Re: [volt-nuts] Bohnenberger electrometer DANGER

[Andre]

Please be VERY VERY careful. To be honest its far safer to use CCFL drivers and 
rectify them with camera diodes in series and the absolute minimum capacitance 
for the job, shunted with a high value resistor.
I have a few inverters , 10M resistor packs and diode strips here if anyone has 
a use on the understanding they are only to be used at your own risk, and for 
the intended purpose.

Microwave capacitors can be deadly (you could DIE!) under the wrong 
circumstances, fibrillation can occur even with quite small shocks down to <8J 
if you get hit badly or have an undetected problem. I don't want to scare 
people but it is a serious risk.
Had to scale back one of my projects because I had a near miss with a setup 
very much like the one described  in earlier posts and despite dual failsafes 
still got a belt large enough to require medical treatment.
(hint: the experiment is on Youtube, saying no more)
Very fortunately my systems weren't seriously affected but I probably did some 
damage.

Still have a 380J 215uF/2.5KV capacitor here and that one is staying shunted 
and under lock and key until I have the appropriate safety knowledge and 
experience. Dielectric memory is a b*t*h!

-A


From: volt-nuts  on behalf of ed breya 

Sent: 07 March 2018 00:11
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Bohnenberger electrometer

I looked at that link that Brooke put up about Bohnenberger's
Electroscope. I don't know what your specific arrangement needs to be,
but it appears you need a plus and a minus HV wrt ground in the most
general form. If so, then this would mean having to split the voltage of
a single cap, or have two caps, one for each polarity.  Then I'd
recommend using good old microwave oven caps. You could charge them both
to say 2 kV from one HV source, then switch them around so they're
stacked and grounded at the midpoint.

Ed

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Re: [volt-nuts] Precision high resistance measurements / calibration of HP 4339B high-resistance meter. Fix?

[Andre]

Maybe one bad resistor? I've read that tin whiskering can occur even on 
relatively recent equipment, slower than lead free but still a problem.
I'd do a visual inspection just to see, shouldn't be an issue.
-A

From: volt-nuts  on behalf of Dr. David Kirkby 

Sent: 02 March 2018 03:16:24
To: Discussion of precise voltage measurement
Subject: [volt-nuts] Precision high resistance measurements / calibration of HP 
4339B high-resistance meter.

I pickup up an HP/Agilent (front says HP, rear says Agilent) 4339B
high-resistance meter from eBay. The 4339B has an internal supply up to
1000 V, an ammeter to measure current, and obviously computes resistance
from Ohms Law. It is supposed to work up to 16 Peta ohms (1.6x10^16 ohms),
which would pass a current of 62.5 fA with 1000 V.

It was sold as non-working, with no output. Even attempting to get some
output was challenging as it had an obscure 6-pin interlock connector, and
there's no information in the manual about this. It also has a trixaxial
input connector with a screw thread. I asked Keysight for some information
about the connectors. I still don't know what the triaxial connector is,
but I have the interlock sussed - a HiroseHR10A-7P-6P(73) plug fits, and
there's some information about the wiring of this in the manual for the
11617C low-noise test leads.

Keysight offered to do a free technical evaluation, so I thought I'd take
them up on it, rather than waste too much time trying myself to get it
working. It was sent to Keysight and they sent me a report showing there is
output voltage, despite it being sold as having no output, and the output
is all in spec. Unfortunately, it was out of spec on one of the current
ranges. It is reading 0.082 nA low with a test current of 10 nA, but the
specification is +/- 0.063 nA. So it is only a little bit out, but it is
still out of spec. Test currents of 100 pA, 1 nA, 10 nA, 100 nA, 1 uA, 10
uA and 100 uA were used, so the 10 nA is neither at the low nor high end of
the range of the meter.

When I received an email copy of the free technical report, I assumed the
4339B had not been subjected to a full calibration as it was only tested
with resistors up to 10^11 ohms, but it is supposed to read resistance up
to 1.6 x 10^16 ohm, so the highest value resistor used during the technical
evualation is 5 orders of magnitude lower than the what the meter can read.
Also the meter was only tested at 100 V when reading resistors, whereas I
would have thought it more sensible to test at a higher voltage, given it
can output 1 kV.

I decided to pay Keysight for a full calibration, so I got a cal
certificate, which shows the out of spec reading.

http://www.kirkbymicrowave.co.uk/tmp/1-9690444179-1-combined-file.pdf

I was rather hoping the cal certificate would have some extra readings, but
I actually received no more technical information than Keysight had given
me for nothing, although they did update the firmware as I requested.

