RE: Ethernet emission - isolated metallic plate
What is the frequency at which the emissions are maximum? And how long is the cable? Dave Cuthbert Linear Technology NARTE Certified EMC Engineer From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Barker, Neil Sent: Tuesday, March 20, 2007 1:51 AM To: 'kbalasubraman...@scmmicro.co.in'; emc-p...@ieee.org Subject: RE: Ethernet emission - isolated metallic plate I am interested in your posting because I am in the middle of my first experience with Ethernet as well, so could very well be interested in your solution. However, I do not think that the effect of the isolated piece of metal is a mystery. Consider what is happening here; your cable is coupling into the plate, both inductively and capacitively, and different potentials will be established at different parts of the plate resulting in currents flowing within the plate. The energy that is circulating in this manner will be absorbed in the plate. I don't expect that it is significant enough to measure the temperature rise in the plate, but that is where it will finally end up. If you had access to one of those scanning measurement tables that are sometimes used for assessing printed wiring board emissions, you could probably plot the currents in the plate. This is similar to the way that a metal box will act as a shield without being grounded; absorption into the metal is retained within the metal by virtue of the impedance mismatch at the surfaces causing reflection within the metal rather than radiated emission from the surface. Best regards Neil R. Barker CEng MIET FSEE MIEEE Manager Quality Engineering e2v technologies (uk) ltd 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK Tel: (+44) 1245 453616 Fax: (+44) 1245 453571 Mob: (+44) 7801 723735 P Please consider the environment before printing this email. From: kbalasubraman...@scmmicro.co.in [mailto:kbalasubraman...@scmmicro.co.in] Sent: 20 March 2007 04:40 To: emc-p...@ieee.org Subject: Ethernet emission - isolated metallic plate Dear Experts, The emission from our ethernet device :- 1. Without the ethernet cable connected to our device the emission is well below the limit line. 2. With the ethernet cable just plugged into our device ethernet port (other end of the cable is left unconnected) emission is above the limits. 3. With the one end of the ethernet cable connected to our device and the other end connected to the laptop computer and 'ping' is continuously active the emission slightly increases. 4. Emission with UTP cable is higher than emission with STP cable. Most interestingly when we place a metallic plate (an MS plate of about 6 inches wide and 2 foot long) on the test table and the ethernet cable is placed on this metal plate, the emission got reduced drastically and now it is well within the limits. The metal plate is not having any connection with ground plane, it is just kept on the wooden test table. How this isolated metal piece is reducing the emission is really a mystery. Sincerely K.Balasubramanian Project Leader - Hardware. Sent by E2V TECHNOLOGIES PLC or a member of the E2V group of companies. A company registered in England and Wales. Company number: 04439718. Registered address: 106 Waterhouse Lane, Chelmsford, Essex, CM1 2QU, 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 emc-p...@ieee.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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald:emc-p...@daveheald.com 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 emc-p...@ieee.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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald:emc-p...@daveheald.com 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 __
RE: Ethernet emission - isolated metallic plate
Mr. Balasubramanian, Is it 10BaseT or 100BaseTX? Which emissions test is it failing? Radiated? I/O conducted? Ethernet TP is a 100-ohm transmission line. For a valid emissions test, each end of the cable should be terminated at 100 ohms per ANSI/IEEE 802.3n (ISO 8802). Cables radiate if unterminated (there is no transmission line without the termination). Obviously unterminated STP radiates less than unterminated UTP because of the shield. You can plug the other end of the cable into an Ethernet switch. I prefer to test emissions with the SWITCH turned on (to establish a 'link'), but CISPR 22 permits testing with a 'terminated cable', i.e. with SWITCH on or off. David From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of kbalasubraman...@scmmicro.co.in Sent: Tuesday, March 20, 2007 12:40 AM To: emc-p...@ieee.org Subject: Ethernet emission - isolated metallic plate Dear Experts, The emission from our ethernet device :- 1. Without the ethernet cable connected to our device the emission is well below the limit line. 2. With the ethernet cable just plugged into our device ethernet port (other end of the cable is left unconnected) emission is above the limits. 3. With the one end of the ethernet cable connected to our device and the other end connected to the laptop computer and 'ping' is continuously active the emission slightly increases. 4. Emission with UTP cable is higher than emission with STP cable. Most interestingly when we place a metallic plate (an MS plate of about 6 inches wide and 2 foot long) on the test table and the ethernet cable is placed on this metal plate, the emission got reduced drastically and now it is well within the limits. The metal plate is not having any connection with ground plane, it is just kept on the wooden test table. How this isolated metal piece is reducing the emission is really a mystery. Sincerely K.Balasubramanian Project Leader - Hardware. - 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 emc-p...@ieee.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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald:emc-p...@daveheald.com 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 emc-p...@ieee.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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald:emc-p...@daveheald.com 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 __
