Can anyone tell me if the new CISPR 16-2 is published? I'm studying section 9 CISPR 16-1987. Not sure if I understand the difference between acceptance probability and confidence. Do you mind explaining it to me in a little detail? Or any other publications or papers discuss this on-going compliance?
Now the target, dB margin: If you have been bored by the topic, just stop here. If your products go to Europe, you have to comply with clause 35 in section 9, CISPR 16-1987. FCC does not define a statistic formula but they do expect to see production variations in EMI. Assume we all follow this 80/80 rule. This is the first assumption. Then /X + k Sn <= L or L - /X >= k Sn where L - /X is the mean value of margin, Sn is the standard deviation of emission level with sample size n, and k is the contant which makes the formula satisfies the 80/80 rule. There are assumptions here as well. If we choose n = 5, then k is 1.51. This can be calculated. The formula can be rewritten as, margin >= 1.51 x standard emission level deviation There are several components in the standard emission level deviation 1. EUT difference, components, shielding, etc. 2. Test setup difference, cable position, accessories, etc. 3. Site imperfection 4. Attenuator, temperature, time 5. Measurement errors 6. Atenna factor error Give 1dB on each item, we have 6 dB. By careful design and the type of product, it's possible to reduce it to 2 to 4 dB. So we need a margin of 3 to 6 dB in order to comply with 80/80 requirement. There are many variables in the calculation. By setting different values, you may have many different results. It eventually becomes your business decision how much risk you want to take. There is one thing for sure. "Limit Is Limit" does not comply. Why can "Limit Is Limit" exist? Because some authorities does not take limit as limit, and chances are that you won't be picked. Just like you won't be stopped when you drive at 60 mph in NJ (55 limit here). It would be nice if someone can analyze the risk a little bit further. By better understanding acceptance probability and confidence, we may be in a better position. More than two years ago, I put a message in TREG saying it's not fair requesting 6 dB margin and agreed with "Limit is Limit". Anyway, if any of the assumptions I made is not realistic, please do point out. Thanks. Regards, Tom http://www.rcic.com
