Low ohm precision resistor standard and testing

[HighVoltage]

And are here the values with switched polarity to negative

Here are the calculated averages of the three voltmeters

3458A:      ( 2.00002 + 1.99875 ) / 2 = 1.999385
34470A:    ( 1.99945 + 2.00035 ) / 2 = 1.999900
7510:        ( 1.99632 + 2.00035 ) / 2 = 2.000004

[VintageNut]

And are here the values with switched polarity to negative

Here are the calculated averages of the three voltmeters

3458A:      ( 2.00002 + 1.99875 ) / 2 = 1.999385
34470A:    ( 1.99945 + 2.00035 ) / 2 = 1.999900
7510:        ( 1.99632 + 2.00035 ) / 2 = 2.000004

For the 7510 on the 100mV range, the uncertainty is 9ppm of range and 25 ppm of reading. The uncertainty of your measurement is 0.9uV for range. The reading uncertainty is about 50nV for a total uncertainty of 950nV.

For your 2.000004 milliohm calculation, drop the last three digits for being completely uncertain.

[chuckb]

The Isabellenhütte RUG series of resistors is physically very large. The factory recommends bolting it to a heat sink for high currents. The factory data sheet shows a 2000 hour test at 110 deg C with no detectable drift. I'm sure the 110 deg C test was in an oven with current only applied while testing it. The resistor is rated for 140 deg C.

NANDblog shared that they saw more drift than they were expecting with the RUG series at low power while bolted to a heat sink.

Could the large package be distorting when bolted to a heat sink and acting like a strain gauge? The package stress could come from the initial connection to the heat sink or a differential metal expansion as it's dissipating power.

[tszaboo]

The Isabellenhütte RUG series of resistors is physically very large. The factory recommends bolting it to a heat sink for high currents. The factory data sheet shows a 2000 hour test at 110 deg C with no detectable drift. I'm sure the 110 deg C test was in an oven with current only applied while testing it. The resistor is rated for 140 deg C.

NANDblog shared that they saw more drift than they were expecting with the RUG series at low power while bolted to a heat sink.

Could the large package be distorting when bolted to a heat sink and acting like a strain gauge? The package stress could come from the initial connection to the heat sink or a differential metal expansion as it's dissipating power.

The shunt was used for a long time. 5 years at least.
The datasheet 1st page specifies 0.2% The drift we read on the traceable calibration paper was less than this. It behaved according to the datasheet.
The drift was more than we expected.
The shunt was mounted on an extruded aluminium heatsink (about 8cm thick in total with fins). There was careful care take, so connecting the shunt assembly did not stress the current terminals of the shunt. Not directly anyway. The shunt had a big semiconductor fuse on it, and overload is not likely.

Again, the drift was within spec. I have high trust and confidence in the manufacturer.

[HighVoltage]

And are here the values with switched polarity to negative

Here are the calculated averages of the three voltmeters

3458A:      ( 2.00002 + 1.99875 ) / 2 = 1.999385
34470A:    ( 1.99945 + 2.00035 ) / 2 = 1.999900
7510:        ( 1.99632 + 2.00035 ) / 2 = 2.000004

For the 7510 on the 100mV range, the uncertainty is 9ppm of range and 25 ppm of reading. The uncertainty of your measurement is 0.9uV for range. The reading uncertainty is about 50nV for a total uncertainty of 950nV.

For your 2.000004 milliohm calculation, drop the last three digits for being completely uncertain.

Thank you VintageNut for pointing this out again about the uncertainty of the measurement.
I am aware of this but just wanted to show the raw data.

Somehow I find it impressive, that we have today instruments that can give us such a resolution of precision and the a 2 mOhm resistor shows up at 0.002000 Ohm.

Although, the absolute accuracy is a different subject, it still gives me the ability to see a trend within the last digits.
 

