Equipment shielding

Goals

formation-objectifs-seointro Equipment shielding :

- Design an electronic box incorporating shielding concepts and optimising protection methods

The aim of this training course is to:
- Understand the theory of shielding
- Be able to analyse and deal with openings
- Master the wiring and filtering of input/output interfaces
- Learn the techniques of case metallisation
- Learn how to measure shielding

Program

1/ Introduction

EMC characterisation of equipment

Common mode / differential mode

Origins of common mode current

The two types of electronic radiation

Card / backplane radiation

Impedance of cylindrical conductors

Roles of a screen

Definition of shielding effectiveness

Connecting 0 V to the chassis

Use of decibels

2/ Shielding: theory

What is a field?

Propagation and coupling between E and H fields

Near field/far field zone

Modes of operation of a screen

Impedance of a screen

Reflection according to field impedance

Skin depth/absorption

Cowdell charts

Shielding: selection criteria

Magnetic and non-magnetic materials

Very low frequency fields

Magnetic field and induction

Field line deflections

Risk of saturation

3/ Actual shielding

Necessity of openings

Calculation principle

Attenuation of a slot

Attenuation of a grid

Case of multiple openings

Effectiveness of a guide opening

Example of guide / honeycomb

Shielding effectiveness of a box

Example of an ‘electrostatic’ screen

Example of a magnetic screen

Examples of shielding on a board

Examples of welded/removable screens

Use of near-field probes

4/ Cable treatment

Antenna effect of cables

Ground plane reduction effect

Example of internal cabling

The three HF common mode methods

Circulation of HF currents

Connecting connectors

Grouping inputs/outputsConnectors

Grouping inputs/outputs

Wall-mounted filters

Filter assembly/examples

Shielded cable transfer impedance

Relationship between Zt and shielding effectiveness

Connection of shielded connectors

Steps in developing shielding

Tubes and textiles for additional shielding

5/ Improving shielding

General principle

‘Hot’ points »

Criticality of leaks

Leak reduction through baffle effect

Value of the baffle effect

Example of baffle effect

Tin-plated iron cover

Enclosure resonance and damping

Example of absorbent material

The two topologies for visualisation

Treatment of accessible components

Shielding accessories: examples

Effectiveness of a conductive seal

Effect of pressure/deformation

Installation of a conductive seal

Be careful with adhesive seal glueof a conductive seal

Beware of adhesive seal glue

Conductive fingers and springs

Electrochemical couples

Use of spring fingers

Required quality depending on the area

Electrochemical couples

Internal wiring

Electronic/mechanical coordination

Makeshift filter connectors

Recurring errors

Visual inspection

Industrialised shielded enclosures

Light bulb method

Aluminium chrome plating

6/ Plastic enclosures Conductive composites Conductive paints Arc/flame zinc coating Vacuum/cathodic metallisation Chemical/electrolytic deposits electrolytic

Metallised plastic enclosures

Simple shielding in plastic enclosure

Simple measurement of a coating

7/ Shielding measurements

Practical attenuation measurement

Calibration before measurement

Measurement of a small enclosure

IEC 61587-3 standard

IEEE 299 standard

Recommended measurement procedure