Re: [volt-nuts] LTZ1000 project build

[Lars Walenius]

My experience is that boxes makes the time constants for humidity longer but 
does not take it away. Heating in boxes takes the change due to humidity down a 
little but it doesn´t go away. I have had boxes with LM399 and amps for 7-10v 
with wirewounds for more than 20 years and they have definitely had seasonal 
variations. Also if you have a completely sealed box with varying temperatures 
the relative humidity in the box changes if the humidity is not close to zero.

A 10V 2ppm ref on Ebay was said to have no humidity effect but my unit 
definitely varied about 20ppm due to humidity during a long humidity test. One 
guess I have is that some units have much longer time constants due to better 
sealing but I am quite sure it doesn´t go away complete. Another problem with 
humidity I have seen is that you may be cheated by humidity changing over the 
season and cancelling the aging. This happened during my first tests of 
AD587KRZ many years ago. During the first four months two samples both had less 
than 2ppm drift and the humidity in the room changed from 45 to 25%RH so they 
looked very promising. But during the next four months when the humidity went 
up they drifted 15ppm.

Probably the 5 and 2ppm/C versions is manufactured in the same way. The 
humidity graph under severe humidity and temperature testing shows a 500pm 
difference for your chosen resistors. So doesn´t say so much. Hopefully they 
are below 1ppm/%RH with low loads.

Lars

Från: Ian Johnston<mailto:i...@ianjohnston.com>
Skickat: den 3 juni 2016 20:42
Till: volt-nuts@febo.com<mailto:volt-nuts@febo.com>
Ämne: Re: [volt-nuts] LTZ1000 project build

Hi,

The product I designed to use the 2ppm/degC resistors is sealed in an
enclosure where the LM399AH etc live, so I don't expect much problem
with humidity.

I use 2K2, 3.3K, 10K & 22K.

It's the RG2012L series from Susumu:-

http://datasheet.octopart.com/RG2012L-103-L-T05-Susumu-datasheet-13139546.pdf
http://www.susumu.co.jp/common/pdf/n_catalog_partition01_en.pdf

The 2nd PDF above is mainly for the 5ppm versions but does contains
various graphs including humidity.

Ian.



On 03/06/2016 17:01, Lars Walenius wrote:
> Hi,
>
> Do you have any idea of the aging and humidity sensitivity of these 2ppm/C 
> resistors?
>
> I have tested many resistors during the years and my opinion is that tempco 
> is not the biggest problem for normal nuts use but of course may be if you 
> sell a product. For a nut it is quite easy to check the tempco but not aging 
> and humidity sensitivity.
>
> Of the resistors I have tested it is only hermetical sealed resistors that I 
> don´t see a humidity sensitivity on. Even if they are bulk metal foil, wire 
> wounds or metal films with low tempco´s they seem to have very varying 
> humidity sensitivity if not sealed. Lower values of resistance (100-1k) 
> normally seems to be better than 10-100kohm values that in all families may 
> have up to 1-2ppm/%RH.
> Last year I bought wire wounds, to be used in a LTZ1000 based design, that 
> were supposed to be insensitive to humidity but they were not. They were even 
> worse than other brands of WW and had several months of time constant. After 
> a while the manufacturer admitted that it was a problem in the manufacturing 
> and they were humidity sensitive. So far I haven´t received a replacement.
>
> Of course if you have a resistor with 2ppm/%RH and a seasonal variation of 
> 50%RH it is only maximum 1ppm seasonal variation on the output on the LTZ. 
> That is not easy to measure for most of us nuts.
>
> Lars
>
> Från: i...@ianjohnston.com<mailto:i...@ianjohnston.com>
> Skickat: den 26 maj 2016 13:35
> Till: il...@xdevs.com<mailto:il...@xdevs.com>; 
> volt-nuts@febo.com<mailto:volt-nuts@febo.com>
> Ämne: Re: [volt-nuts] LTZ1000 project build
>
> Hi all,
>
> TiN, out of interest I spent ages fishing for low ppm/degC resistors for my 
> own reference..ended up with 2ppm units from DigiKey. Yes, they are 
> expensive and send the BOM into the clouds!..so I know how you 
> feel!
>
> Ian.
>
>
> - Original Message -
>   From: Illya Tsemenko [mailto:il...@xdevs.com]
>   To: volt-nuts@febo.com
>   Sent: Thu, 26 May 2016 18:42:54 +0800
>   Subject: [volt-nuts] LTZ1000 project build
>
>   I'm glad my little project got so much attention. Worth to mention few
> points regarding my (or any other LTZ1000) unit:
>
> A. One should consider cost of whole BOM, not only LTZ chip. In my case
> resistors from VPG exceed cost of LTZ1000 by far.
> B. PCB I designed was targeted best to my own application need, where
> compact size and direct output (whatever is coming out of LTZ) were key
> importance. Since modules are part of bigger system with DAC synth,
> specific value, like 7.15

