tongue in cheek mode ON Are we not as EMC engineers supposed to interpret the standards to our economic advantage so we can ship products without delays for redesign and still have some rational for explaining why we did what we did? After all, if there is no foul, there is no fault, because I haven't heard any complaints. That is, the FCC has not yet written me that letter, again. If the license holder have a problem, I'll hear about it. If not, keep shipping. HAMS be damned. Oh wait, news flash, the military uses low frequencies?? who ever heard of such a thing? Why in the world would they want to talk to a submarine? It's underwater!
tongue in cheek mode OFF, and time for another beer. c ya, --- Ken Javor <[email protected]> wrote: > Not going to argue chapter and verse of the > standards, nor make a case they > should be changed been there, done that, waste of > time. However, they have > departed significantly from the original intent and > that leaves one asking: > ³Why are we even doing this?² > > The original intent of conducted emission > requirements was two-fold. One was > protecting against ripple on the bus that could > affect radio reception by > direct conduction through the power supply from the > mains. That (FCC) limit > was originally 48 dBuV for class B. Secondarily, > that limit protected > against electromagnetic radiation from the mains due > to rf currents, and > that protected against radiated interference in a > frequency range where it > would be quite difficult to make radiated > measurements. If you have a > single device that plugs into a single branch > circuit, albeit through > multiple power supplies and multiple power cords, > then all those cords > should indeed plug into a single pair of LISNs. Now > if the power supply > connected to each one of those cords is totally > different from each and > every other power supply, there is likely no harm > done, because in any > single 9 kHz channel, you likely won¹t get any > superposition. But if the > design were such that all power supplies were > identical, then their > emissions would add in quadrature (assuming they are > not phase-locked) and > 18 of them would yield 12.5 dB more signal in each 9 > kHz bandwidth occupied > by a clock harmonic than for a single power supply > running off a single > LISN. > > Another issue, prevalent at and around 150 kHz, is > rectification harmonics. > These will be directly proportional to total current > draw, so that splitting > the total current amongst many LISNs makes it much > easier to meet the limit, > and this isn¹t justified if the equipment plugs into > a single branch > circuit. This isn¹t a problem in the USA, because > we have no BCB receivers > below 530 kHz, but it affects European BCB reception > in the LW band from 150 > 300 kHz. > > My opinion, FWIW, is that if the standards ignore > the original intent, then > the standards are an end in themselves with degraded > contribution to the > original intent to foster controlled levels of rfi. > > Ken Javor > > Phone: (256) 650-5261 > > > > From: "Pettit, Ghery" <[email protected]> > Date: Tue, 3 Jun 2008 14:21:31 -0700 > To: Ken Javor <[email protected]>, > Untitled <[email protected]> > Conversation: Placement of LISNs for Conducted > Emissions Testing to > CISPR22/FCC part 15 > Subject: RE: Placement of LISNs for Conducted > Emissions Testing to > CISPR22/FCC part 15 > > One LISN per power cord is acceptable. One power > cord per LISN is required > for the power cord being measured. That way you > know that the emissions > being measured are from that cord, and not another > one. > > This was simpler with the old design two cords > comes out of the cabinet, > each to its own LISN. Now John has to contend with > a bunch of cords. This > is addressed in CISPR 22, article 9.5.1, which > states: > > ³The mains cable of the unit being measured shall be > connected to one > artificial mains network (AMN). Where the EUT is a > system, which is a > collection of ITE with one or more host units, and > each item has its own > power cable, the point of connection for the AMN is > determined by the > following rules: > > a) Each power cable that is terminated in a power > supply plug of a standard > design (IEC 60083 for example) shall be tested > separately.