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

2017-03-13 Thread Randy Evans 
FYI, I bought two of these used 3458A reference boards for $85 each a few
years ago and they both experience noise bursts.  I plan on replacing the
LTZ1000 chips on them (sometime in the near future).

Randy Evans
AE6YG

On Sun, Mar 12, 2017 at 10:53 AM, m k  wrote:

>
>
> On 12/03/17 17:27, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> > On Sun, 12 Mar 2017 at 17:03, Frank Stellmach <
> frank.stellm...@freenet.de>
> > 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.
> >
> >
> >
> >
> The suspicion is that they may be genuine, but were rejects because of
> noise bursts. I bought one a while ago, but still not sure of its long term
> stability.
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Re: [volt-nuts] Short term "standard" cell?

2017-03-13 Thread m k 


On 12/03/17 17:27, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> 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.
>
>
>
>
The suspicion is that they may be genuine, but were rejects because of noise 
bursts. I bought one a while ago, but still not sure of its long term 
stability.
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[volt-nuts] Short term "standard" cell?

2017-03-12 Thread 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] Short term "standard" cell?

2017-03-12 Thread 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?

2017-03-12 Thread 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?

2017-03-11 Thread David 
How do silver oxide cells compare to mercury cells for voltage
stability?  When I last looked into this, I concluded that there were
two different silver oxide chemistries with a slight variation in
voltage between them.

On Sat, 11 Mar 2017 09:21:02 -0800, you wrote:

>Hi Chris:
>
>I think it was my Heathkit VTVM that said to get a fresh AA battery and use it 
>as a 1.52 Volt standard to calibrate the 
>meter. An even better way was to use a Mercury coin cell since they were 1.35 
>volts and very stable.  They were used for 
>light meters and voltage references because of the very flat discharge curve.
>
>But when you are looking for many more digits of accuracy/precision then a 
>battery may not be the best choice since 
>pretty much everything will cause a variation.   Maybe in order of importance: 
>temperature, atmospheric pressure, 
>humidity, impedance of measuring equipment, 
>
>There are a few low cost voltage standards available where the maker has an HP 
>3458.  For example by Geller and Malone:
>http://www.prc68.com/I/MTE.shtml#DCVR
>
>The care and feeding of chemical standard cells is such a pain and they are 
>inferior to the modern electronic standards 
>so they have become obsolete.  The label on my Eppley shows 5 digits (4 
>printed and the last hand written).  Note since 
>there's liquid involved there is also an "Up" direction.
>http://www.prc68.com/I/Eppley.html#Standard_Cell
>
>http://www.prc68.com/I/Fluke332B.html
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Re: [volt-nuts] Short term "standard" cell?

2017-03-11 Thread Brooke Clarke 

Hi Chris:

I think it was my Heathkit VTVM that said to get a fresh AA battery and use it as a 1.52 Volt standard to calibrate the 
meter. An even better way was to use a Mercury coin cell since they were 1.35 volts and very stable.  They were used for 
light meters and voltage references because of the very flat discharge curve.


But when you are looking for many more digits of accuracy/precision then a battery may not be the best choice since 
pretty much everything will cause a variation.   Maybe in order of importance: temperature, atmospheric pressure, 
humidity, impedance of measuring equipment, 


There are a few low cost voltage standards available where the maker has an HP 
3458.  For example by Geller and Malone:
http://www.prc68.com/I/MTE.shtml#DCVR

The care and feeding of chemical standard cells is such a pain and they are inferior to the modern electronic standards 
so they have become obsolete.  The label on my Eppley shows 5 digits (4 printed and the last hand written).  Note since 
there's liquid involved there is also an "Up" direction.

http://www.prc68.com/I/Eppley.html#Standard_Cell

http://www.prc68.com/I/Fluke332B.html

--
Have Fun,

Brooke Clarke, N6GCE
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

 Original Message 

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

2017-03-11 Thread kc9ieq via volt-nuts 
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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