HI Ken, I have to take exception to the spacing material. First rule of assessing a lab is look for where the lab don't comply... if there's is no criteria, you cant assume or impose anything: opinions are irrelevant. The standards group may be working on something, but thats of no significance: you know what assume spells don't you.....
In my humble opinion, I'd wager that a little humidity on paper ( a small change in a very high resistance ) has less effect than dielectric constant ( the capacitance ) of different plastics. BTW, look at the dielectric strength ratings listed in MacMaster-Carr for a bunch of their plastics. Not many are rated for 8 kv at 20 mils thickness. While were grumbling at standards, especially ESD, what height should the VCP be above the HCP before it's considered adversely loaded? What materials are considered unacceptable for holding the VCP? The Manufacturers are smart, they supply the cables that generate the most profit. If it's coming from off-shore, chances are they were nothing like what was used during testing. As a test lab, it's no business of ours to say what should be supplied, or used, only carefully document what WAS used: the labs are not policemen. I guess I don't separate ongoing compliance from the best performance, on the day, in my lab. A product is expected to work every day of it's life and EMC is no exception. In my automotive days we used to age parts before EMI testing, specifically to prove capability through product life. Man, have we digressed off Mats! Anyone else going to the EMC Symposium this year? Please say hi if you do! Cheers, Derek. -----Original Message----- From: Ken Wyatt <[email protected]> To: Derek Walton <[email protected]> Cc: EMC-PSTC <[email protected]> Sent: Mon, Jul 25, 2011 11:32 pm Subject: Re: [PSES] ESD Spacer While the ESD standard is non-specific regarding the insulation material, I must side with Doug. I would very much hesitate using some unknown withstand-rated material for my ESD testing that likely varies with humidity. For table-top products with feet, the point is probably moot, however many handheld or portable products could be adversely affected. Why take the chance? I'm almost certain the ESD standards working groups are assuming some sort of plastic, as well. >From a manufacturer's point of view, I would look very dimly on using some unknown "used" cables. How would I know whether the shielding or bonding quality to the cable's I/O connector was even good? I agree that from the test center's point of view, the product should be tested with the cables as supplied by the manufacturer. The manufacturer, if they were smart, would supply the best quality cables possible (that's assuming that the cables were "as supplied" with the product and not some "super" cable). Derek, your point about testing with worst-case cables is well taken and really leads to a side-issue regarding the continued compliance properties of a product, but that's another topic for debate. Regards, Ken _______________________ Kenneth Wyatt Wyatt Technical Services LLC Woodland Park, CO Email Me! | Web Site | Blog Subscribe to Newsletter Connect with me on LinkedIn On Jul 25, 2011, at 8:27 PM, Derek Walton wrote: > > Hi All, > > I'd just like to point out here that the EN does not give any criteria for the dielectric withstand nature of the spacer. So, while we can argue best practice, if a lab meets the thickness, all is permissible. > > I also disagree with Doug's statement on cables. You must test with whats supplied by the manufacturer, or with ones that he states you must use. Why, well because cables can make a huge difference in performance. I would call messing with cables like this part substitution and fraud. > > > > > I also disagree about using new cables. The reason for this is that cables will degrade with some flexing and you should be assuring a product meets the EMC requirements for it's design lifetime, not on a good day in a lab, with the wind behind it and rubber boots on. > > Just trying to keep the common sense hat on compliance testing > > Cheers, > > Derek Walton. > > > > > -----Original Message----- > From: Doug Smith <[email protected]> > To: Sundstrom, Michael <[email protected]> > Cc: Bryce Stammerjohan <[email protected]>; EMC-PSTC <[email protected]> > Sent: Mon, Jul 25, 2011 8:59 pm > Subject: Re: [PSES] ESD Spacer > > > If the poster board is 0.5 mm thick as required, you may be failing equipment that might otherwise pass, which I have seen happen. A spark through the poster board will likely be worse than the one you supply >from the ESD simulator in terms of peak current and di/dt. In any case, unless the poster board in 0.5mm thick and you have confirmed there is no spark through, than you cannot say you have tested to IEC 61000-4-2! Maybe OK for a pretest but not for CE marking. It's hardly worth it to save a few cents on test materials (the insulating layer we are talking about, USB cables, Ethernet cables, and many other things) and waste thousands of dollars in the end. I see this happen a dozen times per year. > > I also recommend using new, high quality cables for any performance test. This is especially important for USB and Ethernet cables. > > Doug > > On 7/25/11 10:32 AM, Sundstrom, Michael wrote: > > > Guys, > > I just use poster board, I get 20 sheets at a local office supple house for $5-$6 ? > > Am I missing something? Do you need plastic sheets? > > > > > > > Michael Sundstrom > > OHD / TREQ Dallas > > Electronic Lab Analyst, EMC Lead > > 2170 French Settlement Rd, Suite B > > Dallas, Texas 75212 > > (214) 579 6312 > > (940) 390 3644c > > KB5UKT > > > > Albert Einstein once said, "The definition of insanity is doing the same thing over and over again and expecting different results". > > > > > > > From: Bryce Stammerjohan [mailto:[email protected] <mailto:[email protected]?> ] > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://product-compliance.oc.ieee.org/ > Graphics (in well-used formats), large files, etc. can be posted to that URL. > > Website: http://www.ieee-pses.org/ > 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]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ 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]>
