Lowest drift, lowest noise voltage reference (ADR1000AHZ)

[MaxTesla]

Speaking of drift, I reached 3000 h but I'm not happy with the result. Nevertheless, I guess it is good advice to share such results anyway.

-branadic-

Wow nice work

What temperature setpoint do you use on your ADRs?

[Dr. Frank]

Adding some 6% of gain the reference circuit would still require very stable resistors, not to increase the drift. Added noise would be the least problem.
It it is just about getting a long term stable reference the old type LTZ1000 reference may be the better choice, maybe with a reduced temperature.

So far the limited reports on the ADR1000 are showing very low noise, but also still some drift. There is still some hope to improve on the drift with burn in or annealing, but I would not absolutely count on this. The advantage of the ADR1000 is more that it can get away with lesser grade resistors and still get good stability. With really good resistors the LTZ1000 may still be more stable.

Yes you might be right. But with the limited dataset I still plane on experimenting. I have treated myself with a set of VHP101 for a LTZ (70k,120,13k/1k) and the ADR (acc to the Datasheet). Plane is to put the LTZ in the mix with the ADR in with the same layout and test them side by side. This will take some time though as my ADR resistors are scheduled for march…goal is to compare drift and tempco. This will be done against my well aged 732a so may in a year from now I will have somewhat meaningful results, after that I will have a look at the A9 board project again I think.

Hello Max,
unfortunately, reading every speculation from him, always the complement seems to be correct. No own experience from his own experiments, as far as one can deduce.

A divider being a few % off from "1" is extremely stable.. simply calculate the total differential! A 6% amplification should attenuate all drifts of the implemented resistors by about these 6%. I.e. a resistors T.C. of 2ppm/K will be attenuated to 0.1ppm/K of amplification drift. 5ppm/yr. => 0.3ppm/yr.
Added noise by an OpAmp IS the most severe problem for the ADR1000, as I have demonstrated upwards in this thread, in conjunction with the ADA4522 @ x1 amplification!! Any additional buffer amp might spoil the superior noise performance of the ADR1000.  Therefore the easy replacement of the FW is the best option.. if the 3458A circuit really benefits from the low noise ADR.
   
The long-term stability of the ADR1000 MIGHT initially be worse compared to the LTZ1000. Only branadic has presented so far a single drift result @10V.

My single sample experiment, measured directly at the raw ADR1000 output, w/o to 10V amplification, shows no remarkable drift so far after 500h. That's also no reliable result at all. Others in the background reported that the ADR needs a longer burn-in than the LTZ. So the speculation which chip is more stable, is at the moment completely baseless and speculative.
Spoiler alert: CERN obviously uses the ADR based circuit as an improved 10mA precision source! 

Lower oven-temperature is always a good way to improve timely stability, see P.J. Spreadbury publication from 1990. Chose about 55 .. 60°C in any case. Don't use the ADRs datasheet values for best performance of the ADR. See hints in my post above.

The T.C. of the circuit for both chips have to be trimmed to near zero. There's a lot of potential on the 3458A's LTZ1000A board. Mine has about 0.2ppm/K, half of the overall temperature drift of my instrument.
Use that infamous 200k resistor for T.C. trimming. (or not at all).
The LTZ1000A inside my 3458A drifted -2ppm over about 9 years only, due to the reduced oven temperature, but mainly because the 3458A is running only sparsely. Again, see Spreadbury.

My ADR #3 runs at about 55°C, just at its determined zero TC point of the Reference Amplifier.  Simple thing.

And no, the LTZ1000 does not necessarily need more stable resistors. The timely stability of the circuit is mainly determined by the chip itself, the T.C. drift can be trimmed to near zero. Exactly the same goes for the ADR. So, please, no Vodoo stuff here, again. The ADR has much better noise performance, definitely, and that's the main reason to go for it.

The 3458A is no voltage reference, by all means. Therefore, I might exchange its very stable LTZ1000A by the ADR1000 some day, using the very same PCB with different resistors, and adding Andreas capacitors, for higher noise immunity.

