Indirect discharge – discharging to a horizontal or vertical test planes. I got that
Air and contact are confusing me just a little because the technical rational for the use of the contact discharge method in A.6 of 61000-4-2 A1:1998 and A2:2000 Alludes to the fact that it is used because problems such as the speed of approach influenced the ESD test and was at least partially responsible for non-repeatability. But I notice that with my ESD gun if I use the round tip and do an air discharge I get a visible arc at about 6kV, between the tip and some switch contact points inside the ESD (through an air gap in the housing). If I put the gun to the surface with it set for contact discharge I get an indication of a discharge – but nothing that can be seen as with the air discharge. In fact if I just aim it at the center of the room the contact discharge occurs according to the test gun. So I presume that there must be an internal spark gap inside the gun which is allowing the discharge. But the air discharge goes from gun to circuit, the direct discharge goes through an internal air gap. These are different phenomena – essentially current flow versus electromagnetic field flow. The standard (paragraph 5) says that contact discharge is the preferred method, but it also says contact discharges to the conductive surfaces and to the coupling planes, and air discharge at insulating surfaces. (paragraph 7) I think I’m wrapping myself around the axle with over thinking this. So I presume with a plastics (insulating surfaces) enclosure I must use the air discharge test on the EUT, even though direct is preferred, and regardless of what A.6 says about the rationale of the direct discharge helping reproducibility - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ 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]>