I have two questions.

1) Is 10^11 ohms a practical limit on making resistors that can be used for
calibration purposes? I don't know what the Keysight uncertainty on their
calibration standards are, so maybe 10^11 ohms is all its practical to
make.

2) Does anyone know if the meter can be adjusted on individual ranges? I
find it a bit hard to believe that given the ammeter was tested with
currents covering 6 orders of magnitude (100 pA to 100 uA), that there's no
adjustment on individual ranges. I doubt that it is possible to design a
circuit to cover that range, without switching in some different resistors
at some point.

But I'm told it can't be adjusted, and needs a new board.

I'm wondering if anyone knows anything about this meter, just in case
Keysight are wrong. I know they should not be, but it is not a current
instrument, so it's just possible the engineer did not know it could be
adjusted.

Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford,
Essex, CM3 6DT, United Kingdom
Registered in England and Wales as company number 08914892
http://www.kirkbymicrowave.co.uk/
Tel 01621'680100 / +44 1621-680100
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Re: [volt-nuts] LM3900 (was: HP3458 ADC integrator) Instrumentation Amplifiers (3)

[Andre]

Hi, also have three AD623(?) IA's I purchased for a heart rate monitor.
Can find them as and when needed, pretty sure they are the ones featured in the 
Hackaday article.
At the time if the ECG worked the same circuit would get cloned and used for an 
EEG as the signals are a lot smaller but
in this case I'd use a Pi Zero or Arduino as the input as its already got 
onboard A-D's.

For this project the isolation requirements are insane, 0.1mA permitted leakage 
means you're limited to battery power and
even wireless charging is verboten. One big problem is the brain really does 
*not* like excess electricity, permanent damage is
quite likely even with careless use of a TENS machine etc.
Its feasible to use EM sensors based on old atomic clock "cores" to measure 
brain magnetic fields (maybe thats what DOC BROWN used)
but try getting more than one of them or disciplining them in the presence of 
Earth's magnetic field to make measurements.
Alas this project is going to have to wait until technology radically improves, 
as all the SQUID sensors I've run into use liquid helium and there are very few 
ways to get a piece of niobium-titanium that cold even using laser cooling and 
Linde refrigerators etc.
Ironically this is the main reason why quantum computers suchnas D-wave 2 or 
the IBM one are so heinously £xpen$iv£ as they need to get down to millikelvins 
so sit upside-down in the LHe vat with all the sensors far away from that 
little chip.

-A

From: volt-nuts <volt-nuts-boun...@febo.com> on behalf of Attila Kinali 
<att...@kinali.ch>
Sent: 01 March 2018 19:57
To: Discussion of precise voltage measurement
Subject: [volt-nuts] LM3900 (was: HP3458 ADC integrator)

On Wed, 28 Feb 2018 06:32:58 +
Andre <an...@lanoe.net> wrote:

> Can you make use of an LM3900? I have one here *somewhere*.
> I think its a quad Norton, not sure how long its been there for.

Theoretically yes, in practice you are better off using an opamp
that is not 40 years old and not as quirky as a Norton opamp.
You can buy standard bipolar opamps that beat those old beats
at all metrics, and they only cost little more, if at all.

The only place where these beasts really excell is that the
inputs are basically independent of the supply voltage, given
the maximum input current is not exceeded. Linear has a few
opamps that can do the same trick (though in a slightly different
manner), but they also cost a bit more.

Attila Kinali

--
The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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[volt-nuts] Bits in ancient Panasonic phone

[Andre]

Hi, is there a guide anywhere on "good bits" to salvage from ancient 
Panabrickic (tm) GSM phones please?
I found one here, the display is fandango'd but other than that it did turn on 
very briefly with a "jump start" to its
circa 1998 NiCad pack.
I understand that there are often OCXO and other interesting bits, recall 
vaguely salvaging some of these from ancient
cell base station boards that got flooded out.
kind regards, -Andre
#include "CTC101.h"


From: volt-nuts <volt-nuts-boun...@febo.com> on behalf of Andre 
<an...@lanoe.net>
Sent: 28 February 2018 06:32
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] HP3458 ADC integrator (SPARES)

Can you make use of an LM3900? I have one here *somewhere*.
I think its a quad Norton, not sure how long its been there for.

also have a few canned op-amps etc
-Andre

From: volt-nuts <volt-nuts-boun...@febo.com> on behalf of Attila Kinali 
<att...@kinali.ch>
Sent: 27 February 2018 18:25
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] HP3458 ADC integrator

