Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[kc9ieq via volt-nuts]

I guess I don't see what the issue is.  No, impedance is not infinate when not 
nulled, but this is why V supply #2 Is adjustable by whatever convenient means. 
 Rough adjust, connect, adjust for null, measure.  Rinse and repeat.  If it 
were my project, I'd just run up an HV transformer on a variac, with a 
rectifier, cap, and probably some series R thrown at it to limit current 
through the meter.  Curious to know what the application is, if this will not 
work.  
Good luck with whatever solution you choose.  
Regards, Chris 


Sent from my SMRTphone
 Original message From: "Dr. David Kirkby" 
<drkir...@kirkbymicrowave.co.uk> Date: 3/22/18  8:58 PM  (GMT-06:00) To: kc9ieq 
<kc9...@yahoo.com>, Discussion of precise voltage measurement 
<volt-nuts@febo.com> Subject: Re: [volt-nuts] How can I make a 2000 V DC meter 
with an input resistance of at least 100 T ohms? 
On 23 March 2018 at 01:49, kc9ieq via volt-nuts <volt-nuts@febo.com> wrote:
How about using (or building) an additional 2kV power supply and a sensitive 
meter movement like a differential voltmeter, adjusting for/measuring the null? 
 Impedance at null will be theoretically infinate, current will be 
theoretically zero, and you can measure/monitor the voltage of your second 
supply directly with the probe/meter of your choice.  

Regards,Chris 

No, that will not work for me, as while the impedance at null is infinite, it 
is not when not nulled, and that will mess up the measurements. 

Absolute accuracy is not important. +/- 10% or even 20% would be okay. I want 
to measure a couple of voltages and compare them. As long as the meter reads 
the same with identical input voltages, that is fine. 

Dave 

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Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[kc9ieq via volt-nuts]

How about using (or building) an additional 2kV power supply and a sensitive 
meter movement like a differential voltmeter, adjusting for/measuring the null? 
 Impedance at null will be theoretically infinate, current will be 
theoretically zero, and you can measure/monitor the voltage of your second 
supply directly with the probe/meter of your choice.  
Regards,Chris 


Sent from my SMRTphone
 Original message From: "Dr. David Kirkby" 
 Date: 3/22/18  7:33 PM  (GMT-06:00) To: 
Discussion of precise voltage measurement  Subject: 
[volt-nuts] How can I make a 2000 V DC meter with an input
  resistance of at least 100 T ohms? 
I want to measure a high voltage, but put minimal load on the circuit.
Looking at the Keithley electrometers, the input resistance is at least 200
T ohms, but they tend to have a maximum of 200 V FSD.

A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which
itself is easy to measure. But one can't buy 200 T ohm resistors. I looked
at RS in the UK, and the highest value resistor I could find is 1 T ohm,
and they are £163 each (around $200).

Maybe fabricating ones own resistor is possible, but I suspect there's a
better way. Keithely manage to keep a 200  T ohm resistance on the 200 mV
range, and there's no way that can be measured with an ammeter, which would
require an ammeter with a full scale deflection of 1 fA, which is much
smaller than the 2 pA FSD on its most sensitive range.

Any thoughts?

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] Fluke 893A thoughts?/3458A in the SW Chicagoland area/Geller Labs references?

[kc9ieq via volt-nuts]

Thanks Andy and all for the replies, I have some more reading to do but may 
take one of you up on your generous offers.  
Very cool idea on the traveling reference!  Not sure I can contribute anything 
towards the project since my only "good" meter is a recently calibrated 3456A, 
but may just have to see about getting in on that!  I finally registered on 
EEVBlog, lots and lots to see and learn there.  
In the meantime...  Far as differential voltmeters go for this level of 
accuracy, is a Fluke 893A really worth going to the trouble of overhauling, or 
should I keep my eyes open for something just a little better?  I have two of 
these units, one basically works but is inaccurate, the other has no meter 
deflection.  The reference diode would likely be a candidate for improvement, 
but wonder if the rest of the instrument could really take advantage of it.  
Thinking thst something a little better, or perhaps just getting/rebuilding a 
335A/D would be better bet than the 332B with an external differential meter.  
Open to all thoughts, comments, and set-me-straight-isms!
Regards, Chris 


Sent from my SMRTphone
 Original message From: Andy Lawrence  
Date: 8/12/17  7:44 AM  (GMT-06:00) To: Discussion of precise voltage 
measurement  Subject: Re: [volt-nuts] 3458A in the SW 
Chicagoland area/Geller Labs
references? 
If for some reason the US Cal Club doesn't fit for you:

My parents live north of Chicago in Lindenhurst, and I *might* be visiting
there for X-Mas this year.  Or if you get really motivated I live in Terre
Haute IN, which is probably only 3 hours south of you.  Only one point of
history but I have two recent cal'ed 3458As and a 731B.

