[volt-nuts] A Fluke 732A

[Tom Knox]

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: volt-nuts at febo.com
> From: csteinmetz at yandex.com
> 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
> 
> 
> 
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