EEVblog Electronics Community Forum

Let's start the new segment, fairy-tales of metrology 

Intro

One of engineers doing precision measurement projects at home for own enjoyment contacted me while ago, asking some questions related to nanovolt-meter amplifier front-end and voltage references. His country of residence is Belarus, and I mention this because their customs are really strict about international shipments. Basically everything over 20 $USD mark is troublesome to import and due to high fees, often much more than package value itself. So his instrumentation desk was mostly using some old instruments, made in Soviet Union. We had nice talk about electrometer of his, which is an interesting bit of gear on its own.

On DMM front he has Datron Model 1271, 7½-digit DMM, smaller brother of Model 1281 which our other contributor, Todd, had covered well before. Quickly talk was biased towards voltage references. Buying famous Linear LTZ1000 was not an easy option due to shipping/customs troubles, even worse considering existing lack of access to calibrators or metrology labs nearby. Even though this 1271 is fine instrument, it was not recently calibrated and absolute accuracy was unknown. Since this situation was very familiar for me few years ago, I decided to give a hand and help this engineer to “import” verified DCV standard into his home hobby lab. Agreement to build one KX LTZ1000 voltage reference was made.

Buy some parts, put on PCB with less than 30 components, measure the output and send the board thru mail. Sounds easy job, no rocket science, right?

Parts source and assembly

To make this whole little project more interesting for me, I wanted to try two new ideas, which were not attempted before in previous builds.

*A.* Try 1K?/13K? hermetic resistor network (custom Vishay VHD200, oil-filled +/-3ppm/K two-resistor network) with 0.05% matching. This might give some interesting data, if tightly coupled oven setting thermal point resistors help to improve tempco of the reference.

*B.* Try alternative chopper amplifier, Analog Devices ADA4522-1. Usually I use LTC2057, but both op-amps are rather overkill for this particular circuit, as noise of LTZ1000 zeners itself is magnitudes higher than opamp contribution. But maybe other issues pop up with AD chip. Let's see.


As a base my latest Rev.B02 version of KX LTZ1000 PCB is used. This module 4-layer FR4 ENIG-plated PCB use two single op-amps in SO-8 package, accepts +10-20VDC input


Before soldering resistors down into circuit, I did a quick measurement to check that they don't give some wild deviations.

Custom VPG 120 ?, R3 , -0.8 ppm - +26.4 C, 0.36 ppm/K
VPG VHD200 1 K?, R4 , -75 ppm - +24.0 C   2.5 ppm/K
VPG VHD200 13 K?, R5 , -5 ppm - +24.3 C   1.4ppm/K


First small SMD parts were soldered on, and checked. Used LTZ1000ACH chip, manufactured 36 week of 1993 was soldered on, with maximum soldering time around 0.5 second per pin, to reduce excessive heating. Foil precision resistors were populated last. Assembled module ready for the initial test.


Before we jump in to actual test data, it's important to have good confidence in measurement equipment and lab tools, to make sure that any unexpected phenomenon comes from device under test, not the equipment itself. This also means that even brand new, freshly calibrated equipment must be verified and tested before any solid conclusions to be made.

To satisfy this requirement, I had chance to calibrate my older LTZ1000ACH/LTZ1000CH based references against 15-day calibrated Fluke 732B DC Voltage standard in mid-August 2016. Two Keithley 2002 8.5-digit multimeters we calibrated to same Fluke reference same time, to act as transfer standards and guard-banding tools. I used these DIY standards and DMMs to transfer absolute DCV voltage into my verified and improved HP 3458A, which confirmed to be stable by daily 24/7 operation and monthly checks to both hot and cold external LTZ1000A modules. As a result, I have high confidence that absolute DCV accuracy in my home lab is within +/-2 ppm.

Now with verified gear, initial test conditions are fairly simple. Purpose of first test is to make sure of reference normal operation, and measure initial voltage, drift if any and stability. Output should not deviate more than +/-1 ppm over few days period, and temperature coefficient (change of output voltage from change of ambient temperature) should not exceed +/- 0.1 ppm/K.

Power supply : 12VDC 2A cheap mains power brick.
Measurement  : HP 3458A, calibrated August 31 to +/-2ppm DCV.
Ambient condition : Ambient room temp with aircon, +/-3 C. Monitor by BME280 sensor
Datalogging : Raspberry Pi with linux-gpib + python + NI GPIB-USB-HS
Analysis : D3.js plotting library on xDevs.com site

Test 1


Yes, it's alive, measuring output voltage +7.067329 VDC +/-2 ppm.