Frank

[MaxTesla]

Adding some 6% of gain the reference circuit would still require very stable resistors, not to increase the drift. Added noise would be the least problem.
It it is just about getting a long term stable reference the old type LTZ1000 reference may be the better choice, maybe with a reduced temperature.

So far the limited reports on the ADR1000 are showing very low noise, but also still some drift. There is still some hope to improve on the drift with burn in or annealing, but I would not absolutely count on this. The advantage of the ADR1000 is more that it can get away with lesser grade resistors and still get good stability. With really good resistors the LTZ1000 may still be more stable.

Yes you might be right. But with the limited dataset I still plane on experimenting. I have treated myself with a set of VHP101 for a LTZ (70k,120,13k/1k) and the ADR (acc to the Datasheet). Plane is to put the LTZ in the mix with the ADR in with the same layout and test them side by side. This will take some time though as my ADR resistors are scheduled for march…goal is to compare drift and tempco. This will be done against my well aged 732a so may in a year from now I will have somewhat meaningful results, after that I will have a look at the A9 board project again I think.

Hello Max,
unfortunately, reading every speculation from him, always the complement seems to be correct. No own experience from his own experiments, as far as one can deduce.

A divider being a few % off from "1" is extremely stable.. simply calculate the total differential! A 6% amplification should attenuate all drifts of the implemented resistors by about these 6%. I.e. a resistors T.C. of 2ppm/K will be attenuated to 0.1ppm/K of amplification drift. 5ppm/yr. => 0.3ppm/yr.
Added noise by an OpAmp IS the most severe problem for the ADR1000, as I have demonstrated upwards in this thread, in conjunction with the ADA4522 @ x1 amplification!! Any additional buffer amp might spoil the superior noise performance of the ADR1000.  Therefore the easy replacement of the FW is the best option.. if the 3458A circuit really benefits from the low noise ADR.
   
The long-term stability of the ADR1000 MIGHT initially be worse compared to the LTZ1000. Only branadic has presented so far a single drift result @10V.

My single sample experiment, measured directly at the raw ADR1000 output, w/o to 10V amplification, shows no remarkable drift so far after 500h. That's also no reliable result at all. Others in the background reported that the ADR needs a longer burn-in than the LTZ. So the speculation which chip is more stable, is at the moment completely baseless and speculative.
Spoiler alert: CERN obviously uses the ADR based circuit as an improved 10mA precision source! 

Lower oven-temperature is always a good way to improve timely stability, see P.J. Spreadbury publication from 1990. Chose about 55 .. 60°C in any case. Don't use the ADRs datasheet values for best performance of the ADR. See hints in my post above.

The T.C. of the circuit for both chips have to be trimmed to near zero. There's a lot of potential on the 3458A's LTZ1000A board. Mine has about 0.2ppm/K, half of the overall temperature drift of my instrument.
Use that infamous 200k resistor for T.C. trimming. (or not at all).
The LTZ1000A inside my 3458A drifted -2ppm over about 9 years only, due to the reduced oven temperature, but mainly because the 3458A is running only sparsely. Again, see Spreadbury.

My ADR #3 runs at about 55°C, just at its determined zero TC point of the Reference Amplifier.  Simple thing.

And no, the LTZ1000 does not necessarily need more stable resistors. The timely stability of the circuit is mainly determined by the chip itself, the T.C. drift can be trimmed to near zero. Exactly the same goes for the ADR. So, please, no Vodoo stuff here, again. The ADR has much better noise performance, definitely, and that's the main reason to go for it.

The 3458A is no voltage reference, by all means. Therefore, I might exchange its very stable LTZ1000A by the ADR1000 some day, using the very same PCB with different resistors, and adding Andreas capacitors, for higher noise immunity.

Frank

Hello Frank,

thanks a lot for the insight and the paper, didn't knew that one.
This is highly interesting, out of my guts i would have suspected stabiltiy to be more of an topic, but as the amplifer would be one rougly 1:1.06 you are right of course.
My idea was to implement the amp with a VHD200, so tempco/stability impact is very small.

