Ed Price’s reply demonstrates an A+ approach to testing. In reply to the query which prompted it, any ambient signal adds to any real signal, boosting it. If the ambient is precisely 6 dB lower than the signal, and uncorrelated with it, it will boost the measured signal level 1 dB. If the ambient is more than 6 dB below the signal, the boost is below 1 dB. Hence the requirement that the ambient be at least 6 dB below the limit. Ken Javor Phone: (256) 650-5261
________________________________ From: "Price, Edward" <[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Mon, 16 Aug 2010 16:12:05 -0700 To: <[email protected]> Conversation: [PSES] Calibration supplier for signal generator with pulse modulation - Ambients Subject: RE: [PSES] Calibration supplier for signal generator with pulse modulation - Ambients Ralph: When I do a formal EMC Qualification test, I typically begin with measuring the Ambient. However, I get there in several steps. First, I put a termination on the data acquisition system RF input, and run a scan. This isn’t the ambient, rather it’s a proof of the acquisition system capabilities, and good proof that the acquisition system doesn’t introduce any internal spurious signals that might later be confused as real emissions. (In typical RE102 frequencies, you shouldn’t see anything except your analyzer noise floor. However, do this for CE101, and don’t be surprised to see significant power frequency harmonics.) I do this mainly as a hardware sanity check, and I don’t normally include this in my report. Second, connect my cables and do the “head-end calibration validation test”, which again, is not an ambient. This test validates the signal path that a real signal would follow back into the data acquisition system, plus it validates the processing and presentation of that signal (were the correct correction factors chosen, and did the software handle it as expected). This data is supplied with my report. Third, I place resistive loads across the LISN’s, sized to draw the same power as the EUT. This is the real ambient scan, and shows the background noise within my test chamber. You could also think of this as a facilities quality test. This data is supplied with my test report. Fourth. Almost all equipment that I test needs complex, non-deliverable support equipment, to exercise and monitor the EUT’s operation. For emissions tests, I want to separate the noise coming from this support equipment from the EUT’s noise. So, as much as I can, I turn on and exercise this support equipment, while not applying power to the EUT. This is an ambient of some kind, probably best called the Test Ambient. I will often find signals from the support equipment that must be reduced, or at least analyzed and specifically noted as not originating with the EUT. This data is supplied with my test report. And then I run the real test. For those signals seen in the Test Ambient above, I annotate each of their occurrences if they are within -6 dB or higher than the limit. Life can get very interesting when the operation of the EUT amplifies an emission originally seen in the Test Ambient. On the one hand, you could say that the signal would never have been there except for its source in the support equipment. But on the other hand, you could say that operation of the EUT makes the signal worse, so it is a valid EUT artifact. Ed Price [email protected] <blocked::mailto:[email protected]> WB6WSN NARTE Certified EMC Engineer Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 Military & Avionics EMC Is Our Specialty From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Tuesday, August 10, 2010 1:02 PM To: [email protected] Subject: Re: [PSES] Calibration supplier for signal generator with pulse modulation Does 'ambient scans' mean a measurement done on the spectrum with the EUT turned off or not present? Would an ambient CW or modulated signal affect measurement uncertainty? I suppose it would, because it cannot simply be subtracted from the EUT spectrum. _______________________________________ _____________________________________________ Ralph McDiarmid | Schneider Electric | Renewable Energies Business | CANADA | Regulatory Engineer From: "ce-test, qualified testing bv - Gert Gremmen" <[email protected]> To: [email protected] Date: 08/10/2010 12:51 PM Subject: Re: [PSES] Calibration supplier for signal generator with pulse modulation ________________________________ - 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 http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - 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 http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
