[volt-nuts] Short term "standard" cell?

[Frank Stellmach]

>There are a number of reference boards supposedly removed from 3458As 
on eBay.
>Assuming they are non counterfeit (not necessarily a valid assumption 
for items on eBay), how easy would they be to integrate into a box to 
make a stable reference?
>The LTZ1000A chip is about $50 new, but to make a stable reference you 
need quite expensive resistors, so a used 3458A reference is attractive.
>But I don't know if problems making low thermal EMF joints might 
totally ruin the potential performance.



David,

these 3458A reference boards are also quite expensive, they sell for 
about 150-200$.
They may have problems with high drift and high noise, that's why they 
show up on the 2nd hand market.


It's been demonstrated that it's possible to easily build such stable 
references with an 40$ LTZ1000 (non A), and 5 precision wire wound 
resistors ( <10$ each), and an LT1013, so BOM cost < 100$.


The emfs are not the biggest problem, can be mitigated by proper design 
and thermal shielding.


The biggest problem with the 3458A and the DIY references is to amplify 
precisely to around 10V.


These resistive dividers usually drift too much over time and 
temperature to give reasonably stable 10V references.


I dfesigned an auto-calibration-divider, similar to the 720As 1st 
decade,  which amplifies the 7,15V exactly by 10/7, which is mostly 
sufficient to calibrate the 10V range of a DMM.


Other solutions require these ultra- expensive Vishay hermetically 
sealed, oil filled VHP resistors, which easily double the BOM cost.


Frank

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Re: [volt-nuts] volt-nuts Digest, Vol 91, Issue 1

[Dan Kemppainen]

I'd avoid alkaline batteries. I picked up a high resolution data logger to 
monitor some long term voltages, and as it had extra channels I hooked up a 
battery to it. The battery was meant as a sanity check. As it turned out, the 
battery made a really nice thermometer! 

It turns out the reference I intended to monitor was much more stable than the 
battery.

But, maybe a battery in an oven may work...

Dan


On March 11, 2017 12:00:02 PM EST, volt-nuts-requ...@febo.com wrote:
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>   1. Short term "standard" cell? (kc9ieq)
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>--
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>Message: 1
>Date: Sat, 11 Mar 2017 10:51:52 -0600
>From: kc9ieq 
>To: Discussion of precise voltage measurement 
>Subject: [volt-nuts] Short term "standard" cell?
>Message-ID: 
>Content-Type: text/plain; charset=utf-8
>
>In preparation of (hopefully!) Getting that fluke 332A running and
>sticker shock of what the 732A and similar references go for, I wonder
>about normal, every day alkaline or lithium batteries and their short
>term stability.  
>Here's the half baked idea.  A fresh, standard 1.5V, or 3V lithium,
>alkaline, or silver oxide button cell battery, or even an AA sized
>cell, measured by someone/some place with a known accurate precision
>meter.  Invisioning 6 or so decimal places.  Could that cell then be
>shipped, and used as a reference in another altitude?  I haven't spent
>a ton of time looking, but haven't yet found anything on the web about
>stability of these types of batteries.
>Regards, Chris 
>
>
>Sent from my SMRTphone
>
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Re: [volt-nuts] Short term "standard" cell?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On Sun, 12 Mar 2017 at 17:03, Frank Stellmach 
wrote:

> Hi Chris,
>
>
>
> Therefore,  instead of poking around with these mediocre 10V
> "references", I'd look for a possibility to get access to a 3458A, maybe
> there's a friendly volt-nuts nearby.
>
> Frank
>

There are a number of reference boards supposedly removed from 3458As on
eBay. Assuming they are non counterfeit (not necessarily a valid assumption
for items on eBay), how easy would they be to integrate into a box to make
a stable reference?

The LTZ1000A chip is about $50 new, but to make a stable reference you need
quite expensive resistors, so a used 3458A reference is attractive. But I
don't know if problems making low thermal EMF joints might totally ruin the
potential performance.




-- 
Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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Re: [volt-nuts] Short term "standard" cell?

[Hendrik]

The navel is not just for collecting lint, you can also temp stabilize a 
silver or mercury button cell there. Or in the armpit. Or up in other 
cavities of the body. Preferrably measure very quick or at least at the 
same time of day.


Hendrik


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[volt-nuts] Short term "standard" cell?

[Frank Stellmach]

Hi Chris,

I remember getting an 1.5V mercury cell with a 4 1/2 digit DVM kit, so 
that's about the level of stability you can achieve with such a battery.


Alcaline batteries, and so on, forget about it.

For a Fluke 332A, you need on the order of 5ppm uncertainty for a proper 
adjustment of the 10V range, so all other "references" are just 
gimmicks. Drift and T.C. are way too high.


The only reasonable reference from Joe Geller (about 5ppm uncertainty, 
T.C. trimmed to near zero) is long gone, that's pityful.


Anyhow, a 10V reference alone is also not sufficient for calibration. In 
general, you'll need linearity adjustment (requires a Kelvin Varley 
divider like the 720A, or a 3458A ), and 100V and 1kV range adjustment 
require a Reference Divider like the 752A, or again a 3458A.


Therefore,  instead of poking around with these mediocre 10V 
"references", I'd look for a possibility to get access to a 3458A, maybe 
there's a friendly volt-nuts nearby.


Frank


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Re: [volt-nuts] Short term "standard" cell?

[Charles Steinmetz]

Brooke wrote:


There are a few low cost voltage standards available where the maker has
an HP 3458.  For example by Geller


Geller has been gone as a supplier since 2013 (most of the web site is 
still up as an archive, but he is no longer selling the voltage 
"references").


There are a few low-ish cost "references" or "standards" advertised on 
ebay.  An annotated schematic of one NOT to get (the Calibratory D-105 
"2ppm Voltage Reference") can be found here:




Best regards,

Charles


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