15
EMI MEASUREMENTS EMI MEASUREMENTS OPEN AREA TEST SITE (OATS) Prepared and Presented By Prepared and Presented By ROJI VARGHESE RAJAN Reviewed By K.J.JEGADISH KUMAR AP/ECE

Open Area Test Site

Embed Size (px)

DESCRIPTION

Open site measurement is the most direct and universally accepted standard approach for measuring Radiated Emission/Radiation Susceptibility of an equipment.

Citation preview

Page 1: Open Area Test Site

EMI MEASUREMENTS EMI MEASUREMENTS

OPEN AREA TEST SITE (OATS)

Prepared and Presented ByPrepared and Presented By

ROJI VARGHESE RAJAN

Reviewed By

K.J.JEGADISH KUMAR AP/ECE

Page 2: Open Area Test Site

INTRODUCTIONINTRODUCTION

� Measurement of Radiated Emissions (RE) fromequipment, apparatus or instrument and the RadiationSusceptibility (RS) of such an equipment/ apparatus/instrument constitute the two basic EMI/EMCmeasurements.

� Opensite measurementis the mostdirect anduniversally� Opensite measurementis the mostdirect anduniversallyaccepted standard approach for measuring RE/RS of anequipment.

Page 3: Open Area Test Site

MEASUREMENT OF RADIATED MEASUREMENT OF RADIATED

EMISSION EMISSION

� With the Equipment under test (EUT) switched on,the receiver is scanned over the specified frequencyrange to measure emissions fromthe EUT.

Page 4: Open Area Test Site

MEASUREMENT OF RADIATION MEASUREMENT OF RADIATION

SUSCEPTIBILITYSUSCEPTIBILITY

� The EUT is placed in an electromagnetic field createdwith the help of a suitable radiating antenna.

� Intensity of field is varied by varying the powerdelivered to the antenna by the transmitted amplifieror signal generator.

Page 5: Open Area Test Site

FEATURES OF OATSFEATURES OF OATS

� Low ambient and noise floor

� Oversized ground plane

� Host equipment area

� Weather protected

Page 6: Open Area Test Site

TEST SITETEST SITE

� With the help of a proper test site and a calibratedreceiving antenna, radiated emissions fromequipmentunder test over a specified frequency band can bemeasured.

� Using a calibrated transmitting antenna, susceptibility ofequipmentundertestcanbe checkedunderspecifiedfieldequipmentundertestcanbe checkedunderspecifiedfieldconditions.

� Measurements done in a room, or enclosed area result inreflections or scattered signals fromwalls, floor, andceilings which corrupt the measurements.

� Measurements done in a proper open-area test site (OATS)avoids such scattered signals and reflections.

Page 7: Open Area Test Site

TEST ANTENNASTEST ANTENNAS

� To illuminate an equipment under test with known fieldstrengths, it is convenient to use exact half wavelengthlong dipoles at fixed frequencies.

Page 8: Open Area Test Site
Page 9: Open Area Test Site

MEASUREMENT PRECAUTIONSMEASUREMENT PRECAUTIONS

� Electromagnetic Environment: need to be relatively quietand free fromthe presence of strong signals frombroadcastradio, TV transmitters, manmade electromagneticradiations like automobile ignition systems or arc-weldingequipments.

� Electromagnetic Scatterers: OATS should be free fromsources of scattering such as buildings, electricsources of scattering such as buildings, electrictransmission lines, open telephone and telegraph lines,fences, trees.

� Power and Cable Connections: For improving theaccuracy of measurements, it is necessary that the electricalpower connections to the EUT and the cables between thetransmit/receive antenna located in the test site and thetransmitter/receiver equipment located nearby are placed inunderground trenches.

Page 10: Open Area Test Site

�� The shape and size of the open area test site need to beappropriate to ensure that no scattered signals are present,which could affect the measurements. American NationalStandards recommend that

S and S are the scatteredsignal from obstructions� Sc and Sd are the scatteredsignal from obstructionslocated at the boundary of the OATS and the directsignal between the EUT and the transmit/receiveantenna, respectively.

Page 11: Open Area Test Site

OATS CONFIGURATIONS OATS CONFIGURATIONS

�Stationary EUT

• EUT remains stationary andthe transmit/receive antennais traversed on a circular pathso as to view the equipmentfrom all directions (360° infrom all directions (360° inthe azimuth).

• D‘ ≥ 1.5D• The path length of the

scattered signal is twice thatof the direct signal whichensures the scattered signalstrength is at least 6dB belowthe direct signal strength.

Page 12: Open Area Test Site

�Stationary Antenna

� The EUT is mounted on aplatform which can berotated 360° in the azimuth.

� The transmit/receive antennacan remain stationary and yetlook at the EUT from alllook at the EUT from alldirections.

� The boundary of the test siteis an ellipse with a major axisMD of dimension 2D andminor axis Md of dimension√3D, where D is the distancebetween the EUT and thetransmit/receive antenna.

Page 13: Open Area Test Site

EUT Antenna SeparationEUT Antenna Separation

� In most measurements, the distance D between theEUT and the transmit/receive antenna is arranged tobe1, 3, or 10 m.

� To have D different fromthese standard distances,theresultsfrom themeasurementareextrapolatedtotheresultsfrom themeasurementareextrapolatedtoone of these standard distances by using a suitabletransformation.

Page 14: Open Area Test Site

TERRAIN ROUGHNESSTERRAIN ROUGHNESS

� Maximum allowable terrain roughness is determined usingRayleigh roughness criteria and the applicable limit is

� b is the height of the rough edge of the terrain and λ is the wavelength corresponding to the frequency of measurement.

Page 15: Open Area Test Site

REFERNCESREFERNCES

� V.P.Kodali, “Engineering EMC Principles, Measurements

and Technologies”, Chapter 5 page (79-86).

� C.R.Paul,” Introduction to Electromagnetic Compatibility”,

Chapter 2 pages 52,64Chapter 2 pages 52,64

� http://www.emcdirectory.com/suppliers-28A-open-area-

test-sites-oats-for-fcc-emi-emc-testing.htm