Re: [volt-nuts] LTZ1000 project build

[Lars Walenius]

Hi,

Do you have any idea of the aging and humidity sensitivity of these 2ppm/C 
resistors?

I have tested many resistors during the years and my opinion is that tempco is 
not the biggest problem for normal nuts use but of course may be if you sell a 
product. For a nut it is quite easy to check the tempco but not aging and 
humidity sensitivity.

Of the resistors I have tested it is only hermetical sealed resistors that I 
don´t see a humidity sensitivity on. Even if they are bulk metal foil, wire 
wounds or metal films with low tempco´s they seem to have very varying humidity 
sensitivity if not sealed. Lower values of resistance (100-1k) normally seems 
to be better than 10-100kohm values that in all families may have up to 
1-2ppm/%RH.
Last year I bought wire wounds, to be used in a LTZ1000 based design, that were 
supposed to be insensitive to humidity but they were not. They were even worse 
than other brands of WW and had several months of time constant. After a while 
the manufacturer admitted that it was a problem in the manufacturing and they 
were humidity sensitive. So far I haven´t received a replacement.

Of course if you have a resistor with 2ppm/%RH and a seasonal variation of 
50%RH it is only maximum 1ppm seasonal variation on the output on the LTZ. That 
is not easy to measure for most of us nuts.

Lars

Från: i...@ianjohnston.com
Skickat: den 26 maj 2016 13:35
Till: il...@xdevs.com; 
volt-nuts@febo.com
Ämne: Re: [volt-nuts] LTZ1000 project build

Hi all,

TiN, out of interest I spent ages fishing for low ppm/degC resistors for my own 
reference..ended up with 2ppm units from DigiKey. Yes, they are expensive 
and send the BOM into the clouds!..so I know how you feel!

Ian.


- Original Message -
 From: Illya Tsemenko [mailto:il...@xdevs.com]
 To: volt-nuts@febo.com
 Sent: Thu, 26 May 2016 18:42:54 +0800
 Subject: [volt-nuts] LTZ1000 project build

 I'm glad my little project got so much attention. Worth to mention few
points regarding my (or any other LTZ1000) unit:

A. One should consider cost of whole BOM, not only LTZ chip. In my case
resistors from VPG exceed cost of LTZ1000 by far.
B. PCB I designed was targeted best to my own application need, where
compact size and direct output (whatever is coming out of LTZ) were key
importance. Since modules are part of bigger system with DAC synth,
specific value, like 7.150 was not important for me.
C. If there is large enough group to have this project going, I can
actually modify original design (e.g. for easier hand soldering, or
added buffer or ratio circuits, onboard LDO, you name it) and get PCBs
made for interested nuts, at small cost.

You can also find lot of temco/stability data with
temperature/environment logs with mentioned LTZ modules on my site here:
https://xdevs.com/services/ in LTZ1000 voltage reference tests section.
RAW DSV data are available. I still have 3 modules at hand for any
testing/checks (one was sold while ago, one was installed in HP 3245A
source to replace LM399).

Illya "TiN" Tsemenko

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Re: [volt-nuts] LM399 selection test PCB

[Lars Walenius]

Nice board! Will give you a lot of experience. See forward if you have more to 
report. 


