RE: EMC Emissions vs EFT warning!
Alex, If ever the RJ cable between your unit A an B carries control or data signals that do not have a dedicated current return in addition to the power and ground lines, it may be possible that adding a CMC on the power and ground lines alone may have broken the ground return path for these signals. This could explain your EFT issue if these signals are only used when unit A is connected to unit B. Note also that even differential signals, when not transformer isolated, normally need a current return to avoid excessive common mode voltage swing. You may need to provide more detail about your I/Os and EFT failure mode so the group can better identify the nature of your problem. If the above control/data scheme is representative of your setup, here are some possible fixes, which may not be applicable depending on your specific configuration, but I hope this can help you solve your issue or get an idea of the kind of additional information to provide: 1. Use a CMC that can carry all of the signals through the same core. 2. Use shunt filtering to chassis ground on your ground and power lines instead of a CMC. If there is too much common mode noise from your power circuits, and control/data is slow or differential and associated logic return can be tied to chassis ground, you may still use a CMC on your power circuit input to segregate its noise, this, assuming your shunt filtering provides adequate HF current return for control/data from the RJ connector to logic ground via the chassis. You may also try to improve the power circuit design or layout to avoid such issues. 3. Try to eliminate the need for a CMC or shunt filtering by optimizing your power, I/O and chassis grounding scheme to minimize common mode noise between these points. Define current return paths and minimize associated return impedance and HF current levels. 4. If your control/data is low speed, you may try RC or RLC, filtering on the signals a the receive end, or at both ends if bi-directional. The L should be a ferrite bead, and the C could in some cases simply be the parasitic capacitance of your receive IC if a high value resistor or ferrite can be placed very close to the IC pin. 5. If your signals are differential, a second dedicated very high impedance CMC may also help, but unless you add a dedicated signal return wire in your RJ cable flowing through that same CMC the performance will be limited by the combined common mode impedance of the signals going through the CMC. The common mode impedance is basically the parallel sum of all sources and terminations referred to logic ground (Of unit A or B, whichever is worst; Not A and B in parallel) on the signals going through the CMC. If your signals are single ended, you may also add a dedicated CMC but a dedicated signal return flowing through the CMC would be of even greater importance. Without a dedicated return, excessive crosstalk will likely result between the signals and that case option #4 would be more suitable. 6. If your control/data signals can be more effectively referred to chassis ground than your DC input, you may add a dedicated clean return ground wire in your RJ cable for control/data, which would be referred to the chassis at both ends, and keep the CMC for the power and power return lines. There would certainly be other options to consider if you can provide more detail. Best regards, Eric -Original Message- From: Alex McNeil [mailto:alex.mcn...@ingenicofortronic.com] Sent: May 27, 2002 10:54 AM To: emc-p...@majordomo.ieee.org Subject: EMC Emissions vs EFT warning! Hi Group, I am working on a small Class II product (A) i.e. no earth. The product is powered by 12Vdc via a 1M cable with RJ type connections from another similar Class II product (B) which itself is powered via an external in-line AC/AC power block (basically an AC/ac transformer) and rectified to 12Vdc internally. It has a CMC on the supply lines. The system (A+B) EMC tests were fine. However, since product A may be used in future as a stand alone product i.e. powered from it's own 12Vdc power supply, I had to add a small common mode choke to the input supply lines, the same lines as the RJ connection method, to enable me to meet the EMC requirements. Since I had added a major EMC component I decided to re-test the EMC of the system. To my horror the system (A+B) readily failed the mains EFT tests on product B. Removing the CMC on product A resolved the EFT problem. I now have to create 2 product A builds depending on the option of usage, one with CMC (Stand alone usgae) and one without a CMC (system usage). I am sure I have had a similar problem in the past but at that time I did not realise that the addition of the CMC (to resolve conducted radiated emissions) was the source of the EFT failures. I think the EFT problem must have something to do with high/low impedance mis-match due to the CMC but I am not sure. I would appreciate a more experienced member of the group
