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
Electrostatic voltmeter?
Either the classical version or the modern electronic variant perhaps?
Bruce
On 23 March 2018 at 13:33 "Dr. David Kirkby" <drkirkby@kirkbymicrowave.co.uk> 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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and follow the instructions there.
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 drkirkby@kirkbymicrowave.co.uk 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
volt-nuts mailing list -- volt-nuts@febo.com
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and follow the instructions there.
If buying new equipment is OK, then maybe look at http://www.trekinc.com/
Contacting Voltmeter 1 x 10^15 ohm up to 2 kV, or Non-Contacting models.
Best Regards,
Laurence Motteram
Calibration & Service Manager
Scientific Devices Australia
Ph: +61 (0)3 9569 1366
M: +61 (0)425 765 019
www.scientific-devices.com.au
lmotteram@scientific-devices.com.au
-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces@febo.com] On Behalf Of Dr. David Kirkby
Sent: Friday, 23 March 2018 11:33 AM
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 _______________________________________________
volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
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 volt-nuts@febo.com 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 drkirkby@kirkbymicrowave.co.uk 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
volt-nuts mailing list -- volt-nuts@febo.com
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and follow the instructions there.
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 volt-nuts@febo.com 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 drkirkby@kirkbymicrowave.co.uk 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
volt-nuts mailing list -- volt-nuts@febo.com
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and follow the instructions there.
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and follow the instructions there.
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.griffiths@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" drkirkby@kirkbymicrowave.co.uk 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
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
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and follow the instructions there.
On 23 March 2018 at 01:07, Bob Albert via volt-nuts volt-nuts@febo.com
wrote:
I found several electrostatic voltmeters on ebay. The brand I remember
is Sensitive Research.
Bob
So something like this?
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
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" drkirkby@kirkbymicrowave.co.uk Date: 3/22/18 7:33 PM (GMT-06:00) To: Discussion of precise voltage measurement volt-nuts@febo.com 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
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
On 23 March 2018 at 01:37, Jerry Hancock jerry@hanler.com wrote:
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.
Yes, I can see these are tricky.
I wish my high-resistance meter had a triaxial BNC. It has a triaxial
cable, but screw on. I can't find out what the connector is.
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.
I can't see how to use a voltage divider with the electrometer. If you know
how, please let me know. I don't have an electrometer, but will buy one.
Someone in the UK has one he is going to dig out the garage, so I will
probably buy that.
Regards,
Jerry
Dave