Group-buy for 10V LTZ1000A reference? [Completed, no more boards].

[TiN]

Considering Decided to make 10 completely assembled and tested modules to provide +10.00000 +/-4 ppm buffered output.
One of the challenges is cost and time involved to test and calibrate these things.

Device is based around xDevs.com FX module PCB, which have next design specifications:

Reference source: LTZ1000ACH with datasheet schematics, using LT1013ACN.
LTZ Temperature SP: 13K/1K which provide about +55C oven temp
Resistors: VPG BMF HZ for 120ohm, temperature SP. PTF56 5ppm/K for 70-80K bias resistors
Output 7V->10V stage: Chopper opamp ADA4522-2 in SO8, Hermetic resistor network or BMF resistors. Each unit adjusted by trim resistor for tight output tolerance.
Onboard supply: Linear LT3042 LDO, configured for +11V output to LTZ circuit.
PCB: 4-layer FR4 with ENIG plating
Input power requirements: +12V and -12V.
Power consumption : ~0.6W when operated with +24C ambient
Additional features : isolated section with I2C EEPROM with calibration data/config/history (RPI python app to be provided to maintain data), MAX6610 PCB temperature sensor for tracking
Calibration traceability: <4 ppm to 732B, uncertain with 0.6ppm.
Expected performance: <4 ppm/year long-term stability, <0.1ppm/K tempco over 18-28C ambient temperature.
Assembly type: Hammon metal box with Pomona 3770 low-thermal binding posts.

I'd like to check if there is any interest in expensive hobby-level reference among the members here.
If enough people would be willing to buy one, it will be easier for me to pull the trigger and tie in 4-5K$ into this project.
Estimated delivery date would be March 2018 October 2018, with final good cost $500 USD.

Specs above are on safe side, so the module likely to be 2-5 times more stable, however I wouldn't guarantee it just yet. There is no replacement to actually running reference for 3+ years to determine actual long-term annual stability.

Feel free to comment

Member list, who interested in module

montemcguire - 1 unit [CONFIRMED] [DELIVERED]
dr.diesel - 1 unit [CONFIRMED]  [DELIVERED]
chriswebb - 1 unit [CONFIRMED] [DELIVERED]
PeLuLe - 2 unit [CONFIRMED]
MM - 1 unit [CONFIRMED] [DELIVERED]
bck - 2 unit [CONFIRMED] [DELIVERED]
USA cal club - 1 unit [CONFIRMED] [DELIVERED]
CM - 1 unit [CONFIRMED] [RESERVED]
zucca - 1 unit [CONFIRMED]  [DELIVERED]
No more units available., unless somebody change their mind.

Prototype board overview, test data samples



Initial output after first assembly.

[Vgkid]

Sounds interesting, I would do it if I ever get the money. That would be around 6mo + from now.

[montemcguire]

I'd buy one - count me in!

[lukier]

Does it really need -12V? It would be much simpler to have just one battery (12V lead-acid or 4x18650 LiPo).

[dr.diesel]

Count me in, prepay is no problem to help offset costs.

[maxwell3e10]

Sounds interesting. What would be the specification for 0.1 to 10Hz rms noise? That is primarily what I am interested in.

[mimmus78]

I'm interested too but as I'm building my own version I'm not interested in buying one.

I have a DHL contact with good fee for international shipping ... I can offer few trips for free is some of this board wants to became a traveling standard among EU guys or for just a stop and go.

[nidlaX]

I'm interested, but it's only a run of 10 units?

[chriswebb]

I'd also be interested in picking up a unit if available.

[Kleinstein]

Does it really need -12V? It would be much simpler to have just one battery (12V lead-acid or 4x18650 LiPo).

The circuit should run with less than -12 V. It should be possible to make it run on just a single supply, maybe 14 V. For battery operation something like 12 V min would be nice, but this would not leave much room for driving both the positive and negative side. So getting it down to 4 Li Cells could be a little tricky.

[TiN]

montemcguire, dr.diesel, chriswebb - OK, I'll keep you guys in mind.

Does it really need -12V?