What 2ppm/degC resistors do you use? Do you have any previous experience with 
them? 


Like noise , jumps could have its own thread. I think I have seen 5-10uV jumps 
on most of my 10V refs based on buried zeners. On some it has been years 
between and some very often. For some I have only seen it during temperature 
scans over a span of a couple of °C. Sometimes at low temperature and sometimes 
at higher temperatures. Of course the LM399 is special with its fixed heater. 
On one DMM based on LM399 I can have minutes or sometimes hours with 1.5ppm 
shift in reading but when it goes back for a long time. This have been ongoing 
for 20 years for that particular DMM.

Lars






Från: Ian Johnston
Skickat: ‎onsdag‎ den ‎25‎ ‎november‎ ‎2015 ‎23‎:‎29
Till: Discussion of precise voltage measurement





Hi all,

Thought you guys might be interested in a small PCB I made in order I 
could test, select & check pre-age (if there is such a thing!) my LM399's.

10 channel.
Each channel has it's own chopper op-amp (self bias the LM399),
2ppm/degC tempco resistors throughout,
2x2 sockets for the LM399's (same footprint).
Test points for each channel.
Jumper link on the power rail to disable each channel individually 
(op-amp and heater power).
Holes around each LM399 footprint to help isolate any thermal stress.

Here:-
http://www.ianjohnston.com/temp/lm399select.jpg

So far it's working out great...i've already discovered one of my 
LM399AH's (sitting in ch.4 in the photo) is somehow unstable. It's 
output jumps around by about 10uV's. Need to investigate

The idea is that I can test, select and pre-age LM399AH's before 
soldering them into my target PCB's. I understand that soldering 
can/will reset any aging...but I figured it might help.

I did a pre-test on those Ebay LM399's I bought and they seem to work 
ok...still to properly evaluate.but I do notice that the new 
ones's I bought from Digikey are all giving over 7Vdc, the Ebay ones all 
well under 7Vdc.

Cheers!

Ian.



-- 
IanJohnston.com
/"because it feels good to make stuff"/




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Re: [volt-nuts] Low-cost voltage reference questions

[Lars Walenius]

Mostly a reply to Charles but also to Ian

First of all I should say I prefer 10V reference ICs over 2.5, 5, 7V etc 
references as I think a decent hobby standard should be 10V to be easily 
comparable to a Fluke 732 or other 10V stds. If you have for example a 7V IC 
you have an extra problem to amplify it. So far I have seen no good stable 
amplifier down to a few ppm except if you use very expensive hermetic 
resistors. I am experimenting with the LT5400-3 to get a gain of 1.4 together 
with a zero drift opamp. After four months it still looks good but I have only 
one amp so far so too little statistics. 

I think specifications are a good starting point but not so much more. 
Practical tests are really needed.

As you understand my favorites are ceramic AD587 and metal canned REF102 just 
because I have tested them and found them stable over time, humidity and 
temperature (after compensation)

I have designed in quite a lot of references in my job but normally not to the 
low ppm level. Favorites have been MAX6350 in SMD and AD688 in SMD and long ago 
in ceramic but I have used all sorts from AD, LT and TI. Mostly it has been for 
IO systems.

I don´t have a MAX6350MJA and normally I would like to get IC´s from Digikey, 
Mouser or Farnell. Even in my professional job I have found it worthwhile to 
check if they are available at least on any of these distributors. So a 
question is if anybody knows anything more about the MAX6350MJA especially have 
tested some samples?

For MAX6350 in SMD I have done tests over a couple of years and the problem is 
the humidity sensitivity, I see about 10-15ppm just for a seasonal variation of 
30%RH. A note: sometimes humidity sensitivity cheats people to believe it is 
temperature hysteresis as the package dries during heat up. The drift of two 
MAX6350CSA over 5 years have been 25ppm and quite constant. I have also tested 
just one MAX674 10V ref in SMD that was even worse with about 35ppm seasonal 
variations and 65ppm over 5 years.