On Sat, 24 Feb 2018 12:59:21 +1300 (NZDT)
Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote:

> 1) Reverse the supplies on U4 (in real circuit reversed supplies will fry the 
> chip.)
> 2) Add 10k in series with reset switch
> 3) Swap connections to U4 inputs.
> 4) Use series shunt switch for reset switch as used in an actual 3458A.
> Once done together with swapping in LT1220 for LT1225 rest works as expected 
> and output slews due to gate current of J1 and input bias current of U1

Ok, I played around a bit more and I think I now mostly understand what's
going on. The main problem was really the stability of the opamps chosen.
For the integrator to work, the added up gain and phase shift must still
fulfill the stability condition (obvious, yes, but.. well I am stupid at times)
I am not sure how the intermediate steps in a 3 opamp integrator work,
but I guess that should imediatly be obvious once a complete stability
analyis is done.

Thanks everyone who provided insight and feedback.

Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [volt-nuts] HP3458 ADC integrator (SPARES)

[Andre]

Can you make use of an LM3900? I have one here *somewhere*.
I think its a quad Norton, not sure how long its been there for.

also have a few canned op-amps etc
-Andre

From: volt-nuts <volt-nuts-boun...@febo.com> on behalf of Attila Kinali 
<att...@kinali.ch>
Sent: 27 February 2018 18:25
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] HP3458 ADC integrator

On Sat, 24 Feb 2018 12:59:21 +1300 (NZDT)
Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote:

> 1) Reverse the supplies on U4 (in real circuit reversed supplies will fry the 
> chip.)
> 2) Add 10k in series with reset switch
> 3) Swap connections to U4 inputs.
> 4) Use series shunt switch for reset switch as used in an actual 3458A.
> Once done together with swapping in LT1220 for LT1225 rest works as expected 
> and output slews due to gate current of J1 and input bias current of U1

Ok, I played around a bit more and I think I now mostly understand what's
going on. The main problem was really the stability of the opamps chosen.
For the integrator to work, the added up gain and phase shift must still
fulfill the stability condition (obvious, yes, but.. well I am stupid at times)
I am not sure how the intermediate steps in a 3 opamp integrator work,
but I guess that should imediatly be obvious once a complete stability
analyis is done.

Thanks everyone who provided insight and feedback.

Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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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 <volt-nuts-boun...@febo.com> 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 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 

Re: [volt-nuts] Any list members in UK who can accurately characterise a 732A and a 10K resistor 4HV.org

[Andre]

Maybe I can ask on 4HV.org ? 

From: volt-nuts  on behalf of David C. Partridge 

Sent: 15 January 2018 03:22
To: 'Discussion of precise voltage measurement'
Subject: Re: [volt-nuts] Any list members in UK who can accurately  
characterise a 732A and a 10K resistor

Guildline 9330 nominal accuracy 2.5ppm.

-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Dr. David 
Kirkby
Sent: 14 January 2018 23:03
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Any list members in UK who can accurately characterise 
a 732A and a 10K resistor

On 14 January 2018 at 15:40, David C. Partridge < 
david.partri...@perdrix.co.uk> wrote:

> I've recently rebuilt a 732A and it seems stable, but what I don't
> know is its actual output voltage down to the last ppm
>
> I've also acquired a Guildline 3330 10K standard resistor but again
> don't know its value - my 3458A says it is 10,000.43 ohms which I find
> rather hard to believe (way out of spec.).
>

Is there a tight spec on the nominal value?

I can't find the specification on those from a Google search, but I thought the 
actual value was not very well controlled, but the stability is. So the fact it 
is 0.43 Ohms high, may not mean it is out of spec.

I would imagine there's a trade-off between getting the initial value correct 
and the stability. If you design the resistor for maximum stability, you may 
not be able to simultaneously get the value close to its nominal value. It you 
do things to get the nominal value better, they may degrade the stability.


>
> I know someone with a recently calibrated 3458A (Keysight Calibration,
> not accredited, not Loveland), but can anyone do better?  I'd prefer
> not to have a pay for a formal cal lab report on these.
>

A non-accredited Keysight calibration should be no less accurate than an 
accredited Keysight calibration.  From what I understand, the procedure is the 
same, but you just get a few extra words on the cal certificate if it is 
accredited - and pay quite a bit more. It costs Keysight money to be 
accredited, so they pass the costs of that onto people that need an accredited 
cal certificate.