Regarding the noise and your buffer setup: This suppries me a lot tbh, I mean the ADA4522 with the right kind of input lowpass should not contribute that much, with the assumption that the datasheet noise values are correct, but as you discribed your samples are much lower noise than the spec. Will be interresting to see what my samples do, I have enought of them to get a little bit more "meat at the bone" so to speak.

Thanks for the tipp with the temp setpoint, I don`t have the appropriate means of measuring it myself (yet). So revised plan for tempco/stability test is the following: 6 ADRs in total, 3 with 12K/1K divider (~60°C) and 3 with 11k6/1k (~53°C) setpoint to get a span, each mounted in a housing with the same board, no preconditioning and just accquiring data form the start. This should give me/us a somewhat good idea what is going on, as three is the statistical minimum. Other resitors are 61.9k and 95.3Ohms. Monitoring ambienten contiditions of course to see any kind of correlation during normal weather shifts, all done automaticly every day with my 1281 and 7168 scanner. One channel reserved for a short, one for the 732a. If all goes well we can see a difference in drift with setpoint temperature in two points.
Thats at least the plan so far

After the results comes the tuning...

BR,

Max

[Dr. Frank]

Hello Frank,

thanks a lot for the insight and the paper, didn't knew that one.
This is highly interesting, out of my guts i would have suspected stability to be more of an topic, but as the amplifier would be one roughly 1:1.06 you are right of course.
My idea was to implement the amp with a VHD200, so tempco/stability impact is very small.

Well, a VHD200 is technical overkill, expensive, and has a long leadtime.
Use two appropriate cheaper single resistors from stock, WW or MBF ones, like 6k8 + 470 Ohm, or so.

Regarding the noise and your buffer setup: This surprises me a lot tbh, I mean the ADA4522 with the right kind of input lowpass should not contribute that much, with the assumption that the datasheet noise values are correct, but as you described your samples are much lower noise than the spec. Will be interesting to see what my samples do, I have enough of them to get a little bit more "meat at the bone" so to speak.

I was also surprised, that the MAX4522 (of course with input LPF) adds so much noise. The ADA4522 has typically 115nV pp noise only, which should not affect the ADR1000 noise performance.
This combined noise level is about the same as an LTZ1000 w/o buffer. Maybe I have to look for a better sample of the ADA4522.
It's not only my 5 samples, which have 50% noise of that of the LTZ1000. Other volt-nuts also reported the same.

Inside the 3458A, both LT1001 on A5 board, U160 and U165, which generate the +/- 12V reference for the A/D will definitely spoil the game.
These have 300..600nV pp noise, i.e. at the same level what I've measured for the ADR1000.
These might have to be replaced also.

Thanks for the tipp with the temp setpoint, I don`t have the appropriate means of measuring it myself (yet).

Probably you already HAVE the possibility to measure the oven setpoint by yourself. A faster bench DMM is sufficient, to catch the initial diode voltage @ R.T., with oven disabled, and then extrapolate by using -2.2m/K for the temperature dependency. A 34401A is sufficent for that, and your 1281 will definitely do the job.

You may first test, at which collector current of the Reference Amplifier you get zero T.C. for the (not ovenized) RefAmp at your intended oven temperature.

So revised plan for tempco/stability test is the following: 6 ADRs in total, 3 with 12K/1K divider (~60°C) and 3 with 11k6/1k (~53°C) setpoint to get a span, each mounted in a housing with the same board, no preconditioning and just acquiring data form the start. This should give me/us a somewhat good idea what is going on, as three is the statistical minimum. Other resistors are 61.9k and 95.3Ohms. Monitoring ambient conditions of course to see any kind of correlation during normal weather shifts, all done automatically every day with my 1281 and 7168 scanner. One channel reserved for a short, one for the 732a. If all goes well we can see a difference in drift with setpoint temperature in two points.
That's at least the plan so far

After the results comes the tuning...

BR,

Max

Setpoint of the oven can also be trimmed by changing the collector resistor of the temperature sensing transistor inside the LTZ/ADR circuit.
So you may always use a  12k/1k divider and select the collector resistor instead. The stability requirement on latter is relaxed, especially if you run your circuit exactly at the sweet spot, i.e. at zero T.C.
I do not recommend 11k6/1k, that may be too low a temperature.
Select the zener resistor for a bit more than 5mA @ oven temperature, and select both collector resistors as described above.
Your monitoring capabilities sound pretty good.

