Hello Amund, My guess is that the 20 extra meters of cable allows coupling to be developed between the shield and the conductors contained within. If you do not isolate the one device from the rest of the devices in the loop, is it likely that you are shorting the surge signal to chassis (path of least resistance) without developing the signals on the internal conductors thereby not developing the prescribed signal to the intended device? The set-up figures in the surge standard provide guidance in this regard.
Best regards, Don Umbdenstock Sensormatic Electronics Corp Tyco International > ---------- > From: [email protected][SMTP:[email protected]] > Reply To: [email protected] > Sent: Wednesday, March 20, 2002 4:58 AM > To: [email protected] > Subject: Surge test on a loop > > > Hi all, > > Assume a fire alarm detection system. 10 smoke detectors are connected in > series on a loop and both ends of the loop is connected to the fire alarm > panel. Shielded cable is used and the shield is connected through the > whole > loop. > > So, how do we carry out the surge test on the loop? The alarm panel and > the > detectors are all EUTs. > > As far as I understand IEC61000-4-5:1995 chapter 7.5, I will insert an > extra > 20 meter shielded cable between each detectors and then I will drive the > surge pulse onto the shield in order to test one of the detectors. Then I > move the extra 20m cable to the next detector and surge test it. > > If this is correct, why can't we just put the surge pulse onto the > shielded > loop and assume that the whole loop was tested at once? > > Best regards > Amund Westin, Oslo/Norway > > > > > ------------------------------------------- > 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"
