EMI EMC

Electromagnetic Interference & Electromagnetic

Compatibility

BY

VIKRAM KUMAR

ASSISTANT PROFESSOR

DEPARTMENT OF INSTRUMENTATION & CONTROL

JSS ACADEMY OF TECHNICAL EDUCATION, NOIDA

What are EMI and EMC ?

• An electromagnetic disturbance which may

degrade the performance of an equipment or

causes malfunction of the equipment, is called

electromagnetic interference (EMI).

• Electromagnetic compatibility (EMC) is a near

perfect state in which a receptor functions

satisfactorily in the common electromagnetic

environment, without introducing intolerable

electromagnetic disturbance to any other devices /

equipment's / system in that environment.

Commonly experienced EMI Situations

• Power supply ‘Hum’ in radio sets

• Crackling sound on radio/TV during lightening

• White spots on TV picture due to nearby mobile

• Jitter in Digital signal reading in lab

• Cross talk on telephones

• Radio silence under HT wires.

Critical EMI Situations

• Loss of transmission.

• Malfunction of life support equipment- Pacemaker.

• Malfunction in critical process control in industry.

• Malfunction of aircraft equipment.

• Unintended of detonation of explosive devices.

• Malfunction of Missile guidance system.

Intrasystem Vs. Intersystem EMI

• Intrasystem interface

comes about as a

result of self-jamming or

undesirable emission

coupling within a

system.

• Intersystem EMI is the

interference between

two more discrete

systems or platforms

which are frequently

under separate user

control.

Intersystem EMI is more difficult to control

A system is said to be electro magnetically compatible if :- It doesn't cause interference with other system . It is not susceptible to emissions from other systems. It doesn’t cause interference with itself. The methodologies to prevent EMI are:- Suppress the emissions at source point, the best

method to control EMI . Make the coupling path as inefficient as possible. Make the receiver less susceptible to emission.

Purpose and Methodology for EMC System

EMI on Human Body

An electric field on an

unshielded person

discharges to the

ground, while the

magnetic

field ”permeates" the

body inducing a

magnetic flux that

generates secondary

electric fields inside

the body.

Power line interferences with the human body

50Hz distribution in the body. The red areas show where the strongest currents are.

Absorption of cell phone radiation with concentrations in the neck.

Important techniques to control EMI at source point are

• Proper Grounding–single point, multi point or hybrid grounding

depending upon the frequency of operation.

• Shielding –Metal barrier is used to suppress coupling of radiated EM

energy into the equipment.

• EMI Filtering-used to suppress conducted interference on power, signal

and control lines.

• PCB layout –Proper PCB design from the early design stage is required.

EMI control techniques at source

EM Interference

Independent earth electrodes, a solution generally not acceptable for safety and EMC reasons

Installation with a single earth electrode

EMC - Earthing principles and structures

Installation with multiple earth electrodes

Common Mode & Differential Mode

Interference

An item of equipment with external cables AB and CD, in an electric field. .

Three loops have been created by the above circuit

Loop 1 ABCDA, Loop 2 ABEFA & Loop3 DCEFD

‘First aid’ responses to conducted interference. • Parallel capacitor at (a) reduces differential mode

voltage developed at the input. • Series inductance shown at (b) reduce common mode

current flow to ground by stray capacitance.

Remedial or ‘First Aid’

Example of common-mode impedance coupling

Common Mode Coupling

Types of Interference

Types of Interference

Capacitive Coupling

Example of capacitive coupling Cable shielding with perforations reduces capacitive coupling

Inductive Coupling

Example of inductive coupling

Radiated Coupling

Definition of radiated coupling

Examples of radiated coupling

Countermeasures • Inductive Coupling 1. Twist the wires to reduce the loop area 2. Run the twisted wire close to ground 3. Design ground & return planes with minimal penetrations

• Capacitive Coupling 1. Separating the source and the receiver and properly

connecting shield will reduce capacitive coupling

• Radiated Coupling 1. Reducing bandwidth 2. Using good signal routing 3. Shielded enclosure 4. Reducing the loop Size

References

• Center of Electronics Test and Engineering, Noida.

• SAMEER Kolkata Centre EMI-EMC Division

• SAMEER Chennai – CEM Division

• EMV 2012 Düsseldorf- The latest EMC highlights and trends

• Dr Jeff Chambers, Understanding Common Mode Interference , Westbay Technology Ltd

• Wiki EIG (Electrical Installation Guide)

Thank You!

Q?