Re: [SI-LIST] : Conducted noise emission diagnosis device

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From: Patrick Lawler (plawler@west.net)
Date: Mon Apr 24 2000 - 09:39:32 PDT


One version involves resistively summing the two LISN signals, and
feeding the result to the EMC analyzer. Summing removes the
Differential Mode portion, leaving only Common Mode signals:

LISN1 signal --+---R1----+
                | |
                R2 |
                | +----R1----> To 50 ohm EMC receiver
             ground |
                          |
                          |
LISN2 signal ---+---R1----+
                |
                R2
                |
             ground
 
R1=16.7 ohm
R2=50 ohm

Resistor matching and symmetrical circuit layout is crucial for proper
operation.

Another method involves RF transformers to sum (leaving Common Mode)
or difference (giving Differential Mode) the LISN signals.
Mini-Circuits (http://www.minicircuits.com/) has parts that can do
this. Look for Power Splitters/Combiners - 2 Way - 0 degree/180 degree
I haven't tried this method.

On Fri, 21 Apr 2000 13:27:30 +0800, keng-kok_khoo@hp.com wrote:
>I am looking for a device that will differentiate the dominant component(either
>common-mode or differential-mode current) in the total conducted noise emission
>current of a product measuring through its' power cord using a LISN.
>
>I called this device "common/differential mode current separator". In conducted
>noise emission measurement, both common-mode and differential mode noise
>current are measured by LISN and the LISN can't tell which mode is the dominant
>current.
>
>I came across a paper by Clayton Paul and Keith Hardin which explain the
>usefulness of a separator like this that would identified the dominant current
>from the total current. Hence, the correct capacitor value(either X-caps or
>Y-caps) can be changed accordingly so to reduce the overall conducted noise.
>The book by Clayton Paul "Introduction to Eletromagnetic Compatibility" has
>also mention about this device.
>
>I have contacted a few persons trying to look for the person who have actually
>built this separator himself and I am also looking for any vendor who have this
>product for sale. So far, my effort has yield no results.
>
>Can anybody point me to the right person so that i can try to built this
>separator myself. Any other suggestion and comments are greatly appreciated.

----
Patrick Lawler
plawler@west.net
Nryȥhȥ]ǧu隊[h&ȥi˧r^ءƠzPԔ )b+PԔ ,Xؠz_^nq )b֫rzƫyz"nWm
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