RE: STP vs FTP Ethernet cables (2)
In fact a standard for 150 Ohms STP cable does exist but is intended for FDDI Token Ring applications, to which the ANSI X3.263 standard applies, and I assume not for Ethernet. Maybe the story I heard was about someone who used this type of cable for Ethernet. Although it was a logical guess, the 150 ohms value is not from the combination of the 100 ohm characteristic impedance and the 50 ohm output from equipment. Sorry for the confusion, Eric -Original Message- From: KC CHAN [PDD] [SMTP:kcc...@hkpc.org] Sent: Sunday, September 09, 2001 8:52 PM To: pronc...@cisco.com; james_al...@milgo.com Cc: emc-p...@majordomo.ieee.org Subject:RE: STP vs FTP Ethernet cables (2) I guess this 150 ohms is from the combination of the 100 ohm characteristic impedance and the 50 ohm output form equipment, like the power amplifier for conducted immunity test. Allan, James james_al...@milgo.com 09/07/01 09:03pm Paolo: Try this link to Quabbin wire company. It is a product selector guide with the types of wire used for different applications. All Ethernet applications are 100 ohm characteristic impedance and only have overall shields if shielded. Telecom cable (T1, DSL etc.) if shielded, are also 100 ohm but the shield (if present) is over the individual wire pairs with no overall shield. I find no reference to standard Ethernet cable at 150 ohms. LINK http://www.quabbin.com/finder/finder.cgi?cmd=app_form Jim Allan Manager, Engineering Services Nextira Solutions LLC 1619 N Harrison Parkway Sunrise, FL, 33323 E-mail james_al...@milgo.com Phone (954) 846-3720 Fax (954) 846-6282 -Original Message- From: Paolo Roncone [SMTP:pronc...@cisco.com] Sent: Friday, September 07, 2001 5:28 AM To: Meunier, Eric Cc: emc-p...@majordomo.ieee.org Subject: RE: STP vs FTP Ethernet cables (2) Eric, this 150 ohm story of STP cables sounds completely new to me. Also, my understanding is that both UTP and STP are used for 10bT ethernet. In the STP definition of IEEE802.3, there is no mention about different characteristic impedances from the required 100ohm of 10bT. Unfortunately I haven't yet received an answer to my original question as to how STP cables should be actually made (shielded twisted pairs vs overall shield) . As I already said in previous e-mails, the STP cables that I got look pretty much the same as FTP cables, that is they have just an overall shield (aluminum foil) around all wires. And they are all declared to be 100 ohms. Paolo At 16:56 06/09/2001 -0400, you wrote: Paolo, You may want to check if the FTP cable has a 100 Ohms characteristic impedance which would make it compatible with interfaces designed for UTP cable. STP cable is supposed to have a 150 Ohms impedance which is not compatible with standard 10baseT interfaces which are usually designed for UTP. Eric === Eric Meunier Hardware Architect E-mail: eric.meun...@ca.kontron.com mailto:emeun...@teknor.com Kontron Communication Inc. (Teknor) 616, rue Cure-Boivin Boisbriand, Quebec Canada, J7G 2A7 Tel: 1-450-437-4661 ext. 2419 Fax: 1-450-437-8053 Web: http://www.teknor.com/ http://www.teknor.com/ -Original Message- From: Paolo Roncone [SMTP:pronc...@cisco.com] Sent: Thursday, September 06, 2001 4:18 AM To: Doug McKean Cc: EMC-PSTC Discussion Group Subject:Re: STP vs FTP Ethernet cables (2) Doug, I re-paste the first part of the definition in IEEE 802.3 (2000): 1.4.249 shielded twisted-pair (STP)cable: An electrically conducting cable,comprising one or more ele- ments,each of which is individually shielded.There may be an overall shield,in which case the cable is referred to as
RE: STP vs FTP Ethernet cables (2)