BR
Andy

On Fri, Aug 11, 2017 at 6:51 PM, Jason Pepas  wrote:

> Hi Chris,
>
> You might consider taking a look at the EEVBlog USA Cal Club thread.  We
> are mailing a Geller Labs reference around the country.
>
> The reference doesn't have a lot of history built up yet, and we haven't
> tried shipping it back and forth between the same two parties multiple
> times to characterize shipping-induced instability, but it has been in the
> hands of a couple of 3458A owners, so its uncertainty is a bit of a mixed
> bag at the moment.
>
> Either way, its fun to participate :)
>
> http://www.eevblog.com/forum/metrology/usa-calibration-club/
>
> -Jason Pepas
>
>
> On Fri, Aug 11, 2017 at 4:55 PM, Chris Farley via volt-nuts <
> volt-nuts@febo.com> wrote:
>
> > Greetings all,
> >
> > As suggested several months ago, I'm put out an inquiry/request to see if
> > there's anybody in the area who has an HP3458A or better anywhere near me
> > down here in Sandwich, that I might be able to either A) compare readings
> > to my 3456A, or possibly use (without removing from your premises,
> > obviously) use to calibrate my Fluke 332B.  I have means to keep my units
> > powered during transport, so hopefully would not require hours of sitting
> > to stabilize before taking any readings.  The 3456A's limitations are
> > really being stretched, in trying to calibrate a 332B with it alone.
> >
> > Alternatively, is anybody aware of a Geller Labs (closed) voltage
> > reference available on the used market, or something of equal or better
> > precision available today?  The Malone Electronics VREF10-003 looks very
> > interesting, with supposed 6mos accurace of ±300uV.
> >
> > Regards,
> > Chris
> > ___
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[volt-nuts] Short term "standard" cell?

[kc9ieq via volt-nuts]

In preparation of (hopefully!) Getting that fluke 332A running and sticker 
shock of what the 732A and similar references go for, I wonder about normal, 
every day alkaline or lithium batteries and their short term stability.  
Here's the half baked idea.  A fresh, standard 1.5V, or 3V lithium, alkaline, 
or silver oxide button cell battery, or even an AA sized cell, measured by 
someone/some place with a known accurate precision meter.  Invisioning 6 or so 
decimal places.  Could that cell then be shipped, and used as a reference in 
another altitude?  I haven't spent a ton of time looking, but haven't yet found 
anything on the web about stability of these types of batteries.
Regards, Chris 


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Re: [volt-nuts] Fluke 332B

[kc9ieq via volt-nuts]

Very interesting.  What series resistor did you have these results with?  Very 
interested to compare spec'd temp co.
Regards, Chris 


Sent from my SMRTphone
 Original message From: Jerry Hancock  Date: 
2/20/17  2:51 PM  (GMT-06:00) To: kc9ieq  Cc: Discussion of 
precise voltage measurement  Subject: Re: [volt-nuts] Fluke 
332B 
I took some of the 100K 1/4 watt resistors from my DAS-46 and heated them with 
a soldering iron.  They ran high pretty quickly.  I then used a cheap, 1% 
Chinese brand metal film and they ran high just about as quickly.  The 5% 
Chinese brand ran low a lot faster.  Just bringing the soldering iron near them 
 Interesting in that using one of each, the resistance stayed about right on 
the parallel value.  I then used a high quality Vishay and I couldn’t get it to 
move with the soldering iron without touching it.  These resistors cost about 
.40 per at Mouser.   I was just using my Agilent DMM so I’m sure they were 
moving, just not within the resolution of the meter.  The bottom line is that 
the carbon comp I replaced with the 50 cent per Vishay was a good move.  Had I 
used the 5% I have, it would have been about the same.  


> On Feb 20, 2017, at 12:36 PM, kc9ieq  wrote:
> 
> Very interesting, very curious to hear your conclusion!  
> 
> My thought would be to replace these with standard value 5% resistors having 
> good temp co, as calibration should surely make up for any subpar values--  
> my thinking is that temp drift would be a more major consideration for 
> overall stability.  If this is a false assumption of would certainly like to 
> learn why.  
> Perhaps the old Allen Bradley carbon comps were special in this regard, but 
> the data sheet I've seen for currently available comp resistors had a 
> horrible temperature coefficient--  much worse than the "better" film 
> resistors available today.  I stock the Vishay PR02 metal films for 
> rebuilding old tube stuff, which have a temp comp of +/- 250ppm/K.  There are 
> much more stable options out there, but I chose this line because of the 500V 
> rating and dark red/brown color which blends into an old chassis more so than 
> tan or bright blue.  
> 
> Regards, 
> Chris 
> 

