Ahhh well said Robert.
Dennis Ward Director of Engineering American TCB Certification Resource for the Wireless Industry www.atcb.com 703-847-4700 fax 703-847-6888 direct - 703-880-4841 From: E. Robert Bonsen [mailto:[email protected]] Sent: Thursday, April 16, 2009 5:01 PM To: Dennis Ward Cc: 'Brent G DeWitt'; 'Price, Edward'; [email protected] Subject: Re: [PSES] SV: "Quiet" Laptop To add : even when not taking apart a laptop or abusing it physically EMC performance will deteriorate over time. Low-cost mechanical grounding/shielding solutions are often not robust enough to withstand multiple rounds of transport shock&vibe. Conductive cloth wraps or other types of shielding wraps are not robust under mechanical stress. Materials used for chassis parts or shields can oxidize and subsequently inhibit grounding to fingers and gaskets. These are just a few examples. Normal usage and time can and often will wear out commonly used cheap EMC countermeasures that may be used to achieve initial compliance. Even during manufacturing changes happen, tools deteriorate or manufacturing processes are optimized. These tolerances have an affect on the quality of the out-of-the-box EMI performance of a new unit. A good factory audit program will catch deviations to allow fixing these issues, but that still allows batches of units to go out to customers which are not at the same level as the original compliance unit. It also varies from manufacturer to manufacturer how much emphasis is put on maintaining and auditing compliance during the post-compliance test phase of a project, in which tool changes, parts vendor changes and cost-reductions are commonplace. Also, let's not forget that passing compliance to the legal limit in one compliance test situation does not guarantee compliance under all conditions. "My EMC is better than yours" depends highly on the context of the test. -Robert E.Robert Bonsen Sr. Engineering Consultant Orion Scientific Dennis Ward wrote: I do not think any company is going to do the ‘we have less EMC than brand X” for the simple reason that it just won’t work. Laptops now days are built to be fairly rugged, but they are sold to the general public who think precariously placing a laptop on the stove top while checking email and making dinner is ‘normal’ use. Or who perhaps think that cleaning the fan area is just too much work and ‘hey these things are supposed to work like this’. Of course you then have the cleannicks who tear apart their laptops or desktops routinely to ‘clean’ the dust out. I think I fall into that category. Labs may even have a worse time as they open these things probably on a routine basis for various reasons from putting test boards, WLAN transmitters or other ‘support components’ inside to make the test suitable. Cables are also routinely plugged and unplugged. When running a test lab I even had customers that carried the laptop computer by the cables getting it out to the OATS for testing. There it was, in all its glory dangling, swinging, bouncing and flopping around. All of this to say that buying a pristine laptop out of the box with all EMC fingers in place, all shielding in place and all other EMC fixes used to make it compliant in place is different than using a hard handled PC for compliance testing. You cannot expect a laptop or Desk top to maintain all of the originally testing compliance margins after opening is up even once, how can you expect it to be complaint after many openings, fiddling and fudging? This has always been and probably will continue to be a problem child for compliance testing, but getting, keeping and maintaining a compliant laptop or Desk top for compliance testing lies in the world wishes. If you could get a laptop or Desk top that actually met compliance limits, keeping it in that state would probably cost you more than simply going out and buying a new one every once and a while. Dennis Ward Director of Engineering American TCB Certification Resource for the Wireless Industry www.atcb.com 703-847-4700 fax 703-847-6888 direct - 703-880-4841 From: [email protected] [mailto:[email protected]] On Behalf Of Brent G DeWitt Sent: Wednesday, April 15, 2009 4:25 PM To: 'Price, Edward'; [email protected] Subject: RE: [PSES] SV: "Quiet" Laptop The rate of laptop model replacement by the manufacturer makes it very difficult to recommend something that you can still buy by the time the EMC community has had enough time to seriously evaluate it. I think Ed’s view on the hopelessness of seeing a manufacturer actually advertise EMC/EMI performance would only happen to products targeted to the paranoid financial market, and I haven’t seen any of that. In a previous life we went out and searched eBay to find laptops that had been discontinued by the manufacturer that we knew to be clean. Good luck! Brent DeWitt Westborough, MA From: Price, Edward [mailto:[email protected]] Sent: Wednesday, April 15, 2009 5:11 PM To: [email protected] Subject: Re: [PSES] SV: "Quiet" Laptop > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf > Of Grasso, Charles > Sent: Wednesday, April 15, 2009 12:50 PM > To: [email protected]; Piotr Galka > Cc: EMC-PSTC; John Woodgate > Subject: RE: SV: "Quiet" Laptop > > I sincerely hope that you statement: "Finding a quite laptop > or hub seem to be almost impossible" is wrong! After all > there are many large laptop manufacturers spending zillions > of (in our case) dollars to meet the EMC requirements.!! True, but who markets their product with any claims of EMC excellence? We all may be spending big bucks in our compliance efforts, but all we ever do is slip a required statement in our Users Manual or mold a logo on the bottom of our case. Instead of quietly muttering that "we meet the minimum legally required standards," is anybody daring to say something like "Our Wonderbox has 14 times less annoying electronic radiation!" Or how about something like "Our Wonderbox still keeps working when others have crashed; we built this thing to handle RF noise 3 times stronger than the government said we had to!" Now I doubt your marketing would ever let you get away with anything like that, because claiming how great you are, even if it's true, means alerting the customer to certain problems in life. Marketing usually doesn't want customers to think about problems when they sing their sales pitch. We will have to wait for some maverick company to try this angle; who knows, it just might work. Certainly, RF engineers have a couple of brand names in their head when they think about low-noise pre-amps, so maybe the public reputation of an EMC tough product is possible and desirable. The original poster was asking an interesting question. While you shouldn't choose a "lab queen" product, what's wrong with choosing the quietest among the major brands? But even in this knowledgeable forum, we really didn't have an answer. I'll pose a question; suppose, for your own personal desires, you wanted a very low-emission gadget. If you went to any number of major consumer electronics websites, and looked for compliance data, do you think you would find even one that offers real performance data, not just a bland statement of "meets the minimum requirements," to let you make any intelligent choice? Right now, even we experts can't offer a good answer to the poster's question, because we have no qualitative data. Ed Price [email protected] <blocked::mailto:[email protected]> WB6WSN NARTE Certified EMC Engineer Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 Military & Avionics EMC Is Our Specialty - 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://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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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://www.ieeecommunities.org/emc-pstc 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]>
