[volt-nuts] Voltage Reference Mini-Oven

[WarrenS]

#7) And the greatest solutions of all to reduces any drift caused by the 
OpAmp, is the small three terminal voltage reference used by Fluke.

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Warren Posted:
>
> I did not forget about the opamp, It need not be a limiting factor, which 
> is why I did not include it in MY count.
> True, it does need to be included in the basic "careful analog design 
> considerations", and for many designs I've seen it can be a major source 
> of error.
> There are many options to insure it is not a problem.
> Which one or ones are used depends on what is being made, ones skill 
> level, and the amount of time and money available.
>
>
> 1) Lots of choices for selecting a better opamp.
>
> 2) Many opamps can be zero TC using there offset adjustment, A very OLD 
> trick.
>
> 3) In the 6.2 volt version the effect of the op amp's offset is down 
> about 100 to 1 so it is NOT critical
> 1uv change at the op amp causes a 0.002 PPM change at the 6.2 volt zener.
>
> 4) IN the manual A-Cal 10 volt version, the error of the opamp is removed 
> completely by using the Manual A-Cal method.
>
> 5) The effect of the opamp's TC drift can be zero out (over a limited 
> temperature range)  at the same time the Zener is Zero TCed, by changing 
> the current thru the Zener .
>
> 6) And there are other less simple solutions to insure that the OpAmp does 
> not become a critical part when building a precision voltage reference.
>
> ws
>
> *********************
>>m k m1k3k1 at hotmail.com  wrote:
>
>>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
>>
>> 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
>>
>
>