High Voltage resistors, Measuring M Ohms to high accuracy.
Patrick, Sat Apr 09 2011, 01:06AMI need some help in developing this idea. i dont know if it will work or if its even useful. ProudMary, I and others have run into problems with resistors and there quoted value. i would like to measure high value resistors. typical DMM's max out at 40Mohms, the Hp34401A tops out at 100Mohms. we often need to measure 300+Mohms, so how are we to do such a thing? it gets even worse... as Proud Mary says here...
Proud Mary wrote ...
We all know that resistance can vary with voltage - especially high voltage - but quantifying dR:dV empirically might involve access to HV calibration standards not easily obtained.
We all know that resistance can vary with voltage - especially high voltage - but quantifying dR:dV empirically might involve access to HV calibration standards not easily obtained.
Normal Ohm meter functions are carried out at relatively low voltage, like less then 20V or 9V, perhaps a wise user would fear the difference of a 100Mohm measurement at 9 volts vs. a 100Mohm measurement at the intended circuit voltage of 20+kV.
I am thinking of using a wheatstone bridge, which would be powered by 10-25kV DC, then there would be a known division side, and then the side under test, with the uA and V meter giving the data out. Im not sure about all this, but it has the advantage of testing the resistor more like the conditions it would be expected to operate at, thus perhaps if sig figs are considered we could figure out a useful ohm value? But maybe just a simple known Vin and measured uA out, is good enough, it would be less failure prone then a wheatstone.
I intend to use some of my many HV resistors for oscilloscope HV probes, so I would like to know several resistors are within +0.5% to -0.5% or a total uncertainty of 1% absolute. However, the measurement accuracy of the DMM worries me, having to consider statements like this:
"Accuracy Specifications ± (% of reading + number of counts)" for "10.00000 V @ 0.0015% + 2 counts"
i presume that the meaning is the (+ percent of error , and then + # of counts) which sets the upper uncertainty, while the
( - percent of error, and then - # of counts) which sets the lower uncertainty. and thus the theoretical, exact, perfect value lies within this band of uncertainty? but when they say "counts", what does that mean for a 6.5 digit or a 3.5 digit meter? if 1.375V is displayed on a 3.5 digit meter are there 1375 counts?
i was thinking of using the icl7107cpl A/D conversion IC then i would be able to choose the circuit impedance and accuracy for a scale of 0 to 200.0 uA, and another for 0 to 2.000 mA.
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
James, Sat Apr 09 2011, 01:28AM
I use a 400V power supply and the microamp range on my multimeter then calculate the value with Ohms law. It has worked fine to measure a 200M resistor, that's the higest I've tried.
James, Sat Apr 09 2011, 01:28AM
I use a 400V power supply and the microamp range on my multimeter then calculate the value with Ohms law. It has worked fine to measure a 200M resistor, that's the higest I've tried.
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Patrick, Sat Apr 09 2011, 01:56AM
ProudMary and I had a little snag when we both ran into nanoamp and picoamp quanties being used to develop a V drop, which was then measured. As there was insuffcient current for the saturation of the A/D silicon to function. trying to read less and less current, and then using math can be problematic, given leakage paths, silicon, and other limitations.
Patrick, Sat Apr 09 2011, 01:56AM
James wrote ...
I use a 400V power supply and the microamp range on my multimeter then calculate the value with Ohms law. It has worked fine to measure a 200M resistor, that's the higest I've tried.
Well Ive done this too, for critical components. The problem is 400V/200M = 2uA so if I wanted 1% I would need to see 2.00 uA on the display. (from 2.02 to 1.98 uA) to see the 198M or 202M value of a labeled 200M resistor. So the 40 nanoAmp difference accounts for the 4Mohm variation. I use a 400V power supply and the microamp range on my multimeter then calculate the value with Ohms law. It has worked fine to measure a 200M resistor, that's the higest I've tried.
ProudMary and I had a little snag when we both ran into nanoamp and picoamp quanties being used to develop a V drop, which was then measured. As there was insuffcient current for the saturation of the A/D silicon to function. trying to read less and less current, and then using math can be problematic, given leakage paths, silicon, and other limitations.
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Ash Small, Sat Apr 09 2011, 08:15AM
Can you not overcome this by using a parallel resistor of known, suitable value?
I guess this would (more or less) bring you back to the wheatstone bridge idea?
Ash Small, Sat Apr 09 2011, 08:15AM
Patrick wrote ...
.ProudMary and I had a little snag when we both ran into nanoamp and picoamp quanties being used to develop a V drop, which was then measured. As there was insuffcient current for the saturation of the A/D silicon to function. trying to read less and less current, and then using math can be problematic, given leakage paths, silicon, and other limitations.
