Barry, Your question is very much justified. I use the word "ESD" because in my mind, I play the image of the striking screw driver in slow motion. If you imagine the nickel surface robs the screw driver of its electrons to charge up the screw driver, then the electric field builds up as the screw driver moves away from the nickel surface to the point to cause air break down and screw driver discharge. In slow motion, this is exactly the ESD process. But in real-time, this is RF. Different perspective makes worlds of differences. :)
Thanks, George Tang (Bailin Ma) wrote: > George, > > I think your reasoning is convincing to me. Thanks. > But please allow me to pose a silly question: Are we really sure those > kinds of "shaking coins" interferences can be categorized as ESD > (Electrostatic Discharge) problem? > In your experience, for instance, the screw driver did not carry any > electrostatic charge before striking the nickel surface. Right? We don't > know if coins, keys, and metal door got electrostatic charged before > jangling or slamming in Doug Mckean's experiences, either. > ASSUMING friction and striking between different materials would cause fast > electron transition between materials, back and forth, and then produce > strong RF EM waves, there is no Electrostatics involved. > If we are not sure whether or not those objects were electrostatic charged > before friction, can we try to see if it makes difference? > > Best Regards, > Barry Ma > > > ------------- > Original Text > From: "George Tang" <gt...@convergenet.com>, on 3/15/99 4:25 PM: > Barry, > > No, I did not measure the 15kv on the scope, but I suspect that was the > case. > Here is my reasoning: The system was well shielded with aperture size > smaller > than 1/2 inch with few apertures. The system passed FCC B emi limits with > 8 dB > margin. It seemed very unlikely for a power plane in such a system to pick > up > 8 volts of radiated noise, since large power planes are not efficient > antennas. And to charge the power and ground planes with many caps up to 8 > volts at 100 MHz fundamental and GHz harmonics would seem to require very > high > power of radiated energy, assuming the lumped circuit model is used for the > caps and planes at 100 MHz. But on the other hand, the boards are grounded > to > the chassis, so if the chassis had ESD noise of many kv conducted to it, > it > could generate 8 volts on the power to ground plane. The chassis is low > impedance, so high current noise is likely. With radiated noise, even at > near > field, the propagation impedance would still be higher than conducted, so > high > current noise seemed more unlikely. The system had already passed 15kv ESD > air > (and accidental contact discharge) on most all parts on the chassis, then > the > screw driver noise maybe higher than 15 kv conducted ESD. You can see > there > are many assumptions used. But trying to measure the screw driver to > chassis > ESD voltages directly with differential probes is difficult because a large > current loop formed by the probes is required due to the moving parts and > the > probes may be damaged by the ESD. I did not measure the screw driver > voltage, > but I guessed that it was high voltage/current conducted ESD that caused > the > system error. > > Hope that helps. > > George Tang > > (Bailin Ma) wrote: > > > George, > > > > You mentioned: "the ESD generated by the metal surface was much higher > than > > 15kv." at the end of your note. > > Does that mean you measured the noise between power and ground planes > using > > digital scope, and got the higher than 15 KV reading on the scope when > > striking a screw driver against the nickel plated surface? > > > > Thank you. > > Barry Ma > > Anritsu Company > > Morgan Hill, CA 95037 > > > > ------------- > > Original Text > > From: "George Tang" <gt...@convergenet.com>, on 3/15/99 1:23 PM: > > Douglas, > > > > I have seen similar events in a different way. Years ago, I helped > design > > an electronic system using plastic chassis with nickel surface plating. > > The > > system passed 15kv ESD air discharge and 8kv contact. But in the > hardware > > lab, the system gets data error everytime a piece of metal (like a screw > > driver) is striked against the nickel plated surface on chassis. A > digital > > scope is used to measure the noise generated on power and ground planes > on > > the PCB inside the chassis and the scope captured a noise voltage as high > > as > > 8 volts peak to peak on the PCB from a few hundred MHz to beyond GHz. > The > > PCB was very well decoupled with power next to ground