Ghery, Pages 162-168 of Cobine, James Dillon, Gaseous Conductors: Theory and Engineering Applications. New York: McGraw-Hill, 1941. discuss "The Sparking Potential" and Paschen's Law. For a uniform electric field, Sparking Potential is a function only of pd, where d is the gap length and d is the pressure. (On page 163 Cobine says that we really should use gas density instead of pressure, and page 165 has a table of minimum sparking constants for various gases.)
Thus at higher altitudes, or lower pressure (lower gas density)-- for a given air-discharge electrostatic discharge (ESD) test setup-- in theory we might expect the distance at which an arc starts would be slightly longer than for an identical test (holding umpty-ump other variables constant) performed at low altitude/high pressure. But I have well over 1550 documents on ESD in my library (see http://www.dbicorporation.com/esd-anno.htm ) and I don't recall *any* of them talking about effects of atmospheric pressure on ESD testing. My gut feeling is that even between Denver, Colorado and sea level, atmospheric-pressure's effect on a product's susceptibility to ESD has *at most* a couple percent of the effects of numerous other factors: * What the product happens to be doing during when the arc starts. * Tolerances between production units. * The "pointiness" of the product at the point that we hit. * The speed of approach of the ESD tip to the product. * The angle at which we approach the surface of the product. * Uncontrolled characteristics of the ESD gun. * The position/velocity of the ground strap of the ESD gun with respect to the product when the arc starts. * Etc., etc., etc. John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, SM IEEE dBi Corporation http://www.dbicorporation.com/ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
