Author Topic: Ultra Precision Reference LTZ1000  (Read 747390 times)

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Online MiDi

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Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #2351 on: October 06, 2018, 06:48:25 pm »
Order has been updated to: In production. That took quite long.

-branadic-
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Offline BradC

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Re: Ultra Precision Reference LTZ1000
« Reply #2352 on: October 08, 2018, 07:11:21 pm »
Quick question.
So I re-read this entire thread (and a few others) looking for answers to these questions and can't seem to find anything other than vague subjective handwaving. So I'll ask a couple of questions and hopefully not trigger WW3.

LTZ1000 vs LTZ1000A. I'm under the impression that the standard LTZ1000 is actually likely to age / drift slower if it's run at a low enough temperature (ie with a 12.5k/1k divider). Are there really any real-world advantages to the A model other than power consumption (says he who has just taken delivery of some A units)?

Chopper amps as buffers. There are a number of posts dotted through several threads indicating that if you follow an LTZ1000 with a chopper it might be advantageous to stick an RC network in between to insulate the zener against the chopper input current pulses. My gut reaction is that sounds entirely reasonable and I'm struggling to see a downside. Has anyone done it? What sort of magnitude RC network might one look at if someone was mad enough to hack one into an existing design?

 

Online chekhov

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Re: Ultra Precision Reference LTZ1000
« Reply #2353 on: October 09, 2018, 12:31:06 am »

Chopper amps as buffers. There are a number of posts dotted through several threads indicating that if you follow an LTZ1000 with a chopper it might be advantageous to stick an RC network in between to insulate the zener against the chopper input current pulses. My gut reaction is that sounds entirely reasonable and I'm struggling to see a downside. Has anyone done it? What sort of magnitude RC network might one look at if someone was mad enough to hack one into an existing design?

Not an answer, but a quick hint - I've seen this thing in TiN's article - 'Project 792X - 10V "FX" reference'(https://xdevs.com/article/792x/), look for "RC network R7C1 and R11C3"
There is no deep observations regarding particular component values, put probably it was mentioned somewhere else or deduced from opamp specs.
 
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Offline Magnificent Bastard

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Re: Ultra Precision Reference LTZ1000
« Reply #2354 on: October 09, 2018, 06:46:57 am »
Quick question.
So I re-read this entire thread (and a few others) looking for answers to these questions and can't seem to find anything other than vague subjective handwaving. So I'll ask a couple of questions and hopefully not trigger WW3.

LTZ1000 vs LTZ1000A. I'm under the impression that the standard LTZ1000 is actually likely to age / drift slower if it's run at a low enough temperature (ie with a 12.5k/1k divider). Are there really any real-world advantages to the A model other than power consumption (says he who has just taken delivery of some A units)?

Chopper amps as buffers. There are a number of posts dotted through several threads indicating that if you follow an LTZ1000 with a chopper it might be advantageous to stick an RC network in between to insulate the zener against the chopper input current pulses. My gut reaction is that sounds entirely reasonable and I'm struggling to see a downside. Has anyone done it? What sort of magnitude RC network might one look at if someone was mad enough to hack one into an existing design?

Quote from: DiligentMinds (Private Communication)
Quote from: John R. Pickering (Private Communication)

