Hi Glyn, Here is one way to approach 30kV. First, slide out of your car seat, the Ford Taurus is great for this effect. This puts a charge on your behind. As you get out of the car (everything is plastic so you remain charged with respect to the car) your voltage rises because Q=CV. Q stays the same (charge on your behind) but since C to the car goes down, voltage goes up. Then you go to close the metal door and a huge spark jumps between your hand and the door. Usually this results in jumping into the air muttering a few four letter words sometimes ending in (I am sure this happens with other cars, I just happen to own Fords, which I like) "F O R D".
I wonder why the car companies don't make seat material out of anti-static material.... BTW, contact discharge has the same risetime at all reasonable voltages, as opposed to air discharges, but still some equipment will fail at a low voltage and pass at high voltages. I can imagine a few ways circuits might do this. The effect is more pronunced with air discharge because of the risetime dependence on voltage (really arc length and whatever effects that, including speed of approach). Doug "Glyn Garside(TUV)" wrote: > > >>On the other hand very low voltage (and energy) events, such as jingling > >>change have very high di/dt because of the tens of ps risetimes that > >>occur at low voltage. > > I think this is why, as I recall, some (maybe all?) IEC standards require > you to test not only to the ESD level indicated, but also the lower levels > too. For example, if you are required to test at level 4, you are also > required test at levels 3, 2 and 1. This is counter-intuitive -- "Surely > the highest voltage is the worst case?" -- but apparently grounded in good > physics, which Doug explains better than I would. > > PS: As to testing at higher levels than typical IEC values, I have read > that the human body can, rarely, gain a charge of up to about 30kV(??), in > conditions of low RH. Others may have better insight into this. Also, some > manufacturers may want to build some "margin" into their test results: if > five samples pass at 8kV, how sure can you be that the next 995 production > units would also pass? > > PPS: I have a question of my own, drifting off topic slightly: if the > relative humidity was fairly high when you passed the ESD test, and you > retest (esp. air discharge?, or indirect discharge?) some months later when > humidity is lower, could the same EUT now fail? (I think the answer is, > yes?) > > Best Regards, Glyn > > Glyn R. Garside (mailto:ggars...@us.tuv.com) > Senior Engineer, Industrial Machinery Division > TUV Rheinland of North America, Inc. (Chicago Office) > 1945 Techny Rd, Unit 4, NORTHBROOK, IL 60062-5357, USA > http://www.us.tuv.com > > ------------------------------------------- > 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," -- ------------------------------------------------------- ___ _ Doug Smith \ / ) P.O. Box 1457 ========= Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-----( ) | o | Email: d...@dsmith.org \ _ / ] \ _ / Website: http://www.dsmith.org ------------------------------------------------------- ------------------------------------------- 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,"
