I don’t believe human errors such as described by Bacher (not accounting for a preamp’s gain) and Gremmen (i.e., the 30 – 40 dB he mentioned) should figure in the mix.
-- Ken Javor Ph: (256) 650-5261 From: "Jim Bacher, WB8VSU" <[email protected]> Reply-To: "Jim Bacher, WB8VSU" <[email protected]> Date: Tuesday, October 8, 2024 at 10:50 AM To: <[email protected]> Subject: Re: [PSES] technical musings Back in the 1980s I had a variation in system measurements between labs. Management decided the lab I used wasn't any good. In the process of trying to convince management variations were normal, I came to the conclusion that measuring systems at different labs would likely have a +5 to -7 dB variations. None of our test equipment is perfectly flat. No one calibrates every Hz to account for those imperfections. The frequency being measured is typically not on any of the calibrated frequencies. For testing a system, equipment and cable variations can impact their emmisions significantly. I have seen over 20 dB of variation due to the variations. How much effort was made to peak signals? Then is the test equipment measurement operator an avid Ham DXer (chases weak signals to talk to far away stations)? Reason is a Ham will likely do a more accurate peaking of rotation and height of the search antennas. I have had one government lab fail to compensate for a preamp when reporting levels and said the product failed. I had the agent pull it back for a few days, then take it back and it passed with no changes. So some errors can be to using the wrong calibration factors when calculating the levels. Jim Bacher, WB8VSU [email protected] or [email protected] JBRC Consulting LLC Product EMC & Regulatory Consultant https://www.trc.guru/ email:[email protected] IEEE Life Senior Member On October 8, 2024 11:14:28 AM David Schaefer <[email protected]> wrote: Harry Hodes gave a presentation at the C63 meetings last week on proficiency testing. He runs the ACIL PT program, and the data he shared showed a ton of variance. Many labs were in I think +/-3-4 dB range, but there were outliers – the worst cases being one lab reading 30-40 dB high, another 30-40 dB low. If I recall correctly for one PT program 95 labs participated and around 10 were outside the expected tolerance. Doing a check of the measurement system prior to testing is critical. A comb gen scan takes only a few minutes but should catch these egregious errors. David Schaefer Technical Manager Element Materials Technology 9349 W Broadway Ave Brooklyn Park , MN 55445 , United States O +1 612 638 5136 ext. 10461 [email protected] www.element.com From: doug emcesd.com <[email protected]> Sent: Monday, October 7, 2024 6:08 PM To: [email protected] Subject: [PSES] technical musings CAUTION:This email originated from outside of Element Materials Technology. DO NOT click links or open attachments unless you recognize the sender and know the content is safe. Please contact the TOC if you are in any doubt about this email. I have seen differences of 9 dB on the same measurement on an EUT and comb generator by different accredited labs! Doug This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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To post a message to the list, send your e-mail to [email protected] All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://ewh.ieee.org/soc/pses/listrules.html For help, send mail to the list administrators: Mike Sherman at: [email protected] Rick Linford at: [email protected] For policy questions, send mail to: Jim Bacher at: [email protected] To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1 This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to [email protected] All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://ewh.ieee.org/soc/pses/listrules.html For help, send mail to the list administrators: Mike Sherman at: [email protected] Rick Linford at: [email protected] For policy questions, send mail to: Jim Bacher at: [email protected] To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1 - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to [email protected] All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://ewh.ieee.org/soc/pses/listrules.html For help, send mail to the list administrators: Mike Sherman at: [email protected] Rick Linford at: [email protected] For policy questions, send mail to: Jim Bacher: <[email protected]> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