  • WWIII has already begun-- it is just not nuclear (yet).
  • The 'A' version is the same die, but with a die attach method that is thermally insulating.  This helps a lot if you are running your reference on battery power-- it will save around 20% energy vs. the non-'A' part if run at the same die temperature.  LT (now ADI) applications engineers have said that the 'A' version has less hysteresis through power cycles.  Since the non-'A' version can be run at 10oC lower die temperature, the 20% energy savings is dubious.  The leads on the 'A' version will be cooler-- so that is a big plus in managing thermal EMFs between the Kovar leads and the copper board traces-- (the idea is that you want to keep all of these junctions balanced and at the same temperature).  Because of the die-attach method used in the 'A' version, it is advisable to have a high-temp (125oC) burn-in period where the entire burn-in period is 15-minutes ON and 15-minutes OFF.  This exercises the die-attach so that spurious jumps are suppressed.  This burn-in process must be followed by a conditioning process (like the Pickering Patent).  Because it uses a (more or less) ordinary die attach method, the non-'A' version does not require this special burn-in procedure-- but it still needs a 90-day (or so) burn-in (always ON) to 'settle' before calibration.
  • All you have to do is study the physics behind a lead-acid battery "desulphator" to understand that current pulses can indeed affect crystal lattices.  It's a real stretch, but I suppose it is at least possible that the current pulses on the inputs of a chopper amp can affect the LTZ (if over a year or so, and the effect might only be sub-ppm).  Assuming that this is true, a simple RC on each input will stop all of that (presumably).  This would be a non-microphonic cap to ground on the (+) input (with a resistor between the collector of Q1 and the (+) input), and a non-microphonic cap across the (-) input and the output of the amp-- with a resistor from the (-) input to the 120R resistor.  This way, any current pulses from the inputs of the chopper (due to charge injection from it's internal switching action) will be absorbed by the capacitors.  If you want to (unnecessarily) use a chopper amp for the LTZ current/heater control, the OPA187 looks good (with the above caveats).  A chopper for the 7V->10V boost circuit (or for a 1:1 buffer) is mandatory-- an OPA189 looks good or an LTC2057 (which has better input common-mode headroom).  I don't like resistor based boost circuits because you are at the mercy of the ratio drift of the resistors.  Some kind of filtered PWM technique seems much better IMHO-- but it would still need to be chopper based to eliminate amplifier drift from the equation.
« Last Edit: October 09, 2018, 06:49:20 am by Magnificent Bastard »
 
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Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2355 on: October 10, 2018, 04:02:55 am »


  • The 'A' version is the same die, but with a die attach method that is thermally insulating.  This helps a lot if you are running your reference on battery power-- it will save around 20% energy vs. the non-'A' part if run at the same die temperature.  LT (now ADI) applications engineers have said that the 'A' version has less hysteresis through power cycles.  Since the non-'A' version can be run at 10oC lower die temperature, the 20% energy savings is dubious.  The leads on the 'A' version will be cooler-- so that is a big plus in managing thermal EMFs between the Kovar leads and the copper board traces-- (the idea is that you want to keep all of these junctions balanced and at the same temperature).  Because of the die-attach method used in the 'A' version, it is advisable to have a high-temp (125oC) burn-in period where the entire burn-in period is 15-minutes ON and 15-minutes OFF.  This exercises the die-attach so that spurious jumps are suppressed.  This burn-in process must be followed by a conditioning process (like the Pickering Patent).  Because it uses a (more or less) ordinary die attach method, the non-'A' version does not require this special burn-in procedure-- but it still needs a 90-day (or so) burn-in (always ON) to 'settle' before calibration.



All my LTZ1000 run at about -measured- 50...54°C (12k/1k), and each circuit consumes in total about 25mA.
The PCB and the device are  inside an insulated box, so that assembly heats up to about 10°C above ambient.
At 22°C R.T., that makes about 20°C difference to heat up for the LTZ1000. From the datasheet diagram, that's about 100mW or 20mA heating power @ 240 Ohm heater resistance, which gives exactly these 25mA, when including OpAmps and reference supply.
I did not -yet- check for LTZ1000A, but the same calculation yields: 12.5k/1k => 62°C, about 30°C difference (due to higher thermal insulation) => 80mW, 18mA heater power, which would give 2mA less current consumption only (23mA in total).  Maybe somebody else can confirm that value for the LTZ1000A.
The only advantage of the A version would be a warm-up time of <1sec, compared to 20..30sec for the non-A version.

