Author Topic: Documentation for uCurrent Gold  (Read 22892 times)

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Offline JDWTopic starter

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Re: Documentation for uCurrent Gold
« Reply #25 on: April 12, 2017, 04:29:11 am »
Can you measure the 20 nA with shorted leads, too? This would allow you to measure the offset.

You mean "shorter" leads?  I have more than 10pcs of SMD 10M-ohm resistors and a set of jumper pins like you.  (In my first test I used 10pcs of axial-lead resistors and I put them in a breadboard.)
 

Offline FrankBuss

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Re: Documentation for uCurrent Gold
« Reply #26 on: April 12, 2017, 07:57:50 am »
No, I meant short-circuited, but I might be wrong, maybe better to not connect the leads at all (to avoid any noise). My assumption is, that in this case it shows only the offset, and if you note this and then subtract this when measuring your circuits, then it will be pretty accurate.
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Offline JDWTopic starter

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Re: Documentation for uCurrent Gold
« Reply #27 on: April 12, 2017, 08:51:05 am »
Here's a video for you, Frank, showing probes connected and disconnected, with various PLC settings and AVERAGING:

https://youtu.be/ehCxeM5_ou0
 

Offline FrankBuss

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Re: Documentation for uCurrent Gold
« Reply #28 on: April 12, 2017, 10:04:21 am »
The higher value with shorted probes might be because you are inducing something with your hands or the probes loop receives more noise compared to when it is open. But it is really not very stable and maybe not good to trust that the offset is always the same. Better buy a uCurrent. It might have less burden voltage as well compared to the Fluke.
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Offline 2N3055

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Re: Documentation for uCurrent Gold
« Reply #29 on: April 12, 2017, 01:12:07 pm »
Hello!

Let me just chime in a bit. First, if you don't have it, buy (or make) a shortcut plug like the one in photo.
You can use it to check zero volt offset, zero ohm offset and also small current range offset.

What you see here is probably induced interference, it's nano amperes... Everything should be shielded, your 1V source should be battery powered, shielded cables and such.

And than, last two digits on ANY 6.5 voltmeters are a finicky bunch.

Look here on Metrology section there a several topics of measuring and sourcing nano and even femtoamps...

All the best,

Sinisa
 

Offline JDWTopic starter

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Re: Documentation for uCurrent Gold
« Reply #30 on: April 12, 2017, 09:50:45 pm »
First, if you don't have it, buy (or make) a shortcut plug like the one in photo.
You can use it to check...

Buy it where? You didn't provide any link to the place that sells them.

You also seem to be talking exclusively about the uCurrent even though we've also been discussing the Fluke 8845A.  I wish to point that out for clarity, for those who later come and read through this thread.

As to testing nA currents on battery voltage alone, consider well that such is not practical in that you may need to test small currents when connected to a AC powered source at times.  In other words, just as is the case with any handheld or desktop meter, there are times when we need to test circuits powered by batteries and times when we need to connect them tested to a wall socket because that's the environment in which they will be used.
« Last Edit: April 13, 2017, 12:43:28 am by JDW »
 

Offline casinada

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Re: Documentation for uCurrent Gold
« Reply #31 on: April 12, 2017, 11:12:42 pm »
https://www.digikey.com/products/en/test-and-measurement/accessories/613?k=4%20terminal%20shorting
http://www.newark.com/fluke/884x-short/4-wire-short/dp/55M2652
or you can make one yourself  :)
Check Joe Smith's last video where he modified his multimeter to reduce the burden voltage  :)
« Last Edit: April 12, 2017, 11:15:37 pm by casinada »
 

Offline JDWTopic starter

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Re: Documentation for uCurrent Gold
« Reply #32 on: April 13, 2017, 12:47:46 am »
https://www.digikey.com/products/en/test-and-measurement/accessories/613?k=4%20terminal%20shorting
http://www.newark.com/fluke/884x-short/4-wire-short/dp/55M2652

We're talking about the Fluke 8845A here.  Got it.  Thank you for the links.  $36 for that.  Typical Fluke!

Check Joe Smith's last video where he modified his multimeter to reduce the burden voltage  :)

A Fluke 8845A?  Can you please provide a direct link to that video?

Thanks.
 

Offline Vgkid

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Re: Documentation for uCurrent Gold
« Reply #33 on: April 13, 2017, 01:42:31 am »
Quote from: casinada link=topic
We're talking about the Fluke 8845A here.  Got it.  Thank you for the links.  $36 for that.  Typical fluke.
[/quote
Could be worse. Check out Keysights 200$ offering.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline casinada

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Re: Documentation for uCurrent Gold
« Reply #34 on: April 13, 2017, 05:21:09 am »


He runs extensive test on multimeters. His channel is very interesting. He is also an active eevblog member JOEKSMITH :)
 

Offline 2N3055

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Re: Documentation for uCurrent Gold
« Reply #35 on: April 13, 2017, 06:50:03 am »
First, if you don't have it, buy (or make) a shortcut plug like the one in photo.
You can use it to check...

