Barry:
I'll mostly duck the lightning question, although I think that charge may flow in either direction. Since there are cloud-to-cloud discharges, that means some mechanism must be available to create an excess of electrons in one cloud and a deficit of electrons in another. So any given cloud may be at a different potential from other clouds, and the Earth's surface too. Regarding the ESD event. I used to wonder why we needed to use two polarities? It seems like there should be a symmetry in that the current flow is identical regardless of which way the electrons are moving. But the ESD event affects more than the point of discharge; the currents must flow through the EUT until the charges are equalized (discharged). And as the currents flow, they create voltages across devices which may be polarity sensitive. Now that brings up the question of whether (in real life) objects become positively or negatively charged. Does walking across a floor, blowing air across a surface, separating two sheets of plastic or scratching your ear always induce one polarity of charge? Regards, Ed :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) Ed Price [email protected] 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: Barry Ma [mailto:[email protected]] > Sent: Wednesday, October 04, 2000 2:58 PM > To: [email protected] > Subject: Re: ESD Opportunities > > > > Please allow me to ask a relevant question only for curiosity. > > We have no idea of what charge (positive or negative) would > go to the DUT in ordinary ESD. > That's why we have to test two polarities in ESD immunity test. > > Lightning is a kind of ESD happened between a charged cloud > and objects on earth surface. Some figures imply that an > electron current flows from the charged cloud to the earth. > Is it possible to have an opposite direction - electron flows > from earth to cloud? > > Thanks. > Barry Ma ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
