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

[Bruce Griffiths]

Vibrating capacitor non contact field probe in feedback loop to create a 
voltage follower:

https://www.monroe-electronics.com/ESD/pdf/244a_m.pdf

Bruce

> 
> On 23 March 2018 at 15:12 Neville Michie  wrote:
> 
> Improvise by holding a metal disk over an electronic balance and 
> measuring the force of attraction.
> Calibrate it with a lower known voltage.
> 
> cheers,
> Neville Michie
> 
> > > 
> > On 23 Mar 2018, at 12:58, Dr. David Kirkby 
> >  wrote:
> > 
> > On 23 March 2018 at 01:49, kc9ieq via volt-nuts 
> >  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?

[Neville Michie]

Improvise by holding a metal disk over an electronic balance and measuring the 
force of attraction.
Calibrate it with a lower known voltage.

cheers,
Neville Michie
> On 23 Mar 2018, at 12:58, Dr. David Kirkby  
> wrote:
> 
> On 23 March 2018 at 01:49, kc9ieq via volt-nuts  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]

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" 
 Date: 3/22/18  8:58 PM  (GMT-06:00) To: kc9ieq 
, Discussion of precise voltage measurement 
 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  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?

[Dr. David Kirkby]

On 23 March 2018 at 01:49, kc9ieq via volt-nuts  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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Dr. David Kirkby]

On 23 March 2018 at 01:07, Bob Albert via volt-nuts 
wrote:

>  I found several electrostatic voltmeters on ebay.  The brand I remember
> is Sensitive Research.
> Bob
>

So something like this?

https://www.ebay.com/itm/Singer-ESD-7-Sensitive-Research-Electrostatic-Voltmeter-1500-Volt-Range/122976453378

1500 V would probably do. I must admit, I don't understand how these work.
Do you need to have a power supply to balance the voltage? I can't see how
taking almost no current can physically make a meter needle move, as that
needs energy.

I see some are contact, and some non-contact.

It is 01:45 here, so I am just about to go asleep, but will read any
replies later today.

I would be interested in making a more modern version, but really don't
know how.

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?

[Dr Joe Palsa P.E. via volt-nuts]

How about using a high voltage probe that used to be commonly used to measure 
anode voltages of TV picture tubes. There were probes that had a KV meter built 
into the probe and there are ones that were used with VOM'S.
Joe
K3WRY
 
In a message dated 3/22/2018 8:59:08 PM Eastern Standard Time, 
bruce.griffi...@xtra.co.nz writes:

 
 Electrostatic voltmeter?

Either the classical version or the modern electronic variant perhaps?

Bruce

> 
> On 23 March 2018 at 13:33 "Dr. David Kirkby"  
> wrote:
> 
> 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Jerry Hancock]

The part I struggle with is “make one” as T ohm meters are ridiculously 
sensitive to things like fingerprints, for example.  I had a hard time just 
putting cables together that had the particular… I was going to say insulation, 
but it was more than that, basically everything is important and specific when 
you are dealing with T ohm meters.  Setting aside the stupid tri-bnc connector 
on most of them.

How about just using a voltage divider with a standard electrometer?  I’m sure 
you thought of that though.  I like playing around with my Keithley 616 as you 
can show the kids how electrostatics work.

Regards,

Jerry




> On Mar 22, 2018, at 6:00 PM, Bob Albert via volt-nuts  
> wrote:
> 
> What about an electrostatic voltmeter?  Those have been around for decades 
> and draw zero static current.  You didn't indicate how accurate your 
> measurement needs to be. I am trying to recall the maker of the unit, I think 
> ESI but not sure.
> They were somewhat popular in the 1950s as I  recall and there should be some 
> around, gathering dust and mold, in storage places.  They were large, which 
> is a benefit because they had a long scale with good resolution.
> Bob
>On Thursday, March 22, 2018, 5:33:28 PM PDT, Dr. David Kirkby 
>  wrote:  
> 
> 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Bob Albert via volt-nuts]

 I found several electrostatic voltmeters on ebay.  The brand I remember is 
Sensitive Research.
Bob
On Thursday, March 22, 2018, 6:00:39 PM PDT, Bob Albert via volt-nuts 
 wrote:  
 
  What about an electrostatic voltmeter?  Those have been around for decades 
and draw zero static current.  You didn't indicate how accurate your 
measurement needs to be. I am trying to recall the maker of the unit, I think 
ESI but not sure.
They were somewhat popular in the 1950s as I  recall and there should be some 
around, gathering dust and mold, in storage places.  They were large, which is 
a benefit because they had a long scale with good resolution.
Bob
    On Thursday, March 22, 2018, 5:33:28 PM PDT, Dr. David Kirkby 
 wrote:  
 
 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Bob Albert via volt-nuts]

 What about an electrostatic voltmeter?  Those have been around for decades and 
draw zero static current.  You didn't indicate how accurate your measurement 
needs to be. I am trying to recall the maker of the unit, I think ESI but not 
sure.
They were somewhat popular in the 1950s as I  recall and there should be some 
around, gathering dust and mold, in storage places.  They were large, which is 
a benefit because they had a long scale with good resolution.
Bob
On Thursday, March 22, 2018, 5:33:28 PM PDT, Dr. David Kirkby 
 wrote:  
 
 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Bruce Griffiths]

Electrostatic voltmeter?

Either the classical version or the modern electronic variant perhaps?

Bruce

> 
> On 23 March 2018 at 13:33 "Dr. David Kirkby" 
>  wrote:
> 
> 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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[volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Dr. David Kirkby]

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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