Buy it where? You didn't provide any link to the place that sells them.

You also seem to be talking exclusively about the uCurrent even though we've also been discussing the Fluke 8845A.  I wish to point that out for clarity, for those who later come and read through this thread.

As to testing nA currents on battery voltage alone, consider well that such is not practical in that you may need to test small currents when connected to a AC powered source at times.  In other words, just as is the case with any handheld or desktop meter, there are times when we need to test circuits powered by batteries and times when we need to connect them tested to a wall socket because that's the environment in which they will be used.

Sorry, I didn't provide link, you are literally on the other side of the planet, so I thought you might be able to find something closer to where you live.

And no I didn't even mention uCurrent. I was talking in general about microvolt and nanovolt  and microamperes and nanoamperes measurement with any instrument.

At those voltage and current levels, impedances are so high and measured signal is so low that parasitic emissions, static fields, magnetic fields, triboelectric and thermal effects are sometimes greater than signal you are trying to measure.

Here is the link to a good read.. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwisiuXE56DTAhWmIpoKHeVJDFoQFgg6MAA&url=http%3A%2F%2Fwww.tek.com%2Fdocument%2Fhandbook%2Flow-level-measurements-handbook&usg=AFQjCNGVEOdo-RW87qH4qowipnt8wWqH_A&sig2=eV4eDeg3TGedyhA5b0A9jg

It is the "Low measurement Handbook" by Keithley (says Tektronix but that's corporate crap), a very good overview of the low level measurements and common pitfalls..


As for shorting bars, you can also buy two of these from Pomona:

http://www.mouser.com/ProductDetail/Pomona/5165-2/?qs=%2fha2pyFaduiB6fjNcFfbfg0LjqdcPIiv05%252bYHAJJ%252b9E%3d&utm_source=octopart&utm_medium=aggregator&utm_campaign=565-5165-2&utm_content=Pomona

They are shorts, and can be used in more than one combination.... Including two or more of them connected together..

As for your question, yes, sometimes you need to measure with power grid powered equipment. And then you have complications... Additional filtering, shielding....
You should try to avoid it, if you can..

Hope that helps.

Regards,

Sinisa

 

Offline JDWTopic starter

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Re: Documentation for uCurrent Gold
« Reply #36 on: April 13, 2017, 07:08:38 am »
I was talking in general about microvolt and nanovolt  and microamperes and nanoamperes measurement with any instrument.  At those voltage and current levels, impedances are so high and measured signal is so low that parasitic emissions, static fields, magnetic fields, triboelectric and thermal effects are sometimes greater than signal you are trying to measure.

True, but if you have been reading through this entire thread, especially recently, you will see that Frank kindly repeated my M-ohm resistor test with his uCurrent (because I don't have a uCurrent), and his readings were spot-on.  However, my readings with a US$1k+ Fluke 8845A were way off, as per the table I posted earlier in this thread.  So despite the "parasitic emissions, static fields, magnetic fields, triboelectric and thermal effects," the uCurrent appears to be far more accurate than my Fluke 8845A.

(Thank you for the links and other information you provided.)
 

Offline 2N3055

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Re: Documentation for uCurrent Gold
« Reply #37 on: April 13, 2017, 07:21:06 am »
I was talking in general about microvolt and nanovolt  and microamperes and nanoamperes measurement with any instrument.  At those voltage and current levels, impedances are so high and measured signal is so low that parasitic emissions, static fields, magnetic fields, triboelectric and thermal effects are sometimes greater than signal you are trying to measure.

True, but if you have been reading through this entire thread, especially recently, you will see that Frank kindly repeated my M-ohm resistor test with his uCurrent (because I don't have a uCurrent), and his readings were spot-on.  However, my readings with a US$1k+ Fluke 8845A were way off, as per the table I posted earlier in this thread.  So despite the "parasitic emissions, static fields, magnetic fields, triboelectric and thermal effects," the uCurrent appears to be far more accurate than my Fluke 8845A.

(Thank you for the links and other information you provided.)

uCurrent natively has 1mV/1nA scale...  So 1nA is 0.1% on a 1000mV(1V)/ 1 uA scale..  Fluke has 100uA full scale, and nanoamps are in the few last digits.... And those digits are riddled with errors and offsets.. So yes, uCurrent can make better measurements at that level than a 1000 USD instrument.

