Dr. Frank,
Do you have a way to test your LTZ's against something other than one 3458a? I see that you've produced data, but normally we would never just use another single LTZ to measure against (aka 3458a). For instance if you measure an LTZ circuit with just a single 3458a, in essence you're comparing only the drift of one LTZ die to other LTZ dies, using basically the same circuit for all Vref's. The drift trend direction will tend to be the same, and you can possibly convince yourself into much better results if you're -only- looking at inter-comparing LTZ die.
At least you know you don't have a completely mucked up circuit module, but it is still wise to use other test methods if possible. That's hard to do with an LTZ since that's already at close to the top of the food chain.
It would be interesting to see how the results compare to more than one reference technology to test against - for instance we use multiple cal'd 732's, KVD's, nullmeters & multiple 3458a's to measure a Vref accurately... You'll raise confidence and lower uncertainty of any LTZ absolute value measure / long term drift assessment that way - which is the whole point if you're down in the low ppm range.
Just another example: more tools ===> happier Volt-Nut!!
Hello Mr. Diodes,
your first question and remark is legitimate.
Yes, over the last years, I use the 3458A as a comparator and its LTZ1000A @ 65°C for the baseline reference, plus a Fluke 5442A, plus these two prototype LTZ1000 references.
The LTZs have been running for 12 years now, whereas the 3458A and the 5442A were only switched on when used.
So, the LTZs should have the typical -0.8ppm / year drift, the 3458A a fraction of that drift, down to zero drift, as the references typically do not drift when unpowered. Same goes for the 5442A, which should typically have a positive drift over time.
Starting in 2009, I compared these 4 references regularly, and their relative drifts were as expected, i.e. the 5442A upwards, both LTZs downwards, relative to the 3458A.
The total relative drift per year between the 5442A and both LTZs was less than 1ppm, which was my stability goal.
That's the poor mans way of maintaining Volt, as I don't want to calibrate the standards by a metrology lab, or by usage of commercial instruments, like a 732A.
Btw.: The 100 year-drift of Le Grand K, the kg prototype, was identified by the very same principle.
I doubt, that a KVD or a Null Detector give any advantage over the 3458A as a comparator..
During that time, I had the chance to 'zero' the absolute Volt in my lab, at first when I got the 5442A, then by a comparison to a recently calibrated 8508A, and latest, when I got two brand new 34465A from KS, which agreed within 1ppm to my baseline.
That's all no regular calibration, that's crystal clear.
But for an amateur grade lab, there is high probability, that these artefact calibration points, together with the frequent relative drift measurements, provide good enough accuracy at about a few ppm.
I don't want to say uncertainty, as this would require or imply regular calibration methods by a proven chain from official metrology labs.
And I also want to emphasize, that I do not want to dig into the tenths of ppm region, where all these nice officially accepted standards rule.
The addition of up to five new LTZ1000 may improve the drift statistics, although they will also have a probable negative drift.. so SZA263 based references are lacking.
Anyhow, my current group of 4 references, with their underlying history will be sufficient to measure the drift behaviour of the new references, and that's the most important feature.
Now that I have some more compact LTZs, whith proven low T.C., I can send them to a friendly volt-nuts companion, who might punch another nail in my baseline.
Frank
PS: I also added a Hamon divider for 100:1 and 10:1 transfers (DIY), a 5450A, and recently a 845AR to my lab, and these redundant instruments increased my confidence and insight a lot, over the bare uncertainty of the 3458A.