Very good advice. Actually, there are grounds (!) for using a balanced
filter, i.e. inductors in both L and N.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2018-04-26 19:20, Edward Price wrote:
*Ian:*
**
*It sounds like the low-pass powerline filters that are being used
with your shielded enclosure are very inadequate for removing low
frequency noise. Here is a short description of the filters used on my
shielded enclosures (a main EUT chamber and an auxiliary chamber for
stimulus and monitoring equipment):*
Electrical power (120 VAC 60 Hz Three Phase Wye, 120 VAC 400 Hz Three
Phase Wye and 28 VDC) penetrates the RF shielded enclosures through
low-pass EMI filters mounted on the enclosure walls. Power is
internally distributed, within steel conduit, to convenience outlets
and incandescent lighting fixtures. The primary chamber EMI filters
for the 60 Hz power lines are 100 Amp rated Rayproof 4X100-60 units.
The primary chamber EMI filters for the 400 Hz power lines are 50 Amp
rated Corcom CDSRW2050A4-C units. The primary chamber EMI filters for
the 28 VDC power lines are 100 Amp rated Rayproof ULW-100-400-4 units.
All EMI filters have a rated attenuation of 120 dB or greater from 14
kHz to 10 GHz.
The auxiliary enclosure is equipped with AC and DC power line filters
with a rated attenuation of 90 dB or greater from 14 kHz to 10 GHz.
**
*All of these filters are at least 25 years old now, so the model
numbers may not be current. Further, these filters were intended for a
full-capability military EMC lab, so you probably will not need the
amperage capacity of these filters. However, the attenuations shown
are what you should prefer if you want your lab to be well-equipped.*
**
*It is certainly possible that you could build a pair of heavy current
low-pass filters to augument each powerline that penetrates your
enclosure. I would be thinking of a double-pi section filter using
three 10 uF capacitors and two 100 mH toroidal inductors as a first
trial design. However, home-brewing a powerline filter is more
complicated (and much more dangerous) than it sounds; it would be much
safer for you to just buy some better filters.*
**
*Take a look at places like eBay. Here’s a typical, good quality
2-line EMI powerline filter selling for $600:*
**
*https://www.ebay.com/itm/RAYPROOF-EMI-FILTER-14KHZ-TO-10GHZ-ULW-2X30-60/250998382668?hash=item3a70ab604c:m:mfuCE0sb33zzXWsoekkNGSA*
**
**
*/Ed Price
/**WB6WSN**/
/**Chula Vista, CA USA**//*
**
*From:*McBurney, Ian [mailto:[email protected]]
*Sent:* Thursday, April 26, 2018 3:33 AM
*To:* [email protected]
*Subject:* [PSES] Mains Conducted rf emissions measurements
Dear Colleagues.
I am setting up a mains conducted rf emissions measuring system and am
experiencing excessive mains noise when connecting the LISN to the
240V wall socket. The noise affects my measurements between 150kHz to
400KHz. Beyond that and up to 30MHz I am satisfied. Is there a way of
filtering out this noise. I have tried various EMI mains filter
modules but none appear to attenuate enough at that frequency band.
They are very good at attenuating frequencies beyond 1MHz. I have
tried inserting an isolation transformer before the LISN but this
appears to distort the measurements.
Can anyone recommend a solution?
Many thanks in advance.
Ian McBurney
Lead Compliance Engineer.
Allen & Heath Ltd.
Kernick Industrial Estate,
Penryn, Cornwall. TR10 9LU. UK
T: 01326 372070
E: [email protected]
Allen & Heath Ltd is a registered business in England and Wales,
Company number: 4163451. Any views expressed in this email are those
of the individual and not necessarily those of the company.
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