Author Topic: Documentation for uCurrent Gold  (Read 9998 times)

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Offline JDW

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Re: Documentation for uCurrent Gold
« Reply #50 on: April 13, 2017, 05:08:38 pm »
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.)
 

Online 2N3055

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Re: Documentation for uCurrent Gold
« Reply #51 on: April 13, 2017, 05:21:06 pm »
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 JDW

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Re: Documentation for uCurrent Gold
« Reply #52 on: April 13, 2017, 08:02:53 pm »
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 #53 on: April 13, 2017, 08:34:42 pm »
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, 08:42:00 pm by Wytnucls »
 

Online 2N3055

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Re: Documentation for uCurrent Gold
« Reply #54 on: April 13, 2017, 09:15:45 pm »
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 #55 on: April 13, 2017, 09:25:07 pm »
Why do you think that should make any difference?
 

Online 2N3055

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Re: Documentation for uCurrent Gold
« Reply #56 on: April 13, 2017, 09:28:52 pm »
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 #57 on: April 13, 2017, 09:36:12 pm »
Tell me more...
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #58 on: April 13, 2017, 09:38:54 pm »
10.06MOhm
1.265V
Calculated current: 125.75nA
Measured current: 125.~nA
 

Online 2N3055

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Re: Documentation for uCurrent Gold
« Reply #59 on: April 13, 2017, 09:55:03 pm »
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 #60 on: April 13, 2017, 10:03:44 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, 10:47:41 pm by Wytnucls »
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #61 on: April 13, 2017, 10:23:12 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, 10:48:00 pm by Wytnucls »
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #62 on: April 14, 2017, 12:52:07 am »
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 14, 2017, 01:03:38 am by Wytnucls »
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #63 on: April 14, 2017, 06:13:06 am »
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 14, 2017, 06:15:39 am by Wytnucls »
 
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Offline blueskull

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Re: Documentation for uCurrent Gold
« Reply #64 on: April 14, 2017, 06:43:13 am »
I tested uCurrent with a 10M 1% resistor at 0.1V to 1V, result shows ~-1mv offset plus -1%.
SIGSEGV is inevitable if you try to talk more than you know. If I say gibberish, keep in mind that my license plate is SIGSEGV.
 

Offline JDW

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Re: Documentation for uCurrent Gold
« Reply #65 on: April 14, 2017, 10:20:22 am »
I tested uCurrent with a 10M 1% resistor at 0.1V to 1V, result shows ~-1mv offset plus -1%.

No question.  It's clear I need to buy a uCurrent Gold.  But again, NO STOCK!  A fellow can't win!  :rant:


Wytnucls, after reading your posts it would appear you did not read every post in this thread.  I posted the official word from Fluke regarding nA measurements on the 8845A in my post here:

https://www.eevblog.com/forum/testgear/documentation-for-ucurrent-gold/msg1184028/#msg1184028

My 8845A was purchased in June 2012.  It is only used every now and then, perhaps once every couple weeks for a short period.  It has never been calibrated.  Regardless, see Fluke's reply to my previous post above.  What they wrote would seem to apply to old 8845A and brand spanking new fully just-calibrated 8845A's too.  Besides, even if one wishes to argue my meter is way off and needs to be calibrated, I counter that by presenting this data.  Take note that uA measurements are accurate but only nA measurements are way off in la-la land.  If my meter was messed up calibration wise, I would expect my uA or even mA measurements to be way off too, but they are not.

Anyway...

Anyone know when there will be more stock of the uCurrent?  :-/O
 

Offline evava

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Flukes and offset:
« Reply #66 on: April 14, 2017, 06:45:15 pm »
Flukes and offset:
When I first held Fluke 87V in my hands, I was surprised how much offset it has in DC uA range, I thought that  was faulty instrument. Then I found that thread https://www.eevblog.com/forum/chat/fluke-87v-non-zero-current-reading/ and I finally put up unwillingly with that.
But every time I switch on my second meter UT61e and range to DC uA with 0,00uA dead on, I do not know what to think - maybe it has something with better input protection on Flukes?
How many Flukes is plagued with that feature (large offset on uA range)?
 

Offline Wytnucls

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Re: Documentation for uCurrent Gold
« Reply #67 on: April 15, 2017, 09:09:37 pm »
Fluke is only quoting the accuracy figures for the 8845A that you could have known about before post No.8, if you had bothered to read the manual.
25nA accuracy on low DC currents is the worst it should display, within 1 year of calibration. Most will do a lot better than that.
External influence factors are negligible at nA level.

Best of luck with the uCurrent.

