Author Topic: Low ohm precision resistor standard and testing  (Read 79370 times)

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Offline e61_phil

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Re: Low ohm precision resistor standard and testing
« Reply #50 on: November 30, 2016, 04:19:33 pm »
They keithley 181 is our nano voltmeter with resolution down to 1 nV.

Sorry, I missed the 6.5 digit function. But even with 1nV of resolution it should be very hard to measure 4nV :)

Perhaps with some clever current reverse techniques.
 

Offline CalMachine

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Re: Low ohm precision resistor standard and testing
« Reply #51 on: November 30, 2016, 04:24:29 pm »
They keithley 181 is our nano voltmeter with resolution down to 1 nV.

Sorry, I missed the 6.5 digit function. But even with 1nV of resolution it should be very hard to measure 4nV :)

Perhaps with some clever current reverse techniques.

Yeah it would be pretty difficult, but I would still love the opportunity to give it a go!  If not, I understand. 

What's the max current value?  Could always source more than an 1 amp to achieve a higher potential difference.
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Offline VintageNut

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Re: Low ohm precision resistor standard and testing
« Reply #52 on: November 30, 2016, 06:15:51 pm »
Max current is 5A. Even 20 nV is probably not going to happen for a KE181.
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Offline chuckb

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Re: Low ohm precision resistor standard and testing
« Reply #53 on: December 04, 2016, 07:29:42 am »
My experience with measuring a 50u ohm current shunt. This is a large heavy multi-blade shunt that provides 50mV when 1000 amps passes through.

I used the Keithley 1801 nanovolt preamp to monitor the sense voltage. With 30 seconds of averaging the preamp has a 0.1nV pp noise floor. The K2001 DVM was set to high accuracy mode (100NPLC?), 20uV full scale and a 100 sample moving average.

As citizens of the planet we should all be concerned with not wasting energy. So for the first test I applied 100ua of current to the 50u ohm resistor and then I reversed the current. In the attached pdf you can clearly see the 5nV change in voltage along with the superimposed thermal EMF drift. It looks like the 1000 amp shunt is accurate! The 100ua was supplied by the 10v output of a F732A and a VHP202Z 100k ohm resistor. 

I tried to measure it with 10ua but there was to much voltage drift.

Later I applied 10ma and the voltage was rock steady at 0.5uV. With 2 amps from a bench supply the sense voltage was 100uV.
If the shunt is still accurate at 1000 amps (it should) it will have demonstrated it's linearity over a 10,000,000:1 range. Not to bad. A simple device is really the best.

With a 5 amp excitation current the K1801/K2001 combination should be able to discern 0.1n ohms. A battery powered A10 or A23 preamp from EM Electronics would work just as well.

 

Offline TiN

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Re: Low ohm precision resistor standard and testing
« Reply #54 on: December 04, 2016, 07:51:04 am »
chuckb
Did you also tried to use 2001's 4W function with preamp?
Interesting to see if 2001's current source stability is comparable for the purpose with separate current source.
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Offline chuckb

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Re: Low ohm precision resistor standard and testing
« Reply #55 on: December 04, 2016, 08:05:10 am »
Yes I did but it did not work. I did not take the time to troubleshoot. This K2001 is a used unit that I use just for DCV with the K1801. I have not tested all it's functions. That's one more thing for the to-do list.

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Offline salbayeng

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Re: Low ohm precision resistor standard and testing
« Reply #56 on: December 04, 2016, 09:32:22 am »
Re Zero Ohm standard:
Couldn't one just short the two drive terminals together , and short the two sense wires together , then just connect a thin wire (or 100ohm resistor) between the two shorts?
 

Offline acbern

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Re: Low ohm precision resistor standard and testing
« Reply #57 on: December 04, 2016, 11:40:32 am »
Re Zero Ohm standard:
Couldn't one just short the two drive terminals together , and short the two sense wires together , then just connect a thin wire (or 100ohm resistor) between the two shorts?


Exactly
 

Offline HighVoltageTopic starter

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Re: Low ohm precision resistor standard and testing
« Reply #58 on: December 04, 2016, 12:07:39 pm »
If the shunt is still accurate at 1000 amps (it should) it will have demonstrated it's linearity over a 10,000,000:1 range. Not to bad. A simple device is really the best.
That is a pretty impressive resistor and demonstration of linearity.

What was this 1000A resistor used for?
Any specific application?
 
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Offline chuckb

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Re: Low ohm precision resistor standard and testing
« Reply #59 on: December 04, 2016, 01:21:47 pm »
The 1000 amp resistor is used to monitor current to the engine starter during development. We use it a few times a year.
 

Offline CalMachine

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Re: Low ohm precision resistor standard and testing
« Reply #60 on: December 04, 2016, 02:13:17 pm »
If the shunt is still accurate at 1000 amps (it should) it will have demonstrated it's linearity over a 10,000,000:1 range. Not to bad. A simple device is really the best.
That is a pretty impressive resistor and demonstration of linearity.

What was this 1000A resistor used for?
Any specific application?

The proper term for this is a current shunt. 


The 1000 amp resistor is used to monitor current to the engine starter during development. We use it a few times a year.