planes and many on > > board capacitors. This puzzled me at first. But I remembered a very > > knowledgeable mechanical engineer once told me to never use nickel > material > > in an application where friction takes place. Nickel has a very hard and > > rough surface, so in a frictional application, it always damages the > mating > > surface. Maybe this explains the events that you saw, and the ESD > > generated > > by the metal surface was much higher than 15kv. > > > > Regards, > > > > George Tang > > > > Douglas McKean wrote: > > > > > Hans, > > > > > > That's certainly an interesting explanation, but does > > > not correlate to at least three different scenarios. > > > > > > 1) A calibrated ESD simulator in self discharge > > > mode at 15KV. When the results of the ESD > > > simulator are compared to the results of the > > > coins, the coins have a fairly wideband constant > > > level from 0 - 2 GHz. Both start off at roughly > > > the same level with the only the coins remaining > > > constant throughout. The ESD simulator has approx > > > a -20dB per octave drop off. > > > > > > A side interest is that on the display of the SA has > > > an IF overload indication. This tells me that the > > > transients from the coins are quite possibly a lot > > > higher and much quicker than what the SA can handle > > > within the sampling window. > > > > > > 2) The level from the coins is proportional to the > > > dissimilarity of the metals of the coins. A bag of > > > quarters has a lower profile than a bag of quarters > > > and pennies. Thus, there is some function due to > > > electronegativity differentials. Actually, a > > > significant amount of difference. > > > > > > 3) I can cause the same effect by sliding the coins > > > back and forth as a group within the bag. Thus, > > > the coins are in at least incidental contact with > > > each other so that differing potentials amongst > > > the coins is minor. > > > > > > I'm not sure if anyone knows the reason. > > > > > > Regards, Doug McKean > > > > > > At 11:11 AM 3/11/99 -0800, Hans Mellberg wrote: > > > > > > > > > > > >There is an expanation for this seemingly unlikely event. > > > > > > > >Having coins in a baggie and jingeling them causes the following > > > >events to occur: > > > > > > > >The rubbing of a coin against the polymer causes triboelectric > > > >charging of both the coin and localized areas of the bag. Since there > > > >are multiple coins, each coin will charge at some voltage level but > > > >not necessarily the same as another coin. When two coins of different > > > >charged voltages come within dielectric breakdown distances, a > > > >discharge will occur from one coin to the other in order to equalize > > > >the charge distribution (q1=C1V1 and q2=C2V2. When they touch, the new > > > >q1 will be C1V3 and q2= C2V3 where V3=(q1+q2)/(C1+C2)). Since coins > > > >are electrically small with very small capacitances, the expected > > > >discharge waveform has a very fast risetime hence the radiation at the > > > >GHz region. There will also be discharges from the localized charged > > > >areas of the polymer to coins of different voltages. While separating > > > >two charged surfaces from each other, the voltage rises significantly > > > >since the capacitance is being reduced and the conservation of charge > > > >must be preserved which is the basis for tribolectric voltage > > > >generation. > > > >Hope that helps > > > >Hans Mellberg > > > > > > > > > > > >---b...@namg.us.anritsu.com wrote: > > > >> > > > >> Hi Douglas, > > > >> > > > >> What you described is very interesting! But I cannot understand > > > >"Jingling > > > >> change in a ziplock bag produces very high levels of super fast > > > >transients > > > >> up into the GHz range." It seems to me that jingling coins, jangling > > > >keys, > > > >> and slamming metal door would certainly produce acoustic waves. How > > > >come > > > >> they also produced electromagnetic waves? If do, under what > > > >conditions? > > > >> What is the mechanism to produce "very high level" of transient EM > > > >waves? > > > >> Did that company incorporate those kinds of "Jingling change in a > > > >ziplock > > > >> bag" tests into regular ESD tests for their thereafter products? > > > >What is > > > >> the lessen we all should learn from this particular example? > > > >> > > > >> Hopefully you don't think it's offensive to ask above questions. I > > > >am just > > > >> very curious. > > > >> > > > >> Thank you. > > > >> Best Regards, > > > >> Barry Ma > > > >> (408)778-2000 x 4465 > > > >> > > > >> ------------- > > > >> Original Text > > > >> From: "Douglas McKean" <dmck...