I still do not recommend such a 'burn-in', as it will only introduce big hysteresis, as measured and proven by Pickering, hp in their drift - AN18A, and by my own measurements.
Even if one applies the Pickering method, it's really difficult to get to the virgin state, if ever possible.
I would estimate, that the theoretical relaxation process by burn-in is minor compared to the hysteresis effect, so better never excessively heat the LTZ1000 / A device, neither by soldering (no short leads either), nor by 'burn-in'.

Anyhow, nobody knows -up to now- how LT tests the finalized LTZ1000/A devices.
As it's specified for -55/+125°C operating temperature, maybe they test it 100% for both temperatures at the final tester, although the datasheet implies testing parameters at 25°C only.
That might leave the finished device in an unknown hysteretic state, and some devices will stay there indefinitely, others may drift towards their virgin state.

So the initial drift of several ppm/ x months may arise from such a final test over temperature, but not being the 'real' annual drift.

I have encountered initial drifts between zero and -2.5ppm / yr. for all of my seven LTZ1000 / 50°C references, either after assembly, or after erratically over-heating and re-conditioning.
After that time, all seem to approach the typical -0.8ppm/year, or less.

So I again recommend to just leave them alone, as burn-in may do more harm than will really / practically / measurably improve the long-term drift.

Frank
« Last Edit: October 10, 2018, 08:04:36 am by Dr. Frank »
 
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2356 on: October 10, 2018, 05:13:23 am »
Hello,


All my LTZ1000 run at about -measured- 50...54°C (12k/1k), and each circuit consumes in total about 25mA.
The PCB and the device are  inside an insulated box, so that assembly heats up to about 10°C above ambient.
At 22°C R.T., that makes about 20°C difference to heat up for the LTZ1000. From the datasheet diagram, that's about 100mW or 20mA heating power @ 240 Ohm heater resistance, which gives exactly these 25mA, when including OpAmps and reference supply.
I did not -yet- check for LTZ1000A, but the same calculation yields: 12.5k/1k => 62°C, about 30°C difference (due to higher thermal insulation) => 80mW, 18mA heater power, which would give 2mA less current consumption only (23mA in total).  Maybe somebody else can confirm that value for the LTZ1000A.


the current consumption of my LTC2057 buffered devices is listed here:
(20-24 mA including a LT1763 voltage regulator which should be well below 1 mA)

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560

For ageing: I think it depends more on the individual device or datecode than on the "A" or non A version.
But since we do not have enough samples and a JJA at hand we will never know.

with best regards

Andreas
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #2357 on: October 10, 2018, 05:18:20 am »

...as measured and proven by Pickering, hp in their drift - AN18A,

Would you please link the publications/pdfs you are refering to? Thanks.  :-+

-branadic-
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Online MiDi

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Re: Ultra Precision Reference LTZ1000
« Reply #2358 on: October 10, 2018, 05:45:22 am »
Anyhow, nobody knows -up to know- how LT tests the finalized LTZ1000/A devices.
As it's specified for -55/+125°C operating temperature, maybe they test it 100% for both temperatures at the final tester, although the datasheet implies testing parameters at 25°C only.

Quote
Note 2: All testing is done at 25°C. Pulse testing is used for LTZ1000A to
minimize temperature rise during testing. LTZ1000 and LTZ1000A devices
are QA tested at –55°C and 125°C.

Whatever QA testing means  :-//
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2359 on: October 10, 2018, 06:26:33 am »
Whatever QA testing means  :-//
Usually: you take from each lot a number of samples and test them.
 

Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2360 on: October 10, 2018, 06:59:05 am »
Hello,


the current consumption of my LTC2057 buffered devices is listed here:
(20-24 mA including a LT1763 voltage regulator which should be well below 1 mA)

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560

For ageing: I think it depends more on the individual device or datecode than on the "A" or non A version.
But since we do not have enough samples and a JJA at hand we will never know.

with best regards

Andreas

Andreas,
thank you very much for your hints, which support my rough estimations.
Therefore, the LTZ1000A really has no big advantage regarding power consumption over the non-A device.

