What is Electromagnetic Interference (EMI) Shielding? How to reduce EMI Shielding in cases and racks. The ERack from CP Cases is a lightweight robust rack case. Transporting mission-critical, fragile and heavy rack equipment made easier.

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2019
What is Electromagnetic Interference (EMI)
Shielding?

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EMI and EMI Shielding?
EMI?
Electromagnetic Interference (EMI) is the adverse effect of electromagnetic
fields on other devices. The interference is produced as the fluctuating field
traverses’ other devices or their connecting cables or PCB tracks. Each
traverse induces a voltage which may be quite small. However, data
processing devices run on low voltages and these induced voltages are
relatively large and can easily corrupt input and output data signals.
Environmental electromagnetic conditions are, by their nature, unpredictable
so shielding is designed to remove this performance threat.
EMI Shielding?
It is a form of insulation / conductive barrier that reduces or prevents transfer
of energy, in this case electromagnetic energy, escaping or entering a
system and interfering with other devices in the same environment. So for
example, a gentle hum from the home radio when your mobile phone rings.

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EMI shielding effectiveness
In designing a protective solution, CP Cases has worked
closely with customers to develop enclosures to effectively
shield devices. This enclosure must completely envelope the
device.
Usually there is a need to access the device and so the
enclosure will be in at least two parts. There must be
conductive continuity between these parts or else the
interference may ‘leak’ in through the gap between them.
Continuous face to face contact between a case and its lid
with the precision required is not reliable. Add in other
environmental hazards, such as dust and water, requiring
flexible seals. Flexible seals in rubber are transparent to EMI
and so must be enclosed in knitted metal wire sleeves to
contact both parts.
Some equipment requires air cooling whilst still maintaining
the shield. Holes or slots in the shield would act as aerials and
allow the EMI to re-radiate within the enclosure. Generally, if
any hole or slot is under 3mm an effective shield can be
maintained.
ERack Lightweight 19″ Ruggedised Enclosures are examples of this technology
in practice.

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Reducing EMI interference
A metal shield or screen will block EMI, especially if the barrier is
connected to ground. Audio and video cables, for example, consist
of an inner conductor surrounded by a braided outer shield; EMI
enters the shield and flows directly to ground instead of interfering
with the signals the cable is carrying. A grounded metal equipment
chassis also acts as an EMI shield for circuits inside the cabinet.
The ultimate form of EMI shield is a box called a Faraday cage.
This is a conductive enclosure that keeps voltages out because
charges repel each other sideways. Dimensions of the openings in
the cage determine what voltages will be excluded. For electronic
devices any opening must be small but do not need to be ‘airtight’.
EMI is regulated worldwide and there are standards to follow such
as those set by the FCC in the US, CE in Europe, and ICES in
Canada. This is broken into two main parts; conducted and
radiated.
CP Cases products can be designed in line with Electromagnetic
Compatibility (EMC) directives and the UK defence standard for
EMC, DEF STAN 59-41.

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EMI Best Practise Case Study
CP Cases experience with EMI was put to the
test through a project with the Aircraft Carrier
Alliance (ACA) where Rackmount Enclosures for
QE Class Aircraft Carriers were delivered.
CP Cases supplied more than 1200 custom-
designed rackmount enclosures and more than
4000 adaptors and brackets, for installation on-
board two (QE) Class aircraft carriers to house
datacoms enclosures of various sizes.
The smallest enclosure accommodates two single units of 19” rack-mounted network
switches; the largest cabinet stands almost five feet tall and can accommodate 29
units. Also developed especially for the project were a series of plinths and brackets,
which secure telephone handsets to horizontal and vertical surfaces around the ship.
Working closely with BAE Systems, one of the four Aircraft Carrier Alliance (ACA)
partners, CP also integrated the power supply wiring, voltage filter and cable
management systems to ensure the enclosures were ‘plug & play’ ready.

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About the product
The primary function of the network equipment enclosures was to provide physical and
electromagnetic security to various types of Cisco IE Ethernet network switches and the
thousands of accompanying connecting datacoms, Ethernet and fibre optic cables.
The communications requirement was substantial – the carriers need constant contact
with all in-flight aircraft, the consort group, HQ and land forces. The network switches
process and route this vital communications data.
Each enclosure protects the 19” rack mounted
switches from vibration, impact, particle and
moisture ingress, and also provide screening
from any electromagnetic interference
(EMC/EMI) that could disrupt the mission
communication systems from radar energy
and other strong electromagnetic signals
which are emanating from various positions
on board, ensuring the ship’s sensors do their
job without adversely affecting each other.