And how we looking here? If this would be integrated reference, such as band-gap reference on internal DAC/ADC references, result noise 1.1 ppm could be simply miraculous. However for top-end ovenized buried zeners, which for Linear LTZ1000 is extremely bad. To remind you specifications, this circuit should be able to provide 0.05 ppm/K drift rate and approximate noise levels of 1.2 uVpk-pk. We are getting 7.4 uV instead for noise. Tempco is also horrible, about 1 ppm/K, 20 times worse than expected!

Test 2: TC correction resistor add

For second test we work on mistake and try to address issues on data we saw earlier.

* Improve stability of ambient temperature, so we can isolate TC issue for now.
* Test with 394K R2 populated, even though we use LTZ1000ACH and this compensation not needed.


Some of our readers not familiar with LTZ1000 performance may scream at me right now, how you know that this is bad result. Vertical ppm scale (left green scale is +/-1ppm, which is 0.0001% accuracy!) is blown out to make this amazing reference look bad, you say?

Alright, I hear you. And here's the answer, same condition measurements with good and checked LTZ1000CH voltage reference module, using same schematic and same PCB, just different parts. Horizontal time span of graph below is 11 hours.


See, noise of this good module is mere +/-0.1ppm, no random jumps or other weird crap, everything nice and stable. That's how you want it, not jumpy-jumpy . Of course if you reduce your accuracy demands to 0.002%, everything looks nice even with jumps.


But it does not make sense to pay 250$ USD for such accuracy, so let's continue our journey.

Test 3: Reduction of oven temperature test

Alright, how about reduce LTZ1000ACH oven temperature inside chip, by changing 13K? resistance on divider to lower value? Let's see

Fluke 300K? -1 ppm/K wirewound resistor was soldered in parallel with 13K? on board, and test was repeated.


Test 4: Op-amp kelvin connection test

Here I had cut separate trace between Pin 2 U5 opamp and R6 resistor, and jump-wired connected guard ring point directly at pin 4 of LTZ1000ACH chip. This makes almost Kelvin-like connection for all inverting node connections. Why I did so? Hm, intuition?


Jumpie-jumpie is still there. Noise of LTZ chip noise itself is riding on top of those jumps. Overall it looks nice and stable, just the pesky jumps, which is pink-noise of zener junction. Output voltage changed from +7.064808 to +7.066329 VDC, which is +215 ppm.

Test 5: Replacement of LTZ1000 chip

Now, if we dig a bit into physics, this jumps are nothing but pink-noise, likely caused by zener effect breakdown is due to quick bursts of electrons going thru thin junction on high voltage. This breakdown is just about 7 volts, and that's close to out near 7.06V output of zener inside this LTZ1000ACH. So it does look that no external component tweaks could fix this... Let's see on test result of TEST RUN 5:


t's good now! What is the magic? There is none, actually, just engineering. Now we getting some solid data. Noise over multiple hours is just around 0.2ppm, which translates into around 1.2 uV[~pk-pk~], initial tempco evaluation from +26.6  C to +30.5  C unable to reveal any tempco clearly, no large jumps either.

Bonus

I also built thermal box to test tempco, so jump into full article link down below


Total amount of time for this project ~25 hours, including ~50 hours of datalog time by HP 3458A.

Hope this data helps to better understand hidden icebergs and dangers big enough to sink a project in high-precision field, even for something as simple as direct voltage reference module. It's not enough to buy fancy parts and plonk them on the board to get 1 ppm accuracy.

I have it running tempco test now, from 20C to 55C in 0.1C per hour step.

Full article

If you have own unexpected story, do tell us. 

Important update, calibration offer by community

One of our members, mimmus78 ordered KX LTZ1000 PCBs and sent some to other interested tinkerers at cost, so to support this great initiative, additional "calibration service" is provided by me, plesa and Alex Nikitin to support this.

