Lowest drift, lowest noise voltage reference (ADR1000AHZ)

[Andreas]

Hello,

I now passed 12 kHrs:

the 10V output on ADR#01 seems to further stabilize.
the 6V6 output ageing rates are slowing down/seem slightly goint into drift up phase
And this even with SQRT on the X-Axis.

Divider drift is still rising. (mostly linear with SQRT on X-Axis)
Since spring has passed the humidity rH% is now rising.

with best regards

Andreas

[Andreas]

Hello,

I now passed 13 kHrs:

nothing new against previous observations.

with best regards

Andreas

[alligatorblues]

The stats of the raw regulator IC is irrelevant. Once you get the output to a practical, usable value, like 10VDC, then take your stats. I made 2 LTZ1000 references, used all low-drift components after the regulator IC, and got 1K/C. So, you really have to ovenize everything but the psu.

I have never seen anyone build their own DC Standard that was outstanding, after the output was adjusted to something practical and useful. The only reason Fluke can do it is because it is a ultra-precision resiator manufacturer, but it doesn't sell them.

732As, 732Bs, and 732Cs are all slightly different within the model. No one can obtain Fluke's resistors, so it is impossible to even come close.

[Kleinstein]

With the ADR1000 reference and a 6.6 V raw reference votlage it is actually possible to get a quite stable scaling to something like 10 V as the ratio is very close to 3/2 which can be realized based on a off the shelf resistor array (e.g. LT5400).  It is true that it is difficult for the more common 7 V to start with, but even this is possible, e.g. with PWM based scaling. Even if not super linear it usually is pretty stable over time.

[iMo]

..
I have never seen anyone build their own DC Standard that was outstanding, after the output was adjusted to something practical and useful. The only reason Fluke can do it is because it is a ultra-precision resiator manufacturer, but it doesn't sell them..

I do not know whether my DC standard is outstanding (most probably not with the engineering samples), but the ADR1001 has got all the resistors with useful outputs (7V/5V/10V) ovenized

[branadic]

I've passed 800 days, here is an update of my diagrams.

Edit: I've plotted the differences, both from calculated (cyan) and measure (blue) data taken by the nanovolt meters. From here we can extract that ADR stopped its initial drift roughly after 250 days, before some other drift mechanism took over, which is linear between two references just yet.

-branadic-

[Andreas]

Hello,

I now passed 14 kHrs:

the 10V/7V divider drift is still nearly linear in sqrt(kHrs) display

with best regards

Andreas

Edit: (explanation of the diagrams for those who are not familiar with the history)

I am monitoring 2 ADR1000 samples for ageing drift.

ADR#1 sample built on a PCB from branadic with 6.6V (Vz) and 10V output based on a statistical TDP16031002AUF resistor array.
ADR#1 is operated in a zero TC temperature setpoint of ~55 deg C with -6ppb/K for the 6.6V output and +20ppb/K for the 10 V output
after T.C. adjustment with a copper resistor in series to the 100 Ohm current setpoint resistor.

Ageing measurement started after some run-in phase.

https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg3921830/#msg3921830
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg3931196/#msg3931196


ADR#2 sample is built on one of my LTZ1000 PCBs after 2kHrs burn in (110-130 deg C) of the reference. There is only one 6.6V (Vz) output.
T.C. adjustment is done via variation of the 400kOhms resistor. Resulting in -4.5 ppb/K for a 3.3 Meg resistor.
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg4054810/#msg4054810

20231027_ADR1000A_01_02_ageing_drift.PNG
shows both 6.6V output drifts of ADR#1 in green and ADR#2 in pink.
The 10V output drift is in blue.
LTZ#9 (my 2nd best reference with <1ppm/year) in red is only as sanity check (so can be ignored).

All (corr) readings are corrected with the reference voltage of my LTZ#4 (my most stable reference well below 1 ppm/year)
Otherwise I could not make sub ppm observations with my 6.5 digit multimeters and 24 Bit ADCs.

20231027_ADR1000A_01_02_ageing_drift_sqrt.PNG is the same diagram only with the x-axis in sqrt(kHrs) instead of days.

20231027_ADR1000A_01_divider_drift.PNG shows the calculated 6.6 to 10V divider drift over time with humidity.

 20231027_ADR1000A_01_divider_drift_sqrt.PNG is the same diagram (as suggested by branadic) with x-axis in sqrt(kHrs).

