[volt-nuts] Traveling Standards

Wed Aug 31 18:12:47 UTC 2011

Most Fluke high-precision units used a Motorola buried zener + transistor reference in a metal can -- I forget the Moto part number, but they are pretty much unobtanium now. Units using this reference include, from personal knowledge, the 731B, 732A, 335B/C/D, 5440A/B, 8505/8506, 510A. In some units the reference device is in an oven, in others, notably the 8505/8506 and 510A, they are just at the internal case temperature, but all cleverly use the transistor to provide first-order temp comp.

When ovenized together with the various voltage dividers, the part is very, very good, as shown by the 732A and 5440A/B, which can hold sub-ppm accuracies over periods of weeks to months. I personally found the 732As to be stable through many power-off/-on cycles, so I didn't use the batteries. The need to ship them hot is unnecessary, in my opinion, if 1ppm stability/accuracy is the goal. Don't know about the 731B.

Demian's offer to ship 731Bs around is very helpful, and would be a great adjunct to the original proposal. This sharing of standards is something that I've wanted to see for quite a while, but when I owned the two 732As and 5440B, that just wasn't practical, and shipping high-res DMMs around didn't make much sense either.

Many thanks to Bob for carefully evaluating design decisions and for embarking on this project. Now if someone could just send a 0.1ppm 10k resistor around, too, life would be great.

Dick Moore

On Aug 31, 2011, at 5:00 AM, volt-nuts-request at febo.com wrote:

> 
> Message: 4
> Date: Tue, 30 Aug 2011 18:58:26 -0700
> From: "Demian Martin" <demianm_1 at yahoo.com>
> To: "'Bob Smither'" <smither at c-c-i.com>
> Cc: volt-nuts at febo.com
> Subject: Re: [volt-nuts] Traveling Standards
> Message-ID: <00ed01cc6781$792a01e0$6b7e05a0$@com>
> Content-Type: text/plain;	charset="us-ascii"
> 
> Bob:
> To make a real PPM standard has so many technique pitfalls that it may be a
> really frustrating experience. The late Jim Willians wrote something about
> this in a article on checking precision DAC's. Even with the best stuff a
> real climate controlled environment is more than most of us are able to do.
> If you look at the manuals and construction efforts for these things there
> is a lot of experience in details that's hard to just copy. Even the circuit
> layouts and managing the thermocouples in all the connections is not
> trivial. Here is a good starting point for understanding it:
> http://cds.linear.com/docs/Application%20Note/an74f.pdf 
> 
> Here is an alternate offer I'll make. I just checked and I have 3 Fluke
> 731b's that I'll be happy to provide for travelling standards. They are
> doing nothing but occupying space on a shelf for now. I also have a 732A, a
> Prema DVM and a Fluke 8506a, all of which use LTZ1000 references. Those
> three have tracked each other within 50 ppm for the last 5 years without
> attention. Probably none have been calibrated in the 21'st century and only
> the Flukes have a common origin. Prema makes their own JJ standards. I'll
> fire up the 3 731b's and check them against the trio to get things started.
> I'll get them boxed in a nice reusable shipping case if you will pick up the
> shipping to start this off. They may need service (the batteries are
> probably shot by now), I'll leave that to you. I don't have time for more
> with my "day" job.
> 
> If this is interesting send me a note directly and I'll get it started.
>         Demian
> 
> Date: Mon, 29 Aug 2011 22:52:24 -0500
> From: Bob Smither <smither at c-c-i.com>
> To: Discussion of precise voltage measurement <volt-nuts at febo.com>
> Subject: Re: [volt-nuts] Traveling Standards
> Message-ID: <4E5C5E78.6020109 at c-c-i.com>
> Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"
> 
> Fellow Voltage Fans,
> 
> To review - I would like to have a lab standard here that I can trust to 
> 10 ppm or better to use to calibrate my expanding collection of 
> voltmeters.  I have proposed to built a portable standard that I will 
> ship to participating volt nuts on this list who will record their 
> readings of the standard and share those readings with the list.
> 
> I have designed a Traveling Standard that incorporates two references 
> (an LM199AH and a MAX6350E) along with an LM34 to measure the 
> temperature of the MAX6350 (the LM34 is glued to the top of the MAX6350.
> 
> The schematic is attached to this page:
> 
>   http://www.c-c-i.com/TS
> 
> Following suggestions on this list (thanks!) I will use an external 
> "wall wart" supply for the input 24 Volts.  This reduces any shift 
> caused by the line regulation of the three terminal regulator.
> 
> My design notes are included on the above page.
> 
> I have constructed a bread board of the circuit on a plugboard.  I will 
> move the circuit to a printed circuit version after some testing.
> 
> Some preliminary readings from the breadboard of the LM199AH part are 
> noted on this page:
> 
>   http://c-c-i.com/node/121
> 
> Note that these readings are taken with an HP3455A which has not been 
> calibrated since I bought it new.  I would expect the accuracy to be no 
> better than .01% and may be much worse.
> 
> My plan is to mount the printed circuit board version in a short length 
> of 2" PVC pipe with connectors for the three outputs.
> 
> After the printed circuit board version is aged some it will be ready to 
> ship.
> 
> Are there any more on the list that would be willing to make a 
> measurement of the Traveling Standard?
> 
> I will collect the readings that we collectively get on the TS and make 
> them available to the list.  I anticipate that with some experience we 
> can all benefit from having this TS well aged and with a well known 
> output voltage.
> 
> I will handle the shipping - all I ask is that you take careful 
> measurements and provide them to me, then return the unit.
> 
> Thanks!
> 
> ****************
> 
> 
> 
> 
> ------------------------------
> 
> Message: 5
> Date: Wed, 31 Aug 2011 01:24:25 -0400
> From: "Charles P. Steinmetz" <charles_steinmetz at lavabit.com>
> To: Discussion of precise voltage measurement <volt-nuts at febo.com>
> Subject: Re: [volt-nuts] Traveling Standards
> Message-ID: <20110831052432.5D80111BCE2 at karen.lavabit.com>
> Content-Type: text/plain; charset="us-ascii"; format=flowed
> 
> Demian wrote:
> 
>> To make a real PPM standard has so many technique pitfalls that it may be a
>> really frustrating experience.  *   *   *
>> If you look at the manuals and construction efforts for these things there
>> is a lot of experience in details that's hard to just copy. Even the circuit
>> layouts and managing the thermocouples in all the connections is not
>> trivial. Here is a good starting point for understanding it:
>> http://cds.linear.com/docs/Application%20Note/an74f.pdf
> 
> Linear Technology's Application Notes AN42, AN82, AN86, and AN124 
> also contain valuable information on the topic.  The Linear 
> Technology Design Note DN229 discusses reference hysteresis, 
> including the thermal shock from soldering.
> 
>> I also have a 732A, a Prema DVM and a Fluke 8506a, all of which use 
>> LTZ1000 references.
> 
> I believe the 732A uses a common-substrate zener + transistor in an 
> oven assembly that contains the whole reference circuit.
> 
> Best regards,
> 
> Charles
> 
> 
> 
> 
> 
> 
> 
> 
> 
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