All, Good points on shielded cabling.
Also keep in mind that many products have some form of networking port for LAN use (10/100bT, token ring, etc). In the US, shielding is not used on these cabes. It is not unusual to see excessive bus clock common mode noise (e.g. PCI clock harmonics) on these output port pins if the board layout is especially poor or the common mode rejection of the port is poor. One can have all kinds of problems with Class B emissions. Quad port cards are especially difficult. On the immunity side of things, the common mode rejection of the choke is again critical because one can't use transorbs, clamping diodes or similar devices to protect the output drivers from ESD/EFT events because of the undue capacitive and unbalanced loading that they present to the I/O lines. Multimedia ports can have similar problems of poor shielding due to the types of cables that are used although there are more options for effective filtering. Regards, [email protected] ---------- From: Steve Chin To: Jon D Curtis; Max Cc: comp_lab; EMC-PSTC; Tony Fredriksson Subject: Re: Immunity/Cables List-Post: [email protected] Date: Thursday, February 13, 1997 4:42PM Max, the amount of immunity a cable has is dependent upon the type of shielding it has and how well it is connected to the case ground. I have gone through a whole bunch of gyrations with the cable vendors I work with (my other responsibility at this company is high-speed signal cable development) in order to build EMC-tight cables. If the cable is built and grounded well, then the likelyhood of a failure due to the effects of outside radiation is very low. Steve Chin StreamLogic Corp. Menlo Park, CA, USA -------------------------------------- List-Post: [email protected] Date: 2/13/97 2:18 PM To: Steve Chin From: Max Jon, That's great information--I also anticipate a requirement for heavy industrial immunity in the future and have been wondering what problems I might be in for. With PCs (and computers in general), isn't it the case that if the cables are shielded and grounded to the cabinet there isn't likely to be a problem? For emissions, BTW, I have also had good luck with DEC. Max Kelson [email protected] %> %>I have tested systems to the heavy industrial immunity specification which %>included class B PCs. Both HP Vectra computers and Dell computers faired %>well. Ocassionally the monitors sold with these systems are disturbed to %>the point of turning themselves off (a failure in most books). To date %>I've always been able to solve this problem by upgrading to an NEC %>multisync monitor. The key distinquinction of all these products is that %>they really do meet class B by wide margins and use very good shielding to %>get to that level. Once you have shielding that good and use digital %>techniques inside (as opposed to small signal, high impedance analog %>signals - thermocouples, etc.) heavy industrial immunity compliance is %>usually a given. %> %>Jon D. Curtis, PE %> %>Curtis-Straus LLC [email protected] %>One-Stop Laboratory for EMC, Product Safety and Telecom %>527 Great Road voice (508) 486-8880 %>Littleton, MA 01460 fax (508) 486-8828 %>http://world.std.com/~csweb %>On Wed, 12 Feb 1997, Tony Fredriksson wrote: %> %>> ------------------ RFC822 Header Follows ------------------ Received: by sledgehammer.com with SMTP;13 Feb 1997 13:57:18 -0800 Received: from ruebert.ieee.org by oz.sledgehammer.com (SMI-8.6/SMI-SVR4) id NAA24215; Thu, 13 Feb 1997 13:57:34 -0800 Received: (from daemon@localhost) by ruebert.ieee.org (8.7.5/8.7.3) id LAA15218 for emc-pstc-list; Thu, 13 Feb 1997 11:37:53 -0500 (EST) Message-Id: <[email protected]> To: Jon D Curtis <[email protected]> cc: Tony Fredriksson <[email protected]>, comp_lab <[email protected]>, EMC-PSTC <[email protected]> Subject: Re: In-reply-to: Your message of "Wed, 12 Feb 1997 21:53:28 EST." <[email protected]> List-Post: [email protected] Date: Thu, 13 Feb 1997 09:31:30 -0700 From: Max <[email protected]> Sender: [email protected] Precedence: bulk Reply-To: Max <[email protected]> X-Resent-To: Multiple Recipients <[email protected]> X-Listname: emc-pstc X-List-Description: Product Safety Tech. Committee, EMC Society X-Info: Help requests to [email protected] X-Info: [Un]Subscribe requests to [email protected] X-Moderator-Address: [email protected]