Frank

[Kleinstein]

The resistors for the 6.6 to 7 V gain would still be the most critical one when it comes to drift. They enter with a 6% factor, or a bout a facto 17 attenuation. The resistors at the ADR have a larger attenuation, like 200 times and higher.
For the gain stage one may just get away with an LT5400-7 as a maybe better available resistor.

Az OPs can react to the input impedance and details in the supply decoupling. So there is a potenetial for them to show more than the datasheet noise. They are also a possible source for EMI so that other parts than give the extra voltage.

As a lower noise OP at the ADC I would consider the OPA202 as a possible candidate.

[e61_phil]

And no, the LTZ1000 does not necessarily need more stable resistors. The timely stability of the circuit is mainly determined by the chip itself, the T.C. drift can be trimmed to near zero. Exactly the same goes for the ADR. So, please, no Vodoo stuff here, again. The ADR has much better noise performance, definitely, and that's the main reason to go for it.

It is true that the LTZ1000 CAN be trimmed to ZTC, but without trimming the ADR1000 is much better in terms of TC. In one project exactly that was the reason to move to the ADR1000.

[MaxTesla]

Yeah the lead time on these VPG resistors is horrible but ok, metrology is no hobby for the hasty ones, trying to improve my patience here
I am gathering test gear for this project since nearly two years now (orignally planned with the LTZ of course)...

Thanks for the tipp, didn't thought on that one...in my head I needed a external source (of heat) to do it, not that I don't have a 2510, but I wasn't ready to put the efford in.
So I will think about a proper setup to do it (waiting on some new PCBs anyways which one of them will be modified for that).

Yes I am aware of the trimming, however i would like to get the drift characteristics first (and see how the tempco behaves) and then tweek the refs. Indeed i was wondering about the low setpoint, but I think its worth a shot.

Regarding the exchange of U160 and U165: I assume (not checked) there supply is bipolar +-15V, so a LT1128 would work fine and it has very very low noise...considered it instead of the LT1013 but the bipolar power supply needed to get to (or near) 0V keeped my from implementing it. Didn`t seem necessery at the time, but after this discussion about the really low noise floor this is worth a rethink.

BR,

Max

[Kleinstein]

There should be no absolute need to get really zero TC for the unheated reference. If possible it would help to get the TC without the heater to below 20 ppm/K. Something like the 10 ppm/K range should be perfectly OK with a reasonable stable temperature. A slightly higher current for the zener and/or transistor could do the job.

The LT1128 is low noise for a very low impedance ( e.g. 100 Ohms) source, but not with some 10 K like in the 3458 reference amplification. For the ADR1000/LTZ1000 reference the OPs see some 50-70 K and thus even more impedance. The OP is also behind the gain of the transistor and thus less critical. So the LT1013 should be good enough there.

So if at all the LT1128 may have a small chance to work in the 6.6 to 7 V gain stage, but even there I would prefer a lower noise current OP. The chopper artifacts from a chopper OP could be an issue.
The ADC in the 3458 should react a little to reference noise in the 150 kHz range. The noise in this range may depend on the compensation (including OP speed) around the reference. The curve in the DS looks good for the ADR1000, though not too sure which OP is used and there may be limit of the test system.

Trying to get even lower noise from the ADC in the 3458 is a different topic. Only U160 would see the same frequency band as the reference. For U165 and U110 the chopper action of the AZ mode is effective and thus a relevant frequency of more like 2.5 Hz with an often relatively low BW and some extra gain (around 2.25 for the more critcal U110, should be 1.25 for U165).  For the actual use reference noise at lower frequencies than 0.1 Hz may be relevant. The 0.1 to 10 Hz range is more like a range still easy to measure. It would be mainly U160 to worry about for low frequency noise.

[Andreas]

Hello,

working on alternatives to the statistical divider with a LTC1043 cirquit.
The main amplification is done by a 3 to 2 (factor 1.5) charge pump.

