The Electromagnetic Compatibility of Electronic Equipment'

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The Electromagnetic Compatibility of Electronic
Equipment.

• Joseph Bedford
• Hung Pham
• Bao Duong

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Introduction

• Electromagnetic interference (EMI) leads to
  errors in the transmission of signals, and the
  malfunction and damage of equipment.
• Radio transmission and power supply.
• Radar and telecommunications technology,
  aerospace and satellite technology, and nuclear
  weapons.
• Integrated circuitry and digital electronics.
  

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Definitions

• Electromagnetic Interference (EMI) is the
  degradation of the performance of a device,
  equipment or system by an electromagnetic
  disturbance.
• An electromagnetic disturbance is any
  electromagnetic phenomenon that may degrade the
  performance of a device, equipment or system or
  adversely affect inert or living matter.
  

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• Electromagnetic Compatibility (EMC) is the
  ability of a device, equipment or system to
  function satisfactorily in its electromagnetic
  environment without introducing intolerable
  electromagnetic disturbances to anything in that
  environment.
• Immunity is the ability of a device, equipment or
  system to perform without degradation in the
  presence of an electromagnetic disturbance.
• The Compatibility level is the specified maximum
  electromagnetic disturbance level expected to be
  impressed on a device, equipment, or system
  operated in particular conditions.

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• The Immunity level is the maximum level of a
  given electromagnetic disturbance incident on a
  particular device, equipment or system for which
  it remains capable of operating at the required
  degree of performance.

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There are two main
coupling modes in electromagnetic interference

• Radiative, in which interference arises as a
  result of direct electromagnetic field coupling
  between systems which are otherwise isolated.
• Conductive, in which the interference arises as a
  result of current flow between the source and the
  receiver.

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Important considerations

• Interference is natural and unavoidable and
  should be incorporated as part of the design
  process.
• A phenomenon caused by interference follows the
  same rules as a desired electromagnetic process,
  these being Maxwells equations, and should be
  studied with this in mind.
• A problem of interference will generally exist in
  a certain frequency range.
• Identifying the source of the interference is
  possibly the most important step in dealing with
  such problems.

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The Causes of EMI

• The causes of electromagnetic interference are
  usually divided into natural and man-made or
  artificial sources of interference.

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Natural Sources of EMI

• Celestial Electromagnetic Noise
• Lightning
• Electrostatic Discharge (ESD)

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Man-made or Artificial Sources

• Electromagnetic Pulse
• Electrical and Electronic Sub-systems
• Variations in the Power Supply
• Frequency Spectrum Conservation

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Effects of EMI

• For digital systems
• For non-digital systems
• In control systems

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For digital systems
The error rate

1. a good criterion of the deterioration,
2. defines limit for a given
type of interference
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For non- digital systems

• Criterion for performance
• signal - to - noise,
• signal - to - interference
• power ratios,
• peak voltage ratios,
• loss of intelligibility.

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Control systems

• Criterion for performance
• some measure of error in the controlled output
• peak error in the controlled function must be
  transformed back into the corresponding input
  signal - to - interference ratio.

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The acceptance ratio( or threshold signal - to -
interference ratio )

• Ratio of wanted signal level to unwanted signal
  or noise level that would just permit
  satisfactory functioning of the system

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Management of Electromagnetic Compatibility of
Electronic Equipment

• Minimise emissions from a device or system
• Ensure the device or system is immune to harmful
  interference from other sources

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Three options

• Elimination of source of interference
• Absolute immunity of equipment
• Control of source of interference

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Control of source of interference

• Design process
• Layout
• Grounding
• Shielding
• Filtering

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Other techniques

• Bonding
• Cable and Connector Shielding
• Materials Special Devices ( Gasket, Conductive
  Coatings)
• Standards

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Design process

• Grounding, Shielding Filtering can be
  approached by first considering the overall
  design process
• Three steps in the design process

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Circuit Layout

• Principle of controlling the flow of interference
  into and out of the device
• System partitioning

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Grounding

• Proper partitioned system means proper grounding
• Floating, Single point, and multi-point grounding
  (Preferable).
• Proper Grounding minimises the need for shielding
  and filtering

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Shielding

• Prevent radiated energy from entering a specific
  region
• Reflective shielding and absorption shielding
• Proper grounding will minimise the need for
  shielding

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Filtering

• Reflective filters and lossy filter.
• Proper shielding may reduce the need for
  filtering.

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Summary

• We have seen that electromagnetic interference
  leads to errors in signal transmission and to the
  malfunction and damage of equipment.
• As interference is an unavoidable problem for
  electronic systems the emphasis must be on the
  control of interference and ensuring
  electromagnetic compatibility of electronic
  equipment.