Ken / Deniz, Speaking of significant digit's: I'm still looking for that EMI receiver that will measure to 1/100 of a dB. So I can report to a 1/10 of a dB in reports like I'm asked to.
Michael Sundstrom OHD / TREQ Dallas Electronic Lab Analist, EMC Lead 2170 French Settelment Rd, Suite B Dallas, Texas 75212 (214) 579 6312 From: Ken Javor [mailto:[email protected]] Sent: Wednesday, August 11, 2010 11:59 AM To: [email protected] Subject: Re: [PSES] Calibration supplier for signal generator with pulse modulation This gets back to Mr. Walton's differentiation between EMI testing and calibration laboratories. Clearly modulation, measured with an o'scope, can be measured to the tolerances available from the o'scope. That's plenty good enough. It strains credulity that there is one brand of scope that would give sloppier results making it easier to pass a test. The essence of what Mr. Walton and I are saying is well-expressed by the rules for using significant digits: You don't get four digit accuracy as the result of computations using two digit accuracy inputs. EMI limits are quite arbitrary; trying to meet them with accuracy exceeding the limit placement process is unnecessary. As stated earlier, the only reason for MU control is on the basic facility chambers/OATS so that there is some repeatability from facility to facility, and so that it isn't easier to pass at one facility than another. Anything beyond that is superfluous and an unnecessary expense. Regarding the example of the cable at 10 GHz. The MIL-STD-461 measurement system integrity check does indeed check that the cable is properly accounted for in terms of attenuation. Mr. Demirci is correct that the signal generator can be expected to be a better match to the cable than is the actual antenna used. However, to the limits of accuracy required for EMI testing, the antenna factor calibration takes care of the mismatch between antenna and cable, since the antenna is calibrated in a 50 Ohm system (albeit likely using pads between antenna and cable for calibration). If further accuracy is desired, most manufacturers provide vswr characteristics for their antennas. Fear isn't the issue. The issue is a misapplication of a process where it isn't required, and the patina of precision and accuracy this dishonestly bestows on an inherently inaccurate and imprecise discipline. Ken Javor Phone: (256) 650-5261 > From: Deniz Demirci <[email protected]> > Date: Wed, 11 Aug 2010 08:35:06 -0700 > To: Untitled <[email protected]> > Conversation: Calibration supplier for signal generator with pulse modulation > 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 > > > > -----Original Message----- > From: [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. > > 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. 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]>
