A few tips:
RF emission limits are not difficult to meet, once you have knowledge and experience. If a single ferrite suffices to make the design compliant, you are probably not much more then 0-6 dB over limit. Another test house will certainly test a few dB different, you may pass there. (accuracy of EMI test set-ups do not include the test sample and cable setup) Then consider testing another sample. Standard deviation of RF-emissionbetween samples could be large enough to meet the requirements. Possibly you had a worst case sample. 80 % confidentiality interval of your series production should fall within the limits. ( it is possible to reject a batch of all compliant samples if their variation in RF emission is too large: that's statistics) Any clock oscillator in a metal can should be damped using a series resistor. Best thing is to learn how to get your design compliant, and do that. otherwise: Next time, next project, you will (Murphy) probably need 2 ferrites. Ferrites are always more expensive then re-design (on a commercial scale). Commercial end-user products should have the cable delivered with them and have a pre-confectioned ferrite on it. If you tell your customers how to fix the ferrite themselves and why they have to, they will probably leave the ferrite out. Regards, Gert Gremmen Ing. == Ce-test, Qualified testing == Consultants in EMC, Electrical safety and Telecommunication Compliance tests for European standards and ce-marking Member of NEC/IEC voting committee for EMC. Our Web presence: http://www.cetest.nl List of current harmonized standards http://www.cetest.nl/emc-harm.htm 15 great tips for the EMC-designer http://www.cetest.nl/features01.htm -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: vrijdag 25 juni 1999 21:37 To: [email protected] Subject: emc compliance Here's a question.... If you have a product that, at one particular frequency during radiated RF, you simply cannot get to pass the requirements of the relative CE standard without putting an external ferrite on the cable, is it "legal" , to still mark it, provided you inform your customers via the declaration of conformity or in the manual etc., that they could experience problems at such and such frequencies and if they do, to use a ferrite? (boy, that was a mouthful). Faced with a redesign or a statement, the words would be the easier route to take, since in this case, the customer could probably never see the problem frequency range. Comments? thank you for any advise, Lisa --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