The remaining part can be easily done with standard resistors.
Either up or in a additional buffer stage with a voltage divider down.

Temperature compensation is done with a diode cirquit.
The typical +220 ppb/K can be compensated with the following cirquit.
R8+R9 are meant to be a 50K trim pot where the T.C. can be trimmed from around -300 to +300 ppb/K.

Unfortunately there is a unwanted offset along with the T.C. trimming where I am looking for a solution.
Any ideas?

with best regards

Andreas

[Kleinstein]

The TC adjustment would effect the absolute value in most cases. At best one can eliminate the effect at 1 temperature, but it can be made better than in the circuit shown. Both sides of the trimmer should see about the same voltage at a reasonable temperature.

One could get such a setup with a bridge with 2 diodes and 2 resistors on opposite sides to replace the 2 diodes in series. The main parts is shown in the attachment.

It looks like there should be a little more filtering for the switched capacitor part.
The final circuit should also have supply filtering for the AZ op and LTC1043 to keep the supply clean.

[Andreas]

Hello,

current results of ongoing burn in of ADR1000A#02 in burn in socket.

Procedure is temperature cycling from 110 deg C to 130 deg C within 2 Hours.
so 10 minutes rising with 2 deg C/min 50 minutes plateau and 10 minutes falling with 2 deg C/min.
(see previous post).

At around 200 hours I thougt output voltage would stabilize but obviously this is not the case.
Now at nearly 400 hours I am somewhat unshure:

- will there be a stabiisation point
- or will the device be destroyed (because 130 deg C is too high?)
- or is the temperature still too low (as on MM the temperature of 150 deg C was mentioned)

with best regards

Andreas

[branadic]

Hi Andreas,

I guess what you look at is an exponential drift curve. Multiple times I though myself the reference would now start to stabilize, but then drift moved on and it was just a plateau in the drift curve for whatever reason - such as variation of the meters reference and t.c..
Meanwhile I'm confident to predict the drift by an exponential function, as can be seen in the image below.

-branadic-

[Kleinstein]

If there is a stabilizing point is a good question. There is a chance that there is some process that us not stabilizing but contineously going one direction - kind of aging to wards destruction. One part seems to have stabilized after some 200 hours.

The parts still showing slow drift at some 120 C shoud be quite a bit (e.g. a factor of around 100, maybe more) slower when at a more moderate temperature, like 50 C. So chances are the part should be stable enough by now. So I would not worry too much about the still visible drift.

Another point is that the burn in circuit is more sensitive to the resistors (and maybe the MOSFET). The resistors are not the most stable ones. So the observed drift could also be in parts from the resistors in the burn in circuit and maybe the temperature control part.

It is hard to tell if the 130 C are too low and which annealing process is best. Usually the first and obvious part is to really finish the chemical reaction in the die attach glue. Here the 130 C should be high enough, especially with so much time. For a glassy epoxy I than see 2 possible routes:
A) Get a dense stucture in procedure like this:
 1) anneal near or above Tg to finish the chemical reaction
 2) anneal somewhat (e.g. 30-50K) below Tg to get a dense amorphous structure. This could also be with a slow coold-down, maybe in steps.

B) Get a more open glue stucture to allow better stress ralaxation in procedure like this:
 1) anneal near or above Tg to finish the chemical reaction , so more like short time at a rather high temperature
 2) cool down to room temperature fast, to suppress the densification , so keep the epoxy soft by freezing a more open structure.
 3) wait at room temperature or maybe even slightly below, to allow relaxation of thermal mismatch stress.
   (a lower temperature gives more thermal stress and may this way give faster creep, despite of lower temperture)
 4) anneal at an intermediate temperature (e.g. 70 C) to get the structural relaxation in the glue, but not much new thermal stress.
 
For a more definitive answer one would need to run the reference in a more normal circuit and with better resistors. To get a shorter time scale, this may be with a slightly elevated temperature (e.g. 20 K higher than normally planed for).  There can also be some hystereseis type effect and thus a new relatively fast part when going to a lower temperature. So a test at let's say 60 C may again show a fast initial part. So this test would again need some time.

[Andreas]

I guess what you look at is an exponential drift curve.

