PRESENTATION ON EMC TESTING AND

MEASUREMENT

By Rajat soni MTECHWct

e.no. -140291

What is EMC?Electromagnetic compatibility (EMC) is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects (Electromagnetic interference, or EMI) that such energy may induce.

The goal of EMC is the correct operation, in the same electromagnetic environment, of different equipment which use electromagnetic phenomena, and the avoidance of any interference effects.

• While electromagnetic interference (EMI) is a phenomenon - the radiation emitted and its effects - electromagnetic compatibility (EMC) is an equipment characteristic or property - not to behave unacceptably in the EMI environment.

• Electromagnetic interference divides into several categories according to the source and signal characteristics. But generally

• Types of interference• Continuous interference• Pulse or transient interference

EMC testing

• Open-air test sites, or OATS, are the reference sites in most standards. They are especially useful for emissions testing of large equipment systems.

• Radiated field susceptibility testing typically involves a high-powered source of RF or EM pulse energy and a radiating antenna to direct the energy.

Measurement of Radiated Emissions

Measurement of Radiated

Susceptibility

Test Antennas A convenient approach to illuminate an equipment under

test with known field strengths is to used exact half wave length a long dipoles at fixed frequencies.

This arrangement is superior when compared to connecting a test antenna to a signal source using co-axial cable that might distort the field pattern.

Antenna Type Frequency, MHz

Rod antenna 1 - 30

Loop antenna 1 – 30

Biconical antenna 30 – 220

Dipole antenna 30 - 1000

Log periodic antenna 200 -1000

Conical log spiral 200 – 10000

Wave guide horn Above 1000

1) Electro magnetic environment

It is desirable that the conducted and radiated ambient radio noise

and signal levels measured at the test site with the EUT de-

energized, be at least 6 dB below the allowable limit of the applicable

specification.

2) Electro magnetic scatterers

One method for avoiding interference from underground scatters is to

use a metallic ground plane to eliminate strong reflections from under

ground sources such as buried metallic objects.

3) Power and cable connections

The power leads used to energize the EUT, receiver and transmitter

should also pass through filters to eliminate the conducted

interferences carried by power lines.

Measurement Precautions

Thank you