« Last Edit: April 16, 2017, 10:53:09 am by Wytnucls »
 

Offline JDW

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Re: Documentation for uCurrent Gold
« Reply #68 on: April 17, 2017, 10:15:23 am »
Fluke is only quoting the accuracy figures for the 8845A that you could have known about before post No.8, if you had bothered to read the manual.

Why such a smarty-pants reply? I've read the manual as has Fluke.  And I would encourage everyone to read through all the posts in this thread prior to casting  a stone of judgement.  For as I said earlier in this thread, and as the DATA which I posted clearly shows, my Fluke meter is not a "problem unit" insofar as the uA measurements are quite accurate.  If one wishes to argue "it's been 5 years since you bought it and therefore it needs to be recalibrated" or "you have a problem inside your meter," then logic dictates that even my uA readings should also be "way off" but they are not.  Because they are not, it seems reasonable to conclude that, just as Fluke said, this particular meter (model 8845A), is simply inaccurate in the nA range.  I find that terribly unfortunate but not surprising in light of the fact that such is what drove Dave to create the uCurrent in the first place.

As to uCurrent availability, the good news is that 49pcs magically appeared "in stock" as of today.   :-+  This must mean that there are in fact many units in stock, just untested.  Dave probably tests them before making them appear "in stock," which is a good sign about the quality of the unit.

I still think there should be "official documentation" for the uCurrent -- hence the name of this thread.  But until then we will just have to be diligent about reading through posts in this forum to ensure we avoid common usage pitfalls.

My thanks to everyone who posted test data and otherwise contributed in a positive way to this thread.
« Last Edit: April 17, 2017, 10:18:10 am by JDW »
 

Offline blueskull

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Re: Documentation for uCurrent Gold
« Reply #69 on: April 17, 2017, 11:27:48 am »
No question.  It's clear I need to buy a uCurrent Gold.  But again, NO STOCK!  A fellow can't win!  :rant:

Anyone know when there will be more stock of the uCurrent?  :-/O

It now shows 48 in stock at US $64 each. Also, since I don't need mine anymore, I can sell you mine for $50.
SIGSEGV is inevitable if you try to talk more than you know. If I say gibberish, keep in mind that my license plate is SIGSEGV.
 
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Offline Jacon

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Re: Documentation for uCurrent Gold
« Reply #70 on: April 17, 2017, 08:14:24 pm »
Anyone know when there will be more stock of the uCurrent?  :-/O

Another place, especially for European customers:

http://www.simonselectronics.co.uk/
 

Offline luisprata

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Offline JDW

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Re: Documentation for uCurrent Gold
« Reply #72 on: April 28, 2017, 12:58:55 pm »
I finally acquired a uCurrent Gold and tested it for the first time today.  uA and mA switch settings tested to be highly accurate, but the nA switch setting is so bad I think it is defective.  Here's a video of my testing of all 3 switch settings.  Please watch the entire video and then let me know what could be wrong with the nA switch setting. 



Please bear in mind how accurate my uA and mA test results are when formulating your conclusions.  I used a fresh CR2032 too.

I checked the uCurrent Gold SCHEMATIC and then used my Fluke 8845A & 4W probes to test R2, R1 & R9, which measured as follows:

R2 = 9.870k-ohm (nA switch setting)
R9 = 10.00-ohm
R1 = 0.0129-ohm

Thank you.
« Last Edit: April 28, 2017, 04:50:56 pm by JDW »
 

Offline FrankBuss

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Re: Documentation for uCurrent Gold
« Reply #73 on: April 28, 2017, 06:39:59 pm »
I finally acquired a uCurrent Gold and tested it for the first time today.  uA and mA switch settings tested to be highly accurate, but the nA switch setting is so bad I think it is defective.  Here's a video of my testing of all 3 switch settings.  Please watch the entire video and then let me know what could be wrong with the nA switch setting. 

Might be the same problem I had, see this thread:

https://www.eevblog.com/forum/testgear/problem-with-ucurrent-gold/

TL;DR: Avoid feedback loops and terrible oscillation created by wires coupling from the output to input, and use a 100 nF capacitor at the input, if you need only DC.
So Long, and Thanks for All the Fish
 

Offline JDW

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Re: Documentation for uCurrent Gold
« Reply #74 on: April 29, 2017, 12:25:51 pm »
Thanks for your suggestion, Frank.  Specifically, the 0.1uF cap across the uCurrent's INPUTs:



I left the uCurrent Gold at the office, and we are not closed for the next week in honor of Japan's "Golden Week" Spring holiday, but when I get back to the office I'll try the cap and try isolation and then report back here.
 


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