Stepes in Designing Shielded Enclosures

7/28/2019 Stepes in Designing Shielded Enclosures

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Steps in Designing ShieldedSteps in Designing Shielded

EnclosuresEnclosures

Praveen Pothapragada

Chief Engineer

Equipto Electronics Corporation

351 Woodlawn avenueAurora IL 60506

PH: 630-859-7840 X 122

Email: [email protected]


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OutlineOutline

Reasons for EMC Ways of Reaching EMC

Company Background

Standards Design of Shielded Enclosures

Testing results

Questions

2Copyright 2010 Equipto Electronics Corporation


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Why do we need EMC?Why do we need EMC?

Unintentional Electro Magnetic Interference. Intentional Electro Magnetic Interference.



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Unintentional EMI



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Why do we need EMC?Why do we need EMC?

Unintentional Electro Magnetic Interference. Intentional Electro Magnetic Interference.



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Copyright Equipto Electronics Corporation 6


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Ways of reaching EMCWays of reaching EMC

At the component level (e.g.: Individual PC boards orchassis)

Shielded enclosures

Anechoic Chambers, Shielded Rooms and FaradayCages.



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Advantages of Shielded EnclosuresAdvantages of Shielded Enclosures

Can be incorporated after the system is designed. Portable compared to Shielded rooms.

shielding individual components or the shieldedrooms.



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Applications of Shielded EnclosuresApplications of Shielded Enclosures

Data centers where we need redundancy Industrial production lines for critical operations

Other applications where EMC is critical



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Company BackgroundCompany Background

Started in 1960, EEC specializes in modular design forelectronic packaging solutions.

Our sheet metal fabrication facility is spread over

125,000 sq.ft in Aurora IL and has 50 employees. We specialize in custom solutions for shielded, shock

and vibration and seismic applications.

Our Shielded enclosure line started over 25 yearsago.



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EMC StandardsEMC Standards

IEEE-299-2006 MIL-STD-461

NSA 94-106 FCC Part 15

Tempest MIL-STD-188 (HEMP)



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Design of Shielded EnclosuresDesign of Shielded Enclosures

Selection of Enclosure Material

Galvanic Compatibility

Selection of Gaskets

Input/Output

Testing



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Selection of Enclosure MaterialSelection of Enclosure Material

Radiated Emissions/Susceptibility?

Shielding levels required.

Thickness of material.

Other mechanical properties



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Radiated Emissions/Susceptibility?

For Radiated Emissions we want to choose a

material that absorbs (e.g C.R.S or StainlessSteel).

For Susceptibility we want to choose material

that reflects (e.g Aluminum).



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EnclosureWithoutStren thField


=

nenua o10 StrengthFieldCompliant

og


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=

EnclosureWithoutStrengthField


MHz300@dB885

1012020(dB)sEffectinesShielding

3

10

=

Log

StrengthFieldCompliant


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BRAdB ++=)(S.E

G

fGtdB 3

10338.3)(A

=

=

G relative conductivity (copper)

f frequency (Hz) - relative permeability (free

space)

r1- distance between source to


f

GdB

fGr

GfrdB

rf

6

10P

1

1

10H

2

1

3

10log102.108)(R

354.0136.0462.0

log20)(R

.

+=

++=

t thickness (mils)


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Other mechanical properties

Weldability

Formability Availability

Protection against magnetic fields(Aluminum, 300 series Stainless steels)



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Selection of Enclosure Material Galvanic Compatibility


Input/Output

Testing



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Input/Output

Testing



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Selection of GasketsSelection of Gaskets

Reason for having gaskets Type of opening

Wiping or compression

Shielding effectiveness

Galvanic Compatibility



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Door Opening Design

Advantages:

High level of Shielding

Effectiveness


Must bemanufactured precisely.

Use of heavier gauge

material.


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Input/Output Vents

Power Line Filters Connectors



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Vents

Example: Determine SE @ 10 GHz for 1/8Honeycomb 1 Long.

36.55125.0

92.692.6FrequencyCutoff === GHz

DC


5D

L

for ventsthumbofRule

dB256125.0

13232)(SE

usa e.soneycomez.znce

D

LdB


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Input/Output Vents

Power Line Filters Connectors



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Input/Output

Testing



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TestingTesting

IEEE-299-2006 NSA 94-106



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80

100

120

Equipto R6 Magnetic Field Shielding Effectiveness

Door Latch Top Corner; Horizontal Door Latch Top Corner; Vertical

Door Top Center; Vertical Door Hinge Top Corner; Vertical

Door Hinge Top Corner; Horizontal Door Hinge Side; Middle; Horizontal


0

20

40

60

0.01 0.1 1 10 100

dB

Frequency MHz


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100

120

140

160

180

Resonant Range and High Frequency Shielding

Door Latch Edge; Vertical Door Latch Edge; Horizontal


0

20

40

60

80

10 100 1000 10000 100000

dB

Frequency (MHz)


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60

80

100

120

140

160

dB

Electric Field Shielding Effectiveness

1 kHz

10 kHz

100 kHz

1 MHz


0

20

40

Measurement Location

10 MHz


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40

60

80

100

120

140

160

dB

Plane Wave Shielding Effectiveness - Horizontal Polarization

100 MHz

400 MHz

1 GHz

10 GHz


0

20


Pl W Shi ldi Eff ti V ti l P l i ti


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40

60

80

100

120

140

160

dB

Plane Wave Shielding Effectiveness - Vertical Polarization

100 MHz

400 MHz

1 GHz

10 GHz


0

20



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ReferencesReferences

The design of shielded enclosures by Louis T. Gnecco Chomerics (EMI Shielding Theory)

MIL-F-14072D

NSA 94-106

MIL-STD-461F

EMPrimus SCADA/DCS Testing

www.APELC.com

www.diehl.de



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QuestionsQuestions


Stepes in Designing Shielded Enclosures

Documents

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