-----Original Message-----
From: Muriel Bittencourt de Liz [mailto:mur...@grucad.ufsc.br]
Sent: Friday, December 22, 2000 8:05 AM
To: Lista de EMC da IEEE
Subject: Doubt with conducted emissions measurement
Hello Group!
First of all, I wish a merry christmas and a happy new year for the list
members.
Second, I'd like to solve a doubt. It concerns the methodology of
conducted emissions tests.
Let's suppose a power electronic equipment (static converter) that has a
boost converter in the entrance that's used for power factor correction
(PFC). When I make a conducted emissions test, I plug the converter in a
LISN, then I plug the LISN in the outlet, this way (the classical way):
Equipment => LISN => Outlet (Mains)
Well, the LISN consists of a RLC network that has the purposes of:
- prevent that external interference from the mains contaminate the
measurement
- create a stabilized impedance (50 ohms) in the frequency range of
interest (150kHz-30MHz) to make results repeatable, from site to site.
Ok, what I've said until here is well known and is present in every book
about this subject of EMC.
My doubt is this: The LISN can't interfere in the functional operation
of the converter? Things like resonance, extra ripple can't occur? And,
imagining the worst scenario, can the LISN make my equipment not work
according to what's expected?
Another thing I was thinking about is the fact that the military tests
os conducted emissions are done with a probe, and not using a LISN.
I'm very curious about this subject because I was asked about this
question and I became very surprised, because I have never thought about
this. We are, generally, so interested in results that we forget to ask
the "basic questions" sometimes.
Well, I think that's all. Thanks in advance for those who can help me.
Best Regards
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Eng. Muriel Bittencourt de Liz
EMC Testing and Troubleshooting
Group of Conception and Analysis of Electromagnetic Devices
Federal University at Santa Catarina
Florianópolis, SC, Brazil
Muriel:
The LISN adds only modest (although standardized) amounts of inductance and
capacitance to the powerline. Typically, the LISN has a series inductor of
only 5 to 50 microhenries, and on the power source side, a .1 to 10
microfarad capacitor. The insertion of the LISN into the powerline should
not be electrically significant.
OTOH, it certainly is possible to imagine some scenario where the EUT
interacts with the specific circuit values of the LISN. However, any EUT
which did that would probably be a very unique gadget, and it probably would
encounter problems plugging into random outlets.
Regarding mil testing; Mil-Std-462D specifies an LISN for both Methods CE101
and CE102. For CE101, the noise current into the LISN is measured by a
current probe around the EUT powerline. For CE102, the analyzer is connected
to the LISN signal output port to read noise voltage across the LISN
impedance. The British Def Stan 59-41 Method DCE01 also uses the LISN and
current probe technique.
Regards,
Ed
Ed Price
ed.pr...@cubic.com
Electromagnetic Compatibility Lab
Cubic Defense Systems
San Diego, CA. USA
858-505-2780 (Voice)
858-505-1583 (Fax)
Military & Avionics EMC Services Is Our Specialty
Shake-Bake-Shock - Metrology - Reliability Analysis
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