ANSI X3.263 section 9.1.1.1 specifies that STP interfaces shall be terminated in 150 Ohms and section 9.1.2.1 that UTP shall be in 100 Ohms for qualification testing. It seems that most Shielded Twisted Pair cables on the marked called by the STP acronym are in fact designed according to UTP requirements such that they can be used for standard 10bT applications. I remember seeing a reference about this in a cable catalog, probably Belden, and I was told once that some people got trouble because they had used 150 Ohms STP cable on a 10bT LAN... which all seems to corroborate with the ANSI spec. If someone has time to investigate further... About the wavelengths comment, I guess it is true that one might typically get away with a few wavelengths for a 1.5 impedance mismatch ratio. However, if you want to be sure you will never get a surprise with equipment interoperability I would guess it is better to avoid such significant mismatch over more than a fraction of a wavelength. Equipment manufacturers design for 100 +/-15 Ohms cable impedance. Has anyone got field experience for large volumes and multiple interface vendors about this? Finally, if you are only concerned about getting a waiver for the Intra-building surge requirement, an overall shield would probably do and should be cheaper. Best regards, Eric === Éric Meunier Hardware Architect E-mail: eric.meun...@ca.kontron.com mailto:emeun...@teknor.com Kontron Communication Inc. (Teknor) 616, rue Curé-Boivin Boisbriand, Québec Canada, J7G 2A7 Tel: 1-450-437-4661 ext. 2419 Fax: 1-450-437-8053 Web: http://www.teknor.com http://www.teknor.com -Original Message- From: Allan, James [SMTP:james_al...@milgo.com] Sent: Friday, September 07, 2001 9:04 AM To: 'Paolo Roncone' Cc: emc-p...@majordomo.ieee.org Subject:RE: STP vs FTP Ethernet cables (2) Paolo: Try this link to Quabbin wire company. It is a product selector guide with the types of wire used for different applications. All Ethernet applications are 100 ohm characteristic impedance and only have overall shields if shielded. Telecom cable (T1, DSL etc.) if shielded, are also 100 ohm but the shield (if present) is over the individual wire pairs with no overall shield. I find no reference to standard Ethernet cable at 150 ohms. LINK http://www.quabbin.com/finder/finder.cgi?cmd=app_form Jim Allan Manager, Engineering Services Nextira Solutions LLC 1619 N Harrison Parkway Sunrise, FL, 33323 E-mail james_al...@milgo.com Phone (954) 846-3720 Fax (954) 846-6282 -Original Message- From: Paolo Roncone [SMTP:pronc...@cisco.com] Sent: Friday, September 07, 2001 5:28 AM To: Meunier, Éric Cc: emc-p...@majordomo.ieee.org Subject: RE: STP vs FTP Ethernet cables (2) Eric, this 150 ohm story of STP cables sounds completely new to me. Also, my understanding is that both UTP and STP are used for 10bT ethernet. In the STP definition of IEEE802.3, there is no mention about different characteristic impedances from the required 100ohm of 10bT. Unfortunately I haven't yet received an answer to my original question as to how STP cables should be actually made (shielded twisted pairs vs overall shield) . As I already said in previous e-mails, the STP cables that I got look pretty much the same as FTP cables, that is they have just an overall shield (aluminum foil) around all wires. And they are all declared to be 100 ohms. Paolo At 16:56 06/09/2001 -0400, you wrote: Paolo, You may want to check if the FTP cable has a 100 Ohms characteristic impedance which would make it compatible with interfaces designed for UTP cable. STP cable is supposed to have a 150 Ohms impedance which is not compatible with standard 10baseT interfaces which are usually designed for UTP. Eric === Éric Meunier Hardware Architect E-mail: eric.meun...@ca.kontron.com mailto:emeun...@teknor.com Kontron Communication Inc. (Teknor) 616, rue Curé-Boivin Boisbriand, Québec Canada, J7G 2A7 Tel: 1-450-437-4661 ext. 2419 Fax: 1-450-437-8053 Web: http://www.teknor.com/ http://www.teknor.com
RE: LVD testing suite for ITE devices
For Ethernet ports you may also want to consider the high-voltage isolation requirement specified in the IEEE-802.3 Ethernet specification. I found that Ethernet isolation is usually not required as part of the EN60950 certification process but it may be a good safety feature to consider and can improve product reliability as well. (Sorry for the delayed response; My original reply bounced back due to a problem with my emc-pstc account.) Eric === Éric Meunier Hardware Architect E-mail: mailto:emeun...@teknor.com mailto:emeun...@teknor.com Kontron Communication Inc. (Teknor) 616, rue Curé-Boivin Boisbriand, Québec Canada, J7G 2A7 Tel: 1-450-437-4661 ext. 2419 Fax: 1-450-437-8053 Web: http://www.teknor.com http://www.teknor.com -Original Message- From: Stuart Lopata [SMTP:stu...@timcoengr.com] Sent: Thursday, August 23, 2001 12:35 PM To: emc Subject:LVD testing suite for ITE devices Can anyone point me to specific tests and standards applicable for safety testing for ITE devices? Specifically, we are looking to meet the low voltage directive for computers and computer peripherals ( such as hardware that plugs into the bus slots and wireless networking equipment that connects to pcmia or ethernet ports). Sincerely, Stuart Lopata --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
