Ultra Precision Reference LTZ1000

[branadic]

Here is the reverse engineered schematic and board layout.

[Andreas]

Hello Branadic,

where is the 1 Meg resistor in series to C1 from the datasheet?

R1,R2,R3 are not critical in value. They need only stability.
The R4/R5 value is 12.2 so it would be ok for a LTZ1000 (but not for the A-type).
But I think the 12K resistor is no precision device in your case. (low TC).
The ratio is very critical.

with best regards

Andreas

[branadic]

Andreas,

compared to the datasheet C1 is not 100nF, but some film cap instead (the upper right cap), with now unkown value.
Why? When the board received the solder junction were full with solder flux, so I had to clean it with IPA. The damn thing about that is, that this way I loosed the printing on the caps. WTF!
There is no 1meg resistor in series, as pictured in the datasheet. Also the diode CR2 between heater and ground was added later and not planed in the original board design.
The 12k (11k91 in my case) equals R5 in the photo and I guess it is some precision type too, even though I don't know the manufactor of the resistors.

[CaptnYellowShirt]

  You can read about it here:

http://www.edn.com/design/analog/4427151/The-last-half-century--Wirewound-resistors-Part-one

http://www.edn.com/design/analog/4427940/The-last-half-century--Wirewound-resistors-Part-two

From Part Two:

"Film resistor users should note that most precision film resistor’s specifications calls for operation at a small fraction of their stated power capacity.  This is indicative of the film resistor’s inherent flaws; they cannot operate with any kind of power applied to them and maintain any semblance of stability.  Their TCR curves literally go out the window with power.  Our TCR’s are linear and flat over their operating range, no hyperbolic curves to correct for, no worries about what applying power to them will do; it has no effect upon them.  There are no applied voltage coefficients either and long term stability under power is better than film resistors sitting on a shelf."

[CaptnYellowShirt]

I have some ideas on the LTZ drift but it will cost $100k to test and I can't justify that.

Volt-Nuts bake sale?

[Dr. Frank]

No news at all..

That drift mainly in the negative direction of the LT references had been investigated by Fluke, comparing the 732B drifts of the Motorola against the LTFLU:
"predictability of solid state zener references", D. Deaver, Fluke, ca. 2001

An asymmetrical drift of (-0.8 +/- 0.7) ppm/yr. is already in the datasheet of the Pickering reference, the 7000 reference module, now terminated by Fluke.

I think, that is caused by the physics of the LTZ silicon, degenerative processes, and hardly to be mitigated by any odd "burn in " process. (still no description about that, from Bob Dopkins, I think?)

So the goal of building ultra references is to bring all external drifts (i.e. from the Rs) to near zero and then to compare, and select the reference with the smallest drift.

It will take 1 year of monitoring for 0.5ppm/yr, and 2years for 0.3ppm/yr predictability, typically.

Frank

[Mickle T.]

If anyone is interested, here are some of the Fluke 7000 voltage reference pictures, posted by lymex on the 38hot.

[Galaxyrise]

Nice copper ring, though... soldermasked and not connected to anything... just some thermal mass?  LT1413 instead of LT1013, too, nice little bit of "modernization."

[Mickle T.]

LT1413 opamp for LTZ1000CH was introduced in the Fluke 8508A nearly at the same time (2002) as in the 7000 series. Somewhat later (~2008) Fluke 8508A received a new "modded" reference with LTZ1000A and AD823A/LTC1150 instead of LT1413.

[babysitter]

Nice copper ring, though... soldermasked and not connected to anything... just some thermal mass?  LT1413 instead of LT1013, too, nice little bit of "modernization."

Maybe the same reason as the guard cooper pour on my board besides the electrical: helping the thermal coupling to reduce temperature difference between LTZ1000 pins as advised by the datasheet already on page 4:

It is mandatory to keep the zener and transistor leads at the same temperature, otherwise 1 ppm to 5 ppm shifts in the output voltage can easily be expected from these thermocouples.

[babysitter]

I just got some ceramic hollow feedthrus for soldering.

Great to embed a voltage reference hermetically in my beloved tuner boxes and having one massive copper wire going uninterrupted from the inside to the outside.

i.d. 2.5 mm, length 12mm, thin part od 5mm, thick part od 7mm.

[babysitter]

No Part number, coming from a ham surplus dealer.
The manufacturer was Stettner, which has been first renamed to Stelco and is now
Sumida

http://www.sumida-components.com/en/welcome-to-sumida-components-gmbh/?no_cache=1

They offer pinless feedthru capacitors, thats how you can see those.

[branadic]

No Part number, coming from a ham surplus dealer.

And can you tell us who is the ham surplus dealer? Up to now I only found those feedthrough caps in a leaded version. The one in your picture looks somewhat different.

[babysitter]

Oh, sorry, of course! Didn't want to hide my great personal source to sell 65 cent parts to you for 5 euro/each... only if you really want

http://www.oppermann-electronic.de/

Its in the ceramic section. Sorry, german page for the foreigners, but I have some spare parts

[ltz2000]

Great to embed a voltage reference hermetically in my beloved tuner boxes and having one massive copper wire going uninterrupted from the inside to the outside.

Certainly a major improvement, but don't expect to get hermetic seal comparable to glass-metal. Any pressure difference will slowly equalize.

It is possible to get extremely low leakage (similar to glass-metal) with metallized ceramic feedthrough by carefully selecting the ceramic material and metallization for that purpose. But the material it is attached to (the box, wire and solder) affects the most. Difference in thermal expansion coefficients will cause the plating to peel off when soldered and creates a microscopic route between the inside and the outside world.