[JohnG]

Perhaps if you really interested in high accuracy high current stuff, you'd be better off getting LEM Ultrastab DCCT.
They pop up on ebay from time to time to relatively cheap prices. I've got two with best linearity, Ultrastab IT-600S.
It is 1:1500 ratio CT, and with linearity spec <1ppm, offset error <20ppm and tempco <0.2ppm/K, so high chance that your measurements accuracy with these DCCTs will be limited by your burden resistor stability. There are also lower (and higher) current Ultrastab's with similar specs. Buying older Danfysik DCCT (model 867 is same as IT-600S) might save few $$.

I did a brief test before, with 5700A and 5205A as current source.

CERN using these beasts to calibrate and maintain LHC superconductor magnet currents to ppm levels stability. You can find related research paper, covering their transfer and calibration apparatus. 

Just saw this and want to push for this idea as well. I have used this to calibrate shunts of different current ratings to use for DC-DC converter measurements. I used the Danfysik 866 version, with the following burden resistor: https://www.digikey.com/product-detail/en/vishay-foil-resistors-division-of-vishay-precision-group/Y169010R0000T9L/Y1690-10A-ND/3047016 .

I also use the standard shunts, and have found that by using heat sinks, I can minimize shunt temperature variation. I use a layer of self-adhesive thermal tape between the element and the heat sink, so that there very little pressure on the Manganin element. With fans on the heat sinks, I have found that I can keep the temp rise to < 10-15C at over half rated current.

It is important to make sure the heat sink covers the entire element, because Magnanin is a poor thermal conductor. If you look at one with a thermal camera, you will see temperature variation

I have not characterized this system thoroughly over the long term, sorry.

John

[JohnG]

Or, you could just use a Kelvin Bridge 

John

[TiN]

Got my greedy candies from DE Santa. Thank you, HighVoltage for your help 

These things are MONSTERs 



Quick and dirty check and comparison photo to other related stuff:

[HighVoltage]

Got my greedy candies from DE Santa. Thank you, HighVoltage for your help 

These things are MONSTERs 

That was fast.
Great that they arrived safely and in good condition.

Yes, they are much larger than I had expected them to be.

My Danfysik / LEM sensors also arrived and I am looking forward to some detailed testing in the next few weeks.

[TiN]

Well, I'll get to properly testing these only end of January, as I'll be OOC from this weekend for holidays.

Would be interesting to attempt PCR measurement of these resistors. I'd think first is to measure tempco using low current and sensitive nanovolt detector like Keighley 1801 (EM A10). Then it will be maybe possible to determine thermal part of PCR component. My best source so far is Time Electronics 9823 (10A range).

[VintageNut]

I would like to see the LEM sensor design working as DIY here. I would join in with one if they work.

[Pipelie]

There is a project call feshbach coils you might want to see.
https://www.physics.utoronto.ca/~astummer/pub/mirror/Projects/Archives/2007%20Feshbach%20Coils/Feshbach%20Coils.html

[HighVoltage]

There is a project call feshbach coils you might want to see.

Some nice information, thanks!

Also on that site, one can find a really nice article by Jim Williams from September 2011
Design a 100A load


https://www.physics.utoronto.ca/~astummer/pub/mirror/Projects/Archives/2011%20Fesh-MOT%20Coils%20redux/Docs/EDN%202011-9-22%20%27Design%20a%20100A%20Load%27%20article.pdf

[Pipelie]

yes, I read it before ,even printed out.
app note 133. I'll try to build it some time next year.
http://cds.linear.com/docs/en/application-note/an133f.pdf

[quarks]

because I found an error in HIOKI RM3545 graph I updated my comparison chart from Reply #101
https://www.eevblog.com/forum/metrology/low-ohm-precision-resistor-standard-and-testing/msg1215989/#msg1215989



edit: member onemilimeter found an error in 34470A, chart is now corrected

[e61_phil]

It doesn't make any sense, but it is impressive The 3458A justs says 0.000 06 Ohms.

The shunt is specified with 1000A 60mV class 0.05. But neither the DMM nor the setup is suitable for such a measurement. But it is pretty close.

