Author Topic: Ultra Precision Reference LTZ1000  (Read 1333754 times)

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Offline iMo

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Re: Ultra Precision Reference LTZ1000
« Reply #2850 on: February 16, 2020, 11:22:51 am »
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"
« Last Edit: February 16, 2020, 11:51:57 am by imo »
 

Online Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2851 on: February 16, 2020, 11:51:28 am »
What do others think?

... you need more meters.
otherwise you cannot distinguish wether it is from the LTZ or from the meter.

my K2000 also has from time to time (at certain temperatures) some popcorn noise.
Of course there can also be many other reasons like EMI from mains into the reference or the meter.

of course popcorn noise (at least short duration events) from the reference can also be measured with a 1/f (0.1-10 Hz) amplifier

with best regards

Andreas
 
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Offline hwj-d

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Re: Ultra Precision Reference LTZ1000
« Reply #2852 on: February 16, 2020, 12:37:47 pm »
You seem to have 1.5 uV drift in 10 minutes, which is a lot and may indicate there is something else going on besides ageing. Or is the plot in hours?

Regards, Dieter
Minutes. Looks like a relative fresh assembled new kit to me.
 

Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2853 on: February 16, 2020, 02:47:15 pm »
I can see from time to time these spikes (marked in red in the photo). This is a new ltz1000ach ageing, but the measurements were taken (a) in the temperature oven (b) in the shielded enclosure (c) powered by a battery pack. The only thing which comes to my mind are cables. I’m using ordinary 22AGW cables rather than shielded ones. However, from the DMM I’m running banana to BNC shielded cable with hooks at the end.

What do others think? Where these spikes are coming from? What cables are you using for your boards please (links to Digi-Key would be appreciated)

Alex,
I assume you are using the same PCB and circuit like your already running LTZ1000 reference board?
Have you ever observed these spikes on this non-A version reference with this DMM?
Frank
« Last Edit: February 16, 2020, 02:57:35 pm by Dr. Frank »
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2854 on: February 16, 2020, 03:40:35 pm »
You seem to have 1.5 uV drift in 10 minutes, which is a lot and may indicate there is something else going on besides ageing. Or is the plot in hours?

Regards, Dieter
Minutes. Looks like a relative fresh assembled new kit to me.

It's correct. It is minutes and this has been assembled recently. This is LTZ1000ACH
 
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Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2855 on: February 16, 2020, 03:53:41 pm »
I can see from time to time these spikes (marked in red in the photo). This is a new ltz1000ach ageing, but the measurements were taken (a) in the temperature oven (b) in the shielded enclosure (c) powered by a battery pack. The only thing which comes to my mind are cables. I’m using ordinary 22AGW cables rather than shielded ones. However, from the DMM I’m running banana to BNC shielded cable with hooks at the end.

What do others think? Where these spikes are coming from? What cables are you using for your boards please (links to Digi-Key would be appreciated)

Alex,
I assume you are using the same PCB and circuit like your already running LTZ1000 reference board?
Have you ever observed these spikes on this non-A version reference with this DMM?
Frank


Hallo Dr Frank,

No, this is a different PCB producing a buffered 7.1V. This is the LTZ1000ACH
The idea is to have several LTZ1000 and LTZ1000ACH and then I can monitor the drift against the recently calibrated ones.
Unfortunately, my gear is too useless to monitor
I was conducting some tests with the temperature oven when I noticed this peak noise. I cannot remember observing it with a non-A version.

However, I must admit that the reference has not been aged yet. It probably has to sit on the PSU for months before doing any tests

Thanks
Alex
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2856 on: February 16, 2020, 03:56:41 pm »
What do others think?

... you need more meters.
otherwise you cannot distinguish wether it is from the LTZ or from the meter.


I completely agree with you.
However, we are looking into an expensive territory.
I can do ratio measurement on my DMM between a calibrated LTZ1000 and a new LTZ1000 (after aging it).
Or maybe you can advise on how to measure it properly without spending $$$ for the equipment?
 