[babysitter]

@ltz2000

We discussed pressure relief before; see [url]https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg252548/#msg252548]https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg252548/#msg252548] [url]https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg252548/#msg252548[/url] and SeanB's remark.

Thermal expansion is still there...

[MisterDiodes]

Well, I think I've waited long enough for someone else to say something about this.  The 70xx series was designed long after the Datron 1281 or the 4910.

!!! L@@K !!! NO SLOTS !!!!

I hope this ends [forever] the debate on slots vs. no-slots...

--Ken

<Laughing>  We built some LTZ1000 vrefs almost 20 years with slots, and some in the same batch without.  Tried all sorts of voodoo - even oil-immersed resistors.  Absolutely No difference in the end.  I wish I had a time machine so that my 20-year later self could go back and tell me to quit wasting time and money.

What helped the most out of everything?  Let the Vrefs run about 10 ~15 years or more and quite worrying about yearly drift.  See if they do well over 3~6 months.  They just get better over time, at least any of the ones I've tracked.    Using -good- wirewound resistors worked just as well as any other expensive magical Voodoo resistor in the end.

[TiN]

Finally i got recovered schematics of KI2002's LTZ1000 VREF.

Enjoy.

No voodoo magical resistors, just PTF56 68.1K, wirewound 120ohm and precision 2R network. No slots either, just a plastic cup on top and bottom.

[Andreas]

Hello,
 
can you verify R268?
The value between Pin 1 + Pin 2 makes no sense. It should be more in the 1K - Range (perhaps 1.1K)

So the resistor divider seems to be the most "valuable" resistor pair of the whole cirquit.

With best regards

Andreas

[TiN]

KI's repair manual (page 138) lists R268 as RES NET, 13.1K, 13.3K, 0.1%, 100MW, THINFILM.
You think it's a typo there? and it's 1.1K/13.3K ?

[MisterDiodes]

Also the inclusion of R251 at 200k can be a problem.  That was included for LTZ1000, but for the A version it is not used.  Some people use it anyway, we found it caused more problems with the LTZ1000a over time.  Linear tells you right in the datasheet to not use it for '1000a.  They are correct in most applications.

[MisterDiodes]

Just a note:  The 12k / 12.5k advice is good for applications where ambient temperature is low, but does not apply in every case.  The instrument makers go on the high side of the ratio, say 13k ~15K : 1k or more to raise the temp of the LTZ1000(a).  If the ratio is too low for a warmer ambient climate, then the LTZ1000 zener Vref becomes a thermometer and starts tracking ambient temp.  Its been my experience that if you know you'll be operating at below 85°F ambient, then the lower ratio is good. (Which is probably most of the time).  If you know your device will be above 90°F a lot of the time, then a higher ratio will give you better drift performance.  For instance, if we knew a a Vref would be used on a rack full of hot equipment (Ambient say 105°F to 115°) , the heater ratio would usually be set for 13k or even the standard 15k to 1k.  In other words you need to have the Vref Zener temp. higher than the changing ambient.  The more ambient is fluctuating, you will tend to want a higher ratio.

The other technique that works well is to just forget the on-chip temp transistor and just control the temperature of the space around the LTZ1000 directly with good thermal mass.  It isn't as fast for warm up time, but you'll get as good or better steady Vref performance.   You basically just make yourself an ovenized / potted Vref,  and that can cost a lot less for production than magical, expensive Whoop-Dee-Doo resistors.   Over a long time frame we found this technique is probably one of the better ways to make a solid Vref - IF you can stand a longer warm up, say an hour or two. 

Most of the time the stuff we make is never turned off, so warm-up time is usually not an issue.  That is good advice for any serious PPM-range Vref.

It just depends on application. 

 

[ltz2000]

For the 3458A, it was also designed for use in up to 55C environments [don't ask me why-- I have no clue]

Business? The ratio of instruments sold must be something like metrology labs 1 - automated test systems 100.

[HighVoltage]

I'm reminded of the book "Foundations of Mechanical Accuracy" in which the story of replicating the meter standard in the 1970's was told. The Moore Tool Co would send a rep to France with a briefcase that contained what they though was some fraction of a meter. The guy hops on a transatlantic flight, sets up the standard next to the one in Sèvres, waits how ever many hours/days you need to make sure everything's at the right temperature, and finally shines a laser at the ends of each to figure out how much they are off. The guy gets the report, flies back home, sets up the standard in a room inside a room in the sub-basement of the Moore Tool Co. and they take like a month to file off their best guess at another nanometer. All this just to fly back to France and try again and again until they've gotten "close enough" or they've gone too far.

Sounds like an interesting book, that I never heard of before.
 .... but it is $ 186 on Amazon

http://www.amazon.com/Foundations-mechanical-accuracy-Wayne-Moore/dp/B0006CAKT8/ref=sr_1_1?ie=UTF8&qid=1405788804&sr=8-1&keywords=Foundations+of+Mechanical+Accuracy

May be I can find a PDF of it.

[jpb]

Sounds like an interesting book, that I never heard of before.
 .... but it is $ 186 on Amazon

http://www.amazon.com/Foundations-mechanical-accuracy-Wayne-Moore/dp/B0006CAKT8/ref=sr_1_1?ie=UTF8&qid=1405788804&sr=8-1&keywords=Foundations+of+Mechanical+Accuracy

Out of curiosity I had a check on Abe books and they are even more expensive....
http://www.abebooks.co.uk/servlet/SearchResults?an=Wayne+R+Moore&sts=t&tn=Foundations+of+mechanical+accuracy