Rules to participate are simple:

STEP 1. Build your KX-module, publish short worklog in this thread (few photos of assembled PCBA, photo of it running with DMM hooked up showing 7V)
STEP 2. Leave it running for 200 hours, so initial drifts get stabilized. Module should be enclosed in some box without vents.
STEP 3. Measure it again, record the temperature and voltage and put a label with values on the box
STEP 4. Ship the box to me (Taiwan) or other member (Europe) after agreement via EEVBlog PM. You pay shipping.
STEP 5. I'll power your box with +15V for 48 hours to have everything stabilize
STEP 6. Test 7V output voltage in temperature span +20....+30C, record the graph
STEP 7. Unit will be shipped back (from me via EMS Express (~30-40$USD, 4-7 days to USA, bit more to EU)). You pay shipping.

All steps are mandatory, to make sure that reference is good and stable, otherwise it would be no much point in ppm-level calibration, if initial aging drifts are not removed first.
This is standing offer, without schedule or specific date deadlines, unless my homelab changes or other force majeure events occur.

Even though I don't have official calibration performed on my equipment, thanks to volt-nut community and multiple cross-checks I'm confident that my DCV accuracy is around ±2 ppm.
And to make this even better, few other EEVBlog members also backed up this initiative to provide same calibration offer in their regions.

Calibration by	Accuracy / Standard	Region/Country	Contact for participants
xDevs.com	<2ppm / 3458A-mod + 2*K2002	Asia/Taiwan	EEVBlog forum PM
plesa	<4ppm / 3458A-002	Europe/Sweden	EEVBlog forum PM
Alex Nikitin	<4ppm / 3458A-002	Europe/UK	EEVBlog forum PM

Article was also updated for same information

This jumpy LTZ was the one from the A9 board that TiN bought on flebay for is 3458.

The resolution is in the full article in TiN's website, he then replace the LTZ with another one and no more jumps.

To make this whole little project more interesting for me, I wanted to try two new ideas, which were not attempted before in previous builds.

*A.* Try 1K?/13K? hermetic resistor network (custom Vishay VHD200, oil-filled +/-3ppm/K two-resistor network) with 0.05% matching. This might give some interesting data, if tightly coupled oven setting thermal point resistors help to improve tempco of the reference.

TiN do you notice any diference yet, with the exchange of the voltage divider in relation to previous method, of two independent resistors?
This way the tracking of Tempco should be better since they are inside the same encapsulation.

BTW, in a conversation with Edwin Pettis he told me, that the Engineers from LT told him that for the last few years they recommend the all LTZ's to be drive by 15K/1K, but this was already cover in the LTZ thread .

Good story and nice photos/charts. Slightly worrying for me too because I did not test all of my 2nd hand LTZ1ks fully.

TiN is the thermistor hermetic? It seems to be very stable over time.

One time I was repairing Data Precision 8200 DC calibrator.
I did many measurements to prevent good old precision components from heating during soldering.
Unfortunately the problem was LM399 (see plot).
Maybe it is a problem with contact resistance inside IC.
I assume that Data Precision would not release a product with such issue, so it is very likely that this LM399 broke down during normal use.

For humidity, pressure and temperature I think that the BME280 is hard to beat. And you can do like TiN, sample it together with your measurements via GPIB. 

Or send that 7510 to us for check  3458 vs 7510... I think that's not equal fight   

Good points Tin. I will connect my model 2000 in parallel with the 7510 and let it run for a few days to see if the drift is detectable on the 2000 as well.

I am reasonable certain that the drift is the 731B but only proper measurements and analysis of the data will make it certain.

I accept the challenge to find out for sure.

Do you collect your data for this type of analysis with Python?

I am sorry Ilya and others if this not relevant but anybody has experience about same jump/popcorn noise from LM399 ?

The choice is up to application. Lower noise at cost of long term stability - run high temp. Better long term stability (thats what most people here after) at cost of noise - reduced temp.

Have you placed one of these reference boards in an ordinary freezer at 0 deg F to test the idea?

I'd expect difference at 0 would be just down in measurement errors and uncertainty.

Does the noise reduction only happen at some magic very low temperature or is the noise reduction a linear function of temperature?

Because the Zener in the LM399 is operated at such a low current [no matter how much current you pump into the device], you will see this "popcorn noise" more often with that part.

This is worth emphasising because a lot of people miss this. Internal to the LM399 is an, internally regulated, constant current supply that pushes 250 uA through the zener. Any excess current is shunted off by a pair of transistors that just turn the excess into heat. This doesn't mean that you can get away with feeding the LM399 with an unregulated current but you won't gain anything by going over the recommended 1 mA.