Offline exe

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Re: Ultra Precision Reference LTZ1000
« Reply #2857 on: February 16, 2020, 04:15:46 pm »
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"

Afaik the reference inside is SZA263 .
 

Offline hwj-d

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Re: Ultra Precision Reference LTZ1000
« Reply #2858 on: February 16, 2020, 05:40:19 pm »
Something to compare. This is 10V PX LTZ-CH, now ca. 20 month at 15V. Such a peek happens ca. 1/month last 6 month.
Weather is quite stormy, last 2h.

« Last Edit: February 16, 2020, 05:44:47 pm by hwj-d »
 
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Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2859 on: February 16, 2020, 06:17:08 pm »
Something to compare. This is 10V PX LTZ-CH, now ca. 20 month at 15V. Such a peek happens ca. 1/month last 6 month.
Weather is quite stormy, last 2h.

So it is a 20 months old Vref? 31uV p-t-p!!!
Do you think it has been caused by a storm? I remember reading a thread where MisterDiodes mentioned that LTZ1000 was picking up a train several blocks away.
 

Offline Conrad Hoffman

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Re: Ultra Precision Reference LTZ1000
« Reply #2860 on: February 16, 2020, 07:44:35 pm »
I don't know if this applies to buried zeners but a friend used to build commercial instruments with voltage references. He selected his TC zeners based on noise. The zeners with the lowest noise were also the most stable over time. This was in the days of 1N82x types. I believe popcorn noise is the result of defects in the crystal lattice and I'd be surprised if it improved over time. Naturally at the level we're talking here, noise can sneak in from anywhere and everywhere! As for that LT1052 failure some posts above, I always found they were quite fragile and managed to pop more than a couple. They also aren't very good at driving their own feedback network, preventing the use of low values for low noise. Regardless, the zero drift makes up for everything else.
 
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Offline hwj-d

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Re: Ultra Precision Reference LTZ1000
« Reply #2861 on: February 16, 2020, 07:51:52 pm »
Something to compare. This is 10V PX LTZ-CH, now ca. 20 month at 15V. Such a peek happens ca. 1/month last 6 month.
Weather is quite stormy, last 2h.

So it is a 20 months old Vref? 31uV p-t-p!!!
Do you think it has been caused by a storm? I remember reading a thread where MisterDiodes mentioned that LTZ1000 was picking up a train several blocks away.
This PtP is the single popcorn peak. Std Dev under this circumstances with 10V upward regulation is 1.77µV, without popcorn <1.5µV for this 10V-PX, without upward regulation <1.3µV.
Think about, this DMM6500 isn't better. The PtP limit of this meter itself isn't better than ~ 10 to 12µV. Below that, you are looking to the limit of your 6.5 meter, not the DUT.  ;)
 

Offline alex-sh

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Re: Ultra Precision Reference LTZ1000
« Reply #2862 on: February 16, 2020, 08:14:14 pm »
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"

Afaik the reference inside is SZA263 .

IMHO DMM7510 has got LTFLU (SZA263?).
DMM6500 has got LM399AH voltage reference with Keithley marking - https://xdevs.com/review/dmm6500/
 
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Offline hwj-d

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Re: Ultra Precision Reference LTZ1000
« Reply #2863 on: February 16, 2020, 08:18:18 pm »
Because of the "storm". Maybe the quickly falling air pressure caused the slight upward trend that can be seen at the end of the curve.
 

Offline BU508A

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Re: Ultra Precision Reference LTZ1000
« Reply #2864 on: February 16, 2020, 08:36:09 pm »
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"

Afaik the reference inside is SZA263 .

IMHO DMM7510 has got LTFLU (SZA263?).
DMM6500 has got LM399AH voltage reference with Keithley marking - https://xdevs.com/review/dmm6500/

The 7510 has the LTFLU-1 inside.


