In message <[email protected]>, dated Fri, 2 Feb 2007, Doug Smith <[email protected]> writes >For the February Technical Tidbit, I discuss a technique that has been >used in protection of telephone systems for many years, and has many >potential uses in other settings, Coupled Bonding Conductors (CBS).
This technique is strongly advocated by some, but not all, audio engineers for professional sound installations, as a better technique than interrupting the shielding of a cable to eliminate a large low-frequency current flowing in a ground loop. The interruption (at the receiving end of the cable for preference) is bridged by a low-inductance capacitor to preserve shielding for high-frequency signals. This technique is also used for cables for the DMX data system for controlling theatrical luminaires. You wrote in the article: I am not aware of any problems caused by mains current flowing in coupled bonding conductors. The magnetic field created can cause serious interference with audio-frequency induction-loop systems for assisted hearing in theatres and cinemas. While the fundamental frequency is not very audible, the current is usually rich in harmonics, especially odd-order, up to 1 kHz and even beyond in some cases. Variable-speed drives, used for scenery-handling equipment, can produce high-frequency ground currents, unrelated to the mains frequency (so-called 'interharmonics'). -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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 email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
