Bingo. Clearly another driver for inserting MU where it doesn't belong is a desire to replace the need for competent personnel with an algorithmic process that works for any personnel. But the same personnel who don’t know how to properly perform the test will also not know how to run the algorithm. Hence Mr. Walton’s observations on how poorly MU is executed in reality. Ken Javor
Phone: (256) 650-5261 ________________________________ From: Dennis Ward <[email protected]> Reply-To: <[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Wed, 11 Aug 2010 09:50:21 -0700 To: <[email protected]>, <[email protected]>, <[email protected]> Subject: RE: Calibration supplier for signal generator with pulse modulation I think I would only add that while measurement uncertainties for EMC is nebulous at best, at the same time we do not want to get into the habit of a slam dunk mentality of ‘oh, just a number, it doesn’t matter.” That is why Derek’s statement of “What’s really needed is a competent individual with adequate equipment” is so important. Where electromagnetic compatibility is concerned, competence of the engineers doing the measurement is probably much more important than uncertainties. I know that one of the biggest benefits to testing in the radio approvals industry is competence of test personnel. Compliance does matter and the best way to keep unneeded uncertainties out of the EMC measurement industry, is to keep competence of test personnel in. Dennis Ward Director of Engineering American TCB Certification Resource for the Wireless Industry www.atcb.com <http://www.atcb.com/> <http://www.atcb.com/> 703-847-4700 fax 703-847-6888 direct - 703-880-4841 From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Wednesday, August 11, 2010 9:00 AM To: [email protected]; [email protected] Subject: Re: Calibration supplier for signal generator with pulse modulation Hi Deniz, this is where "real" EMI guys differ from Metrology guys. We really don't need to be piddling with little numbers.... with the exception of frequency. Most of these modulations are compromises, and measuring a compromise accurately is a silly thing to do: in reality. You may want to get on board with the proof of the pudding phrase, it's OK in EMI: otherwise we expend all sorts of effort for no VALUE in return. The compliance world is obsessed with meeting a number, when the REAL reason for doing this testing is to ensure successful operation in use. I strongly disagree with Gerts statement MU is simple, it's not. Of the 140+ labs I've visited as an assessor, only a handful have a valid effort, and less than 1/2 doz believe it was of real value. Precision and EMI do not go together. I for one like it like that. Whats really needed is a competent individual with adequate equipment. If a committee would like MU, then as test labs we should isolate the cost that adds, and identify it on peoples invoices when that test is run. It's an effective way of making the standard unpopular. The reason I'm on a soap box about this is because unless silly requiremnts like this re CHALLENGED, and not just carte-blanche accepted, they become requirements. For calibration, I believe MU is useful, but for EMI, it has no place. Sincerely, Derek. From: Deniz Demirci <[email protected]> To: Untitled <[email protected]> Sent: Wed, Aug 11, 2010 10:35 am Subject: RE: Calibration supplier for signal generator with pulse modulation Could you define how precise? What is your acceptance criteria for the modulation dept? Let's say for basic 80 % AM modulation. Is your tolerance 0.1 % or between 60 % to 90 % is good enough. There is more than a dB peak difference in the signal for 60 % AM and 80 % AM modulations. You won't realize the difference with a field probe in radiated immunity tests with modulated signal. (Simple math; 20*Log(1.6/1.8) = -1.02 dB) It seems not very insignificant to me Another case; If you are using 6 meter cable for radiated emission at 10 GHz, your cable characterization uncertainty is more than 1.5 dB even with a quite high grade cable (Experimental measurements). Check the cable vswr figures in their specs measured in ideal conditions. Even a simple cable is a significant uncertainty contributor. Your measurement antenna is not exactly 50 Ohm at 10 GHz also. Site imperfection is another story. Those figures are not accounted for in the MIL-STD-461 RE102 verification. Everything seems to be very good when you terminate the measurement cable with a signal generator (50 ohm) output. I don't agree with this <quote> an ultimate "proof-of-the-pudding," </quote> You can use all your engineering skills for the tests but you have to quantify your risk using type B measurement uncertainty analysis and do the Type A if you can afford to see where you stand. As Mr. Gremmen said " MU is not difficult" No need to be afraid, OOO (Own opinions only) Best regards, Deniz Demirci National Technical Systems (NTS Canada) Phone: 403-568-6605 ext 244 fax: 403-568-6970 email:[email protected] web: http://www.ntscorp.com/about/locations From: [email protected] [mailto:[email protected] <mailto:[email protected]?> <mailto:[email protected]?> ] On Behalf Of Ken Javor Sent: Wednesday, August 11, 2010 7:55 AM To: Untitled Subject: Re: Calibration supplier for signal generator with pulse modulation Precisely. Ken Javor Phone: (256) 650-5261 > From: Cortland Richmond <[email protected]> > Reply-To: <[email protected]> > Date: Wed, 11 Aug 2010 08:27:34 -0400 > To: emc-pstc <[email protected]> > Subject: re: Calibration supplier for signal generator with pulse modulation > > Not quite what you need to know but I've used signal taps or directional > couplers with a 'scope to watch the RF waveform and set modulation depth, > and a calibrated counter, or even a receiver or analyzer will for > frequency. One always has recourse to calibrated devices to monitor > another, uncalibrated one. It's a good idea anyway! If a detector must be > used whose linearity is unknown, one can use calibrated attenuators to find > out. > > > Cortland Richmond > KA5S > > >> [Original Message] >> From: Wendy Nya <[email protected]> >> To: <[email protected]> >> Date: 8/10/2010 4:23:29 AM >> Subject: Calibration supplier for signal generator with pulse modulation >> >> Dear All, >> >> I am looking for a calibration supplier that can provide accredited > service for >> AR SG6000. It has built-in pulse modulation option (for Radiated Immunity > use). >> >> By the way - Is anyone using this model? It seems to be OEM from Agilent > (it >> came in an agilent box) but the equipment is marked AR >> and works with Agilent N5181A driver. Agilent is saying that it is not > able to >> provide accredited calibration service for this model. >> >> Thanks & Regards, >> Wendy Nya > > - > ---------------------------------------------------------------- > 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]> - 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. 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