Source:
https://hiveminer.com/Tags/dmm7510,pcb

The SZA263 has been produced by Motorola and is obsolete since a very long time (back in the 1980's I think).
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Offline Edwin G. Pettis

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Re: Ultra Precision Reference LTZ1000
« Reply #2865 on: February 17, 2020, 12:35:00 am »
Yes Motorola originated this part and a whole laundry list of zener based references, some of which live on in various newer reincarnations such as the LTFLU (you might call it the grandchild).  There were several pages of data sheets on various reference zeners and reference amplifiers (aka the SZA263 that eventually morphed into the LTFLU).

Besides the many zener references such as the 1N82xA series, 1N4565-1N4580, 1N3154/A, 1N4775/A, 1N4780/A, series1N935A/B/C, 1N216xA series and 1N941/A-1N945/A series
The precision ref zener series MZ605, MZ610, MZ620 and MZ640
Amplifying regulator diodes, MCA1911 - MCA2234
Low voltage zeners, MZ2360/61

Plus a host of house numbered variations like the SZA263.

Today, the LTFLU is only sourced by Linear Tech and sold only to Fluke, any of these that show up on the flea bays are either from recycled/resold equipment or fakes.  How the LTFLU 'legally' found its way inside a TEK piece of gear is up for speculation, perhaps a quiet agreement between TEK/Fluke/LT but Fluke was the only buyer of these that I had heard of.

Yes I'm aware that ADI took over LT but it is still LT making these parts, ADI doesn't make them.  No I didn't like the take over, I think ADI is messing LT up.
« Last Edit: February 17, 2020, 12:38:00 am by Edwin G. Pettis »
 
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Offline chuckb

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Re: Ultra Precision Reference LTZ1000
« Reply #2866 on: February 17, 2020, 03:25:51 am »
The Danaher Corporation bought Fluke in 1998. Then Fluke was spun off as part of Fortive a few years ago. Danaher also bought Tektronics in 2007 and Keithley in 2010. So Fluke, Keithley and Tektronics were all related for awhile. So at one point they may have shared their best technology like the LTFLU.
 

Offline Edwin G. Pettis

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Re: Ultra Precision Reference LTZ1000
« Reply #2867 on: February 17, 2020, 04:11:47 am »
Interesting, that may have been a viable situation although I'd bet Fluke wasn't too happy about it, never know about these corporate dealings, insanity lives for these <laughing>.
 

Offline MiDi

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Re: Ultra Precision Reference LTZ1000
« Reply #2868 on: February 17, 2020, 10:05:04 am »
Wondering if the LTFLU is orderable as a replacement from Keithley/Tektronix :-/O
 

Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #2869 on: February 18, 2020, 12:38:55 am »
Buying LTFLU without matching resistors is feat with little benefit vs "usual" LTZ.
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Offline Conrad Hoffman

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Re: Ultra Precision Reference LTZ1000
« Reply #2870 on: February 18, 2020, 12:44:40 am »
I was able to improve the thermal performance of my Fluke 731A by tweaking the resistors. The old cardboard box and light bulb trick. It took a few days but was well worth it. That leads me to believe it would work with any of 'em.
 

Offline notfaded1

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Re: Ultra Precision Reference LTZ1000
« Reply #2871 on: February 18, 2020, 01:06:59 am »
Buying LTFLU without matching resistors is feat with little benefit vs "usual" LTZ.

Speaking of this I was wondering... I recently (for the heck of it) picked up an F8842A.  Can I use it to make a decent voltage reference to help with comparing to my new 3458?  I'm already planning on two LTZ1000A's and have the LTZ's but what about using the resistor network from the F8842A with it's reference zener?  I saw someone else did this and boosted the output to make 10V reference.  I was hoping to do something similar.  No one's figured out how to use these resistor networks from an F8842A with an LTZ have they?  Or is that out of the question because they're all matched and you couldn't make it work?  That's the first thing that came to mind... wow a well aged resistor network... with the right ratios could be golden with an old aged LTZ1000A... maybe I'm dreaming?