Hi,

I have two left, but I need them for few items in near future. Somebody here is waiting for fab using my gerbers, I believe.
Btw, I done log with K2001 for you, but have no time recently to make pretty graph. Live graph and RAW data is here. Plenty of data there to run STDEV, noise pk-pk analyze and such. K2001 column is k10v.

plesa
How's your datalogging setup going on? If you wish, I can give you space on my serv and script, so your Pi can upload CSVs periodically and I can have live plot page for you

I'd love to see some data too 

@ mimmus78

Anyway just ordered 20 pcb of your project, if someone needs some I have few spares.

Just to be sure, I have the right "project" in mind. Does you have ordered this?
https://xdevs.com/doc/xDevs.com/KX_STR/top.jpg

If so, I would be interested into 2 to 4 boards.

There is no need for the Vishay VHP, you can use UXB, UPW20/50 or from Edwin, 0.1% 3ppm/C°

I would like 3 if available still
Mimmus78: 3pcs
Nuno_pt: 3pcs
msliva: 3pcs
pelule: 3pcs
klaus11: 2pc
VK5RC ;3pcs

If there are any left, I take 2 pieces, thanks


Mimmus78: 3pcs
Nuno_pt: 3pcs
msliva: 3pcs
pelule: 3pcs
klaus11: 2pc
VK5RC ;3pcs
t2kv: 2pc
HighVoltage: 2pcs

It looks like a classic case of popcorn noise and not pink noise.  The level is awfully low and I cannot say that I have seen popcorn noise in a zener diode but the base-emitter transistor junction in series with the LTZ1000A zener could be responsible and combined with the low impedance at the collector would explain the low level.

Screening for popcorn noise is very difficult because of its often intermittent nature.  Long test times, hours to days, make it economically impractical for most customers.  I thought I remembered a note from LT about screening LTZ1000s for something but I looked and did not find it.

Quote from: David Hess on October 30, 2016, 02:13:01 am

It looks like a classic case of popcorn noise and not pink noise.

Agreed that it looks like popcorn noise, but I think the explanation is wandering between zener and avalanche modes. Intrinsic to these low TC zeners is the balancing of the opposite tempcos of zener and avalanche effects. I think that's already been suggested hereabouts as a cause but I'm not sure. Popcorn noise is classically associated with relatively 'dirty' semiconductor processes which is why it's generally much less of a problem than it was, say, thirty years ago. We're dealing with a buried zener here, and the burying is done precisely to keep the junction away from the surface where impurities may lurk of the sort that cause popcorn noise.

The buried zener in this case is temperature compensated by the roughly -2mV/C Vbe of a series transistor so I am suggesting that the popcorn noise is actually coming from the transistor and not the buried zener reference.

maybe a a "two value" reference

That's assuming both levels not change over time.

I don't see much sense in cooling and that way possibly destroying the chip

I don't see either, but desired to close this topic once and for all. Maybe we could see something in doing this (not necessarily at 77K temperature). Having 24/7 cooled to -30°C unit with TEC or phase-change loop (modified window AC) isn't that difficult, if there is point in it. I've ordered copper block at CNC shop to enclose module in hermetic box to place in dewar. This way there will be less rapid shock from contact with cooling liquid.

Quote from: David Hess on October 30, 2016, 06:04:07 am

The buried zener in this case is temperature compensated by the roughly -2mV/C Vbe of a series transistor so I am suggesting that the popcorn noise is actually coming from the transistor and not the buried zener reference.

Yes, the LTZ is using V_BE compensation (and a lot of heat) rather than relying on zener versus avalanche tempco, but the zener versus avalanche thing is still going on because that's determined by the diodes 'set point*' voltage. I'm just influenced by the fact that there's some identifiable physics that we know goes on around this point. Anyway, the only way to be sure is to try the zener current versus transistor current experiment that's been suggested.

*Awkward terminology here because you'd normally say "zener voltage" or "avalanche voltage" but both are in play.

As you pointed out, the zener is buried to prevent exactly this sort of problem.  I did a search but found nothing about popcorn noise in zener diodes which may just mean that it is such a minor problem that it takes an LTZ1000 before it becomes apparent since zeners are so noisy anyway.  I thought I remembered a comment from LT about special screening options for the LTZ1000 which included low frequency noise but was not able to find it.  In transistors, it is usually more apparent because of transistor gain but in this case, the low impedance collector load limits gain.