-3V can be fine too, I checked today, output change was less than 0.4ppm.
But I will be validating only +12/-12 +/-5%. Negative voltage is used on the output stage, not the LTZ-ref itself.

Sounds interesting. What would be the specification for 0.1 to 10Hz rms noise?

I expect ~3 uV perhaps. Will know better once I test first 3 prototypes I have now.

I'm interested, but it's only a run of 10 units?

Even to make 10 boards, lot of time and money will be tied in, so I'd rather spend some resource for other projects, using this reference, instead of making just the reference. I originally did not plan to make any extra's at all, and still need to run the numbers to pull the trigger.

Also each output resistor network must match the used LTZ chip value, so it's NOT simple assemble/hook to fancy meter/write value/sell process.

[pelule]

Count me for 2 (if such many left available), min. 1.
Prepayment possible.
BR
/PeLuLe

[wn1fju]

Could I buy one volt for $50USD

[VintageNut]

Hi TiN

I am curious about the 0.1 ppm/deg C temp dependency. If the temp changes +/- 3 deg C, then the output will change +/- 3uV?

The temp in my home/office can change +/- 5 deg, which is 10 deg p-p. That would translate to 10uV p-p or 1 ppm p-p.

My 731B which cost $250 is pretty much that good for temp dependency.

I think that if your LTC ref were in an oven like the KE DMM7510, THAT would be very attractive. \

One reason that I like my DMM7510 so much is that the ovenized reference makes the DMM rock solid stable in my home/office where the temperature is not stable.

[TiN]

VintageNut
Will have to see if can do better. Current data looking like this:



Ignore the steep jump on the end, that shows reference ran out of oven thermal margin, with resulting +150ppm raise of zener voltage and output voltage.

[texaspyro]

So 17 uV over 10 degrees C...

My ancient scrap heap salvaged EDC MV100 seems to drift around 20 uV over 3 degree C... not too shabby for an un-modified, non-ovenized 1N829 zener diode referenced clunker with a 6 decade adjustable divider... I've been looking at seeing what some LTZ1000 / LM199 / better chopper love could do for it.

[bson]

I'd be interested in a few (say 3) known to be genuine LTZ1000 references, just the parts without a board - if you can get a few extra!

[TiN]

So 17 uV over 10 degrees C...

Actually more like 22 uV over 22.6C, here's live data.
So that's about 1uV/C, or -0.1ppm/K.

LTZ reference itself was tested last week to ~-0.03ppm/K over 20-50C span. TC is not exactly linear due to compensation.
Sweet spot with nearly zero TC is to run with ambient temp 30 to 40C.

I'd suggest to move discussion about the design to thread.

There will be no parts/kits, only fully assembled and tested module is in question.

[texaspyro]

I already have a couple of 732A's and a 732B,  but if you need a another taker to meet your minimum build I'm game.  Might even be interested, otherwise.

The main difficulty I see with the unit is the +/- 12V power.   I'd like to do a small unit with LiPo (18650) backup batteries.  There are some nice, isolated, low noise DC-DC's out there that should be able to take care of that.. hopefully without slathering the system with switching noise.

[Echo88]

Maybe a capacitor charge pump suffices for the negative voltage while ensuring low noise? Or a big LED + solarcell. 

[Zucca]

TiN let's the magic happen, it's Xmas time!

I am in. Yes Yes Yes!

PS: anyone with connections for custom resistor arrays/dividers (Fluke 2464707)

https://www.eevblog.com/forum/metrology/tin-livestreaming-layout-of-new-ltz1000a-10v-reference-module/msg1345273/#msg1345273

[TiN]

zucca
OK. What did you do with previous ref, btw?

ALL
No more boards, so far I got all allocated, unless somebody from the list wanna change the mind.
Ordering parts (LTZs from LT direct, resistors from VPG direct, rest are from Digikey) next week.

[Zucca]

zucca
OK. What did you do with previous ref, btw?

I needed first a HP 3245A, now I am going to upgrade it...
Following your path.. very slowly my friend.

[TiN]

LTZs, opamps and LDO's ordered from LTC  .

[TiN]

Linear parts and Fluke network resistors arrived.