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Re: [volt-nuts] Fluke 332B

[kc9ieq via volt-nuts]

Very interesting, very curious to hear your conclusion!  
My thought would be to replace these with standard value 5% resistors having 
good temp co, as calibration should surely make up for any subpar values--  my 
thinking is that temp drift would be a more major consideration for overall 
stability.  If this is a false assumption of would certainly like to learn why. 
 Perhaps the old Allen Bradley carbon comps were special in this regard, but 
the data sheet I've seen for currently available comp resistors had a horrible 
temperature coefficient--  much worse than the "better" film resistors 
available today.  I stock the Vishay PR02 metal films for rebuilding old tube 
stuff, which have a temp comp of +/- 250ppm/K.  There are much more stable 
options out there, but I chose this line because of the 500V rating and dark 
red/brown color which blends into an old chassis more so than tan or bright 
blue.  
Regards, Chris 


Sent from my SMRTphone
 Original message From: Jerry Hancock <je...@hanler.com> Date: 
2/20/17  2:19 PM  (GMT-06:00) To: kc9ieq <kc9...@yahoo.com>, Discussion of 
precise voltage measurement <volt-nuts@febo.com> Subject: Re: [volt-nuts] Fluke 
332B 
I have a D model but I would thin Dr. Frank would be able to address the 
difference D to B.

I recently went thru a Dial a Source DAS-46 finding so many (most) of the 
carbon comp resistors had changed value +30%.  But, and this is the important 
‘But’, the typical 1% metal film resistors don’t have good tempco.  So I wonder 
if replacing these 40yr old resistors was a good idea.  Yes, they have drifted 
higher, but since they all drifted up by the same percentage, the circuit still 
worked.   I bought most of the high value from Mouser using Vishay  as the 
default unless I couldn’t get them for some reason.  I am running a test of the 
stability over 36,750 seconds (has to do with 10K samples with the 3457A in 
NPLC 100 taking about 3.675 seconds per) to see if the stability is better now 
vs with the carbon comp.  Not that I would swap them back in, just curious.




> On Feb 20, 2017, at 12:01 PM, kc9ieq via volt-nuts <volt-nuts@febo.com> wrote:
> 
> Thanks John and Jerry for the replies.  
> After a visual inspection and noting one questionable looking capacitor, 
> (breached seal), I've systematically gone through and checked every single 
> electrolytic capacitor in the unit for C and ESR.  No fewer than NINE have 
> been identified as definitely defective-  A few of which have effectively 
> failed open.  Surprisingly, most of these are Sprague 30D and TVA series.  
> There are also a dozen or so by Amperex/Phillips (some made in Mexico), and 
> three by Mepco/Electra.  The three large 125uF 450V can capacitors are 
> Mallory, and reformed to full voltage with acceptable leakage current.  Given 
> the multiple defective capacitors found, I will be replacing all bur the 
> three large can caps before attempting to power up again and troubleshoot 
> further.  
> I do wonder if anyone on list has personal experience with the 332B and 332D, 
> and just exactly what makes the 332D one decade more accurate according to 
> the spec?  Although the ones checked so far are within tolerance, I am 
> considering the replacement of all carbon comp resistors with more stable 
> metal films.  Perhaps this would be a bit overkill and not yield much in the 
> ratio of effort:performance though?
> Regards,Chris 
> 
> 
> Sent from my SMRTphone
>  Original message From: Jerry Hancock <je...@hanler.com> 
> Date: 2/14/17  11:38 AM  (GMT-06:00) To: Chris Farley <kc9...@yahoo.com>, 
> Discussion of precise voltage measurement <volt-nuts@febo.com> Subject: Re: 
> [volt-nuts] Fluke 332B 
> Most likely the relay in the back left of the box is not opening because the 
> switch that controls it (the power/standby/operate) switch is fouled.  If 
> that relays contacts were cleaner then the tripping voltage would be lower.  
> I had this happen and heard later it is a common problem.  There is a long 
> shaft that could be misaligned from the front to the back where the switch 
> wafers are located.  If that gets misaligned, the switch doesn’t open the 
> relay which keeps the outputs shorted.  The don’t short to a very low 
> resistance when they are dirty.  With the unit turned off, measure and record 
> the resistance across the output high and low terminals.  Use ohms law to 
> determine if this is your problem.  The current trips at 50mA.  If it is 
> tripping at 3v, then your resistance would be about 60 ohms.  Once you get it 
> working, go back and clean that relay.
> 
> The other common problem is having the vernier current limit set too low.  In 
> that case, just turn the current limit dial all the way clockwise.   Note 
> that there is