.ProudMary and I had a little snag when we both ran into nanoamp and picoamp quanties being used to develop a V drop, which was then measured. As there was insuffcient current for the saturation of the A/D silicon to function. trying to read less and less current, and then using math can be problematic, given leakage paths, silicon, and other limitations.
Can you not overcome this by using a parallel resistor of known, suitable value?
I guess this would (more or less) bring you back to the wheatstone bridge idea?
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Proud Mary, Sat Apr 09 2011, 08:31AM
Before I forget, Patrick, measurements made with Coleman's Patent Galvanic Engine must be ultimately traceable to the Quantum Hall Effect Resistance Standard - "the QHE Ohm."
I'd expect to see a paragraph or two on primary and secondary resistance standards in your dissertation. Standards are the common language that makes scientific discourse possible. Without them, measurement is arbitary, and comparison nonsense.
Séminaire Poincaré 2 (2004) 39 - 51
The Quantum Hall Eff ect as an Electrical Resistance Standard
B. Jeckelmann and B. Jeanneret
Swiss Federal Office of Metrology and Accreditation
Lindenweg 50
CH-3003 Bern-Wabern
Switzerland
Proud Mary, Sat Apr 09 2011, 08:31AM
Before I forget, Patrick, measurements made with Coleman's Patent Galvanic Engine must be ultimately traceable to the Quantum Hall Effect Resistance Standard - "the QHE Ohm."
I'd expect to see a paragraph or two on primary and secondary resistance standards in your dissertation. Standards are the common language that makes scientific discourse possible. Without them, measurement is arbitary, and comparison nonsense.
Séminaire Poincaré 2 (2004) 39 - 51
The Quantum Hall Eff ect as an Electrical Resistance Standard
B. Jeckelmann and B. Jeanneret
Swiss Federal Office of Metrology and Accreditation
Lindenweg 50
CH-3003 Bern-Wabern
Switzerland
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Bored Chemist, Sat Apr 09 2011, 07:01PM
There;'s a nice trick for measuring small currents to fairly high accuracy. You use a cheap digital multimeter.
I presume that you have access to a decent meter too.
Use the good meter to verify/ calibrate the cheap one on it's lowest voltage range- typically 200 mV.
Then check the input resistance on that range- it's typically very close to 1MOhm.
Now connect a known voltage- say 10.0 V in series with your cheap meter ( set on the 200mV range ) and the high resistor. Say its 200 M.
OK with 10 V and 200+1 MOhms you will get 10/201000000= 49.8nA
That will flow through the 1M resistor in the meter and give 0.0498V or 49.8 mV.
That's the clever bit- the meter reads directly in nanoamps. Reading 2µa is easy- you just use the 2V range on the meter.
You have to remember to subtract off the 1MOhm from the meter when you do the calculation- but that's no hassle.
Incidentally, if your "good" meter is calibrated to the QHE ohm, (and the HQ volt) then the measurement is too.
If you are prepared to take the meter manufacturer's word for it that your meter input resistance is what it says in the manual then you don't need a second meter. You only need that so you can use the good meter to measure the input resistance.
You still need to worry about leakage currents , but with high resistors like this you are going to be stuck with that anyway.
At lest the equipment is cheap.
Bored Chemist, Sat Apr 09 2011, 07:01PM
There;'s a nice trick for measuring small currents to fairly high accuracy. You use a cheap digital multimeter.
I presume that you have access to a decent meter too.
Use the good meter to verify/ calibrate the cheap one on it's lowest voltage range- typically 200 mV.
Then check the input resistance on that range- it's typically very close to 1MOhm.
Now connect a known voltage- say 10.0 V in series with your cheap meter ( set on the 200mV range ) and the high resistor. Say its 200 M.
OK with 10 V and 200+1 MOhms you will get 10/201000000= 49.8nA
That will flow through the 1M resistor in the meter and give 0.0498V or 49.8 mV.
That's the clever bit- the meter reads directly in nanoamps. Reading 2µa is easy- you just use the 2V range on the meter.
You have to remember to subtract off the 1MOhm from the meter when you do the calculation- but that's no hassle.
Incidentally, if your "good" meter is calibrated to the QHE ohm, (and the HQ volt) then the measurement is too.
If you are prepared to take the meter manufacturer's word for it that your meter input resistance is what it says in the manual then you don't need a second meter. You only need that so you can use the good meter to measure the input resistance.
You still need to worry about leakage currents , but with high resistors like this you are going to be stuck with that anyway.
At lest the equipment is cheap.
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Patrick, Sat Apr 09 2011, 10:06PM
I beleive I can calibrate the ICPl7017 and can be made to measure a High value resistence now, and of the QHE standard later.
Patrick, Sat Apr 09 2011, 10:06PM
Proud Mary wrote ...
Before I forget, Patrick, measurements made with Coleman's Patent Galvanic Engine must be ultimately traceable to the Quantum Hall Effect Resistance Standard - "the QHE Ohm."
