[volt-nuts] Traveling Standards

Thu Aug 25 20:35:33 UTC 2011

It is allready difficult to get a home made Vref stable in my own home.
I think it must be possible to do it but it must be build very stable
and oven controlled, in that case humidity will have less influence too
(I think)
No use of potentiometers. I use them in a homebuild one. To fine adjust
you do not need a screwdriver, it I can do it by tapping on the
cabinet ;-)

It is a nice plan (not for me, shipping will be no fun from here and I
have some references) That way you can make your own and calibrate it to
the know one.
I have a solartron 7601, I hook it up to my Westoncells and calibrate
the meter that way. (in the cal menu you can tell the meter what the
refernce voltage is you feeding the meter. I know the value of my cells
(worst case within 10uV) so this is a handy way. I then monitor my 332
or 735A with that meter so I know the correction.

Fred

Andreas Jahn schreef op do 25-08-2011 om 21:41 [+0200]:
> Hello Bob,
> 
> Im experimenting for some years with different references.
> For a traveling reference with 10ppm I would use a heated reference like a 
> LM399.
> You will find it in most of the serious 6,5 Digit Multimeters like HP34401A 
> or Keithley 2000.
> 
> I use them battery powered (NIMH-Cells) with a voltage stabilizer.
> (the heater voltage has some influence on the output voltage).
> 
> Time stability can be determined by building several of them pre-ageing for 
> some 1000 hours
> and then sorting out the extremes.
> Of my 2 LM399s  one is running pretty close to 2 LTZ1000A references
> the other (a desoldered part from a old measurement card) is drifting around 
> by +/-25uV.
> 
> For unheated references like a MAX6250 you will have to determine the 
> temperature
> very exactly. I use NTCs mounted directly at the ground pin of the Reference 
> to get
> nearly the temperature of the reference with a resolution of 0.1 K.
> When selecting some 3rd order compensated LT1027CCN8-5 references
> you will be able to find some with a low TC near room temperature.
> 
> But all plastic references suffer from 2 things:
> 
> first: mechanical stress will shift output voltage.
> So I solder only one pin directly to the pcb the others with thin wires
> So for a traveling reference you will run into trouble.
> 
> 2nd: when having calibrated the temperature out humidity will play a role.
> On my LT1027 the humidity change is around 0.4ppm for each per cent of 
> relative humidity.
> so for a change of 30% you will not get your 10ppm level.
> The problem is that the humidity shift has a long time constant. Which is 
> around 4 or 7 days
> with my 2 LT1027 references. So you will have to record the history.
> 
> With best regards
> 
> Andreas
> 
> 
> ----- Original Message ----- 
> From: "Bob Smither" <smither at c-c-i.com>
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Sent: Thursday, August 25, 2011 7:14 PM
> Subject: [volt-nuts] Traveling Standards
> 
> 
> > Fellow voltage aficionados ,
> >
> > If this has already been discussed - my apologies.  I could not find
> > this topic in the past several months of list archives.
> >
> > Like many of us, I have an ever growing collection of voltmeters and
> > related instruments.  Like the man with two clocks who is never sure of
> > the time, I now have enough volt meters to have doubts about all of them.
> >
> > So - I was wondering if those on this list with really good voltage
> > measurement capabilities would be willing to help those of us without.
> >
> > What I have in mind is creating a small voltage reference circuit based
> > on one of the many available IC references that is stable enough in both
> > time and temperature to use as a transfer standard.  I am thinking that
> > the actual voltage is not important, just the stability.  Using the ICs
> > that I am familiar with the actual reference voltage would be around 5,
> > 7, or 10 volts.  Said reference would be mailed to a willing list member
> > who would record his reading of the reference and mail it back.
> >
> > I don't have such a reference yet, but have breadboarded a couple and
> > the idea seems like it might work.
> >
> > My first objective would be to obtain a reference that I could use to
> > get all my meters to agree.  Since the best meters I have are an HP3455A
> > (best accuracy about 20 - 40 ppm, and only for 24 hours) and an ancient
> > (but very usable) Fluke 883AB (best accuracy is 100ppm), I would be very
> > happy to have a reference that I could trust to 10ppm.
> >
> > So - two questions for the list:
> >
> > 1.  Does this sound feasible?  Am I overlooking anything that would keep
> > me from being able to transfer a 10ppm known reference?
> >
> > 2.  Any list members that would be willing to help with this?  I
> > envision mailing a small package with the reference in it along with an
> > enclosed, postage paid, return box.  I am asking for a member that would
> > take the reference, apply power, let it warm up, record the room
> > temperature and the reference voltage to within 10ppm, and return it to
> > me.  If you prefer to respond off-list - smither at c-c-i.com.
> >
> > BTW - I live in Friendswood, Texas (near Houston).  Any fellow nutters
> > close enough that I could hand deliver the reference?
> >
> > Best regards,
> >
> > Bob Smither
> >
> >
> 
> 
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> 
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