Since access is provided to the node between the buried zener and transistor base and actually every terminal of the transistor, testing to find the source is straightforward if not easy.

Tracking down popcorn noise was my motivation for expanding my collection of Tektronix oscilloscopes to include the 7A13 (1mV/div), 7A22 (10uV/div), and AM502 (10uV/div) differential vertical amplifiers.  It took me weeks to track down the example shown below because of its low level and especially intermittent nature where it was clean for hours at a time.

Hi mimmus78,

Thank you, if there is still left.

Mimmus78: 3pcs
Nuno_pt: 3pcs
msliva: 3pcs
pelule: 3pcs
klaus11: 2pc
VK5RC ;3pcs
t2kv: 2pc
HighVoltage: 2pcs
fanOfeeDIY: 2pcs

Hi everybody,

pcb were fabricated and are now travelling to my home.
I should receive it tomorrow or Wednesday.
I will post PCB photo here when they arrive.

Ciao,

Domenico

-------------------------------------------------------------------------------------------------------------

Mimmus78: 3pcs
Nuno_pt: 3pcs
msliva: 3pcs
pelule: 3pcs
klaus11: 2pc
VK5RC ;3pcs
t2kv: 2pc
HighVoltage: 2pcs
fanOfeeDIY: 2pcs

Echo88, I don't think soo ... I already have some overbooking.

PCBs will arrive today.

Hi guys here are problems with those PCB I received today.
If for you is OK I will ask to fab to redo the lot.
Let me know what you think.

Especially if they send a second batch of good boards out. Then you can pick and choose...

How do the boards look with a gerber viewing tool?

I do not have enough experience with LTZ1000 PCB's to judge if this is a real problem or not.

I  suppose that open guard is not big difference if any. The majority of trace is still guarded.
Similar to solder mask covering guard trace. If someone is curios about difference you can measure it by electrometer.
Of course you can ask for some discount on PCB.

So I submitted the original project from xdevs.com and those pcb where fabricated at Easyeda

I checked the gerber files with their online tool before submitting project and it was shown like the attached image.
At fist sight seemed OK to me including ring guard, but it's clearly not now, I should have checked better!
The problem is that on this part of the pcb the "solder mask" mask layer is not aligned with the trace.
They removed the solder mask, but there is no trace down. Il will check with TiN this point as the problem is likely in the files I downloaded from xdevs.com.

Anyway, as told you can still scrub this piece to get exposed guard.
As for the other problem I'm convinced too what plesa said: "I suppose that open guard is not big difference if any. The majority of trace is still guarded.".

So at this point, who still wants the PCB please send me by PM the address and if they prefer "registered mail" or "standard mail".
I will get quote for shipping and back to you with costs.

Mimmus, I'll stay with my two boards, if you have a post on how to correct the problem, why I still do not understand where the problem is due to my ignorance of English language comprehension

I am also stay to word and take 2 boards
PM sent

Paypal sent

I have not received PM message 

Packaging:

 - VK5RC              3pcs       -      PM SENT - Paid - Registered
 - HighVoltage       2pcs       -      PM SENT - Paid - Registered - overbooking list
 - Mimmus78         3pcs       -      that's me

Confirmed waiting for payment:

 - klaus11              2pcs       -       PM SENT - Spain zone 1 - priority mail 3.50 EUR - registered 7.90 EUR
 - t2kv                    2pcs       -       PM SENT - Australia zone 3 - priority mail 5.50 EUR  - registered 9.95 EUR
 - Nuno_pt             3pcs       -       PM SENT - Portugal zone 1 - priority mail 3.50 EUR - registered 7.90 EUR
 - msliva               3pcs       -       PM SENT - Czech Republic  - zone 1 - priority mail 3.50 EUR  - registered 7.90 EUR

Confirmed but in overbooking list (do not pay - wait):

 - SvanGool          2pcs        -       Netherlands  zone 1 - priority mail 3.50 EUR  - registered 7.90 EUR - overbooking list
 - fanOfeeDIY      2pcs       -       Japan - priority mail 5.50 EUR  - registered 9.95 EUR - overbooking list


=======================
TOTAL                  22 pcs
REMAINING         0 pcs


Waiting or confirmation

 - pelule               3pcs       -        please confirm and send me address for shipment quotation
=======================
TOTAL                3pcs


TOTAL CONFIRMED + UNCONFIRMED = 25

Paypal sent

PM sent, still in for the 3 pcs.