One test I haven´t done with any other IC is to short circuit it. I did this a 
couple of years ago with a MAX6350CSA by accident while testing a couple of 
years ago. The short was only during a couple of minutes. First it went down 
50ppm but  during a couple of months went back so it was 30ppm low and now have 
stayed so for two years compared to another MAX6350 in the same box. 

I haven´t tested the AD588KQ. I found it on Digikey but it was really expensive 
so I will probably not test it (like the VRE310 that I haven´t tested either). 
What I don´t like with the AD588 is the dual supplies needed. This is the same 
for the AD688 that I have done some long term tests on. The ceramic is good 
with drifts over 5 years up to 10ppm. What I have seen a couple of times are 
jumps over 2-4ppm that hasn´t gone back the worst I have seen once is 20ppm!). 
Another problem with the AD688 is the large internal heating that I think makes 
it more difficult to temperature compensate. It also has a longer warm-up. My 
only long time tested AD688 in SO-16 have had seasonal variations of about 
10ppm for 30%RH and a drift of 40ppm over 5 years.

The new LT refs in LS8 packages I have just started to test so I have no real 
experience more than that they seems to have more temperature hysteresis (or 
humidity? ). My ceramic AD587 normally have 0.5-1ppm over a temperature scan of 
15C but the LT1236LS8 I have tested have been up to 5ppm hysteresis. Also LT 
warns for humidity sensitivity if not special mounting is used. Seems as a 
drawback.

Why I think the REF102CM is worse than the AD587LQ is that the first years 
drift was +-10ppm and also power-off for a month after a long power on is much 
worse. On the REF102CM I have seen 5ppm but not more than a ppm on the AD587LQ.

About AD587 and REF102 in plastic packages my experience is that the AD587 has 
both less humidity sensitivities (10-15 versus 15-20ppm over 30%RH) and lower 
long term drift (up to 30ppm versus up to 80ppm over 5 years) compared to the 
REF102.

On this EEVblog page you can see four of my REF102CM compared to an AD581 over 
the last 14 years.

http://www.eevblog.com/forum/projects/dc-voltage-references-battle-overview-of-market/msg803679/#msg803679
  

Noise from voltrefs used for calibrating voltmeters is an interesting subject 
that might have its own

Lars





Från: Ian Johnston
Skickat: ‎onsdag‎ den ‎25‎ ‎november‎ ‎2015 ‎12‎:‎28
Till: Discussion of precise voltage measurement






Hi all,
 
Just a note:
On my own project, I had used the MAX6350 in the prototype and the major 
downside for me was the thermal hysterysis it had. Then again, I had mounted 
a small crystal heater on top of it (set to 32degC +/- 0.1degC)..and I 
was pushing the limits as I was trying to resolve down to 38uV on a 0-10Vdc 
range using the 6350 as the 18bit DAC's 5V ref.
 
Ian.
 


-Original Message-
From: Charles Steinmetz 
To: Discussion of precise voltage measurement 
Date: Wed, 

Re: [volt-nuts] Low-cost voltage reference questions

[Lars Walenius]

Yes they are similar but I have used the old Philips/BC Components like Digikey 
BC2301-ND for more than 20 years. Ordinary SMD NTC will also work.




I normally check the trimpin on for example an AD587 with a 1M or 10Mohm 
resistor to +10 and Ground. By checking how the trimpin voltage and output 
voltage changes it has been quite easy to set up a model in Excel for 
calculation. That together with a temperature  scan can be used to select 
components compensation. I think Joe Geller used an automated model with 
Labview to calculate the NTC and resistors to get the right compensation.




Lars​





Från: Russ Ramirez
Skickat: ‎tisdag‎ den ‎24‎ ‎november‎ ‎2015 ‎17‎:‎52
Till: Discussion of precise voltage measurement





Wow, there's a ton to know about NTC thermistors by themselves! Lars, is
the part for the Geller style of unit similar to this one, (
http://www.digikey.com/product-detail/en/NXRT15XH103FA1B030/490-8601-ND/3788625)
or very different?

