Humidity is not the only variable, and may not be your major variable. Repeatability of ESD results is a statistical problem. Consider the variables: -humidity -approach speed (for non-contact discharge) -angle of the probe (for non-contact discharge) -synchronization of the ESD application with the various logic states of the EUT -rise time and peak di/dt variance as applied ESD voltage is changed -variance between ESD guns
And I am sure there are more variables. The only way one can really determine a product's real ESD immunity is to apply thousands of hits at different voltage levels and apply a statistical evaluation. In the end, one can only say that the equipment is immune to X volts with Y confidence. Good luck, Richard Woods Sensormatic Electronics Tyco International -----Original Message----- From: Gibling, Vic [mailto:[email protected]] Sent: Wednesday, June 12, 2002 3:26 AM To: [email protected] Subject: An ESD question Dear Group I tried to find David Pommerenke article's in the Journal of ESD on the Web but alas no downloadable version was found, so may I ask the group a question? We have an ESD field failure which is occurring in dry hot countries ( no surprise )which can be recreated with an ESD of -800V. In an attempt to get a high incidence of discharges we used a dehumidifier to create a dry environment. The result was a reduction in discharges. Thinking the problem through -now- as a dry atmosphere will encourage the production of high level ESD and a humid environment inhibits the charge to a lesser level, presumably because it 'leaks' away. Then is it wrong for us to attempt to 'dry' the local atmosphere in the hope of gaining consistent ESD from an ESD gun, that is to say the more humid the environment the more efficiently the discharge will transfer to the victim? Incidentally, to add to the thread regarding intermediate level testing for ESD and EFT. This exercise has revealed different failure mechanisms at different ESD levels. Your views would be appreciated. Vic Gibling Compliance Engineer Marconi Applied Technologies ------------------------------------------- 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