Regarding ageing, I think it's possible to make at least a well educated guess, even w/o a JJA.

If you have a history, and a big enough amount of LTZ1000, you can identify these minute deviations.

Frank
 

Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2361 on: October 10, 2018, 07:09:04 am »
Whatever QA testing means  :-//
Usually: you take from each lot a number of samples and test them.

There's different philosophies, or requirements on testing, which I have seen at different manufacturers at their production lines...

If you have commercial grade devices, you would only take some random samples and test them to the limits (e.g. over temperature), and rely on predictive statistics.
If you have high grade devices, like military, or critical automotive parts (e.g. non-volatile memory), you would really test them 100% (each device) at the limit temperatures.

I don't know, how serious LT takes the expensive LTZ1000, but I could imagine that because of the price tag, they really test it to 100%.

Maybe we should contact them, which tests they really perform on the devices.
And maybe they are not really aware of the pitfall of such handling.
 

Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2362 on: October 10, 2018, 07:45:39 am »

...as measured and proven by Pickering, hp in their drift - AN18A,

Would you please link the publications/pdfs you are refering to? Thanks.  :-+

-branadic-

I refer to the patent of Pickering, and his explanations on the 7001 reference.
AN18a should be well known, so I don't put a link here. You just have to extract from that AN18a, that the 3458A may basically suffer from hysteresis, if left unpowered (which is not included in the specifications).

branadic, when you have measured my LTZ #3 last January, it was quite cold, below 0°C, during the transport. You see the graph before, and after this ring comparison, and over the following year after initialization, referenced to my home 3458A and 5442A. Latter seem to be constant within < 1ppm.
This #3 reference made a hysteretic jump of about +1ppm, due to the low temperatures, which is obviously a permanent, and constant one.
You also see two baseline points for the 3458A, the first is from acbern, the 2nd is taken recently at the Hannover Maker Faire, using this same #3 compared to the PTB 3458A.
The ring comparison before/after the transport to the Maker Faire shows no change, in contrast.

This event, and several others, support my own experience with hysteresis behaviour of the LTZ1000 device, at sub-ppm level, even w/o JJA.

Frank
« Last Edit: October 10, 2018, 07:56:05 am by Dr. Frank »
 
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Offline martinr33

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Re: Ultra Precision Reference LTZ1000
« Reply #2363 on: October 10, 2018, 11:05:42 am »
So... ife we could add a little bit of logic to the 3458a to deliver that ramping waveform to the LTZ1000A on startup, it would improve the drift on the 3458a?

I think that the circuit could be noise-free - it would have a "suicide mode" that cut all power once the warmup was completed. There would certainly be some digital noise in the window. Problem is, it is 4 hours long which seems a bit much for day to day operation. but is the spec for true precision.

Or maybe the 3458a devices were selected for low hysteresis.
« Last Edit: October 10, 2018, 11:15:28 am by martinr33 »
 

Offline 3roomlab

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Re: Ultra Precision Reference LTZ1000
« Reply #2364 on: October 10, 2018, 10:43:57 pm »
reading the pickering pdf and refering back to post #2251 (todd's wavetek conditioning posted by Tin). any idea why was the wavetek using a longer time of 8.5hrs? longer time / more cycles = more thorough conditioning process I assume?
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Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #2365 on: October 12, 2018, 08:33:41 pm »
UPDATE: Got the info today, that the boards have been shipped on Wednesday, October 10, 2018. What should I say, they today already received at my location. Attached is a picture on how they looked like, before they where shipped.

Time to send out some mails this weekend.

