Derek, MIL-STD-461 requires that the power source be loaded resistively at the same rms level as the test sample loads it, to perform an ambient. I realize that 600 60 Watt light bulbs mounted on a couple 4x8 sheets of plywood isn't a palatable approach, but it is the reason for this that is important.
You need to know that the power source is not overloaded and not distorted at the (resistive) load equivalent of the test sample. Aside from that, consider that the -461 LISN inserts around 5 Ohms at 10 kHz, but this is in shunt with the line, not in series. Whereas the facility EMI filters insert 100 dB of insertion loss at 10 kHz, and that is a combination of shunt and series impedances. The EMi filters will be way more of a factor here than is the LISN. You can check the facility EMi filters, but most likely they are simply doing their jobs. Another alternative for resistive loading (for a short period of time) is electric hot water heater elements, immersed in enough water to last long enough to check the ambient. Dirt cheap, and it doesn't take near as many as with lightbulbs. Ken Javor 256/650-5261 Quoting Derek Walton <[email protected]>: > HI Ed, > > yep, I terminated the LISN port when I did the CP test. > > At 101 Amps per phase, I cant resistively load the network..... > > I was thinking that a network amalyser looking into the LISN port ( > power disconnect outside the room ) would perhaps show something > impedance wise. Facility power appears clean under no load. > > Cheers, > > Derek. > ----- Original Message ----- > From: Price, Ed > To: Derek Walton ; IEEE EMC Discussion Group > Sent: Wednesday, November 14, 2007 9:46 AM > Subject: RE: Interaction between EUT and LISN and Wall filter > > > Derek: > > Did you also replace the current probe with a 50-ohm termination, > and do you then not get the hump? > Next, did you try using a resistive load on the LISN's and see if > the hump is there? > Finally, do you still see a hump with just a resistive load and no LISN's? > > I would suspect either a facility power noise source or a > resonance in the chamber powerline filters. > > Ed Price > [email protected] WB6WSN > NARTE Certified EMC Engineer & Technician > Electromagnetic Compatibility Lab > Cubic Defense Applications > San Diego, CA USA > 858-505-2780 (Voice) > 858-505-1583 (FAX) > Military & Avionics EMC Is Our Specialty > From: [email protected] [mailto:[email protected]] On Behalf Of > Derek Walton > Sent: Wednesday, November 14, 2007 7:03 AM > To: IEEE EMC Discussion Group > Subject: Interaction between EUT and LISN and Wall filter > > > HI All, > > I'm watching a MIL STD 461 test on a stand alone EUT. Between 10 > kHz and 20 kHz we have developed a Hump in out profile that wasn't > present at our last test lab. > > The hump is identical looking with a current probe on the input > to and from the LISN, so I believe I'm seeing no isolation from the > LISN between the EUT and room wall filter. > > So, I was curious if anyone has looked into the impedance of the > power supply in a room from 10 kHz to say 100 kHz? I'm thinking > that my EUT and the room filter may be interacting.... > > We have dismised other sources nearby and in the room. > > Thoughts anyone? > > Thanks, > > Derek Walton > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Jim Bacher: [email protected] > David Heald: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
