Hi Charles; Perhaps you are correct. I work in the research area of metrology. I just assumed a number of labs have multi-cell standards like the Wavetek 4910 or Fluke 7010s or 734A and if recently cal'ed they should be more then capable of calibrating a 732A for home use. True the documentation is not there but does that matter in a majority of Volt-Nut applications. And if you ship VS local calibration you may have documentation stating lower uncertainty, but a local cal may actually be more accurate. I also think the number of JJA's is larger then most think. Just this week a couple labs added 10 Volt Programmable Josephson voltage standards capable of producing AC and DC voltages. http://www.wmi.badw.de/teaching/Lecturenotes/AS/AS2013_Chapter6_Slides.pdf Again my point is do you need the documentation, and if not there are alternatives. Especially in a non temperature and humidity controlled environment that will affect both your standards and DUT. Don't get me wrong I am all about documentation and repeatability but not everyone needs or has the $300,000+ for a 10 Volt Programmable Josephson voltage standard. Again I float the idea of Volt-Nuts creating their own network to compare standards locally after a recent calibration.
Thomas Knox > Date: Sun, 9 Mar 2014 04:18:07 -0400 > To: [email protected] > From: [email protected] > Subject: Re: [volt-nuts] A Fluke 732A > > Thomas wrote: > > >You may find a local lab with less accreditation charging half then > >price that is fully capable of of calibrating to the limit of the > >732A but cannot document to the level of a primary standards lab. > > Very, very doubtful. Very few cal labs have a 732A or equivalent, > much less anything better. The only labs with *better* uncertainty > than a properly working 732A are those with JJAs. If you look at the > NIST NVLAP accreditation list and run down it, looking at each lab's > "Scope of Accreditation," you will only find 4 or 5 labs on the list > with better uncertainty than a properly working 732A (I'm not sure > you will find *any* on the A2LA accreditation list, but I haven't run > down it lately). The Fluke cal lab and the Los Alamos and Sandia > standards labs are three of those four or five (plus, of course, NIST > itself). Boeing (Seattle) is another. Interestingly, you will find > many labs that are rigorously accredited to only .003% or so (30 > ppm), because the best voltage standard they own is an HP 34401A > DMM. Even the HP Houston cal lab is certified to only 0.0007%, or 7 > ppm (using a Fluke 5700A calibrator). > > >Yes a 1-2PPM Cals is not as sexy as a .1PPM Cal but in the real > >world the results when used in you home lab my be the same. > > To get a calibration with an uncertainty of 1 or 2 ppm, the lab would > need, at a minimum, a 732A or 732B to compare with (as well as a 720A > Kelvin-Varley bridge, or equivalent, and a null meter that can > reliably be read to 0.1uV, if you want the calibration certified to 1 > or 2 ppm at voltages other than 10v). I don't think there are even > ten labs on the NVLAP list that claim to have a 732A or B (the > equipment used is often listed in the "remarks" column). > > It does not take long to run down the whole list -- it's a short list > and the "Scope of Accreditation" documents load fast. I recommend > the exercise, to get a feel for what's out there. Same with the A2LA > list, but it is longer and not as well organized and it usually takes > 2 or 3 steps (running off to the lab's site) to get to the "Scope of > Accreditation." (If you look at A2LA labs, pay attention to the lab > class and only look at "open" commercial labs -- the non-commercial > ones do not take in third-party calibration work.) > > A list of NVLAP-accredited labs can be found here: > > <http://ts.nist.gov/standards/scopes/dclow.htm> > > There seems to be this myth of cal labs that can do just as good a > job as the expensive, accredited labs, but don't bother with > accreditation so they are much cheaper. First, note that to do a job > as good as an expensive, accredited lab, any lab would have to do the > same documentation as the accredited lab. If there is no > documentation, there can be no claim as to the calibration's > uncertainty. Having done the documentation, which is the > time-consuming (thus, expensive) part, no commercial cal lab is going > to do without the accreditation (which is nothing but an audit of the > lab's procedures and documentation). I stress again -- if there is > no documentation, there can be no claim as to the uncertainty of a > lab's work. And since the documentation is the part that contributes > most to the cost, there simply are not any commercial labs that can > claim to have uncertainties on par with accredited cal labs, but are > not themselves accredited. > > Best regards, > > Charles > > > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
