Re: ESD Design, non-earthed products
John Woodgate wrote: Doug McKean inimitably wrote: One of the requirements in 1950 is to ground any exposed metal parts accessible to the end user. Surely that applies only to Class I products? IF not, it would rule out Class II and III products entirely. Battery-operated hand-helds are Class III. Thanks John, I've deleted the original post. In my haste, I assumed it was Class I and was thinking in regards to a product which used plastic entirely for enclosure, had no chassis ground, and mains primary ground was connected only the power supply chassis. Sorry guys ... - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: ESD Design, non-earthed products
000601c11949$ae3488b0$3e3e3...@corp.auspex.com, Doug McKean dmck...@corp.auspex.com inimitably wrote: One of the requirements in 1950 is to ground any exposed metal parts accessible to the end user. Surely that applies only to Class I products? IF not, it would rule out Class II and III products entirely. Battery-operated hand-helds are Class III. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk This message and its contents are not confidential, privileged or protected by law. Access is only authorised by the intended recipient - this means YOU! The contents may be disclosed to, or used by, anyone and stored or copied in any medium. If you are not the intended recipient, please advise the sender yesterday at the latest. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: ESD Design, non-earthed products
I can attest to John's recommedations. Many years ago I worked in a company which had as an aftermarket product a vinyl cutting division. Machines which took large reels of vinyl, ran off specific lengths at high speed to spools which were shipped off to customers. The speeds were up in the 50 or so feet per second level. The side of this fast moving vinyl could easily slice one's hand off if your hand happened to be in the wrong place at the wrong time. The vinyl was run through several rollers to maintain the proper tension and holes were cut along the sides. Amazingly high ESD levels were generated. The machines were drawn to my attention when one of the workers had to go to the emergency room. According to him, a spark about 18 inches long hit him when he was changing spools. I measured the distance later and he wasn't that far off. IIRC, research provided three ways to reduce the charge: one with tinsil or strapping of some sort, one with a slight radioactive charge generation device, and one with a +/- charge generator much like what's used in an air deionizer. We chose the tinsil and it worked great. BUT, they had to be changed on a regular basis. As far as designing for ESD in ungrounded products, I think you'll be forced to make provisions somehow with say braiding to ground anyway. One of the requirements in 1950 is to ground any exposed metal parts accessible to the end user. Not sure if this applies to your product, but something to that I think should be considered. If you're using a plastic housing with conductive coating, that coating won't be enough since it's not a reliable for grounding and is not accepted as a means of grounding by safety. - Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: ESD Design, non-earthed products
Alex, I have written an article for Printed Circuit Design magazine on Designing Electronic Equipment for ESD Immunity. Part 1 appeared on pages 18-26 of the July 2001 issue (volume 18 number 7), and Part 2 will be in the August issue. Printers and copiers can be quite nasty generators of ESD, with the moving paper acting like the belt of a Van de Graaf generator to generate voltages of thousands of volts. One defense is to use tinsel or static-discharger brushes to bleed charge off the paper (rule L4 in my article) as it leaves the printhead area. Dogpile ( http://www.dogpile.com ) searches for antistatic +tinsel, static +tinsel, static +brush*, and antistatic +brush* gave these hits, for example: * http://www.westmontinc.com/price.htm * http://www.fraser-antistatic.co.uk/products.htm * http://www.takk.com/takktins.htm * http://kinetronics.com/ * http://www.stopstatic.com/printer.html * http://www.chapman-static.com/oemtinsel.html * http://www.amstat.com/html/passive.html Another technique is to make plastic parts in the paper path of antistatic materials, and make sure that every shaft has a grounding contact (usually on one end of the shaft) to bleed off charge (rule L3). An alternative to the grounding contact is to use conductive grease in the bearings (rule L5). Establishing a chassis ground for any ungrounded device is difficult. About the best you can do is choose a large piece of metal close to the switches/operating controls, and tie circuit common, shields, and grounding wires from the mechanism to it (rule B14). John Barnes Advisory Engineer Lexmark International --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
