Good luck.
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Arun Kaore <[email protected]> on 06/16/99 08:18:53 PM
Please respond to Arun Kaore <[email protected]>
To: "'[email protected]'" <[email protected]>
cc: (bcc: Robert E. Heller/US-Corporate/3M/US)
Subject: NEAR/ FAR FIELD CORRELATION ISSUES
Greetings and Salutations! I was wondering if this could be mailed out via
the epc-pstc channels.
I want to know if anyone is doing any work in "near/ far field correlation
to commercial EMC standard limits" area and possibly correspond with them
with a view to exchanging notes.
Brief Follows:
Brief:
"Application of Near Field and possibly Surface probe techniques in
Evaluating Emissions from source equipment and correlating/quantifying this
data to an OATS, LISN, Absorbing Clamp etc based measurement.."
Details:
We assume that the current EMC compliance regime around the world has
quantified limits of compliance to which if every source equipment adheres
to, then it has a reasonable chance of performing as intended in a real
life
situation, noting that the immunity threshold test levels are much more
stringent than EM emission limits.
Current EMC measurements are very cumbersome, require large expense in
setting up and maintaining (calibrating) OATS, LISNS, Absorbing Clamps,
Ferrite tiled lined semi- anechoics etc. Despite this expense, the
measurement uncertainities are still of the order of 6 to 10dB (inherent).
Every newly released EMC standard by IEC CISPR or CENELEC has potentially
new transducers and new headaches from point of view of sourcing and
maintenance, calibration. EMC today is where Safety was 10 years ago. I am
of the opinion that EMC testing should be simplified and reasonably
accessible to all end users.
Continued progress and urban development has led to increasing levels of
broad and narrowband noise to the extent that ambient profiles sometimes
swamp out the limits; this has led to most test houses in the EU to opt for
GTEMS or semi-anechoics (referred to as "alternative all weather test
sites") at considerable expense.
Current techniques such as emission E Field prescanning in shielded rooms
prior to OATS based testing with biconilog antennae have the drawbacks of
"peaking" the emissions and reflections/standing waves.
Hence:
I propose to develop near or surface probe H (inverse of E) field
techniques which actually senses the emission profiles and correlate them
to
an Absorber clamp, or OATS or LISN (Common mode fix) or whatever. Cables,
panels, slots etc could be "sniffed" with a Loop and if it is possible to
correlate this near or induction field data to compliance limits then it
becomes very easy for individuals and organisations to do precertification.
Transducers could be simple and light weight, rugged, and physically
defined
so that minimal calibration is required. EMI receivers will still need
calibration.
With these techniques, you measure actually what comes off the source and
not the "peak" value of the bounced and direct rays within say the Fresnel
ellipse, or move the Absorbing clamp up and down the rail and peak the
field.
Conducted emissions could be scanned by common mode techniques and radiated
emissions by surface or near scans.
Currently, these techniques are used only qualitatively for precompliance
at
board levels and more work needs to be done to bring them of age and
reliability. (Am I right?)
What I am proposing has a corollary with the bulk current or damped
sinusoid
(NEMP- Nuclear EM Pulsing) or lightning injection techniques (CS 114, 115
and 116 of 462D). With these methods, it was possible to achieve identical
or several orders of magnitudes higher levels of RF injection power at a
fraction of the cost of say an RS03 OR RS05(at least for the bulk cable
loom!). What resulted was a cheap, powerful and a more repeatable test.
Arun Kaore
EMC Engineer
ADI Limited
Systems Group
Test & Evaluation Centre
Forrester Road, St Marys, NSW 2760
P O Box: 315, St Marys NSW 1790
Tel: 61 2 9673 8375
Fax: 61 2 9673 8321
Email: [email protected]
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