All, I do not recommend that you use heavy filtering at the chamber egress wall to control emissions for a couple of reasons:
1) In good faith, you need to duplicate the actual *system* cabling and loading of the end-target platform equipment or user. With filtered connectors installed at the chamber egress wall, you certainly have isolated the exercise equipment emissions away from the Equipment-Under-Test) EUT, but that is not real world. While you may pass test limit line requirements, when the product is used in the final application it may either radiate or be susceptible. While you can always say you met the specification, it isn't worth losing a customer or degrading your reputation. 2) Filter Connectors can (depending on type and values), present a very low impedance at the chamber egress wall. This is undoubtedly NOT the end of the cable (cabling connected to exercise equipment in the Ante Room). This may cause unforeseen reflections on cables and shields creating worse emissions or degraded susceptibility (alternate return paths) during testing. One way to solve your problem is to specify shielded (overbraided) cabling if you have the ability to. This would have to be something agreed upon between you and your customer. Be careful of product safety concerns in some countries with ungrounded power cabling. The real way to solve the problem is to fix the common mode noise on the cable by source suppression. Sometimes a painful solution but often the best in the long run. This is painful if you are out of schedule (many do EMC testing at the end of their development schedule), working with a difficult OEM device, or cost is an issue. If you can't source suppress it, you're back to containing it with the shielded cabling. Be careful about cable shield pigtails or ferrules and wires. You will almost always have better success with 360 degree overbraid shielding to EMI backshells. Philip Ross Wellington Mgr. Signal Integrity & EMI L-3 Communications CSW From: Cortland Richmond [mailto:72146....@compuserve.com] Sent: Wednesday, February 19, 2003 1:25 PM To: neve...@attbi.com; ieee pstc list Subject: Re: RE02 cabling problem I was looking over Dries' post again and note that I overlooked something important: He says that short shield goes on the *wall plate* -- which I presume to be the shielded room wall. This doesn't change my recommendation he test with unshielded wires. But it serves as a reminder that support equipment must be protected from immunity stresses of its own. I hope there are filters between the support equipment outside, and signal lines from the chamber. Cortland 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
