Summary before teardown
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- The years of release and stop are estimate. Correct me if anyone know the accurate.
- Oven: small dot for chip level, large for board level
- There are evidents indicating that the voltage of most LTZ1000 and LTFLU-1 go down with time while SZA263 go up.
- The order of the teardown is roughly chronological
- The order on the list is according to the annual drift(and the time of release of same)
- The teardown will focus to the most important part: the 7V reference and the 7V to 10V conversion.
- Of course I don't have the teardowns of all listed(the list is not complete on its own). If anyone has, contribute.
- There is no release of new voltage standard for sometimes now, until recently by ADCMT, 'The highest performance 6900 in the world':
http://www.adcmt.com/news/press/press-2015/press20150624.html
Fluke 731A![](https://www.eevblog.com/forum/metrology/teardown-voltage-standards/?action=dlattach;attach=211481;image)
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One of the basic circuit.
If delete R3 and R4, connect neg input of the opamp to base of the refamp, then we get the simplest refamp circuit.
Fluke 731B![](https://www.eevblog.com/forum/metrology/teardown-voltage-standards/?action=dlattach;attach=211503;image)
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There are three major modifications compare to 731A
- output current limiting circuitry added
- use hermetic WW. Those WW became widely used by Fluke later
- use SZA263 as refamp. This refamp became widely used by Fluke later
Fluke 732A(See attachment)
There are some modifications compare to 731B
- board ovenized.
- use lead-acid batteries instead of NiCad.
- small-sized hermetic WW were used
- refamp protected by Q5(for later version of LTFLU-1, the protection is build-in)
- formalize the output as 'series pass'
- use 'binary' scheme on major part of the 10V adjustment, but not all.
The basic circuitry is not changed even for the designator