There is no technical ground for the difference
In H versus V ground plane.
Just that if the set-up is compared by dummies
they look different and may be justification for
challenging test results.
The loop to consider for CM current is:
EUT – 80 cm of mains wire – LISN – 50 Ohm (both phases) - ground plane
– 40 cm distance capacitor – EUT
Where:
- One of the 50 Ohms loads is the measuring receiver.
- The ground plane does not need to be grounded, just a convenient
low impedance conductor
- The 80 cm of mains wire is critical in the way excess length is
folded
- The LISN needs to be bonded to the ground plane with 30cm wide
conductors to prevent 25-30 MHz resonances
- The 40 cm is arbitrary chosen a long time ago
I do not think the setup was to mimic a file cabinet.
Gert Gremmen
Ce-test, qualified testing.
Van: [email protected] [mailto:[email protected]] Namens Ken Javor
Verzonden: woensdag 23 september 2009 17:59
Aan: [email protected]
Onderwerp: Re: [PSES] Conducted emission measurements
It is understood that capacitance between the test sample and ground will
affect common mode emissions. What is the significance of vertical over
horizontal grounds, and why specifically 40 cm? The file cabinet example
mentioned previously is not terribly convincing in that file cabinets (in my
experience) are not usually grounded.
Ken Javor
Phone: (256) 650-5261
________________________________
From: "ce-test, qualified testing bv - Gert Gremmen" <[email protected]>
List-Post: [email protected]
List-Post: [email protected]
List-Post: [email protected]
Date: Wed, 23 Sep 2009 17:47:54 +0200
To: Ken Javor <[email protected]>, <[email protected]>
Conversation: [PSES] Conducted emission measurements
Subject: RE: [PSES] Conducted emission measurements
The capacitance between EUT and 40 cm plane (be it V or H)
Is the return path for the common mode current on the mains lead.
Make the capacitance smaller (d> 40 cm) then emission decrease,
Make it higher (d < 40 cm) then emissions increase.
40 cm is a good compromise for EUT with irregular surfaces and common
sizes. Only for CM current !
There are proposals to allow for measurement of house-hold equipments
such as vacuum cleaners on a 10 cm from ground. This definitely means
more conducted emissions. Rationale: Vacuum cleaners normally
operate close to a conductive ground.
Note that the LISN measures both CM and DM current, with
a coupling factor of -6 dB
There is discussion about the coupling factors when ground lead
Is connected, so be aware of that.
Gert Gremmen
Ce-test, qualified testing bv
Van: [email protected] [mailto:[email protected]] Namens Ken Javor
Verzonden: woensdag 23 september 2009 17:24
Aan: [email protected]
Onderwerp: Re: [PSES] Conducted emission measurements
Rephrase the question: From an electrical point-of-view, how does the presence
of a vertical ground plane at 40 cm separation affect conducted emissions?
Ken Javor
Phone: (256) 650-5261
________________________________
From: <[email protected]>
List-Post: [email protected]
List-Post: [email protected]
List-Post: [email protected]
Date: Wed, 23 Sep 2009 10:16:11 -0500
To: Ken Javor <[email protected]>
Cc: <[email protected]>
Subject: Re: [PSES] Conducted emission measurements
Ken and List,
It was explained to me as: to simulate a file cabinet next to a desk in an
office environment type of setup.
This is just one example I recall from the various audits I've been through
over the years.
Michael Sundstrom
Electronic Lab Analyst
Overhead Door
TREQ Center, Dallas
[email protected]
OFC: 214-579-6312
CELL: 940-390-3644
KB5UKT
Ken Javor <[email protected]> 09/23/2009 09:56 AM
Please respond to
Ken Javor <[email protected]>
To
[email protected]
cc
Subject
Re: [PSES] Conducted emission measurements
What is the rationale behind a vertical conducting surface for conducted
emissions?
Ken Javor
Phone: (256) 650-5261
________________________________
From: Wan Juang Foo <[email protected]>
List-Post: [email protected]
List-Post: [email protected]
List-Post: [email protected]
Date: Wed, 23 Sep 2009 13:46:27 +0800
To: <[email protected]>, <[email protected]>
Cc: Wan Juang Foo <[email protected]>
Subject: Re: Conducted emission measurements
Hello Tim,
I may be missing. Is there such a 40 cm height? Here is my 5 ¢ worth.
These are some of the the special provision for conducted emission testing:
To meet EN 55011, I suppose since 1999?? the measurement may be carried out:
- on the radiated emission test site (same EUT configuration)
- above a metal ground plane which shall extend at least
50 cm beyond the boundary of the equipment under test
and have a minimum size of 2m x 2m
- within a screened room; either the floor or one wall of
the screened room shall act as the vertical ground plane
.. CISPR 22 since (1993) and Amendment 1 (1995)
Table- top EUTis to be placed 40 cm from a vertical metal reference plane
(e.g. a wall of a screened room/enclosure)
"The EUT, where intended for table-top use, shall be placed 0,4 m from a
vertical metal reference plane of at least 2 m by 2 m and shall be kept at
least 0,8 m from any other metal surface or other ground-plane not being part
of the EUT. If the measurement. is made in a screened enclosure, the distance
of 0,4 m may be referred to one of the walls of the enclosure."
Floor- standing EUT on a horizontal metal ground- plane, not in metallic
contact with the ground- plane. Metal floor of a screened room may replace
the reference ground- plane
best regards,
Tim Foo
Expert Witness, EMC and Product Safety
ECE, School of Engineering,
http://www.np.edu.sg/ece/ <http://www.np.edu.sg/ece/>
<http://www.np.edu.sg/ece/> DID: +65 6460 6143
Ngee Ann Polytechnic,
535 Clementi Road, Fax: +65 6467 1730
Singapore 599489
[email protected] wrote on 23/09/2009 06:06:05 AM:
> Hello Group,
>
> I have a question about the conducted emission measurements
> performed in a semi-anechoic chamber.
>
> CISPR 22 requires the use of a vertical ground plane when testing
> tabletop EUTs, unless you mount your EUT on a non-conductive table
> 40cm above the horizontal ground plane (instead of the traditional 80cm)
>
> I did not find a requirement for a vertical ground plane when
> testing floorstanding equipment. If one opts to use the alternative
> method of not using the vertical ground plane, can floorstanding
> equipment also be tested without the vertical ground plane? The
> horizontal ground plane is always present since that is the chamber floor.
>
> What are most labs using? We have the option of making a removable
> vertical ground plane "wall" or mounting the equipment on a 40cm table.
>
> Thanks,
> Tim Pierce
> -
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