That’s what I meant, EMC is very imprecise compared to some other areas of engineering.
Because of that I would not hesitate to test at a second lab if I needed a few more dB, although that may not help much in Silicon Valley where labs agree closely. Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email: [email protected] Website: http://dsmith.org ________________________________ From: Brent DeWitt <[email protected]> Sent: Monday, October 7, 2024 5:49:12 PM To: [email protected] <[email protected]> Subject: Re: [PSES] technical musings Well said Ralph! On 10/7/2024 8:12 PM, Ralph McDiarmid wrote: “I have seen differences of 9 dB on the same measurement on an EUT and comb generator by different accredited labs! “ NkdkJdXPPEBannerStart Be Careful With This Message >From (Brent DeWitt ><[email protected]>)<https://godaddy.cloud-protect.net/email-details/?k=k1&payload=53616c7465645f5f09bf7f11ed81a54ce2d1b2bd4cc6dc207c03183ee33d6f5d240ebbf179455c71895e30e3997b36896ca5465abadf54c3c20d8b715d0dd92383eac085bdafe5a2846c66c944169e1578f1bb6272bd4405732e160ff314073b8758636f77c600eb318036bf99ed035dcd864dc5b42b21134a15420a4659290b1ce3df12ba6dbb32731f87bd284c9586ce4dd9ea34693e304320ed5cdb37127fdfa5810f2de0e9b8d4145b2e6c26bec5a1a8d945e30f54437d5371e228896d53ce3d1b03d6b9d22f5b742b7a7a0b5eb0f06e9d257ef51b8c4f5149076b4e25d9> Learn More<https://godaddy.cloud-protect.net/email-details/?k=k1&payload=53616c7465645f5f09bf7f11ed81a54ce2d1b2bd4cc6dc207c03183ee33d6f5d240ebbf179455c71895e30e3997b36896ca5465abadf54c3c20d8b715d0dd92383eac085bdafe5a2846c66c944169e1578f1bb6272bd4405732e160ff314073b8758636f77c600eb318036bf99ed035dcd864dc5b42b21134a15420a4659290b1ce3df12ba6dbb32731f87bd284c9586ce4dd9ea34693e304320ed5cdb37127fdfa5810f2de0e9b8d4145b2e6c26bec5a1a8d945e30f54437d5371e228896d53ce3d1b03d6b9d22f5b742b7a7a0b5eb0f06e9d257ef51b8c4f5149076b4e25d9> Potential Impersonation The sender's identity could not be verified and someone may be impersonating the sender. Take caution when interacting with this message. NkdkJdXPPEBannerEnd Well said Ralph! On 10/7/2024 8:12 PM, Ralph McDiarmid wrote: “I have seen differences of 9 dB on the same measurement on an EUT and comb generator by different accredited labs! “ Doug, I recall this has been the case for decades. There are a lot of variables to consider, and some are hard to assign a value. The equipment has been refined somewhat over those same decades, but the physics remains unchanged and still produce the same challenges with measurement uncertainty. It’s only a problem if that uncertainly creates, well… a problem. Otherwise, EMC measurement is an approximate science, all but impossible to model accurately, and yet universally accepted as fit for purpose. Ralph From: doug emcesd.com <[email protected]><mailto:[email protected]> Sent: October 7, 2024 4:08 PM To: [email protected]<mailto:[email protected]> Subject: [PSES] technical musings Hi All, When I was a young engineer at AT&T Bell Labs, about 50 years ago, my designs had to have an amplitude tolerance of +/- 1/10th dB to meet requirements (even without computer simulation). So when I came across EMC topics later on I was initially surprised to see tolerances like +/-2 dB or more. To me this means either the engineers do not understand the designs, or (and I think this is the case) there are too many uncontrolled variables to allow a narrower tolerance. I have seen differences of 9 dB on the same measurement on an EUT and comb generator by different accredited labs! I personally think that Silicon Valley is the best place to do EMC testing because there are so many labs, very close to each other, there that they are driven to be very close to each other in measurement results (otherwise the outliers would go out of business, quickly). Given a choice, I would test in Silicon Valley. On a separate topic, I am 77 years old but have the physical and mental capabilities of a 30 year old from my 50 year experiment to slow the aging process, which has proven to be a success for me. We often unofficially discus this after my seminars are finished for the day. On a recent seminar, the attendees kept me over for two hours after the seminar, questioning me and taking notes. This is not part of the seminar, but a significant freebie available to the attendees. I run 3,000+ miles per year, even on 120°F days in the Southern Nevada desert. Such heat does not even feel stressful to me! I design my own hydration. I designed my own nutrition and supplement plans as well. I never get sick, and am immune from sunburn from one of my supplements, astaxanthin. This comes from applying science and engineering to my mind and body. I have read many, many thousands of pages of medical research in my life and make use of it! Another topic, my classes are focused on finding hidden design flaws in designs that can cause a manufacturing or field disaster, especially flaws that result in a problem once in a week or month of significant consequence that cannot be found by normal engineering methods. Next one is in a few weeks, mid-October. Contact me if interested. Doug [https://lh4.googleusercontent.com/_HuR3Ky2TF_XhFHyxnYRmiq7nHQldnMsPNYFaLG6kb5T4y8MeCe-BDC_BscJtSFgszSSjssihHS-pjM3-jwNP8S0CwE-gN8fsRsPkojiAlmpBwb20vIVizS-siCUywW_jqrefbVr] ________________________________ This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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