Re: [volt-nuts] Low noise reference

[jasonpepas]

Apologies, the last message went out before I was finished drafting it. 

See these links:

https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/

https://www.eevblog.com/forum/metrology/factory-2dw23x-order-aggregation-thread/

Note that these zeners are quite cheap. You could parallel a number of them for 
ever further noise reduction, yet still be cheaper than an LTZ. 



Sent from my iPhone

> On Feb 17, 2018, at 7:24 PM, jasonpe...@gmail.com wrote:
> 
> Hello,
> 
> Are you familiar with the 2DW232, a Chinese zener?  There is one particular 
> factory in China which is somehow producing exceptionally low noise units 
> (much lower noise than the LTZ1000). 
> 
> There is an EEVBlog forum member who lives in China and has graciously 
> volunteered to perform group buys from this factory and then distribute the 
> pets to the individual buyers. 
> 
> 
> 
> Sent from my iPhone
> 
>> On Feb 17, 2018, at 9:07 AM, Randy Evans  wrote:
>> 
>> Thanks for the feedback.  I don't think I am having problems with leakage
>> in the test setup, thermal, or shielding issues.  I used aluminum cast
>> boxes (Pomona 2391) which have BNC M and F connectors, which use teflon
>> insulators.  The cast boxes have enough thermal mass and not subject to
>> moving air currents, so it is unlikely that the wide voltage extremes, over
>> periods of a few to 10's of milliseconds, I am seeing are due to thermal
>> changes.  Also, I had a typo in the original message (I said pA when I
>> meant to type nA) in that the last sentence in the second paragraph should
>> read:  "and around 1 nA at 0.1V, but with widely varying leakage current of
>> 0.5 to 1.5 nA, with occasional peaks of -0.5 to 2 nA.  This would equate to
>> about +/- 2 uV voltage variation across R1, making a 10 V 0.1ppm stable
>> voltage reference of questionable value."  the first sentence in the fourth
>> paragraph should also be referencing nA's.  Sorry about the brain lapse.
>> 
>> The wide variations in current through the 100uF cap-1Kohm resistor are my
>> main concern since I can't explain it.  It is absolutely not present in the
>> 100 Mohm cal resistor in the same type aluminum cast box and is completely
>> stable.  I originally suspected interference but the cap-resistor and
>> calibration resistor are mounted in identical shielded boxes but the 100
>> Mohm cal resistor is clean and stable.
>> 
>> I suppose I need to bite the bullet and build the circuit and see how
>> stable it is.  I can check it with my two Fluke 732As and two HP-3458As.
>> 
>> Rrandall Evans
>> 
>> 
>>> On Sat, Feb 17, 2018 at 4:38 AM, Andre  wrote:
>>> 
>>> also see https://workmanship.nasa.gov/lib/insp/2%20books/links/
>>> sections/407%20Splices.html
>>> 
>>> -Andre
>>> 
>>> 
>>> From: volt-nuts  on behalf of Randy Evans <
>>> randyevans2...@gmail.com>
>>> Sent: 16 February 2018 18:39
>>> To: Discussion of precise voltage measurement
>>> Subject: [volt-nuts] Low noise reference
>>> 
>>> I have a question for the group.  I was looking at an article for building
>>> an ultra-low noise voltage reference by Walt Jung, published in Electronic
>>> Design June 24, 1993 and a URL to the article is below.  I want to filter
>>> the output of an LTZ1000 based 10V reference I am building and this circuit
>>> has a very low freq corner of 1.6 Hz.  I was concerned about the leakage
>>> through R1-C1.  If C1 had as little as 1ua leakage, it would drop the
>>> voltage through R1 by 1 mV.  The spec on 100 uF electrolytic and tantalum
>>> capacitors show a leakage of 20 ua  at rated voltage so this could be of
>>> great concern.  However, at the low few tenths of a volt that should be
>>> across C1, the capacitor should have a much lower leakage amount, which is
>>> the theme of the article.
>>> 
>>> To get a better appreciation of the issue, I connected a precision 0 to 10
>>> V source (100uV resolution steps) to a series combination of a 1 Kohm
>>> resistor and a 100 uF electrolytic and, later, another 47uF tantalum and a
>>> 47 uF electrolytic capacitor.  In all cases the leakage, as measured with a
>>> Keithley 414 picoammmeter, showed a leakage or around 0.08 uA at 10V and
>>> varying 0.04 to 0.12 uA, around .1uA at 1V and varying , and around 1 pA at
>>> 0.1V, but with widely varying leakage current of 0.5 to 1.5 pA, with
>>> occasional peaks of -0.5 to 2 pA.  This would equate to about +/- 2 uV
>>> voltage variation across R1, making a 10 V 0.1ppm stable voltage reference
>>> of questionable value.
>>> 
>>> I also tried a 0.68 uF polystyrene capacitor and also saw leakage current
>>> variations, although much less than the electrolytic and tantalum
>>> capacitors, as one would expect.
>>> 
>>> Thinking the problem might be the the picoammeter, I put a 100 megohm 0.1%
>>> precision resistor in place of the capacitor across the precision voltage
>>> source set 

Re: [volt-nuts] Low noise reference

[jasonpepas]

Hello,

Are you familiar with the 2DW232, a Chinese zener?  There is one particular 
factory in China which is somehow producing exceptionally low noise units (much 
lower noise than the LTZ1000). 

