My apologies to the group. I see what Ed is driving at. I should have specified "Direct Air Discharge" as opposed to just "Air Discharge". I assumed that everyone would assume the "Direct" part. It would have saved Ed, and possibly others, some confusion. IEC 1000-4-2 takes great pains to describe at least four different types of discharges, it takes the full definition in order to tell one from the other.
> -----Original Message----- > From: Price, Ed [SMTP:ed.pr...@cubic.com] > Sent: Tuesday, April 24, 2001 10:04 AM > To: 'Gary McInturff'; 'Chris Maxwell'; 'EMC-PSTC Internet Forum' > Subject: RE: ESD generators max Contact discharge level > > Chris: > > Sorry, my ignorance is showing! I was assuming that an "air discharge" was > just that; i.e., a test electrode to test electrode discharge in air some > specific distance from the EUT. From your elaboration, I now see that > "contact discharge" is a deliberate conductive connection before > application > of the discharge. And an "air discharge" is actually a "touching" > discharge > to some surface, like paint or the non-conductive membrane over a keypad, > which may then penetrate the dielectric and discharge onto the conductive > paths below. > > Gary; don't forget that many industrial processes create ESD events, from > chip handlers to conveyor belts to fuel transferring. > > Regards, > > Ed > > Ed Price > ed.pr...@cubic.com > Electromagnetic Compatibility Lab > Cubic Defense Systems > San Diego, CA USA > 858-505-2780 (Voice) > 858-505-1583 (Fax) > Military & Avionics EMC Services Is Our Specialty > Shake-Bake-Shock - Metrology - Reliability Analysis > > > > >-----Original Message----- > >From: Gary McInturff [mailto:gary.mcintu...@worldwidepackets.com] > >Sent: Monday, April 23, 2001 3:39 PM > >To: 'Chris Maxwell'; 'EMC-PSTC Internet Forum' > >Subject: RE: ESD generators max Contact discharge level > > > > > > > >Hi Chris, > > I agree with your whole heartedly. If it weren't for > >people there > >wouldn't be an ESD problem. We are wither walking around > >charging others > >stuff like furniture or worse yet we charge ourselves and the go around > >touching stuff. For the most part I know of nobody that is > >able to hold a > >charge until they contact a surface and then dump it to ground > >at will. Even > >though somewhat less repeatable I think the test should > >attempt to model the > >discharge mode - Through air as people approach the equipment. > > I also have a hunch, and I have no data nor have I studied real > >hard, but I believe that if the guns are designed be more and > >more alike, a > >great deal of the variability goes out of the test. The test > >operator comes > >next, but they can be trained for reasonable repeatability when the are > >taught some of the issues. > > Even some of that gets leveled out if the test is run > >carefully and > >uses multiple test levels, say every 2k or even at 1K increments. > > Gary > > > >-----Original Message----- > >From: Chris Maxwell [mailto:chris.maxw...@gnnettest.com] > >Sent: Monday, April 23, 2001 11:36 AM > >To: 'EMC-PSTC Internet Forum' > >Subject: FW: ESD generators max Contact discharge level > > > > > > > >> Hi Ed, > >> > >> I fully agree that membrane keypads are one of the most common places > >> where a finger could discharge to the instrument. > >> > >> However, I disagree that contact discharge is the > >appropriate test method > >> for these surfaces. Current state of the art in test instruments and > >> methods dictates air discharge testing of such surfaces. Just for > >> clarity's sake, when I say air discharge testing, I mean > >approaching the > >> device under test with a blunt, charged ESD gun tip. If the > >device under > >> test has a weak insulator, an air discharge will occur. > >> > >> The IEC standards use contact discharge testing as the > >"preferred" method > >> because it is more repeatable than air discharge testing. The IEC > >> standards recognize air discharge testing on surfaces that > >won't allow a > >> contact discharge. > >> > >> I could write a book explaining why air discharge testing is > >the closest > >> simulation to real life (unless you're in a vacuum) and > >another book about > >> why contact discharge is used as a repeatable model for air > >discharges > >> but I'll spare everyone the details. I could explain more > >fully if anyone > >> is interested. > >> > >> The manual for my ESD gun (Keytek MiniZap, which is a > >compliance grade > >> instrument) recommends against contact discharges to > >insulated surfaces as > >> it has the potential to damage the high voltage relay in the > >product. I > >> can't speak for other guns. > >> . > >> For insulated membrane switches, the IEC standards and the > >equipment that > >> I have dictates that I use air discharge testing. > >> > >> Until a better test method comes along, I stand by my > >original answer to > >> Dan's question. > >> > >> Best regards, > >> > >> Chris > >> > >> P.S. Being forever curious, If anyone knows of an ESD > >simulator or test > >> method that does perform contact discharges to insulated > >surfaces, I'd > >> love to hear about it. I'm sure that it would be of > >interest to the group > >> as well. > >> > >> > >> ************************ Ed's email attached > >***************************** > >> > >> > >> Chris: > >> > >> I don't understand why a membrane switchpad would not be tested for > >> contact > >> discharge. It think that this is the absolutely most likely > >place where a > >> finger, attached to a charged human body, might be applied > >to the EUT. It > >> seems to me that you would want to be testing the dielectric > >strength of > >> the > >> insulation over the keypad conductive traces. > >> > >> The issue of whether a triggering of the testing gun, > >without a completed > >> discharge current, would damage the gun, isn't relevant to > >the need for > >> the > >> test. Dumping 15 or 20 kV to a probe tip, while not exactly > >trivial, still > >> shouldn't be critically sensitive to load conditions. > >> > >> Regards, > >> > >> Ed > >> > >> > > ------------------------------------------- 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 Heald davehe...@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,"