Packaging:

 - VK5RC              3pcs       -      PM SENT - Paid - Registered
 - t2kv                    2pcs       -      PM SENT - Paid - Registered
 - klaus11              2pcs       -      PM SENT - Paid - Priority
 - HighVoltage       2pcs       -      PM SENT - Paid  - Registered - overbooking list
- pelule               3pcs       -        PM SENT - Germany zone 1 - priority mail 3.50 EUR - registered 7.90 EUR
 - Mimmus78         3pcs       -      that's me

Confirmed waiting for payment:

 
 - Nuno_pt             3pcs       -      PM SENT - Portugal zone 1 - priority mail 3.50 EUR - registered 7.90 EUR
 - msliva               3pcs       -        PM SENT - Czech Republic  - zone 1 - priority mail 3.50 EUR  - registered 7.90 EUR

Confirmed but in overbooking list (do not pay - wait I receive second lot):

 - SvanGool          2pcs        -     Netherlands  zone 1 - priority mail 3.50 EUR  - registered 7.90 EUR - overbooking list
 - fanOfeeDIY      2pcs       -       Japan - priority mail 5.50 EUR  - registered 9.95 EUR - overbooking list
 - little                   2pcs.    -        Germany overbooking list

=============================
TOTAL                                  22 pcs
wait list (overbooking)          3  pcs

I contacted Edwin and Vishay. Finished to order some resistor from Edwin. I really don't even checked if this resistors will fit, but I'm also going to build my PCB version so for sure I will use it.

Still waiting for Vishay response, I really liked the idea to have this first board I build with Vishay. I asked fancy pants VHP101 for the heater divider a some other normal in plastic for the others 3.

The main problem I have is that I still don't have 3458A ... I'd like to try to buy same old rusty broken one if it will pop out somewhere, but you must be brave to do this extreme repairs like TiN.

Inviato dal mio Nexus 6P utilizzando Tapatalk

I would like to thank both TiN,  for putting his hard work designs up for open review/reproduction and Mimmus78 for putting in the pcb gerbers etc and doing all the postage / customs etc.
TiN,  if that offer re calibration check is open in a month or so,  it will be hard to refuse!
Robert

TiN this offer of free calibration will be interesting but we should find a way to ship back and forth without paying customs.

I should check how this can be done.

Inviato dal mio Nexus 6P utilizzando Tapatalk

Plesa that's very nice for all European guys to have this opportunity.

O men you have JJA near home! I cannot even comment it.

Anyway regards Edwin resistors, despite last problems with quality in last year I think it is the best and cost effective way to get reasonably TC matched resistors for the heater.

Keep this ratio constant is 10 times more important that all other factors.

I read somewhere that resistors made by same person, one after the other can have similar drift and TC.
You can ask Vishay for this, but I this it will increase even more the costs. So I just asked Erwin for this and this seems to be the most practical and cheap way to get this point.
Hope he really solved issues with his epoxy in meantime.

plesa, Alex Nikitin
If you OK, I can add this section into article on my site, with links to your profile, to keep this program afloat?

Fist shipment is ready ... I'm still waiting payment from other 4 members. Let me know if someone have any problem.

Inviato dal mio Nexus 6P utilizzando Tapatalk

plesa, Alex Nikitin
If you OK, I can add this section into article on my site, with links to your profile, to keep this program afloat?

Yes, sure.

Cheers

Alex

I am still in the middle of getting to know my 3458A (8 ppm) and will have it officially Keysight calibrated in a few month time. If anyone needs its KX reference board measured in Germany, you can send it to me, as long as you pay shipping. I can also offer a comparison to my 34470A and DMM7510.
But, until now I can not change the temperature, that is a future project.   

This is going to be huge ... a global volt nut club.

Thanks to plesa I asked to rhopointcomponents.com too for a quote of the resistors. I will let you know what happens.

Quote from: plesa on November 12, 2016, 10:53:57 am

I can offer you similar service like TiN in Europe.
1. Measure it with calibrated 3458A/002 in reasonable temperature range.

I can do a similar service in the UK, if somebody needs it, as the HP3458A Opt 002 just came back from calibration at Keysight. I don't have a temperature chamber yet (though it may change soon), however I can monitor the lab temperature (or the reference enclosure temperature).

