[volt-nuts] Voltage Reference Mini-Oven

[m k]

Dont forget that you can have 1uV per C just from the opamp offset voltage. That makes three critical parts.

> From: warrensjmail-one at yahoo.com
> To: volt-nuts at febo.com
> Date: Thu, 15 Sep 2011 15:29:55 -0700
> Subject: Re: [volt-nuts] Voltage Reference Mini-Oven
> 
> 
> 
> Using a circuit similar to
> http://www.febo.com/pipermail/volt-nuts/attachments/20110903/b7da2eca/attachment-0001.gif
> 
> A 10 reference standard can be built so that there are only TWO really 
> critical parts that limit its performance.
> The reference  Zener and the 5/3 gain matched resistors.
> The rest just takes careful analog design considerations.
> The way I hope to remove the resistor matching limitation is to do that part 
> digital.
> 
> As far as more details on the Mini-Oven, nothing else to say. It is just 
> three small parts "Taped" together.
> One is the device to be controlled, one is the heater and the last is the 
> temperature sensor. Same as any oven, just smaller.
> I don't know how this mini-oven would apply to a standard cell.
> 
> ws
> 
> *******************
> zbigniew169 wrote:
> I would be appreciate if You will send some details concerning construction 
> of Your mini-oven.
> 
> *******************
> m k m1k3k1 at hotmail.com wrote
> 
> Hi Warren,
> 
> That does seem a very simple way to get the diode at a steady temp, but then 
> you need to keep the rest steady to stop all the other uncertainties 
> swamping the nice steady diode you have just created.
> 
> ******************
> 
> > From: 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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> 
> 
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