Hello Reginald,
the LTZ100 has been discussed and investigated thoroughly, over on eevblog.
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/
https://www.eevblog.com/forum/metrology/the-ltflu-(aka-sza263)-reference-zener-diode-circuit/
There you'll find chip and assembly pictures of the LTZ1000 / A, LTFLU,
and SZA 263 as well.
A lot of speculation and investigation about the time, temperature (T.C.
trimming), and hysteretic drift can also be found there.
It's a very long thread, anyhow.
Spoiler: The LTZ1000A shows more hysteresis and also random dips, than
the LTZ1000.
Then I also can recommend John R. Pickerings famous patent to mitigate
hysteresis effects after temperature excursions.
The timely drift of the LTZ1000 is linearly affected by the oven
temperature in a quite predictable manner, as you already assumed.
This has already been investigated and quantified by P J Spreadbury in
1990 "The Ultra Zener .. is it a portable replacement for the Weston
cell?". This basic article I don't find any more on the net, but I have
it in my archive.
The same has been done for the SZA263 and the LTFLU chips inside the
732A/B references:
PREDICTABILITY OF SOLID STATE ZENER REFERENCES, by David Deaver, Fluke.
Myself, I have collected the relative drift data of 4 references, 2x
LTZ1000, 1x 1000A, 1x double SZA263, over about ten years. The first two
references have been running continuously over that time, the other two,
only when used, because these are sitting inside a 3458A, and a 5442A.
All their individual drift rates seem to confirm the mentioned papers.
Recently, about 2 years ago I started another 5 virgin LTZ1000s, nicely
showing the typical initial timely drift of < 2ppm/year @ 50°C.
If you are interested, let's discuss how to exchange these data.. I'm
very interested in a drift estimation model for these relative
measurements, equivalent to the Three Cornered Hat method of the time-nuts.
Frank
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