[volt-nuts] Voltage Reference Mini-Oven

Fri Sep 16 05:56:04 UTC 2011

Ok, i will look it up for you and mail you,  it is on my other computer.
http://www.pa4tim.nl/?p=2141 these are my cells. ( text is dutch but there is a Translate button on the right menubar)
My best cells changed about the same rate as you wrote. I have all calibrations from new upto theire retirement in 1988. Then the lab from that company was closed but it stayed there,  unpowered, on the same shelf until this year. The lab was , over he years, turned in to a climatized computerroom. Now they needed space so the still remainig calibration stuff ( including a 19 inch rack with Flukes) had to be destroyed.  A friend who workes there in a high function could not let that happen and did a lot of work to try and save as much as possible. Still a lot is distroyed, like precision resistor decades, the Fluke line compensator and lots of spare parts, but what is saved he brought to me. Besides the Guildline the Fluke 720, 750, 760, 731A, 535, 332, 8500 some HP stuff like a Hi- Z source meter, decade capacitor and sinewave generator and a Tek 576 curvetracer.

Fred PA4TIM

Op 16 sep. 2011 om 01:21 heeft zbigniew169 <zbigniew169 at gmail.com> het volgende geschreven:

> I would e grateful for a copy of such documentation.
> 
> By the way; Weston saturated standard cells are still in use in our polish
> equivalent of american NBS; they kept about 400 units in Glowny Urzad Miar
> in Warsaw.
> In 1937 modified Weston cell was build it has 11% Cd 15% Bi and remain Hg as
> amalgamate. It had 13 ppm tempo almoust 5 time less than original Weston
> cell. In 1964 Roger G. Bates wrote a paper regarding stability o a such
> secondary standard; the EFM of such cell was 1.0188 V at 25 Cel.deg., Six
> cells after 26 years changed their EMF average by 0.03 mV. Because I am
> biochemist, so electrochemisty was slightly close to my interest. Sometimes
> I am dreaming to build such a cell...
> 
> Best regards, from Warsaw,
> 
> 2011/9/16 Fred Schneider <pa4tim at gmail.com>
> 
>> I have the original guildline enclosure with schematic. There is an oven in
>> there and the circuit is rather straight forward using some tranistors.
>> Maybe you can use this as an example. The saturated cells must be hold at 30
>> degrees. They must kept vertical allways and viberation free. After moving
>> them arround they need about two weeks to stabilize and do not use a 10M
>> meter on them. Mine are from 1971 and still in very good shape.
>> 
>> Fred PA4TIM
>> 
>> Op 16 sep. 2011 om 00:03 heeft zbigniew169 <zbigniew169 at gmail.com> het
>> volgende geschreven:
>> 
>>> He I am Zbigniew W. Kaminski from Warsaw Poland. I was member-observer up
>> to
>>> this time. I am user of Prema 6040D 7 & 1/2 digits multimeter.
>>> 
>>> I would be appreciate if You will send some details concerning
>> construction
>>> of Your mini-oven. I need something similar for Weston saturated standard
>>> cell. In my case the stability must be even better than 0.1 Celsjus
>> degree,
>>> because of Weston temco in the range about 50 ppm. I think that in my
>>> project I should use patinium resistor rathen than termistor, because
>> it's
>>> much long term stable than termistor. Platinium element is much less
>>> sensitive to temperature, therefore the cuircuit  will be much
>> complicated.
>>> I am an owner of single Weston cell which stays in my lab during last 20
>>> years, and I am curious how stable it is.
>>> 
>>> 2011/9/15 WarrenS <warrensjmail-one at yahoo.com>
>>> 
>>>> 
>>>> It is well known that by changing the nominal operating current of a
>> 1N825
>>>> type reference diode, that its voltage turn over temperature point can
>> be
>>>> moved.
>>>> Usually the turn over temperature can be set to the nominal operating
>>>> temperature,  there by giving a Zero TC reference voltage over a limited
>>>> temperature range.
>>>> For the parts I'm testing, the voltage changes less than 0.1 PPM with a
>> 5
>>>> deg F temperature variation, and 1PPM over a 20 deg F range when the
>> zero TC
>>>> current is set for room temperature.
>>>> Not bad, but being an extreme Volt Nut, I always want to do better.
>>>> 
>>>> Two ways to make it better, Add an X^2 (second order) temperature
>>>> compensator or put the reference in an oven.
>>>> 
>>>> What I did was make a very simple Mini-Oven using an 1N825, a glass
>>>> thermister & a 1/4 resistor,
>>>> all heat shrink together  in a small package about the size of a 1 watt
>>>> resistor.
>>>> Now by Appling about 1/8 W nominal power to the resistor from a simple
>>>> temperature controller, the thermistor can be held at a constant
>>>> Temperature.
>>>> This allows setting it up so that normal temperature changes have true
>> ZERO
>>>> effect on the zero TCed zener voltage.
>>>> Next thing I want to make is a simple times 8/5 digital gain amp so that
>>>> the gain resistors will have no effect when amplifying the 6.25x volt
>> zener
>>>> up to 10.000000 Volts.
>>>> (or times 10/7 for use with other types of voltage references)
>>>> 
>>>> ws
>>>> 
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>>> 
>>> 
>>> 
>>> --
>>> Zbyszek
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> 
> 
> 
> -- 
> Zbyszek
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