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 >

#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. ****************** 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 >> > >