But your Fluke is not purpose built low current instrument.  If you need to really measure such low currents, you will need instrument made for that purpose...

And, you are very welcome, I'm glad if I was of any help..

All the best,

Sinisa

 
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Offline JDWTopic starter

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Re: Documentation for uCurrent Gold
« Reply #38 on: April 13, 2017, 10:02:53 am »
For crying out loud...

I get myself through this entire thread so that I am now prepared to purchase a uCurrent and I see today they are OUT OF STOCK:

https://www.eevblog.com/product/ucurrentgold/

 |O
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #39 on: April 13, 2017, 10:34:42 am »
Have you considered that there might be something wrong with your meter?
Without trying very hard, I can measure down to nA accuracy with my 6 1/2 Gossen Metrahit 30M. There is only some fluctuation in the last digit. (100pA)

Voltage: 1.265V
Resistor: 4.04 MOhm
Calculated current: 313.12nA
Measured current: 313.~ nA (uA scale)
« Last Edit: April 13, 2017, 10:42:00 am by Wytnucls »
 

Offline 2N3055

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Re: Documentation for uCurrent Gold
« Reply #40 on: April 13, 2017, 11:15:45 am »
Have you considered that there might be something wrong with your meter?
Without trying very hard, I can measure down to nA accuracy with my 6 1/2 Gossen Metrahit 30M. There is only some fluctuation in the last digit. (100pA)

Voltage: 1.265V
Resistor: 4.04 MOhm
Calculated current: 313.12nA
Measured current: 313.~ nA (uA scale)

Try it with 100MOhm like he did...   ^-^
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #41 on: April 13, 2017, 11:25:07 am »
Why do you think that should make any difference?
 

Offline 2N3055

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Re: Documentation for uCurrent Gold
« Reply #42 on: April 13, 2017, 11:28:52 am »
Why do you think that should make any difference?
25 times smaller current ?😁
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #43 on: April 13, 2017, 11:36:12 am »
Tell me more...
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #44 on: April 13, 2017, 11:38:54 am »
10.06MOhm
1.265V
Calculated current: 125.75nA
Measured current: 125.~nA
 

Offline 2N3055

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Re: Documentation for uCurrent Gold
« Reply #45 on: April 13, 2017, 11:55:03 am »
Well,
 I already suggested to short the input at the terminals and check for instrument offset. Maybe autozero is not on. Maybe instrument is noisy and/or damaged... But fact is that he tries to measure 10 nA with precision, and that is last two digits on his instruments (10 ppm of full scale).
So even 1-2 LSD flicker represent 10-20% error. He might even try to enable filter to try to suppress interference.

Also, your Gossen is a very fine instrument... It probably works much better that guaranteed specs.. And his might just be border line on specs..

I remember reading about 8845A  being susceptible to interference and having problems with CMMR...
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #46 on: April 13, 2017, 12:03:44 pm »
Best I can do with the last bits in my box:

18.13MOhm
1.265V
Calculated current: 69.77nA
Measured current: 70.~nA

Gossen offset: 700pA zeroed.
Instrument published worst 1 year accuracy: 2nA (0.002% of range + 0.02% of reading)
« Last Edit: April 13, 2017, 12:47:41 pm by Wytnucls »
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #47 on: April 13, 2017, 12:23:12 pm »
Agreed. Instrument offset is probably the major culprit, with the addition of some instrument inherent limitations.
I don't think he mentioned yet when the meter was last calibrated.

Fluke 8845A published worst 1 year accuracy: 0.05% of reading + 0.025% of range: 25nA
He'd be lucky to measure within 10nA with a perfect instrument.
The Gossen 30M is an order of magnitude more accurate than the Fluke on small currents, with the same count.
« Last Edit: April 13, 2017, 12:48:00 pm by Wytnucls »
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #48 on: April 13, 2017, 02:52:07 pm »
Found some more high value resistors:

31.8MOhm
1.265V
Calculated current: 39.78nA
Measured current: 40.~nA

31.8MOhm
0.806V
Calculated current: 25.35nA
Measured current: 25.~nA

Accuracy of the Gossen seems to be on par with the uCurrent, as measured by FrankBuss.
« Last Edit: April 13, 2017, 03:03:38 pm by Wytnucls »
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #49 on: April 13, 2017, 08:13:06 pm »
CMRR on the Fluke 8845A is supposedly pretty good at 140dB (50-60Hz), compared to the Gossen's >80dB.

Here is a thread about problems encountered (mostly AC related):
https://www.eevblog.com/forum/testgear/fluke-8845a-ac-current-has-poor-cmrr-agilent-better/
« Last Edit: April 13, 2017, 08:15:39 pm by Wytnucls »
 
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