Re: Ethernet emission - isolated metallic plate
In message of133fb7be.3bf2ff51-on652572a4.00152301-652572a4.0019b...@scmmicro.co.in , dated Tue, 20 Mar 2007, kbalasubraman...@scmmicro.co.in writes: The emission from our ethernet device :- 1. Without the ethernet cable connected to our device the emission is well below the limit line. 2. With the ethernet cable just plugged into our device ethernet port (other end of the cable is left unconnected) emission is above the limits. 3. With the one end of the ethernet cable connected to our device and the other end connected to the laptop computer and 'ping' is continuously active the emission slightly increases. 4. Emission with UTP cable is higher than emission with STP cable. All this seems quite normal for common-mode emission, where the source of emission is not a very low-impedance source. The shield of the STP probably has more capacitance to the surroundings, acting as 'ground' (strictly, the surrounding form paths back to the other terminal of the emission source; 'ground' is actually irrelevant), which is reducing the common-mode voltage. Most interestingly when we place a metallic plate (an MS plate of about 6 inches wide and 2 foot long) on the test table and the ethernet cable is placed on this metal plate, the emission got reduced drastically and now it is well within the limits. The metal plate is not having any connection with ground plane, it is just kept on the wooden test table. How this isolated metal piece is reducing the emission is really a mystery. The plate increases the capacitance to the surroundings. Putting the three wires to the Ethernet connector inside your device together through a big ferrite bead may cure the problem. -- 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 emc-p...@ieee.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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald:emc-p...@daveheald.com 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 __
RE: Ethernet emission - isolated metallic plate
I am interested in your posting because I am in the middle of my first experience with Ethernet as well, so could very well be interested in your solution. However, I do not think that the effect of the isolated piece of metal is a mystery. Consider what is happening here; your cable is coupling into the plate, both inductively and capacitively, and different potentials will be established at different parts of the plate resulting in currents flowing within the plate. The energy that is circulating in this manner will be absorbed in the plate. I don't expect that it is significant enough to measure the temperature rise in the plate, but that is where it will finally end up. If you had access to one of those scanning measurement tables that are sometimes used for assessing printed wiring board emissions, you could probably plot the currents in the plate. This is similar to the way that a metal box will act as a shield without being grounded; absorption into the metal is retained within the metal by virtue of the impedance mismatch at the surfaces causing reflection within the metal rather than radiated emission from the surface. Best regards Neil R. Barker CEng MIET FSEE MIEEE Manager Quality Engineering e2v technologies (uk) ltd 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK Tel: (+44) 1245 453616 Fax: (+44) 1245 453571 Mob: (+44) 7801 723735 P Please consider the environment before printing this email. From: kbalasubraman...@scmmicro.co.in [mailto:kbalasubraman...@scmmicro.co.in] Sent: 20 March 2007 04:40 To: emc-p...@ieee.org Subject: Ethernet emission - isolated metallic plate Dear Experts, The emission from our ethernet device :- 1. Without the ethernet cable connected to our device the emission is well below the limit line. 2. With the ethernet cable just plugged into our device ethernet port (other end of the cable is left unconnected) emission is above the limits. 3. With the one end of the ethernet cable connected to our device and the other end connected to the laptop computer and 'ping' is continuously active the emission slightly increases. 4. Emission with UTP cable is higher than emission with STP cable. Most interestingly when we place a metallic plate (an MS plate of about 6 inches wide and 2 foot long) on the test table and the ethernet cable is placed on this metal plate, the emission got reduced drastically and now it is well within the limits. The metal plate is not having any connection with ground plane, it is just kept on the wooden test table. How this isolated metal piece is reducing the emission is really a mystery. Sincerely K.Balasubramanian Project Leader - Hardware. Sent by E2V TECHNOLOGIES PLC or a member of the E2V group of companies. A company registered in England and Wales. Company number: 04439718. Registered address: 106 Waterhouse Lane, Chelmsford, Essex, CM1 2QU, 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 emc-p...@ieee.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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald:emc-p...@daveheald.com 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 __