There is an EEVBlog forum member who lives in China and has graciously 
volunteered to perform group buys from this factory and then distribute the 
pets to the individual buyers. 



Sent from my iPhone

> On Feb 17, 2018, at 9:07 AM, Randy Evans  wrote:
> 
> Thanks for the feedback.  I don't think I am having problems with leakage
> in the test setup, thermal, or shielding issues.  I used aluminum cast
> boxes (Pomona 2391) which have BNC M and F connectors, which use teflon
> insulators.  The cast boxes have enough thermal mass and not subject to
> moving air currents, so it is unlikely that the wide voltage extremes, over
> periods of a few to 10's of milliseconds, I am seeing are due to thermal
> changes.  Also, I had a typo in the original message (I said pA when I
> meant to type nA) in that the last sentence in the second paragraph should
> read:  "and around 1 nA at 0.1V, but with widely varying leakage current of
> 0.5 to 1.5 nA, with occasional peaks of -0.5 to 2 nA.  This would equate to
> about +/- 2 uV voltage variation across R1, making a 10 V 0.1ppm stable
> voltage reference of questionable value."  the first sentence in the fourth
> paragraph should also be referencing nA's.  Sorry about the brain lapse.
> 
> The wide variations in current through the 100uF cap-1Kohm resistor are my
> main concern since I can't explain it.  It is absolutely not present in the
> 100 Mohm cal resistor in the same type aluminum cast box and is completely
> stable.  I originally suspected interference but the cap-resistor and
> calibration resistor are mounted in identical shielded boxes but the 100
> Mohm cal resistor is clean and stable.
> 
> I suppose I need to bite the bullet and build the circuit and see how
> stable it is.  I can check it with my two Fluke 732As and two HP-3458As.
> 
> Rrandall Evans
> 
> 
>> On Sat, Feb 17, 2018 at 4:38 AM, Andre  wrote:
>> 
>> also see https://workmanship.nasa.gov/lib/insp/2%20books/links/
>> sections/407%20Splices.html
>> 
>> -Andre
>> 
>> 
>> From: volt-nuts  on behalf of Randy Evans <
>> randyevans2...@gmail.com>
>> Sent: 16 February 2018 18:39
>> To: Discussion of precise voltage measurement
>> Subject: [volt-nuts] Low noise reference
>> 
>> I have a question for the group.  I was looking at an article for building
>> an ultra-low noise voltage reference by Walt Jung, published in Electronic
>> Design June 24, 1993 and a URL to the article is below.  I want to filter
>> the output of an LTZ1000 based 10V reference I am building and this circuit
>> has a very low freq corner of 1.6 Hz.  I was concerned about the leakage
>> through R1-C1.  If C1 had as little as 1ua leakage, it would drop the
>> voltage through R1 by 1 mV.  The spec on 100 uF electrolytic and tantalum
>> capacitors show a leakage of 20 ua  at rated voltage so this could be of
>> great concern.  However, at the low few tenths of a volt that should be
>> across C1, the capacitor should have a much lower leakage amount, which is
>> the theme of the article.
>> 
>> To get a better appreciation of the issue, I connected a precision 0 to 10
>> V source (100uV resolution steps) to a series combination of a 1 Kohm
>> resistor and a 100 uF electrolytic and, later, another 47uF tantalum and a
>> 47 uF electrolytic capacitor.  In all cases the leakage, as measured with a
>> Keithley 414 picoammmeter, showed a leakage or around 0.08 uA at 10V and
>> varying 0.04 to 0.12 uA, around .1uA at 1V and varying , and around 1 pA at
>> 0.1V, but with widely varying leakage current of 0.5 to 1.5 pA, with
>> occasional peaks of -0.5 to 2 pA.  This would equate to about +/- 2 uV
>> voltage variation across R1, making a 10 V 0.1ppm stable voltage reference
>> of questionable value.
>> 
>> I also tried a 0.68 uF polystyrene capacitor and also saw leakage current
>> variations, although much less than the electrolytic and tantalum
>> capacitors, as one would expect.
>> 
>> Thinking the problem might be the the picoammeter, I put a 100 megohm 0.1%
>> precision resistor in place of the capacitor across the precision voltage
>> source set for 0.1 V and measured the current through the resistor at a
>> very stable 0.9 pA on the Keithley 414 (sb 1pA but accurate enough for my
>> measurements - the resistor shielded box likely has some sub pA leakage
>> also).  Note that I used shielded cables for all measurements, and the
>> resistor and capacitor were in a shielded box, as well as the 100 Mohm
>> calibration resistor.  Touching the cables or boxes did not change the
>> picoammeter reading at all, indicating to me that the shielding was
>> reasonable.
>> 
>> I suppose the best approach is to build it and characterize it, but 

Re: [volt-nuts] Help needed identifying triaxial connector on HP 4339B high resistance meter - measures to 1.6 x 10^16 ohms.