Russ

On Tue, Nov 24, 2015 at 8:51 AM, Lars Walenius 
wrote:

> Hello,
>
>
> My name is Lars Walenius and I live in Sweden. I am new to this forum but
> a volt nut for decades. I must admit I have to many DIY voltage reference
> boxes. Some years ago I was fortunate to work with Joe Geller on the SVR-T.
> For me the SVR-T still is the best 10V hobby reference sold. So it is a
> pity the AD587LQ isn´t available any more as my opinion is that the
> reference IC is the most important in a DIY reference.
>
>
> I can just second what Andreas say. Maybe the comment about metal cans
> need to be commented. Metal cans are good for humidity but I have seen high
> long term drifts on LT1031 that I have several powered on for years. Also
> if power is off for a or two month they go back many ppms. On REF102CM in
> metal cans (obsolete) I have seen about 5ppm if turned off a longer time.
> In the same test AD587LQ (obsolete) changed less than a ppm. AD587JQ and
> AD587UQ are still available but I would not recommend the UQ as my and
> others observations are in the 10ppm/C class ( probably due to adaption to
> a very wide temp range). I have several JQ with reasonable (less than
> 5ppm/C that can be compensated with NTC) but you should check noise (LF). I
> have seen several ppm p-p on some. So by selection I think the AD587JQ is
> the best 10V ref available today (from eg Digikey).
>
>
> Charles, I have to say thank for all your good comments both here and in
> time nuts but if the 130USD ref is the D105 on Ebay have a look on EEVBlog
> and my humidity tests. The 2ppm ref has 20ppm drift for a change 40 to
> 90%RH in just a week!!
>
>
>
> http://www.eevblog.com/forum/testgear/calibratory-d-105-dc-precision-voltage-reference-standard/630/
>
>
>
>
>
>
> Lars
>
>
>
>
>
>
> Från: Russ Ramirez
> Skickat: ‎tisdag‎ den ‎24‎ ‎november‎ ‎2015 ‎15‎:‎29
> Till: Discussion of precise voltage measurement
>
>
>
>
>
> Thank-you all for your valuable insights and the book reference Jahn. I can
> see clearly now that doing such a project with a LM399 for example as a
> learning project would be interesting. Designing the board to use the
> MAX6126, and finding reasonably priced low tempco parts was a useful
> exercise.
>
> Russ
>
> On Tue, Nov 24, 2015 at 5:55 AM,  wrote:
>
> > There are many things to factor in. Drift of reference itself over time
> > and temperature (399 is 1ppm/K worst case alone, over say 10K, i.e.
> > 23C+/-5K). Drift of the gain setting resistor is critical (assuming you
> > have an amp generating 10V out of the 399 output voltage). and so on.
> > Also, you need a precise reference to calibrate the units (low cal
> > uncertainty and low drift).
> > Selection, statistical validation and aging is needed.
> > All doable but costly and more complicated than one might expect.
> >
> > Thats why I think the target price has to be reasonable, any thoughts
> here?
> >
> >
> >
> >
> > > Gesendet: Dienstag, 24. November 2015 um 10:05 Uhr
> > > Von: "Ian Johnston" 
> > > An: "Discussion of precise voltage measurement" 
> > > Betreff: Re: [volt-nuts] Low-cost voltage reference questions
> > >
> > > Hi all,
> > >
> > > I can relate to this...and only last night I was pouring over it
> > > wondering what to do!
> > >
> > > I have just designed a Handheld Precision Digital Voltage
> > > Source.LM399AH & uController controlled.
> > >
> > > About to start selling them, and so I am writing the manual & spec
> sheet
> > for
> > > it...but can't decide without a years worth of data & testing
> behind
>

Re: [volt-nuts] Low-cost voltage reference questions

[Lars Walenius]

Hello, 


My name is Lars Walenius and I live in Sweden. I am new to this forum but a 
volt nut for decades. I must admit I have to many DIY voltage reference boxes. 
Some years ago I was fortunate to work with Joe Geller on the SVR-T. For me the 
SVR-T still is the best 10V hobby reference sold. So it is a pity the AD587LQ 
isn´t available any more as my opinion is that the reference IC is the most 
important in a DIY reference. 


