[volt-nuts] Traveling Standards

[John Devereux]

"Andreas Jahn" <Andreas_-_Jahn at t-online.de> writes:

Hi Andreas,

In view of your comments, shouldn't we be looking at a LTZ1000 for the
"traveller"? It's relatively expensive but not out of reach I would
think.

John

Shouldn't 

> 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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-- 

John Devereux