Hi guys, Sorry for the "late" response, been pretty busy lately.
I think we fool ourselves a little with this calibration stuff. I agree with Brian's statement that much of this boils down to going through the motions to satisfy a process, whether it's ISO, A2LA, NVLAP ... I'm not against calibration or "the process", I just think that "calibration worship" can be taken to an extreme. I can understand that everyone is scared of equipment going out of cal after it has been put back into "rough and tumble" service. But, I wonder if anybody thinks about the fact that the roughest tumbling that the equipment will see all year probably occurs while the equipment is being shipped back to you after calibration. (Handheld equipment is probably an exception to this statement) Also, it probably undergoes more thermal stress in a shipping van or aircraft cargo hold than it does all year in a climate controlled lab. The equipment also undergoes more of other kinds of "abuse" than normal during the calibration itself. Many times fasteners are un-fastened, connectors are un-connected, socketed chips are un-socketed :-) Modern solid state electronics, in some instances, can run a lifetime if used within their specifications in a nice climate controlled lab as long as they aren't dropped or shaken or tampered with. Once you ship them away, have them opened up, have them shipped back ... No calibration in the world will save us from Murphy's law and the Samsonite Guerilla (if you can remember who that is, you're my 70's trivia lifeline for "who wants to be a millionaire!) I have a small in-house lab with just a few pieces of equipment. As such, my equipment has undergone a total of 15 cal "events". (approx 5 pieces of equipment times 3 years). Out of 15 cal events, I have had equipment come back in worse condition twice (one time, my EFT generator came back non-operational). Calibration is necessary but it isn't the be all and end all. It doesn't preclude or replace common sense. I don't see anything wrong with guys at test labs taking a freshly calibrated instrument and checking the other equipment in the lab against it or using it to calibrate other equipment. If they apply common sense, the act of checking the calibrated instrument against a group of unknowns helps find whether the uncalibrated (or not-so-recently calibrated) instruments are off and also checks to see if the calibrated instrument has indeed been calibrated correctly. It also checks the calibrated instrument to see if it came back fully functional. The idea of sending everything out for cal at once and then checking instruments against each other when it comes back would be nice, but I don't think a lab could afford to be out of business for a couple of weeks waiting for cal. No calibration at all is a bad idea, but trusting calibration without a sanity check can be just as bad. Combining well placed and timed calibrations with sanity checks is, in my humble opinion, the most effective solution. Catch ya's later. Chris Maxwell Design Engineer NetTest 6 Rhoads Drive, Building 4 Utica,NY 13502 email: chris.maxw...@gnnettest.com phone: 315-266-5128 fax: 315-797-8024 > -----Original Message----- > From: Brian O'Connell [SMTP:boconn...@t-yuden.com] > Sent: Tuesday, February 27, 2001 2:20 PM > To: 'emc-p...@ieee.org' > Subject: RE: Calibration of test equipment > > > >As soon as a "reference" device goes out into the general lab population, > >it's subject to physical and electrical abuse. It may take you quite a > while > >to notice that some device has just one attenuator range that's damaged > (but > >not completely blown, just shifted a bit). > > > >As far as I'm concerned, once a device hits the general lab population, > it's > >no more reliable than anything else out there. (Although I may put a bit > >more faith in the most recently calibrated item, simply since it's likely > to > >have had the least exposure to trouble.) > > > >Regards, > >Ed > > Another P.O.V. : > > Anecdotal experience: at the last three companies I've worked, the biggest > single source of test equipment/instrumentation failure has been directly > from the Calibration Process. When a fully functional instrument is > submitted for calibration, and a device is returned that has no (or > severly > decreased functionality), it valid to assume that the calibration process > does not always insure measurement integrity, nor add value to the > development lab receiving the calibration services. It serves The Process > (ISO 9k-speak). > > Brian O'Connell > Taiyo Yuden (USA), Inc. > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > majord...@ieee.org > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: pstc_ad...@garretson.org > Dave Heald davehe...@mediaone.net > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > All emc-pstc postings are archived and searchable on the web at: > http://www.rcic.com/ click on "Virtual Conference Hall," ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