It looks like that:

When I make the x-Axis as sqrt(kHrs) and the y-Axis as ppm instead of mV then I get (nearly) a linear curve.
Regression is -62.4 ppm/sqrt(kHr) at 120 deg C.

So with Arrhenius and factor 2 every 10 deg C and 60-70 deg C (including self heating) we would get something like 1-2 ppm/kHr which is still too high for a voltage standard. I want to get down to better than 1-2 ppm/year.

with best regards

Andreas

[branadic]

I want to get down to better than 1-2 ppm/year.

Then run the aging process longer. As you can see with my non-pre-aged reference it takes some time. Fit your drift curve with an exponential curve, predict the drift for the future - say for 8760 h - and monitor, if your prediction changes/stabilizes over time. Once the drift prediction stabilized you will see how long it will take to run this procedure.
We can then compare how long it took your reference to stabilize with my one and see, if this process did anything good at all. 

-branadic-

[Andreas]

Hello Branadic,

I calculated roughly -2.3 ppm/kHr for your ageing curve at ~50-60 deg C which is around that what I theoretically would get if lowering the temperature.
Perhaps I will put my setpoint some 5 deg C higher to 115-135 deg C (the maximum I can use with my curent setup) to prove whether the drift increases.

with best regards

Andreas

[Kleinstein]

The drift in the burn in circuit can be more than just from the chip. This can also include other parts, like the resistors.
50-60 C would be usually the die temperature, including self heating. Depending on how the temperature is measured during burn in there may be some self heating to add there.

The doubling every 10 K rule is only a first approximation. The actual number can vary depending on the process. The difference can be especially large when it comes to epoxy close to the glass temperature. There is the Arrenius factor and an additional change in structure.

If an exponential fit is suitable depends.  Aging processes can also follow different laws like square root or stretched exponentials or teh suposition of several effects.
The relaxation of stress can be nonlinear as plastic processes often are. Pure viscose creep is more like the exception.
It probably takes more data to really decide if an exponential is suitable. An exponential fit normally corresponds to a single relatively simple process.
Especially the initial phase has usually more contributions, some faster will decay full to later only leave the slowest visible process and other processes that are too slow to see.  An exponential decay is more like an optimistic case.

I don't think the drift measured for the simple burn in circuit is good to estimate the later drift at some 60 C. The circuit is different (more drifting components) and the temperature is very different, and thus quite some extrapolation.

[Andreas]

Hello,

since the statistical voltage dividers are in plastic packages I also examined influence of humidity to the voltage ratios.

Setup is as follows.
ADR1000A#01 in my cooling box. Environment is kept to 27 deg C on the heat spreader. (so a little more on the ADR PCB).
Humidity is changed either near 30% rH or up to near 80% rH.
Divider Ratio is measured with the ratio functionality of my HP34401A (100 NPLC).

Results:
The output ratio (nominal 1500 mV/V = 1R/2R built from 6 resistors) changes up to 0.3 ppm for a near 50% rH change within 2 weeks.
The setpoint ratio (nominal 12500 mV/V = 11.5R/1R built from 8 resistors) changes up to 2.2 ppm for the near 50% rH change.
The second ratio drift is larger maybe because the ratio needs several "single" resistors/dividers and so is not really "statistical".
A ratio with 12:1 with 6 resistors in series and 2 resistors in parallel would have the chance to be better in this regard.

And it seems that 2 weeks settling time is still not enough for final settling.

with best regards

Andreas

[Kleinstein]

A 2.2 ppm change in the temperature set point would not be so bad for the ADR1000, as the drift is attenuated quite a bit (e.g. like 200 times - depends on the unheated TC).
The 0.3 ppm drift of the output gain would be the larger effect. This number is still not so bad, as 50% change in RH is already quite some change.
The actual RH change at the resistors would be smaller, as a higher temperature would reduce the RH (about a factor 0.7 for 5 K higher). It still makes sense to use the environmental RH, as the a similar situation would be common in applications.

80% RH is quite humide and may reach the range where surface film may form, adding extra surface leakage currents. This effect may be highly nonlinear, with a material dependent critical RH for the film to form. This part would be relatively fast and not take weeks, more like minutes.

