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Precision voltage references...?
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Conrad Hoffman:
I have an old Analogic/Data Precision AN3200 6-digit calibrator. It uses the LM399 as a reference and I've found it to be extremely stable over time, a couple ppm per year. It probably helps that everything I own is ancient and whatever drift was going to happen, already has.
Andreas:

--- Quote from: imo on February 04, 2020, 11:31:16 am ---Ok, thus with 10V you are still <1LSB with 13bit ADC/DAC :)
Anyhow, all those references I listed above were not designed for something like >5 digits, imho. We use them as they are cheap and easy to apply.

--- End quote ---


--- Quote from: imo on February 03, 2020, 11:02:48 pm ---The LT1027 metal can H package - LT databook '92:
Hysteresis delta 25C  typ 10ppm
Long term stability    typ  20ppm/month

--- End quote ---

You make them worse as they are when properly handled.
The 13 Bit are without further calibration.

the ageing in the data sheet is more or less for the first 1000 hrs after soldering stress.
After some time most of the buried zener references stabilize to ~1-2 ppm/year.
This is at least valid for the metal can housing and often for the CERDIP package.


--- Quote from: Conrad Hoffman on February 04, 2020, 02:56:11 am --- Interesting that both went up, or maybe chance?

--- End quote ---

I think it is more the influence of the resistors so by chance. (I guess that the references were not active 24/7)

My 2 LT1027 (PDIP-based) ADCs (temperature compensated) are ageing in different direction compared to my LTZ#2 which itself drifts down 1-2 ppm/year.
When the reading goes up (thin lines) then the LT1027 goes down in reference voltage.
The 2:1 divider itself is LTC1043 based so is very stable over time.
The humidity (right axis 0.5 = 50%) is a sliding average over the last 5 days which gives the best fit for the LMS calculation of humidity (0.5 ppm/%rH) and ageing (ppb/year against LTZ#2) coefficients.
When correcting by these ccefficients you get the dotted resulting curves.

with best regards

Andreas
branadic:
The problem of the different CTEs and thus the CTE mismatch, the ceramic package has a CTE of about 7ppm/K (https://global.kyocera.com/prdct/semicon/material/), while the copper and the FR4 board have about 17ppm/K and as a rule of thumbs a CTE mismatch of 10ppm/K will result in problems, might be overcome by using a flexible pcb, which is only 100µm in thickness and behaves not as a solid body compared to the FR4 circuit board or LS8 package. So putting the LS8 package on a flexboard, which itself is soldered to the FR4 board on one side only or on a rigid-flex board with the reference on the flex part might solve the issue using industrial standard technics and without using manual dead bug style technics.

-branadic-

srb1954:
Is the Analogic/Data Precision AN3200 similar to the Data Precision AN8200 6-digit calibrator?

I acquired a faulty AN8200 really cheap and managed to repair it quite easily but I was wondering how good its accuracy and stability is. It was last cal'd in 2012.

I don't have ready access to any cal lab facilities to check this sort of thing.

Thanks
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