-branadic-

EDIT: Just for sanity check. Everyone should have received an email with all the further details. Hopefully we will see some pictures of assembled LTZ-boards soon.
« Last Edit: October 14, 2018, 12:30:17 am by branadic »
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Online Vgkid

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Re: Ultra Precision Reference LTZ1000
« Reply #2366 on: October 14, 2018, 05:53:29 am »
Received email , monies will be sent.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #2367 on: October 14, 2018, 07:44:57 am »
All extra boards are sold.  :-+

-branadic-
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Offline 3roomlab

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Re: Ultra Precision Reference LTZ1000
« Reply #2368 on: October 14, 2018, 06:48:25 pm »
this is just a simulation, the pickering "pulser thingy". it is a trashy attempt very likely everything is concieved from the wrong side of the brain with all the stars in wrong alignment.
basically a 1 shot monostable running a astable (to stop the astable @ 30k seconds), and a bunch of opamps trying to swing stuff around 550mV.

(anticlockwise from top left, ends at top right)
the ramp from the monostable @N03 (and switching on/off power node "VP" thru 2 badly drawn NMOS/PMOS), gets added to the smaller pulse @N05, reshaped @T001. level shifted to fit around 550mV @ T003. and goes thru a relay (SW) to inject into a fake LTZ.

a 1farad as timer? I dont suppose there is a better way to get to 10k-30k seconds?
I might have gotten some things very wrong, but maybe this could inspire a real working version?
« Last Edit: October 14, 2018, 06:53:09 pm by 3roomlab »
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2369 on: October 14, 2018, 09:01:01 pm »
Hello,

when I see the effort I would rather make something with a small processor and a DAC (LT1257).
similar to the cirquit here:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg844021/#msg844021

In any case I would use a relay to disconnect the hysteresis cirquit after the full time.

with best regards

Andreas
 

Online MiDi

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Re: Ultra Precision Reference LTZ1000
« Reply #2370 on: October 17, 2018, 10:41:43 am »
First impression of branadics (Dr. Franks) design - could not wait and bodged test-pcb together - thank you very much!

« Last Edit: October 18, 2018, 09:54:53 am by MiDi »
 
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Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #2371 on: October 17, 2018, 05:52:35 pm »
Wonderful, hope it is alive  :-+

BTW: The second bunch with boards went to the post office this morning and should receive their owners within the next days.
Thanks to all those of you sending a beer or two extra.

-branadic-
« Last Edit: October 17, 2018, 07:22:34 pm by branadic »
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2372 on: October 17, 2018, 06:36:08 pm »
First impression of branadics (Dr. Franks) design - could not wait and bodged test-pcb together - thank you very much!

But why do you use IC-sockets in a precision cirquit?
I had horrible drifts (several ppms) in my LM399#3 until I removed the sockets.

with best regards

Andreas
 

Online borghese

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Re: Ultra Precision Reference LTZ1000
« Reply #2373 on: October 17, 2018, 08:01:53 pm »
Boards arrived
High resolution image https://islandlabs.eu/_media/Black%20Boards.jpg
« Last Edit: October 17, 2018, 08:11:27 pm by borghese »
Cheers
Borghese
 

Online MiDi

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Re: Ultra Precision Reference LTZ1000
« Reply #2374 on: October 17, 2018, 09:02:21 pm »
Short test was successful  :-+

But my heart went into my boots after power it on  :o

The output of +REFbuf was sitting at ~6.9V for a felt eternity until it suddenly went to stable ~7.10V  :phew:

Is this expected behaviour?

I triple checked everything before power it on and went step by step through initial operation:

1) supply check (only components for this installed)
2) chopper check (simple zener & for safety 330Ohm heater resistor installed, missing LT1013 & LTZ1000)
3) final test with all components

But why do you use IC-sockets in a precision cirquit?
I had horrible drifts (several ppms) in my LM399#3 until I removed the sockets.

I knew someone would ask that  8)
This pcb is just to practice and for testing purposes.
In the productive units there will be no sockets and no jellybean (0815) resistors wacked together  ;)
 


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