What he said!  They come in all kinds of ranges.  The smallest current shunt value I've seen is like 1 mA and there are some that go up to several kA.
« Last Edit: December 04, 2016, 02:14:50 pm by CalMachine »
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Offline VintageNut

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Re: Low ohm precision resistor standard and testing
« Reply #61 on: December 04, 2016, 05:08:56 pm »
Re Zero Ohm standard:
Couldn't one just short the two drive terminals together , and short the two sense wires together , then just connect a thin wire (or 100ohm resistor) between the two shorts?

That is essentially what the PCB cal short that Fluke and Keithley are. It is not a nano-ohm magnitude device. It is a micro-ohm magnitude device. These devices are good for setting the floor of a DMM. They are not a metrology-grade zero. The Ohm Labs 100-0 is a metrology-grade zero. The 100-0 in my possession is no grater than 4 nano ohms at room temperature. I have measured it at 4 nano ohms. It is quite the pain in the butt to measure. If I had a KE1801, it would be a breeze to measure. An A23 amplifier is on my list for future acquisition.
working instruments :Keithley 260,261,2750,7708, 2000 (calibrated), 2015, 236, 237, 238, 147, 220,  Rigol DG1032  PAR Model 128 Lock-In amplifier, Fluke 332A, Gen Res 4107 KVD, 4107D KVD, Fluke 731B X2 (calibrated), Fluke 5450A (calibrated)
 

Offline zlymex

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Re: Low ohm precision resistor standard and testing
« Reply #62 on: December 05, 2016, 02:36:59 am »
I don't know other places, but here in China, there is an regulation(JJG 1069-2011) saying that shunt must be calibrated(and tested or measured) at rated current(10%, 20%, 60%, 80%, 100% of rated to be precise). This is mainly to avoid the changes result from TCR at the very high temperature rise usually associated with large current.
Here is the regulation(in Chinese): http://www.docin.com/p-284172614.html
 
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Offline chuckb

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Re: Low ohm precision resistor standard and testing
« Reply #63 on: December 18, 2016, 01:57:06 am »
chuckb
Did you also tried to use 2001's 4W function with preamp?
Interesting to see if 2001's current source stability is comparable for the purpose with separate current source.

The correct operation became clear when I read the actual K1801 preamp manual. I needed to move the output wires of the preamp card to the other set of K2001 input terminals. The meter forces current out the normal voltage input terminals in 4 wire ohms mode.

All is good now. With a 9.6ma excitation current from the DVM (offset comp on), 10 sample filtering and SLOW filtering on the K1801 the current shunt measure 50.4 u ohms. The stability was about 0.1u ohms. It is graphed over 15 minutes in the attached pdf.

I really like the 2m ohm full scale feature.

 
 
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Offline VintageNut

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Re: Low ohm precision resistor standard and testing
« Reply #64 on: December 18, 2016, 03:28:15 pm »
chuckb
Did you also tried to use 2001's 4W function with preamp?
Interesting to see if 2001's current source stability is comparable for the purpose with separate current source.

Hello Tin

It is not a current source stability issue. It is a simple ohms law issue coupled with the uncertainty+noise of the 1801 voltage measure.

The maximum current forced by the 2001 is 9.2mA (per the factory spec). This develops 460 nano-volts across Chuck's 50 micro ohm shunt. The 1801 does not have the ability resolve 460.0000 nano-volts. My experience with the 1801 was that 0.1 nano-volts is stable but not below 0.1 nano-volts.

This agrees pretty well with Chuck's observation that the bottom 3 digits are not stable. The least significant digit is 10^-13 VDC. Anything 10^-11 and smaller is noise at room temperature from my experience.

working instruments :Keithley 260,261,2750,7708, 2000 (calibrated), 2015, 236, 237, 238, 147, 220,  Rigol DG1032  PAR Model 128 Lock-In amplifier, Fluke 332A, Gen Res 4107 KVD, 4107D KVD, Fluke 731B X2 (calibrated), Fluke 5450A (calibrated)
 

Offline chuckb

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Re: Low ohm precision resistor standard and testing
« Reply #65 on: December 18, 2016, 06:00:38 pm »
I connected the K2002 (without preamp) to a nice Julie Research Labs NB-102 4 wire, oil filled, 100 ohm wire wound resistor. This resistor was probably over 30 years old. Setting the K2002 up in 4 wire, offset comp, 30 sample avg I had less than 100u ohm of measurement noise over 20 minutes. This would indicate 1 ppm measurement noise or short term stability.
I will check the K2001 later.
 

Offline HighVoltageTopic starter

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Re: Low ohm precision resistor standard and testing
« Reply #66 on: January 25, 2017, 04:28:34 pm »
Original Leeds Northrup good quality calibration resistors seem to be very expensive.
But somehow I am lucky to find BURSTER Made in Germany, resistors.