I wonder what ones chances of going to NPL on their open-day (17 May 2018) and 
getting a measurement performed as a favor?  If you don't want an official cal 
certificate, but just a number you scribble on a bit of paper, you might be 
able to get it done free of charge. I know the lab with a primary voltage 
standard (Josephine Junction), was open to the public on the last open-day, 
which was in 2016. I don't think there was any lab open that measured resistors 
though.


> Thanks
> Dave
>

Dave
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Re: [volt-nuts] Need Fluke 332B PCB contacts (possible source?)

[Andre]

I will have a look in my box of Tek stuff!
It would also be worth asking someone at Offshore Electronics or Polar, as they 
often have strange stuff which
gets recycled otherwise.
Can someone please send me a picture of the component and I will check with the 
folks at "Lightbulb Nights" too.


From: volt-nuts  on behalf of Dave M 

Sent: 14 October 2017 16:29
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Need Fluke 332B PCB contacts

Hi Chris,
I haven't found a stocking source for the contacts.  Elco/AVX requires an
order of at leasst 5000 units before they will tool up for a run.  I looked
extensively for some of these contacts at our local hamfest a few weeks ago,
but came up empty.

One of the forum members (from Australia) saw my post and sent me a salvaged
contact strip having about 20 of the contacts.  The strip was in good
condition, none of the contacts were damaged, and fits nicely on the new
PCB.  Don't know if he has any more of the contact strips.

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Re: [volt-nuts] Best way to measure micro Ohms

[Andre]

Hi, just my $0.02 worth.
I have some instrumentation amplifiers here also looked into low resistance 
connections for my other projects.

If I recall correctly you need to look at the electrochemical series. For 
interconnects on Al you want a metal similar on the ES.
The oxide is a problem but if you connect it properly eg with an oil droplet 
and clamp connnector using compatible vernier it should be fine.

Looking at how wiring in the US is done might give you some ideas.

Kind regards, -Andre

From: volt-nuts <volt-nuts-boun...@febo.com> on behalf of Charles Steinmetz 
<csteinm...@yandex.com>
Sent: 19 September 2017 21:30
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Best way to measure micro Ohms

David wrote:

> A practical problem is the tools available to me. The U-channel was
> machined by someone in my radio club, and the rest I made myself using
> nothing more than a drill and hand tools. It would be nice to make more out
> of one piece, but it would require better tools than I have readily
> available. There are certainly engineering companies that could do a better
> job, but it would be quite costly.

If you can make a decent drawing of what you need (it doesn't have to be
a draughtsmanlike job, as long as the form and measurements are clearly
shown), I bet you can find someone in your radio club, or a personal
friend, or someone on a list you frequent to make it for a nominal cost
(you would probably need to pay for the raw material, although I don't
charge for anything that comes out of my scrap pile and this is true of
many other home shop machinists).  HSMs are behind every third or fourth
garage door in the UK.

Another option would be to build up the parts as you have done, then
have someone TIG weld the pieces together.

Best regards,

Charles


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Re: [volt-nuts] 732A drift

[Andre]

Hi, first post!
Yeah, I ran into this issue a while back. Fortunately for most applications 
10mV resolution is fine (eg measuring charge state on Li-ion cells) but I did 
find that old meters do seem to experience random drift failures of precision 
resistors and more so trimpots. Would it be a good idea for someone to do a 
"732 FAQ" with likely faults that would cause a particular matrix of symptoms?

Also how do you deal with failures where a precision component has "gone bad" ? 
Surely all the calibrations are suspect which is why any sensible engineer 
always has two references at a bare minimum and sets up a master/slave or 
main/backup then maintains a calibration table of each? so if a drift is seen 
then the "bad" unit can be dealt with sternly.

I looked into making a 10.Vref a while back and had some success with 
active feedback via thermal pad: it almost worked but in the end it was cheaper 
and simpler to buy one ready made (cough REF02 /cough)
Also relevant, since originally buying my RS IDM65 you can now get I2C 
precision CT references which can replace the troublesome parts
with something that does not drift, ever!

-Andre



From: volt-nuts <volt-nuts-boun...@febo.com> on behalf of Alan Ambrose 
<alan.ambr...@anagram.net>
Sent: 30 August 2017 17:33
To: volt-nuts@febo.com
Subject: [volt-nuts] 732A drift

>>> My 732A e.g. has a drift of only about 0.2ppm 
>>> pa over a couple of year

Hope you don't mind me jumping on this thread and asking a basic question: is 
there any kind of procedure for the 'enthusiast' (say with single 3458A/single 
732 and not say 4x732) to measure the drift of a particular 732.

Alan
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