I can just second what Andreas say. Maybe the comment about metal cans need to 
be commented. Metal cans are good for humidity but I have seen high long term 
drifts on LT1031 that I have several powered on for years. Also if power is off 
for a or two month they go back many ppms. On REF102CM in metal cans (obsolete) 
I have seen about 5ppm if turned off a longer time. In the same test AD587LQ 
(obsolete) changed less than a ppm. AD587JQ and AD587UQ are still available but 
I would not recommend the UQ as my and others observations are in the 10ppm/C 
class ( probably due to adaption to a very wide temp range). I have several JQ 
with reasonable (less than 5ppm/C that can be compensated with NTC) but you 
should check noise (LF). I have seen several ppm p-p on some. So by selection I 
think the AD587JQ is the best 10V ref available today (from eg Digikey).


Charles, I have to say thank for all your good comments both here and in time 
nuts but if the 130USD ref is the D105 on Ebay have a look on EEVBlog and my 
humidity tests. The 2ppm ref has 20ppm drift for a change 40 to 90%RH in just a 
week!!


http://www.eevblog.com/forum/testgear/calibratory-d-105-dc-precision-voltage-reference-standard/630/
 






Lars






Från: Russ Ramirez
Skickat: ‎tisdag‎ den ‎24‎ ‎november‎ ‎2015 ‎15‎:‎29
Till: Discussion of precise voltage measurement





Thank-you all for your valuable insights and the book reference Jahn. I can
see clearly now that doing such a project with a LM399 for example as a
learning project would be interesting. Designing the board to use the
MAX6126, and finding reasonably priced low tempco parts was a useful
exercise.

Russ

On Tue, Nov 24, 2015 at 5:55 AM,  wrote:

> There are many things to factor in. Drift of reference itself over time
> and temperature (399 is 1ppm/K worst case alone, over say 10K, i.e.
> 23C+/-5K). Drift of the gain setting resistor is critical (assuming you
> have an amp generating 10V out of the 399 output voltage). and so on.
> Also, you need a precise reference to calibrate the units (low cal
> uncertainty and low drift).
> Selection, statistical validation and aging is needed.
> All doable but costly and more complicated than one might expect.
>
> Thats why I think the target price has to be reasonable, any thoughts here?
>
>
>
>
> > Gesendet: Dienstag, 24. November 2015 um 10:05 Uhr
> > Von: "Ian Johnston" 
> > An: "Discussion of precise voltage measurement" 
> > Betreff: Re: [volt-nuts] Low-cost voltage reference questions
> >
> > Hi all,
> >
> > I can relate to this...and only last night I was pouring over it
> > wondering what to do!
> >
> > I have just designed a Handheld Precision Digital Voltage
> > Source.LM399AH & uController controlled.
> >
> > About to start selling them, and so I am writing the manual & spec sheet
> for
> > it...but can't decide without a years worth of data & testing behind
> me
> > what figures to use!
> > I've got the reference, DAC and op-amp figures, all the tempo's I need
> etc
> > etc.
> >
> > H!
> >
> > Ian.
> >
> >
> >
> > -Original Message-
> > From: acb...@gmx.de
> > To: volt-nuts@febo.com
> > Date: Tue, 24 Nov 2015 09:35:24 +0100
> > Subject: Re: [volt-nuts] Low-cost voltage reference questions
> >
> >
> > Charles and group,
> > another persons opinion:
> >
> > I guess the reference to the "standards" means those sold on ebay US. If
> so,
> > I would think it is a false expectation this would meet 3ppm acc.
> guaranteed
> > within a year.
> > There is a lengthy chat in eevblog about it, in case you are not aware,
> and
> > while the unit typically may not be too bad, it is certainly not
> seriously a
> > 3ppm guaranteed standard (even in its best version). It starts with the
> > traceability, and goes on with the design and build standard. Details in
> the
> > blog. In summary, it is not even really spec'ed, also because it can't be
> > (at least not close to what it seems to raise in expectations). But at
> that
> > price, it would be unfair to expect more than a hobbyist item with
> > relatively unclear real specs. But if you mean another item, let us
>