Hi Derek,
So, we all are comfortable with 20 dB differences on round robins J No need to improve anything Please enlighten us about the “Low hanging fruits” Regards, Deniz From: lfresea...@aol.com [mailto:lfresea...@aol.com] Sent: Thursday, August 12, 2010 7:34 PM To: Deniz Demirci; b...@toprudder.com; emc-p...@ieee.org Subject: Re: Calibration supplier for signal generator with pulse modulation Hi Deniz, what entity is going to do something of little value unless forced to? Of course MU is done for auditing reasons. Very few tests require it in EMC.. Please do not bring up radio tests, I'm referring to EMC. Clause 5.4.1 states... ".....and, where appropriate, an estimation of the measurement uncertainty as well as statistical techniques for analysis of test and/or calibration data." If you are ASKED to do MU outside of this it's either because your assessing body is over zealous, or your assessor is uneducated. You must push back and say NO! Failure to do this is punishing your client, and more important the consumer, which includes me and I'm taxed enough already! I wouldn't consider myself a novice in MU, or EMC testing, but I can learn. That said, I have yet to see a genuine advantage for MU improving measurement. What does calculating MU have to do with quantifying accuracy? All it does is put windows about what you might be measuring. Now, here's a chance to back a stance by a fellow assessor who has campaigned for ( and I support his idea ) that ISO 17025 should be split into two documents: one for test, the other for calibration. I wholeheartedly support the addressing of MU in the calibration document, and there being NO mention in the test document. ( Dan, if your reading, these are my words not yours... ) Cheers, Derek. From: Deniz Demirci <deniz.demi...@ntscorp.com> To: lfresea...@aol.com; b...@toprudder.com; emc-p...@ieee.org Sent: Thu, Aug 12, 2010 7:59 pm Subject: RE: Calibration supplier for signal generator with pulse modulation If MU is only for audit purpose, it won’t help at all. If you are using MU for your benefit, there are always some improvement opportunities in your test setup. If you can’t quantify how inaccurate you are, how do you improve anything? <quote> I'm amused to read you make adjustments for your MU being larger. Keep in mind were kind of measuring jello...</quote> Uncertainty and measurement errors are different. Systematic error can only be compensated, not MU You should not make any adjustments based on MU. It is an uncertainty not a correction factor (don’t get amused) Plain EMC may be still measuring a jello. But more accuracy is necessary in “Radio” certifications. It will be really odd if your measurements are +/- 4 dB off for the radiated power J MU is a nice tool if you know/want how to use it OOO (Own opinions only) Best regards, Deniz Demirci National Technical Systems (NTS Canada) Phone: 403-568-6605 ext 244 fax: 403-568-6970 email:deniz.demi...@ntscorp.com <mailto:deniz.demi...@ntscorp.com> web: http://www.ntscorp.com/about/locations <http://www.ntscorp.com/about/locations> From: lfresea...@aol.com <mailto:lfresea...@aol.com> [mailto:lfresea...@aol.com <mailto:lfresea...@aol.com?> ] Sent: Thursday, August 12, 2010 5:43 PM To: Deniz Demirci; b...@toprudder.com <mailto:b...@toprudder.com> ; emc-p...@ieee.org <mailto:emc-p...@ieee.org> Subject: Re: Calibration supplier for signal generator with pulse modulation Again, how do you guarantee / justify what you are doing if you don't care about the MU. I don't see how MU helps improve any measurement. How does it? Does it make the instrument magically more accurate? Does VSWR magically get lower? etc etc etc... No, it doesn't, nor will it ever. I'm amused to read you make adjustments for your MU being larger. Keep in mind were kind of measuring jello... I am strongly disagree with the “I did it and it is correct” attitude in EMC discipline. Maybe it explains the overall situation and measurement deviations between the laboratories Ironically, the "studies... round robins etc " that reported differences of 20 dB and up, included acredited labs, with MU budgets... So much for that. Quite simply, the only way for good consistent results is a good test technique, a competent operator, and good equipment. Please notice, MU is not mentioned here... Now, just for the record, I'm not being flippant. I prefer to focus where its worth the effort. I keep going back to measuring some limit, which I still maintain is somewhat arbitrary. If you fail by a few dB, so what... In real life you should be held accountable for your products performance. If you get calls because it malfunctions, then you don't have a good design. If you never get a call, then it's probably fine. We need to forget about MU and address the other low hanging fruit first... Sincerely, Derek Walton From: Deniz Demirci <deniz.demi...@ntscorp.com <mailto:deniz.demi...@ntscorp.com> > To: Bob Richards <b...@toprudder.com <mailto:b...@toprudder.com> >; emc-p...@ieee.org <mailto:emc-p...@ieee.org> Sent: Thu, Aug 12, 2010 2:51 pm Subject: RE: Calibration supplier for signal generator with pulse modulation I've been performing in-house calibrations of LNA's, LISN's, CDN's, Current clamps and they have been accepted by the auditors. There is no restriction in terms of 17025 if you follow the requirements such as dedicated calibration instrumentation and MEASUREMENT UNCERTAINTY assessment. I admit my MU figure for calibration is larger than a calibration laboratory and it is accounted in EMC measurements. Again, how do you guarantee / justify what you are doing if you don't care about the MU. I am strongly disagree with the “I did it and it is correct” attitude in EMC discipline. Maybe it explains the overall situation and measurement deviations between the laboratories OOO (Own opinions only) Best regards, Deniz Demirci National Technical Systems (NTS Canada) Phone: 403-568-6605 ext 244 fax: 403-568-6970 email:deniz.demi...@ntscorp.com <mailto:deniz.demi...@ntscorp.com> web: http://www.ntscorp.com/about/locations <http://www.ntscorp.com/about/locations> From: emc-p...@ieee.org <mailto:emc-p...@ieee.org> on behalf of Bob Richards Sent: Thu 8/12/2010 7:51 AM To: emc-p...@ieee.org <mailto:emc-p...@ieee.org> Subject: Re: Calibration supplier for signal generator with pulse modulation --- On Thu, 8/12/10, Ken Javor <ken.ja...@emccompliance.com <mailto:ken.ja...@emccompliance.com> > wrote: And similarly, not because of MU but because of 17025 or perhaps ISO 9000, I've seen test equipment that could easily have been calibrated in house, such as current probes, LISNs and a 41 inch rod antenna have to be sent to the calibration lab. This is totally unproductive, except for the calibration lab. And I would argue further that it is detrimental to the discipline, because if you do your own calibration, you understand better how things work. This is a subject near to my heart. I've performed in-house calibrations of cables, LISNs, CDNs, current probes etc, and I agree 100% with what you said. Knowing the procedure helps to understand how things work and, just as important, gives a person the knowledge of how to perform quick verifications of a test setup in case there is ever any question as to the proper operation of that equipment. Every so often, a conversation comes up in the lab about whether we should do in-house calibrations. The issue is never about MU, cost or validity of data, it usually hinges around 17025 and what auditors will say. IMHO, shipping LISNs and/or CDNs to have calibrations performed by a cal lab is less reliable than in-house calibrations. This has little to do with the cal lab's ability, but from the possibility of damage during shipping. I've had CDNs come back with stuff rattling around inside (possibly chips off of ferrites?). If I can't perform an impedance verification in house, then what should I do to insure it is not damaged - send it back to the cal lab? Bob R. - 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 <emc-p...@ieee.org <mailto:emc-p...@ieee.org> > All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc <http://www.ieeecommunities.org/emc-pstc> Graphics (in well-used formats), large files, etc. can be posted to that URL. 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