I'd expect to see a paragraph or two on primary and secondary resistance standards in your dissertation. Standards are the common language that makes scientific discourse possible. Without them, measurement is arbitary, and comparison nonsense.
Dam you Proud Mary! If I get my Ph.D., it will be in large part due to you Proud Mary. Someday were going to have to meet. Before I forget, Patrick, measurements made with Coleman's Patent Galvanic Engine must be ultimately traceable to the Quantum Hall Effect Resistance Standard - "the QHE Ohm."
I'd expect to see a paragraph or two on primary and secondary resistance standards in your dissertation. Standards are the common language that makes scientific discourse possible. Without them, measurement is arbitary, and comparison nonsense.
Bored Chemist wrote ...
There;'s a nice trick for measuring small currents to fairly high accuracy. You use a cheap digital multimeter.
I presume that you have access to a decent meter too.
Use the good meter to verify/ calibrate the cheap one on it's lowest voltage range- typically 200 mV.
Then check the input resistance on that range- it's typically very close to 1MOhm.
Now connect a known voltage- say 10.0 V in series with your cheap meter ( set on the 200mV range ) and the high resistor. Say its 200 M.
OK with 10 V and 200+1 MOhms you will get 10/201000000= 49.8nA
That will flow through the 1M resistor in the meter and give 0.0498V or 49.8 mV.
That's the clever bit- the meter reads directly in nanoamps. Reading 2µa is easy- you just use the 2V range on the meter.
You have to remember to subtract off the 1MOhm from the meter when you do the calculation- but that's no hassle.
Incidentally, if your "good" meter is calibrated to the QHE ohm, (and the HQ volt) then the measurement is too.
If you are prepared to take the meter manufacturer's word for it that your meter input resistance is what it says in the manual then you don't need a second meter. You only need that so you can use the good meter to measure the input resistance.
You still need to worry about leakage currents , but with high resistors like this you are going to be stuck with that anyway.
At lest the equipment is cheap.
I was considering this too Bored Chemist, but it still uses low volatge for which dR:dV at HV, cannot be included.There;'s a nice trick for measuring small currents to fairly high accuracy. You use a cheap digital multimeter.
I presume that you have access to a decent meter too.
Use the good meter to verify/ calibrate the cheap one on it's lowest voltage range- typically 200 mV.
Then check the input resistance on that range- it's typically very close to 1MOhm.
Now connect a known voltage- say 10.0 V in series with your cheap meter ( set on the 200mV range ) and the high resistor. Say its 200 M.
OK with 10 V and 200+1 MOhms you will get 10/201000000= 49.8nA
That will flow through the 1M resistor in the meter and give 0.0498V or 49.8 mV.
That's the clever bit- the meter reads directly in nanoamps. Reading 2µa is easy- you just use the 2V range on the meter.
You have to remember to subtract off the 1MOhm from the meter when you do the calculation- but that's no hassle.
Incidentally, if your "good" meter is calibrated to the QHE ohm, (and the HQ volt) then the measurement is too.
If you are prepared to take the meter manufacturer's word for it that your meter input resistance is what it says in the manual then you don't need a second meter. You only need that so you can use the good meter to measure the input resistance.
You still need to worry about leakage currents , but with high resistors like this you are going to be stuck with that anyway.
At lest the equipment is cheap.
I beleive I can calibrate the ICPl7017 and can be made to measure a High value resistence now, and of the QHE standard later.
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
mikeselectricstuff, Mon Apr 11 2011, 08:52AM
mikeselectricstuff, Mon Apr 11 2011, 08:52AM
wrote ...
I need some help in developing this idea. i dont know if it will work or if its even useful. ProudMary, I and others have run into problems with resistors and there quoted value. i would like to measure high value resistors. typical DMM's max out at 40Mohms, the Hp34401A tops out at 100Mohms. we often need to measure 300+Mohms, so how are we to do such a thing?
Many Fluke DMMs have a NanoSiemens conductance range, manually ranged from the ohms range, which will get you a bit further. Most DMMs have a default Rin of 10M, so this can be used as a voltage divider to easily measure into Gohms, possibly after some calibration to verify the Rin.I need some help in developing this idea. i dont know if it will work or if its even useful. ProudMary, I and others have run into problems with resistors and there quoted value. i would like to measure high value resistors. typical DMM's max out at 40Mohms, the Hp34401A tops out at 100Mohms. we often need to measure 300+Mohms, so how are we to do such a thing?
wrote ...
Normal Ohm meter functions are carried out at relatively low voltage, like less then 20V or 9V, perhaps a wise user would fear the difference of a 100Mohm measurement at 9 volts vs. a 100Mohm measurement at the intended circuit voltage of 20+kV.