Today I got a 200 milli Ohm version.
And look how accurate it shows up on my 3458A
It seems that Burster knew what they were doing, when these resistors were built

 
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Offline e61_phil

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Re: Low ohm precision resistor standard and testing
« Reply #67 on: January 25, 2017, 09:06:46 pm »
You were a bit faster than me :)

nice resistor
 

Offline HighVoltageTopic starter

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Re: Low ohm precision resistor standard and testing
« Reply #68 on: January 26, 2017, 10:27:31 am »
You were a bit faster than me :)

nice resistor
Yes, indeed a very nice resistor.
Actually I was surprise that it was still there, when I looked.
There are some more on ebay Germany but far too expensive.

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Offline e61_phil

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Re: Low ohm precision resistor standard and testing
« Reply #69 on: January 26, 2017, 10:31:58 am »

Yes, indeed a very nice resistor.
Actually I was surprise that it was still there, when I looked.
There are some more on ebay Germany but far too expensive.


The others on eBay are close to the new price with certificate. I ask Burster a while ago and the 200mR resistor was around 230€.
I think the 200mR is very nice, because it is the lowest resistor value with the good TC. 100mR is worse in TC.


BTW: The resistor should show 200,04mR at max, if it is still in 0,02% spec. The 3458A shows a bit high. But I don't think the 3458A is capable to measure this.
« Last Edit: January 26, 2017, 10:35:49 am by e61_phil »
 

Offline HighVoltageTopic starter

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Re: Low ohm precision resistor standard and testing
« Reply #70 on: January 26, 2017, 10:39:35 am »
The others on eBay are close to the new price with certificate. I ask Burster a while ago and the 200mR resistor was around 230€.
I think the 200mR is very nice, because it is the lowest resistor value with the good TC. 100mR is worse in TC.
Interesting... I did the same thing and got a written quote from Burster and decided that the remaining resistors on ebay are too expensive.

Model: 1240-0,1
Kalibrierwiderstand 0,1 Ohm
Toleranz 0,02 %
Euro 235

They also offer an official DAkkS calibration certificate.

Here is the datasheet:


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Offline HighVoltageTopic starter

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Re: Low ohm precision resistor standard and testing
« Reply #71 on: January 28, 2017, 05:49:46 pm »
I had the newly acquired 200 mOhm resistor all day on my Keithley 2450 at 1.000 A source current and this is the result I got.
It seems this Burster resistor is right on the spot, even with 1A constant current for many hours.

 
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Offline Vgkid

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Re: Low ohm precision resistor standard and testing
« Reply #72 on: March 06, 2017, 04:01:49 am »
Does anyone have any experience with the ex ussr milli-ohm standard resistors?
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Offline HighVoltageTopic starter

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Re: Low ohm precision resistor standard and testing
« Reply #73 on: May 20, 2017, 03:36:32 pm »
Does anyone have any experience with the ex ussr milli-ohm standard resistors?
I think I found one and it is on its way from Russia, so I will post it here when I have it.

--------------
Just today I got another really nice low resistance calibration resistor.
This one has 1 mOhm with a 0.05% tolerance

What I find amazing is, how accurate the reading is with a modern instrument that was not
available 30 years ago, when this resistor was built.
The 2460 just sits at one value extremely stable.

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Offline HighVoltageTopic starter

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Re: Low ohm precision resistor standard and testing
« Reply #74 on: May 21, 2017, 11:59:52 am »
A forum member asked me for the resolution of the Keysight 34470A in the low Ohms reading.

So, I thought to make a comparison to measure this 1 mOhm resistor with a few different Ohm-Meters.
It seems that such low resistance is a challenge even for high end multimeters.


Keysight 3458A
100 Ohm range
Bias current: 10 mA
Measurement: 0.00100 Ohm (movement between 0.00099 to 0.00101)
10 uOhm resolution
7 1/2 digits available


Keysight 34470A
100 Ohm range
Bias current: 1 mA
Measurement: Seems to be out of calibration with a minus Ohm value
6 1/2 digits available


Keysight 34410A
100 Ohm range
Bias current: 1 mA
Measurement: 0.0010 Ohm
100 uOhm resolution
1 nOhm ! resolution shown in Average Statistic mode (very unstable in all uOhm and nOhm digits)
6 1/2 digits available


Keithley DMM7510
This is the 7 1/2 digit Keithley top of the line multimeter
1 Ohm range
Bias current: 10 mA
Measurement: 0.0010614 Ohm
100 nOhm resolution
100 pOhm ! resolution shown in Average Statistic mode
7 1/2 digits available



Keithley 2450 SMU
This is the 6 1/2 digit Keithley SMU

OHM-Mode
2 Ohm range
Bias current: 100 mA
Measurement: 0.001118 Ohm
100 uOhm resolution
5 1/2 digits available

SMU-Mode
20 mV range
Bias current: 1 A
Measurement: 0.001011 Ohm
1 uOhm resolution
6 1/2 digits available



Keithley 2460 SMU
This is the 6 1/2 digit Keithley SMU

OHM-Mode
2 Ohm range
Bias current: 100 mA
Measurement: 0.001167 Ohm
1 uOhm resolution
6 1/2 digits available

SMU-Mode
200 mV range
Bias current: 1 A
Measurement: 0.001000 Ohm
1 uOhm resolution
6 1/2 digits available



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