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EMC Functionality
CP Cases introduced and utilised novel designs embracing
the same materials developed specifically for EMC/EMI
screening used as part of the ‘ERACK’ series of portable
Anti- Vibration rackmount containers, which are
performance certified to provide a high level of
electromagnetic shielding.
The solution for providing electromagnetic compatibility throughout all sizes of
enclosures, also manages interference which could potentially emanate where the data
transfers cables enter and exit the enclosures. CP Cases developed a unique Cable
Entry Port (CEP) which allows cables, with accompanying connectors, to be fed into
and out of the enclosure through a simple “foam flap” letterbox system.
This specially designed (and EMI/EMC performance certified) CEP, uses conductive
closed-cell polyethylene foam, which compresses around individual data cables.
Conventionally, each cable would have been installed via an individual four part metallic
cable gland, and bearing in mind that many enclosures have up to 144 individual cable
entry & exit points, the CEP system provides significant advantages on installation
labour hours, providing substantial cost benefits and ensures any future systems
upgrades are implemented efficiently.

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Internal Functions
Cable management rails inside the enclosures
with hook-n-loop cable ties ensure that the
recommended bend radius for each data-coms
cable is never compromised and that network
switch gear connections are safe-guarded against
accidental disconnections.
In parallel with EMI/EMC security, a primary
function was to provide simplicity during
equipment installation, maintenance and cable
connectivity. Top and front covers are secured with
unique tamper-resistant TORX PLUS® fasteners
ensuring access is limited to authorised service
personnel. Ventilation panels in key areas, provide
natural convection that dissipates any heat build-
up.
The thermoplastic powder coated surface finish is
applied onto an etch primed base; pale grey, it’s
applied electrostatically without solvents and
cured with heat to provide a hard wearing semi-
gloss surface finish. This is tougher and much less
hazardous than conventional liquid paint coatings
and has exceptionally high corrosion resistance.

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Erack® Range
Designed for transporting fragile and heavy rack equipment - 30% lighter than most
other rack cases.
Accredited to MIL-STD-810F, DEF STANN 00-35, IP rating 65, RoHS compliant with
NATO stock numbers.
ERacks design is constructed from a high-tensile aluminium alloy
Suitable for heavy payloads of up to 70kg plus
Delivers exceptional strength to weight ratio
Folded rim makes the cases stronger, lighter and more dust/water resistant
Easy re-positioning of the rack chassis
Braided earth grounding strap
Font and rear access
Interchangeable lids
Climate control COOL portable air conditioning units optional
Erack Cases

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Climate Control
Solid state climate control Thermoelectric Unit (TEU)
Ideal for remote locations and extreme temperatures
Not sensitive to orientation
Long lifetime and low maintenance
Available for Amazon Racks or ERack, and as COOL-COLLAR™
or built in to rack-body .
Available in Thermoelectric or Vapour Compression Cycle formats.
Recessed, sprung handles and inboard lid latches
Stackable with inter-locating ribs on container top & bottom
surfaces
Compatible with most Amazon and ERack accessories.
Suitable for 6U to 12U height equipment.
Maintaining optimal operating conditions of electronics

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CP Cases Customers

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About CP Cases
CP Cases design and manufacture rugged, impact
resistant cases, containers and electronic racks
For transport, storage and operation of essential
equipment
Well equipped factories in North America & UK/Europe
Established more than 45 years
Skilled designers, engineers and craftsmen using
CAD/CAM software and manufacturing processes
Export >50 countries
5 star financial rating

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ISO 9001 - quality assured certification (since 1993)
SSE - Society of Environmental Engineers
GSA Advantage - assisting Federal employees worldwide by
meeting today's acquisition challenges
MAKEuk - The Manufacturers’ Organisation
DMA - The Defence Manufacturers Association
ADS - UK Aerospace, Defence, Security and Space sectors
WEAF - West of England Aerospace Forum
IABM - International Association of Broadcast Manufacturers
GTC - Guild of Television Camera Professionals
About CP Cases

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THANK YOU
For more information contact:
CP Cases
W: cpcases.com
E: info@cpcases.com
T: 44 (0) 208 568 1881
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