I am thinking of using a wheatstone bridge, which would be powered by 10-25kV DC,
As soon as you start using that sort of voltage for low-current measurements I think you will start to run into major corona leakage problems.Normal Ohm meter functions are carried out at relatively low voltage, like less then 20V or 9V, perhaps a wise user would fear the difference of a 100Mohm measurement at 9 volts vs. a 100Mohm measurement at the intended circuit voltage of 20+kV.
I am thinking of using a wheatstone bridge, which would be powered by 10-25kV DC,
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Patrick, Tue Apr 12 2011, 12:28AM
First, the dR:dV which is V dependent, and which needs to be part of the measured and operating conditions of each resistor.
Second, the surface, and body leakage paths must be "seen" as well if one is to expect 1% accuracy or preciscion. (Often leakage occurs at the interface layer between solid and liquid insulation.)
For both cases corona would be as great or greater of a loss, thus it must be effectivley suppressed.
Patrick, Tue Apr 12 2011, 12:28AM
mikeselectricstuff wrote ...
As soon as you start using that sort of voltage for low-current measurements I think you will start to run into major corona leakage problems.
I dont see why. It will be under oil, with ball bearing spheres, and other anti-corona strategies for connections. besides the important "unplanned factors" are what i want to include in the measurement, ill give you two examples.As soon as you start using that sort of voltage for low-current measurements I think you will start to run into major corona leakage problems.
First, the dR:dV which is V dependent, and which needs to be part of the measured and operating conditions of each resistor.
Second, the surface, and body leakage paths must be "seen" as well if one is to expect 1% accuracy or preciscion. (Often leakage occurs at the interface layer between solid and liquid insulation.)
For both cases corona would be as great or greater of a loss, thus it must be effectivley suppressed.
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Bored Chemist, Thu Apr 14 2011, 08:24PM
"I was considering this too Bored Chemist, but it still uses low volatge for which dR:dV at HV, cannot be included."
Then use a higher voltage and turn up the volts range on the meter.
You are still going to be stuffed by corona losses at high voltages however you measure the current.
Bored Chemist, Thu Apr 14 2011, 08:24PM
"I was considering this too Bored Chemist, but it still uses low volatge for which dR:dV at HV, cannot be included."
Then use a higher voltage and turn up the volts range on the meter.
You are still going to be stuffed by corona losses at high voltages however you measure the current.
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Patrick, Thu Apr 14 2011, 10:32PM
ok ill try this when i get the time.
Patrick, Thu Apr 14 2011, 10:32PM
ok ill try this when i get the time.
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Sulaiman, Fri Apr 15 2011, 09:03AM
I made six 'sticks' of 46x (2M2 VR37 resistors in series) for 6x 100 MOhm (approx.)
(due to 5% resistor tolerance.........they were supposed to be 45x 2M2 for 99 MOHM)
The resistance, dR/dT and dR/dV can be measured individually at say 0-1 kV (1/2 Watt)
each string would then be characterised for up to 46 kV dc..
Since each resistor is rated for 3500 V, each 'stick' is nominally rated at 161 kV
Using each stick at say 16.1 kV peak puts only 10% rated voltage across each.
dR/dT becomes more significant than dR/dV.
I used 2M2 because I got 1000 pieces cheap off eBay,
You could use say 100x 10 MOhm for a 1 GOhm 'reference' resistor.
Cheap & simple.
Sulaiman, Fri Apr 15 2011, 09:03AM
I made six 'sticks' of 46x (2M2 VR37 resistors in series) for 6x 100 MOhm (approx.)
(due to 5% resistor tolerance.........they were supposed to be 45x 2M2 for 99 MOHM)
The resistance, dR/dT and dR/dV can be measured individually at say 0-1 kV (1/2 Watt)
each string would then be characterised for up to 46 kV dc..
Since each resistor is rated for 3500 V, each 'stick' is nominally rated at 161 kV
Using each stick at say 16.1 kV peak puts only 10% rated voltage across each.
dR/dT becomes more significant than dR/dV.
I used 2M2 because I got 1000 pieces cheap off eBay,
You could use say 100x 10 MOhm for a 1 GOhm 'reference' resistor.
Cheap & simple.
Re: High Voltage resistors, Measuring M Ohms to high accuracy.
Patrick, Fri Apr 15 2011, 05:37PM
Patrick, Fri Apr 15 2011, 05:37PM
Sulaiman wrote ...
...The resistance, dR/dT and dR/dV can be measured individually at say 0-1 kV (1/2 Watt)...
...dR/dT becomes more significant than dR/dV....
yes that is what i would have expected, i was going to calculate the temp vs field change to see which would be the greater deciding factor....The resistance, dR/dT and dR/dV can be measured individually at say 0-1 kV (1/2 Watt)...
...dR/dT becomes more significant than dR/dV....
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