[Florian Teply]

Hi David,

Am Sat, 17 Feb 2018 15:32:15 +
schrieb "Dr. David Kirkby" :

> In order to use the meter, I would obviously need to be able to make
> connections to it.
> 
> Is there anyone here that knows what the triaxial (tri-axial?)
> connector in the attached pictures ? One picture is of the female on
> the 4339B and the other the male plug on a fixture that I don't have.
> 
> The picture of the meter is not the one I have,  since the meter is at
> Keysight. But it has a better picture of the triaxial connector than
> the meter I have.
> 
> Does anyone have a bit of trixial cable with one of these connectors
> on?
> 
Unfortunately, I don't know this kind of connector either. 
I can confirm however - which probably does help a bit still - that it
is neither the three-lug BNC triax HP/Agilent/Keysight uses on all
measurement equipment capable of going down to picoamp levels I have
ever seen, nor  the two-lug BNC triax that Keithley uses for the same
purpose. To me it seems to be a threaded connector, and dimension-wise
should be pretty close to BNC, so TNC-style triax it might indeed be.

But be prepared that these are a bit pricey, the last time I bought the
standard three-lug BNC-style triax connectors they were about 80 Euros
a piece.

HTH,
Florian
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Re: [volt-nuts] Low noise reference

[Andre]

also see 
https://workmanship.nasa.gov/lib/insp/2%20books/links/sections/407%20Splices.html

-Andre


From: volt-nuts  on behalf of Randy Evans 

Sent: 16 February 2018 18:39
To: Discussion of precise voltage measurement
Subject: [volt-nuts] Low noise reference

I have a question for the group.  I was looking at an article for building
an ultra-low noise voltage reference by Walt Jung, published in Electronic
Design June 24, 1993 and a URL to the article is below.  I want to filter
the output of an LTZ1000 based 10V reference I am building and this circuit
has a very low freq corner of 1.6 Hz.  I was concerned about the leakage
through R1-C1.  If C1 had as little as 1ua leakage, it would drop the
voltage through R1 by 1 mV.  The spec on 100 uF electrolytic and tantalum
capacitors show a leakage of 20 ua  at rated voltage so this could be of
great concern.  However, at the low few tenths of a volt that should be
across C1, the capacitor should have a much lower leakage amount, which is
the theme of the article.

To get a better appreciation of the issue, I connected a precision 0 to 10
V source (100uV resolution steps) to a series combination of a 1 Kohm
resistor and a 100 uF electrolytic and, later, another 47uF tantalum and a
47 uF electrolytic capacitor.  In all cases the leakage, as measured with a
Keithley 414 picoammmeter, showed a leakage or around 0.08 uA at 10V and
varying 0.04 to 0.12 uA, around .1uA at 1V and varying , and around 1 pA at
0.1V, but with widely varying leakage current of 0.5 to 1.5 pA, with
occasional peaks of -0.5 to 2 pA.  This would equate to about +/- 2 uV
voltage variation across R1, making a 10 V 0.1ppm stable voltage reference
of questionable value.

I also tried a 0.68 uF polystyrene capacitor and also saw leakage current
variations, although much less than the electrolytic and tantalum
capacitors, as one would expect.

Thinking the problem might be the the picoammeter, I put a 100 megohm 0.1%
precision resistor in place of the capacitor across the precision voltage
source set for 0.1 V and measured the current through the resistor at a
very stable 0.9 pA on the Keithley 414 (sb 1pA but accurate enough for my
measurements - the resistor shielded box likely has some sub pA leakage
also).  Note that I used shielded cables for all measurements, and the
resistor and capacitor were in a shielded box, as well as the 100 Mohm
calibration resistor.  Touching the cables or boxes did not change the
picoammeter reading at all, indicating to me that the shielding was
reasonable.

I suppose the best approach is to build it and characterize it, but it's
not fruitful if someone has already done this. So my question is: has
anyone built this circuit and characterized it, particularly over
temperature for stability at the sub ppm level?

Thanks,

Randall Evans







http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdf
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Re: [volt-nuts] Low noise reference

[Andre]

Yes I have relevant experience with Lifters, fingerprints generally are a 
nightmare.

May also be worth mentioning that different grades of IPA are more or less 
useful, it absorbs water
in its pure form so this needs to be taken into account.
Use "no clean" fluxed solder if possible as it works well.

Also relevant, don't forget that NASA like using splice joints where the wire 
is tied into essentially a reef knot.
This is for all sorts of reasons not least visual inspection of the joint at 
regular intervals and anti-
vibration measures are used like clear heatshrink.



From: volt-nuts  on behalf of Poul-Henning Kamp 

Sent: 17 February 2018 09:10
To: Discussion of precise voltage measurement; Randy Evans
Subject: Re: [volt-nuts] Low noise reference


In message