Cheers

Alex

Plesa, Alex, and also HighVoltage:

What kind of KS calibration and report for your 3458As did /will you get?

The single page report, which only confirms that the instrument is in 1 years specification limits, or the elaborate, much more expensive, multi page calibration report, with all measurement results (as found) including test limits?

I think, if it's only the first kind, it won't be sufficient for this purpose, as the 1 year DCV specification is 8ppm / 4ppm for option 002 only, and about <= 1ppm uncertainty is required.

Frank

Dr.Frank,
My plan is to have my 3458A adjusted and calibrated to the higher specs and I want the multi page calibration report. But I have not even started to talk to KS. May be I will visit KS Boeblingen first to see their capabilities and then make my mind up. On the other side, I can also have it calibrated in Hamburg against a calibrated 732A. But first I will have the instrument running for a few more month to get it stable.

Alex, definitely.. your 10VDC uncertainty will be around 3ppm, probably better, as the 10Vdc reading of your instrument is given to < 1ppm resolution, and the "Golden 3458A", which defined the limits, may have been less uncertain than 1ppm.

I have same uncertainties like Alex, because we are sharing calibration lab

mimmus78 please consider to do more boards when you are ready. I would like to buy one... may I?

mimmus78 please consider to do more boards when you are ready. I would like to buy one... may I?

Added you to overbooking list.

I still have 8 spare from some users here they didn't confirmed, I will wait up to the end of the day and than offer to the one that are on queue on the overbooking list ... anyway another lot is going to be fabricated.

D.

UPDATED:

Packaging and shipping on Friday:

 - Nuno_pt             3pcs       -      PM SENT - Portugal zone 1 - priority mail 3.50 EUR - registered 7.90 EUR

Shipped:

 - VK5RC              3pcs       -      PM SENT - Paid - Registered
 - t2kv                    2pcs       -      PM SENT - Paid - Registered
 - klaus11              2pcs       -      PM SENT - Paid - Priority
 - HighVoltage       2pcs       -      PM SENT - Paid  - Registered - overbooking list
- pelule               3pcs       -        PM SENT - Germany zone 1 - priority mail 3.50 EUR - registered 7.90 EUR
 - Mimmus78         3pcs       -      that's me

Confirmed waiting for payment:
 
 - msliva               3pcs       -        PM SENT - Czech Republic  - zone 1 - priority mail 3.50 EUR  - registered 7.90 EUR

Confirmed but in overbooking list (do not pay - wait I receive second lot):

 - SvanGool         2pcs        -     Netherlands  zone 1 - priority mail 3.50 EUR  - registered 7.90 EUR - overbooking list
 - fanOfeeDIY      2pcs       -       Japan - priority mail 5.50 EUR  - registered 9.95 EUR - overbooking list
 - kutte                2pcs.    -       Germany  zone 1 - priority mail 3.50 EUR  - registered 7.90 EUR - overbooking list

=============================
TOTAL                                  22 pcs
wait list (overbooking)          4  pcs

Ohh I got a PM from Mimmus confirming that the boards in discussion is the TiN one... but I meant the Mimmus new design one, which is not ready yet. Soo please take me out from the list and put me in he new one of your design.

Thanks TiN again for sending me his wonderful KX LTZ1000A board.

I don't understand why use VR801 as integrator reference? Any reason why not route LM399 ref signal there?

3 more PCB to go.

Thanks Guys, PCB are over.
I didn't hear from the fab for the "fixed" batch, I will let you know when then new batch will arrive.
Anyway let me know if someone else is interested.

Hi mimmus78,

Thank you for your message. I am in the overbooking list.
I missed reading it last night, but it is fine. I will wait for the next batch.

So this is what I elaborated. This is based mainly on last revision of battery powered reference from "andreas".

I added reverse polarity power protection.
Removed some caps that Dr. Frank defined as "fear" caps.
I removed the MOS that drive current to the zener.
Using LTZ1000 (not A version)

I was thinking to add some basic output protection to the REF ... what you think to add something like this (with opportune op-amp):



 just after the buffered output of the LTZ1000A?



As usual care to thermal EMF is a must. Hope it will not upset much the output.

I don't understand why use VR801 as integrator reference? Any reason why not route LM399 ref signal there?

+1 I really don´t know why...

