[volt-nuts] Voltage Reference Mini-Oven

Fred Schneider pa4tim at gmail.com
Thu Sep 15 22:30:07 UTC 2011


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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