I have seen equipment that have drifted just out of tolerance but otherwise function perfectly. _______________________________________ _____________________________________________
Ralph McDiarmid | Schneider Electric | Renewable Energies Business | CANADA | From: Ken Javor <ken.ja...@emccompliance.com> To: EMC-PSTC@LISTSERV.IEEE.ORG List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: 01/06/2010 07:12 AM Subject: Re: [PSES] Equipment back from Calibration ________________________________ Mr. Price is giving a lot of good advice, but I'm going to ask a question that no one is either contemplating, or willing to ask. If Mr. Price, or anyone else doing such a detailed incoming inspection were to do it before sending equipment out for calibration, and if the device were to be found satisfactory, then what possible reason, other than regulatory compliance, can there be for shipping the equipment off to the calibration facility? Ken Javor Phone: (256) 650-5261 > From: "Price, Edward" <ed.pr...@cubic.com> > Date: Wed, 6 Jan 2010 06:06:01 -0800 > To: <emc-p...@ieee.org> > Conversation: Equipment back from Calibration > Subject: RE: Equipment back from Calibration > > I'd like to add a pessimistic note to John's example. In the case of a > complicated device, like a spectrum analyzer, coming back from > "calibration", we need to remember the limits of the effort that we > imposed by what we were willing to pay to that calibration lab. > > When we get that analyzer back, we expect the amplitude and frequency > accuracy to be within the manufacturer's original specs. But what about > other things, like internal spurious signals, or bandwidths (resolution > & video),or sweep linearity, or those lesser-used detector functions? > And what about those dozen or so odd little outputs on the rear panel > (the Volts/dB, the Volts/MHz, the reference oscillator output)? And does > the software actually report the same data that is displayed locally on > the analyzer? > > Probably just like you, I don't pay for what would be a huge effort. > (Actually, I don't pay at all, since my company has an internal > calibration lab. OTOH, I can't threaten to take my business elsewhere, > so...) However, when I get an important and complicated instrument back > from my Metrology, I don't trust it at all until I can get around to > personally verifying the basic performance. I check amplitude and > frequency accuracy, verify the front panel calibrator output, do a noise > floor scan, and compare what the software tells me to what I see on the > display. If I were normally using any of those rear-panel IO ports, I > would also spot-check those too. Takes maybe 3 hours, so you can do it > during lunchtime. > > For simple devices, like an antenna, I always make a plot of the > reported antenna factor, gain, and VSWR. I look for anything that looks > odd (strange deviations or periodic perturbations; it's difficult to > define "strange"). Then I compare the new data to the same data from the > previous periodic calibration, again looking for anomalies (data offsets > or new small resonances). More than a few times, I have found mistakes > in the data. My lab (for antennas, I use an independent lab) knows I > will look closely at their data, so I think that gives them an incentive > to review it better themselves. <g> Just as an example, I had a previous > lab that measured antenna gain, and then calculated the antenna factor. > Their computer spit out two beautiful columns of detailed data. Real > nice, until I ran a few pairs by hand, and found that the computer was > incorrectly programmed, yielding a couple of dB error in each pair. > Beautiful data, and beautifully wrong. > > Ed Price > ed.pr...@cubic.com WB6WSN > NARTE Certified EMC Engineer > Electromagnetic Compatibility Lab > Cubic Defense Applications > San Diego, CA USA > 858-505-2780 > Military & Avionics EMC Is Our Specialty > > >> -----Original Message----- >> From: emc-p...@ieee.org [mailto:emc-p...@ieee.org <mailto:emc-p...@ieee.org> ] On Behalf Of John >> Woodgate >> Sent: Wednesday, January 06, 2010 5:17 AM >> To: emc-p...@ieee.org >> Subject: Re: Equipment back from Calibration >> >> In message >> <2a93eb061001060416k2adb43d1l21a7c0fa96e0...@mail.gmail.com>, >> dated Wed, 6 Jan 2010, Grace Lin <graceli...@gmail.com> writes: >> >>> What is the procedure to check equipment back from calibration? I >>> assume the equipment is fine after calibration. Is this assumption >>> acceptable (from laboratory accreditation point of view)? >> >> I don't know the official view, but I have personal experience of >> equipment not working correctly due to changes in transit after >> calibration. It's probably much less common now. >> >> If the equipment has a self-calibration feature, run it. If it > doesn't, >> keep a simple test object for checking it. For example, for a spectrum >> analyser I use a simple passive band-pass filter (single tuned circuit >> - >> keep it as simple, and thus reliable, as possible). If it measures as > I >> expect, I assume that the SA is working correctly. >> -- >> OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk >> John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK >> I should be disillusioned, but it's not worth the effort. > > - > ---------------------------------------------------------------- > 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 <emc-p...@ieee.org> 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 <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com>
