Russell, The margin issue is usually a much discussed subject when it comes to initial product EMC emission certification. As most experienced EMC engineers know that variances in production units will occur. Also to ensure that if a production unit is tested in a different 'accredited lab' a product margin to account for the lab site attenuation differences and measurement uncertainty is also required.
Additionally when a product has little or no margin at initial certification, the product when going through EMC audits will almost certainly require 'tweaking' to 'pass the limit' and for any component/product design changes they will also affect the emission profile. [A real 'headache!!] Some companies operate a mandated margin (below the limit) of 4dB or greater at initial product certification and the sub-sequent production EMC audits usually 'pass' without any troubles. Other companies that do not have the 'margin' usually have an on-going struggle to get through EMC audits with a 'pass' below the limits. A suitable margin to aim for may depend on various factors e.g. expected production volume, number of product features offered, likely hood of product enhancements/developments to the electronics, market areas product is to be sold etc. The greater the 'margin' at the initial product certification will generally help during production audits and future product enhancements. Andy White Senior EMC Engineer Ericsson Wireless Communications Inc. San Diego CA -----Original Message----- From: Russell [mailto:r....@totalise.co.uk] Sent: Wednesday, February 27, 2002 1:41 AM To: emc-pstc Subject: EMC Emissions Safety Margins What safety margin below the statutory limits for emc emissions should one aim to achieve to ensure all product samples are likely to pass when a single, peraps two, samples only have been tested. Are there any hard and fast rules? Is being just below the limits considered good enough? Thanks in anticipation for your views and advice. Russell. ------------------------------------------- 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@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: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