[branadic]

Andreas, would you mind sharing a plot with all of your ADR1000s and briefly summarize what your legend means? I find it hard to understand what the meaning of "LTZ#9 corr", "ADR#01 Vz corr", "ADR#01 10V corr" or "ADR#02 corr" is and everyone has to go through the thread to see what treatment which reference has seen. Would be neat to have it summarized in one post. Thanks.

-branadic-

[Andreas]

Hello branadic,

I updated some information in my last post.

with best regards

Andreas

[branadic]

Thanks Andreas, now the diagrams make way more sense to me. 
So from here we sort of can conclude that the 2kHrs burn-in (110-130 deg C) procedure on ADR#2 didn't change the drift behavior compared to ADR#1. Furthermore, both references seem to have changed drift behavior after ~300 days (from log or square root to something more linear, by the looks of it).
However, the divider drift over time seems to stabilize too. And we can conclude, that the network is not directly affected by humidity, which is also very conviencing.

-branadic-

[Andreas]

Hello,

made a power off state of 124 hours followed by a 4 hours warm up time for my both samples.

Result (see day 600 in measurement) a "dent" with ~ 0.3 ppm after power off phase on both references (and 10V output of #1).
So somewhat better than the "dent" on day 180 with ~ 0.5 ppm on ADR#2 which was accidently running flat for some days (forgot to attach the charger).

The question is: is the "power off" hysteresis getting better when ageing the references?

with best regards

Andreas

[alm]

The question is: is the "power off" hysteresis getting better when ageing the references?

Based on my understanding of "power off" hysteresis being caused by the current taking a different path through the silicon, I'd expect it to be random with a spread that covers zero shift. So I don't think you can draw any conclusions from 2 experiments.

[iMo]

The hysteresis is so small compared to other factors surrounding the chip and the measurement itself, that it would be hard to finger-point at the ref chip, imho. If the "dent" was 3ppm, I would point at the reference..

[Kleinstein]

The question is: is the "power off" hysteresis getting better when ageing the references?

Based on my understanding of "power off" hysteresis being caused by the current taking a different path through the silicon, I'd expect it to be random with a spread that covers zero shift. So I don't think you can draw any conclusions from 2 experiments.

AFAIK the picture of different paths is a thing for simple surface zeners and old stabilzer tubes, not for burried zener diodes.

There are several effect that could contribute to the hysteresis: With a heated reference part of the hysteresis can be from mechanical stress from differences in the thermal expansion. This stress may in parts (specially at stress concentrations) relax in both the cold and hot state. Another possible factor could be water vapor moving between parts/surfaces inside the sealed metal can. Also electrical transients on power on / off may be an issue trapping charge somewhere on or inside the chip. With part of the circuit still separete also the external parts like resistors may contribute.

Still the effect seen is rather small and it is hard to tell if the difference is real or just noise.

[Andreas]

Hello,

I now passed 15 kHrs:

the 10V/7V divider on ADR#01 drift seems to stabilize (so no longer linear in sqrt(kHrs) x-Axis)

The 7V outputs of ADR#01 and ADR#02 drift ~1 ppm in 5 kHr now.

Detailed explanation of the diagrams see previous post (14 kHrs)
https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg5138967/#msg5138967

with best regards

Andreas

[Dr. Frank]

Well,

I haven't reported about my ADR #3 for a while, because I switched it off after June 18th.

In between, I got a new baseline comparison @ ab precision, and after several iterations at his lab, the mean value of my 8 references agreed within 0.25ppm with his 732B reference, which itself has 0.3 uncertainty, confirmed by a fresh calibration of the 732B afterwards. You'll see the baseline point in the diagram, which also is another confirmation for the recent ring comparison, branadic had organized around June 2022, with similar uncertainties by each Philipp and ab precision.

At first, the ADR #3 had stabilized before the shut-off. I powered it on again on 30th November 10 p.m., letting it warm up with the 3458A and the 5442A over night, for about 12 hours. So the transfer measurements showed a +5ppm shift, very huge compared to the other shifts, when I switched the ADR1000 off for several days or weeks.

Anyhow, a measurement on December 16th showed, that the ADR 1000 evidently returned to his recent voltage within a few tenth ppm.

All of my LTZ1000 and LTZ1000A, especially in my 3458A which is only switched on for measurements, never ever showed such a shift after being powered down.
They all return within 2h at most to their nominal value.
This effect - if it turns out to be inherent to the ADR1000's technology - is not convenient for usage as a intermittently used reference, like in DMMs or cold travelling standards.

