Yes, as I said in the first line of my post I can't release client data - it isn't open source. Sorry. Someday I can. I'm trying to leave at least a few bread crumbs for you guys from the real world beyond EEVblog - I'm trying to give you at least a clue as to what you want to look at to make your LTZ age well. Use the information or not - up to you.
Well, I'm not expecting, that you would ever really reveal any profound data.
That sentence is really disturbing me: '..to leave at least a few bread crumbs for you guys..', because that's always the feeling I had, after reading through your posts.
Believe me, if I thought it wasn't important, I sure wouldn't waste time posting.
...
I 100% agree the scientific approach is best, and use every opportunity to question everything for yourself. DON'T LISTEN TO ME! I sure as hell wouldn't, we agree on that point!
Mr. Diodes, I really would like to listen to you, if you would prove your statements by evidence, but this way, again, it's quite useless for me, even if it's on a hobbyist level forum only
That's why you build a TIA and look at the input current spikes on your chopper amp (This info is usually not published, so find out for yourself like we did), and then explain why it -doesn't- affect the LTZ die. The LTZ Zener would be considered low impedance yes - but it's a current mode device and with the crystal lattice is being modulated by the chopper spikes. Guaranteed to happen without an RC between the chopper and LTZ. HINT: It's not always the amplitude of the spikes, but the rise time. Also notice the spikes are very asymmetrical - that should be another big clue if you're a student of slower crystalline structure aging.
What I'm trying to get across: I don't think you've measured the '2057 (or any chopper amp) input current noise directly?. Until then, please don't discount mine or Kleinstein's points either.
I did not doubt the existence and the weight of these spikes, that's already well known and documented.. so I don't have to measure that again, on my own.
Up to date, I never have seen any documentation about that said destructive effect on Si lattices, so maybe you can explain or cite instead, why this energy should be high enough to get into the necessary activation energies for measurable changes of the reference voltage.
Again: If you don't have the resources to test these effects long term on many LTZ's, I recommend using even a modest RC filter on your chopper. LT/ADI recommends the same practice, noted in several conversations with their apps engineering team, and they see a lot more feedback from bigger customers.
That's also a
argument, sorry.
As you don't even at this point present any numbers for that said effect, nobody can possibly judge, if this effect is measurable with reasonable amateur equipment, or the other way round, which level of equipment or stability would be required to provide evidence for that.
As the information from LT seems not to fall under NDAs to your customers, please provide details, numbers, facts.
In fact, my both prototype references run since about 2004, or so, the first with an 7650 practically directly coupled to the LTZ1000, and the other w/o any chopper behind.
Both drift meanwhile in parallel over several years, about -0.5ppm/year drift.
Conclusion from that? None in your direction.. Only, that it's possible to realize a very low drift of < 1ppm/year, as expected from the mentioned publications.
I also recommend you fix the thermal issues on your LTZ circuit before adding extra caps that wouldn't normally be required. Especially look at drawing heat from Pin 6 of your LTZ - sometimes that thermal problem looks like an electrical issue. Not saying that's exactly what you've encountered, but that is a real "trap for young players".
Exactly. I don't see any thermal issues, in contrary, the DIY references perform extremely well over temperature, with a 'simple' T.C. trimming, but w/o any mysterious gimmicks.
I still don't understand, how additional caps would influence the T.C.? Thermal Problem??
These additional capacitors clearly suppress dips and spikes of the output voltage.
In the Datron 4910, they've used exactly the same extra circuit, for some reason.
I'm really curious about the reverse engineering of the 7001 reference, by TiN, maybe we'll meet again such caps..
Dr. Frank: Our circuits are always in a primary steel housing, with a minimum 2mm wall, usually 3mm or more. Box is a part of the inguard system. By the time it's mounted in the field it will have a double steel enclosure, like any piece of quality test gear. Sometimes we'll use a drawn MuMetal box depending on application. Ambient temp range can be spec'd 10 ~ 40C, but customer will want testing done usually -10~50C or more and looking for noise spec 10mHz to 10Hz or 1mHz to 10Hz. GENERALLY we have to spec drift rate for 24 hr, 30 day, 90 day and 1 yr , and specify a maximum cal test interval as part of documentation deliverables. That's why we're burning in LTZ's 18 ~ 24 months before they go into service. Not hobbyist level specs, but something to learn from...because that's how we have to do it. Your needs (and circuit topology) might be different.
In the end, you've finally lifted the curtain a bit..
Therefore, your applications are like the 3458A, inside a doubly shielded box, probably w/o any direct influence from the outside onto the LTZ1000s output.
The needs for a voltage calibrator are definitely different, apart from the temperature range, that's similar.. and the drift rate is also on an annual timescale only, not these 5 .. 20 years, you've mentioned.
Again, you also missed out the information, if the drift specification of your LTZ is really much less , than the usual specs for 732 / 4910 / 7001 references, what a pity.
So I'm really keen on learning about the 7001 topology.. the supply filtering looks extremely interesting, and I think that there really lies the design focus, besides appropriate shielding, and other means for EMI suppression.