In message <1005820019.761571237930343770.javamail.r...@sz0149a.emeryville.ca.mail.c omcast.net>, [email protected] writes >I am asking strictly from the safety/regulatory hard requirement point >of view, not trying to discuss which would be better for EMC. Is there >an simple answer? Did I miss any key info or question?
Yes, you missed the question of what is better for the system's basic functioning. If you ground the cable shield at both ends, there WILL be a noisy current in the screen, and because it's not a superconductor, there WILL be a voltage drop along it. This is inextricably mixed up with the video signal, that also flows along the shield, so your pictures will be degraded. If you can, run twin shielded cable and keep the 'cold' video to one inner conductor, not the shield. If you can't do that, open-circuit the shield at the central unit (receiving end) and connect a very low inductance capacitor across the gap. A 10 nF SMD cap is ideal, of the highest voltage rating you can get. Put across it a surge-limiter or gas spark gap of 3 kV rating. This is likely to work. It can be criticized, but then most things in practical engineering can be criticized. Another way is to bond the ground points at the two ends of the cable with a MUCH thicker cable, so that most of the noise current flows down the bonding cable, but this may be a costly solution, and some might see a code violation implied. -- This is my travelling signature, adding no superfluous mass. John M Woodgate - 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://www.ieeecommunities.org/emc-pstc 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]>