[Vgkid]

That is impressive. One thing I have noticed is that the 8508a is in a lot of labs that specialize in resistance measurements.

[tszaboo]

That is impressive. One thing I have noticed is that the 8508a is in a lot of labs that specialize in resistance measurements.

Just got a cal certificate for a precision resistor (50 Ohm) and they used that Fluke for calibrating it.

[Zermalmer]

That is impressive. One thing I have noticed is that the 8508a is in a lot of labs that specialize in resistance measurements.

Just got a cal certificate for a precision resistor (50 Ohm) and they used that Fluke for calibrating it.

They used only the multimeter?

[e61_phil]

They used only the multimeter?

8.5ppm isn't that bad for 50Ohms. Is it?

[tszaboo]

That is impressive. One thing I have noticed is that the 8508a is in a lot of labs that specialize in resistance measurements.

Just got a cal certificate for a precision resistor (50 Ohm) and they used that Fluke for calibrating it.

They used only the multimeter?

Yes. I believe it was a few PPM uncertainty (8-ish), I needed some 50-100ppm. Just something better than what's inside the 34465A at work.
Strange thing, that technically, I could have used the 34465A to calibrate my resistor, and then use that as a transfer standard. But it is better to spend that money, than to re-call a production run.

[Zermalmer]

That is impressive. One thing I have noticed is that the 8508a is in a lot of labs that specialize in resistance measurements.

Just got a cal certificate for a precision resistor (50 Ohm) and they used that Fluke for calibrating it.

They used only the multimeter?

Yes. I believe it was a few PPM uncertainty (8-ish), I needed some 50-100ppm. Just something better than what's inside the 34465A at work.
Strange thing, that technically, I could have used the 34465A to calibrate my resistor, and then use that as a transfer standard. But it is better to spend that money, than to re-call a production run.

I know that this 'baby' is really nice and the 8.xx ppm is a also a very nice number.
(I didn't want to criticize the device or the lab)

And naturally it is good invested money instead of throwing away one or more  production runs.

I commonly run it more the "old way" with the DC current resitance, but this is more historical based.

[TiN]

I took some pretty photo while ago too.
Short resistance of Fluke 5700A in 4-wire mode, using 5440B-700x cable.

[tszaboo]

That is impressive. One thing I have noticed is that the 8508a is in a lot of labs that specialize in resistance measurements.

Just got a cal certificate for a precision resistor (50 Ohm) and they used that Fluke for calibrating it.

They used only the multimeter?

Yes. I believe it was a few PPM uncertainty (8-ish), I needed some 50-100ppm. Just something better than what's inside the 34465A at work.
Strange thing, that technically, I could have used the 34465A to calibrate my resistor, and then use that as a transfer standard. But it is better to spend that money, than to re-call a production run.

I know that this 'baby' is really nice and the 8.xx ppm is a also a very nice number.
(I didn't want to criticize the device or the lab)

And naturally it is good invested money instead of throwing away one or more  production runs.

I commonly run it more the "old way" with the DC current resitance, but this is more historical based.

OK, I looked up the cal certificate, they wrote 12 PPM uncertainty on it forr a 50 Ohm resistor, with EA 4/02
http://www.european-accreditation.org/publication/ea-4-02-m-rev01--september-2013

[e61_phil]

I commonly run it more the "old way" with the DC current resitance, but this is more historical based.

Can you explain that a bit further?

I took some pretty photo while ago too.
Short resistance of Fluke 5700A in 4-wire mode, using 5440B-700x cable.

Nice    The 8508A showed 35µ Ohms on my Fluke 5450A.

OK, I looked up the cal certificate, they wrote 12 PPM uncertainty on it forr a 50 Ohm resistor, with EA 4/02
http://www.european-accreditation.org/publication/ea-4-02-m-rev01--september-2013

Das anyone know how they calculated the 12ppm? Is it the 99% Tcal +/-5K spec? That would give 11.2ppm