² > > There is no question that the power cords are tested > one at a time. A later > paragraph in 9.5.1 calls for one or more additional > AMNs for the additional > power cables. > > Article 7.2.1 of ANSI C63.4:2003 has different text > that conveys the same > message. > > So, if your thought is to be accepted, both ANSI > C63.4 and CISPR 22 (and > probably other standards, as well) will have to be > changed. Given the > success in reducing or largely eliminating > interference from ITE that the > current standards have demonstrated over the past > 20+ years, I doubt that > will gain much traction. At least, I certainly hope > not. J > > Ghery S. Pettit, NCE > Convener, CISPR SC I WG3 > Member, C63 SC 1 > > > > > From: [email protected] [mailto:[email protected]] > On Behalf Of Ken Javor > Sent: Tuesday, June 03, 2008 2:09 PM > To: Untitled > Subject: Re: Placement of LISNs for Conducted > Emissions Testing to > CISPR22/FCC part 15 > > First a direct response to the question posed, then > a challenge to the > premise upon which it is based. The second comment, > if legitimate, is more > important than the first. > > You could use one dual LISN, or one LISN per > current-carrying power > conductor, if you had eighteen different > make-before-break switches that > would allow each power cord to draw current either > from the LISN power > output port, or the LISN input power side. If you > want to go with eighteen > LISNs, I think it is technically acceptable to stack > them, but you want the > ground strap to maintain a lower than 5:1 > length-to-width ratio, so that > likely means stacking no more than three high. > > But here¹s an interesting and likely unwelcome > thought, which I invite other > forum members to comment upon. The point of meeting > a conducted emissions > requirement is to protect radios operating below 30 > MHz that might be > powered from the same branch circuit, or in the case > of class A which likely > applies here, operated within some distance of the > equipment, but plugged > into a different branch. If the equipment in your > two racks operates > simultaneously, it isn¹t obvious to me that you are > even allowed different > LISNs presumably all your rack equipment plugs > into the same branch > circuit, which should be represented by a single > pair of LISNs. Immediate > problem solved, but potentially more noise to > filter, especially if power > supplies operating off each cord operate at same > switching frequencies. > > Ken Javor > > Phone: (256) 650-5261 > > > From: "Flavin, John" <[email protected]> > Date: Tue, 3 Jun 2008 16:40:10 -0400 > To: <[email protected]> > Conversation: Placement of LISNs for Conducted > Emissions Testing to > CISPR22/FCC part 15 > Subject: Placement of LISNs for Conducted Emissions > Testing to CISPR22/FCC > part 15 > > > > Our company sells ITE systems that are housed in > commerial 19" racks. The > system is designed to be fault tolerant and > redundant, so each rack has two > AC mains cords. > > We do our own EMI certification testing (we're an > accreditted lab), and our > typical EUT consists of two of these rack, so there > are 4 AC Mains cords to > test, which we connect to 4 LISNs. > > A modified version of this system is now in the > works, where the dual AC > mains cords are replaced by multiple cords (with > lower current per cord). > The design now would have 10 AC mains cords out of > one rack, and 8 from the > other. This means the two rack EUT would have 18 AC > Mains cords to test. > > In a perfect world, where cost were no object, we > would have 18 LISNs, since > this is the most efficient for testing -- set it up > once, and test > everything. > > Our question is how to place a relatively large > number of LISNs and satisfy > the standards' requirement of the 80cm spacing of > the EUT and LISN. > Specifically: > > 1) Are we allowed to place LISNs around all sides of > the EUT, maintaining > the 80cm spacing (i.e. have LISNs at the front face > of the EUT, and run the > mains cord from the back to the LISN)? > > 2) Are we allowed to stack LISNs on top of each > other, as long as the LISN > is bonded to the ground plane? > > Since we have to test each cord in turn, we could > reduce the number of LISNs > by combining a number of the cords not currently > being tested through a > second (or third) LISN. The downside of this is > having to re-plug the cords > after each cord is tested, which requires shutting > the system down and > restarting, which is a non-trivial task (and takes > longer than it does to > test one cord). > > > John D. Flavin > Teradata TCP Engineering > 17095 Via del Campo > San Diego, CA 92127 > [email protected] > V: (858) 485-3874 > F: (213) 337-5432 > - > > 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 > 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 > - Bill You can say what you want about the South, but you never hear of anyone retiring and moving North!!! - 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