[Andreas]

Hello,

news from the burn in cycling of ADR1000A#02

After  ~500 hrs I actually increased the temperature cycling from 110-130 deg C to 115-135 deg C.
But I recognized that the overtemperature switch was actuating at the end of the temperature rising
so I finally adjusted the cycle to 114-134 deg C.
Expectation was that with ~5 deg C increase of the average temperature the ageing would increase by ~factor 1.4
Or somewhat lower (1.32) for ~4 deg C.

The first new measurement trendline (in blue beginning at sqrt(0.5 kHrs) = 0.7) shows something like 200 ppm/sqrt(kHr).
Which is around factor 3 above the 4 deg lower temperature (was 62 ppm/sqrt(kHr)).
So something is different above 130 deg C.

Unfortunately I do not have a good noise measurement "before" with the ADR#02.
Fortunately I remembered that Jason (cellularmitosis) has done a good job (thank you for that) in publishing several LTZ1000 PCBs.
So overcome this for ADR#03 I built a noise measurement cirquit from one of Jasons PX PCBs.

with best regards

Andreas

[miro123]

Hello Adreas,
Thanks for sharing. I have two questions related to your last two posts.
1. How do you control the humidity by resistor test? - I want to do similar test. My goal is to create resistor divider model. I want to find certain pattern between humidity, temperature and resistor divider ratio. I expect to determine Humidity behavior like - humidity coefficient. humidity time constant & hysteresis. I hope that  a. Observed behavior is repeatable and model can by build b. Expect simple polynom fits the model.
2. At your last post mentioned T 114...134C Is this environmental temperature or Die / Transistor base emitter temperature? I'm afraid that you are going far beyond the specs. Epoxy is just one component in the whole picture. e.g. How SiO2 react to such temperatures, and what about chip multilayered structure, are you casing permanent damage with it? That are all questions that i dont have answer

[Kleinstein]

The higher temperature speeds up the termally activated porcesses. However there is more change in getting a different equilibrium state.
For the epoxy part, relatively close to or above the glass temperature the structure can reach an equilirium, with a more open structure at a higher temperature. The more open structure also makes things faster, in addition to thermal activation.

With a different equilibrium state (especially for stress) the question is a bit if the aging at the high temperatre actually helps with the later performance at a considerably lower temperature. At least the higher temperature aging can not replace all the burn in time needed also at the final temperature.
There are still hysteresis effects, that than start a new settling / ageing.

[Andreas]

1. Control of the humidity is done with a 1 kg Dry pack (Silica gel) for the ~35 % rH.
    For the ~80% rH I used acryl polymere crystals like these:
    https://www.amazon.de/GERMANUS-Humidor-Befeuchter-Kristalle-AcrylPolymere/dp/B0796GG83B

    All is within my cooling box. (isolated and humidity tight).

    Essential is a constant environment temperature (here ~27 deg C)
    PWM controlled by heater foils on a aluminium sheet as heat spreader.


2. it is the temperature of the PT1000 sensor which is bound (with strong copper wire) to one of the heater resistors.
   (unfortunately I did no photo). But perhaps you can imagine the setup from the linked pics.

https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg3788051/#msg3788051

https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg3758498/#msg3758498

   Connection is via the heat spreader (aluminium bar) to the housing of the ADR.
   All is cotton cloth isolated within the thermo mug.
   So the measured temperature is nearly case temperature.
   With self heating of the ADR I think that the chip temperature is ~3 degrees warmer.

with best regards

Andreas

[RikV]

All this is very nice, but I would like to play along! Where and how can I get ADR100's? Are they reserved for VIP's? No sign of life on AD's site.

[RandallMcRee]

All this is very nice, but I would like to play along! Where and how can I get ADR100's? Are they reserved for VIP's? No sign of life on AD's site.

Somewhere in this thread (or was it a different one?) it is explained that you need to type "ADR1000AHZ" directly into the shopping cart search bar. When you do this it pops up with an order for 100, you can then update it to a lesser amount. Not sure, if this will be honored of course since I dare not check out at this time!