Hi guys, I got called from DHL because there is a new parcel for me (and I wasn't home) ... so guess what it will be?
I will let you know when back in home if it's some gift from unknown or if it's the new KX pcb batch.

So this is what I elaborated. This is based mainly on last revision of battery powered reference from "andreas".

Hello,

are you shure that C10 is on the "right" side of the resistors?

With best regards

Andreas

Hello,

Using chopper OPs for the LTZ1000 circuit can get tricky. They produce quite some RF spikes can have higher noise in kHz range, where the transistor in the LTZ is not helping anymore. There is no real need to replace the LT1013 or similar OP. The LT1013 is not that expensive. But at least dual OPs use the same pinout.

Do you have founded measurement values on this?
I have not measured any differerence between LT1013 and LTC2057 on my latest 4 references.

For the extra butter, the AZ OP is suitable, as here the error from the OP fully enters.
One might think about having some RC filtering here - to reduce higher frequency noise from the reference and keep spikes from the AZ OP away from the reference.

+1
I fully agree I measured large differences between filtered and unfiltered buffer regarding EMI sensitivity.

With a relatively high current, there was a good reason to have a transistor / JFET to drive the reference current. If one really wants to save on this, one could still use a bridge or diode like shown, but I would really have the space for the transistor on the board.

The main intention of the FET-Buffer was LT1013-related together with reduced power supply voltage.
keep heating away from LT1013 with relative high offset drift
+ extend output voltage range of the LT1013 (level shift) for reduced battery voltage.

So with a rail to rail chopper I see no reason to use a (now obsolete) FET.
The initial design is now already 6 years old.

With best regards

Andreas

The "filter" around R15,R16 C10 is there to make the buffer amplifier tolerant to capacitive load.

I don't really understand the protection circuit shown at the output -  to me this makes little sense. If needed at all I would more expect kind of a beefy 8 V zener diode or equivalent circuit.

One point where an extra protection might make some sense would be the unbuffered output. This is known to be sensitive to a short or overload (e.g. large uncharged capacitor), as this would cause the heater to activate all the way. A protection could check for a drop of the output by more than an few millivolts and in this case turn down the heater. It could take as little as a tl431 and a few resistors and a diode.

UPDATED 2016 Nov 25 - 22:30 Italy time

We still have: 8 PCBs with 1mm guard missing

Waiting for payment:
 
 - msliva               3pcs
-  bingo60            2pcs

=========================================================

Shipped 25/11/2016:

 - z01z                  3pcs (new pcb)
 - SvanGool          2pcs (new pcb)
 - fanOfeeDIY       2pcs (new pcb)
 - villas                  2pcs (new pcb)

=========================================================

Shipped 18/11/2016:

 - Nuno_pt             3pcs      -     PM SENT - Paid - Priority
 - SvanGool           2pcs      -     PM SENT - Paid - Priority
 - kutte                   2pcs      -     PM SENT - Paid - Priority
 - dr.diesel           5pcs       -       PM SENT - Paid - Registered

=========================================================

Shipped 11/11/2016:

 - VK5RC              3pcs       -      PM SENT - Paid - Registered
 - t2kv                    2pcs       -      PM SENT - Paid - Registered
 - klaus11              2pcs       -      PM SENT - Paid - Priority
 - HighVoltage       2pcs       -      PM SENT - Paid  - Registered - overbooking list
- pelule               3pcs       -        PM SENT - Germany zone 1 - priority mail 3.50 EUR - registered 7.90 EUR
 - Mimmus78         3pcs       -      that's me

=========================================================

I would like to build one reference, but I probably will not be able to find the resistors here and I don't like the idea getting these from eBay.
Do you guys plan to group buy the low TC resistors from VPG or some distributor?

this R is used for temperature compensation in LTZ1000A and is not necessary in not A version.

It's the other way around per data sheet-  don't use resistor for "A" version.

Hello,

I use R9 also for the A version to fine adjust the T.C.
But not always 400K is the right value:

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=253898

with best regards

Andreas

Did you already ordered resistors? They have extra long leadtime or you are going to use some thin film like PTF56/UXB series?
Good choice can be Rhopoint ( they will fit to TiN boards )
https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-miniohm-3ppmc-5e10-5g10-series.html

Wow, they stock a big range of 3PPM parts!  I don't have any experience with these guys unfortunately, might be a good alternative depending on how busy Edwin's shop is.