material, relocating equipment and maintenance procedures.

Performance Tests:
Following any EMI Problem Correction it is necessary to repeat
th
e testing that led to the problem to ensure that it has in fact been solved. Spot
checking other functions is also recommended to ensure that the problem hasn’t
just shifted frequencies or moved to another mode of operation.

EMI Reporting:
The EMI proble
ms, solution techniques, tests, results and solutions
should be reported in an EME Database. This is necessary in case similar
problems arise in the future. In addition, this information is essential when
overall EMI tests and trials are performed during

inspection and maintenance
since the correction may influence the EMC integrity of other systems. At the
present time the CF Navy has an on
-
line EME Database that is not functioning.
Until that time that it is made functional, the EMI Reporting should b
e filed
manually under an EMI heading so that it can be accessed in the future. A
sample blank EMI Incident Report form is shown in Figure 2.4
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2.



Shipboard EM/EMI/EMC & RADHAZ



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Figure
2.4
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1
: Flowchart of

trouble
-
shooting strategy.

NO

FAIL

FAIL

Victim
Identification

Source
Identification

EMI?

Co
rrection:

Filter

Ground

Shield

RAM

Relocation…


EMI Report

OUT

Intentional
source

Remove source

Shield source

TEST

END

Coupling Path
identification

TEST

END

NO

PASS

PASS



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Ship EMI Incident Report


Date:________________

Name:__________________


Ship Class:_____________________

Name:__________


Victim Equipment:_______________________________


EMI Description:








Testing Done:





Action Take
n:




Conclusions:








Figure
2.4
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2: Sample of a blank EMI Incident Report


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Electromagnetic Compatibility

EMI problems are generally not dealt with until they show up in the operational
environment, or, at best during testing. At this
stage it is very costly, or almost
impossible to mitigate the problems and to achieve EMC integrity.




Built in EMC is required



Costly and difficult to justify in terms of budget and time.



Also, it is not perfect, therefore, EMI problems can still arise.



No
netheless, a certain amount is essential.


It is necessary to realise that EMI does not only depend on the individual components
but on the entire environment of emitters, receptors and coupling path. Off
-
the
-
shelf
EMC certified equipment will not necessa
ry function correctly in a ship environment.
The ship compartments can be thought of as waveguides or resonant cavities, EM field
levels in the interior and topside can be very highly concentrated in certain locations thus
creating a severe EME.

This is a

particular concern when a ship is modernised or retrofit, in this case new and/or
old equipment is required to function in an existing (and altered) environment.



competition for frequency bands (intentional or unintentional)



introduction of higher freque
ncies which were not previously considered in
the EMC baseline.

For new designs, there will always be trade
-
offs based on EMC impact, such as:



equipment selection



antenna placement



frequency assignments



cable bundling



cable routing



cable separation



system
and subsystem placement



shielding considerations



grounding & bonding



functionality



etc...



WAIVERS
(relief from
unachievable

situations)



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2.5

Spectrum Management

Navy Vessels use different frequencies for various different applications. From LF
Communication to

millimeter wave radars, a very broad spectrum is used on the ship. It
is essential to ensure that these frequencies are managed so that, for example,
communication frequencies (along with their known harmonics) do not overlap with each
other or with Elec
tronic Warfare (EW) frequencies. This is necessary for compatible
own
-
ship operation and also during fleet operation.


The Spectral Management department of DND allocates the different frequencies used
throughout the Canadian Forces


land and sea.


Com
munications Canada also has a Spectral Management department for civilian uses
of the spectrum.


When tests, trials and special training operations are performed using the CF Navy
Vessels, special temporary licences must be granted stating the allowable fr
equencies
that can be used.


Many EMI problems can be avoided by proper spectral management, especially when
known intentional emitters are concerned.


2.6

Shipboard EMC Analysis

The following lists the basic considerations for predicting and analysing interfe
rence in
the shipboard environment. How these characteristics effect Shipboard EMI shall be
discussed throughout the remainder of this course.

Ship characteristics:



material properties (wooden hull, metallic,…)



topside arrangement and structures



compartme
nt structure



compartment exposure (windows, hatches, doors…)



compartment arrangement



state of the hull (rust, holes, …)


Emitter characteristics:



power output



tuned frequency



emission spectrum in the vicinity of the tuned frequency



spurious emission levels

and frequencies (including harmonics)



equipment placement




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Receptor Characteristics:



similar to emitter



sensitivity



tuned frequency



selectivity curve



spurious response levels



spurious response frequencies



distance from emitters



equipment placement



couplin
g path between emitter and receptor


Antenna:



antenna placement



gain patterns (azimuth & elevation beamwidth)



antenna power



bandwidth (frequency response)


Antenna
-
to
-
Antenna:



propagation loss associated with an electromagnetic coupling path



free space tr
ansmission



shading due to the ship structures



antenna patterns



antenna powers



antenna bandwidths


Cabling:



external field interaction



induced currents



coupling between bundled wires (capacitive & inductive)



shielded wires (single or double)



unshielded



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twi
sted pair



grounded single side



grounded two sides



multi grounded


Shielding:



shielding effectiveness



distance between cases



apertures



seams



doors & hatches



gasketing



grounding


Filters:



low and high pass



bandpass



insertion loss (reduction in delivered powe
r due to insertion of a filter)


Ground plane:



ground loop coupling



common ground interference



single or multipoint point grounding



ship’s hull



antenna ground plane structure



antenna ground plane placement

2.7

A two box system


To gain an appreciation of the c
omplexity of an EMI analysis, one can look at a simple
two box system. This system consists of two shielded cases each with an interior
ground plane and some simple circuitry (i.e. pc board, etc...). By evaluating every
possible current path and groundin
g arrangement, one can quickly see that the number
of possible interference paths is over 500 Million [White].



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Figure
2.7
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1
: A two box system [Courtesy of
emf
-
emi control, Inc.
].








Extrapolate to a com
plex system such as a ship!






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Figure
2.7
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2
: Ship extrapolation.





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