@corp.auspex.com>, on 3/10/99 2:55 > PM: > > > >> At 08:03 AM 3/8/99 PST, Bailin Ma wrote: > > > >> >Hi Group, > > > >> > > > > >> >We have already seen awards for the most misleading ads, worst > > > >attire, > > > >> >worst films, ..... > > > >> >Why not awards for worst EMC and PS qualities? > > > >> > > > > >> >Barry Ma > > > >> >Morgan Hill, CA 95037 > > > >> > > > >> > > > >> Long ago in another company, I was completing the testing > > > >> for a large rack mounted device, i.e. emissions, immunity, > > > >> safety, some parts of Bellcore. We got a call from one > > > >> of our customers complaining about how sensitive our equipment > > > >> was and how susceptible it was to ESD events during their own > > > >> testing of our equipment. This was deemed unacceptable by them. > > > >> This decision of theirs jeopardized a sale of several million > > > >> dollars. The finger was duly pointed by everyone right to yours > > > >> truly. My head was literally in no uncertain terms put on the block. > > > >> > > > >> I contested producing repeatable and acceptable ESD test results > > > >> that were BELOW the BER levels specified by Bellcore with ESD test > > > >> levels ABOVE that specified by the test standard. I wanted as much > > > >> margin as possible for our product. > > > >> > > > >> Well, it ended up that if you stood three to four feet in front of > > > >> the rack and jingled change in your pocket or jangled a set of keys > > > >> in front of it, the product would RESET. Jingling change in a > > > >ziplock > > > >> bag produces very high levels of super fast transients up into the > > > >GHz > > > >> range. Worse, slamming the metal door to the lab in which the > > > >equipment > > > >> was setup would also reset the product. The lab door was say 20 or > > > >so > > > >> feet from our equipment under test. It took six months of a > redesign > > > >> cycle to straighten out that one, but it was finally done. > > > >> > > > >> I always wanted to find out who in God's name could have come > > > >> up with such an insidious ESD test by simply putting some change > > > >> in a zip lock bag and jingling it in front of equipment. > > > >> But, I figured "he", whoever he was, was lost in time. > > > >> > > > >> And wouldn't you know it? ... > > > >> > > > >> I now work for that man. > > > >> > > > >> > > > >> --------- > > > >> This message is coming from the emc-pstc discussion list. > > > >> To cancel your subscription, send mail to majord...@ieee.org > > > >> with the single line: "unsubscribe emc-pstc" (without the > > > >> quotes). For help, send mail to ed.pr...@cubic.com, > > > >> j...@gwmail.monarch.com, ri...@sdd.hp.com, or > > > >> roger.volgst...@compaq.com (the list administrators). > > > >> > > > >> > > > >> > > > >> --------- > > > >> This message is coming from the emc-pstc discussion list. > > > >> To cancel your subscription, send mail to majord...@ieee.org > > > >> with the single line: "unsubscribe emc-pstc" (without the > > > >> quotes). For help, send mail to ed.pr...@cubic.com, > > > >> j...@gwmail.monarch.com, ri...@sdd.hp.com, or > > > >> roger.volgst...@compaq.com (the list administrators). > > > >> > > > >> > > > > > > > >_________________________________________________________ > > > >DO YOU YAHOO!? > > > >Get your free @yahoo.com address at http://mail.yahoo.com > > > > > > > > > > > >--------- > > > >This message is coming from the emc-pstc discussion list. > > > >To cancel your subscription, send mail to majord...@ieee.org > > > >with the single line: "unsubscribe emc-pstc" (without the > > > >quotes). For help, send mail to ed.pr...@cubic.com, > > > >j...@gwmail.monarch.com, ri...@sdd.hp.com, or > > > >roger.volgst...@compaq.com (the list administrators). > > > > > > > > > > > > > > > > > > --------- > > > This message is coming from the emc-pstc discussion list. > > > To cancel your subscription, send mail to majord...@ieee.org > > > with the single line: "unsubscribe emc-pstc" (without the > > > quotes). For help, send mail to ed.pr...@cubic.com, > > > j...@gwmail.monarch.com, ri...@sdd.hp.com, or > > > roger.volgst...@compaq.com (the list administrators). > > > > --------- > > This message is coming from the emc-pstc discussion list. > > To cancel your subscription, send mail to majord...@ieee.org > > with the single line: "unsubscribe emc-pstc" (without the > > quotes). For help, send mail to ed.pr...@cubic.com, > > j...@gwmail.monarch.com, ri...@sdd.hp.com, or > > roger.volgst...@compaq.com (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
