I remember I had to use 50121-4 once and I wondered the same thing. It would be natural to expect something connected to ground to be tested without any limiting resistor. But since the specific standard gives the final word on this the 40 ohm coupling resistor is the way to go. Regarding the 61000-4-5, note that in new version Clause 7.6.1 specifies that the cable grounded at one end only shall placed on ground plane with 10 cm separation, so this way the capacitance to ground is set by the setup. The old 4-5 did not care much about ground planes, maybe that was the reason why the old version had that capacitor. But that is history now... Regards, Ari Honkala Nokia Siemens Networks Finland
_____ From: [email protected] [mailto:[email protected]] On Behalf Of ext [email protected] Sent: 17. joulukuuta 2007 18:56 To: [email protected] Subject: EN50121-4: surges on shielded lines Dear list members, I'm writing the EMC test spec. for a wayside railway equipment, reference standard is EN50121-4. I've got an interpretation problem on the surge test on I/O shielded cables: it's a balanced RS-485 like communication line, the shield is connected only at the EUT side. Cable lenght may sometimes exceed 30m. EN50121-4 Table 3 (note 3) recommends a generator source impedence of 42 Ohm, both for line-to-line and line-to-gnd test and with no specific reference to shielded lines. But if I look at the test setup according IEC 61000-4-5 par. 7.6 (fig. 17), it requires a generator source impedence of 2 Ohm. Am I right supposing that the specific EN50121-4 standard has anyway priority over the 61000-4-5 and I have to use 42 Ohm ? Moreover, previous version of IEC 61000-4-5 suggested (in the above quoted fig.17) to add a 10nF termination capacitor between shield open end and gnd to simulate cable capacitance, why has it been removed ? Thanks in advance for your precious time Best Regards Francesco Campedelli Product Engineering - HW Design ALSTOM Ferroviaria s.p.a. E-mail: [email protected] :.________________ CONFIDENZIALE: Questo messaggio e gli eventuali allegati sono confidenziali e riservati. Se vi è stato recapitato per errore e non siete fra i destinatari elencati, siete pregati di darne immediatamente avviso al mittente. Le informazioni contenute non devono essere mostrate ad altri, né utilizzate, memorizzate o copiate in qualsiasi forma. CONFIDENTIALITY : This e-mail and any attachments are confidential and may be privileged. If you are not a named recipient, please notify the sender immediately and do not disclose the contents to another person, use it for any purpose or store or copy the information in any medium. - ---------------------------------------------------------------- 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 - ---------------------------------------------------------------- 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