I switched on my equipment on Thursday, 14th, and the next morning, I found my Fluke 5442A got a defect, the processor PCB obviously freaked out, so I have something to do Between The Years. Strangely, the transfer measurement of my other baseline references revealed, that my oldest prototype references Ref_1 and Ref_2, which were still not optimized and not in a tuner box enclosure, like all the others, both show an unexpected +0.4 ppm shift.
Something has happened during the night, damaging the 5442A, and influencing both the references.

By chance, the Solar outbreak just has begun on 14th December, but that influence is quite improbable.
Maybe there was another E.M.C. impact, or a short circuit occurred inside the 5442A, like a burnt tantalum, which impacted the references. We'll see.

Frank     

[iMo]

You had several highly correlated shifts with the REF1 and REF2 in past..

[Dr. Frank]

You had several highly correlated shifts with the REF1 and REF2 in past..

That only seems to be the case from view of this diagram, but had different reasons.
E.g. I preliminarily have adapted a new normalization factor for the whole group, that gave a discontinuity.. I have to find a better algorithm for averaging the reference group, smoothly integrate new baseline measurements, and a method to remove/ add members. I have another 3 or 4 references, which might replace the defect 5442A.

 This shift really is unique.
Frank

[Andreas]

By chance, the Solar outbreak just has begun on 14th December, but that influence is quite improbable.

Hello,

When exactly did you recognize the shift? In the morning of 15th?
I also had a strange reading on one of my AD586LQ based (unshielded ADCs):
In the morning of 14th and 15th the reading of ADC13 was about 2 ppm too high when reading PCB#2 of my ADR1399.
The reading healed on 16th

Normally I would think of a bad contact on the negative power supply of ADC13 which gives together with PSRR a too high reading.
But the idea with a solar outbreak is also tempting ...

with best regards

Andreas

[Dr. Frank]

Andreas, I actually measured on 16th, so I cannot assign this event to the fault of the 5442A. Normally, I don't report such singular observations, but this time, I could not resist. 
Frank

[branadic]

This is rather interesting, as I observed increased standard deviations and some sort of jumps in my 1h measurements of ADR1399 I take every day automagically within the last days, which I couldn't correlate with similar changes in ambient conditions.

-branadic-

[Dr. Frank]

Here's my New Years datalogging.
The ADR1000 definitely recovered to the previous value, after it's been powered off for several months:



My 20y/o Ref_1 and Ref_2 as well seem to recover from their shift, but still are not back to normal:



The environmental data logging (UNI-T UT330C) shows the usual rise during warm up and measuring session on 15th and 16th December, when my 5442A failed, and both references drifted upwards,



but what's really interesting is the quite fast and huge pressure rise exactly during that time period. I never have seen such a big rise before.
Maybe I'll ask the DWD (German Weather Service), what has happened.



The other references, LTZ1000As #6 and #7, as well my F7000 had also not been affected.



@ branadic: The F7000 meanwhile has stabilized during the last 8 months, or so.
   

[branadic]

but what's really interesting is the quite fast and huge pressure rise exactly during that time period. I never have seen such a big rise before.
Maybe I'll ask the DWD (German Weather Service), what has happened.

Indeed, quite some change I observed too:

but found a similar change about 300 days ago in my data 

@ branadic: The F7000 meanwhile has stabilized during the last 8 months, or so.

Nice to hear that 
It seems like that for no obvious reason references can start random excess drift that settles after quite a while for again no obvious reason, hence why they show up on ebay. Illya reported a settling of a drifting F732B he got after some years. Although we monitor ambient conditions it's still hard to explain the mechanism behind it 

-branadic-

[maat]

Maybe I'll ask the DWD (German Weather Service), what has happened.

This was the high pressure area FIONA. See for here: https://www.dwd.de/DE/wetter/thema_des_tages/2023/12/11.html (unfortunately only in German).

Attached is a data dump I got from from someone working at DWD It's their data from Frankfurt/Main.

[ramon]

... surface pressure around 1045 mbar ...

Marko Korosec (16/12/2023)  -  A Massive Heat Dome Develops over Europe
https://www.severe-weather.eu/global-weather/powerful-heat-dome-warm-wave-forecast-europe-christmas-december-2023-mk/