To add to this... I've kinda come to the conclusion that making or remaking some refs makes more sense than buying old (maybe not working) 732A.  It's a little let down I'd think to pay that much then be stuck trying to take that old foam apart inside and then being afraid of messing up the way it's put together if it doesn't work right.  I can see replacing the batteries and some minor on the edges repairs but tearing into the guts doesn't look like it's for the faint at heart?  I may get one anyhow and try... I'm looking in other places now vs. just Ebay.  I found the 3458 that way.

I'd almost rather sleuth for a 732B I think.  The search for the 3458 was long but maybe it's worth the wait vs. one of your types of teardowns to try and fix an A.

What do you cut out the PCB section with without tearing it up so you have clean cut?  Some kind of dremel or saw of some kind?

Thanks,

Bill
« Last Edit: February 18, 2020, 01:48:31 am by notfaded1 »
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Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #2872 on: February 18, 2020, 03:51:26 am »
Yes and no. With 732A/B/C you get much more than just a reference chip and some resistors. There is far more attention to make everything rugged, battery backed-up and robust enough for everyday use and transport, which is a project on its own, compared to just LTZ module. I've bought 732A some time ago, and it had jumping SZA263 chip. Thread: https://www.eevblog.com/forum/metrology/fluke-732a-with-popcorn-noise-sza/

Since I didn't care about history, I've butchered original SZA chip, replaced it with SZA263 from donor 8842A, and... jumps are gone... yay.... but noise is 20 times worse now... That made me think 8840/8842A's get worse bin of SZA chips. Now I got 5440B reference board, where I can steal two SZA263's and matching PWW resistors to transplant it into 732A to make it useful... But that project sits abandoned since September. I'll revisit it some day.

With LTZ it's easier and cheaper (time wise) to get all parts and get it going. You don't need to dick around resistors and matching, unlike SZA/LTFLU. In worst case if you buy bad 732A, you get nice project box with oven, battery power, low thermal posts where you can put LTZ1000A circuit inside and have fancy looking DIY REF for your lab. ;) One of the benefits that SZA/LTFLU have - you can use same resistors to scale output voltage to 10V directly, instead of additional active components in case of LTZ. Making sub-ppm stable 10V out of 7V is much more difficult task than ultra-stable 7V.
« Last Edit: February 18, 2020, 03:55:03 am by TiN »
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Offline notfaded1

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Re: Ultra Precision Reference LTZ1000
« Reply #2873 on: February 20, 2020, 01:25:06 am »
Making sub-ppm stable 10V out of 7V is much more difficult task than ultra-stable 7V.
Yes and isn't this just what you need to compare with your 3458(s) right?  Maybe not to calibrate with but at least to compare and see how they agree... see what's drifting and which are staying more the same as a group giving some confidence.  I suppose either way measuring both the default 7V stable reference and the boosted 10V would be a good idea anyhow.  Perhaps your unboosted 7V reference is pretty stable but something happened with your boost resistors drifting and now your 10V is off because the boost part of the circuit changed?  I'm thinking this because I'm at the point of ordering PCB's and resistors vs. only looking for 732A/B.  I really like the red FX PCB btw... bummed I missed out on the FX reference.  How did you get so many Fluke-custom hermetic film resistor network P/N 2464707?  Ironically I think the company that makes them is just south of where I work... I think they're in Tempe, AZ.

Bill
« Last Edit: February 20, 2020, 01:49:00 am by notfaded1 »
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Offline Villain

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Re: Ultra Precision Reference LTZ1000
« Reply #2874 on: February 20, 2020, 03:20:44 pm »
Hi,

i have a quick side question. Is it possible to buy a LTZ1000 reference board fully assembled somewhere? Or from someone on the forum? I would pay an appropriate price obviously.

Regards,

Alex
 


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